Effect of Lateral Cyclic Loading on Screw Loosening in Morse Taper Implant-Straight Abutment Connection

Abstract

Background: Screw loosening is a common problem that can lead to mechanical and biological failure of dental implants. This study aimed to assess the effect of lateral cyclic loading on screw loosening (detorque value) in Morse taper implant-straight abutment connection.
 Methods: This in vitro, experimental study evaluated 12 dental implants with Morse taper implant-abutment connection. Dental implant-abutment assemblies were mounted in transparent acrylic resin blocks with 45-degree angle relative to the acrylic surface. The abutment screw was torqued to 30 N/cm by a digital torque-meter and retorqued after 10 minutes. The assemblies were then randomly divided into two groups (n=6). In the test group, lateral cyclic loads with 75 N magnitude and 1 Hz frequency were applied at 45-degree angle relative to the longitudinal axis of the fixture. After 500,000 cycles, the detorque value was measured at the implant-abutment interface by a digital torque-meter. The assemblies in the control group did not undergo cyclic loading. The detorque values were compared between the two groups using the Student t-test (alpha=0.05).
 Results: The mean detorque value was 23.17±1.33 N/cm in the control and 21.3±3.38 N/cm in the test group. According to the Student t-test, this difference was not significant (P=0.4).
 Conclusion: According to the present results, application of lateral cyclic loads had no significant effect on screw loosening (detorque value) of Morse taper implant-straight abutment connection but insignificantly increased the torque loss.