The effect of the design of the abutment screw on the loosening force

This study aimed to assess the stability of the screw joint by comparing the implant abutment screw with a Morse-tapered design in the head with the existing implant abutment screw with a butt joint design.After the implant was fastened with either a support screw with a Morse-tapered design or an abutment screw with a butt-joint design, the specimens were divided into six groups.The nonloaded specimens were assigned to two groups: Group 1 (Morse taper) and Group 2 (butt joint).The specimens subjected to 100,000 loading cycles were assigned to Groups 3 and 4. Those subjected to 500,000 loading cycles were assigned to Groups 5 and 6.Each abutment screw was tightened to 35 Ncm.For Groups 1 and 2, the removal torque was measured 1 hour after tightening.For the other four groups, prostheses were fabricated and connected, and a cyclic loading of 50 N was applied before measuring the removal torque.The mean removal torques for Groups 1-6 were 34.241.67,27.300.74,31.801.61,27.200.93,32.820.90, and 26.841.39Ncm, respectively.Under all loading conditions, the abutment screws with the Morse-tapered design showed a higher mean removal torque than those with the butt-joint design.Implants assembled with abutment screws having a Morse-tapered connection design showed greater stability than those with a conventional butt-joint connection design.