Bibliometric analysis of research publications in three major orthodontic journals during 2012–2021

INTRODUCTION

Orthodontics is a constantly evolving field of dentistry that involves exciting advancements both within and outside clinical settings. As the number of orthodontic publications grows worldwide, indicating an increasing interest in orthodontic research, the publication characteristics and citation profiles may well reveal the trends in orthodontics and thereby convey the latest discoveries and research prospects to the scientific community. Bibliometrics has emerged as a critical tool for assessing scientific activities and the publication trends of journals over time; they provide a complete picture of the general research landscape in a particular field.^[1,2] Bibliometrics involves the quantitative analysis of publication characteristics, such as authorship, institutions, countries, topics, publication journals, citation profiles, and other variables.^[1,2]

Considered an effective approach for information retrieval and stratification, numerous bibliometric studies have been conducted in the various fields of medicine and dentistry specialties, including endodontics, periodontology, pediatric dentistry, implantology, prosthodontics, and oral and maxillofacial surgery.^[3-11] Several bibliometric studies have been conducted to gauge the performance and impact of orthodontic research in recent years. Most of these bibliometric studies have focused on the most-cited articles^[12-15] or specific parameters^[16,17] or have not included the most recent studies;^[18,19] thus, the overall orthodontic research profile of studies published in the past decade has not yet been comprehensively investigated.

To bridge this knowledge gap, this study conducted a comprehensive bibliometric analysis of all of the publications from 2012 to 2021 in three high-impact orthodontic journals: The American Journal of Orthodontics and Dentofacial Orthopedics (AJODO), The Angle Orthodontist (AO), and European Journal of Orthodontics (EJO). In the era of big data, the findings of this study will offer valuable insights into the past, present, and future of the orthodontic research field.

MATERIAL AND METHODS

RESULTS

Journal profiles

The trends in impact factors of the AJODO, AO, and EJO from 2012 to 2021 are shown in [Figure 1]. The impact factors of all three journals exhibited an upward trend over the past decade. The AJODO had the highest impact factor in 2012–2013, 2015, and 2018 before being replaced by EJO toward the end of the decade. A total of 4001 original articles published in the three journals from 2012 to 2021 were retrieved. The number of publications by AJODO (1821) was the highest, accounting for 45.5% of the total publications, followed by AO (1251, 31.3%) and EJO [929, 23.2%; Figure 2].

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Figure 1:

Trends in the impact factor of the American Journal of Orthodontics and Dentofacial Orthopedics, The Angle Orthodontist, and European Journal of Orthodontics from 2012 to 2021.

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Figure 2:

Number of publications and publication trends in the American Journal of Orthodontics and Dentofacial Orthopedics, The Angle Orthodontist, and European Journal of Orthodontics from 2012 to 2021.

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Country profile

Ninety-five countries contributed 4001 articles to the AJODO, AO, and EJO from 2012 to 2021. The top countries contributing the most articles are shown in [Figure 3 and Table 1]. The United States (US) published the highest number of articles (1003) and had the most citations (11,955) followed by Brazil (545 articles and 5416 citations). Italy ranked first in terms of the average citation/publication ratio (15.32) followed by Switzerland (13.52) and the United Kingdom (UK; 13.51). A map of the collaborative relationships between countries is shown in [Figure 4]. The US was heavily engaged in international collaborations, especially with South Korea and Brazil, whereas the UK had more collaboration with European countries.

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Figure 3:

Trends in the number of publications by the top 10 most prolific countries from 2012 to 2021.

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Table 1: Top 20 countries with the most publications in the AJODO, AO, and EJO from 2012 to 2021.

Country	Publications	Citations	Citation/ publication ratio
United States	1003	11,995	11.96
Brazil	545	5416	9.94
South Korea	351	3643	10.38
China	301	2723	9.05
Turkey	295	3393	11.50
United Kingdom	265	3579	13.51
Italy	250	3829	15.32
Japan	244	2268	9.30
Switzerland	219	2960	13.52
Canada	179	1815	10.14
Germany	173	2856	16.51
Sweden	144	1792	12.44
Greece	112	1771	15.81
Australia	97	1011	10.42
Saudi Arabia	86	982	11.42
Netherlands	86	1251	14.55
India	82	1036	12.63
Egypt	69	827	11.99
Finland	67	641	9.57
Denmark	59	654	11.08

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Figure 4:

Collaborative relationships between countries.

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Keywords

The top 20 most common keywords in the AJODO, AO, and EJO from 2012 to 2021 are listed in [Table 5]. The most frequently used keyword was “children” followed by “orthodontic treatment” and “malocclusion.” The top 20 keywords with the strongest citation bursts revealed a shift in research interests over the past decade [Figure 5]. Early in this decade, research related to “orthodontic bracket,” “mechanical property,” and “screw” attracted the most interest. Toward 2021, the research frontiers shifted to “maxillary expansion,” “maxillary canines,” “functional appliance,” “Invisalign,” and “oral health.”

Table 5: Top 20 most frequent keywords in the AJODO, EJO, and AO from 2012 to 2021.

Key words	Frequency
Children	348
Orthodontic treatment	296
Malocclusion	291
Prevalence	229
Skeletal	222
Stability	213
Growth	213
Appliance	199
Tooth movement	187
Teeth	187
Accuracy	187
Cone-beam computed tomography	182
Reliability	179
Anchorage	151
Therapy	150
Morphology	134
Adult	134
Perception	121
Force	117
Extraction	110

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Figure 5:

Top 20 keywords with the strongest citation bursts. The green line represents the whole period and the red line represents the citation burst period.

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DISCUSSION

This bibliometric study mapped the publication output across three high-impact orthodontic journals – AJODO, AO, and EJO – from 2012 to 2021. In this period, the authors from 95 countries and 370 institutions contributed 4001 original articles to these three orthodontic journals. The publication characteristics during this time can represent the current research trends and predict the prospects in the field of orthodontics.

The US had the highest number of publications, followed by Brazil, South Korea, China, and Turkey. This finding is largely consistent with a previous study conducted by Baumgartner et al., which identified the US, Brazil, Japan, Turkey, and South Korea as the top publishing countries in the AJODO, AO, and EJO between 2008 and 2012.^[19] The number of articles from China has increased in recent years, resulting in a spot among the top five countries with the most publications. In addition to quantifying the publications, we also measured the recognition and impact of publications by calculating the citation counts per article. Italy (15.32), Switzerland (13.52), and the UK (13.51) were the countries with the highest average citation to publication ratios.

Although the US ranks first in terms of article output, when the contributing institutions of the publications were analyzed, institutions in South Korea and Brazil were found to be more productive than those in the US. This was probably because the US has more institutions than any other country and therefore contributed the highest number of publications, whereas some institutions in Korea and Brazil published more articles per institution. Specifically, the University of São Paulo was the most prolific, contributing 145 articles followed by the University of Bern (112 articles) and Kyung Hee University (111 articles). Interestingly, three of the top 10 institutions were in South Korea, two were in Brazil, and two were in Switzerland. Aura-Tormos et al. analyzed the top 10 institutions published in seven orthodontic journals and found that the top three most prolific institutions were Seoul National University (South Korea), Yonsei University (South Korea), and the Federal University of São Paulo (Brazil).^[18] In their results, six of the top 10 most prolific institutions were Asian, with four from Korea, one from China, and one from Japan.^[18] Their study included the Korean Journal of Orthodontics, in which nearly 30% of the publications were from the same four Korean universities, which is one reason their list of the top 10 most prolific institutions differs from ours.^[18] Moreover, they only counted the institution of the first author, whereas we counted the institutions of all co-authors.^[18] Furthermore, the present study innovatively analyzed the total number of citations and the average number of citations per article for the top 10 institutions. The University of Bern was the most cited and had the highest average number of citations per article (16.03), reflecting the recognition and impact of their publications.

Two other studies analyzed only the most-cited articles in the field of orthodontics, and their results were different from those of this study.^[12,15] Fernandes et al. analyzed the publishing institutions of the top 100 most-cited orthodontic articles published between 2000 and 2020 and found that the University of North Carolina (US) contributed the most articles (six articles and 978 citations) followed by Okayama University (Japan; four articles and 1169 citations) and the University of Illinois (US; four articles and 588 citations).^[12] In contrast, Tarazona et al. analyzed the top 100 most-cited articles in orthodontics published between 1946 and 2016 and discovered that the most productive institutions were the University of Oslo (Norway; 10 articles), Ohio State University (US; nine articles), and the University of North Carolina (US; nine articles).^[15] There were 21 US universities among the 42 institutions that contributed two or more articles.^[15]

Unlike other studies,^[18,19] we counted the profiles of all authors rather than just the first authors of the publications to map the research collaborations among different countries. The country collaboration map revealed that a large proportion of research output from 2012 to 2021 was from international collaborative efforts. In addition to publishing the most articles, the US had the most international collaborations, especially with South Korea and Brazil. Most Swiss publications were in collaboration with other countries. The UK mostly collaborated with other European countries, whereas other prolific countries, such as Turkey and China, tended to conduct research independently. The varied collaborative patterns among countries might be explained by differences in regional practices, research interests, funding resources, and the English proficiency of authors.

The top 20 most prolific authors are shown in [Table 3], representing the most active researchers in the field of clinical orthodontics. From 2012 to 2021, the most prolific author was Pandis N (76 articles and 1176 citations) followed by Janson G (70 articles and 466 citations) and Park JH (66 articles and 541 citations). However, when assessing citations, we did not consider the year of publication. Articles published in recent years are likely to be less cited than those published closer to 2012. Therefore, some authors whose publications are more recent may have received fewer citations. The top 20 authors most cited in the AJODO, AO, and EJO publications from 2012 to 2021, shown in [Table 4], represent the most influential orthodontic researchers in the field in recent decades. Their articles or books have been cited hundreds of times in the AJODO, AO, and EJO articles in the past decade, regardless of their year of publication. The top three most-cited authors were Proffit W, Bishara SE, and McNamara, JA Jr. from the US followed by Baccetti T from Italy. Notably, three authors – Pandis N, Janson G, and Fleming PS – were among the most prolific and most-cited authors.

The top 10 most-cited articles were all published during the first 3 years (2012–2015) included in our analysis.^[21-30] Flügge et al. were cited over 200 times, with an average of 31.13 citations per year, indicating its high scientific impact.^[21] Among these top 10 most-cited articles, four were related to digital dental techniques, that is, intraoral scanners, digital dental casts, and imaging software;^{[21,25,29,30]} two investigated the risks of orthodontic treatments, namely, white spot lesions and mini-screw failure;^[23,26] two assessed the efficacy of tooth movement, one using clear aligners and one using micro-osteoperforations;^[22,24] and the remaining two were related to dental public health and statistics.^[27,28] These topics reflect the most popular research hotspots in the past decade. The top 100 most-cited articles in the three journals from 2012 to 2021 were shown in the supplementary file. Unlike our results, Aura-Tormos et al. reported bone anchorage to be the most recurrent topic in articles published from 2007 to 2017.^[18] A recent study analyzed the 100 most-cited articles in orthodontics in the past 20 years and found that anchorage (16 articles) was the most frequent thematic field followed by root resorption (eight articles) and rapid maxillary expansion (seven articles).^[12] Another study analyzed the 100 most-cited orthodontic articles between 1946 and 2016 and found that mini-implant (18 articles) was the most frequently cited topic followed by biomechanics and biology (15 articles).^[15] These differences could be explained by the difference in periods and journals analyzed. Based on our results, digital orthodontics was a more popular research topic in the past decade, probably because the three orthodontic journals we analyzed were more accepting of orthodontic clinical studies. In contrast, biology, material, or basic science studies in orthodontics were published in a broader range of scientific journals.

Regarding the study types of the most-cited studies, three were systematic reviews, representing the highest level of evidence because they summarized all valid scientific evidence at the time of publication.^[31] Four were cross-sectional studies, one was a randomized and controlled trial, and one was a retrospective case series. Cross-sectional studies are an excellent option for research in dentistry, considering their effectiveness, benefit-to-cost ratio, rapid implementation, and roles as sources for planning and organizing oral health programs.^[32] Gibson and Harrison found that surveys were the most prevalent research method, accounting for 33.9% of the publications in the AJODO, AO, EJO, and the Journal of Orthodontics from 1999 to 2008.^[17] Among the 100 most-cited articles in orthodontics from 2000 to 2020, cross-sectional studies were the most common study type (37 articles); this study design is more relevant to research topics in anchorage, digital models, and cone-beam computed tomography.^[12]

The top 10 articles most cited by AJODO, AO, and EJO publications from 2012 to 2021 are shown in [Table 7].^[28,33-41] Among these articles, three were related to functional appliances or Class II correctors,^[37,40,41] and the rest described retention protocols,^[36] white spot lesions,^[34] digital models,^[35] quality of life,^[28] and cone-beam computed tomography.^[38] Regarding the study types, five were systematic reviews, one was a non-randomized controlled trial, one was a cross-sectional study, and the other three could not be classified.

One of the limitations of this study is that we only included articles published in the three major orthodontic journals, namely, AJODO, AO, and EJO; other orthodontic-related studies published in other scientific journals or other languages were not included in the study. In addition, we analyzed all coauthors of each publication, allowing for country collaboration analysis; however, this approach does not consider the level of contributions made by each author. Furthermore, when assessing the citation profiles of articles, the most-cited articles are ranked according to the total number of citations. It is acknowledged that older articles are highly likely to receive more citations than those published recently. The results would be different if articles were ranked according to the average number of citations per year, which would reflect a more objective and up-to-date impact. Finally, the present study did not provide information about the quality of the included publications, as the quality may vary greatly among studies.^[42]

CONCLUSION

This bibliometric analysis provides a complete picture of orthodontic publications over the past decade (2012–2021). It reveals the most prolific and influential journals, countries, institutions, authors, and keywords in three major orthodontic journals.

1. The AJODO, AO, and EJO published 4001 articles from 370 institutions in 95 countries from 2012 to 2021. The AJODO published the most articles (45.5%) followed by AO (31.3%) and EJO (23.2%)

2. The country with the most publications was the US, while the country and institution with the highest citation counts per publication were Italy and the University of Bern (Switzerland), respectively

3. Pandis N was the most prolific author with the most publications and citations, and Proffit W was the most-cited author

4. Four of the 10 most-cited articles were related to digital dental technology. Cross-sectional studies and systematic reviews were the most common study types among the 10 most-cited articles and the 10 articles most cited by the 4001 publications analyzed, respectively.