Position of lower wisdom teeth and their relation to the alveolar nerve in orthodontic patients treated with and without extraction of premolars: a longitudinal study

The present longitudinal study aimed to compare changes in the lower third molar position and nerve involvement in orthodontically treated patients with and without premolar extractions. The sample consisted of pretreatment and posttreatment panoramic radiographs of 349 orthodontically treated patients subdivided into a non-extraction group (n = 263) and an extraction group (n = 86). Patients did not present dental agenesis in the lower jaw. The mandibular third molar position was assessed by classifying the teeth according to Pell and Gregory, Winter, and two new classifications. The relation between third molars and the mandibular canal was assessed based on Whaites' classification. The development of third molars was evaluated based on Demirjian's classification. Data were analyzed using frequency analysis, Mann-Whitney U test, Fisher's exact test, and chi-square testing. There was a significant difference (p < 0.05) in eruption space between pretreatment and posttreatment panoramic radiographs for both groups. For pretreatment panoramic radiographs, chi-square tests revealed no significant differences between both groups. For posttreatment panoramic radiographs, significant differences appeared for extraction versus non-extraction patients for Pell and Gregory horizontal classification, Winter's classification, and a potential relationship between third molars and the alveolar nerve (p < 0.05). Orthodontic treatment without premolar extractions shows significantly more eruption problems of wisdom teeth than those with premolar extractions. Third molars in the non-extraction group were more frequently found in close relationship to the mandibular nerve compared to the extraction group. Orthodontists should be aware of the effect of orthodontic treatment on the development of the lower third molars.