Nanomaterial is defined as a “natural, incidental, or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50% or more of the particles in the number size distribution, 1 or more external dimensions is in the range 1–100 nm” according to the European Commission’s Recommendation [1]. These materials consist of nanoparticles with 1, 2, or 3 outer dimensions at the nanoscale [2]. Following the landmark lecture by Richard P. Feynman, nanomaterials have been used in various medical applications in parallel with technological developments [34].

The use of nanoparticles has become an attractive topic in many types of research in health sciences, including dentistry, with the advancement of technology and the introduction of new inventions [256]. Some unique chemical, biological, and physical features have led to these particles being desirable in endodontics as well as other specialties in dentistry [478]. Especially, the higher antimicrobial characteristics having a large surface area and smaller sizes, which can enhance the efficacy of endodontic materials, are the most favorable factors since endeavors in the field of endodontics are directed toward ensuring complete disinfection of the root canal system and preventing reinfection [910]. In this sense, nanoparticles have been used alone or in combination with different endodontic materials such as calcium hydroxide, irrigation solutions, root canal sealers, gutta-percha, and calcium silicate-based cements in order to improve the efficiencies of materials [1112]. Furthermore, these materials also have been employed in contemporary applications as follows: coating instruments, drug delivery systems, and tissue regeneration [13]. Although numerous types of nanoparticles are produced, chitosan, bioactive glass, and silver compounds are basically utilized in endodontic practice due to their antimicrobial and osteoinductive effects [141516].

Bibliometrics is the quantitative analysis of academic publications in various aspects in order to assess the historical progression of research fields and the scientific productivity of researchers, countries, institutions, and journals [17]. These analyses allow researchers to define past and present trends, identify gaps in the literature, and guide future studies [18]. Citation analysis is the most commonly performed method in bibliometrics and aims to describe the impact of publication by observing the citation data that a scientific study receives [1920]. Similarly, Scientometric analysis aims to examine the data, usually by visualizing the information obtained from bibliometrics [21]. This analysis provides readers with a scientific map of the bibliometric output by examining collaborations between authors, institutions, or countries.

Although several bibliometric studies have already been conducted on different topics in endodontics, the publication trends related to nanoparticles have not been investigated yet [22232425]. Since nanotechnology is rapidly growing and affecting many treatments in endodontics, the main trends and future expectations need to be addressed. Thus, this bibliometric study aims to identify and analyze the top most-cited 100 articles about nanoparticles in endodontics from 2000 to 2022.

An advanced electronic search was conducted in the “Clarivate Analytics Web of Science (WoS)” (http://www.webofknowledge.com) since WoS contains peer-reviewed, high-quality scientific journals published worldwide. The search strategy was designed by 2 investigators (SNU and KD) with experience in endodontics and/or bibliometrics. A detailed search strategy was performed using frequently used keywords related to the nanoparticles. This bibliometric study included only articles written in English between 01.01.2000 and 01.01.2022 since the studies on nanoparticles in endodontics have shown an increase after the 2000s. The articles that were not related to the usage of nanoparticles in endodontics, conference papers, and editorial letters were excluded from the scope of this study.

Initially, the below-mentioned 2 search queries were constructed on 9 September 2022, and articles were recovered:

These 2 queries were combined as (Q1 AND Q2), and 1,727 articles were obtained in total. Subsequently, the data were downloaded in Microsoft Excel 15.0 (Microsoft, Redmond, WA, USA) format for bibliometric analysis, and the articles were ranked in descending order according to their citation counts. When more than one article had the same number of citations, the article had a higher citation density value was ranked first [19]. All articles were screened and analyzed by 2 independent investigators (SNU and ZUA) to specify whether they were related to nanoparticles in endodontics. Investigators accessed the full text when they could not receive adequate information from the abstract and/or title. Any disagreements were resolved by consulting with the third researcher (CA) until a consensus was reached. The search process is outlined in Figure 1.

The following variables were recorded for each article: citation count, citation density, publication year, journal, country, institution, first author, co-authors, study field, study design, evidence level (EL), and keywords. The citation density was calculated by dividing the total number of citations by the number of years since the article was published. The included years were divided into 2 groups (2000–2010 and 2011–2022) to detect time-dependent alterations of metrics. The study fields were categorized by a consensus among all investigators, taking into account the main focuses of the articles. Moreover, each article was assigned to 1 of the designed groups, according to the nature of design, as follows: review (narrative and systematic), in vitro (this sector includes studies of parts of dental tissue, sections of the tooth, and cell cultures), ex vivo (teeth and complete root from humans or animals). The top 100 most-cited articles were also evaluated regarding the used nanoparticles, the usage field, and the main findings.

After conducting the bibliometric analysis, scientometric analysis was performed to generate a network model and identify research areas. The selected articles were further analyzed according to the geographical distribution of the authors who contributed the most. Moreover, domestic and international collaborations between authors were determined and visualized. In addition, keywords with more than 2 co-occurrences were also evaluated and visualized.

The VOSviewer (version 1.6.18; Leiden University Center for Science and Technology Studies, Leiden, The Netherlands, available at https://www.vosviewer.com) was used to summarize and visualize the bibliometric data downloaded from the WoS by creating a science map. The minimum number of documents per author and country is set to “1” and for citations to “0” to optimize analysis. The size of the nodes indicates the frequency of the analyzed parameters; consequently, larger nodes are associated with a higher frequency. Moreover, the thickness of the edges presents the relationship of the interactions between 2 nodes, while their colors indicate the cluster to which the keyword belongs.

All statistical analyses were performed using Statistical Package for Social Sciences (SPSS) for Windows software, version 26.0 (SPSS Inc., Chicago, IL, USA). Shapiro-Wilk test was performed to check the normality of both the number of citations and citation density. Kruskal-Wallis test was used to compare these metrics among decades. When the results were statistically significant, Mann-Whitney U test was used for pair-by-pair comparisons. The correlation between citation, citation density and age of publication was assessed using the square of the Spearman linear coefficient. The significance level was set at p < 0.05.

Many studies have been carried out over the years about nanoparticles since there is an enormous interest in nanotechnology and the properties of nanomaterials [27]. Thus, this bibliometric study aimed to highlight the global research trends about nanoparticles in endodontics based on citation counts. Receiving more citations partially reflects the scientific impact of the publication since it is a time-dependent metric and is affected by various other factors, such as the reputation of the authors, the institutions with which the authors are affiliated, or even the countries in which the authors are located [28]. Therefore, evaluating the quality of the paper is challenging. Even so, drawing a citation-based ranking list allows researchers to set a time period for literature analysis and provides a comprehensive guide to the research topic [25].

Due to the nature of citation analysis, old articles are expected to receive more citations than recently published ones [29]. Accordingly, a positive association was found between the number of citations and the age of publication. Although lower citation values were observed in 2010–2022, the total citation counts were higher in this period than in 2000–2010. This could be because fewer articles about nanoparticles in the previous decade were published. The improvement in knowledge and experience of researchers about nanoparticles with the development of technology has increased the number and quality of studies in recent times. However, time is needed to evaluate the long-term scientific contributions of new studies to the literature. Therefore, the evaluation of citation density as a time-independent metric could be an alternative analysis to measure the influence of an article.

While older articles are expected to be cited more often, interestingly, the study with the highest citation count and density was performed by Yin et al. [30] in 2020 in this bibliometrics. Although it was published very recently, the broad scope of the article about the antibacterial mechanism of silver nanoparticles and its application might have led to its being highly cited. The second most-cited article performed by Wu et al. [16] aimed to evaluate the antibacterial efficacy of silver nanoparticles against E. faecalis biofilm. And the third most-cited article was published by Waltimo et al. [31] intended to describe the antimicrobial effect of bioactive glass 45S5. These 3 studies have purposed to underline the antimicrobial properties of nanoparticles. Since the primary goal of utilizing nanoparticles in endodontics is to take advantage of their disinfection abilities, these results are in line with current knowledge.

A large number of articles have been published in the Journal of Endodontics and the International Endodontic Journal, which are considered to be the leading journals in the field of endodontics [32]. However, most of the journals were multidisciplinary, prioritizing publications on nanomaterials and nanotechnology. This can be explained by the fact that the design, the production stage, and the usage areas of nanoparticles require the collaboration of different working fields.

Anil Kishen and Annie Shrestha were the most productive authors, and this has led to Canada and the University of Toronto having the highest number of articles as a country and an institution, respectively. These 2 authors are well-known researchers in the field of endodontics due to the large number of influential articles about nanoparticles they have published [3334]. In this context, it is concluded that the investments of countries and institutions in scientific studies affect the outputs significantly.

In this bibliometrics, more than half of the studies were designed in vitro, followed by narrative reviews. In vitro studies are essential for evaluating the efficacy of relatively newly produced materials before conducting animal and in vivo studies [17]. However, clinical studies with high evidence levels are needed to apply the developed materials and technologies in routine dental practice. Furthermore, reviews are more likely to be cited because they provide general information on the topic and can guide a large number of researchers by addressing the subject from different aspects [35]. Reviewing the first most-cited article in this study is consistent with the above-mentioned information.

The main study field was the antibacterial effect of nanoparticles in endodontics. This is an understandable result since complete disinfection of the root canal system still poses a challenge due to the various anatomical and meteorological factors, and this promotes researchers to discover alternative materials and technologies [4]. The superior antibacterial properties of nanoparticles have made these molecules favorable in endodontic treatments [30]. In line with the mostly investigated study field, keywords such as E. faecalis, biofilm, and antibacterial also highlight the main interest in using these particles in endodontics.

Some limitations should be indicated in the scope of this bibliometric study. One of those is that it is unclear whether the preferred database WoS includes all the articles related to the topic, although it is considered a very appropriate database. Moreover, the time-dependent nature of citation analysis is insufficient to accurately determine the scientific value of studies and makes it impossible to evaluate fairly recent published influential articles [36]. In addition, self-citations may be considered a bias factor since the authors promote the citation of their studies. Finally, only the institutional address and the countries of the first authors were recorded and assessed; therefore, multicenter studies could not be identified.

Antibacterial effects of nanoparticles, in particular, have a promising scope for various endodontic applications. With the development of nanotechnology and gaining more experience in this field, very influential studies have been published in recent years. It is considered that this bibliometric study serves as a guide for future studies by demonstrating the current knowledge and frontiers of these materials.