Intraindividual Patterns and Associations of Three-Rooted Mandibular Molars in Deciduous and Permanent Dentition: A Radiographic Cohort Study.

Purpose: To determine the prevalence of 3-rooted mandibular molars (3RMMs) in pediatric patients and evaluate associations between their occurrences across different teeth. Methods: A retrospective analysis of digital bitewing and panoramic radiographs from children 4 to 12 years of age was performed. Prevalence was calculated at both the patient and tooth levels. Associations examined included bilateral versus unilateral occurrence, sex and side differences, and correlations between adjacent primary molars as well as between primary and permanent molars. Results: Radiographs of 998 children were evaluated. Of 5,988 mandibular molars assessed, 52 exhibited an additional root (0.9%). At the patient level, 32 children (3.2%) had at least one 3RMM. Prevalence was 1.2% in primary first molars, 1.3% in primary second molars and 1.3% in permanent first molars. Bilateral involvement (43.8%) was significantly more frequent than in unilateral cases (P=0.035). A left-side predominance was noted for primary second molars (P=0.049), while no sex differences were observed. The presence of a primary 3RMM increased the likelihood of a permanent 3RMM (13.6% vs 1.3%; P=0.002). When the first primary molar was 3-rooted, the prevalence of a 3-rooted primary second molar was higher (25% vs 1% in children without a 3-rooted first primary molar, P<0.001), as was the prevalence of a 3-rooted permanent first molar (23.1% vs 1% in children without a 3-rooted first primary molar, P<0.001). Conclusions: Although rare, 3RMMs demonstrate consistent associations between adjacent and successive teeth, supporting a developmental link. Early radiographic recognition in primary molars may help anticipate similar anatomy in permanent molars and reduce the risk of procedural complications.