Differences and similarities of third molar impaction in the mandible and in the maxilla

Aims: Characteristics of erupted and impacted third molars in the mandible and the maxilla were compared. Materials and Methods: A total of 400 individuals over the age of 20 were included. The eruption status of the third molars in both jaws were examined on orthopantomographs by measuring the distance from the line tangent to the highest points of occlusal cusps of the third molar to that of the adjacent second molar. The presence of available space for the eruption was determined by the ratio of the mesiodistal length of the third molar crown to the length of the alveolar arch distal to second molars. The angle formed between the intersected lines tangential to the highest points of occlusal cusps of the second and third molars were used to measure the degree of third molar inclination. The analysis of variance and Student's t-tests were performed to determine the differences between each class structured according to parameters related to third molars. A Pearson correlation test was performed to determine any correlation between parameters. Results: In the mandible available space for the eruption of third molars was smaller, and the mesiodistal lengths of the third molars were longer as opposed to their maxillary counterparts. In both jaws, vertical position was the most frequent inclination both in the impacted and erupted states. On the other hand, even in the presence of favorable parameters for eruption (teeth having both vertical orientation and sufficient eruption space), 26.7% of mandibular and 59.2% of maxillary third molars had a chance to fully erupt. The presence of favorable parameters does not warrant full eruption of third molars in both jaws. Conclusions: We considered the age of 20 as the stable time point for the eruption and angulation movements of the third molars and therefore included subjects older than 20 years of age in the present study. Likewise, the absence of favorable parameters does not always lead to third molar impaction.