Background: The purpose of the present longitudinal study was to evaluate the association between root proximity and the risk for alveolar bone loss (ABL).

Methods: We used data from the Veterans Affairs Dental Longitudinal Study, a closed-panel longitudinal cohort study of 1,231 men enrolled in 1968 with triennial follow-up examinations. Periapical radiographs of mandibular incisors from subjects with ≥10 years of follow-up were selected. Interradicular distance (IRD) at the cemento-enamel junction and alveolar bone levels at baseline and last follow-up were measured using digitized radiographs. The rate of progressive ABL was determined and expressed as millimeters per 10 years. Site-specific multivariate regression models were fit to evaluate the association between IRD and ABL rate, adjusting for age and smoking. Empirical standard errors and generalized estimating equations were used to account for the correlation among sites within subjects.

Results: There were 473 dentate subjects, aged 28 to 71 years at baseline, with ≥10 years of follow-up data available for analyses. The mean follow-up time was 23 years. The mean IRD was 1.0 ± 0.3 mm, and the mean ABL rate during 10 years was 0.61 ± 0.59 mm. There was a significant non-linear association between IRD and ABL rate (P <0.005). Compared to sites with IRD ≥0.8 mm, sites with IRD <0.6 mm were 28% (95% confidence interval [CI]: 11% to 48%) more likely to lose ≥0.5 mm of bone during 10 years (relative risk: 1.28 [95% CI: 1.11 to 1.48]) and 56% (95% CI: 11% to 117%) more likely to lose ≥1.0 mm of bone during 10 years (relative risk: 1.56 [95% CI: 1.11 to 2.17]).

Conclusions: IRD <0.8 mm is a significant local risk factor for alveolar bone loss in mandibular anterior teeth. Measurement of IRD may have important prognostic value in making treatment decisions.