Objectives: The purpose of this study was to investigate the potential risk of incident caries, bone loss, and/or periodontal pocket on the distal of a 2nd molar when both 1st and 2nd molars are present, depending on whether a 3rd molar is (1) absent, (2) erupted, (3) soft-tissue impaction, or (4) full bony impaction.
Methods: Study subjects were participants in the US Department of Veteran Affairs (VA) Dental Longitudinal Study (DLS). For inclusion in the study, both 1st and 2nd molars needed to be present at baseline. A total of 416 subjects were included in the study with the following distribution of 3rd molars: 460 missing, 230 erupted, 25 soft-tissue impactions, 89 full bony impactions. Risk of incident distal caries, increased distal bone loss, and increased distal probing depth of 2nd molars over time according to 3rd molar status at baseline was compared using multivariate survival analysis.
Results: 2nd molars adjacent to erupted 3rd molars were at greatest risk for incident caries at 2.5 times the risk of incident distal caries compared to 2nd molars adjacent to missing 3rd molars. 2nd molars adjacent to soft-tissue impacted 3rd molars were at greatest risk for incident bone loss at 9.2 times the risk of >40% distal bone loss over time compared to 2nd molars adjacent to missing 3rd molars. 2nd molars adjacent to soft-tissue impacted 3rd molars were at greatest risk for increased distal pocket depth over time at 6.4 times the risk of >3 mm increased distal pocket depth compared to 2nd molars adjacent to missing 3rd molars.
Conclusions: Soft-tissue impacted 3rd molars increase the risk of periodontal disease of adjacent 2nd molars. Evidence supports extraction of soft-tissue impacted 3rd molars, although it does not support routine extraction of bony impacted 3rd molars.
Keywords: Decision-making, Diagnosis, Epidemiology, Oral surgery and Prognosis