INTRODUCTION

Endodontics is the study of the basic and clinical sciences of the dental pulp, as well as the aetiology, diagnosis, prevention, and treatment of pulpal diseases and injuries (European Society of Endodontology 2006). Endodontics has progressed enormously in recent years, as shown by a surge in the number of articles in the endodontic literature (Fardi et al. 2011; Yilmaz et al. 2019). The consequence of this evolution is a growing number of publications in each issue of dental journals, as well as a rise in articles, published ahead of print. Scientific fundamental and clinical research are an important keystone of clinical practice and a necessity for a high quality of delivered oral health care in the era of evidence-based dentistry (Brignardello-Petersen et al. 2014). Original scientific papers published in peer-reviewed journals are the most common method of evaluating the quality of science in any scientific area (Triaridis & Kyrgidis 2010). 

Bibliometric analyses of academic output are critical in assessing a country’s scientific performance and have ignited significant interest in recent days (Tzanetakis et al. 2015; Fardi et al. 2011). Bibliometric analysis helps research stakeholders to evaluate and filter published articles, allowing them to identify the most relevant published studies, the most active research aspects and topics, and their evolution over time. Scientometrics is a tool for assessing the progress of science, allowing us to evaluate the output of authors, institutions, countries, or specific thematic areas (Bueno-Aguilera et al. 2016). Such analysis offers useful and comprehensive evidence for designing research and development projects. There have been several bibliometric reviews on endodontics published in the literature (Fardi et al. 2011; Tzanetakis et al. 2015; Yilmaz et al. 2019), but none of them specifically focused on articles published from Malaysia. Hence, this attracted the authors’ interest in the exploration of previously published manuscripts from scholars affiliated with Malaysia. 

Scopus (Elsevier)’s prominence has escalated in recent years as a result of its increased inclusivity and representativeness (de Moya-Anegón et al. 2007). It was first introduced in November 2004 by Elsevier Science, which soon became the main competitor in dominating the international market for scientific databases. Scopus is recognised as the world’s largest abstract and citation database of peer-reviewed literature covering a broad range of topics (Md Khudzari et al. 2018). According to SCImago Journal & Country Rank, which is driven by the Scopus database, Malaysia is the eighth country in the Asiatic region with the most dental articles published annually since 1996 (SCImago Journal & Country Rank). In 2019, Malaysia climbed to the sixth position with a total of 227 articles published by authors affiliated with Malaysia. These articles earned 71 citations (28 self-citations), culminating a citation rate of 0.31 per paper (SCImago Journal & Country Rank). The rise in international scientific output from Malaysia in recent years has been accompanied by the increased demand for dental research.  

A paramount scientific literature explicitly on endodontics has been published and these studies should be reviewed and analysed to ascertain their impact on current and future development in the field of endodontics (Yilmaz et al. 2019). To the best of the authors’ knowledge, no comprehensive study is available on the scientific production in endodontics among dental researchers in Malaysia. Hence, the purpose of this study was to perform a bibliometric analysis of the scientific research output among researchers in Malaysia dedicating to endodontology from 2001 to 2021 based on Scopus database. This study also aimed to identify the characteristics of selected articles and provide insight into current and historical publishing patterns in the field of endodontics. 

MATERIALS AND METHODS

Search Strategy

An electronic search based on the Scopus® database was performed by 2 investigators in the first week of March 2021 to identify the published articles. The following search equation was applied: TITLE-ABS-KEY (endodontic OR endodontics OR endodontology OR root AND canal OR roots AND canals) AND (LIMIT-TO [AFFILCOUNTRY, “Malaysia”]). The search was performed from January 2001 to February 2021. The inclusion and exclusion criteria for the study selection are shown in Table 1. Only articles written in English and the first author’s affiliation from Malaysia were selected. If the first author has more than one affiliation, only the first affiliation was counted. Editorials, letters to the editor, conference abstracts and opinion pieces were not included. However, there was no constraint on the number of publications and journals that could be included. Any disputes regarding articles that could be included or omitted during the search were discussed with the assistance of the third and fourth investigators. The SCImago Journal & Country Rank (SJR) database was used to determine the journal impact and ranking of each selected article.

Data Collection

The following parameters were extracted from each article: title of the articles, authors’ name(s), number of author(s), institution(s) or affiliation(s), name of journal, year of publication, type of publication, source of the article, keywords, and number of citations. The authors were subsequently refined and normalised manually to eliminate typographical, transcription, and/or indexing errors, as well as to unify the terminology. If multiple entries for a single author were discovered, the authors’ institutional affiliations were reviewed to see if the entries belonged to the same author. The selected articles were ranked according to the number of citations in descending order. If more than one article had the same citation number, the article published more recently was ranked higher. The first author’s affiliation was used to evaluate the ‘source of the article’ (Tzanetakis et al. 2015), whereby articles were classified based on the first author’s affiliation department, such as ‘endo’ for the department of endodontics, ‘cons’ for the department of conservative dentistry or ‘resto’ for the department of restorative dentistry. They were also split into two subcategories i.e. ‘Academic’ for scholarly papers from universities and ‘Non-academic’ for articles from professional private practices or private organisations. 

Each article was further analysed to include the article type and thematic categories. For article type, it was divided into research, review, case reports and case series, whereas research articles were subdivided into basic research, clinical research, or others. If the study involved in-vitro experimental works on extracted teeth or cell tissue culture, it was considered basic research. On the other hand, study involved an in-vivo approach or study involved microbiological samples from living human’s root canals, the study was then considered a clinical article (Fardi et al. 2011). Articles that do not fall in these two groups were categorised as others. The selected articles were also classified into 12 thematic categories including microbiology, pulp biology or pathology, root canal morphology, chemical preparation, mechanical preparation and instrumentation, working length determination, obturation, endodontic materials, restoration, endodontic surgery, epidemiological studies, and clinical or radiographic outcomes (Tzanetakis et al. 2015). Articles that did not fit into either of these groups were listed as others. The classification of thematic categories was calibrated for all four investigators, and any disagreements were addressed with an experienced endodontist. Kappa test was performed to assess the inter-examiner agreement among all investigators.

Data Analysis

Descriptive analyses were performed using SPSS version 24.0 (IBM, Corp, Armonk, NY, USA) and Microsoft Excel software (Redmond, WA, USA). Comparison of the number of articles published and total citation counts between the period of (2001-2010) to (2011-Feb 2021) were analysed using Pearson’s Chi-square test, whereas the association between number of publications and citation counts were analysed using Pearson’s Correlation test. The significance level was set at P=0.05. The keywords and collaboration network among the authors were analysed using VOSviewer software version 1.6.16 (Centre for Science and Technology Studies, Leiden University, The Netherlands).

RESULTS

From the search, a total of 220 articles were remained after preliminary screening based on titles and abstracts, followed by removing the duplicated articles. However, only 119 articles of which the first author affiliated with Malaysia were included (Figure 1). The Kappa test was score 8 among all investigators. The selected articles were ranked in descending order based on their citation counts as listed in Table 2. The top-cited article was cited 69 times, while 11 articles were found to have a citation count of 20 or greater, making them the top 9% among the selected articles. However, 43 articles were noted with no citation count.

Authors

A total of 72 researchers from Malaysia who had contributed to the scientific publication in endodontics as the first authors. The first author with the greatest number of publications was Hany Mohamed Aly Ahmed with 12 articles, followed by Nagendrababu Venkateshbabu and Afaf Yahya Al-Haddad with 8 and 7 articles, respectively. Meanwhile, only 15 authors with 2 or more articles published in Scopus database were found (Figure 2a). The mean number of authors was 3.97, median of 4, and a range of 1 to 15 authors (Figure 2b). 

The state-wise distribution of publications revealed the maximum number of authors were 4 (24.4%), followed by 5 authors (21.8%) and 3 authors (19.3%). After an exhaustive analysis of all the first contributing authors, it was discovered that they had also appeared as second, third, fourth, and fifth authors in other articles. For coauthors who contributed to three or more papers from the chosen article list, a collaboration network was developed (Figure 3). The number of articles published by each author is represented by the node size, and the strength of collaborations among the authors is represented by the joining lines.

Journals, Year of Publication and SJR Score

Table 3 shows the lists of top-5-journal in which the articles were published in descending order. Journal with similar number of articles published were ranked based on their score according to the SJR. The International Endodontic Journal published the greatest number of articles, followed by International Medical Journal, Australian Endodontic Journal, Journal of Endodontics, and lastly BMC Oral Health. Based on Figure 4a, 32 out of 119 selected articles (26.89%) were published in endodontic related journal. Among them, 15 articles (46.88%) were published in International Endodontic Journal which accounted for the greatest number of publications, followed by 5 articles (15.63%) published in Australian Endodontic Journal, and 4 articles (12.5%) each published in Journal of Endodontics and Iranian Endodontic Journal, respectively. 

Based on the SJR (Figure 4b), 39 of the selected articles (32.77%) were presented in Quartile 1, followed by 22 articles (18.49%) in Quartile 2, 31 articles (26.05%) in Quartile 3, and 22 articles (18.49%) in Quartile 4. There were 3 articles (2.52%) published in journals that are not assigned in any quartile yet, while 2 articles (1.68%) published in journals that could not be found from the SCImago Journal Rank. 

From Table 4 and Figure 4c, the greatest number of articles published was found in the year 2020, while the highest number of total citations was noted in the year 2017. A drastic increase (P<0.05) of articles published, and total citation counts were noted when comparing the first decade (year 2001 to 2010) to the second decade (2011 to Feb 2021). Besides, a significant association (P=0.038) was also found between number of articles published and total citations. 

Institutions, Source and Origin

A total of 118 articles (99.16%) were academic-based which distributed across 13 institutions in Malaysia, while only one article was non-academic-based from a private practice. Among the 118 academic-based articles, the Universiti Sains Malaysia (USM) produced the highest number of publications (37.3%), followed by Universiti Malaya (UM) (18.6%), International Medical University (IMU) (16.9%), Universiti Kebangsaan Malaysia (UKM) (9.3%) and Malaysia Allied Health Sciences Academy (MAHSA) University (5.1%) (Figure 4d). The source of each article was analysed based on the department where the studies were produced. 

Table 5 shows that the Department of Conservative Dentistry was the most prolific, producing the highest number of articles with 29 articles each, followed by department of restorative dentistry which produced 28 articles and department of clinical dentistry with 13 articles. Amongst all the articles, the origin of 118 articles was from journals. Only 1 of them was originated from a book chapter (Bindal et al. 2017).

Article Type, Thematic Category and Keywords

Of all the selected articles, 75 articles (63.03%) were research, in which 62 articles (52.1%) were basic research, 5 articles (4.2%) were clinical research, and 8 articles (6.72%) were classified as others. 27 articles (22.69%) were reviews, followed by 16 (13.45%) case reports (Table 5). Of the total publications, thematic categories of endodontic materials and others had the most number of articles which were 19 each (16%), followed by 17 articles (14.3%) themed as root canal morphology, 10 articles (8.4%) each for restoration, clinical or radiographic outcomes and microbiology. However, only 1 article (0.8%) was about epidemiological studies (Nie et al. 2013). A total of 954 unique keywords were identified. However, after setting the minimum number of occurrences of a keyword to 5, only 74 keywords met the threshold, and they are provided in Figure 5. The top three most frequently used keywords were ‘endodontics’, ‘tooth root canal’ and ‘root canal filing material’.

DISCUSSION

The present bibliometric study is the first of its kind to assess the scientific contribution of researchers in Malaysia in the field of endodontics. Nation-based bibliometric analysis in areas of dentistry, especially endodontics, may provide readers with current literature or discoveries in endodontics on a national level, as well as assist in determining future research direction (Abraham et al. 2018). Such analysis often helps researchers to determine the status of national research and equate it to global research performance. Even though it is beyond the scope of this bibliometric review to include and address all the research contents of the selected articles, the present review has managed to extract and outline some pertinent aspects related to the main objectives. According to our findings, the bulk of the publications have more than three authors. The emergence of interest across different institutes in Malaysia and among different researchers could explain the increase in the number of coauthors over the years. Hence, more collaboration among researchers can be expected in the future. 

Most of the articles were published in the International Endodontic Journal (Q1 journal), which is regarded as one of the most reputable publications in the field of endodontic research and clinical practice. This journal has, understandably, published the greatest number of articles (12.7%) in endodontics. However, this contradicts previous bibliometric studies which revealed that Journal of Endodontics was the journal with the highest number of research publications (Fardi et al. 2011; Adnan & Ullah 2018). UM and USM were the two institutions that contributed to the most number of articles in this esteemed journal with 6 articles published each. The high impact factor also reflects the journal’s importance as a source of knowledge for researchers interested in advanced and groundbreaking approaches in the field of endodontics (Abraham et al. 2018). A noteworthy finding is that the International Medical Journal (Q4), which contributed 8 articles to the list of selected articles, was ranked as the second most-published journal. Seven of the eight publications were published by the first authors from USM. Several factors, including open access, fast track review, acceptance rate, and a reasonable article processing fee, may have affected the submission of papers to the stated journal considering its low impact factor (Gaston et al. 2020; Calcagno et al. 2012).

In the present review, we evaluated the number of articles published in endodontic related journals. The top three journals with the most publications were International Endodontic Journal, Australian Endodontic Journal, and Journal of Endodontics. The comparatively lower number of publications published in European Endodontic Journal and Giornale Italiano di Endoddonzia, may be attributed to author preference and recent Scopus coverage in European Endodontic Journal as this journal being recent and still in its infancy. Since endodontics has attracted a great amount of attention over the years, it is expected that a vast number of related articles will be published in these two journals in due time.

An important distinction of this analysis was that the largest number of publications were published in 2020, while the highest number of citations were reported in 2017. This reflects recent trends among researchers in Malaysia, who are developing a greater interest in endodontics research. Studies released after 2020 have earned no citation, but it is too early to conclude if these papers would gain more citations over time and suggest a different pattern from the one seen in this report. The dramatic spike in publication from the second decade (2011-Feb 2021) may also be attributed to an increase in the quantity and efficiency of conservative dentistry and endodontics researchers, improvements in advanced laboratory technologies that allow for more well-standardised testing, and widespread interest in improving endodontic materials (Krishnan et al. 2020; Abraham et al. 2018; Yilmaz et al. 2019). The SJR indicator assesses both the number of citations per journal and the relevance of journals that have external citations. The SJR metric is based on an average estimation of weighted citations the journal gets over the preceding three years, and the journals are divided into four quartiles (Falagas et al. 2008). More than half of the articles chosen were published in Q1 and Q2 journals, showing the high quality of study performed by researchers in Malaysia.

The USM was ranked first among the institutes where the bulk of the first authors were affiliated. A large amount of in-vitro basic research experiments has been discovered in this institution (Farea et al. 2011; Abdo et al. 2012; Aal-Saraj et al. 2012; Abdo et al. 2012; Ong et al. 2012; Razali et al. 2013; Hui Hui et al. 2013; Masudi et al. 2014; Thauk et al. 2014; Muttlib et al. 2016; Salim et al. 2018; Abdul Ghani et al. 2019; Alhajj et al. 2020; Lin et al. 2018; Lin et al. 2020; Lin et al. 2020; Lin et al. 2021). UM has the second-highest number of endodontic publications, but it pales in contrast to the vast amount of research generated by the first authors associated with USM. The frequent collaboration between academic institutions in Malaysia, as seen in the graphical mapping of co-authorships, may account for the rise in endodontics publications from researchers associated with these two universities. An interesting fact is that one private practitioner in Malaysia (Tan Endodontic Dental Specialist Centre Private Practice) has also contributed to the literature on endodontic (Ong 2017). This is a positive aspect because private practitioners may see a lot of unusual cases, and their participation in the research literature can offer a thought-provoking insight into various endodontic treatment procedures and outcomes. Another interesting discovery was that conservative and restorative dentistry departments tended to produce a considerable number of articles. This can be explained as most institutions incorporate endodontics into ‘conservative’ or ‘restorative’ departments and the term ‘endodontic’ or ‘endodontology’ were not used. Such a phenomenon was also found to be more prominent in European countries according to a previous study (Tzanetakis et al. 2015).

Although in-vitro study designs are not regarded at the top of the evidence ladder, they have been seen in the majority of published studies (Burns et al. 2011). The second most popular category of article published is a review, followed by case reports. Clinical research using an in-vivo methodology is still limited according to the current review (Kim et al. 2012; Deng et al. 2018; Soh et al. 2019; Pan et al. 2019; Karobari et al. 2020), and only one paper derived from a book chapter (Bindal et al. 2017). As a result, prospective experiments should concentrate on clinical settings and follow-ups, as these studies will provide more predictable and reliable outcomes, as well as reinforce the clinical validity of in-vitro studies.

The two major focuses of studies included in the list were related to endodontic materials and root canal morphology which corroborates with a previous study (Tzanetakis et al. 2015). This is a major predictor of Malaysia’s researchers to success in dealing with a large spectrum of endodontic studies, as endodontic materials cover not only dental knowledge but also material sciences and chemical engineering viewpoints. Root canal morphology research is also essential in ensuring the safety and efficacy of endodontic treatments and offers clinicians a greater understanding during root canal cleaning and shaping (Chai & Thong 2004; Ahmed & Abbott 2012; Pallivathukal et al. 2015; Ahmed & Hashem 2016; Ahmed et al. 2017; Kacharaju et al. 2019; Pan et al. 2019; Karobari et al. 2020; Abdul Rahman et al. 2020). These study results can also be extrapolated and validated in clinical trials, enabling clinical decisions to be made in light of them. On the other hand, only one epidemiological study was reported related to the occurrence of C-shaped canals in Malaysian population (Nie et al. 2013). Therefore, highlight should be made for future researchers to explore more in this theme of endodontics to provide more in-depth information on the distribution of pulp and periapical diseases and factors affecting them among Malaysian population. 

One of the potential limitations of bibliometric analysis is that older articles have more time to receive citations (Adnan & Ullah 2018). Therefore, prejudice may emerge when the articles were also tabulated according to the citation counts. Since new research may be a continuation of this current literature or novel research, subsequent publications could supersede current data and obtain even more citations. Despite this, there is no system in place to distinguish publications with a higher number of citations because of self-citation. Another drawback may be the inclusion of publications with only the first author affiliated with Malaysia. Furthermore, the current study relied entirely on the Scopus database to evaluate the scientific contribution of Malaysia’s researchers in endodontics. Significant evidence could also be lost since published papers in other languages, opinions, or conference proceedings were not included.

CONCLUSION

This is the first bibliometric analysis that portrayed an original and comprehensive review of the scientific contribution of Malaysia’s researcher in the field of endodontics. Despite certain shortcomings, it provides a thorough review of endodontic studies over the last two decades. Ignoring the fact that only about 10% of the articles had 20 or more citations, more than half of the articles were published in journals ranked in the first and second quartiles by SCImago. In the Scopus database, 15 of the 72 authors had two or more publications. Moreover, there has been a rise in the number of publications and citations in recent years, suggesting an increasing interest in endodontics among researchers in Malaysia. The USM ranked first with the highest number of publications, whereas International Endodontic Journal was the journal with the most articles published. The majority of the publications came from the department of conservative dentistry. The primary theme of endodontic research was basic research experiments on endodontic materials, indicating that researchers prefer in-vitro laboratory studies focusing on developing or enhancing the properties of endodontic materials. Nevertheless, a more detailed analysis of the validity of evidence in the articles used in this analysis is warranted.