Objective To compare the efficacy of hydroxyapatite（HA）, calcium hydroxide（CH） and Vitapex on root formation of immature teeth of dogs.Methods Sixteen 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.Results 1）CBCT showed that four weeks later, all roots in every groups became longer（PConclusion The 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.
