Bibliometric Analysis of the 100 Most Cited Articles on Dental Stem Cells

INTRODUCTION

Mesenchymal stem cells are obtained from adult tissues and they possess a major role in regeneration of tissues in various diseases.¹ Mesenchymal stromal cells (MSCs) are multipotent and possess the capacity to differentiate into other types of cells like chondrocytes, cardiomyocytes, osteoblasts, hepatocytes, and adipocytes.^1,2 Usually, MSCs are isolated from tissues like skin, bone marrow, brain, adipose tissue, myocardium, Wharton’s jelly in the umbilical cord, umbilical cord blood, and granulocyte colony-stimulating factor-mobilized peripheral blood.^1,2

Odontogenic progenitor cells have been identified as another possible origin of MSCs by Gronthos et al.³ Tissues of the pulp were used to isolate these cells. This diverse population of dental stem cells (DSCs) located in developing teeth and their surrounding tissues includes stem cells derived from pulpal tissues,³ stem cells derived from apical papilla,⁴ stem cells obtained from the periodontal ligament,⁵ and dental follicle precursor cells.⁶ Many studies have reported the presence of DSCs in deciduous teeth as well. Dental stem cells mainly arise from neural crest cells but a major proportion is of the glial origin.

Over the past few years, odontogenic tissues have turned out to be an appealing source of mesenchymal stem cells.¹ Various studies have been performed, which has led to the publication of many papers on DSCs. Researchers and clinicians might possibly face difficulties to evaluate the quality of these formidable number of publications. Thus, bibliometrics facilitate scientists to figure out the significant research fields and to get an updated version of a particular field.⁷ It enables researchers to determine the impactful articles among the published literature.⁸

Citation study is a bibliometric tool to assess the scholarly effect of a research paper in a particular discipline. Citation rating identifies journals, countries, institutions, and authors in a certain specific scientific fraternity.^7,9,10

Studies on bibliometric analysis have been performed in several disciplines and have been reported in dentistry as well on subject matters as oral submucous fibrosis,⁷ cone-beam computed tomography,⁸ oral leukoplakia,⁹ oral potentially malignant disorders,¹⁰ ameloblastoma,¹¹ endodontics,¹² orthodontics,¹³ maxillofacial surgery,¹⁴ and oral cancer.¹⁵ However, to our knowledge, a bibliometric and citation study on DSC papers has not been documented yet. Hence, the present study concentrated on determining papers on DSCs, which received maximum citations and studying their attributes to acknowledge the advances and the current research trends in the field.

MATERIALS AND METHODS

RESULTS

The original search identified a total of 400 articles. The overall h-index and h-index after excluding self-citations are 48 and 46, respectively.

KEYWORDS

DISCUSSION

The citation analysis is a good means to spot the prominent articles in different fields of research. The number of times an article has been listed in the reference column of other articles is generally accepted as a mark of distinction.¹⁶ Such bibliometric study approaches help readers without any prior deep knowledge of a specific field to get an overview of the topics, the set of promising researchers, or the most significant papers in that particular field.¹⁷ Garfield has stated that papers receiving citations of 100 and above are marked as classic papers.¹⁸ A comprehensive study of the classic papers will help the new researchers to be updated and aware of such kind of classic knowledge.⁷ A total of 15 classic papers were a part of this study.

Odontogenic tissues, in the past few years, have been a favorable mesenchymal stem cell source and are usually preferred over conventional mesenchymal stem cells derived from the bone marrow because of easy availability by a noninvasive method, high proliferative capacity, and capability of multilineage differentiation.^1,19 Tissues of pulp polyp have also been reported to comprise of cells with stem cell properties.² Studies have been done on DSCs with respect to their isolation methods, cryopreservation, and role in regenerative medicine. Some researchers have indicated the potential application of DSCs in various clinical conditions like neurodegenerative diseases, myocardial infarction, and diabetes.¹ For the very first time, a bibliometric analysis has been done on DSC articles briefing the features of the articles that have received the maximum citations.

For publication of high-quality papers, authors usually prefer journals having high IFs.^7,8 Previous bibliometric studies have shown positive correlation between journal’s IF and citation frequency.^20,21 However, the results of this study contradict the previous study reports. In recent times, researchers tend to choose specialty journals over the high IF journals for publishing their high-quality papers. Most of the top articles have appeared in the Journal of Dental Research (IF = 5.38), one of the illustrious journals related to various aspects of research in dentistry. It is quite evident that the maximum number of papers (n = 7) on DSC has been published in this journal.

The greatest output was from the decade 2010s with 75 articles. Time has a significant impact on citation analysis. Ample time is available for older articles to gather enough citations compared to the articles published in recent times regardless of their scientific impact. However, in this study, three papers from recent 2017 acquired positions in the top 100 list. The papers of 2017, “Therapeutic potential of dental stem cells,” “Evaluation of cytocompatibility of calcium silicate-based endodontic sealers and their effects on the biological responses of mesenchymal dental stem cells,” and “Cryopreservation of human dental follicle tissue for use as a resource of autologous mesenchymal stem cells” were cited 37, 26, and 22 times, respectively. The citation density of each and every article was calculated to rule out the time bias. It brought forward each article’s scientific impact, annually. The value of R = 0.4928, p value < 0.00001 (the result is significant at p < 0.05). Technically, a positive correlation was observed between two factors, i.e., duration of publication and number of citations achieved. Yet their relationship was found to be weak.

The United States was the productive country of all as it had a contribution of 32 publications. It is noted that the United States is always ahead in terms of research works in the field of health sciences, which might be due to the huge support it gets financially for conducting the research projects.^9,10 This is in concurrence with other bibliometric studies.^9,15,22 Increasing volume of dental research in DSC can also be seen in other emerging countries, such as China, South Korea, Japan, and Germany. A major share of publications from Asian countries was also similarly noted in other studies.^17,23 In terms of papers by individual authors, Rodra-guez-Lozano and Nakahara were leading with four and three articles, respectively, as the first author. The coauthorship network analyzed herein shows that most of the authors collaborate frequently with authors of the same institution or of the same country.

Majority of the papers were original research projects (n = 59). There were no papers in the category of case reports and editorials. Analysis of levels of evidence (also known as hierarchy of evidence) of research articles helps in making clinical decisions. In a bibliometric analysis in the field of health science, the study of the level of evidence of papers is quite common. A careful analysis of its classification system reveals that the classifications are related to clinical studies that have a clinical outcome.²⁴ Hence, levels of evidence analysis could not be carried out.

There are certain limitations in this kind of bibliometric studies. The Scopus Database provided the citation data. There are possibilities that the good impactful papers included in databases such as Google Scholar and Web of Science might got omitted in this citation analysis study. The advantage of the Scopus database of automatically excluding self-citations was the reason for preferring and using this database for the current study.^9,10 Another advantage of Scopus over Web of Science is that Scopus provides a 20% more coverage, whereas results of inconsistent accuracy are provided by Google Scholar.^25–27 A bibliometric analysis generally gives a quantitative measure of an article rather than reflecting its quality.^7,8 Authors usually incline to refer previous highly cited research works regardless of their content. This is referred to as the snowball effect. Moreover, bibliometric studies also face “obliteration by incorporation” effect, wherein the sources of the widely accepted results are usually forgotten.²⁸ Thus, those landmark studies struggle to achieve few numbers of citation over the years. There is also a major effect of time on the citation analysis. Previously published articles have a privilege of receiving more citations than the recent ones. Despite the limitations, the study provides a brief summary of the characteristics of the DSC literature.

CONCLUSION

As far as we are aware, a study on the citation and bibliometric analysis of the 100 most cited articles on DSCs has been done for the very first time. The 100 selected papers in this study were all published in English language. Most of the publications were in the 2010s decade. Authors from the United States and Asian countries like China, South Korea, and Japan had major shares in publications. The top 100 list selected in this present study will certainly be an essential source of information for scientists and researchers. Scientists and researchers will benefit from such a study to figure out the focus of research in the field and it will also guide them to plan out the subsequent works and advances to be done in the particular field.

APPENDIX

References

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