Risk factors for third molar occlusal caries: a longitudinal clinical investigation

To study the third molar occlusal caries incidence and identify related patient-level sociodemographic, dental behavior, and clinical risk factors.

A prospective cohort study was used to study caries risk (crude increment and incidence rate) on retained and erupted to the occlusal plane third molars among a moderate-size (n = 215) group of healthy (American Society of Anesthesiologists class I and II) young adults (median age, 26 years) followed up for a mean of 4.6 years. Clinical data were gathered by calibrated examiners using visual-tactile and radiographic diagnostic methods on all molar teeth. The covariates included age at enrollment, gender, race, income, education, frequency of dental visits, oral hygiene behaviors, and smoking. Summary statistics and visual methods were used for data description. The analyses relied on bivariate and multivariate methods using generalized estimating equations, extensions of Poisson modeling.

Of the 215 patients, 33% developed occlusal caries on 1 or more retained third molars. The incidence rate was 0.11 (95% confidence interval 0.09 to 0.13) third molar "increments"/person-year. Those with any molar caries at baseline were 80% more likely to have a new third molar caries lesion at the end of follow-up compared with those with caries-free molars (prevalence ratio, 1.80; 95% confidence interval, 1.08 to 3.00). The third molar caries rate was halved for every approximately 9 years of the subjects' baseline age. Favorable oral hygiene behaviors and better socioeconomic status were associated with decreased caries risk. However, independent of other covariates, smoking increased the third molar caries risk twofold.

Younger patients from lower socioeconomic strata, smokers, and those with poor oral hygiene behavior are at an increased risk of occlusal caries development on their retained third molars.