Comparison of the treatment duration and effects of magnetic mandibular repositioning appliances and non-magnetic twin block in the treatment of growing patients with skeletal Class II malocclusion due to mandibular retrognathism – A systematic review

Knowledge gap

This systematic review was done in an attempt to evaluate that magnetic mandibular repositioning appliances corrects skeletal Class II malocclusion in a shorter duration with greater skeletal and less dental effects than non-magnetic twin block. Furthermore, there is no systematic review and literature available where a direct comparison between magnetic mandibular repositioning appliances and non-magnetic twin block is given. Hence, this review would prove to be useful for further research.

Information sources

To identify the published studies or research, we searched the electronic databases from PubMed through MEDLINE, Google Scholar, and Cochrane central register of controlled trials. The database was searched from January 1970 to June 2021, since the rare earth magnets which are commonly used in functional appliances had their commercial start from the 1970s with no restriction on a date and without using any filter for magnetic mandibular repositioning studies, whereas randomized control trial filter was used for searching non-magnetic twin block studies without any limits which were applied for the English language and human subjects. All stages were conducted according to the current Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) checklist. The international database of PROSPERO (prospectively registered systematic reviews in health and social care) and register of systematic reviews were searched in February 2020 showing no existing or current review protocols on comparison between magnetic mandibular repositioning appliances and twin block appliance.

Additional hand searching of reference lists of relevant articles, gray searching in Google Scholar, and correspondence with experts in the field were conducted for the location of any additional studies. Keywords and truncation symbols were utilized to retrieve all potential combinations of the search MeSH terms. Keywords and strategy and MeSH terms for PUBMED through Medline are shown in [Tables 1 and 2].

Eligibility criteria

1. Articles published till June 2021

2. Articles providing information of the growing participants undergoing functional orthopedic correction due to mandibular retrognathism

3. All articles in the English language

4. Studies with one-step mandibular jaw advancement

5. Full-text articles.

Exclusion criteria

1. Articles that were abstracts, letters to editorials, editorials, and animal studies

2. Articles that were unclear about the effect of magnetic mandibular repositioning appliances

3. Non-growing individuals

4. Syndromic cases.

PICO

• Participants – Growing children

• Intervention – Magnetic mandibular repositioning appliances.

• Comparative – Non-magnetic twin block appliance

• Outcome – Treatment effects.

Study selection

Screening of retrieved articles, assessment of the risk of bias, and extraction of data were conducted independently and any two discrepancies in results were resolved by discussion before combination. First, title and abstract screening were performed, followed by a full-text assessment for second-level evaluation. Any study where no abstract was available or the information available was inconclusive in reaching a decision was assessed in full text. During the screening, researchers were blinded to the author of the article, and journal to minimize potential biases in the selection process of primary studies. Where questions remained after full-text evaluation, efforts were made to contact relevant authors for clarification. The number of articles identified through electronic database search and manual hand search was 263. After a thorough reading of titles, 11 articles warranted relevance. Furthermore, duplicate articles were removed. Full texts of eight articles that were found potentially eligible were obtained and thoroughly assessed for eligibility. The distribution of the journals in which these articles were published is tabulated in [Table 3].

Quality assessment

The Newcastle–Ottawa scale was applied to assess the quality of the controlled CTs.^[6] The studies were appraised and were designated “stars” based on three objectives:

1. Selection of study groups

2. Comparability of groups

3. Determination of outcome of the study.

The items and criteria of assessment were specified in [Tables 4 and 5].

Methodological assessment of the quality of the included studies/CTs (clinical trials) was assessed using the Newcastle-Ottawa scale. The scores ranged between 3 and 8, indicating that the quality of the studies was moderate to high.

The quality assessment of the RCT was done employing the checklist by the Cochrane Collaboration risk of bias tool.^[7] The checklist provided by the Cochrane Collaboration risk of bias tool to assess the quality of RCTs was specified in [Tables 6 and 7]. Furthermore, the risk of bias was assessed using Rob tool 2^[8] and not much difference was observed.

Study characteristics

The study characteristics are summarized in [Tables 10 and 11]. Two different types of appliances, that is, magnetic mandibular repositioning appliances and non-magnetic twin block were compared. Both skeletal and dental parameters were considered in this systematic review with treatment duration as a primary objective. The treatment modalities included magnetic mandibular repositioning appliances in four studies that employed MAD II, FOMA II, Sydney Magnoglide, and non-magnetic twin block in four studies to correct skeletal Class II malocclusion.

Treatment duration

Treatment time plays an important role during orthodontic treatment since many orthodontic patients are concerned about the amount of time that they will be required to wear functional appliances. In this systematic review, we have compared the treatment duration of magnetic appliances with non-magnetic twin blocks. The average treatment duration with a magnetic mandibular repositioning appliances was 4–5 months which was approximately half as that of a non-magnetic twin block appliance (10–12 months).

Skeletal effects

Darendeliler and Joho^[5] in their case report observed that the amount of skeletal versus dental response depends on the intensity of the magnetic force. If the force is too strong, it maintains the two appliances together and forms a traditional activator. Above 500 g, the muscle force necessary to unlock the magnets is transmitted through the appliances to the dental anchorage and seems to produce unwanted or exaggerated dental movements. Below 200 g, the magnetic force seems to be insufficient. Hence, a force of 300 g on each side seems to be appropriate. The study did not mention much about angular and linear changes. The ANB was reduced by 2°–3° when the MAD II appliance was used.

Darendeliler^[12] in his study observed that MAD II produced combined skeletal and dental effects. There was a maxillary restraining effect (SNA reduced by 1.4°) and anteriorly repositioned mandible (SNB increased by 0.94°). The reduction of SNA by 1.4° is similar to Illing et al.’s twin block study^[13] but greater than the result of the Trenouth^[14] study, where the reduction in SNA was only 0.6°.

In Yüksel et al.^[15] the study, SNA showed that the MAD II appliance inhibited maxillary growth by 0.9° which was insignificant in Yüksel et al.^[15] study. SNA decreased non-significantly with MAD II application, which might be due to the observed increase in SN distance as a consequence of growth and development. ANB angle was significantly decreased during treatment (P < 0.01). The change in SNB angle was not statistically significant, however, a significant increase in mandibular length was observed with Barbre and Sinclair.^[16] Mandibular effective length (Co–Gn) showed a significant increase by 4.8 mm (P < 0.05), which is in agreement with the previous studies (Kalra et al., 1989).^[17]

Phelan et al.^[18] carried out a prospective clinical study that demonstrates that the Sydney Magnoglide is an effective appliance for functional Class II correction. The corrections of the overjet and molar relationship achieved in all patients treated with the Sydney Magnoglide were mainly associated with favorable skeletal mandibular changes. The outcomes of the orthopedic phase of treatment with the Sydney Magnoglide showed that 51.5% of the overjet correction was due to skeletal changes, almost exclusively in the mandible, the skeletal changes with the Sydney Magnoglide were due to skeletal modifications exclusively in the mandible. At the end of functional appliance therapy, the treated group showed an average gain of 5.2 mm in mandibular length; this is an average of 2.5 mm more than in the control group and therefore almost twice the effect. The outcome for the Sydney Magnoglide was similar to that of the functional magnetic system,^[9] which also had a 2-fold increase in mandibular length but was less favorable than the Herbst appliance, which enhances mandibular growth on average 3 times as much as the untreated control subjects.^[19,20] There was a statistically significant increase in the SNB angle at the end of treatment. The Sydney Magnoglide had a negligible effect on the growth of the maxilla. There was on average 0.1 mm more forward maxillary growth in the treated subjects during the functional appliance phase of therapy compared with the controls. Investigations on twin block therapy also demonstrated no effect on the sagittal position of the maxilla.^[21-23]

Twin block appliance increased the duration of treatment by a factor of 2.2 months compared with the Herbst appliance with shorter treatment times, compared with a factor of 1.5 months in with longer duration which was observed in O’Brien et al.^[24] study. Pancher’s analysis showed both the appliances twin block and Herbst produced almost similar effects with a greater increase in mandibular length with twin block.

Burhan et al.^[25] in their RCT observed that both appliances (bite-jumping appliance and twin block) were effective in correction of skeletal Class II malocclusion. That conclusion appears obvious from the significant decrease in the ANB angle and the overjet during the treatment. The forward motion of mandible was demonstrated by a significant increase in the SNB angle by 2.88 degrees in the BJA group and 3.13 degrees in the TBA group. A significant increase in the dimensions of the mandible including the length of the mandible by 3.13 ± 1.20 mm (P = 0.008) and 2.42 ± 1.45 mm (P < 0.001) in the BJA group and TBA group and of the height of the mandible by 2.63 ± 1.28 mm (P = 0.006) and 2.52 ± 1.63 mm (P < 0.001) in the BJA group and the TBA group, respectively. Martina et al.^[26] referred to a significant increase in the length of the mandible but an insignificant increase in the height of the mandible with the BJA. Conversely, Baysal and Uysal^[27] reported a significant increase in the height of the mandible but an insignificant increase in the length of the mandible with TBA. No significant changes were observed in the maxilla in the sagittal plane. No significant changes were observed in the SNA angle in both study groups. This finding with some caution may indicate that the two appliances were able to restrict the growth of the maxilla. The upper incisors in this study were significantly proclined in the two groups. The root apices might have moved anteriorly and point A might have been advanced as a result of alveolar bone reshaping. The SNA angle did not increase under these circumstances, so it could be assumed that some restriction of maxillary growth had occurred. Studies of O’Brien et al.^[24] and Tumer and Gultan displayed restriction of the maxilla,^[28,24] whereas the study of Baysal and Uysal^[27] did not. The differences in results between their study and the Burhan et al. study could be attributed to the differences in working methods.

Parekh et al.^[29] the study was the first to demonstrate no significant differences in key dental and skeletal parameters between adolescent patients treated with a functional appliance prescribed for either part-time (PT) or full-time (FT) wear. No clinically or statistically significant differences between the PT and FT groups were noted concerning skeletal changes. However, a greater increase in mandibular length was observed with the FT wear group. SNB angle between groups increased approximately 1.5º over the 12 months. This mirrors previous research; by Baysal and Uysal.^[27] Negligible changes in SNA angle were noted in both groups (0.03–0.5) with the FT group demonstrating slightly more maxillary restraint.

Dibiase et al.^[30] in their RCT observed that the patients treated with the twin block appliance showed a greater reduction in the overjet and greater skeletal change for all parameters except the horizontal movement of A point. Fifteen months of therapy with the twin block was associated with a forward movement of the chin of 3.5 mm, similar to that reported in other studies.^[23,24] The forward growth of the chin with the Dynamax was limited to 1.7 mm. There was some evidence of restraint in the maxillary growth in the Dynamax group with a forward movement of A point of only 0.2 mm over 15 months. The main skeletal change, however, is in the mandibular length, which increased by 6.2 mm in the twin block and 4.1 mm in the Dynamax. The twin block finding is similar to that of Lund and Sandler^[23] with an increase in length by 5.1 mm and De Vincenzo of 6 mm.^[31]

Dental effects

Extreme overjet of 13 mm reduced to 7 mm to achieve Class I relationship within 4 months in Darendeliler and Joho’s^[6] study.

Darendeliler^[12] observed that with MAD II, the upper incisors were retroclined (1/SN reduced 3.6°), there was proclination of lower incisors (1/Md 2.2°), the change in upper incisor inclination (1/SN reduced 3.61°) is less than other studies using twin blocks (Illing et al.;^[13] 1/PP reduced by 9.2°, Trenouth;^[14] 1/PP reduced by 9.2°, and Trenouth; 1/PP reduced by14.27°). This difference may be due to the design of the appliances with the twin blocks incorporating a labial bow, whereas the MAD II utilized anterior torquing springs. The lower incisors proclined by 2.2° in the MAD II, which was not statistically significant when compared with the control group. This effect was similar to that produced by the twin block appliance where the lower incisors were proclined by 2.1°38 and 1.13°.3.

Yüksel et al.^[15] found that the MAD II appliance produced a change in L1–NB angle was also significant (P < 0.05). Overjet showed a significant decrease (P < 0.001), but the change in overbite was not significant. Overjet decreased significantly (P < 0.001) because of forwarding movement of the mandible and retroclination of the upper incisors.

Phelan et al.^[18] in her study observed that the magnetic forces acting on the dentition are not continuous, leading to less dental movement with the Sydney Magnoglide. The average overjet and molar corrections at the end treatment were 3.5 and 4.7 mm, respectively. The molar correction with the Sydney Magnoglide compares favorably with studies of the twin block^[22] and the functional magnetic system^[9] demonstrating molar corrections of about 4.8 and 4.5 mm, respectively.

In Burhan et al.^[25] RCT, the lower incisors were significantly proclined in the two groups. Lingual movement of lower incisor roots may allow alveolar remodeling, lingual movement of point B, and reduction of the SNB angle. Thus, an increase in the SNB angle in these circumstances demonstrates significant improvement. These results are in agreement with other studies on TBAs^[32] and BJAs.^[26] The lower incisors were significantly proclined by 3.25 ± 2.38° (P = 0.007) and 3.63 ± 1.62° (P = 0.002) in the BJA group and the TBA group, respectively. Lund and Sandler^[23] and Mills and McCulloch^[33] reported significant lower incisor proclination during functional treatment by 7.9° and 5.2°, respectively.^[23,33] It can be noticed that although all of these studies mentioned significant lower incisor proclination, the lower incisor proclination in the current study is less than that in the above-mentioned studies because acrylic capping was done for lower incisors. The upper incisors were significantly retruded by −3.78 ± 1.07° (P < 0.001) and −4.12 ± 1.83° (P = 0.005) in the BJA group and TBA group, respectively. The retrusion of the upper incisors is a consistent finding in many previous studies.^[26,27,34] This finding can be interpreted as a posterior reaction resulting from the anterior advancement of the mandible. The labial bow of maxillary plates in both study groups was not activated to avoid the upper incisor retrusion and consequently to avoid a dental constraint on mandibular growth stimulation.^[26]

In a study by Parekh et al.,^[29] overjet reductions between 6.5 and 7 mm were observed in both groups. These levels were significant and confirmed the potency of the appliance with both treatment regimens but also reflected the magnitude of the baseline overjet (10.3–11.1 mm). This much overjet reduction compares favorably with a previous meta-analysis (5.2 mm)^[13] and mirrors findings by O’Brien et al.,^[24] who noted a reduction of 6.2 mm in patients treated with a twin block appliance for a mean period of 11 months.

Dibiase et al.^[30] in his study observed that a mean overjet reduction occurred of 7 mm (±2.3) with the twin block and 5.8 mm (±2.1) with the Dynamax [Tables 1-3]. This was associated with retroclination of the upper incisors by −5.8° (±10.0) in the twin block group and −5.7° (±11.2) in the Dynamax group (P = 0.97). The lower incisors were proclined by 5.3° (±4.8) in the twin block group and by 5.4° (±6.0) in the Dynamax group (P = 0.96) Over a 15-month treatment period, the maxilla had a mean forward movement at A point of 0.8 mm (±1.7) with the twin block and 0.2 mm (±1.5) with the Dynamax (P = 0.06) [Tables 1-3]. Statistically, significant differences were found in the forward movement of the chin at pogonion of 3.5 mm (±2.5) with the twin block and 1.7 mm (±2.1) with the Dynamax (P < 0.01). There was an increase in the mandibular length by 6.2 mm (±2.5) with the twin block and 4.1 mm (±2.6) with the Dynamax (P = 0.007).

Limitations

There are relatively a small number of studies included in this systematic review. The methodological flaws in the magnetic appliance studies group reflected a high risk of bias because of non-randomized control trials. Long-term follow-up in both groups was not considered. Another limitation is the lack of a control group in magnetic appliance groups. The reason for not conducting meta-analysis was as follows:

1. If studies are clinically diverse, then a meta-analysis may be meaningless and genuine differences in effects may be obscured. A particularly important type of diversity is in the comparisons being made by the primary studies. Often, it is not very meaningful to combine all included studies in a single meta-analysis, sometimes, there is a mix of comparisons of different treatments with different comparators, each combination of which may need to be considered separately. Further, it is not important to combine outcomes that are too diverse

2. Meta-analyses of studies that are at risk of bias may be seriously misleading. If bias is present in each (or some) of the individual studies, meta-analysis will simply compound the errors and produce a “wrong” result that may be interpreted as having more credibility.