Is third molar development affected by third molar impaction or impaction-related parameters?

OBJECTIVE: To evaluate the effect of third molar impaction and impaction-related parameters on third molar development. MATERIALS AND METHODS: Panoramic radiographs (N=3972) from 473 males and 558 females between 3.2 and 23.5 years old were analysed. Three parameters of impaction were examined: hindering contact between third and adjacent second molar, retromolar space availability (only in lower third molars), and angulation between the third and adjacent second molar. From the separate parameters, a definition for impaction was derived. Third molars' development was staged according to a modified Köhler et al. staging technique. A linear model was used to compare within-stage and overall age, as a function of hindering contact, retromolar space, and impaction. Furthermore, a quadratic function was used to study the correlation between age and angulation. RESULTS: Significant differences were found in mean age as a function of hindering contact and retromolar space, depending on third molar location and stage. There was a significant relation between angulation and age, depending on the stage, with all third molars evolving to a more upright position (closer to 0°). Mean ages of subjects with impacted third molars were significantly lower in certain third molar stages, but the differences were clinically small (absolute differences ≤0.65 years). Moreover, after correction for stage differences, no significant differences in age could be demonstrated. CONCLUSIONS: The development of impacted and non-impacted third molars can be considered clinically equal in our study population. CLINICAL RELEVANCE: There is no distinction required between impacted and non-impacted third molars for dental age estimation.

Radiographic prediction of mandibular third molar eruption and mandibular canal involvement based on angulation.

OBJECTIVES: The aim of our study was to identify and predict patients at risk of impeded mandibular third molar eruption and potential relation between the third molar roots and the mandibular canal, based on molar angulations in an early development stage. SETTING AND SAMPLE POPULATION: A total of 1011 adolescent orthodontic patients were included in this longitudinal study. MATERIALS AND METHODS: We analysed pre-eruptive rotational changes and root development of mandibular third molars on 2022 panoramic radiographs (two time-points). Five variables were evaluated: third molar eruption level, development stage, risk of relation between the third molar and the mandibular canal, the molar angulations and orthodontic treatment. The relation between early third molar angulation and mean annual angulation change was assessed using a linear mixed model. Logistic regression was applied to investigate a potential correlation of the radiographic variables with the eruption potential and risk of developing a relation between the third molar and the mandibular canal. RESULTS: Mandibular third molar follicles with an initial angulation exceeding 27.0° relative to the second molar tend to progressively increase their angulation during further development. A significant correlation was found between the hemimandibular molar angulations and the probability of eruption (P < 0.0001). The second to first molar angulation was predictive for potential development of a relation with the mandibular canal (P = 0.005). CONCLUSION: From the present data, it appears that severely angulated mandibular third molars (>27.0°) have a minimal chance of future eruption and a maximal risk of developing a relation with the mandibular canal.