Radiographic Survey of the Morphology and Formation of Maxillary Third Molars and Their Actual Condition in Adulthood

Abstract

The maxillary third molars, compared to the mandibular third molars, have a wider range of clinical applications as well as extraction options. In this study, we investigated the time of formation, morphological evaluation, and location of maxillary third molars using panoramic radiographs and CT images. We also studied the number of third molars in each age group and patients' awareness of those teeth. We found that about 90% of patients with one or more third molars had one or more maxillary third molars. The presence of maxillary third molars decreased with age, with 69.6% of patients in their 40s and 33.5% in their 70s. The percentage of patients who answered that they intentionally preserved their maxillary third molars was 5.2%. We also found that root formation of maxillary third molars progressed mainly from 19 to 21 years of age and was completed around 24 years of age. The eruption of the third molars progressed with the root formation. However, only 3.1% of the third molars reached the occlusal plane although the root formation was completed. CT images of the maxillary third molars showed that 25.7% had a mesial inclined tooth axis and 23.8% had a distal inclined tooth axis after the completion of root formation. Of these, 2.6% had a large medial inclination angle that could cause root resorption of the second molar. Regarding the number of cusps of the third molars, 31.2% had four cusps, 46.2% had three cusps, and 22.6% had another number of cusps. In conclusion, panoramic radiographs and three-dimensional data can be used to make more accurate clinical diagnoses after understanding the characteristics of maxillary third molars.