Effect of Different Retightening Procedures on Screw Stability in External-hex and Internal Tri-channel Connections: An In Vitro Study.

PURPOSE To evaluate the effect of different procedures for retightening the abutment screw on the screw stability between the abutment and implant. MATERIALS AND METHODS External hexagon connection (EHC) and internal tri-channel connection (ITC) implants were employed in this study. Each abutment screw was used for the following applications (n = 5 for each group): group 0 = abutment was tightened and retightened with a 10-minute interval; group 1 = abutment was tightened and retightened with a 10-minute interval, then loaded for 500,000 cycles; group 2 = abutment was loaded for 83,000 cycles during tightening and retightening and then loaded for 500,000 cycles; group 3 = abutment was loaded for 167,000 cycles during tightening and retightening and then loaded for 500,000 cycles; and group 4 = abutment was loaded for 250,000 cycles during tightening and retightening and then loaded for 500,000 cycles. Both tightening and retightening torques were set at 35 Ncm, and dynamic oblique loading between 0 N and 200 N was applied on the abutment in all groups. The settlement of the abutments (settling value) after retightening and the abutments' removal torque values (RTVs) after testing were measured. RESULTS No significant differences in settling values were found for EHC or ITC. There were significant differences in the RTVs on EHC implants, but ITC implants showed no difference in RTV with different prosthetic retightening applications. CONCLUSION The retightening application affected the joint stability of EHC implants, but did not affect the settlement or joint stability of ITC implants.