Abstract : The present study was carried out to investigate histologically and histometrically the effect of experimental unilateral traumatic occlusion on periapical tissue after pulpectomy in rats.

 Sixty rats were divided into 4 groups. The animals in Group A received no treatment as a control. The animals in Group B received pulpectomy of the left mandibular first molar, those in Group C, a resin plate was cemented onto the occlusal surface of the left maxillary molars, and those in Group D, pulpectomy of the left mandibular first molar and a resin plate installed of the left maxillary molars. All animals were killed at 1, 3 and 7 days after treatment, and the periapical periodontal ligament and the interradicular furcation of the left mandibular first molar were examined histologically. Moreover, the area of the periapical periodontal ligament was measured histometrically.

 In the periodontal ligament at 7 days, no changes were found in Group A. In Group B, infiltrates of inflammatory cells and an increased amount of fibrous connective tissue were seen. In Group C, compression of the periodontal ligament was noted. In Group D, inflammation equal to that in Group B and undermining resorption were found.

 The area of the periapical periodontal ligament in Group C was significantly smaller (p<0.01) than that in Group A at 7 days.

 The results of the present study suggest that traumatic occlusion may delay the recovery of the periapical lesion in experimental animals.