The present, past and future of orthodontic research


The objective of this paper is to evaluate past and present research efforts, and provide directions for future orthodontic research initiatives. Bibliometric indices show that the highest quality and most impactful research is currently being conducted in the United States, United Kingdom, Germany, Brazil and Italy. While the quality of orthodontic research has improved substantially over time, more and higher quality randomized controlled trials need to be conducted. Research efforts must be devoted toward developing evidence-based standards of care, which are necessary to protect the orthodontic profession from incursions by charlatans and outside entities. Future research in the areas of genetics, technology, artificial intelligence and craniofacial orthopedics offer great opportunities to advance the profession, individualize treatments and make them more effective and efficient.

Research is the mainspring in the chronometer of science. It is the register of a profession’s achievement and standing. With it there is life, and growth, and effectiveness, and enthusiasm in those who devote themselves to the high calling of a profession. Without research, however, empiricism, stagnation, inefficiency, and discouragement impair the usefulness of those who earnestly seek to render their best profession ”.


Research is undertaken to increase knowledge; it provides a means to establish and confirm facts, investigate problems, validate new treatment approaches, and affirm previous results. The history of orthodontics , is replete with examples of how fundamentally important research has been in defining and elevating the practice of orthodontics. The clinical research told the orthodontist what to do, when to do it and how to do it; the experimental research told him/her why to do it. While a thorough accounting of the advances that have occurred is beyond the scope of this review, enormous progress was made during the 20th century in the development of material and appliances, interdisciplinary care (especially oral surgery), as well as in orthodontists’ understanding of biomechanics and craniofacial growth. Most recently, consider the profound effects that mini-screw implants and aligners have had, opening up new opportunities and vistas for practicing orthodontist. These breakthroughs would not have been possible without research.

The purpose of this review is twofold. The first part focuses on the past and present orthodontic literature because it is presently unclear how the journals publishing orthodontic related studies vary in terms of their quality and impact. It is also unclear how the quality of orthodontic research has changed over time. The specific objectives were to 1) compare the journals to identify those currently publishing the highest quality articles, 2) evaluate secular changes in the top three journals to ascertain how the quality of research has changed over time, 3) compare the number of citable studies and study quality worldwide to determine the countries producing the most and best quality research, and 4) quantify the relative number of case reports, RCTs, and systematic reviews/meta-analyses published over the last 26 years to find out how the quality of research designs have changed over time.

Secondly, this review will identify five areas that hold future potential for elevating the orthodontic profession and bringing it into the 21st century. All five of the areas will require future research before their potential can be realized. The future of the orthodontic profession depends on progress in these areas, as well as others.

Past and present orthodontic research

Journal quality

Using Scopus ( ) as the source, the journals that published orthodontic research in 2018 were compared based on four indices ( Table 1 ). These indices are bibliometrics commonly used to determine a journal’s quality and impact. Importantly, they are external sources that provide more comprehensive, more sophisticated and objective evaluations, less subject to bias, than previously used indices. For example, the CiteScore index, which was developed by Scopus, extends the two year window during which citations were traditionally counted (e.g. Journal Impact Factor) to three years. Three years ensures that disciplines with long publication times have sufficient literature available for citation. The H-index evaluates both the quality, as represented by the number of citations, and the quantity, as represented by the number, of publications. It was originally developed to evaluate the individual scientist’s contribution to the field, but now is used to evaluate journals’ impact. A journal has an H-index of 50 if 50 of its articles have been cited at least 50 times. The SNIP index uses data from Scopus to determine the citation’s value and corrects for field specific differences in citation rates over a period of three years. Similarly, the SJR index, which also uses the Scopus dataset, takes into consideration the weight of the citation based on the journal’s subject field, quality and reputation. , Importantly, the ranking of a citation from a journal with high a SJR index would be different than the same citation from a journal with a low SJR index. An important advantage of the SJR index is that it limits journals’ self-citations to only one third, which prevent manipulative citation practices. The SJR index has become one of the most authoritative indices for the evaluation of a journal’s impact. ,

Table 1
The four bibliometric indices used to determine journals’ impact and quality.
Index Full Name Computation
CiteScore N/A 2018 citation/publications 2015–2017
H Hirsch index Number of articles (h) that have received at least h citations
SNIP Source Normalized Impact per Paper Actual citations received relative to citations expected for the journal’s subject field
SJR Scientific Journal Rankings Average number of weighted citations received in 2018/ number of articles published in the journal in 2015–2017.

The results showed a 10 fold difference between the highest and lowest ranked journals ( Fig. 1 ). Based on the SJR and SNIP indices, the Angle Orthodontist (AO) was ranked the highest, followed by the American Journal of Orthodontics and Dentofacial Orthopedics (AJODO), European Journal of Orthodontics (EJO), Korean Journal of Orthodontics (KJO) and Progress in Orthodontics (PO). In contrast, the H index ranked the AJODO as the top journal, followed by the AO and the EJO, which were in turn followed by Orthodontics and Craniofacial Research (OCR) and the Journal of Orthodontics (JO). CiteScore ranked the EJO slightly higher than the AO, followed in order by PO, KJO, and the AJODO. Based on the averages ranks derived from all four indices, the AO was the top ranked journal, followed by the EJO, which was in turn followed closely by the AJODO ( Fig. 2 ). All three of these journals were ranked at least twice as high, and have at least twice the impact, of the KJO, PO and OCR, which are the 4th, 5th and 6th highest ranked journals, respectively.

Figure 1
Comparison of journals based on the SJR, CiteScore, SNIP and H indices.

Figure 2
Average journal rankings of the top 7 journals based on the SJR, CiteScore, SNIP and H indices.

The SJR index was used to evaluate secular changes in the quality and impact of research published in the top three journals ( Fig. 3 ). Between 1999 and 2018, the quality of the EJO, AO, and AJODO increased 289%, 384% and 416%, respectively. Journal quality increased markedly (316–618%) between 1999 and 2013. In 2013, the year showing the greatest between-journal differences, the AJODO was ranked higher than the AO, which was in turn ranked higher than the EJO. While there were little or no between-journal differences from 1999 to 2004, the EJO had somewhat lower rating than the other two journals thereafter. The AO had lower ratings than the AJODO from 2009 through 2013, with only minimal differences thereafter. Importantly, the quality of all three journals appears to have decreased or, at best, maintained between 2013 and 2018. In summary, the quality of published orthodontic research has improved dramatically since 1999, with the journals being more similar than different, except during the period 2008–2013. The profession should be concerned about the lack of improvement since 2013.

Figure 3
Secular changes in the quality based of the American Journal of Orthodontics and Dentofacial Orthopedics (AJODO), the Angle Orthodontist (AO), and the European Journal of Orthodontics (EJO) based on the SJR index.

The SJR website ( ) was also used to evaluate worldwide differences in the quality of research being conducted in 2018. The evaluation was based on the number of citable documents and the H index. The comparison was limited to the top 25 countries ( Fig. 4 ). The H index was used because it was the only index available allowing for worldwide comparisons, which is probably due to the fact that it is not limited to a fixed time period. The United States, United Kingdom, Germany, Brazil and Italy were the 5 countries with the highest H indices. The United States was ranked more than 4 times higher than the countries with the lowest H indices. With the exceptions of Brazil, Italy and, most notably, India, the numbers of citable documents general followed the same pattern as the H index (i.e. higher H index with more citations). India had the second lowest H index and the most citable documents.

Figure 4
H Index for 2018 (Dentistry, Orthodontics) of 25 countries.

Study designs used

PubMed searches were conducted to evaluate secular changes of research designs published in the orthodontic literature. Using the medical subject headings (MeSH) “Orthodontic, Preventive”, “Orthodontics, Interceptive” or “Orthodontics, Corrective”, the number of randomized controlled trials (RCTs), systematic reviews and meta-analyses combined, and case reports that were published each year between 1992 and 2018 were counted and evaluated relative to the total number of journal articles published, excluding letters, editorials, news, etc. The focus was on case reports and RCTs because they provide the weakest and strongest designs, respectively, of primary clinical studies ( Fig. 5 ). The systematic reviews and meta-analyses are secondary studies designed to provide the strongest evidence available.

Figure 5
The evidence hierarchy based on research designed modified from Fletcher and Fletcher 1979.

The results showed that the number of journal articles published increased from 1992 until 2011, and then decreased ( Fig. 6 ). The relative number of case reports remained at approximately 30% between 1992 and 2012, decreased steadily to approximately 17% in 2017, and then increased to 23% in 2018. RCTs increased from 0.7% in 1992, to 1.7% in 1999, 4.7% in 2009, and 11.9% in 2018. There were no meta-analyses or systematic reviews published prior to 1997. The percentages of meta-analyses and systematic reviews remained below 1% until 2010, after which they increased to 7.7% in 2017, and then decreased to 5.9% in 2018. The decrease in the relative numbers of case reports published after 2012 was more than made up for the increase in the relative number of RCTs, systematic reviews, and meta-analyses published. More systematic reviews and meta-analyses, and especially more RCTs, are needed in order to establish best practices and develop treatment guidelines.

Figure 6
Relative numbers of case reports, meta-analyses and systematic reviews (Meta & System), and randomized controlled trials (RCTs) published in the orthodontic literature.

The quality of RCTs published in the AJODO, AO, EJO, and JO have previously been evaluated based on the 19 essential items that, according to the consolidated standards of reporting trials (CONSORT), should be included in the abstract. From 2006 to 2011, the JO had a significantly higher quality score than the other three journals ( Fig. 7 ). During that same period, the AJODO had a higher score than the AO and JO, which did not differ significantly. All of the journals showed substantial and statistically significant improvements after 2011, especially the AJODO and AO, which reported the highest quality abstracts between 2012–2017. However, the average quality scores remained below 76, suggesting that the reporting of abstract items in the orthodontic literature according to the CONSORT statements remains inadequate. Higher quality RCT abstracts and, by implication, designs are needed.

Figure 7
Mean abstract reporting quality score (with 95% CI) as reported by Fleming et al. (2012) from 2006 to 2011 and by Alharbi et al. (2019) from 2012 to 2017.

Future orthodontic research

Standards of care

Standards of care (SOC) provide informal or formal treatment guidelines that are accepted by the clinical community. They represent authoritative statements that will tell the dental community what should be done and what should not be done. Once established, deviations from SOC hold important ethical and legal implications. As such, the development of standards requires both a consensus among orthodontics and solid scientific evidence.

Currently, there is only one standard of care in orthodontics. The “Clinical Practice Guidelines for Orthodontics and Dentofacial Orthopedics” state that diagnostic records, along with a comprehensive examination and history, are a standard of orthodontic care. They suggest that a documented plan “should be” a standard of care. There are also numerous guidelines pertaining to diagnostics, treatment plans and treatment outcomes. The question arises, is there evidence supporting these guidelines?

Based on a survey of over 800 orthodontists, the ABO identified four domains of orthodontic practice, including data gathering and diagnosis, treatment objectives and planning, treatment implementation and management, and outcomes assessments. Starting with the existing guidelines, a concerted effort should be made to develop the evidence necessary to establish SOC in each of these domains. The AAO and AAO Foundation should devote significant resources toward research that will provide the necessary evidence. An evidence-based SOC is vital for A) preventing charlatans and quacks from performing their deceptions, B) protecting patients and C) identifying what actually works best so that improvements can be made.


Genetic variability plays a role in determining subject-to-subject differences in response to treatments and individual predispositions to malocclusions. In the future, individuals’ genetic information will make it possible to optimize diagnostics, improve treatments, and more critically assess treatment outcomes. Patient variability is, to varying degrees, genetically determined; the trick is to understand how the individual genetically determined responses interact with the epigenetic and environmental factors that play contributory roles. As demonstrated in medicine, knowing the patient’s genetic profile helps guide the selection of treatment protocols, making successful outcomes more likely. Future orthodontic research is needed to A) shift the present-day emphasis on intervention to prevention, B) individualize treatments, and C) enhance patient compliance ( Fig. 8 ).

Figure 8
Potential opportunities provided to orthodontists by future genetic research.

Given the genetic predisposition for Class III malocclusion, future research should be focused on determining individuals’ developmental susceptibility. To this end, it needs to be established how the individual’s genetic potential affects craniofacial growth, when and how it influences the changes the take place, and how it impacts the stability of early treatments. Such information would make it possible for orthodontists to intervene early, before Class III skeletal and dental abnormalities become fully established.

More genetic research is also needed to understand the iatrogenic risks associated with orthodontic treatments. The risk of external apical root resorption (EARR) could be identified prior to treatment based on the patient’s genetic profile. Genetic polymorphisms of RANK and OPG have been associated with EARR. These associations are important because orthodontic tooth movements appear to increase the concentration of RANKL and decrease interleukin-1 receptor antagonist. Future study of these, as well as other polymorphisms in blood and gingival crevicular fluid, need to be conducted in both humans and experimental animals to more fully understand EARR. It has been reported that genetic differences among patients, combined with treatment-related variables, explain up to 2/3 of the individual variation in EARR. , Genetics also plays a role in host-bacterial interactions when periodontal disease is associated with elevated level of cytokines. To this end, more research is needed to identify the link between the interleukin-1 genotype and periodontal disease.

Genetics are also essential for understanding individual variation in skeletal growth and response to treatment. Studies of twins and siblings show substantial genetic effects determining the growth the cranial, maxillary and mandibular bases. , Recently, Tiro et al identified significant differences between monozygotic and dizygotic twin pairs in cranial base, maxillary and mandibular size, with 2.6–3.5 times less environmental effects on the sizes of these structures among MZ twins ( Fig. 9 ). Further research is needed to determine individual differences in the craniofacial structures’ adaptive plasticity, which would provide orthodontists with a way to predict structures’ responses to treatment. It is also likely that genetics play a role in determining individual differences in rates of tooth movement. A well designed split-mouth study evaluating canine retraction showed substantial differences, of up to 4 times, between patients when the same forces were applied ( Fig. 10 ). The individuals who exhibited faster rates of tooth movements had decreased levels of interleukin-1 receptor antagonist. Given this, as well as the previously described effects of genetic polymorphisms on bone, future research could make it possible to more accurately determine treatment times and rates of tooth movement based on the patients’ genetic makeup.

Jan 9, 2020 | Posted by in Orthodontics | Comments Off on The present, past and future of orthodontic research
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