Materials and Methods: Dental and radiographic records of a group of Chinese schoolchildren were studied retrospectively. Cases of impaction of 1 or both permanent mandibular second molars were selected. Demographic data and dental and radiographic findings were recorded and analyzed. The angle of the impacted second molars was measured on panoramic radiographs.

Results: Among the 3,053 records reviewed, 32 cases of impaction of permanent mandibular second molars were identified and studied. Mesial impaction was found in all but 1 case. The angle of the mesially impacted teeth ranged from 13° to 75°. Mandibular crowding and the presence of third molars were common. Dens evaginatus, taurodontism and Class III malocclusions were significantly more prevalent in the study group than in the general population of Chinese children of similar age.

Conclusions: The prevalence of impaction of permanent mandibular second molars in Chinese children was estimated to be 1%. Thorough and regular examination of the child's developing dentition is recommended to diagnose dental impaction promptly.