Associations among internet addiction, lifestyle behaviors, and dental caries among high school students in Southwest Japan.

Internet addiction (IA) negatively affects adolescents' lifestyle behaviors. Inappropriate lifestyle behaviors could have negative effects on dental health. This cross-sectional study aimed to test whether IA was indirectly associated with dental caries through unhealthy lifestyle behaviors among high school students in southwest Japan. IA was characterized by a Young's Internet Addiction Test score of >/= 50, unhealthy lifestyle behaviors by a cumulative count of 8 different lifestyle behaviors (termed the unhealthy lifestyle behavior index [ULBI]), and dental caries by the number of decayed, missing, and filled permanent teeth (DMFT). Poisson regression and linear regression models were fitted to the relationship, with IA as the exposure, the ULBI as the mediator, and the DMFT as the outcome. The natural indirect effect (NIE) and the proportion mediated by the ULBI were estimated by performing a mediation analysis. Overall, 1562 high school students were included. IA was observed in 406 participants and was associated with a larger DMFT. The ULBI significantly mediated the association between IA and the DMFT (NIE: incidence rate ratio = 1.05, 95% confidence interval = 1.03-1.07, proportion mediated = 64.3%). Dental caries was more common in our cohort of high school students with IA, which is partially explained by these students having unhealthy lifestyle behaviors.