Positional changes and eruption of impacted mandibular third molars in young adults. A radiographic 4-year follow-up study.

OBJECTIVE: To measure changes in angular position and eruption status of mesially impacted mandibular third molars (M3) during 4-year follow-up period. STUDY
DESIGN: Standardized panoramic radiographs were taken at the start of the study (the average age of the subjects was 19.7 years) and 4 years later. Angulation and degree of impaction of M3 were determined by their sagittal relationships to the adjacent second molars. The impacted M3 were either partially erupted or unerupted.
RESULTS: Initial examination showed that among a total of 59 mesioangular M3, 49 (83%) had inclination between 5 and 30 degrees. The proportion of M3 that became upright (zero tilt) was 76% (13/17) with initial angulations of 5 to 10 degrees, 61% (11/18) with initial angulations of 15 to 20 degrees, and 14% (2/14) with initial angulations of 25 to 30 degrees. None of the M3 originally presented at 35 degrees or more became upright, but an average decrease of 12 degrees in angulation was registered. In total, 26 M3 of 59 (44%) became upright during the follow-up period. Initial examination of levels of eruption showed that among 59 M3, 13 (22%) were partially erupted and the rest were unerupted. Of the 46 M3 initially unerupted, 17 (37%) became fully erupted and 7(15%) erupted partially during the 4-year follow-up. Of the total sample, 25 (42%) had erupted to full occlusion during the observation period.
CONCLUSION: A significant proportion of mesially impacted mandibular M3 had changed their angulation and became fully erupted by the time the individual reached 24 years of age. Positional changes and eruption of impacted M3 are unpredictable phenomena.