Impact of the Visible Presence of Third Molars on Periodontal Health in Middle-Aged Americans

Problem: Document the presence of third molars in a population of middle-aged Americans and evaluate the impact of the presence of third molars on periodontal health on non-third molars in these same subjects. Subjects and Methods: This cross-sectional analysis included the 6,793 dentate subjects ages 52-72 years from four U.S. communities who underwent a periodontal exam in the 1996-1998 Dental Atherosclerosis Risk in Communities (ARIC) Study. Calibrated examiners measured probing depths (PD) at six sites per tooth on all visible teeth including third molars and noted third molar absence clinically without the aid of radiographs. Indicator variables for periodontal pathology were periodontal probing depths at least 4mm (PD 4mm) and clinical attachment levels at least 3mm (CAL 3mm). Outcome variables were demographic characteristics and clinical characteristics (mean periodontal probing depths, % periodontal probing sites with PD 4mm, and % periodontal probing sites with CAL 3mm) grouped by tooth-type: anterior teeth, premolars, and first/second molars. Explanatory variables were the presence or absence of visible third molars. Differences in outcomes between subjects with and without third molars were compared by Chi-square statistic and t-tests with significance 0.05. Results: Most of the subjects were Caucasian (80%) or African American (18.5%). Most subjects were female (54%) and were ages 62-72 years (53%). One or more visible third molars were found in 30% subjects; 14% had only one visible third molar and 7% had at least three visible third molars. Demographic outcome variables significantly (P 0.01) associated with having a visible third molar included: male gender, African American ethnicity, age less than the mean of 62.4 years (SD 6.5 years), higher income, and no current or history of tobacco use. Periodontal pathology was detected more frequently on molars than on premolars or anterior teeth. Mean periodontal probing depths were greatest on visible third molars and progressively less on more anterior teeth. If visible third molars were detected, subjects had significantly deeper mean periodontal probing depths on first/second molars as compared to subjects with no visible third molars (P 0.01). Mean probing depths were not significantly different for more anterior teeth compared by the presence or absence of third molars. The % of probing sites with PD 4mm on first/second molars was significantly different compared by the presence or absence of third molars (17.9 vs. 15.3, P 0.001). The % of probing sites with PD 4mm on premolars or anterior teeth as not significantly different compared by the visible presence or absence of third molars. The % of probing sites with CAL 3mm on first/second molars was significantly different compared by the presence or absence of third molars (20.7 vs. 18.4, P 0.001). The % of probing sites with CAL 3mm on anterior teeth was lower (less than 10%) than on posterior teeth for all study subjects. However, the % of probing sites on anterior teeth with CAL 3mm was significantly associated with the noted absence of third molars (P 0.001). Conclusion: In this middle-aged American population, visible third molars present in a third of the subjects were associated with more severe periodontal pathology on adjacent first and second molars.