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Critical Review
14 (
1
); 3-27
doi:
10.25259/APOS_215_2022

Clear aligner therapy in contemporary orthodontics: A scoping review of scholarly literature

Department of Orthodontics, Faculty of Dentistry, Alexandria University, Alexandria, Egypt
Department of Orthodontics, European University College, Dubai, United Arab Emirates
Department of Orthodontics, Saveetha Medical and Technical University, Chennai, Tamil Nadu, India
Corresponding author: Samar M. Adel, Department of Orthodontics, Faculty of Dentistry, Alexandria University, Alexandria, Egypt. orthosamar@gmail.com
Licence
This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 4.0 License, which allows others to remix, transform, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.

How to cite this article: Adel SM, Hansa I, Vaid NR. Clear aligner therapy in contemporary orthodontics: A scoping review of scholarly literature. APOS Trends Orthod. 2024;14:3-27. doi: 10.25259/APOS_215_2022

Abstract

Objectives:

Over the last two decades, clear aligners have become a mainstay in contemporary orthodontic practice primarily due to improvements in digital and 3D printing technologies, a growing interest in esthetic orthodontics, especially in the adult population, and aggressive manufacturer marketing internationally.

Material and Methods:

PubMed, Google Scholar, Cochrane Library, and EMBASE databases were searched from January 1998 to November 2021. The search terms used were “Invisalign” OR “clear aligner.” A total of 7000 records were searched, of which 369 potentially relevant articles were retrieved in full. 190 studies met the selection criteria following screening and were included in the scoping review.

Results:

This review scopes and analyses published orthodontic literature about CA according to a year-wise distribution into 3 groups, 2001–2010/2011–2020/2021. Most of the studies were published in the period between 2011 and 2020, with 138 studies accounting for 73%. The year 2021 followed, with 31 studies accounting for 16%, which was greater than the number of studies published in 10 years from 2001 to 2010. Studies were also classified based on the study designs with most of the published studies representing the lowest level of evidence including case reports, case series, narrative reviews, expert opinions, and editorials accounting for 137 studies, whereas case-control studies were the least reported studies with only 4 studies reported in the literature. In addition, they were categorized into seven main domains: (1) Biological considerations associated with clear aligner therapy (CAT), (2) Treatment outcomes considerations associated with CAT, (3) Geometrical considerations associated with CAT (clinical), (4) Biomechanical considerations associated with CAT (Laboratory/Finite element analysis), (5) Biomaterial considerations associated with CAT, (6) Patient education and experience and aesthetic and social perception of CAT, and (7) Miscellaneous. Treatment outcome considerations associated with CAT had the greatest percentage representing 36% of the total published domains, while the final place was occupied by the biomechanical considerations associated with CAT accounting for only 4% of the published domains about CAT.

Conclusion:

Treatment outcome was the domain most commonly reported by studies accounting for (36%). Most of the published studies are at the lowest level of evidence including case reports, case series, narrative reviews, and expert opinions. The vast majority of studies utilized only a single clear aligner brand. There is a greater need for research that studies CAT from a holistic perspective.

Keywords

Clear aligner therapy
Invisalign
Scoping review
Treatment effects
Aligners

INTRODUCTION

Over the last two decades, clear aligners have become a mainstay in contemporary orthodontic practice primarily due to improvements in digital and 3D printing technologies, a growing interest in esthetic orthodontics, especially in the adult population, and aggressive manufacturer marketing internationally.[1-3]

Although clear aligners have become widely utilized, there is a paucity of scholarly research testing this treatment modality.[4-9] Contrary to expectations, orthodontic products are often clinically adopted without appropriate clinical evidence. However, if the specialty has to obtain precision and proficiency with this modality, a thorough investigation of existing clear aligner literature is imperative. This will allow future studies to target areas of deficiency within this field.

The discrepancy between the predicted and actual clinical outcomes with clear aligner therapy (CAT) is around 50% necessitating midcourse corrections, refinements, additional aligners, or even a conversion to fixed appliances before the end of treatment.[10] This percentage accuracy was further found to be affected by the registration algorithm software used for the superimposition of digital models.[4] Studies assessed different aspects of CAT effectiveness including biological aspects, treatment outcomes, geometrical and biomechanical considerations, biomaterials as well as patient-related outcomes.

Scoping reviews (ScRs), in general, aim to study the extent, range, and type of research on a given topic and to help direct future research. ScRs are especially beneficial when applied to novel topics, in which a scarcity of randomized controlled trials prevents systematic reviews from providing meaningful conclusions, as is the case for orthodontic clear aligners. This ScR, therefore, aims to determine the scope and extent of the published literature on clear aligners in orthodontics, as well as identify the types of studies published, and summarize the outcomes studied.

MATERIAL AND METHODS

A ScR of the published literature was performed following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) extension for PRISMA-ScRs guidelines [Figure 1]. A review protocol was created to address the research questions and studies’ eligibility criteria [Table 1] but was not previously registered. PubMed, Google Scholar, Cochrane Library, and EMBASE databases were searched from January 1998 to November 2021. In addition, Google Scholar and OpenGrey were searched for grey literature. Reference lists of relevant articles were manually searched and “Citation Networks” of relevant articles in Web of Science were checked to identify studies that could have been missed in the electronic database searches. A search alert was created for each database using its respective search strategy to be notified of any new relevant studies, and alerts were monitored on regular basis until the end of November 2021. The initial date was chosen as it coincided with the initial development of Invisalign. The search terms used were “Invisalign” OR “Clear Aligner” OR “Aligner.” Although no specific language restriction was applied, the search terms used were only in the English alphabet. Titles and abstracts were screened to satisfy the ScR eligibility criteria.

Figure 1:
Preferred reporting items for systematic reviews and meta-analysis.
Table 1: Scoping review selection criteria.
Inclusion criteria Exclusion criteria
Study design: All types of studies including randomized controlled trials, controlled clinical trials, cohort studies, retrospective studies, and case-control studies
Participants: Patients aged 10 years and older receiving orthodontic treatment
Intervention: Any type of clear aligner therapy
Comparison: Any type of comparison with conventional mode of orthodontic treatment method or approach
Outcomes: All types of reported outcomes (primary and secondary)
Case reports and case series
Studies with <10 participants
Personal opinion and descriptive technique papers
Letters to editors or interviews
Editorials
Proceedings from research summits
Systematic reviews, meta-analyses, narrative reviews and scoping reviews
Proof of concept, workshops, and presentations
Pilot studies and retracted articles

The abstracts of all suitable articles were evaluated by two reviewers independently. Full texts of those articles meeting the selection criteria and those that were ambiguous were then obtained for screening. A third reviewer aided in resolving uncertainty regarding final inclusion until a consensus was reached. Excluded studies with reasons were tabulated [Table 2]. Full-text analysis of the identified original research was performed and data extraction was charted according to “PICO” guidelines with collected information that included the first author and year of publication, study design, number of participants, interventions, comparison, outcomes (both primary and secondary), method of measurement, and outcome domain [Table 3]. The primary and secondary outcomes were determined from within the text of the study. If not explicitly mentioned, the aim, sample size calculation, or first reported outcome in the results section were used, respectively. Any other outcomes reported were designated as secondary outcomes. The data extraction and outcome domains were chosen after a review of the results and refined independently by two reviewers. The outcome domains were thus categorized into seven main domains, as enumerated below:

  1. Biological considerations associated with CAT

  2. Treatment outcomes considerations associated with CAT

  3. Geometrical considerations associated with CAT (clinical)

  4. Biomechanical considerations associated with CAT (laboratory/finite element analysis [FEA])

  5. Biomaterial considerations associated with CAT

  6. Patient education, experience and aesthetic/social perception of CAT

  7. Miscellaneous.

Table 2: Studies excluded from the scoping review (n=179).
Author/Year Reason for exclusion
Weir 2017[11] Review article
Robertson et al., 2020[12] Systematic review
Ke et al., 2019[1] Systematic review
Rossini et al., 2014[13] Systematic review
Caminiti and Lou 2019[14] Less than 10 participants
Lagravère and Flores-Mir 2005[15] Systematic review
Tamer et al., 2019[16] Literature review
Papadimitriou et al., 2018[17] Systematic review
Rossini et al., 2014[18] Systematic review
Hennessy and Al-Awadhi 2016[19] Opinion article
Zheng et al., 2017[20] Systematic review and meta-analysis
Galan-Lopez et al., 2019[21] Systematic review
Sword and Haywood 2020[22] Case report
Kook et al., 2019[23] Case report
Flores-Mir 2019[24] Systematic review with meta-analysis
Lu et al., 2018[25] Meta-analysis
Kuncio 2014[26] Review article
Kassam and Stoops 2020[27] Systematic review
Cardoso et al., 2020[28] Systematic review
Phan and Ling 2007[29] Opinion article
Zhang et al., 2020[30] Systematic review
Shotell 2020[2] Opinion article
Tripathi et al., 2016[31] Case report
Iliadi et al., 2020[32] Systematic review and meta-analysis of clinical and in vitro research
Lombardo et al., 2020[33] Case report
Blevins 2019[34] Editorial
Marya et al.,2020[35] Review
Staderini et al., 2019[36] Case report
Al-Jewair et al., 2020[37] Case series with less than 10 participants
Kim and Echarri 2007[3] Narrative article
Fang et al., 2019[38] Systematic review and meta-analysis
Gierie 2018[39] Overview
Al-Zainal et al., 2020[40] Systematic review and meta-analysis
Kravitz et al., 2018[41] Technique article
Fry 2017[42] Opinion article
Ojima et al., 2018[43] Case report
Pinho and Rocha 2020[44] Case series
On Tse 2019[45] Case report
Ruan and Jiang 2017[46] Case report
Yu et al., 2013[47] Systematic review
Caruso et al., 2020[48] Case reports
Feizi et al., 2020[49] Narrative review
Keim 2017[50] Editorial/opinion article
Boyd 2008[51] Participants less than 10
Kaur et al., 2020[52] Scoping review
Kankam et al., 2018[53] Case series and technique article
Gandhi et al., 2021[54] Systematic review and meta-analysis
Boyd 2009[55] Case reports [3 cases]
Shipley 2018[56] Pilot study
Park and Kim 2009[57] Case report
Harnick 2012[58] Case report
Hannequin 2020[59] Case report
Hennessy and Al-Awadhi 2016[60] Narrative review
Chang et al., 2021[61] Narrative review
Ojima et al., 2020[62] Case report
Mheissen et al., 2020[63] Systematic review
Lee et al., 2011[64] Case reports [3 cases]
El-Bialy 2020[65] Case series: Less than 10 participants
Lombardo et al., 2017[66] Less than 10 participants
Joffe 2003[67] Opinion article
Peck 2021[68] Editorial
Zhu et al., 2019[69] Case report
Ojima et al., 2020[70] Case report
Giancotti et al., 2020[71] Case report
Sheridan 2014[72] Opinion article
Chang et al., 2019[73] Case report
Wheeler 2004[74] Editorial
Keser and Dibart 2011[75] Case report
Tartaglia et al., 2021[76] Narrative review
Huang and Huang 2018[77] Case report
Malik et al.,2013[78] Narrative review
Bous et al., 2020[79] Technique article and case report
Schwartz 2012[80] Case report
Cetta 2018[81] Technique article
Park and Kim 2009[82] Case report
Wong 2002[83] Narrative review
Waring et al., 2013[84] Narrative review
Reinhardt 2016[85] Opinion article
Kau et al., 2020[86] Case report
Bawaskar 2015[87] Case report
Eckhart 2009[88] Case report
Chami et al., 2018[89] Pilot study
Owen 2001[90] Technique article
Cassetta et al., 2020[91] Case report
Ellis 2004[92] Letter to editor
Greco et al., 2020[93] Case report
Miller 2009[94] Case report
El-Bialy 2020[95] Case report
Melkos 2005[96] Narrative review
Putrino et al., 2021[97] Scoping review
Whitehouse 2004[98] Opinion article
Ojima et al., 2014[99] Case report
Eliades and Bourauel 2005[100] Editorial
Turpin 2005[101] Editorial
Voudouris et al., 2018[102] Opinion article
Wu 2014[103] Letter to editor
Pagani et al., 2016[104] Case report
Levrini et al., 2012[105] Case report
Awosika et al., 2017[106] Case report
Fry 2017[107] Case report
Ojima et al., 2016[108] Case report
Beers et al., 2003[109] Narrative review
Jyothikiran et al., 2014[110] Narrative review
Lou and Caminiti 2021[111] Opinion article
Zawawi 2014[112] Case report
Ellis 2012[113] Letter
Johal and Bondemark 2021[114] Opinion article
Antelo et al., 2018[115] Case report
Park and Kim 2010[116] Case report
Levrini et al., 2015[117] Case report
Needham et al., 2015[118] Case report
Smallwood 2009[119] Narrative review
Christensen 2002[120] Opinion article
Garino et al., 2014[121] Opinion article
Frongia and Castroflorio 2006[122] Case report
Giancotti et al., 2006[123] Case report
Kim and Park 2008[124] Case report
Garino and Park 2012[125] Opinion article
Feinberg et al., 2016[126] Opinion article
Mampieri and Giancotti 2013[127] Review
Eissa et al., 2018[128] Pilot study
Lin et al., 2014[129] Case report
Giancotti and Mampieri 2012[130] Case report
Ali and Miethke 2012[131] Narrative review
Brezniak and Wasserstein 2008[132] Case report
Torres et al., 2011[133] Case report
Abraham et al., 2016[134] Case report
Womack and Day, 2008[135] Case report
Giancotti et al., 2014[136] Case report
Vlaskalic and Boyd 2002[137] Opinion article
Rocke 2008[138] Technique article
Schupp et al., 2010[139] Case report
Schupp et al., 2010[140] Case report
Barlattani et al., 2010[141] Case report
Aulakh 2013[142] Case report
Norris et al., 2002[143] Case report
Giancotti et al., 2015[144] Case series
Cassetta et al., 2016[145] Case report
Fischer 2010[146] Case report
Ruiz et al., 2009[147] Less than 10 participants
Schupp et al., 2010[148] Case report
Wheeler 2005[149] Opinion article
Kumar et al., 2021[150] Letter to Editor
Hönn and Göz 2006[151] Case report
Lombardo et al., 2021[152] Case report
Uribe et al., 2011[153] Case report
Dickerson 2017[154] Case report
Miller et al., 2002[155] Case report
Levrini et al., 2013[156] Pilot study
Long 2012[157] Case report
Maganzini 2006[158] Letter to editor
Giancotti and Di Girolamo 2009[159] Case report
Patient’s Page, 2013[160] Opinion article
Giancotti et al., 2008[161] Case report
Sheridan 2004[162] Opinion article
Galluccio 2021[163] Narrative review
Chenin et al., 2003[164] Case report
Crosby and Lee 2009[165] Opinion article
Womack 2006[166] Case report
Boyd 2007[167] Case report
Boyd 2005[168] Case report
Sousa Dias and Tsingene 2011[169] Case report
Cai et al., 2021[170] Opinion article
Giancotti and Farina 2010[171] Case report
Vlaskalic and Boyd 2001[172] Case report
Marcuzzi et al., 2010[173] Case report
Bradley 2013[174] Opinion article
McFarland 2007[175] Case report
Corsair 2007[176] Case report
Sterental 2008[177] Narrative review
Turatti et al., 2006[178] Case report
Hamula and Brewka 2005[179] Opinion article
Bishop et al., 2002[180] Case report
Giancotti and Ronchin 2006[181] Case report
McKenna 2001[182] Opinion article
Barzilay and Dayan 2016[183] Case report
Salomone and Turatti 2020[184] Technique article
Lin et al., 2016[185] Retracted article
Pithon et al., 2019[186] Systematic review
Table 3: List and details of studies included in the scoping review n=190.
Author (year) Study type Participants Intervention Comparison Outcome (Primary) Outcome (Secondary) Outcome Domain
Miethke and Vogt2005[257] Prospective controlled clinical trial 30 consecutive patients each with FA and with CA Periodontal health of patients during treatment with the Invisalign system and with FA • CA and FA
• Three consecutive control visits
Evaluation of the periodontal health in patients during treatment with either FA or the Invisalign system A
Miethke and Brauner2007[258] Prospective cohort study 30 patients each with aligners or fixed lingual appliances Periodontal health of patients during treatment with the Invisalign system and with fixed lingual appliances CA and FA Evaluation of the periodontal health of patients during treatment with the Invisalign system or fixed lingual appliances A
Eliades et al., 2009[259] Experimental in vitro study Three sets, each consisting of a maxillary and a mandibular appliance, of as-received aligners Cytotoxicity and estrogenicity of Invisalign appliances Samples of eluents were diluted to 3 concentrations (5%, 10%, and 20% vol/vol) Study the in vitro cytotoxic and estrogenic properties of Invisalign appliances A
Sombuntham et al., 2009[260] Animal study 15 rats were divided into 3 groups Early tooth movement with a clear plastic appliance in rats • Group I was the untreated controls; group II received a clear plastic appliance made from a model, with the maxillary left first molar repositioned mesially 0.5 mm from the origin; and group III had a closed-coil spring to move the molar mesially, changes in paradental tissues were evaluated on days 1, 4, and 7 Investigate early histologic changes of paradental tissues in response to a clear plastic appliance in rats A
Low et al., 2011[261] Prospective clinical trial 56 Chinese male/female volunteers (aged 19–39 years) Ultrastructure and morphology of biofilms on thermoplastic orthodontic appliances in “fast” and “slow” plaque formers • Slow and fast plaque formers
• Tiles were collected at intervals of 1, 3, 6, 12, 24, and 48 h, as well as 3, 7, and 14 days
Investigate the morphological features and distribution of biofilms on Invisalign orthodontic appliances, in a sample of “slow” and “fast” plaque formers using SEM A
Shalish et al., 2012[189] Prospective cohort study 68 adult patients (45 females and 23 males) who comprised 3 groups: 28 Buccal, 19 Lingual, and 21 Invisalign patients Adult patients’ adjustability to orthodontic appliances: Labial, Lingual, and Invisalign™ • Labial, Lingual, and Invisalign™
• First week and again on day 14
Assess patients’ perception of pain and analgesic consumption Assess 4 areas of dysfunction: oral dysfunction, eating disturbances, general activity parameters, and oral symptoms A and B
(Aadjustability to CA)
Krieger et al., 2013[262] Retrospective radiometric cohort study 100 patients (17–75 years of age) with a class I occlusion and anterior crowding before treatment, treated exclusively with Invisalign Apical root resorption during orthodontic treatment with aligners • Pre- and post-treatment panoramic radiographs
• Different teeth, gender, age or sagittal and vertical orthodontic tooth movement
Investigate the incidence and severity of apical root resorptions during orthodontic treatment with aligners A
Fujiyama et al., 2014[263] Prospective cohort study 145 cases for the edgewise group (EG; n=55), Invisalign group (IG; n=38), and edgewise and Invisalign group (EIG; n=52) Analysis of pain level in cases treated with Invisalign aligner in comparison with FA • CAT and FA
• VAS scores were collected during the first three stages (first stage: 0–7 days, second stage: 14–21 days, and third stage: 28–35 days) and at the end of the treatment (overall VAS score
Evaluate and compare the difference in the level of pain using the VAS between cases treated with the edgewise appliance and Invisalign Identify the cause of pain and discomfort in the Invisalign cases A
Premaraj et al., 2014[264] Experimental in vitro study Plastic was powdered with a 12-in half-circle, flat-bottom file, producing particles that were about 86×56 µm to 186×161 µm in size (length×width) Oral epithelial cell reaction after exposure to Invisalign plastic material Soaking Invisalign plastic in either saline solution or artificial saliva for 2, 4, and 8 weeks Evaluate the cellular responses of oral epithelium exposed to Invisalign plastic in vitro A
Han 2015[265] Retrospective cohort study 35 patients who underwent orthodontic treatment Combined periodontal and orthodontic treatment with FA and CA in patients with periodontitis • CA and FA
• Clinical parameters were assessed at baseline and after orthodontic treatment and the duration of treatment was compared between these two groups
Evaluate the effect of orthodontic treatment on periodontal tissue Compare orthodontic treatment with FA to CAT in periodontitis patients A
Azaripour et al., 2015[266] Cross sectional study 100 patients (FO=50, Invisalign®=50) Gingival parameters and patient satisfaction with CAT CAT and FA Evaluate gingival and PDL parameters during orthodontic treatment of patients with FOA or Invisalign® Evaluate patient’s satisfaction during orthodontic treatment of patients with FOA or Invisalign® A
Abbate et al., 2015[267] Randomized prospective clinical trial 50 teenagers aged 10–18 years with similar initial orthodontic conditions Periodontal health in teenagers treated with removable aligners and FA • CAT and FA patients
• Comparisons done at beginning of treatment and 3, 6, and 12 months later
To explore the microbiological and periodontal changes occurring in adolescents during 12 months of orthodontic therapy with CA and FA Assess compliance with oral hygiene procedures, full mouth plaque score, and full mouth bleeding score at the beginning of treatment and 12 months later A
Levrini et al. 2015[268] Prospective controlled clinical trial 77 patients Periodontal health status in patients treated with the Invisalign(®) system and FA • Invisalign(®) group, FA group and control group
• T0 (beginning of the treatment), T1 (1-month) and T2 (3-months)
Compare the periodontal health and the microbiological changes via real-time polymerase chain reaction in patients treated with FA and Invisalign(®) system A
Hellak et al., 2016[269] Retrospective cohort study 60 digital CBCT scans from 30 patients (28 women, two men; 30 CBCTs pre-treatment, 30 posttreatment) Influence of Invisalign treatment with IER on bone volume for adult crowding • 30 CBCTs pre-treatment, 30 post-treatment
• Mandible and maxilla
Use 3D datasets to identify associations between treatment for adult crowding using Invisalign and IER and changes in the bone volume A
Levrini et al., 2016[270] Prospective clinical study 20 subjects (6 males and 14 females) undergoing orthodontic therapy with CA ATP Bioluminometers analysis on the surfaces of CA after the use of different cleaning methods Different cleaning methods (water, brushing with toothpaste, and brushing with toothpaste and use of sodium carbonate and sulphate tablet) Quantify the bacteria concentration on the surface of Invisalign using three different cleaning methods Validate the efficacy of the bioluminometer in assessing the bacteria concentration A
Allareddy et al., 2017[[271] Retrospective cohort study 173 medical device reports Adverse clinical events reported during Invisalign treatment Examine adverse clinical events after the use of the Invisalign system Provide an overview of the actions taken by the manufacturer to address these events A
Gay et al., 2017[272] Prospective cohort radiometric study 71 class I adult healthy patients (mean age 32.8±12.7) treated with aligners Root resorption during orthodontic treatment with Invisalign Root and crown lengths of 1083 teeth were measured in panoramic radiographs at the beginning (T0) and at the end (T1) of CAT Investigate the incidence and severity of RR in adult patients treated with aligners A
Castroflorio et al., 2017[273] Prospective split mouth clinical trial 10 healthy, adult patients Biochemical markers of bone metabolism during early orthodontic tooth movement with Invisalign aligners • 1 w and 3 w
• Tested teeth and control teeth
Evaluate the expression of receptor activator of nuclear factor-kappa ligand, osteoprotegerin, osteopontin, interleukin 1β, and transforming growth factor ß1 in the gingival crevicular fluid of teeth subjected to orthodontic forces released by aligners A
Iglesias-Linares et al., 2017[274] A case–control genetic association study 372 Caucasian patients treated with CA (Invisalign) or FA OIEARR in patients treated with FA versus CA CA and FA Determine whether orthodontic treatment with CA versus FA is associated with a different frequency of OIEARR when genetic, radiographic, and clinical factors are accounted for A
Hellak et al., 2018[275] Retrospective cohort 3D CBCT study 60 CBCT scans from 30 adult patients (28 women, 2 men; 30 CBCTs pre-treatment, 30 post-treatment) Influence on interradicular bone volume of Invisalign treatment for adult crowding with IER • Four levels in the anterior tooth areas of the maxilla and mandible
• Differences in bone between T0 and T1
Use 3D datasets to identify associations between treatment for adult crowding, using Invisalign aligner and IER Assess changes in the volume of interradicular bone A
Almasoud 2018[276] Prospective cohort study 64 patients Pain perception among patients treated with passive self-ligating FA and Invisalign®aligners during the 1st week of orthodontic treatment • Self-ligating FA and Invisalign®aligners
• Their responses were recorded at 4 h, 24 h, day 3, and day 7
Compare the perception of pain between patients treated with passive self-ligating FA and those treated with Invisalign aligners A
Aman et al., 2018[277] Retrospective cohort study using CBCT 160 patients who received comprehensive orthodontic treatment with CA Apical root resorption during orthodontic treatment with Invisalign clear aligners using CBCT • Pre-treatment and post-treatment CBCT examinations
• Maxillary central and lateral incisors
Investigate the incidence and severity of orthodontically induced inflammatory root resorption on maxillary incisors with CA therapy using CBCT Identify possible risk factors for orthodontically induced inflammatory root resorption A
Yi et al., 2018[278] Retrospective cohort study 80 non-extraction patients EARR in non-extraction cases after CAT or FA CAT and FA Comparatively evaluate the amount of EARR in non-extraction patients receiving CAT or FA Investigate the potential predictive factors of EARR: duration of treatment, gender, age, skeletal pattern or degree of malocclusion A
Katchooi et al., 2018[279] Randomized prospective clinical trial 26 adult subjects Effect of supplemental vibration on orthodontic treatment with aligners Either an active (A) or a sham (B) AcceleDent Aura device (OrthoAccel Technologies, Inc) • Investigate the effects of AcceleDent on Invisalign treatment
• The outcomes were the ability to complete the initial set of aligners and the incisor irregularity measurements for those who completed their regimen of aligners
Assess aligner compliance, pain levels, and oral health-related quality of life data A
Guo et al., 2018[280] 3m prospective cohort study 10 female patients with CA Profiling of subgingival plaque biofilm microbiota in female adult patients with CA 3 time points: before orthodontic treatment (T0), 1 month after orthodontic treatment (T1) and 3 months after orthodontic treatment (T2) Investigate changes of the subgingival microbial community Examine subgingival microbial community association with clinical characteristics during the first 3 months of CAT A
Patini et al., 2018[281] Retrospective cohort study A CA (TG) of 68 patients and a control group of 33 untreated patients (UG) Invisalign Clear aligners’ effects on aesthetics: evaluation of facial wrinkles • Treated with CA and untreated
• Comparison based on age: subgroup 1 if under 40 years of age and subgroup 2 if over 40 years
• Facial aesthetics of the lower third was evaluated at the beginning (T0) and at the end (T1) of the study period
Evaluate the facial esthetic effects of orthodontic treatment performed with CA and to compare it to an untreated control group, on lower third facial aging in adult patients through the use of the Wrinkle Severity Rating Scale at the beginning (T0) and at the end (T1) of the study period A
Parrini et al., 2018[282] Prospective cohort study 15 untreated patients and 15 patients treated with CA Postural changes in orthodontic patients treated with CA • Treated patients with CAT and untreated patients
• Patients treated with CA were compared at baseline, after 1, 3 and 6 months
Evaluate possible correlations between orthodontic treatment and posture:
the kyphotic angle, the lordotic angle, the upper thoracic inclination, and the pelvic inclination
A
Farouk et al., 2018[283] Retrospective study 30 patients with an average age of 26±11 years and Class I malocclusion Effect of the application of HFV on tooth length concurrent with CAT • Group I received adjunctive HFV
• Group II, the control, did not receive adjunctive mechanical treatment
• Before (T1) and after (T2) treatment
Evaluate the possible change in teeth lengths as an indicator of OITRR after HFV treatment concurrent with Invisalign Smart Track®aligners as evaluated by CBCT A
Pogal-Sussman-Gandia et al., 2019[284] Prospective cohort study 30 patients undergoing active two-arch Invisalign®treatment were examined Effects of Invisalign®treatment on speech articulation Patients’ speech was recorded once with the trays inserted and once with the trays removed Determine the effects of Invisalign®aligners on patients’ perception on speech articulation and abilities to articulate consonants Assess quality
and rate of speech
A
Oliverio et al., 2019[285] Randomized prospective clinical trial 38 volunteers who were undergoing orthodontic treatment with F22 aligner Tooth whitening in association with CAT • Group 1 (8 patients): Application of 3% hydrogen peroxide for 9 h/day on days 7–14 of aligner wear
• Group 2 (8 patients): Application of 10% carbamide peroxide for 9 h/day on days 7–14 of aligner wear
• Group 3 (8 patients): Application of 16% carbamide peroxide for 9 h/day on days 7–14 of aligner wear
• Group 4 (14 patients): Application of 16% carbamide peroxide for 9 h/day on days 1–14 of aligner wear
Evaluate the efficacy of different at-home whitening protocols during orthodontic CAT • Qualitative analysis of whitening agent distribution within the F22 aligners
• Assess difference in transparency of aligners
• Compare the light transmittance and absorbance of the aligners before and after whitening
A
Wang et al., 2019[286] Prospective cohort study 15 subjects aged 20–25 years, non-smokers, without any diagnosed systemic diseases, and having received no antibiotics in the 3 months before sampling Alterations of the oral microbiome in patients treated with the Invisalign system or with FA Comparison between CAT group, FA group and no treatment group Influence of different treatments on oral microbotome regarding the diversity of oral microbial composition and the richness and evenness of samples • Investigate oral microbotome at phyla and genus levels between different treatments regarding predominancy and abundancy
• Investigate differences in microbial function
A
Abu Alhaija et al., 2019[287] Randomized prospective clinical trial 45 subjects: 25 in FA group and 20 in CA group Comparative study of initial changes in PBF between CA and FA • CA and FA
• Maxillary right and mandibular left teeth
• Different time intervals (20 min, 48 h, 72 h, and 1 month) after the fitting of the nickel titanium archwire in group 1 and after the delivery of the second aligner in group 2
Evaluate and compare the initial changes of PBF using clear aligner and fixed orthodontic treatment A
Lombardo et al., 2020[288] Prospective cohort longitudinal study 2 groups of patients to be treated, respectively, with CAs (14 patients; 9 females and 5 males; mean age 21 years±0.25) and FAs (13 patients; 8 females and 5 males; mean 14 years±0.75) Short-term variation in the subgingival microbiota in 2 groups of patients treated with CA and FA • CA and FA
• The right upper central incisor and right first molar at four different time points: before appliance fitting (T0), and at 1 month (T1), 3 months (T3) and 6 months (T6) thereafter
Evaluate the subgingival microbiological changes during the first 6 months of therapy with CAs and FAs A
Antonio-Zancajo et al., 2020[289] Prospective clinical trial 120 patients (54 men, 66 women) divided into 4 groups of 30 patients each Pain and oral-health-related quality of life in orthodontic patients during initial therapy with CON, low-Friction, and lingual Brackets and aligners (Invisalign) Different types of orthodontic appliances: CON and CON low-friction brackets, lingual brackets, and aligners Compare pain and its relationship with the oral quality of life of patients with different types of orthodontic appliances: CON and CON low-friction brackets, lingual brackets, and aligners A
Tran et al., 2020[290] Multi-site prospective cohort study 27 adults about to start CAT Impact of CAT on tooth pain and masticatory muscle soreness Comparison between baseline, dummy aligner, Invisalign first active aligner and second active aligner Investigate tooth pain and masticatory muscle soreness and tenderness in patients undergoing CAT Explore whether psychological traits affected these primary outcomes A
Albhaisi et al., 2020[291] Prospective randomized clinical trial 49 patients (39 female, 10 males; mean age±standard deviation, 21.25±3 years)
(42 completed the study)
Enamel demineralization during CAT compared with FA Comparison between CAT and FA groups before treatment (T0) and 3 months later (T1) Investigate the relationship between CAT and the development of white spot lesions and compare it with FA therapy by means of mean amount of fluorescence loss (ΔF) Assess number of newly developed lesions, deepest point in the lesion (ΔFMax), lesion area (pixels), and plaque surface area (ΔR30) A
Mulla Issa et al., 2020[292] A cross-sectional study 80 patients coming for regular appointments undergoing orthodontic treatment Periodontal parameters in adult patients with CAT versus three other types of brackets CAT versus the three other types of brackets, that is, CON metal, CON ceramic, and metal self-ligating Assess the gingival parameters in the CAT versus the 3 other types of brackets, that is, CON metal, CON ceramic, and metal self-ligating A
Zhao et al., 2020[293] 6-month prospective clinical study 25 adult patients receiving Invisalign aligner Dynamics of the oral microbiome and oral health among patients receiving CAT Comparison between before the treatment (Group B) and at a 6-months follow-up (Group P) Assess the impacts of Invisalign appliances on the oral bacterial community and biodiversity Record clinical periodontal parameters and daily oral hygiene habits A
Li et al., 2020[294] Retrospective cohort study A total of 373 roots from 70 subjects, with similar baseline characteristics and ABO discrepancy index scores Prevalence and severity of apical root resorption during orthodontic treatment with CA and FA by CBCT CAT and FA Investigate and compare the prevalence and severity of ARR in patients treated with CA and FA using CBCT Investigate which types of teeth had the greatest severity of RR A
Levrini et al., 2020[295] FEA in vitro study and prospective clinical study 10 patients were selected for the clinical study Dental bleaching during orthodontic treatment with aligners • 3 sample areas of gel application on the maxillary central incisors (the incisal edge, the middle part, and the gingival edge) were analyzed
• Teeth 41 and 32 (control teeth, with reservoirs) were compared with that on teeth 31 and 42 (study teeth, without reservoirs)
Determine the tooth whitening effectiveness of trays with no reservoirs (Invisalign aligners or Vivera retainers used as bleaching trays), initially with a FEA and subsequently with a clinical study using spectrophotometry A
Al Nazeh et al., 2020[296] Prospective longitudinal cohort study 50 patients (26 females and 24 males; mean age=27.62±8.25 years, SE=1.17, 95% CI=24.71–29.89 years) Relationship between oral health impacts and personality profiles among orthodontic patients treated with CA Before and after treatment with Invisalign orthodontic treatment Assess oral health impacts before and after Invisalign orthodontic treatment and their relationships with personality characteristics A
Meazzini et al., 2020[297] Prospective cohort study 100 syndromic Caucasian patients affected by various CFA from 2 different hospitals Comparison of pain perception in patients affected by cleft and CFA treated with FA or Invisalign CA and FA Compare the difference in pain perception CAT and FA in patients affected by cleft and CFA A
Barreda et al., 2020[298] Prospective clinical trial 19 patients with orthodontic expansion requirement treated with Invisalign®aligners Clinical and tomographic evaluation of PDL health status and maxillary buccal bone changes in expansion treatment using CA • Measurements were done before starting treatment (T0) and at 12 months (T1)
• Bone thickness was measured at two levels: 4 mm (CEJ+4) and 6 mm (CEJ+6) apical to the CEJ
Evaluate changes in periodontal status and maxillary buccal bone by considering clinical and tomographic parameters during the first year of orthodontic expansion with Invisalign®aligners A
Kaur and El-Bialy 2020[299] Retrospective clinical study 34 patients (9 males, 25 females; average age 41.37±15.02) who finished their orthodontic treatment using an intraoral LIPUS device and Invisalign CA in a private clinic Shortening of overall orthodontic treatment duration with LIPUS • 34 patients who finished their orthodontic treatment using an intraoral LIPUS device and Invisalign clear aligners
• A control group (34) matching for the same malocclusions was randomly selected from finished treatment cases of the same clinician
Determine if there is a reduction in the overall treatment duration in orthodontic patients using low-LIPUS and Invisalign SmartTrack®clear aligners Assess compliance of the patients using LIPUS with CA in comparison to control group A
Xie et al., 2020[300] Experimental in vitro study and animal study 6 mm disc from the aligners to represent the aligners Gold Nanoclusters-Coated orthodontic devices can inhibit the formation of Streptococcus mutans Biofilm • Highest concentration of QA-GNCs in well 1 and gradient diluted QA-GNCs in well 2–11
• The well 12 was the negative control group without any drug
Test modifying orthodontic devices (e.g., Invisalign aligner) with QA-GNCs as an antibiotic reagent to prevent bacterial contamination and biofilm formation Test the effect of incubation time (2, 4, 6, 8, 10, 12, 24 h) on the coatings A
Zhang et al., 2020[301] Both in vitro and in vivo animal assays Biological Safe Gold Nanoparticle-Modified dental aligner prevents the Porphyromonas gingivalis biofilm formation Compared with the traditional oral administration method Investigate the anti-P. gingivalis properties of surface-modified Invisalign with a stable antimicrobial coating system, optical antibacterial density measurement, contact assay, and SEM were performed • Investigate the effect of AuDAPT on biofilm formation
• Evaluate the biocompatibility of AuDAPT- based coating, including its influence on human periodontal ligament fibroblast cell (hPDLC) viability and irritation of the rat oral mucosa
A
Xie et al., 2020[302] Experimental in vitro study The whole Invisalign aligners (the maximum length, width, and height are about 6, 5, and 1 cm, respectively) Near-Infrared Light-Activated phototherapy by Gold Nanoclusters for dispersing biofilms DNase-AuNCs TG with untreated control groups
Ordinary medical gargle (compound chlorhexidine gargle) and alcohol (75%) in biofilm dispersing
• Design and synthesize and assess DNase-decorated AuNCs (DNase-AuNCs), which are capable of dispersing bacterial biofilms and killing the encapsulated bacteria
• Examine phototherapy of bacterial biofilms on an Invisalign Aligner
• Assess effect of irradiation time and Laser intensity on the phototherapy effects of DNase-AuNCs
• Biosafety test of DNase-AuNCs
A
Nemec et al., 2020[303] Experimental in vitro study One set of aligners (Invisalign, Align Technology, San Jose, CA, USA) containing 69 upper and lower aligners was ordered Behaviour of human oral epithelial cells grown on Invisalign®SmartTrack®Material Examine the cell functional and morphological parameters of human oral squamous carcinoma cells directly grown on aligners made of SmartTrack material • Investigate cell morphology, proliferation/viability, cell death, and gene expression of several functional proteins
• Investigate inflammatory cytokines, such as interleukin (IL)-8, and IL-6 and intercellular adhesion molecule 1
A
Gao et al., 2020[304] Prospective cohort study Total of 110 patients
(55 pairs)
Comparison of pain perception, anxiety, and impacts on oral health-related quality of life between patients receiving CA and FA during the initial stage of orthodontic treatment • CA and FA
• Different days: first to day 14
Compare pain perception, anxiety, and impacts on oral health-related quality of life between adult patients receiving CA and FA during the initial stage of orthodontic treatments A
Wang et al., 2020[305] Randomized prospective controlled clinical trial 28 subjects were enrolled in the investigational arm and 15 in the control group Effects of root resorption after orthodontic treatment using pulsating force Effect of the device on root resorption during orthodontic treatment was compared with a control group of patients who received Invisalign treatment Study the effect of the device on root resorption during orthodontic treatment using CBCT and compared with a control group of patients who received Invisalign treatment A
Lou et al., 2021[306] Prospective cohort study 17 healthy adults without TMD (16 females, 1 male; mean age±standard deviation, 35.3±17.6 years) Evaluation of masticatory muscle response to CAT using ambulatory electromyographic recording Comparisons over 4 weeks
week 1 without aligners (baseline), week 2 with a passive aligner (dummy), week 3 with their first active aligner (active1), and week 4 with their second active aligner (active2)
Measure the activity of the masseter during CAT using ambulatory electromyography Explore whether psychological traits modulate the masticatory muscle response to CAT A
Campos Zeffa et al., 2021[307] Prospective cohort longitudinal Study 12 Angle Class I and II orthodontic patients undergoing treatment with FA and 15 patients treated with CA Influence of CON or Invisalign treatment on mineral and trace element salivary levels with Total Reflection X-ray Fluorescence • CAT and FA
• Before treatment (pre) and after 3 months of treatment (post)
Evaluate the salivary concentration of chemical elements in patients undergoing orthodontic treatment with FA and removable aligners Evaluate secretion rate of chemical elements A
Liu et al., 2021[308] Retrospective study 320 incisors from 40 Class II patients treated with aligners (Invisalign) Volumetric CBCT evaluation and risk factor analysis of EARR with CAT Pretreatment (T0) and posttreatment (T1) Investigate the prevalence and severity of EARR volumetrically with CAT using CBCT Determine the possible risk factors and develop a prediction model for EARR A
Al-Dboush et al., 2021[309] Retrospective study 84 subjects who were treated using CAT Impact of photobiomodulation and LIPUS adjunctive interventions on orthodontic treatment duration during CAT 28 patients were treated using CAT with a daily use of LIPUS for 20 min, 28 patients were treated using CAT with a daily use of PBM for 10 min, and 28 patients were treated using CAT alone Assess the efficiency of LIPUS and PBM interventions in accelerating orthodontic tooth movement during CAT A
Antonio-Zancajo et al., 2021[310] Prospective clinical trial 120 patients divided into four groups Comparative analysis of periodontal pain according to the type of precision orthodontic appliances: vestibular, lingual and aligners Four groups: Conventional (CON), Low Friction (LF), Lingual (LO) and Aligners (INV) Analyze the pain (intensity, location and type) that patients presented after the placement of different types of orthodontic appliances: CON, LF, lingual and aligners A
Seleem et al., 2021[311] Prospective clinical controlled trial 28 patients at Western University dental center Effect of 10% carbamide peroxide on tooth shade, plaque index and gingival index during invisalign treatment Two groups where the experimental Group applied daily bleaching material (10% CP, Ultradent Inc., South Jordan, UT, USA), while the control group did not for 4 weeks at baseline and in 2-week intervals for 6 weeks Investigate whether 10% CP use during Invisalign treatment can enhance tooth shade esthetics while decreasing plaque levels and improving gingival health indices A
Miller et al., 2003[190] Retrospective validation study Two identical digital models of one subject’s orthodontic treatment Validation of Align Technology’s Treat III digital model superimposition tool and its case application Compare two identical digital models using 12 selected points from the palatal rugae Assessment of the efficacy and accuracy of three-dimensional computer-based predictive orthodontic systems requires that new methods of treatment analysis be developed and validated B
(Translation and rotation)
Djeu et al., 2005[191] Retrospective cohort study 48 patients (Invisalign and braces groups) Outcome assessment of Invisalign and traditional orthodontic treatment compared with the American Board of Orthodontics objective grading system Comparison between Invisalign group and FA group Objectively compare treatment outcome of Invisalign compared with braces Assess duration, strengths and weaknesses of Invisalign compared with braces B
(ABO-OGS)
Duong and Kuo 2006[192] Prospective clinical trial n=20 Finishing with Invisalign. EX40 Aligner was compared to thinner aligner E×30 and compared to ClinCheck goal Explore procedure for finishing and the optimal material for finishing Obtain data regarding the types of tooth positions that require overcorrection and the amount of overcorrection required to achieve the results shown at the final stage on Clincheck B
Miller et al., 2007[193] Prospective, longitudinal cohort study 60 adult orthodontic patients (33 with Invisalign aligners, 27 with FA) A comparison of treatment impacts between Invisalign aligner and FA therapy during the 1st week of treatment • CAT and FA
• A baseline survey was completed before the start of treatment; diary entries were made for 7 consecutive days to measure various impacts of the subjects’ orthodontic treatment over time
Evaluate the differences in quality of life impacts between subjects treated with Invisalign aligners and those with FA during the 1stweek of orthodontic treatment B
(Quality of life impacts)
Kuncio et al., 2007[194] Prospective cohort study Final sample size for both groups was 11 Invisalign and traditional orthodontic treatment postretention outcomes compared using the American Board of Orthodontics objective grading system • CA and FA
• Cases were evaluated immediately after appliance removal (T1) and at a postretention time (T2), and 3 years after appliance removal
Compare the postretention dental changes between patients treated with Invisalign and those treated with FA B
(Postretention dental changes)
Kravitz et al., 2009[195] Pprospective clinical study 37 Patients treated with anterior Invisalign Efficacy of tooth movement with Invisalign Comparison between predicted and achieved tooth movement Evaluate the efficacy of tooth movement with Invisalign B
(Expansion, constriction, intrusion, extrusion, mesiodistal tip, labiolingual tip, and rotation)
Schaefer and Braumann 2010[196] Prospective cohort study 31 patients with good periodontal health Halitosis, oral health and quality of life during treatment with Invisalign(®) and the effect of a low-dose chlorhexidine solution • Group 1: CHX/no CHX,
• Group 2: no CHX/CHX)
Examine how halitosis, oral dryness and general oral health were impacted during treatment with the Invisalign(®) system Evaluate the effect of a low dose chlorhexidine solution (CHX) B
(Quality of life)
Krieger et al., 2011[197] Retrospective study 35 patients aged between 15 and 59 were measured Accuracy of Invisalign®treatments in the anterior tooth region Pre-and post-treatment models as well as the initial and final position of the ClinCheck Analyse to what extent the pretreatment model at the beginning of the treatment corresponds to the initial position in the ClinCheck® Analyze to what extent the predicted treatment result corresponds to the actual result of the therapy at the end of the treatment B
(Overjet, Overbite, dental midline shift)
Pavoni et al., 2011[198] Prospective clinical study 20 subjects Analysis of dento-alveolar effects in using Self-ligating versus Invisalign LF self-ligating brackets TIME 3 compared to the Invisalign technique Evaluate the changes in the transverse dimension and the perimeter of the maxillary arch produced by LF self-ligating brackets TIME 3 compared to the Invisalign technique Assess difference between the treatment durations of both modalities B
(Changes in the transverse dimension and the perimeter of the maxillary arch)
Krieger et al., 2012[199] Retrospective study 50 patients (15–63 years of age) Achievement of predicted tooth movement in anterior region by Invisalign Pre-and post-treatment casts as well as initial and final ClinChecks®models Compare casts to their corresponding digital ClinCheck®models at baseline Compare the tooth movement achieved at the end of aligner therapy (Invisalign®) to the predicted movement in the anterior region B
(upper/lower anterior arch length and intercanine distance, overjet, overbite, dental midline shift, and the irregularity index according to Little Irregularity Index)
Simon et al., 2014[200] Split mouth retrospective design 30 consecutive patients who required orthodontic treatment with Invisalign® Treatment outcome and efficacy of an aligner technique-regarding incisor torque, premolar derotation and molar distalization • Different movements were compared (1) Incisor Torque>10°, (2) Premolar derotation >10° (3) Molar distalization>1.5 mm.
• The groups (1–3) were subdivided: in the first subgroup (a) the movements were supported with the use of an attachment, while in the subgroup (b) no auxiliaries were used (except incisor torque, in which Power Ridges were used)
• Achieved OTM compared with predicted
Investigate the efficacy of orthodontic treatment using the Invisalign®system Analyze the influence of auxiliaries (Attachment/Power Ridge) as well as the staging (movement per aligner) on treatment efficacy B and C
(Incisor torque, premolar derotation and molar distalization)
Ercoli et al., 2014[201] Prospective clinical study 20 patients in age from 16 to 45 years (mean 31.7±8.7 years) Comparison of two different clear aligner systems Compare two different clear aligner systems: “Nuvola®” system with “Fantasmino®” system Compare the “Nuvola®” system with “Fantasmino®” system (patient’s satisfaction, improvement of the irregularity index, speech impairment, and mean wear time) Examine their material properties, and define the indications for use of the aligners B and E
(patient’s satisfaction, improvement of the irregularity index, speech impairment, and mean wear time)
Li et al., 2015[202] A multicenter
randomized prospective controlled trial
152 adult orthodontic patients The effectiveness of the Invisalign appliance in extraction cases using the the ABO model grading system CAT and FA patients Assess treatment outcomes of the Invisalign and compare results with braces using ABO model grading system in extraction cases B
(Extraction cases)
Grünheid et al., 2016[203] Retrospective study 30 patients treated with CA and 30 patients treated with FA Effect of CAT on the buccolingual inclination of mandibular canines and the intercanine distance • CAT and FA
• Pre- and post-treatment measurements
Compare the changes in buccolinugal inclination of mandibular canines and intercanine distance in patients treated with CA to those treated with preadjusted edgewise appliances B
(Buccolingual inclination of mandibular canines and the intercanine distance)
Duncan et al., 2016[204] Retrospective chart review 61 adult white patients Changes in mandibular incisor position and arch form resulting from Invisalign correction of the crowded dentition treated nonextraction • 20 mild (2.0–3.9 mm), 22 moderate (4.0–5.9 mm), and 19 severe (>6.0 mm)
• T0 and T1 values
Investigate changes in mandibular incisor position resulting from Invisalign correction of the crowded dentition without extraction B
(Mandibular incisor position without extraction)
Best et al., 2016[205] Cross sectional study Orthodontists (n=1000) and general dentists (n=1000) who were providers of aligner treatment Treatment management between orthodontists and general practitioners performing CAT Orthodontists and general practitioners Investigate differences in case selection, treatment management, and aligner treatment expertise between orthodontists and general practitioners B
(Expertise)
Hennessy et al., 2016[206] Randomized prospective clinical trial 44 patients (mean age, 26.4±7.7 years) Comparing mandibular incisor proclination produced by fixed labial appliances and CA CA and FA
Comparing pretreatment and near-end treatment lateral cephalograms
Compare the mandibular incisor proclination produced by FA and third generation CA B
(Mandibular incisor proclination)
Ravera et al., 2016[207] Multicenter retrospective study 40 lateral cephalograms obtained from 20 non-growing subjects (9 male, 11 female; average age 29.73 years) Maxillary molar distalization with aligners in adult patients (T0) pretreatment and (T2) post-treatment Test the hypothesis that bodily maxillary molar distalization was not achievable in aligner orthodontics B
(Maxillary molar distalization)
Weir 2016[208] Prospective clinical study 12 patients, consecutively treated by the removal of a single lower incisor and Invisalign appliances Invisalign treatment of lower incisor extraction cases Pretreatment, treatment and post-treatment photographic records Demonstrate the use of the Invisalign appliance in lower incisor extraction cases B
(Lower incisor extraction cases)
Moshiri et al., 2017[209] Retrospective study 30 adult patients with anterior open bite treated using Invisalign (22 females, 8 males; mean age at start of treatment: 28 years and 10 months; mean anterior open bite at start of treatment: 1.8 mm) Cephalometric evaluation of adult anterior open bite, non-extraction treatment with Invisalign Compare pre-and post-treatment cephalograms Evaluate, by means of cephalometric appraisal, the vertical effects of non-extraction treatment of adult anterior open bite with clear aligners B
(Vertical movements)
Houle et al., 2017[210] Retrospective study 64 adult white patients Predictability of transverse changes with Invisalign ClinCheck measurements with the post-treatment measurements Investigate the predictability of arch expansion using Invisalign B
(Transverse)
Gu et al., 2017[211] Retrospective case-control study Records of 48 Invisalign patients and 48 fixed appliances patients Evaluation of Invisalign treatment effectiveness and efficiency compared with CON FA using the Peer Assessment Rating index Invisalign patients and FA patients Compare the treatment effectiveness and efficiency of the Invisalign system with CON FA in treating orthodontic patients with mild to moderate malocclusion in a graduate orthodontic clinic Analyze improvement between the Invisalign and FA groups B
(PAR Index/mild to moderate malocclusion)
White et al., 2017[212] A blinded randomized, prospective trial 41 adult Class I nonextraction patients to either traditional fixed appliance (6 males and 12 females) or aligner (11 males and 12 females) treatment Discomfort associated with Invisalign and traditional brackets • CA and FA
• Initial treatment appointment, after 1 month and after 2 months
Evaluate differences in discomfort levels between patients treated with aligners and traditional FA Assess analgesic consumption and sleep disturbances B
(Discomfort level)
Grünheid et al., 2017[213] Retrospective cohort study 30 patients who had nonextraction Invisalign treatment Accuracy of Invisalign in nonextraction cases Differences between actual treatment outcome and predicted outcome Evaluate the accuracy of Invisalign technology in achieving predicted tooth positions with respect to tooth type and direction of tooth movement B
(Mesial-distal, facial-lingual, and occlusal-gingival directions, as well as for tip, torque, and rotation)
Shin 2017[214] Retrospective cohort study 68 normal overbites, 40 deepbites and 12 openbites Management of overbite with Invisalign appliance Normal overbites, deepbites and openbites Investigate the vertical dimension changes in patients with various pretreatment overbites who were treated with Invisalign appliance Identify the dental and skeletal changes associated with this bite closing or opening B
Solano-Mendoza et al., 2017[215] Retrospective study 116 patients subjected to expansion with Invisalign® Effectiveness of the Invisalign®system in expansion movement with EX30’ aligners Planned expansion with ClinCheck®and actual clinical quantification using upper post-treatment model comparisons Validate a new method for quantifying the predictability of expansion movement with the Invisalign®system Determine whether there are statistically significant differences between planned expansion with ClinCheck®and actual clinical quantification using upper post-treatment model comparisons B
(Expansion)
Khosravi et al., 2017[216] Retrospective study 3 practitioners, all experienced with the Invisalign technique
120 adult patients who underwent orthodontic treatment only with the Invisalign appliance
Management of overbite with Invisalign appliance Comparison between normal overbites patients, deep bite patients and open bite patients Assess changes in anterior and posterior vertical dimensions during treatment with Invisalign by linear and angular measurements Assess the primary mechanism by which aligners manage the vertical dimension B
(Vertical control)
Pacheco-Pereira et al., 2018[217] Prospective cohort study 81 patients, 29.6% men and 70.4% women, exclusively treated with the Invisalign system participated Patient satisfaction and quality of life changes after Invisalign treatment Assess patient satisfaction and changes in oral health-related quality of life immediately after orthodontic treatment using the Invisalign system B
(Patient satisfaction)
Garnett et al., 2018[218] Retrospective study 17 FA patients and 36 CA patients Cephalometric comparison of adult anterior open bite treatment using CA and FA Compare FA and CAT Compare FA and CAT in correcting anterior open bite and in controlling the vertical dimension in adult patients with hyperdivergent skeletal patterns B
(Vertical movements)
Crouse 2018[219] Retrospective study Records of 220 cases Patient compliance with Removable CAT Comparisons between genders and ages Investigate levels of cooperation with CA and differences based on age and sex B
(Compliance)
Charalampakis et al., 2018[220] Retrospective study 20 Class I adult patients treated with Invisalign; they completed their first series of aligners and had to have a “refinement” series Accuracy of specific tooth movements with Invisalign • Predicted tooth movement was compared with the achieved amount for each movement
• Initial, predicted models and achieved models were compared
Determine the accuracy of specific tooth movements with Invisalign B
(Vertical, horizontal, rotational movements, and transverse widths)
Lanteri et al., 2018[221] Retrospective study 100 patients treated with Invisalign compared with a control group treated with FA The efficacy of orthodontic treatments for anterior crowding with Invisalign compared with FA using the Peer Assessment Rating Index CAT and FA Determine the efficacy of Invisalign in a large sample of patients compared to FA Assess need for refining aligners and for fixed retainers after treatment and duration of treatment B
(Amount of anterior dental crowding (Little Index) and the Peer Assessment Rating (PAR Index) scores)
Tepedino et al., 2018[222] 3D Retrospective cohort study 39 adult patients, who were consecutively treated with CA Movement of anterior teeth using clear aligners Comparison between predicted and achieved torque movements of anterior teeth Evaluate the predictability of Nuvola®aligner system in achieving torque movements of anterior teeth B
(Torque of anteriors)
Sfondrini et al., 2018[223] Retrospective study Cephalometric data of 25 patients with similar skeletal and dental pretreatment parameters were collected Buccolingual inclination control of upper central incisors of aligners CON brackets (Victory, 3M), self-ligating appliances (Damon Q, Ormco), and aligners (Invisalign, Align Technology) Compare the radiographic buccolingual inclination of upper incisors in patients treated with three different orthodontic techniques B
(BL inclination)
Flores-Mir et al., 2018[224] Cross sectional survey Adult patients (n=145) treated with bracket-based or Invisalign therapy; 122 patients were assessed Patient satisfaction and quality of life status after 2 treatment modalities CA and FA Assess patient satisfaction and quality of life among adults through 2 validated comprehensive questionnaires Compare patient satisfaction and status in oral health-related quality of life immediately after orthodontic treatment in patients treated with Invisalign and those who received standard bracket-based treatment B
(Patient satisfaction)
Ko et al., 2018[225] Cross sectional study 16 orthodontists, all of whom were in practice for a minimum of 5 years and did not routinely use digital models (other than for Invisalign®cases) Recommendations for CAT using digital or plaster study casts Digital model versus plaster model Assess which types of malocclusions are recommended for treatment with clear aligners Determine if recommendations for aligner treatment differed when using digital versus plaster models B
(Recommended treated malocclusions)
Kankam et al., 2019[226] Retrospective chart review and 3D morphometric study 33 patients, with a mean age of 19.99 years undergoing triple-jaw surgery (LeFort I osteotomy, bilateral sagittal split osteotomy, and genioplasty) Comparing outcomes in Orthognathic Surgery using CA Versus CON FA Comparison outcomes between CAT and FA groups in surgical cases Evaluate perioperative outcomes (operating time, concurrent extraction of teeth, fat grafting, duration of hospital stay, diet advancement, and use of narcotic analgesics) between CAT and FA 3D quantify postoperative edema between CAT and FA B
(Surgical cases)
Christou et al., 2019[227] A case-control study Records from 58 patients, 29 of whom received Invisalign treatment (mean age 19.03 years) and 29 of whom received traditional fixed-appliance treatment (mean age 13.83 years) Smile outcome comparison of Invisalign and FA treatment • Patients treated with CAT and FA
• Pretreatment scores, post-treatment scores, and differences between within-group smile score before and after treatment were determined for each group
Evaluate and compare smile treatment outcomes between patients treated with Invisalign CA and those treated with traditional FA by integrating variables such as lip symmetry, smile index, smile cant, buccal corridors, and gingival display into smile outcome evaluation B
(Smile)
Caruso et al., 2019[228] Retrospective study 10 subjects (8 females 2 males; mean age 22.7±5.3 years) Impact of molar teeth distalization with clear aligners on occlusal vertical dimension Analyse the effects on vertical dentoskeletal dimension of young adults treated with sequential distalization with orthodontic aligners
(SN-GoGn between T0 and T1)
Measure linear position of the upper molars, the molar class relationship parameter, and the upper incisive inclination B
(Molar distalization with vertical control)
Dai et al., 2019[229] Retrospective study 30 patients who received maxillary first premolar extraction treatment with Invisalign First premolar extraction treatment with Invisalign Achieved and predicted tooth movement of maxillary first molars and central incisors Compare achieved and predicted tooth movements of maxillary first molars and central incisors in first premolar extraction cases treated with Invisalign Explore the influence of age (adolescents vs. adults), attachment (G6-optimized vs. 3-mm vertical, 3-mm horizontal, and 5-mm horizontal), and initial crowding on the differences between predicted and achieved tooth movement B
(Premolar extraction)
Izhar et al., 2019[230] Prospective clinical study 10 cases with mild anterior crowding treated with aligner therapy Comparative assessment of clinical and predicted treatment outcomes of CAT • Compare predicted software models showing orthodontic tooth movement
and clinical models
• Compare the stage models of both the groups
Assess the predicted software models and clinical models and compare the stage models of both groups so as to evaluate the efficacy of tooth movement with CA B
(Irregularity scores)
Alajmi et al., 2020[231] Retrospective cohort study 60 adult patients Short-Term Oral impacts experienced by patients treated with Invisalign or CON FA Comparison between CAT group, FA group Rate the experience of patients after appliance activation in regard to oral impact experience and satisfaction of both treatment modalities (speech, chewing abilities, food restrictions, mucosal ulcerations) Assess effects on daily routine, use of analgesics, and overall treatment satisfaction B
(Short-Term Oral Impacts)
De Felice et al., 2020[232] Randomized prospective clinical trial 10 clinicians were randomly recruited using the Doctor Locator by Align Technology (California)
Four consecutive patients treated with CAT and manual stripping were selected for a total of 40 subjects and 80 dental arches
Accuracy of IER during CAT Planned IPR versus actual IPR performed Compare the accuracy of the actual space obtained through IPR compared to the amount of IPR planned through the digital setup during CAT B
(IPR)
Haouili et al., 2020[233] Prospective follow-up clinical study 38 patients treated with Invisalign Full or Invisalign Teen Efficacy of tooth movement with Invisalign Comparison between predicted and achieved tooth movements with Invisalign Provide an update on the accuracy of tooth movement with Invisalign Assess the strengths and weaknesses of tooth movement with Invisalign B
(Mesial-distal crown tip, buccal-lingual crown tip, extrusion, intrusion, and mesial-distal rotation)
Long et al., 2020[234] Cross-sectional study 120 eligible patients (100 patients for developing and testing the evaluation system and 20 patients for validating this system) An objective system for appraising CAT difficulty: CAT complexity assessment tool (CAT–CAT) Develop an objective evaluation system for assessing CAT difficulty Examine the independent association of each variable (e.g., overbite and crowding) with the complexity level and to select appropriate clear aligner patients B
(CAT difficulty)
Harris et al., 2020[235] Single-center retrospective study 45 patients with a mean age of 30.73±8.0 years and initial open bite of−1.21±1.15 mm Open bite closure using clear aligners Evaluate the dental and skeletal effects that occur in the correction of anterior open bite with CA B
(Vertical movements)
Borda et al., 2020[236] Retrospective study 56 teenage patients with mild malocclusions Outcome assessment of CA versus FA treatment in a teenage population with mild malocclusions Comparison between CAT and FA Assess the efficacy and efficiency of treatment in adolescents presenting with mild malocclusions, comparing outcomes using CA to FA B
(Mild malocclusions)
Zhou and Guo 2020[237] Prospective clinical trial 20 Chinese adult patients who underwent arch expansion with Invisalign aligners Efficiency of upper arch expansion with the Invisalign system Comparison between the expected and actual expansion amounts between pretreatment records and immediately after expansion • Quantify the efficiency of arch expansion using the Invisalign system in patients
• Investigate the movement patterns by comparing actual expansion outcomes of crown and root with virtual planned expansion in ClinCheck software
Ascertain whether the preset expansion amount and initial molar torque correlated with the efficiency of bodily expansion movement B
(Expansion)
Morales-Burruezo et al., 2020[238] Retrospective study 114 patients with transverse malocclusion Efficacy and predictability of arch expansion with Invisalign • Comparing planned measurements (width of canines, premolars and molars rotations and inclinations) with the real measurements achieved at the end of the first treatment phase
• Three data sets; T1: initial measurements at start of treatment; T2: Clincheck predicted measurements at end of first treatment phase; T3: measurements taken at start of the second treatment phase
Determine the efficacy of the Invisalign system for arch expansion Assess the predictability of the measurements planned by Clincheck software for the use of the transparent aligners at the end of the first treatment phase B
(Arch expansion)
Lucchese et al., 2020[239] Retrospective study 72 digital models of 18 consecutive patients treated with Invisalign and Smart Track aligners Arch depth and arch perimeter measurements before and after CAT • Invisalign and Smart Track
• T0–T1 (14 weeks)
• Upper arch was compared to lower arch
Assess values of arch depth and perimeter of arch before and after the treatment using CA B
(Arch depth and perimeter of arch)
Deregibus et al., 2020[240] Prospective clinical study 27 class II patients Morphometric analysis of dental arch form changes in Class II patients treated with CA Maxillary and mandibular digital casts were compared at three different times: pretreatment (T0), the accepted Clincheck®(Align Technology, San José, CA, USA) (T1), and retention phase models (T2) Evaluate the arch form changes in Class II Caucasian patients treated with Invisalign® B
(Class II)
Hansa et al., 2020[9] Retrospective cohort study 90 consecutively treated Invisalign patients (45 control, 45 DM) Outcomes of CAT with and without DM CAT with and without DM The effects of Invisalign CAT with and without DM were compared for treatment duration, number of appointments, number of emergency appointment, refinements and refinement aligners, time to first refinement Assess accuracy of Invisalign in achieving predicted tooth positions (aligner tracking) B
(Maxillary anterior dentition in rotational movements and mandibular anterior dentition for buccal-lingual linear movement)
Amodeo et al., 2020[241] Retrospective study 12 patients affected by class III dento-skeletal malocclusion
(4 females and 8 males), with age range from 22 and 42 years old)
Surgery First and Invisalign System: Combined Digital Approach The CON orthognathic approach, or an orthodontics-first approach Analyzing the benefits and reporting the experience and results of complex cases using surgical treatment with Surgery First and those of an orthodontic treatment with Invisalign technique B
(Surgery first with CAT)
Hansa et al., 2020[242] Retrospective cohort study A sample of 155 consecutively treated Invisalign®patients (67 control, 88 DM) Clinical outcomes and patient perspectives of DM®GoLive®with Invisalign® Control group with no monitoring and DM group Compare the effects of Invisalign®with and without DM®GoLive®on the following parameters: treatment duration, number of appointments, number of refinements, total number of refinement aligners, and time to initial refinement The patients’ perspectives on DM®were also evaluated using an online questionnaire B
(Dental Monitoring)
Gaffuri et al., 2020[243] Prospective clinical study 24 patients Comparative effectiveness of Invisalign FA in First-Premolar Extraction Cases CA and FA Compare the efficacy of clear aligners with that of preadjusted edgewise appliances (MBT) in premolar-extraction treatment, as scored by the ABO Objective Grading System and ABO standard cephalometric analysis B
(Premolar-extraction treatment)
Al-Nadawi et al., 2021[244] Prospective clinical study 80 patients Effect of CA wear protocol on the efficacy of tooth movement • Group A (7-day changes), group B (10-day changes), and group C (14-day changes)
• Post-treatment scans were compared with the final virtual treatment simulations
Compare the efficacy of orthodontic tooth movement with three aligner wear protocols: 7 day, 10 day, and 14 day B
(Posterior segment for maxillary intrusion, distal-crown tip and buccal-crown torque, and mandibular intrusion and extrusion)
Lione et al., 2021[245] Prospective clinical study 28 subjects (16 females, 12 males, mean age 31.9±5.4 years) Maxillary arch development with Invisalign system Before treatment (T1), at the end of treatment (T2), and on final virtual models (T2 ClinCheck)
Different teeth in maxillary arch
Evaluate tooth movements during maxillary arch expansion with CAT B
(Maxillary arch expansion)
Kalemaj and Levrini 2021[246] Prospective cohort study 50 patients treated with CAT by six orthodontists were included Quantitative evaluation of implemented IER during aligner therapy At the beginning of treatment and after the first set of aligners
p-IPR and i-IPR
Investigate the correspondence between p-IPR and i-IPR in an everyday-practice scenario Estimate factors that might influence i-IPR to make the process more efficient B
(IPR)
Al-Balaa et al., 2021[247] Retrospective study 22 patients, with a mean age of 23.74 years Predicted and actual outcome of anterior intrusion with Invisalign assessed with CBCT • Pretreatment and posttreatment CBCT scans
• Comparison between the predicted and actual measurements of anterior intrusion of the teeth was performed
Compare predicted anterior teeth intrusion measurements with the actual clinical intrusion measurements using CBCT B
(Anterior teeth intrusion)
Jiang et al., 2021[248] Retrospective cohort study Pre-CBCT and posttreatment CBCT scans from 69 patients who completed nonextraction treatment with CA were collected How well do integrated 3D models predict alveolar defects after treatment with clear aligners? Pre-CBCT and post-treatment CBCT Evaluate the accuracy of integrated models constructed by pre-CBCT in diagnosing alveolar defects after treatment with CA B
(Prediction of alveolar defects)
Jiang et al., 2021[249] Retrospective clinical study Pretreatment and posttreatment CBCT scans were collected from 69 patients Efficacy of incisor movement with CA • Assessment of incisor pure tipping, controlled tipping, translation, and torque
• Pretreatment model, post-treatment model, virtual model
Evaluate the efficacy of different types of incisor movements with CA in the sagittal plane B
(Incisor pure tipping, controlled tipping, translation, and torque)
Laganà et al., 2021[250] Retrospective study 30 Subjects (14 males, 16 females; mean age of 24.53±13.41 years) Enamel interproximal reduction during treatment with clear aligners: digital planning versus OrthoCAD analysis Digital planning versus OrthoCAD analysis Compare the amount of IPR provided on ClinCheck software with the amount of IPR carried out by the orthodontist during treatment with CA B
(IPR)
Dianiskova et al., 2021[251] Retrospective study 49 Consecutively patients (mean age±SD 12.9±1.7 years), 32 females and 17 males Treatment of mild Class II malocclusion in growing patients with CA versus fixed multibracket therapy CA and FA Compare the dental and skeletal effects of intermaxillary elastics on the correction of mild Angle’s Class II division 1 malocclusion with CA versus fixed multibracket in growing patients B
(Class II)
Caruso et al., 2021[252] Retrospective controlled study 20 patients were examined, 10 of whom treated with MA and 10 treated with TB MA with clear aligners in the treatment of skeletal Class II • MA (Invisalign MA) versus TB
(TB Appliance)
• Pre-treatment and post-treatment lateral skull radiographs
Analyse the dentoskeletal effects of the Invisalign MA device in the treatment of skeletal Class II malocclusions B
(skeletal Class II malocclusions)
Patterson et al., 2021[253] Retrospective study 80 adult patients Class II malocclusion correction with Invisalign • Group 1 with Class I molar malocclusions
• Group 2 with Class II molar malocclusions
• Comparisons between the 2 groups at pre-treatment, post-treatment ClinCheck (Align Technology) prediction, and post-treatment
Determine whether Class II malocclusion can be treated with clear aligners after completing treatment with the initial set of aligners B
(Class II)
Riede et al., 2021[254] Retrospective study 30 patients Effectiveness of CAT in maxillary expansion or contraction and occlusal contact adjustment • A pre-treatment model, a scan-based CC model, a post-treatment clinical model, and a CC model reflecting the treatment outcome as initially simulated
• SmartTrack®compared to previously used E×30®material
Evaluate the precision of aligner (Invisalign®) treatment with the current material (SmartTrack®) in achieving expansion or contraction of the maxilla Evaluate occlusal contacts as simulated in the proprietary planning software (ClinCheck®, CC) B
(Maxillary expansion or contraction and occlusal contact adjustment)
Henick et al., 2021[255] Retrospective study Invisalign group (n=24), FA (n=24) Effects of Invisalign (G5) with virtual bite ramps for skeletal deep overbite malocclusion correction in adults CA and FA Investigate the skeletal and dentoalveolar effects of Invisalign’s G5 protocol with virtual bite ramps in the treatment of adults with skeletal deep bites B
(Vertical movements)
Graf et al., 2021[256] Retrospective study 98 adult patients of whom 33 patients were treated according to predefined inclusion and exclusion criteria Effectiveness and stability of CAT using the Peer Assessment Rating Index Baseline (T0), after finishing orthodontic treatment with Invisalign®(T1; Align Technology Inc., Santa Clara, CA, USA) and after a mean retention period of 10 months (T2) Measure treatment effects of aligner treatments in adult patients directly after treatment Assess the stability of these effects after a short-term retention period using the PAR Index B
(PAR Index/Stability)
Kravitz et al., 2008[359] Prospective clinical study 53 canines (33 maxillary and 20 mandibular) were measured from the virtual TREAT models of 31 participants treated with anterior Invisalign Influence of attachments and interproximal reduction on the accuracy of canine rotation with Invisalign • Three treatment modalities: AO, interproximal reduction only (IO), and neither attachments nor interproximal reduction (N)
• Pretreatment virtual model of the predicted final tooth position was superimposed on the post-treatment virtual model
Evaluate the influence of attachments and interproximal reduction on canines undergoing rotational movement with Invisalign C
Castroflorio et al., 2013[360] Prospective cohort study 12 Upper incisors in Invisalign patients needing lingual root torque as part of their treatment. Six consecutive patients (four females, two males, age 26.3±10.2 years) Upper-incisor root control with invisalign appliances Test the efficiency of Align Technology’s Power Ridge in controlling the buccolingual inclination of upper incisors C
Dasy et al., 2015[361] Experimental in vitro study 3 casts were manufactured Effects of variable attachment shapes and aligner material on aligner retention • Two casts contained attachments (ellipsoid and beveled) were compared with one without any attachments to serve as a control
• Four types of aligners were thermoformed: CA-soft, CA-medium, and CA-hard, with various thicknesses, and Essix ACE
Evaluate the retention of four types of aligners on a dental arch with various attachments C
Simon et al., 2014[362] Experimental study with split mouth design 970 Aligners of the Invisalign system (60 series of aligners). The aligners came from 30 consecutive patients Forces and moments generated by removable thermoplastic aligners: incisor torque, premolar derotation, and molar distalization • 3 Tooth movements (incisor torque, premolar derotation, molar distalization)
• With and without attachments
Quantify the forces and moments delivered by a single aligner and a series of aligners (Invisalign; Align Technology, Santa Clara, Calif) Investigate the influence of attachments and power ridges on the force transfer C and D
Mantovani et al., 2019[363] Experimental in vitro study 6 resin casts obtained from STL files of a patient SEM analysis of aligner fitting on anchorage attachments • 3 different aligners (Invisalign [Align Technology, Santa Clara, CA, USA], CA Clear Aligner [Scheu-Dental, Iserlohn, Germany] and F22 [Sweden and Martina, Due Carrare, Italy])
• 2 different types of resin used to build attachments: CON bulk-fill resin and flowable resin
Evaluate the fitting of three different aligners (Invisalign [Align Technology, Santa Clara, CA, USA], CA Clear Aligner [Scheu-Dental, Iserlohn, Germany] and F22 [Sweden and Martina, Due Carrare, Italy]) on anchorage attachments using SEM Analyze the influence of 2 different types of resin used to build attachments on aligner fitting C
Barreda et al., 2017[364] Randomized prospective clinical trial 40 attachments were bonded to the buccal surface of maxillary teeth Surface wear of resin composites used for Invisalign®attachments Comparison between two resin composites (Filtek Z350 XT, 3MESPE and Amelogen Plus TW, Ultradent Products Inc.) used for making Invisalign®attachments over 6 months period Evaluate surface wear over 6 months in two resin composites (Filtek Z350 XT, 3MESPE and Amelogen Plus TW, Ultradent Products Inc.) used for making Invisalign®attachments Evaluate attachment shape C
D’Antò et al., 2019[312] Experimental in vitro study 25 attachments for each group and a total of 75 attachments Influence of dental composite viscosity in attachment reproduction Three composite resins were selected based on three different degrees of viscosity: A low-viscosity flowable resin (ENAMEL plus HRi®Flow HF, GDF GmbH), a medium-viscosity orthodontic composite (Bracepaste®Medium Viscosity Adhesive, AO), and a high -viscosity dental restorative material (ENAMEL plus HRi®Enamel, GDF GmbH) Evaluate the role of different composite materials in the correct reproduction of attachment shape and position C and E
Thai et al., 2020[365] Case control study 250 adult subjects Esthetic perception of CAT attachments using eye-tracking technology Clear aligner with minimal attachment Assess and compare esthetic perceptions of CAT with attachments and esthetic brackets by measuring differences in eye fixations using eye-tracking technology Importance of appliance esthetics during treatment on a scale of 1 (not important) to 10 (very important) C
Cortona et al., 2020[366] Experimental in vitro study A CAD model including a complete lower dental arch (with element 4.5 mesially rotated 30°) Orthodontic rotational movement of a lower second premolar obtained with CA Comparing different staging and attachment configurations Evaluate, using the finite element method, the orthodontic rotational movement of a lower second premolar obtained with CA, analyzing different staging and attachment configurations C
Lin et al., 2021[367] Split-mouth prospective clinical study 55 participants (13 men and 42 women, mean age±SD: 24.2±5.9 years) Assessment of preparation time and 1-year Invisalign aligner attachment survival using flowable and PC FC group (Filtek Z350XT Flowable Restorative) and the PC group (Filtek Z350XT Universal Restorative) Compare preparation time of aligner attachment between a FC and a PC Compare 1-year Invisalign aligner attachment survival between a FC and a PC C
Yaosen et al., 2021[368] Prospective cohort Study 94 patients undergoing CAT (27 males and 67 females) Risk factors of composite attachment loss in orthodontic patients during orthodontic CAT Assess the incidence of attachment loss during orthodontic CAT Identify rick factors that may predict such event C
Vardimon et al., 2010[369] Prospective cohort study Maxillary aligners (n=61) were examined from 3 patients requiring maxillary incisor retraction and stationary anchored premolars In vivovon Mises strains during Invisalign treatment Series 1 was worn by the patient during the biweekly course of treatment, and series 2 was used for the in vivo von Mises strain measurements worn by the patient only during strain measurements location (incisor and premolar) and time (days 1, 2, 9, and 15). Evaluate the force behavior by analyzing the von Mises strains developed in an aligner during biweekly wear Compare the changes in von Mises strains between the active and anchorage dental units D
Mantovani et al., 2018[370] Experimental in vitro study (STL) files obtained by intraoral scanning of a patient with a Class I malocclusion,
a total of 160 micrometric measurements were obtained
SEM evaluation of aligner fit on teeth • 2 aligner systems, Invisalign and CA-Clear Aligner
• Different teeth and different regions on teeth
Determine how well aligners fit the teeth using SEM Determine whether there were differences in fit between aligners made by Invisalign (Align Technology) and CA-Clear Aligner (Scheu-Dental, Iserlohn, Germany) D
Skaik et al., 2019[313] Experimental in vitro study A series of clear aligners was designed and fabricated Effects of time and clear aligner removal frequency on the force delivered by different PETG -modified materials determined with thin-film pressure sensors CON PET-G and the second material was modified PET-G Identify the various factors (time and CA removal frequency) that influence the force changes generated by PET-G materials D and E
Son et al., 2020[371] Experimental in vitro study Clear aligner and pressure sensor Pressure differences from CA movements 0 mm, 0.25 mm and 1.00 mm movements Assess pressure differences from CA movements assessed by pressure sensors D
Kim et al., 2020[372] Experimental FEA Through 3D FEA, simple tooth shape and mandibular canine shape were extracted Optimal position of attachment for removable thermoplastic aligner on the lower canine using FEA • Lingual side of the tooth compared to the buccal side
• Various shapes of attachments for each of the four orthodontic treatment situations (extrusion, intrusion, rotation, and torque)
Simulate various shapes of attachments for each of the four orthodontic treatment situations (extrusion, intrusion, rotation, and torque) using the FEA to derive the optimum shape of attachment for each situation Analyze the best position for attachments by simulating various attachment positions for each orthodontic treatment situation using the derived attachment shapes. D
Jiang et al., 2020[373] 3D in vitro experimental finite element study A 3D FEM of maxillary dentition was constructed for first premolar extraction Clear aligners for maxillary anterior en masse retraction Compare three protocols with different amounts of retraction and intrusion on incisors Evaluate tooth behaviours under various maxillary incisor retraction protocols for CAT Evaluate location of PDL stresses D
(Incisor retraction and intrusion)
Ma and Li2021[374] In vitroexperimental FEA The CBCT data of a patient received invisible orthodontics without diabetes and other systemic diseases were collected Optimal orthodontic displacement of CA for mild, moderate and severe periodontal conditions Stage I: mild periodontitis, (M1); Stage II: moderate periodontitis, (M2); Stage III: severe periodontitis, (M3)
Left lower lateral incisor, left lower central incisor, right lower lateral incisor, and right lower central incisor
Three different periodontal conditions (M1, M2, and M3) with axial inclination 90° and 100°
Explore an optimal orthodontic displacement of clear aligner using a three-dimensional (3D) FEM for periodontally compromised patient D
Seo et al., 2021[375] In vitroexperimental FEA Three 3D dental FE models were constructed Comparative analysis of stress in the periodontal ligament and center of rotation in the tooth after orthodontic treatment depending on CA thickness 0.75 mm-thick aligner
0.05 mm-thick aligner
Investigate the biomechanical and clinical effects of aligner thickness on stress distributions in the periodontal ligament and changes in the tooth’s center of rotation D
Bollen et al., 2003[187] Propsective clinical trial 51 subjects Activation time and material stiffness of sequential removable orthodontic appliances • 2 distinctly different materials (hard and soft)
• 2 activation frequencies (1 week and 2 weeks)
Compare 2 distinctly different materials (hard and soft) Compare 2 activation frequencies (1 week and 2 weeks) for this technique E
Schuster et al., 2004[314] Prospective clinical trial Samples of Invisalign appliances were randomly selected from 10 patients Structural conformation and leaching from in vitroaged and retrieved Invisalign appliances • Before intraoral placement and after retrieval
• Artificial aging for 2 weeks
Investigate the structure of Invisalign appliances (Align Technology, Santa Clara, Calif) after intraoral exposure Qualitatively and quantitatively characterize the substances leached from the aligners after accelerated in vitro aging E
Gracco et al., 2009[315] Experimental in vitro study One “as-received” Invisalign aligner and 10 Invisalign aligners worn by 10 randomly selected patients Short-term chemical and physical changes in Invisalign appliances Aligner immersed in artificial saliva for 14 days and 10 Invisalign aligners worn by 10 randomly selected patients for 14 days Investigate the short-term optical, chemical and morphological changes in Invisalign appliances E
Schott and Göz, 2011[316] Experimental in vitro study • 7 Invisalign TeenH aligners (A) were obtained directly from the manufacturer (Align Technology Inc, Santa Clara, Calif)
• 14 Invisalign TeenH aligners (B) were provided by an orthodontic office that routinely uses the InvisalignH system
Color fading of the blue compliance indicator encapsulated in removable clear Invisalign TeenH aligners • Color fading was observed as a function of time, pH, and temperature while compliance indicators were stored in drinking water or sour soft drinks and in conjunction with the use of cleaning tablets and a dishwasher
• Color Fading of the Blue Compliance Indicators after soaking of unused aligners (A) in 250 mL of different aqueous media at different temperatures, pH, and time in comparison to the color change of the compliance indicators of 50 aligners after use by patients for 17–22/24 h over 14 Days (B)
Evaluate the color fading in aqueous solutions of the blue dot wear-compliance indicators of the Invisalign Teen®System outside the oral cavity Compare findings of color fading outside oral cavity to the color changes observed when the aligners were being worn by patients E
Lombardo et al., 2015[317] Experimental in vitro study 9 samples of orthodontic aligners Optical properties of orthodontic aligners- spectrophotometry analysis of three types before and after aging • Three different manufacturers (Invisalign, Align Technology, Santa Clara, CA, USA; All-In, Micerium, Avegno, GE, Italy; F22 Aligner, Sweden and Martina, Due Carrare, PD, Italy)
• Before and after two cycles of in vitro aging
Assess and compare absorbance and transmittance values of three types of CA before and after two cycles of in vitro aging E
Alexandropoulos et al., 2015[318] Experimental in vitro study 8 appliances were fabricated from each material Chemical and mechanical characteristics of contemporary thermoplastic orthodontic materials Four thermoplastic materials were tested: Clear Aligner (Scheu-Dental), ACE and A+ (Dentsply), and Invisalign (Align Technology) Characterise the chemical and mechanical properties of contemporary thermoplastic orthodontic materials E
Liu et al., 2016[319] Experimental in vitro study 60 CA produced by three manufacturers (Invisalign, Angelalign, and Smartee) Colour stabilities of three types of orthodontic clear aligners exposed to staining agents • Three manufacturers (Invisalign, Angelalign, and Smartee)
• Three staining solutions (coffee, black tea, and red wine) and one control solution (distilled water)
• After 12-h and 7-days immersions
Evaluate and compare the colour stabilities of three types of orthodontic clear aligners exposed to staining agents in vitro E
Gerard Bradley et al., 2016[320] Experimental in vitro study Appliances were cut
(n=25)
Do the mechanical and chemical properties of InvisalignTMappliances change after use? Samples of Invisalign appliances were collected following routine treatment for a mean period of 44±15 days (group INV), whereas unused aligners of the same brand were used as reference (group REF) Investigate the mechanical and chemical alterations of Invisalign appliances after intraoral aging E
Bräscher et al., 2017[321] Cross sectional survey 72 patients (68% women, 32% men, mean age: 29.3±9.2 years) who had worn the new material for a mean of 6 months Comparing (corrected) the SmartTrack®material to the previously used (corrected) aligner material The SmartTrack®material was compared to the previously used (corrected) aligner material Test how the transition from the previous material used for Invisalign to the new material SmartTrack®
was accepted by patients during ongoing Invisalign®treatment, in terms of pain, pressure upon insertion, comfort, mucosal irritation, phonetics, discoloration, and taste
E
Condo’ et al., 2018[322] Experimental in vitro study 40 Invisalign®aligners Mechanical properties of “two generations” of teeth aligners 20 LD30 aligners and 20 EX30 aligners
Two subgroups, never used and intra-orally aged
Investigate and compare main technical and morphological features of Invisalign®aligners made with two different polymer blends: Exceed30 (EX30) and Smart Track (LD30), before and after use • Evaluate the chemical structure of the two different polymers.
• Evaluate, compare and analyze crystalline phases in the two materials and then identify the physical-chemical properties describing their mechanical behaviors before and after clinical use.
• Compare possible differences in the mechanical behavior starting from samples with the same geometry
E
Agarwal et al., 2018[323] Experimental in vitro study 70 specimens, (n=10 per method, 50.8 mm×12.7 mm×1.0 mm) Long-term effects of seven cleaning methods on light transmittance, surface roughness, and flexural modulus of polyurethane retainer material Invisalign®cleaning crystals (Align Technology Inc), Polident®(GlaxoSmithKline®, Brentford, UK), Listerine®mouthwash (Johnson and Johnson®, New Brunswick, NJ, USA), 2.5% vinegar, 0.6% sodium hypochlorite, 3% hydrogen peroxide, and toothbrushing with distilled water Evaluate the long-term effects of seven different cleaning methods on light transmittance, surface roughness, and flexural modulus of a polyurethane retainer material E
Wible et al., 2019[324] Experimental in vitro study Standardized polypropylene/ethylene copolymer retainer specimens (n=70, 50.8 mm×12.7 mm×1.0 mm) Long-term effects of various cleaning methods on polypropylene/ethylene copolymer retainer material Seven chemical cleaning solutions: Invisalign cleaning crystals, Retainer Brite, Polident, Listerine mouthwash, 2.5% acetic acid, 0.6% NaClO, and 3% H2O2for 6 months
Another group of specimens (n=10) were brushed with a standardized toothbrushing machine for 2 min twice a week
Evaluate long-term light transmittance, surface roughness, and flexural modulus of polypropylene/ethylene copolymer retainer material after exposure to different cleaning methods E
Papadopoulou et al., 2019[325] Experimental in vitro study 40 appliances with attachments were retrieved after the end of orthodontic treatment from different patients Changes in roughness and mechanical properties of Invisalign®Appliances after one and 2 weeks use CA used for 1 week and CA used for 2 weeks and unused control group Estimate the possible changes of surface roughness and the mechanical properties of Invisalign®appliances over one-and 2-weeks of service E
Ihssen et al., 2019[326] Experimental in vitro study A total of 60 specimens made from PETG aligner films (CA Clear Aligner, Scheu Dental, Iserlohn, Germany) Effect of in vitroaging by water immersion and thermocycling on the mechanical properties of PETG aligner material Three groups (immersed in distilled water, subjected to accelerated ageing by thermocycling, control) Investigate elastic properties of PETG aligner films in vitro under extreme temperature changes simulated by thermocycling, environmental temperature and water absorption E
Lombardo et al., 2020[327] Experimental in vitro study A total of 204 linear 2D measurements were made on 18 microtomographic images MicroCT X-ray comparison of aligner gap and thickness of six brands of aligners • 6 aligner systems (Airnivol, ALL IN, Arc Angel, F22, Invisalign and Nuvola)
• Different regions regions were the central incisor, canine and first molar
Investigate and compare the gap (i.e. fit) and thickness of six aligner systems (Airnivol, ALL IN, Arc Angel, F22, Invisalign and Nuvola) using industrial CT E
Bernard et al., 2020[328] Experimental in vitro controlled trial Removable appliances (300 specimens, 100 per brand) Colorimetric and spectrophotometric measurements of orthodontic thermoplastic aligners exposed to various staining sources and cleaning methods • Different staining agents common in a regular diet (coffee, black tea, red wine, cola) are compared to a control solution in vitro over 12 h or 7 days
• Three brands evaluated were Invisalign®, ClearCorrect®and Minor Tooth Movement®
• I nvisalign®cleaning crystals or the Cordless Sonic Cleaner combined with a Retainer Brite®tablet
Evaluate the color stability of the polymer forming three different American brands of aligners Evaluate stain-removal potential of two cleansers either Invisalign®cleaning crystals or the Cordless Sonic Cleaner combined with a Retainer Brite®tablet E
Fang et al., 2020[329] Experimental in vitro study 20 sets of “as-received” (0-week) and retrieved (2-week; worn for 2 weeks, 20±2 h/day) Invisalign aligners collected from 4 different patients Changes in mechanical properties, surface morphology, structure, and composition of Invisalign material in the oral environment “As-received” (0-week) and retrieved (2-week; worn for 2 weeks, 20±2 h/day) Invisalign aligners Fill in the current knowledge gap by systematically evaluating LD30 before and after clinical treatment Attempt to demonstrate the aging of aligner materials from intraoral use by examining material surface morphology, internal structure, and chemical composition changes, as well as illus- trating a corresponding change of mechanical properties E
Tamburrino et al., 2020[330] Experimental in vitro study 3 thermoplastic polymers Mechanical Properties of thermoplastic polymers for aligner manufacturing 3 thermoplastic polymers commonly used to fabricate clear aligners, namely Duran®, Biolon®and Zendura® Evaluate the effect of the thermoforming process, storage in artificial saliva and their combination on the mechanical properties of three thermoplastic polymers commonly used to fabricate CA E
McCarty et al., 2020[331] Experimental in vitro study n=10/group Effect of print orientation and duration of ultraviolet curing on the dimensional accuracy of a 3D printed orthodontic CA design • 3 different build angles with respect to the build platform: parallel (Horizontal), perpendicular (Vertical), and 45° (45−°)
• 3 postprint processing treatment groups: 0 min of UV light and heat exposure (No Cure); 20 min of UV light exposure at 80°C (20 min), and 40 min of UV light exposure at 80°C (40 min)
Investigate the effect of print orientation and UV light curing duration on the dimensional accuracy of a CA design fabricated directly using 3D printing E
Memè et al., 2021[332] Experimental in vitro study 12 new Invisalign®aligners ATR-FTIR Analysis of orthodontic Invisalign®Aligners subjected to various in vitro aging treatments Coffee, tea, Coca Cola®and UV radiation for 24 and 48 h. Assess a new objective approach, coupling spectroscopic and chemometric tools, to evaluate the changes occurring in Invisalign®aligners, the most widely used brand, exposed in vitro to coffee, tea, Coca Cola®and UV radiation for 24 and 48 h E
Palone et al., 2021[333] Experimental in vitro study 6 passive upper aligners of different brands were adapted to a single printed cast Micro-computed tomography evaluation of general trends in aligner thickness and gap width after thermoforming procedures involving six commercial CA • Tooth type (central incisor, canine, and first molar), 2D reference points, and aligner type
• (Airnivol, ALL IN, Arc Angel, F22, Invisalign, and Nuvola)
Evaluate and compare the general effects of thermoforming processes on both gap width and thickness via micro-CT investigation of passive aligners with the same nominal thickness obtained from six manufacturers E
Isman andIsman 2021[334] Experimental in vitro study 5 different orthodontic materials Identification of various orthodontic materials as foreign bodies Titanium-molybdenum alloy wire (TMA; ORMCO, Orange, CA, USA; 0.017×0.025 in cross-sectional dimensions and 1 cm long); stainless steel bracket tooth #34 (American Orthodontics, Sheboygan, WI, USA); a monocrystalline, sapphire ceramic bracket tooth #34 (Skyortho Dental Supplies Medical, China); a polycrystalline alumina clear bracket, Damon clear bracket tooth #34 (ORMCO); and a 1×1 × 0.1 cm polyurethane-based thermoplastic material, Invisalign clear aligner (Align Technology, San Jose, CA, USA)
Panoramic radiography, CBCT, MRI, and ultrasonography
Evaluated the in vitro detection sensitivity of orthodontic materials (serving as foreign bodies) using panoramic radiography, CBCT, MRI, and ultrasonography E
Mantovani et al., 2021[335] Experimental in vitro study 20 different aligners Micro computed tomography evaluation of Invisalign aligner thickness homogeneity Different regions (molar, canine, incisor) and in different sites (gingival–buccal, buccal, occlusal, lingual, and gingival–lingual) Measure the thickness homogeneity of Invisalign (Align Technology Inc, San José, Calif) aligners with micro-CT scans E
Meier et al., 2003[188] Cross-sectional survey 89 patients Analysis of patient profiling for CAT Gender, age, profession, motivation for treatment, accepted treatment duration, and initial source of information Produce a profile of those patients who are interested in treatment with the Invisalign system F
Nedwed and Miethke 2005[336] Cross-sectional questionnaire 55 patients Motivation, acceptance and problems of invisalign patients • After 3–6 months of Invisalign treatment
• Lingual technique
Examined how well patients accepted and to what extent they were impaired by Invisalign treatment: adaptation time, occurrence and duration of pain, possible speech impairment, lingual and mucosal irritations, TMJ problems and subjective assessment of the success of therapy F
Jeremiah et al., 2011[337] Cross-sectional study 130 undergraduates from the UK Social perceptions of adults wearing orthodontic appliances Five modified photographs of the same young adult female were used: (1) No appliance, (2) stainless steel fixed orthodontic appliance, (3) ceramic fixed orthodontic appliance, (4) gold fixed orthodontic appliance, and (5) clear colourless aligner Ascertaine the influence of orthodontic appliances on subjective ratings for social competence, intellectual ability, psychological adjustment, and attractiveness in young adult orthodontic patients F
Cooper-Kazaz et al., 2013[338] Prospective clinical study 68 adult patients divided into three groups (28 buccal, 19 lingual, and 21 clear aligners) The impact of personality on adult patients’ adjustability to orthodontic appliances Three groups (28 buccal, 19 lingual, and 21 clear aligners) Evaluate the impact of psychological traits on patients’ choice of orthodontic appliances and their adjustability to orthodontic treatment F
Kuhlman et al., 2016[339] Cross-sectional study n=276 Esthetic perception of orthodontic appliances by Brazilian children and adolescents • Different ages, sex and socioeconomic standards
• Eight different situations: (A) with fixed sapphire esthetic brackets, clear elastomeric ligatures (American Orthodontics, Wisconsin, USA) and 0.020-in stainless steel archwire (GAC International, New York, USA); (B) with a clear tray aligner with attachments; (C) with fixed golden orthodontic brackets and clear elastomeric ligatures (American Orthodontics, Wisconsin, USA); (D) with a fixed metallic self-ligating system; (E) with fixed traditional metallic brackets with gray elastomeric ligatures; (F) with fixed sapphire esthetic brackets, clear elastomeric ligatures (American Ortho-dontics, Wisconsin, USA) and 0.018-in esthetic nickel titanium coated archwire (American Orthodontics, Wisconsin, USA); (G) with a clear tray aligner without attachments; (H) similar to (E), but with green elastomeric ligatures (Morelli, São Paulo, Brazil)
Understand how children and adolescents perceive esthetic attractiveness of a variety of orthodontic appliances Analyze preferences according to patients’ age, sex and socioeconomic status F
Arun et al., 2017[340] Cross-sectional study 119 websites were included for analysis Qualitative assessment of Internet information regarding Orthodontic treatment modalities • Specialist orthodontists
• General dentists
• Cosmetic braces, fixed braces, removable braces, Quick braces and risks
Determine the quality, accuracy, reliability and usability of Internet information, regarding different orthodontic treatment modalities F
Noll et al., 2017[341] Cross-sectional study 419,363 tweets applicable to orthodontics were collected Twitter analysis of the orthodontic patient experience with braces versus Invisalign CA and FA Examine the orthodontic patient experience having braces compared with Invisalign by means of a large-scale Twitter sentiment analysis F
Livas et al., 2018[342] Cross-sectional study 40 reviewed testimonials Content, metrics and comment sentiment analysis of the most popular patient testimonials on YouTube Investigate the popularity, content, metrics of Invisalign patient testimonials on YouTube, as well as the sentiment of the related comments F
Ustdal and Guney 2020[343] Cross-sectional survey From the first 140 results, 100 videos were selected for analysis YouTube as a source of information about orthodontic clear aligners Evaluate the content, reliability, and quality of videos about orthodontic clear aligners on YouTube F
Bustati and Rajeh 2020[344] Online questionnaire cross-sectional study 388 responses were analyzed: mean age 20.4±4 years, 75% (291) female, and 58% (226) received their treatment at a public clinic The impact of COVID-19 pandemic on patients receiving orthodontic treatment CA and removable appliances compared to FA Assess the challenges faced by patients receiving orthodontic treatment and their preferred solutions to overcoming these challenges during this pandemic F
Adobes-Martin et al., 2021[345] Cross-sectional study 1564 tweets were analysed Invisalign treatment from the patient perspective Pre-treatment related, treatment related and patient/clinician relationship Qualitatively describe the content of Twitter posts related to the treatment with Invisalign to get a better understanding of patient experience F
Zybutz et al., 2021[346] Cross-sectional survey 68 patients Patient experiences with removable functional appliances ITMA and TB appliances Compare patients’ experiences with the TMA and TB appliances, both initially and after several months of wear F
Noble et al., 2009[347] Cross-sectional survey 335 e-mails from 37 programs were obtained Future practice plans of orthodontic residents in the United States Sex, age, and year of program Investigate the future clinical practice plans of orthodontic residents in the United States G
Noble et al., 2009[348] Cross-sectional survey 54 residents in Canada Motivations and future plans of Canadian orthodontic residents Investigate factors influencing career choice and to identify future plans of Canadian orthodontic residents G
Vicéns and Russo 2010[349] Cross-sectional survey A total of 406 questionnaires were mailed: 284 to general practitioners and 122 to orthodontists Comparative use of Invisalign by orthodontists and general practitioners Orthodontists and general practitioners Test the hypothesis that there is no difference in the use of Invisalign between orthodontists and general practitioners G
Al-Hamlan et al., 2013[350] Cross-sectional survey 36 orthodontic residents Motivations and future practice plans of orthodontic residents in Saudi Arabia Explore the criteria used by graduate students while selecting a career as orthodontists and their future aspirations G
Jauhar et al., 2016[351] Cross-sectional survey 362 final year undergraduate students in four dental institutes in the UK Undergraduate orthodontic teaching and factors affecting pursuit of postgraduate training Assess the levels of knowledge of occlusal problems among final year undergraduate dental students Assess their interest in various orthodontics techniques and training G
Mackay et al., 2017[352] Interrupted time series
Cross-sectional analysis
1,871 GP and orthodontic practices worldwide
319 low-volume, North American GPs
Impact of digital scanning in GDPs and orthodontic practices to determine the percent increase in gross receipts of Invisalign®treatment • 48 months (24 pre- and 24 post-scanner introduction) of Invisalign receipt
• GP and orthodontic practices located worldwide
Evaluate the impact of digital scanning in GDPs and orthodontic practices to determine the percentage of lift, that is, the percent increase in gross receipts, of Invisalign®treatment starts following the introduction of an iTero®intraoral scanner G
Didier et al., 2019[353] Cross-sectional survey Evaluators included 236 individuals, divided into 4 groups according to age and gender: males between 18–35 years (M), males over 35 years (M>35), females between 18–35 years (F), and females over 35 years (F>35) Influence of orthodontic appliance design on employment hiring preferences • One image was produced without orthodontic appliances, and 6 simulated the use of orthodontic appliances, including a CON metallic appliance with a gray elastic ligature, a CON metallic appliance with blue elastic ligature, a CON appliance with a transparent elastic ligature, a self-ligating metal appliance, a self-ligating esthetic appliance, and a clear aligner
• Evaluators were divided into 4 groups according to age and gender: males between 18–35 years (M), males over 35 years (M>35), females between 18 and 35 years (F), and females over 35 years (F>35)
Evaluate the extent to which different types of orthodontic appliances influence the hiring process of an individual applying for a customer service position G
d’Apuzzo et al., 2019[354] Web based cross-sectional survey 129 members of the European Aligner Society and 200 doctors of dental surgery Different perspectives between orthodontists and general dentists in CAT • Orthodontists were compared to general dentists
• Clinicians using or not using CAT
Evaluate experience with clear aligners • Evaluate patient demand and perception
• Evaluate types of patients
• Malocclusion treated with CA
• Reasons for not using CAT
G
Batarse et al., 2019[355] Retrospective study 20 cases
Forty-one panel members (56.1% male, 43.9% female) evaluated the survey
Referral patterns of pediatric dentists and general practitioners to orthodontists based on case complexity General dentists (n5 21; 51.2%) and pediatric dentists (n5 20; 48.9%) Investigate and compare general and pediatric dentists’ subjective judgments of orthodontic case complexity Determine how their perceptions of case complexity influence their decisions to refer the patient to an orthodontist G
Linjawi et al., 2020[356] Cross-sectional electronic survey n=195 Awareness, perception and readiness regarding CAT among orthodontists and other dental specialists • GDPs, orthodontists, and other dental specialists
• Age, gender, nationality, specialty, education level, and place of work
Compare the differences in awareness, perception and readiness for clear aligner usage among orthodontists, GDPs, and other dental specialists in Saudi Arabia G
Hellyer 2021[357] Cross-sectional survey 21 such sites (USA=13, UK=3, Australia=4) Poor information on clear aligner websites Assess sites for readability, quality of information provided and measured against American Medical Association benchmarks for websites G
Bruni et al., 2021[358] A bibliometric and visualized cross-sectional analysis Total of 378 articles The 50 most-cited articles on CAT Perform a bibliometric and visualized analysis to identify and critically assess the 50 most highly cited articles on CAT G

OIEARR: Orthodontically induced external apical root resorption, VAS: Visual analogue scale, LIPUS: Low-intensity pulsed ultrasound, CON: Conventional, IER: Interproximal enamel reduction, CFA: Cranio-facial anomalies, SEM: Scanning electron microscopy, FEM: Finite element model, PAR: Peer assessment rating, LF: Low friction, TG: Treated group, EARR: External apical root resorption, QA: Quaternary ammonium, CAT: Clear aligner therapy, ITMA: Invisalign Teen with Mandibular Advancement®, MA: Mandibular advancement, TB: Twin block, PETG: Polyethylene terephthalate glycol, CA: Clear-aligner, FEA: Finite element analysis, AO: Attachments only, IO: Interproximal reduction only, p-IPR p-IPR: programmed interproximal reduction, i-IPR: Implemented interproximal reduction, DM®: Dental monitoring®, FC: Flowable composite, PC: Packable composite, PBM: Photobiomodulation, PBF: Pulpal blood flow, GPs: General practitioners, GDPs: General dental practices, QA-GNCs: QA-modified gold nanoclusters, CBCT: Cone beam computed tomography, MRI: Magnetic resonance imaging, GP: General Practitioner, STL: Standard Tessellation Language, FA: Fixed Appliances, ABO-OGS: American Board of Orthodontics’ Objective Grading System, CEJ: Cemento-Enamel Junction, TMD: Tempromandibular Disorders, OTM: Orthodontic Tooth Movement, DM: Dental Monitoring, HFV: High Frequency Vibration

RESULTS

Search and selection of studies

The initial database and additional search resulted in 7000 records, of which 369 potentially relevant articles were retrieved in full. 190 studies met the selection criteria following screening and were included in the ScR with the results of the search depicted in the PRISMA flow chart [Figure 1]. The studies included in the review are shown in [Table 3] and represented graphically in [Figures 2-4], whereas 179 excluded studies with reasons are enumerated in [Table 2] and represented graphically in [Figure 5].

Figure 2:
Bar graph showing the percentages of published studies in 3 time frames.
Figure 3:
Hierarchy of evidence for studies published about clear aligner therapy.
Figure 4:
Pie chart illustrating the percentage distribution of the seven main domains reported in the literature. CAT: clear aligner therapy; FEA: Finite Element Analysis.
Figure 5:
Bar graph showing the percentage distribution of different reasons for studies exclusion.

General characteristics of included studies in the ScR

Year-wise distribution of studies

Studies were classified into three groups according to a year time frame

  1. 2001–2010: 21 studies

  2. 2011–2020: 138 studies

  3. 2021: 31 studies.

The included publications ranged in date from 2001 to 2021. The bar graph in [Figure 2] demonstrates that most of the studies were published in the period between 2011 and 2020, with 138 studies accounting for 73%. Interestingly though, the year 2021 followed, with 31 studies accounting for 16%, which was greater than the number of studies published in 10 years from 2001 to 2010 with only 21 studies representing 11%.

Study designs of included studies

The Hierarchy of evidence for studies published about CAT in [Figure 3] illustrates that most of the published studies were at the lowest level of evidence including case reports, case series, narrative reviews, expert opinions, and editorials accounting for 137 studies. This was followed by cohort studies with 79 studies that were either retrospective or prospective in nature. Animal and laboratory studies were equal to the prospective clinical trials accounting for 39 studies each. 20 systematic reviews and meta-analyses were identified and represented the highest level of evidence. Case–control studies were the least reported studies with only four studies reported in the literature.

Distribution of seven outcome domains reported in the literature

The pie chart reveals the percentage distribution of the seven main outcome domains reported in the literature about CAT. Treatment outcome considerations associated with CAT had the greatest percentage representing 36% of the total published domains. Biological considerations associated with CAT come in next, accounting for 29.5% of the domains reported. This was followed by the biomaterial considerations associated with CAT representing 12.1%. At comparable percentages, came the patient education, experience, aesthetic and social perception, miscellaneous considerations, as well as geometrical considerations associated with CAT, representing 6.3%, 6.3%, and 5.8%, respectively. The final place was occupied by the biomechanical considerations associated with CAT accounting for only 4% of the published domains about CAT.

Most of the excluded studies were case reports with a total number of 86 articles. This was followed by opinion articles, narrative reviews and systematic reviews and meta-analyses with 25, 21, and 20 articles, respectively. Other types of articles and reasons for exclusion represented only a small number of studies.[1-3,11-186] [Figure 5 and Table 2].

DISCUSSION

Clear aligners have revolutionized the practice of orthodontics since the introduction of Invisalign in 1998. The first mention of clear aligners in the academic literature occurred in 2001 and included an article on technique,[90] a case report,[172] and an opinion article.[182] The first scientific study of clear aligners occurred in 2003. Bollen et al.[187] studied the effect of different plastic stiffness and wear time on tooth movement, while Meier et al.[188] investigated the patient profile of those requesting and undergoing clear aligner treatment. Over the next decade, between 2001 and 2010, just 21 studies have been published. 138 studies have been published in the next decade (2011–2020). In 2021, 31 research articles have already been published, continuing this exponential increase. This surge of research output reflects the larger trend of increases in the usage and popularity of clear aligners.

The studies investigating CAT were characterized into seven outcome domains. The majority of clear aligner research focused on treatment outcome considerations (36%),[9,189-256] which is rightfully the most researched domain as it is fundamental to assessing the treatment effectiveness of CAT and comparing it to more established treatment modalities including fixed appliances using ABO-OGS, irregularity index, and PAR index. The efficacy of CA in achieving different tooth movements, in different planes of space, in extraction and surgical cases, and the recommended types of malocclusions to be treated with CA were also studied. Accuracy of predicted movements and IPR versus achieved ones, finishing and stability with CA, quality of life impacts, evaluation of smile with CA, evaluation of treatment outcomes with and without dental monitoring and the effect of CA wear protocol on the efficiency of tooth movement were additionally investigated in different studies under this domain. Biological considerations made up 29.5%.[189,257-311] This domain investigated and contrasted topics such as biofilm changes, periodontal health, gingival parameters, pain perception, masticatory muscle soreness and anxiety, apical root resorption, early tooth movement, bone metabolism and volume, pulpal blood flow, enamel demineralization, mineral and trace elements in saliva, adult patient’s adjustability, oral health-related quality of life, cytotoxicity, and epithelial cell reaction after exposure to CA material. In addition, the effect of the use of vibration, photo-biomodulation, and ultrasound on CAT was also studied. The effect of the use of CA on facial wrinkles, postural changes, speech articulation, as well as on tooth whitening was moreover investigated. This domain was followed by biomaterial considerations representing 12.1% of the studies and investigated factors such as mechanical, optical and chemical properties, the fit of aligners, colour stability and aging, different thickness and materials of aligners, different composite materials in the reproduction of attachments shape and position, the effect of different cleaning methods, and effect of print orientation on the dimensional accuracy of CA.[187,201,312-335] At 6.3% came patient education, experience, esthetic and social perception and adjustability,[188,336-346] as well as miscellaneous considerations including factors influencing career choice, future aspirations, use of CA by orthodontists and general practitioners, the impact of digital scanning on CA popularity and the documentation of the most highly cited articles.[347-358] Geometrical considerations associated with CAT, representing 5.8% of the studies, primarily explored attachment configurations clinically, the efficiency of power ridges, retention, and fit of CA with various attachments and incidence of attachments loss.[200,312,359-368] The final place was occupied by biomechanical considerations accounting for only 4% of the published outcome domains.[313,362,369-375] This domain examined in vitro studies on the force distribution applied by CAT and pressure differences from different movements, with some studies using FEA to further study the forces and moments produced by CA in different tooth movements. Future studies investigating clear aligners should perhaps place greater focus on Biomechanical, Geometrical, and Biomaterial considerations of clear aligner treatment. Studies of these domains will allow for a greater understanding of CAT as a whole, as opposed to studying a single brand.

With the rapid technological development of 3D printing, artificial intelligence (A.I.) and machine learning, and material sciences, an increase in customized appliances can be expected in the future, whether CAT or fixed appliances. A.I. is being used by commercial companies to improve CAT, but this has not been done independently. This area of study will hopefully be researched in the near future.

Another noteworthy result found was that the vast majority of research on CAT only studied a single brand, that is, Invisalign. Although some articles were unclear about which brand of aligners or materials were used,[230,265,278,280,282,304,306,326,339] only eight studies utilized other brands of aligners or materials[201,285,287,288,291,330,333,361] other than Invisalign. Are the results of the majority of studies then relevant to CAT as a modality, or a given brand? This seems to be a significant limitation in the current CAT literature. Ercoli et al.,[201] in 2014, were the first authors to compare two different aligner systems. These were then followed by Lombardo et al.[317] in 2015 and Mantovani et al. in 2019.[363] Lombardo et al.[327] and Palone et al.[333] have also recently compared the aligner thickness and gap width of 6 aligner systems.

In the future, independent research should be carried out to investigate outcomes of the various clear aligner systems and material components involved, to understand CAT in its entirety, as opposed to a single aligner brand of aligners. While aligners are an established clinical reality today, the incipient scholarly literature indicates many unanswered questions and unstudied domains. Future researchers can dwell on the findings of this ScR, before embarking on projects that can augment aligner literature.

While we attempted to determine the scope and extent of the published literature on clear aligners in orthodontics, as well as identify the types of studies published, and summarize the outcomes studied, some limitations are present. Our search terms were in the English language; hence, articles in languages other than English may have been missed. Similarly, some articles may not have been found due to the search terms used. Studies with <10 participants were excluded which was done in an attempt to obtain more meaningful data which could assist in identifying the more common outcome domains. ScRs do not assess the methodologies and risk of bias of the included studies, rather the goal is to explore the literature as an overview.

CONCLUSION

Outcome domains studied in literature were: Treatment outcomes (36%); Biological considerations (29.5%); Biomaterial considerations (12.1%); Patient education, experience, esthetic and social perception (6.3%); Miscellaneous (6.3%); Geometrical considerations (5.8%); and Biomechanical considerations (4%).

Most of the published studies were at the lowest level of evidence including case reports, case series, narrative reviews, expert opinions, and editorials accounting for 137 studies. This was followed by cohort studies with 79 studies. Animal and laboratory studies and prospective clinical trials accounting for 39 studies each. 20 systematic reviews and meta-analyses were identified. Case–control studies were the least reported studies with only four studies reported in the literature.

The vast majority of studies utilized only a single clear aligner brand. There is a greater need for research that studies CAT from a holistic perspective.

Ethical approval

The research/study complied with the Helsinki Declaration of 1964.

Declaration of patient consent

Patient’s consent not required as there are no patients in this study.

Conflicts of interest

Prof. (Dr.) Nikhilesh R. Vaid is the Emeritus Editor-In-Chief and Dr. Ismaeel Hansa is one of the assistant editors of the journal.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Financial support and sponsorship

Nil.

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