Method: The 15 implants were mounted in the acrylic blocks. The abutment screws were tightened to the torque of 35 N-cm to connect the implants and abutments with the 3 tightening methods as following; method1: The screws were tightened one time, method2: the screws were tightened and after 10 minutes they were retightened again, method3: the screws were tightened, after 3 minutes the screws were loosened and then retightened again, then 10 minutes the screws were retightened in the third time. The fatigue loading (60N) was applied for 106 times. The reverse torque values were measured by the torque gauge. The screw loosening resistance was expressed as the reverse torque value in the percentage of initial tightening torque. The data was analyzed by the Kruskal-Wallis and the Conover-Inman.
Result: After fatigue loading, the means of the screw loosening resistance after fatigue loading in the method 1, 2 and 3 were 51.08%, 69.54% and 70.23%, respectively. The screw loosening resistances of the method1were lower than those of the method2 and the method3 (p<0.05). The method2 and the method3 showed no significant difference on screw loosening resistance (p=0.15).
Within the limitation of this study, it suggested the important of the screw retightening method the screw loosening before retightening was not affect screw loosening resistance after fatigue loading. The method2 can be recommended for screw tightening method in this implant system.
Keywords: screw loosening