Eruption of mandibular third molars after second-molar extractions: a radiographic study

The purpose of the present study was to analyze the posteruptive contact relationship and inclination of mandibular third molars after extraction of second molars and to determine whether predictors could be formulated for the dental relationships observed. In all, 140 mandibular quadrants were evaluated from 95 sets of panoramic radiographs taken at the time of second molar extraction (T1) and at the time of final evaluation (T2). For analysis of a consecutive sample of patients, a subsample of 25 sets of radiographs from all the patients who had received such treatment during one calendar year was also quantified. Subjective evaluation indicated that 46% of the sites examined had satisfactory tooth contact relationship between the first and third molars at T2. Third-molar impaction was found in 4% of the sites in the subsample of 25 consecutively treated patients. Measurements of crown axis inclination revealed that the third molar invariably erupted into a mesially tilted position. The first molar showed only minor distal tipping between T1 and T2. Inclination of the third molar bud at the time of second molar extraction was not found to be a useful predictor for posteruptive third molar position. The clinical significance of these results and the need for studies regarding a rationale for mandibular second molar extraction are discussed.