Introdouction: Impacted and partially erupted third molars can cause various symptoms and pathologies. The aim of this study was to determine the association between commonly observed pathological conditions and the impaction depth of lower third molar teeth.

Materials and methods: In this retrospective study, 370 panoramic radiographs including 724 lower third molars were evaluated to assess several pathologies according to impaction depth. The patients were also examined clinically for pericoronitis. Impaction depth was defined according to horizontal indices in class I, II, or III, where none, less than half, or more than half of the crown was in the ramus of the mandible, respectively. The vertical indices for teeth, classes A, B, and C, were defined by the highest portion of the tooth being on a level with or above the occlusal plane, below the occlusal plane but above the cervical line of the second mandibular molar, or below the cervical line of the second mandibular molar, respectively. The data were analyzed using Chi-squared tests.
Results: Of the teeth analyzed, 57%, 28.4%, and 14.6% were at vertical level A, B, and C, respectively. Of the 605 mandibular third molars, 363 (60%) were in horizontal class I, 212 (35%) were in class II, and 31 (5%) were in class III. Incidence of pericoronitis was significantly associated with partially erupted third molars and impactions of class AII (P = 0.028). Class A impaction showed a stronger association than classes B or C with all conditions (P = 0.04) except for bone loss and root resorption of second molars (P = 0.07).

Conclusion: Class A impaction depth, where the highest portion of the tooth was on a level with or above the occlusal plane, was associated with more pathological conditions than classes B or C.