Purpose: We sought to determine the incidence of caries experience on the occlusal surface of asymptomatic third molars erupted to the occlusal plane and to examine the association between the prevalence of caries experience in third molars and other molars.
Patients and methods: Clinical data were collected from healthy patients (ASA Class I, II) with asymptomatic third molars enrolled at 2 clinical centers in an institutional review board-approved clinical trial. All patients with at least one third molar at the occlusal plane and with data at baseline and from the most recent of at least 2 follow-up visits were compared in the analysis. At each visit, the presence or absence of caries experience on the occlusal surface of third molars and on any surface of the first and second molars was recorded during clinical and radiographic examinations.
Results: Median time between baseline and the most recent follow-up examination was 2.9 years (interquartile range, 1.6 to 4.0 years). Patients (N = 211) were more often female (55%) and white (79%). Median age at baseline was 26.6 years (interquartile range, 22.7 to 32.6 years). At baseline, 29% of patients were affected by third molar occlusal caries, increasing to 33% at follow-up. Older patients at baseline had more caries in a third molar than those younger than 25 years (43% versus 9%). However, patients who were younger at baseline were more likely to develop caries in third molars at follow-up (9% versus 19%). Mandibular third molars were affected more often than maxillary third molars: 25% versus 19% at baseline and 29% versus 22% at follow-up. At baseline and at follow-up, nearly all patients with third molar caries, 98% and 99%, also had caries in first/second molars.
Conclusions: The 3-year caries incidence in third molars erupted to the occlusal plane was highest among younger patients and mandibular teeth. The presence of caries in first/second molars at baseline was highly predictive of the development of third molar caries during the ensuing 3 years.