Abstract: Objective: To speculate the influence of filling depth of Z350 composite resin on the porcelain surround the access hole of screw retained implant denture. Methods: The samples were randomly divided into three groups according to the depth of the access hole of the screw retained implant dentures, i.e. 2.0mm, 3.5mm and 5mm respectively after packing the cotton ball. The access holes were restored by Z350 composite resin. After occlusal adjustment and polishing, 10 samples were loaded with 0~100N and 1Hz force along the long axis of the implant for 20000 times. The cracks in the area around 0.5mm from the access holes were observed with field emission electron microscope. The number of the cracks in three groups was counted. Results: There was no significant difference between 3.5mm group and 5.0mm group. However, there was significant difference between 2.0mm group and 3.5mm group as well as 5.0mm group. Conclusion: The depth of 3.5mm has obvious effect on the strength of porcelain and resin. Further increase of resin depth to 5mm is not meaningful.