This study was undertaken to access the effect of toothash combined with plaster of Paris in the filling of jaw defect and the substitution as new bone during the follow up period. We used the toothash and plaster after the cyst enucleation, the apicoectomy, the extraction of supenumerary tooth with ratio of 2 : 1 by weigh. 15 consecutive patients were evaluated retrospectively. Complications were swelling, perforation, infection and treated without problems using incision & drainage, aspiration, antibiotic treatment, 2ndary buccal flap. The follow-up period ranged from 28 to 35 months. Based on radiographic and clinical observation, it may be concluded that toothash and dental plaster of Paris($CaSo_4;{cdot};1/2H_2O$) are useful for bone substitute.