METHODOLOGY: A total of 700 maxillary premolars were examined using CBCT in an Egyptian subpopulation. The number of roots was identified, and root canal configurations were classified according to Vertucci's classification and a new system for classifying root and canal morphology. In addition, the position where roots bifurcated and the levels where canals merged or diverged were identified. Fisher's exact test and independent t-test were used for statistical analysis, and the level of significance was set at 0.05 (P = 0.05).

METHODOLOGY: STROBE guidelines were used to design a study using 60 periodontal ligament samples obtained from healthy lower premolars where extraction was indicated for orthodontic reasons. Prior to extraction 40 of these premolars were equally divided into four groups and root canals were prepared using different systems: Mtwo, Reciproc Blue, HyFlex EDM and Plex-V. Ten premolars were prepared with hand files and served as a positive control group. The remaining 10 premolars where extracted without treatment and served as a negative control group. All periodontal ligament samples were processed to measure the expression of SP, CGRP and their receptors by radioimmunoassay. Kruskal-Wallis and Duncan tests were performed to determine statistically significant differences between the groups for each variable.

METHODOLOGY: The Clarivate Analytics' Web of Science 'All Databases', Elsevier's Scopus, Google Scholar and PubMed Central were searched to retrieve the 50 most-cited articles in the IEJ published from April 1967 to December 2018. The articles were analysed and information including number of citations, year of publication, contributing authors, institutions and countries, study design, study topic, impact factor and keywords was extracted.

RESULTS: The number of citations of the 50 selected papers varied from 575 to 130 (Web of Science), 656 to164 (Elsevier's Scopus), 1354 to 199 (Google Scholar) and 123 to 3 (PubMed). The majority of papers were published in the year 2001 (n = 7). Amongst 102 authors, the greatest contribution was made by four contributors that included Gulabivala K (n = 4), Ng YL (n = 4), Pitt Ford TR (n = 4) and Wesselink PR (n = 4). The majority of papers originated from the United Kingdom (n = 8) with most contributions from King's College London Dental Institute (UK) and Eastman Dental Hospital, London. Reviews were the most common study design (n = 19) followed by Clinical Research (n = 16) and Basic Research (n = 15). The majority of topics covered by the most-cited articles were Outcome Studies (n = 9), Intracanal medicaments (n = 8), Endodontic microbiology (n = 7) and Canal instrumentation (n = 7). Amongst 76 unique keywords, Endodontics (n = 7), Mineral Trioxide Aggregate (MTA) (n = 7) and Root Canal Treatment (n = 7) were the most frequently used.

METHODOLOGY: The Web of Science database was searched to retrieve all the manuscripts published in the IEJ and JOE between 1980 and 2019. The articles were analysed using the VOS viewer software and the terms within the titles extracted. The top-10 terms were categorized according to the number of occurrences and the decade of publication. Maps were created using the text data for each decade of publication. Classic papers were identified when the number of citations was >400. During the same period of time, highly cited studies were identified including the authors, institutions and countries associated with these papers.

RESULTS: Terms such as canal, molar and periapical lesion were the most commonly used in titles between 1980 and 1999. The terms instruments, expression, case report and cell were the most often terms used between 2000 and 2019. During the last 10 years, an increase in the number of reviews and papers on cone beam computed tomography occurred. The organizations with the largest number of citations in each decade were University of São Paulo, University College London, Loma Linda University and United States Army. The country with the largest number of citations and greatest number of top 10 and top 100 manuscripts was the United States. A paper had to be associated with more than 167 citations to be included in the top-100 most-cited list; at least 14 papers met the criteria to be categorized as a citation classic (>400 citations).