Objective To evaluate the marginal adaptation between the new nano-hydroxyapatite composite resin and tooth.Methods Thirty extracted healthy premolars were randomly assigned to three groups according to the ma-terial employed: New nano-hydroxyapatite composite resin（Group A）, Karisma composite resin（Group B）, and glass ionomer cement（Group C）. After the thermal cycling, the teeth were immersed in 2% methylene blue dye, and the depth of microleakage between the composite and tooth structure were observed.Results The microleakage depth of group A, B and C were （1.20±0.81）, （1.94±0.70）, and （1.73±0.54） mm, respectively. No statistically significant differences were found among the three groups（P>0.05）. There was no significant difference in the degree of microleakage （P>0.05）.Conclusion As a new dental restorative material, new nano-hydroxyapatite composite resin has good bon-ding performance to the tooth structure.
