OBJECTIVETo compare the efficacy of hydroxyapatite (HA), calcium hydroxide (CH) and Vitapex on root formation of immature teeth of dogs.

METHODSSixteen roots of permanent incisors in two dogs (about five to six months old) were used. After the pulpectomy, roots were randomly divided into four groups. Group A, B and C were experimental groups and filled with HA, CH and Vitapex, respectively. Group D was control group and filled with AH plus. The changes of root length and apical areas were measured by cone beam CT(CBCT), meanwhile, paraffin sections with hematine-eosin (HE) staining were used to observe the shape of root tips; frozen sections with alkaline phosphatase (ALP) staining were used to observe the osteoplastic activity of cells.

RESULTS1) CBCT showed that four weeks later, all roots in every groups became longer (P < 0.05), and the apical areas in three experimental groups decreased (P < 0.05). However, eight weeks later, high density image could be detected in every root. 2) Histological examination showed that there was no inflammation in every group, and after four weeks, none of apicals were closed, but partial cementum and peridental membrane had extended into canals. After eight weeks, a complete cementum barrier and an intensive distribution of positive cells of ALP staining could be seen in group A, however, some spaces could be seen in the cementum barrier of group B and C, which were filled with periodontal membranes, and the positive cells of ALP staining were dispersed. Moreover, scattered cementum, cementoid and abundance fiber or blood vessels could be seen in group D, in which ALP staining was negative.

CONCLUSIONThe root formation of immature teeth can go on after pulpectomy when there is no inflammation, the tissue source is probably the periodontal membrane, and HA which can induce root formation faster is a better material in the apexification.