Coronectomy is an effective treatment to avoid inferior alveolar nerve injury （IANI） associated with extraction of mandibular third molars. Extraction of the remaining root is usually not necessary after coronectomy, because it is buried in tissues. However, the remaining root is sometimes removed in patients with wound dehiscence.
Patients who underwent coronectomy were regularly followed up at our hospital. We examined the remaining roots and surrounding tissue by panoramic radiography. We report 9 patients in whom extractions of remaining roots proved necessary after coronectomy. Of the 9 patients, the remaining roots were extracted because of wound dehiscence in 8 patient （90％） and pulpitis in 1 （10％） for a period of 1 month to 2 years. Acute periapical inflammation did not occur until extraction of the remaining roots in 8 patients with wound dehiscence because the surrounding gingiva was cleaned by the patient. However, in 1 petient with severe pulpitis, we extracted the remaining roots, which were associated with expansion of the periodontal space, but did not migrate away from the inferior alveolar nerve. IANI was not found in any patient. The extracted roots were histologically evaluated in 5 petients. The pulp was vital in 4 of the 5 patients （80％） and non-vital in 1 （20％）.
After coronectomy, we consider evaluation of the need and timing for extraction of the remaining roots to be important. The following are the criteria for extraction of the remaining roots after coronectomy: (1) If the root is exposed to the oral cavity, extraction should not be performed until the remaining roots recede from the inferior alveolar canal, provided that acute inflammation does not occur. (2) In patients with severe pulpitis or inflammation of surrounding tissues, extraction of the remaining roots is done without waiting for the remaining roots to recede from the inferior alveolar canal.
