Introduction
Research on clear aligner treatment (CAT) has increased in recent years. In this study, we aimed to perform a bibliometric and visualized analysis to identify and critically assess the 50 most highly cited articles on CAT.
Methods
Web of Science was selected as a data source and consulted until March 2020 to identify all articles potentially relevant to the analysis. All the eligible articles were collected until 50 manuscripts were listed. Article-based parameters, journal-based parameters, and author-based parameters were registered to perform the bibliometric analysis. Keywords were automatically harvested from the selected articles to implement the visualized analysis.
Results
The search identified a total of 378 articles; the total number of citations of the selected articles varied from 15 to 112. The average number of citations per year varied from 1.15 to 13.83. The predominant study design was clinical (31.7%). Over the 15 journals in which the most cited articles were published, the American Journal of Orthodontics and Dentofacial Orthopedics published the majority of those included in the list (14) and also received the greatest number of citations (671). A total of 195 authors contributed to the 50 most cited articles; a significant portion of them (26) were unaffiliated with academic institutions. A total of 184 keywords were gathered from the article list.
Conclusions
The number of citations on CAT is expected to grow steadily in parallel with the rising number of research projects. The present work identifies the most influential articles on CAT and their characteristics, placing emphasis on the journals, the authors, and the topics addressed.
Highlights
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The average number of citations on CAT is minimal compared to other medical disciplines.
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Advances in CAT mainly depend on studies of lower position in the evidence hierarchy.
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Two leading journals published the largest part of influencing articles.
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Unaffiliated authors participated in many of the most cited articles on CAT.
Clear aligner treatment (CAT) has a long-standing history in orthodontics, but the recent advancements in applied biomechanics and the achievements in biomaterials design and engineering have led to its adoption as a suitable technique in dealing with several clinical conditions.
Despite the advantages in patient comfort and acceptability, oral hygiene maintenance , and esthetics, the efficiency of clear aligners is still under debate, and a broad consensus on their clinical performance has not been reached in academia.
As a result, a significant surge in research activities has been observed over recent years, in line with the growing number of publications on CAT.
To evaluate and track the research output in a specific field, we employed several analytical instruments with the final aim of determining the historical trend of a topic and speculating on the direction in which the research is proceeding. Bibliometric analysis is a means by which any measurable information pertaining to published scientific articles can be retrieved, collected, and analyzed. Citations are the primary measure used to quantify the impact—and often the quality—of a publication in a specific area; citations also reveal a connection between authors, groups of researchers, topics of study, or countries. The establishment of a citation ranking list identifies published works that can potentially influence trends in clinical practice and future research. In addition, the use of visualized analyses to map bibliometric networks, often referred to as science mapping , can provide an intuitive yet comprehensive overview of a large dataset.
When submitting a manuscript, it is important for authors to refer to common journal metrics, such as the journal impact factor (JIF), the 5-year journal impact factor (5-JIF), the Scimago Journal Ranking (SJR) and the Eigenfactor (EF), to decide which journal is right for the proposed research. The JIF measures the average number of citations received by an article in a specific journal during a predefined timeframe (2 years for JIF and 5 years for 5-JIF). In contrast, the SJR and Eigenfactor use an original algorithm to appraise the number of citations received and consider the weight of the source of the citations. Authors choose a particular journal for a variety of reasons; one of the most important is the prestige or impact of the journal. Therefore, these metrics can provide a measure of the supposed quality of the published papers in a specific field.
Author metrics are used to track how often an author’s work is cited and demonstrate the reach and impact of a researcher’s work for use in grant applications, tenure, promotion, and performance reviews. An author’s impact is frequently quantified in terms of the number of citations of their publications. A well-known author-level metrics is the h-index, which is equal to the number of an author’s publications (h) that have h or more citations (eg, if the h-index of a scientist is 50, it means that each of the 50 articles of the author has been cited at least 50 times).
Bibliometric analysis has been widely employed in several fields of dentistry, including orthodontics, but a study identifying and analyzing the most cited articles on CAT has not yet been performed.
The aim of the present bibliometric and visualized analysis is to assess and benchmark research performance, to identify significant trends and underinvestigated areas, and to rank influential men or women, institutions, papers, journals, and countries in the field of CAT. The analysis takes into account all of the aforementioned journal and author metrics.
Material and methods
The study was designed to answer the following research question: What are the most cited articles in the field of clear aligner treatment? The research question was formulated according to the FINER (feasible, interesting, novel, ethical, relevant) criteria.
On March 22, 2020, a computerized database search was performed independently by 2 authors (S.F.G and G.V) to detect all the published papers about CAT. Because of its ability to provide a systematic citation search through multiple repositories, the Web of Science Core Collection (Clarivate Analytics, Philadelphia, Pa) was the source used to identify all potentially relevant studies regardless of the year, type of publication, or language.
The following complex search query was adopted without field restrictions:
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(((orthodont∗ OR clear OR removable OR thermoplastic) AND (aligner∗ OR “aligner∗ therap∗” OR “aligner∗ treatment∗”)) OR Invisalign) .
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Titles and abstracts were independently screened by 2 authors (S.F.G and G.V), who had been previously instructed how to use the Web of Science platform to assess the eligibility of the studies: articles not directly relevant to CAT were excluded.
The full records of the retrieved publications were downloaded or manually entered into Microsoft Excel spreadsheet software (Microsoft Corp, Redmond, Wash) by each author. The abstract of each article was analyzed manually to check its pertinence. The residual manuscripts were sorted in descending order according to their total number of citations, and among them, only the first 50 were listed. Cohen’s kappa (κ) coefficient was calculated to measure the interrater agreement in the selection process. The resulting κ coefficient was 1.0, showing perfect agreement. Any potential disagreement concerning the inclusion of studies would be resolved through discussion and consensus with a third author (C.T).
Bibliometric analysis
Three sets of parameters were independently collected for each article by 2 researchers (S.F.G and G.V): (1) article-based parameters (title, authors, journal, publication year, study design, total citations, average citation per year); (2) journal-based parameters (title, JIF 2018, 5-JIF, SJR, quartile, number of citations, number of manuscripts in top 50, EF), and (3) author-based parameters (name, affiliation/s, h-index, number of articles, authorship position, number of citations).
For the evaluation of the study design of each selected article, the authors used an adapted form, obtained from the classification of different study types proposed by Röhrig et al, integrated with the Cochrane Collaboration glossary definitions.
The JIF, the 5-JIF, and the EF score of each journal included in the list were identified using the Incites Journal Citation Reports (Clarivate Analytics) dataset.
Author’s affiliations, country of origin, and h-index data were retrieved in the Scopus (Elsevier BV, Amsterdam, The Netherlands) database. The most productive institutions were identified using author-level fractional counting ; the total citations and the number of manuscripts in the top 50 were equally distributed among the number of their authors to obtain normalized results. All the collected data were subsequently analyzed using Graphpad Prism (version 8.4; GraphPad Software, La Jolla, San Diego, Calif) for descriptive statistics and chart making.
Visualized analysis
Keywords were extracted automatically from the dataset and used to construct a co-occurrence network on the basis of bibliographic data. Keywords were counted using full counting, meaning that each co-occurrence link had the same weight. To avoid redundancy, 2 authors (B.A and S.F.G) manually inspected and revised all the terms to collate a custom thesaurus ( Supplementary Material ). To include keywords in the analysis dataset, we set the requested minimum number of occurrences of keywords was set to 2. Thus, each identified keyword was tabled jointly with its occurrences and total link strength. VOSviewer (Centre for Science and Technology Studies, Leiden University, Leiden, The Netherlands) was used for keyword mapping. The generated networks consist of nodes, representing the keywords, and edges, representing the relationship between keywords. A distance-based approach was selected to display the network visually; the distance between 2 nodes would approximately indicate the relatedness of the nodes. Similar keywords were grouped in clusters.
Cluster resolution determines the level of detail of the clustering process. The higher the value, the higher the number of keyword subgroups created. The cluster resolution was set to 1.0, which means that small clusters were merged into larger clusters.
Results
The search strategy applied returned a total of 378 papers. Only those unambiguously referred to CAT were used to create the list of the 50 most cited articles, and from those 50 papers, data were extracted. The articles listed were published from 2002 to 2017 inclusive; 2017 was the most frequently occurring publication year in the dataset. All the 50 articles included in the list were written in the English language.
The 50 most cited articles are shown in Table I , listed in descending order according to the total number of citations received. The number of citations collected by each article between 2002 and 2020 varied from 15 to 112, 1724 overall (mean, 34.48; standard deviation [SD], 20.93); the self-citation rate measured for the listed papers was 11%. The annual number of citations collected by all 50 articles included in the list is increasing over time, as shown in Figure 1 , from 6 in 2003 to 306 in 2019, with a peak in 2017 with 313 citations. Citations of the current year were not embedded in Figure 1 because they would represent a misleading trend.
| Ranking position | Title | Authors | Journal | Year of publication | Study design | Total citations | Citation density |
|---|---|---|---|---|---|---|---|
| 1 | How well does Invisalign work? A prospective clinical study evaluating the efficacy of tooth movement with Invisalign | Kravitz ND, Kusnoto B, BeGole E, Obrez A, Agran B | American Journal of Orthodontics and Dentofacial Orthopedics | 2009 | Clinical study (clinical trial) | 112 | 9.33 |
| 2 | Outcome assessment of Invisalign and traditional orthodontic treatment compared with the American Board of Orthodontics objective grading system | Djeu G, Shelton C, Maganzini A | American Journal of Orthodontics and Dentofacial Orthopedics | 2005 | Cohort study (historical) | 92 | 5.75 |
| 3 | Efficacy of clear aligners in controlling orthodontic tooth movement: a systematic review | Rossini G, Parrini S, Castroflorio T, Deregibus A, Debernardi CL | Angle Orthodontist | 2015 | Systematic review | 83 | 13.83 |
| 4 | Association of orthodontic force system and root resorption: a systematic review | Roscoe MG, Meira JBC, Cattaneo PM | American Journal of Orthodontics and Dentofacial Orthopedics | 2015 | Systematic review | 71 | 11.83 |
| 5 | Invisalign A to Z | Wong BH | American Journal of Orthodontics and Dentofacial Orthopedics | 2002 | Short communication | 61 | 3.21 |
| 6 | The treatment effects of Invisalign orthodontic aligners–a systematic review | Lagravere MO, Flores-Mir C | Journal of The American Dental Association | 2005 | Systematic review | 59 | 3.69 |
| 7 | Activation time and material stiffness of sequential removable orthodontic appliances. Part 1: ability to complete treatment | Bollen AM, Huang G, King G, Hujoel P, Ma T | American Journal of Orthodontics and Dentofacial Orthopedics | 2003 | Clinical study (RCT) | 54 | 3 |
| 8 | Forces and moments generated by removable thermoplastic aligners: incisor torque, premolar derotation, and molar distalization | Simon M, Keilig L, Schwarze J, Jung BA, Bourauel C | American Journal of Orthodontics and Dentofacial Orthopedics | 2014 | Clinical study (clinical trial) | 50 | 7.14 |
| 9 | Treatment outcome and efficacy of an aligner technique–regarding incisor torque, premolar derotation and molar distalization | Simon M, Keilig L, Schwarze J, Jung BA, Bourauel C | BMC Oral Health | 2014 | Clinical study (clinical trial) | 49 | 7 |
| 10 | A comparison of treatment impacts between Invisalign aligner and fixed appliance therapy during the first week of treatment | Miller KB, McGorray SP, Womack R, Qunitero JC, Perelmuter M, Gibson J, Dolan TA, Wheeler TT | American Journal of Orthodontics and Dentofacial Orthopedics | 2007 | Cohort study (prospective) | 47 | 3.36 |
| 11 | Invisalign and traditional orthodontic treatment postretention outcomes compared using the American Board of Orthodontics Objective Grading System | Kuncio D, Maganzini A, Shelton C, Freeman K | Angle Orthodontist | 2007 | Cohort study (historical) | 45 | 3.21 |
| 12 | A comparison between customized clear and removable orthodontic appliances manufactured using RP and CNC techniques | Martorelli M, Gerbino S, Giudice M, Ausiello P | Dental Materials | 2013 | Clinical study (cross-over trial) | 43 | 5.38 |
| 13 | Activation time and material stiffness of sequential removable orthodontic appliances. Part 2: dental improvements | Clements KM, Bollen AM, Huang G, King G, Hujoel P, Ma T | American Journal of Orthodontics and Dentofacial Orthopedics | 2003 | Clinical study (RCT) | 43 | 2.39 |
| 14 | A comparison of the periodontal health of patients during treatment with the Invisalign (R) system and with fixed lingual appliances | Miethke R, Braunerl K | Journal of Orofacial Orthopedics-Fortschritte Der Kieferorthopadie | 2007 | Case-control | 40 | 2.86 |
| 15 | Influence of attachments and interproximal reduction on the accuracy of canine rotation with Invisalign–a prospective clinical study | Kravitz ND, Kusnoto B, Agran B, Viana G | Angle Orthodontist | 2008 | Clinical study (clinical trial) | 39 | 3 |
| 16 | Periodontal status of adult patients treated with fixed buccal appliances and removable aligners over one year of active orthodontic therapy | Karkhanechi M, Chow D, Sipkin J, Sherman D, Boylan RJ, Norman RG, Craig RG, Cisneros GJ | Angle Orthodontist | 2013 | Case-control | 38 | 4.75 |
| 17 | Esthetic orthodontic treatment using the Invisalign appliance for moderate to complex malocclusions | Boyd RL | Journal of Dental Education | 2008 | Case series | 38 | 2.92 |
| 18 | A novel pressure film approach for determining the force imparted by clear removable thermoplastic appliances | Barbagallo LJ, Shen G, Jones AS, Swain MV, Petocz P, Darendeliler MA | Annals of Biomedical Engineering | 2008 | Case series | 36 | 2.77 |
| 19 | Initial forces and moments delivered by removable thermoplastic appliances during rotation of an upper central incisor | Hahn W, Engelke B, Jung K, Dathe H, Fialka-Fricke J, Kubein-Meesenburg D, Sadat-Khonsari R | Angle Orthodontist | 2010 | Theoretical study (analytical measurement procedure) | 35 | 3.18 |
| 20 | Structural conformation and leaching from in vitro aged and retrieved Invisalign appliances | Schuster S, Eliades G, Zinelis S, Eliades T, Bradley TG | American Journal of Orthodontics And Dentofacial Orthopedics | 2004 | Theoretical study (analytical measurement procedure) | 35 | 2.06 |
| 21 | Braces versus Invisalign®: gingival parameters and patients’ satisfaction during treatment: a cross-sectional study | Azaripour A, Weusmann J, Mahmoodi B, Peppas D, Gerhold-Ay A, Van Noorden CJF, Willershausen B, | BMC Oral Health | 2015 | Case-Control | 33 | 5.5 |
| 22 | Invisalign® treatment in the anterior region: were the predicted tooth movements achieved? | Krieger E, Seiferth J, Marinello I, Jung BA, Wriedt S, Jacobs C, Wehrbein H | Journal of Orofacial Orthopedics-Fortschritte Der Kieferorthopadie | 2012 | Cohort study (historical) | 33 | 3.67 |
| 23 | Periodontal health during clear aligners treatment: a systematic review | Rossini G, Parrini S, Castroflorio T, Deregibus A, Debernardi CL | European Journal of Orthodontics | 2015 | Systematic review | 31 | 5.17 |
| 24 | Adult patients’ adjustability to orthodontic appliances. Part I: a comparison between Labial, Lingual, and Invisalign ™ | Shalish M, Cooper-Kazaz R, Ivgi I, Canetti L, Tsur B, Bachar E, Chaushu S | European Journal of Orthodontics | 2012 | Clinical study (clinical trial) | 31 | 3.44 |
| 25 | Effects of mechanical properties of thermoplastic materials on the initial force of thermoplastic appliances | Kohda N, Iijima M, Muguruma T, Brantley WA, Ahluwalia KS, Mizoguchi I | Angle Orthodontist | 2013 | Theoretical study (analytical measurement procedure) | 30 | 3.75 |
| 26 | Activation time and material stiffness of sequential removable orthodontic appliances. Part 3: premolar extraction patients | Baldwin D, K, King G: Ramsay D, S, Huang G, Bollen AM | American Journal of Orthodontics and Dentofacial Orthopedics | 2008 | Clinical study (RCT) | 28 | 2.15 |
| 27 | Periodontal health in teenagers treated with removable aligners and fixed orthodontic appliances | Abbate GM, Caria MP, Montanari P, Mannu C, Orru G, Caprioglio A, Levrini L | Journal of Orofacial Orthopedics-Fortschritte Der Kieferorthopadie | 2015 | Clinical study (RCT) | 25 | 4.17 |
| 28 | Initial force systems during bodily tooth movement with plastic aligners and composite attachments: a three-dimensional finite element analysis | Gomez JP, Peña FM, Martínez V, Giraldo DC, Cardona CI | Angle Orthodontist | 2015 | Theoretical study (analytical measurement procedure) | 25 | 4.17 |
| 29 | Torquing an upper central incisor with aligners-acting forces and biomechanical principles | Hahn W, Zapf A, Dathe H, Fialka-Fricke J, Fricke-Zech S, Gruber R, Kubein-Meesenburg D, Sadat-Khonsari R | European Journal of Orthodontics | 2010 | Theoretical study (analytical measurement procedure) | 25 | 2.27 |
| 30 | Initial forces generated by three types of thermoplastic appliances on an upper central incisor during tipping | Hahn W, Fialka-Fricke J, Dathe H, Fricke-Zech S, Zapf A, Gruber R, Kubein-Meesenburg D, Sadat-Khonsari R | European Journal of Orthodontics | 2009 | Theoretical study (analytical measurement procedure) | 25 | 2.08 |
| 31 | Cytotoxicity and estrogenicity of Invisalign appliances | Eliades T, Pratsinis H, Athanasiou AE, Eliades G, Kletsas D | American Journal of Orthodontics and Dentofacial Orthopedics | 2009 | Cell study | 24 | 2 |
| 32 | Orthodontic treatment with a series of removable appliances | Chenin DA, Trosien AH, Fong PF, Miller RA, Lee RS | Journal of The American Dental Association | 2003 | Case series | 24 | 1.33 |
| 33 | Root resorption following treatment with aligners | Brezniak N, Wasserstein A | Angle Orthodontist | 2008 | Single case report | 23 | 1.77 |
| 34 | Ultrastructure and morphology of biofilms on thermoplastic orthodontic appliances in ‘fast’ and ‘slow’ plaque formers | Low B, Lee W, Seneviratne CJ, Samaranayake LP, Hagg U | European Journal of Orthodontics | 2011 | Clinical study (clinical trial) | 22 | 2.2 |
| 35 | Evaluation of Invisalign treatment effectiveness and efficiency compared with conventional fixed appliances using the Peer Assessment Rating index | Gu J, Tang JS, Skulski B, Fields HW, Beck FM, Firestone AR, Kim DG, Deguchi T | American Journal of Orthodontics and Dentofacial Orthopedics | 2017 | Case-Control | 21 | 5.25 |
| 36 | Maxillary molar distalization with aligners in adult patients: a multicenter retrospective study | Ravera S, Castroflorio T, Garino F, Daher S, Cugliari G, Deregibus A | Progress In Orthodontics | 2016 | Cohort study (historical) | 21 | 4.2 |
| 37 | Accuracy of Invisalign® treatments in the anterior tooth region | Krieger E, Seiferth J, Saric I, Jung BA, Wehrbein H, | Journal of Orofacial Orthopedics-Fortschritte Der Kieferorthopadie | 2011 | Cohort study (historical) | 20 | 2 |
| 38 | Short-term chemical and physical changes in Invisalign appliances | Gracco A, Mazzoli A, Favoni O, Conti C, Ferraris P, Tosi G, Guarneri MP | Australian Orthodontic Journal | 2009 | Theoretical study (analytical measurement procedure) | 20 | 1.67 |
| 39 | Clinical limitations of Invisalign | Phan X, Ling PH | Journal of The Canadian Dental Association | 2007 | Short communication | 20 | 1.43 |
| 40 | Efficiency, effectiveness and treatment stability of clear aligners: a systematic review and meta-analysis | Zheng M, Liu R, Ni Z, Yu Z | Orthodontics & Craniofacial Research | 2017 | Methanalysis | 18 | 4.5 |
| 41 | In-vivo von Mises strains during Invisalign treatment | Vardimon AD, Robbins D, Brosh T | American Journal of Orthodontics and Dentofacial Orthopedics | 2010 | Clinical study (clinical trial) | 18 | 1.64 |
| 42 | Discomfort associated with Invisalign and traditional brackets: a randomized, prospective trial | White DW, Julien KC, Jacob H, Campbell PM, Buschang PH | Angle Orthodontist | 2017 | Clinical study (RCT) | 17 | 4.25 |
| 43 | Twitter analysis of the orthodontic patient experience with braces vs Invisalign | Noll D, Mahon B, Shroff B, Carrico C, Lindauer SJ | Angle Orthodontist | 2017 | Cross-sectional study | 15 | 3.75 |
| 44 | The combined use of computer-guided, minimally invasive, flapless corticotomy and clear aligners as a novel approach to moderate crowding: a case report | Cassetta M, Altieri F, Pandolfi S, Giansanti M | Korean Journal of Orthodontics | 2017 | Single case report | 15 | 3.75 |
| 45 | The predictability of transverse changes with Invisalign | Houle JP, Piedade L, Todescan R, Pinheiro FH | Angle Orthodontist | 2017 | Cohort study (historical) | 15 | 3.75 |
| 46 | Orthodontically induced external apical root resorption in patients treated with fixed appliances vs removable aligners | Iglesias-Linares A, Sonnenberg B, Solano B, Yanez-Vico RM, Solano E, Lindauer SJ, Flores-Mir C | Angle Orthodontist | 2017 | Case-Control | 15 | 3.75 |
| 47 | Stress relaxation properties of four orthodontic aligner materials: a 24-hour in vitro study | Lombardo L, Martines E, Mazzanti V, Arreghini A, Mollica F, Siciliani G | Angle Orthodontist | 2017 | Theoretical study (analytical measurement procedure) | 15 | 3.75 |
| 48 | The effectiveness of the Invisalign appliance in extraction cases using the ABO model grading system: a multicenter RCT | Li W, Wang S, Zhang Y | International Journal of Clinical and Experimental Medicine | 2015 | Clinical study (RCT) | 15 | 2.5 |
| 49 | Variables affecting orthodontic tooth movement with clear aligners | Chisari JR, McGorray SP, Nair MR, Wheeler TT | American Journal of Orthodontics and Dentofacial Orthopedics | 2014 | Cohort study (historical) | 15 | 2.14 |
| 50 | The clear plastic appliance–a biomechanical point of view | Brezniak N | Angle Orthodontist | 2008 | Editorial | 15 | 1.15 |
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