Effect of cyclic loading on torque loss of abutment screws
Objective: To find out and compare the effect of cyclic loading on torque loss of abutment screws of a conventional implant-supported fixed dental prosthesis (ISFDP) and an implant supported cantilevered prosthesis (ISCP)
Methodology: Four implants (two-3.5 by 10mm and two-5.0 by 10 mm) with standard abutments, embedded in acrylic blocks were used as test specimens. A three-unit conventional fixed prosthesis and a three-unit cantilevered prosthesis with two abutments were fabricated. Loading tests were performed by a universal testing machine. Retainers and pontics of each group were loaded at 600 N. Torque measurement was done before and after cyclic loading (50,000 cycles) using a digital torque gauge.
Results: Mean reverse torque values measured for cantilever bridge was 19.28 Ncm and 25.08 Ncm (mesial and distal abutment respectively) in comparison to 29.01 Ncm and 29.47 Ncm (mesial and distal abutment respectively) for the conventional bridge
Conclusion: Upon cyclic loading, significant abutment screw loosening occurred with the implant-supported cantilever bridge. In an estimated one year period, in cantilever prosthesis, 40% torque loss was found in mesial abutment and 21% in distal abutment. In conventional bridge, the mean torque loss was only 9%.