Finite Element Analysis Generates an Increasing Interest in Dental Research: A Bibliometric Study

INTRODUCTION

Dental applications of finite element (FE) analysis have grown exponentially in the last decade as a way to assess the mechanical behavior of dental materials, teeth and implants. Finite element analysis is a computer-based method that calculates stresses and strains in computer-aided design models. It does so by splitting complex calculations into a large number of simple equations [1-3]. Software programs used to perform FE analysis are based on models of partial differential equations with boundary conditions. The simplification inherent in FE analysis has several limitations considering the linear simulation of material properties, interrelations and geometries. Nevertheless, these programs enable accurate comparison of models, which approach closer to reality as the calculation power of computers increases [4, 5]. Structural modeling is getting faster with graphical interfaces and tools for computer aided design. The evolution of dental materials, prosthodontics and orthodontics has created a stimulating environment in which to use FE analysis in dental biomechanics.

Dental literature involving FE analysis has also grown because of the increase of authors. All around the world, many dental researchers have learned how to use FE analysis software. Indeed the increasing accessibility of informatics has led more countries to compete in the computer-based research. In addition, many other dental researchers have preferred collaborating with FE-skilled people. As a matter of fact, mastering the software can be a long and demanding process. But at the end, all these researchers are authors trying to find out the most relevant journal, and to maximize the impact on their field. Papers involving FE analysis are now very common in dental research, and young researchers may wonder if specialised journals are not overwhelmed by FE studies. Unfortunately to our knowledge, a study providing a longitudinal overview of dental FE-related (DFE) literature does not exist.

The aforementioned question prompted us to investigate whether authors and publishers in dental research are still interested by FE papers. This bibliometric study sought to quantify the evolution of the DFE literature during the last decade (from 1999 to 2010) using the SCI-expanded database of Web of Science^® (WoS, Thomson Reuters).

MATERIAL AND METHODS

The data for this study was obtained in November 2011 from the SCI-expanded database of Thomson Scientific Web of Science^TM (WoS). To retrieve a comprehensive set of DFE literature, all primary articles or reviews published in journals with at least “finite element” and one of the following keywords in the titles/abstracts were included: endodont*, dentist*, dental, periodont*, temporomandibul*, gingiv*, molar, incisor, "alveolar bone", orthodont*, dentin*, enamel, maxillar*, mandibul*, oral, caries, lingual, jaw, "root canal", prosthodont*, denture, premolar, where the asterisk replaces any subsequent string of characters.

Data sets were selected, analyzed, and ranked in decreasing order of productivity by country and journal, using Microsoft Excel. Multi-authored publications were assigned equally to each country appearing in the author address field. Finally, publications from England, Wales, Scotland, and Northern Ireland were collectively assigned to the United Kingdom.

RESULTS

DFE Literature Grew Exponentially and Faster than the Overall Dental Literature (Fig. 1)

Dental-related FE literature increased 10-fold faster than the overall scientific literature between 1991 and 2010 (from 12 to 257 papers: 21 fold, and from 689,645 to 1,436,479 papers: 2 fold, respectively). Dental-related FE literature has grown exponentially since 1991, and even faster than the dental literature (which also increased exponentially) during the last decade. The overall scientific literature and FE literature since 1991 increased linearly in time. The first DFE papers appeared in 1973, eight years after the first FE papers.

The DFE literature is not the only responsible of the global FE literature increase during the last decade, as DFE literature represents only 2.5% in 2010.

DISCUSSION

The results of this bibliometric study showed that FE literature in dental research generates increasing interest from scientific authors and publishers around the world. The evidence is that the volume of DFE publications increased exceptionally fast (Fig. 1), the number of countries involved in authorship doubled the last decade (Table 1), collaborations are frequent (Table 2), and the mean impact factor of the top 10-publishing journals rose by 75% (Table 3).

Finite element analysis in dental research is a promising field. Our first finding, that DFE literature has grown exceptionally fast, is supported by the comparison with the literature from related scientific domains. The number of publications on DFE increased from 3 in 1990 to 257 in 2010, whereas all scientific publication went through a twofold increase (Fig. 1). An explanation may be that DFE literature combines both the rising interests in dentistry and in FE analysis. Furthermore, the continuous development of FE

Software and its availability on personal computers has supported the increase of the DFE authors. The second finding, that the number of countries involved in DFE authorship grew substantially from 24 to 54 in one decade (Table 1), also supports the idea of an increasing community. Nearly half of these countries in 2009-2010 published at least five papers, showing that the country contribution is not accidental or isolated. Furthermore, the fact that the USA, the country that published the most DFE papers, collaborated on 45% of its publications in 2009-2010 confirms that the DFE field is expanding across national frontiers (Table 2). A hypothesis for this high level of collaboration may be that clinical researchers can ask for help from researchers skilled in DFE who do not necessarily live nearby. Finally, we showed that the impact factor of journals publishing DFE studies has increased the last decade, evidence that DFE studies were likely cited by peers, and consequently of interest for editors and publishers.

United States leadership in DFE productivity may be soon challenged. We observed that USA was the most publishing country of DFE papers, as in all fields of research [6]. However, several lines of evidence support the hypothesis that this leadership may come to an end. First, our finding that USA share of publications was decreasing is consistent

With the global trend described in science and technology [7]. Second, the emergence of South Korea in the top 10 (from 23^th in 1999-2000 to 10^th in 2009-2010) and the increased leadership of China (including Taiwan, from 6^th to 2^nd) were also noted in different fields of research [8-11]. Indeed these countries are driven by a strong economic growth and invest massively in research competition. Third, we also found that EU share of total publications was greater than the USA’s at both time periods. However this observation was also made by Albarran (2010) [12], who interestingly added that USA publications were still more cited than EU’s.

Africa remained under represented in 2009-2010, consistently with other bibliometric studies [8, 10, 13]. The only African countries to be reported were Egypt (ranking 22, 5 papers), Algeria and South Africa (ranking 31 ex aequo with 2 papers; Table 1).

“Dentistry” and “material science” journals support the interest for DFE literature. Our results suggest that journals publishing DFE literature were related with implant biomechanics (such as dental materials, prosthodontics and orthodontics) (Table 3). The International Journal of Oral & Maxillofacial Implants was the most publishing journal of DFE studies in 2009-2010, with 35 papers (Table 3) which represented 8% of its publications. This journal was already ranking second in 1999-2000 with 6 papers. Its most cited DFE papers were in 2001 a review article with 7 citations [14] and in 2011 an original research article with 16 citations [15]. In 10 years, its IF increased by an average of 2.5% per year, which is similar to the average rate of 2.6% per year described for all journals listed in the Thomson Scientific Journal Citation Reports (Science and Social Science editions for the years 1994-2005) [16]. This natural IF increase has been shown to be mainly due to the increase of references listings in all papers over the years [16]. An explanation to this stabilized situation may be that articles about dentistry were hardly exportable to journals outside the disciplinary field, limiting the expansion of dental journals through scientific impact metrics [17]. As these indexes tend to determine the quality not only of papers and journals, but researchers as well [18], authors tried to publish outside the strictly dentistry field. This trend led to an IF increase of DFE literature and the diversification of WoS categories (Biophysics; surgery; engineering, biomedical, Table 3). Interestingly, most of the journals in the 1999-2000 ranking were either considered as “Dentistry” or “Material science”. However, a new and promising WoS category of journal emerged in the top 10 ranking of 1999-2000, combining both “Dentistry” and “Materials science” (“Dental Materials” created in 1984 and “Dental Materials Journal” in 1981). These highly specialized journals may contain the new audience of DFE papers.

Dental-related FE papers are not “classic” citations yet. The DFE papers represented 0.22% of the dental literature in 1999-2000, and only 0.72% ten years later. Interestingly, the percentage of papers mentioning “finite element” in their title remain 36%. This could mean that the same proportion of studies were pure FE studies, as opposed to those performing FE analysis among other methods to achieve their demonstration. In studies analysing the top 55 cited-papers in periodontology [19] (2007) and top 100 in endodontics [20] (2011), DFE papers were not yet part of the “classic articles”. However in these previously studied journals, some DFE papers can reach more than 30 citations in periodontology [21-23] and more than 60 in endodontics [24-26]. In a selected panel of orthodontic journals, only one paper [27] (published in 1987) was part of the 2013 top 100 [28]. Even in the implantology and prosthodontics fields, DFE papers still represent less than 4% of the top 100 (data not shown).

The period covered by this bibliometric study is a limitation. First, the Science Citation Index (SCI) Expanded^® has coverage only since 1991 for 70% of the articles of full-length, English-language, author, abstracts, (http://images.webofknowledge.com/WOK45/help/WOS/h_database.html). The 1991 improvement of the coverage was associated with a sudden 2.7 fold increase for dental literature in the WoS database between 1990 and 1991 (data not shown). However, the SCI-Expanded provides complete bibliographical information over 8,500 major international journals across 150 disciplines, dating back to 1900. Second, some journals are referenced later than others, and IF are released six months after the year of publication. As a consequence, we could not analyse accurately publications retrieved from the last couple of years. Third, in order to have bigger numbers of publication, we studied publications retrieved from periods of a couple years. As these represented a lot of manual analyses, we did not compare more than two periods. Anyway, we do believe that our assumptions were reasonable as trends in DFE publications evolved exponentially with predictability (Fig. 1).

CONCLUSION

In conclusion, the results of this bibliometric study showed that FE literature in dental research generates an increasing interest from authors and publishers around the world. The evidences are that the volume of DFE publications increased exceptionally fast, the number of countries involved in authorship doubled the last decade, collaborations are frequent, and the number of publishing journals increased while the mean impact factor of the top 10 publishing journals arose by 75%. It is hoped that the present study showing the richness, importance, and diversity of DFE research provides a useful description of the scientific literature and will encourage researchers to further advance this field.

REFERENCES