Presence and Maturation Dynamics of Mandibular Third Molars and Their Influence on Late Mandibular Incisor Crowding: Longitudinal Study

Abstract

OBJECTIVE: To investigate the relationship between the presence and dynamics of mandibular third molar development and the occurrence and amount of late mandibular incisor crowding. MATERIALS AND METHODS: Dental plaster casts and panoramic radiographs of 72 orthodontically untreated subjects from the Nittedal growth study, Norway were analysed. The subjects were recalled for check-up at 12, 15, 18 and 21 years of age. Mandibular incisor crowding was assessed using the Little’s irregularity index and dental maturation of the third molars by the Cameriere’s index.RESULTS: The majority of the subjects (64%) had ≥1mm increase in irregularity; 22% experienced increase of 0.1-0.9mm and 14% had unchanged or decreased irregularity. Incisor irregularity increased with age, regardless of absence or presence of third molars. The amount of change in incisor irregularity from 12 to 21 years did not differ significantly between subjects with hypodontia of third molars, extraction and those with third molars present. No differences were observed between erupted, unerupted or impacted third molars. No correlation was found between the amount of change in irregularity and maturation of the third molars.CONCLUSIONS: Occurrence and amount of mandibular late incisor crowding is not significantly influenced by presence or development dynamics of mandibular third molars.