How has the dental literature evolved over time? Analyzing 20 years of journal self-citation rates and impact factors.

Objective: As journal impact factors (IFs) can be artificially inflated by excessive journal self-citation practices, research quality evaluation based solely on IF ranking may be manipulated and, therefore, ethically challenged. This study aimed to analyze the longitudinal development of journal self-citation rates (SCRs) and IFs in dental literature and to determine possible confounders. Methods: Twenty-eight journals with scope within general dentistry and (sub)specialties listed in 1997-2016 Journal of Citation Reports® were scrutinized. The following information was retrieved: publication year, total number of citations, number of self-citations, IF, corrected IF, and SCR. Results: Endodontic journals had the highest SCR (median = 35.3, IQR = 21.6-47.5), journals related to periodontics had the lowest (median = 14.7, IQR = 8.9-25.5). Periodontics had the highest IF (median = 2.1, IQR= 1.7-2.8) and general dentistry had the lowest (median = 0.9, IQR = 0.7-1.2). SCR significantly decreased over time ( p  < .0001) by 1 unit per year. Additionally, 1 unit increase in corrected IF resulted in 15.2 units decrease in SCR. IFs significantly increased 0.06 units per year ( p  < .000). Conclusions: Overall, favourable changes in citation metrics have been observed for dental journals during the 20-year observation period. SCR significantly decreased per observation year whereas IFs significantly increased, indicating a healthy publishing environment in the dental literature. SCR was regulated both by time and corrected IF.