Nonimpacted Third Molars Affect the Periodontal Status of Adjacent Teeth: A Cross-Sectional Study

Most previous studies of the effect of third molars (M3s) on the health of adjacent second molars (A-M2s) have focused on impacted M3s (I-M3s). The purpose of this study was to investigate whether nonimpacted M3 (N-M3s) could affect the periodontal status of A-M2s.

In this cross-sectional study, patients (≥18 years) who had at least 1 quadrant with intact first and second molars and a nonimpacted or absent M3 were enrolled in this study. The periodontal measurements of M2 (6 sites) in the examined quadrants included the gingival index (GI), plaque index (PLI), probing pocket depth (PPD), clinical attachment level (CAL), gingival recession, and bleeding on probing (BOP). The mean GI, PLI, PPD, CAL, and BOP proportion and the proportion with at least 1 site with a PPD of at least 5 mm (PPD5⁺) were compared using the t test or χ² test. The association of PPD5⁺ (percentage) or BOP (percentage) with the presence of N-M3s was assessed using a 2-level logistic regression model (quadrant-based analysis).

One hundred thirty-five patients (43.7% men; 40.6 ± 11.5 yr old) were enrolled in this study. Patients who had at least 1 quadrant with 3 intact molars and an N-M3 were enrolled in group A (105 patients), and patients who had at least 1 quadrant with intact first and second molars without an M3 were enrolled in group B (30 patients). The periodontal parameters (ie, GI, PLI, PPD, CAL, BOP, and PPD5⁺) were markedly greater in group A. When other factors associated with periodontal disease were controlled, N-M3s were associated with the PPD5⁺ (odds ratio = 6.7) and BOP (odds ratio = 4.0) of the A-M2s. Other factors positively associated with A-M2 PPD5⁺ were location on the mandible, age older than 35 years, and smoking.

The presence of N-M3s is a potential risk factor for the development of periodontitis in A-M2s.