Unerupted Third Molars and Risk of Loss of Adjacent Second Molars

Objectives: Determine if second molars adjacent to unerupted third molars are at greater risk of loss than those adjacent to absent third molar spaces.
Methods: Participants were 388 men (mean baseline age 48±8 years, mean number of teeth 24±5) in the Department of Veterans Affairs (VA) Dental Longitudinal Study, followed up to 45 years with triennial oral examinations. They are not VA patients, but receive medical and dental care in the private sector. Status of second and third molars was assessed clinically and confirmed on radiographs at each examination. Alveolar bone loss (ABL), number of decayed and filled surfaces (DFS) and calculus score for each 2^nd molar were recorded. Hazards ratios (HR) of 2^nd molar tooth loss during follow-up according to baseline status of the adjacent 3^rd molar (unerupted or absent) were estimated from tooth-level Cox proportional hazards regression models. Covariates were quadrant, baseline age and socioeconomic status, and time dependent values of smoking status and 2^nd molar ABL>40%, DFS, and calculus score. A total of 1042 tooth pairs were used in analyses.
Results: At baseline, 82 men had 120 unerupted 3rd molars. The reference group was 306 men with all 3^rd molars absent. Second molars adjacent to unerupted 3^rd molars were no more likely to be lost (HR=0.9, 95%CI=0.6 to 1.3) than those adjacent to absent 3^rd molar spaces. Further analysis indicated that if the unerupted 3^rd molar was subsequently extracted (n=19), the adjacent 2^nd molar was twice as likely to be lost (HR=2.1, 95%CI=1.1 to 4.3) compared to 2^nd molars adjacent to absent 3^rd molar spaces. Second molars adjacent to 3^rd molars that remained unerupted (n=101) were not at increased risk of loss (HR=0.6, 95%CI=0.4 to 1.0).
Conclusions: Second molars adjacent to unerupted third molars are not at increased risk of loss if the 3rd molar remains unerupted.