Influence of Non-Impacted Third Molars on Pathologies of Adjacent Second Molars: A Retrospective Study

Background: Although removal of impacted third molars (I-M3s) is common in dental clinics, the decision to retain or remove asymptomatic non-impacted third molars (N-M3s) presents a significant challenge. This study investigates influence of N-M3s on pathologies of adjacent second molars (A-M2s). Methods: Clinical status of M3s was evaluated, and presence of distal caries, external root resorption (ERR), and alveolar bone loss (ABL) of A-M2s was assessed by orthopantomograms (OPGs). Prevalence of A-M2 pathologies was evaluated and association between N-M3s and pathologies of A-M2s was analyzed by multivariate logistic regression. Significance level was set at 0.05. Results: OPGs from 1,958 patients were included in the present study. Among these patients, 45.1% presented with at least one N-M3, and 44.2% of retained M3s were non-impacted. Where N-M3s were present, prevalence of distal caries, ERR, and ABL of A-M2s was 10.0%, 0.8%, and 40.4%, respectively. Although N-M3s did not increase the odds of caries or ERR of A-M2s, presence of N-M3s was associated with 1.77 times higher likelihood of ABL from A-M2s when data were adjusted for age and sex. Conclusions: Presence of N-M3s, even if they are asymptomatic, represents an important risk factor for periodontal health of A-M2s. This finding should be considered during clinical decision making regarding retention or extraction of N-M3s, especially when these teeth are non-functional or when their removal will not affect overall occlusal function.