Abstract: ［Abstract］ Objective〖HTSS〗To observe the effects of extraction of the mandibular third molar by coronectomy on inferior alveolar nerve injury.
〖WTHZ〗Methods〖HTSS〗Sixty-two patients who requested for extraction of the mandibular third molar(root apex of the wisdom tooth connecting with mandibular canal) were selected and divided into the coronectomy group and the traditional extraction group according to the extraction method. The incidence of inferior alveolar nerve injury, bleeding rate, duration of postoperative pain and patient's satisfaction were compared between the two groups at 1 week after surgery. The incidence of infection in both groups at 18 months after surgery, the situation of root fracture displacement at different time points(6 months, 12 months and 18 months after surgery) were observed.
〖WTHZ〗Results〖HTSS〗There was no significant difference in the bleeding rate between the two groups at 1 week after surgery(P＞0.05). The incidence of inferior alveolar nerve injury in the coronectomy group was significantly lower than that in the traditional extraction group(0.00% vs 18.52%)(P＜0.05). The duration of postoperative pain in the coronectomy group was significantly shorter than that in the traditional extraction group(P＜0.01). The satisfaction of the coronectomy group was significantly better than that of the traditional extraction group(P＜0.05). There was no significant difference in the incidence rate of infection between two groups at 18 months after surgery(P＞0.05). The root fracture displaced(0.51±0.06) mm, (1.14±0.13) mm, (1.48±0.17) mm and (1.50±0.18) mm at 3 months, 6 months, 12 months and 18 months respectively after surgery, tending to be stable. 21 patients had their roots removed by secondary extraction.
〖WTHZ〗Conclusion〖HTSS〗Extraction of the mandibular third molar by coronectomy can alleviate the injury to the inferior alveolar nerve and relieve postoperative pain. It is satisfactory and with clinical feasibility.

Key words: tooth extraction, coronectomy, mandibular third molar