It is important, in the prosthetic therapy, to pre vent the alveolar ridge from the bone resorption after tooth extraction and denture insertion. For the purpose of preservation, the authors have studied the procedure of root−submergence in which only the root of a tooth is retained intentionally in the alveolar socket below the mucoperiosteum. However it should not be applied to the fractured roots, the decayed roots, and the roots with an extended periapical infection. These cases should be

more »

... garded as a contraindication of the root−sub mergence procedure, to which the authors apply a hydroxyapatite ceramics implant(HAC)inserted into the fresh alveolar socket just after tooth extraction. There are two types of cone and particle in the HAC. It has been reported in a study comparing the effect of the two forms, that the cone type is more effective than the particle type to prevent bone resorption. The authors utilize the cone type HAC