Publication trends in micro-CT endodontic research: a bibliometric analysis over a 25-year period

Abstract

Aim: To conduct a bibliographic analysis of the research studies published in Endodontics using micro-computed tomography (micro-CT) as an analytical tool over a 25-year period.

Methodology: The Web of Science electronic database was accessed, and an advanced search using strict criteria was undertaken from January 1995 to June 2020 for studies in the field of Endodontics that used micro-CT as an analytical tool. A further search was conducted between January and August of 2020 for a combination of specific terms and descriptors. For each selected article, the following parameters were recorded: field of the study, analysed specimen, publication title and year, authorship, journal of publication, institution and country of origin, collaborating institutions and countries, and number of citations. The acquired data were analysed using descriptive statistics and graphical mappings.

Results: The screening process identified 877 relevant articles that were classified into 30 thematic categories. The main fields of research were root canal preparation (23.8%), root canal anatomy (17.4%), canal filling (9.2%) and root canal retreatment (7.0%). The most productive half-decade comprised the period of 2015–2019 (n = 513; 58.5%), with the highest number of articles published in 2019 (n = 146; 16.6%). The authors who lead the list as first authors were G De-Deus, A Keleş, F Paqué, MA Versiani and Y Gu, respectively, whilst Versiani was the most productive (n = 51). The leading countries regarding the number of studies were Brazil, China and Turkey with 236, 130 and 65 publications, respectively. The University of São Paulo (n = 90; 10.3%) followed by Wuhan University (n = 37; 4.2%) and the University of Zurich (n = 18; 2.1%) were the prominent contributors by producing the largest number of articles, whilst the University of Zurich was the most-cited institution. The selected studies were published in 140 scientific journals, but the Journal of Endodontics and International Endodontic Journal accounted for almost 50% of the publications.

Conclusion: This bibliometric analysis portrayed an original and comprehensive view on the progress and trends of the use of micro-CT technology in endodontic research, and enabled a deep understanding of the development process in this field over the last 25 years.

Introduction

The evaluation of citations received by articles, scientists, countries or other aggregates of scientific activity is defined as citation analysis in the bibliography of science (Garfield 1972). Even though the number of citations received by an article may not reflect its scientific quality or its impact on clinical practice, this number is considered an objective indicator for researchers and clinicians to follow new trends and make evidence-based decisions with technological advancements within that field (Mishra et al. 2018, Yilmaz et al. 2019). In Endodontics, the first bibliometric analysis addressed the trends in endodontic research by studying the top 100 most-cited papers (Fardi et al. 2011). Latter, Tzanetakis et al. (2015) analysed and classified articles published from 2009 to 2013 into 16 thematic categories. More recently, this method was used to evaluate the bibliometric characteristics of the most-cited articles in different areas within Dentistry (Ahmad et al. 2019a,b, Ordinola-Zapata et al. 2020, Yilmaz et al. 2019, Kolahi et al. 2020).

In the last 30 years, technological advancements in the imaging field allowed a considerable range of techniques to be successfully employed to visualize oral and facial structures three-dimensionally. Amongst these techniques, the invention of X-ray computed tomography undoubtfully provided a significant step forward not only as advanced diagnostic aid, but also as a nondestructive testing tool for laboratory research  (Rhodes  et  al. 1999, Peters et al. 2000). More specifically in the endodontic field, application of high-resolution X-ray micro-computed tomography (micro-CT) has gained increasing popularity since its first recognition as an advanced system for detailed research (Nielsen et al. 1995). Micro-CT technology is currently considered the most important and accurate research tool for the study of the root canal system and, amongst other applications, to understand the influence of its complex morphology on the different stages of endodontic treatment (Versiani & Kele s 2020). From the first attempt to use this analytical method in  Endodontics  (Nielsen et al. 1995), hundreds of scientific articles have been published in specialized journals. Thus far, however, the recognition of these publications and the significant contributions of particular authors, institutions, countries and journals within the endodontic field remains unknown. Therefore, in order to highlight the most prominent topics, research centres, and study designs, as well as, the scientific impact, measured by citations, the aim of this study was to conduct a bibliographic analysis of the research studies published in the endodontic field using micro-CT technology as an analytical tool over a 25-year period.

Materials and methods

Thomas Reuter’s Web of Science, Scopus, PubMed, Embase and ScienceDirect electronic databases were accessed and an advanced search was undertaken from January 1995 to June 2020 for studies in the field of Endodontics that used micro-CT as analytical tool. A further search was conducted between January and August of 2020, excluding languages other than English, for a combination of subject headings, in which a first-term denominates “micro-CT” OR “micro-computed tomography” OR “x-ray microto-mography,” with a second term denominating “endodontics” OR “root canal treatment” OR “root canal therapy” and their combinations. The titles of the papers in this initial search were screened by one author, and only articles related to the topic were included. Then, a further selection process using strict criteria was performed independently by two other authors based on the critical appraisal of the full text, including title and abstract, to determine their eligibility. The inclusion criteria based on article type comprised research articles and case reports. Reviews, conference abstracts, editorial material, letter to the editors, reprints or corrections were not included, as well as, studies on primary teeth, age estimation, veterinary, paleontological and anthropological sciences. Further, studies that did not use micro-CT imaging as analytical method or the main focus was not related to Endodontics were also described as irrelevant and excluded from the analysis. In the event of duplicate publications, companion papers, or overlap between studies regarding the same population or sample, only the most recent and complete study was included. Disagreements between the evaluators were resolved by additional discussions and by consulting a third reviewer. The field of study, the analysed specimen, publication year, leading authors, institutions and countries, leading journals and citations were recorded independently for each article by two authors, using standardized lists according to the Cochrane  Collaboration guidelines  (Higgins et al. 2019). The data were analysed using descriptive statistics.

The graphical mappings of the bibliometric material were conducted using the Visualization of Similarities Viewer software (VOSviewer v.1.6.15; Centre for Science and Technology Studies, Leiden University, Netherlands; available at https://www.vosviewer.c om). Bibliographic networks were built based on the co-authorship network, co-authorship network of countries, and keywords co-occurrence. To increase the clarity of co-authorship network maps, the minimum number of published articles by authors has been set to five, and the minimum number of published articles by the countries has been set to four. When constructing the keyword co-occurrence map, “micro-ct,” “micro-computed tomography,” “micro-computed tomography,” “micro computed tomography,” “x-ray microtomography,” “micro-computed tomography imaging,” “microct,” “micro tomography,” “micro-computed tomography scan” terms were excluded in order to clearly reveal the keywords of interest in each article. In the network maps, the size of the nodes represented the frequency of the analysed item (keyword, author and country), with larger nodes indicating higher frequency. The thickness of the edges was related to the closeness of the interactions between two nodes, whilst their colours indicated the cluster to which the item belongs.

Results

The screening process identified 877 relevant articles (Table S1) that were classified into 30 thematic categories, according to the field of study (Fig. 1a). The top 10 research fields related to "micro-CT in endodontics" were determined as root canal preparation (23.8%), root canal anatomy (17.4%), canal filling (9.2%), root canal retreatment (7.0%), apical periodontitis  (6.7%), diagnosis  (5.7%),  irrigation (5.6%), finite element study (4.1%), physicochemical properties of endodontic materials (3.6%) and vital pulp therapy (3.0%), (Fig. 1a), whilst the most frequently occurring keywords were “root canal preparation” and “endodontics” followed by “retreatment,” “root canal anatomy,” and “reciprocating motion,” as revealed by the network map analysis (Fig. 1b). The analysed specimens in the studies were categorized in 17 different types (Fig. 2a) including animal models, artificial resin teeth (printed teeth), endodontic materials, root canal devices and cadaver bone blocks, but in most of the selected publications (n = 688; 78.4%), extracted teeth were used and analysed as samples. In addition, the most productive half-decade comprised the period of 2015–2019 (n = 513; 58.5%) (Fig. 2b), with the highest number of articles published in 2019 (n = 146; 16.6%), 2018 (n = 105; 12.0%) and 2017 (n = 103; 11.7%), respectively. In 2020, one-hundred and two articles were published in the first six months.

The most productive authors, their countries and the total number of studies included as first or co-author were also noted. The authors associated with the most publications as first authors were G De-Deus (n = 20), A Keleş (n = 16), F Paqué (n = 10), MA Versiani (n = 10) and Y Gu (n = 10), whilst Versiani was the most productive with a total of 51 articles (5.8%) (Table 1). Well-differentiated clusters were observed in the co-authorship network map (Fig. 3). According to the country of origin, the highest number of published articles was led by Brazil (n = 236; 26.9%), followed by China (n = 130; 14.8%) and Turkey (n = 65; 7.4%). Brazil had also the highest number of citations in Scopus (n = 2720) and Web of Science (n = 2081), (Fig. 4), but Switzerland was the most-cited country per article (Table 2). The articles originated from 283 research institutions and 48 countries were identified through the first author’s institution. The University of São Paulo (n = 90; 10.3%)  followed by  Wuhan  University (n = 37; 4.2%), the University of Zurich (n = 18; 2.1%), Sichuan University (n = 18; 2.1%) and Fluminense Federal University (n = 18; 2.1%) were the most prominent contributors by producing the largest number of articles; however, the University of Zurich was the most-cited institution in Scopus (n = 1762) and Web of Science (n = 1532; Table S2).

The selected studies (n = 877) were published in 140 different scientific journals but the highest impact journals in the field of Endodontics, namely the Journal of Endodontics and International Endodontic Journal, accounted for almost 50% of the publications (Table S3). The analysis of the top 10 most-cited micro-CT studies in Endodontics also revealed that 8 were published in either the International Endodontic Journal (n = 4) or the Journal of Endodontics (n = 4), and 5 of them were published by Peters and colleagues (Peters et al. 2000, 2001a,b, 2003a,b) (Table 3).

Discussion

This bibliographic review is the first of its nature that attempted to identify and analyse the main features of micro-CT studies published in the last 25 years in the field of endodontic research, aiming to reveal trends for guiding future studies. In this review, 877 articles that used micro-CT as an analytical tool were identified, classified into 30 different thematic categories and analysed regarding several parameters including contributions of authors, institutions, countries and journals by means of descriptive analysis and bibliometric mapping. The latter is a powerful way of visualization for studying the structure and the dynamics of scientific fields in order to get better understanding of a specific scientific field or discipline and to make predictions about the future trends (van Eck et al. 2010a). This analysis was performed by using VOSviewer software, a freely available software package that was developed for creating, visualizing and exploring bibliometric maps of scientific data (van Eck & Waltman 2010b). Several bibliographic studies published recently in the dental field used this tool to perform the author keywords co-occurrence and co-authorship network analysis (Yilmaz et al. 2019, Ahmad et al. 2020, Kolahi et al. 2020, Ordinola-Zapata et al. 2020).

Overall, the present analysis revealed an increased number of publications from 2010 to 2020 (Fig. 2b) probably as a result of the great potential of this non-invasive technology to enhance the ability to characterize and understand dynamic processes, such as the ones involved in the endodontic treatment, but also because benchtop micro-CT scanners became more affordable and popular over the years (Stock 2009).

This report also revealed that root canal preparation (n = 209; 23.8%) and root canal anatomy (n = 153; 17.4%) themes accounted for nearly half of the publications (n = 362; Fig. 1a) and, as it would be expected, extracted teeth were used in most of the studies (n = 688; 78.4%; Fig. 2a). In laboratory-based studies, the reproduction of the clinical situation might be regarded as the major advantage of using extracted human teeth (Nawrocka & Łukomska-Szymańska 2019). On the other hand, the wide range of variations in root canal morphology makes standardization difficult (Versiani et al. 2013). Thus, in experimental studies using extracted teeth, if anatomical bias is not taken into account for sample selection, then certain conclusions drawn might be incorrect and results might demonstrate the effect of canal anatomy rather than the variable of interest (Peters et al. 2001b, De-Deus 2012). The advent of micro-CT technology overcome limitations of conventional methods allowing to evaluate the root canal anatomy not only qualitatively, but also to extract morphometric quantitative three-dimensional data without damaging the specimens (Versiani & Keleş 2020). Therefore, on the basis of micro-CT data, it is possible to further improve sample selection using established morphological parameters to provide a consistent baseline (De-Deus et al. 2020). On the other hand, although endodontic teaching and researching are being based mostly on the use of natural extracted human teeth, it also has bioethical limitations.  Consequently, several papers tested the replacement of natural teeth by artificial CT-based resin replicas produced by 3D printing technology (Fig. 2a). Unfortunately, the tactile perception during endodontic procedures using these replicas is still far from real teeth, and therefore, future studies should be focused in developing artificial resin models with similar hardness to dentine. Interestingly, in this review 112 in vivo studies (12.8%) using small animals and micro-CT method (Fig. 2a) on the evaluation of apical periodontitis and alveolar bone loss in the periapical region (n = 59; 6.7%) were observed, as well as, formation of mineralized tissue after direct pulp capping procedures (n = 26; 3.0%) and basic biological processes of pulp tissue (n = 19; 2.2%). An in vivo approach using micro-CT technology is not an easy task due to the requirements for high spatial and temporal resolution (du Plessis et al. 2017), but it also has a critical role in providing a basic understanding of mechanisms of disease (Torabinejad et al. 2011). Therefore, further studies using laboratory animal models associated with micro-CT may provide a better understanding of the effects of therapeutic drugs and methods on reparative dentine formation, pulp wound and apical periodontitis healing.

In the last decade, several technologies were introduced in the endodontic practice by manufacturers worldwide on a scale and at a speed that increased the need for testing them using accurate research models. Amongst these technologies, the properties and use of nickel–titanium instruments account for most of articles published in the highest impact journals in Endodontics since 1980 (Ordinola-Zapata et al. 2020). Currently, for instance, there are more than 160 nickel–titanium (NiTi) mechanical preparation  systems available  in  the  market  (Gavini et al. 2018) and the clinical safety and efficiency of most of them have not been confirmed from a scientific perspective. Considering the noninvasiveness, high accuracy and ability to reconstruct the root canal system three dimensionally, micro-CT method has been widely used in the last decade for evaluating the shaping ability of different NiTi systems (Alves et al. 2016, Leoni et al. 2017, Zuolo et al. 2018, Silva et al. 2019, Keleş et al. 2020). In previous bibliometric reviews, the term ‘instrumentation’ was reported as the most frequently used in titles (Ordinola-Zapata et al. 2020) and in the 103 top-cited articles in endodontics (Yilmaz et al. 2019). Taken together, this information helps to explain ‘root canal preparation’ as the most-cited keyword extracted from the selected studies (Fig. 1).

The most commonly used method in bibliometric analysis is the citation analysis. It deals with the study of how frequently other authors have cited a publication and serves to evaluate the clinical and scientific importance of a publication in a specific area of knowledge (Garfield 1972). Further analysis of the most often cited articles not only provides a historical perspective on scientific progress, but also reveals trends in research. It has been recognized that an article having 100 or more citations can be regarded as a ‘classic’ based on the field of research (Andersen et al. 2006). Therefore, in the present study, the 10 top-cited micro-CT articles (Table 3) could be considered as ‘classic’ based on their citation counts. Interestingly, the top 4 cited articles were published by O Peters and colleagues in the University of Zurich, at the early 2000 (Table 3). These papers reported not only the use of micro-CT as an innovative and nondestructive technique to be used in endodontic research, but also described in detail how to extract qualitative and quantitative parameters to evaluate the root canal anatomy before and after different procedures. It must be remembered that micro-CT scanners became more affordable and, consequently, available worldwide after 2009 (Stock 2009), which explains the increasing number of articles since then (Figs 2a and 4a). Therefore, these earliest reports served as important references for subsequent studies in the endodontic field, and supported the highest citations per article (64.7) observed in Switzerland as country of origin (Table 2), as well as, the third ranked institution of the University of Zurich (Table S2). On the other hand, the highest number of articles (n = 236) and citations per country (2720 in Scopus and 2081 in Web of Science) was observed in Brazil (Fig. 4a). Accordingly, four of the top 10 institutions (Table S2), 7 out of 10 top-cited authors (Table 1, Fig. 3), as well as, 18 of the top 25 authors (Table 1) ranked by the number of published articles in endodontics were from Brazil. Besides, the most prominent institution associated with micro-CT analysis studies in endodontics was the University of São Paulo with 90 articles (Table S2). Accordingly, Ordinola-Zapata et al. (2020) also identified the University of São Paulo as the top institution in last decade regarding the number of citations associated with articles published in the International Endodontic Journal and Journal of Endodontics. In Brazil, there are several public funding agencies responsible to support projects in private and public dental schools all over the country, facilitating researchers to apply for research grant. Considering the applicability and multidisciplinary use of micro-CT technology, in the last years for instance, one of these agencies provided grants and scholarships for more than 1300 micro-CT research projects (https://bit.ly/3cWptEM), being almost half of them (n = 522) to the University of São Paulo (https://bit.ly/2yq1TRM), which may partially explain the present findings.

A journal’s impact factor is accepted as an indicator of the quality and importance of a journal. Journals with high impact factors that also reflect the frequency of citing articles tend to publish high-quality research  (Tzanetakis  et  al. 2015, Ahmad et al. 2019b). On the other hand, even though many high-quality journals criticize the use of the impact factor as a criterion for evaluating research quality and consider the impact factor as a controversial metric, such journals are inclined to attract high-quality research articles and the authors who are experts in their own research fields tend to submit articles to journals with high  impact factors  (Ahmad et al. 2019b). The fact that 8 out of the top 10 most-cited articles (Table 3) and half of all selected papers in this study (Tables S1 and S3) were published in the highest impact factor journals in Endodontics, namely the International Endodontic Journal and Journal of Endodontics, confirm this trend.

Even though the present bibliometric analysis generated important insights and ideas for future research, it has also limitations. First, the data were extracted from five database and although they comprise the most-influential publications on the analysed topic, it may not encompass the entire scientific literature. Secondly, the data collection in this study was restricted to research papers and case reports. Future investigations might include other types of publication. Finally, the employing of data selecting process is somewhat subjective and different researchers may have different cognitions and interpretations even on the same content. Therefore, the present study tried to overcome the subjective perceptions of the researchers through multiple discussions between authors.

Conclusion

This bibliometric analysis portrayed an original and comprehensive view on the progress and trends of the use of micro-CT technology in endodontic research, and also enabled a deep understanding of the development process in this field over the last 25 years. Overall, research studies published in high-impact endodontic journals had the highest citation rates.

Authors: U. Aksoy, M. Küçük, M. A. Versiani, K. Orhan

References:

1. Ahmad P, Dummer PMH, Chaudhry A, Rashid U, Saif S, Asif JA (2019a) A bibliometric study of the top 100 most-cited randomized controlled trials, systematic reviews and meta-analyses published in endodontic journals. International Endodontic Journal 52, 1297–316.
2. Ahmad P, Dummer PMH, Noorani TY, Asif JA (2019b) The top 50 most-cited articles published in the International Endodontic Journal. International Endodontic Journal 52, 803–18.
3. Ahmad P, Vincent Abbott P, Khursheed Alam M, Ahmed Asif J (2020) A bibliometric analysis of the top 50 most cited articles published in the Dental Traumatology. Dental Traumatology 36, 89–99.
4. Alves FR, Andrade-Junior CV, Marceliano-Alves MF et al. (2016) Adjunctive steps for disinfection of the mandibular molar  root  canal  system: a  correlative  bacteriologic, micro-computed tomography, and cryopulverization approach. Journal of Endodontics 42, 1667–72.
5. Andersen J, Belmont J, Cho CT (2006) Journal impact factor in the era of expanding literature. Journal of Microbiology Immunology and Infection 39, 436–43.
6. De-Deus G, Simões-Carvalho M, Belladonna FG et al. (2020) Creation of well-balanced experimental groups for comparative endodontic laboratory studies: a new proposal based on micro-CT and in silico methods. International Endodontic Journal 53, 974–85.
7. De-Deus G (2012) Research that matters – root canal filling and leakage studies. International Endodontic Journal 45, 1063–4.
8. du Plessis A, Broeckhoven C, Guelpa A, le Roux SG (2017) Laboratory x-ray micro-computed tomography: a user guideline for biological samples. Gigascience 6, 1–11.
9. Fardi A, Kodonas K, Gogos C et al. (2011) Top-cited articles in endodontic journals. Journal of Endodontics 37, 1183–90. Garfield E (1972) Citation analysis as a tool in journal evaluation. Science 178, 471–9.
10. Gavini G, Santos MD, Caldeira CL et al. (2018) Nickel-titanium instruments in endodontics: a concise review of the state of the art. Brazilian Oral Research 32, 44–65.
11. Higgins JPT, Thomas J, Chandler J et al. (eds.) (2019) Cochrane handbook for systematic reviews of interventions, 2nd edn. London: Wiley-Blackwell.
12. Kele s A, Keskin C, Alqawasmi R, Versiani MA (2020) Evaluation of dentine thickness of middle mesial canals of mandibular molars prepared with rotary instruments: a micro-CT study. International Endodontic Journal 53, 519–28.
13. Kolahi J, Khazaei S, Iranmanesh P, Khademi A, Nekoofar MH, Dummer PMH (2020) Altmetric analysis of the contemporary scientific literature in Endodontology. International Endodontic Journal 53, 308–16.
14. Leoni GB, Versiani MA, Silva-Sousa YT, Bruniera JF, Pécora JD, Sousa-Neto MD (2017) Ex vivo evaluation of four final irrigation protocols on the removal of hard-tissue debris from the mesial root canal system of mandibular first molars.  International  Endodontic  Journal 50, 398–406.
15. Mishra L, Kim HC, Singh NR, Rath PP (2018) The top 10 most-cited articles on the management of fractured instruments: a bibliometric analysis. Restorative Dentistry G Endodontics 44, e2.
16. Nawrocka A, Łukomska-Szymańska M (2019) Extracted human teeth and their utility in dental research. Recommendations on proper preservation: A literature review. Dental and Medical Problems 56, 185–90.
17. Nielsen RB, Alyassin AM, Peters DD, Carnes DL, Lancaster J (1995) Microcomputed tomography: an advanced system for detailed endodontic research. Journal of Endodontics 21, 561–8.
18. Ordinola-Zapata R, Peters OA, Nagendrababu V, Azevedo B, Dummer PMH, Neelakantan P (2020) What is of interest in Endodontology? A bibliometric review of research published in the International Endodontic Journal and the Journal of Endodontics from 1980 to 2019. International Endodontic Journal 53, 36–52.
19. Peters OA, Laib A, Rüegsegger P, Barbakow F (2000) Three dimensional analysis of root canal geometry using high resolution computed tomography. Journal of Dental Research 79, 1405–9.
20. Peters OA, Schönenberger K, Laib A (2001a) Effects of four Ni-Ti preparation techniques on root canal geometry assessed by micro computed tomography. International Endodontic Journal 34, 211–30.
21. Peters OA, Laib A, Göhring TN, Barbakow F (2001b) Changes in root canal geometry after preparation assessed by high-resolution computed tomography. Journal of Endodontics 27, 1–6.
22. Peters OA, Peters CI, Schönenberger K, Barbakow F (2003a) ProTaper rotary root canal preparation: effects of canal anatomy on final shape analysed by micro CT. International Endodontic Journal 36, 86–92.
23. Peters OA, Peters CI, Schönenberger K, Barbakow F (2003b) ProTaper rotary root canal preparation: assessment of torque and force in relation to canal anatomy. International Endodontic Journal 36, 93–9.
24. Rhodes JS, Pitt Ford TR, Lynch PJ, Liepins PJ, Curtis RV (1999) Micro-computed tomography: a new tool for experimental endodontology. International Endodontic Journal 32, 165–70.
25. Silva EJNL, Carvalho CR, Belladonna FG et al. (2019) Micro-CT evaluation of different final irrigation protocols on the removal of hard-tissue debris from isthmus-containing mesial root of mandibular molars. Clinical Oral Investigations 23, 681–7.
26. Stock SR (2009) Microcomputed tomography: methodology and applications. Boca Raton: CRC Press.
27. Torabinejad M, Corr R, Buhrley M, Wright K, Shabahang S (2011) An animal model to study regenerative endodontics. Journal of Endodontics 37, 197–202.
28. Tzanetakis GN, Stefopoulos S, Loizides AL, Kakavetsos VD, Kontakiotis EG (2015) Evolving trends in endodontic research. An assessment of published articles in two leading endodontic journals. Journal of Endodontics 41, 1962– 8.
29. Versiani MA, Kele s A (2020) Applications of micro-CT technology in endodontics. In: Orhan K, ed. Micro-computed tomography (micro-CT) in Medicine and Engineering, 1st edn. Switzerland: Springer Nature, pp. 183–211.
30. Versiani MA, Pécora JD, Sousa-Neto MD (2013) Microcomputed tomography analysis of the root canal morphology of single-rooted mandibular canines. International Endodontic Journal 46, 800–7.
31. Yilmaz B, Din col ME, Yal cin TY (2019) A bibliometric analysis of the 103 top-cited articles in endodontics. Acta Odontologica Scandinavica 77, 574–83.
32. van Eck N, Waltman L, Noyons E, Buter R (2010a) Automatic term identification for bibliometric mapping. Scientometrics 82, 581–96.
33. van Eck N, Waltman L (2010b) Software survey: VOSviewer, a computer program for bibliometric mapping. Scientometrics 84, 523–38.
34. Zuolo ML, Zaia AA, Belladonna FG et al. (2018) Micro-CT assessment of the shaping ability of four root canal instrumentation systems in oval-shaped canals. International Endodontic Journal 51, 564–71.