The effects of screw torque maintenance and re-applying screw torque on the retention of implant abutment screws in single implant restorations
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Purpose: To investigate if screw tightening protocol modification through torque maintenance or abutment screw retightening on an internal Tri-lobe connection implant influences abutment screw reverse torque values (RTV). To also investigate if torquing and retorquing the same implant screw has an influence on the RTV of the screw. Methods: Nine implants with an internal Tri-lobe connection (Nobel Replace Select, Nobel Biocare) were placed in cold-cure acrylic (ProBase Cold, Ivoclar) to simulate bone and a final abutment (Esthetic Abutment NobelReplace RP, Nobel BioCare) was inserted. Nine screw tightening protocols were tested: 1) torque to 35Ncm, 2) hold torque for 10 seconds, 3) hold torque for 20 seconds, 4) retorque at 2 minutes, 5) retorque at 10 minutes, 6) hold torque for 10 seconds and retorque at 2 minutes, 7) hold torque for 10 seconds and retorque at 10 minutes, 8) hold torque for 20 seconds and retorque at 2 minutes, 9) hold torque for 20 seconds and retorque at 10 minutes. Peak RTVs were measured after 30 minutes using a torque meter (MTT03-05, Mark-10). Each implant screw was changed after each insertion with 10 total screws used per implant. After determining the protocol with the highest average RTV, the specific protocol was used to evaluate if cycles of insertion on a single screw would have an impact on the reverse torque values. Five implants were used with the same five abutments. A single screw was torqued with the specified protocol and de-torqued after 30 minutes with the RTV measured. This was conducted another nine times over for a total of 10 cycles. Results: Protocol 2 (holding torque for 10s) had the highest average reverse torque value of 22.63Ncm and the Protocol 1 (control) had the lowest at 20.21Ncm with no statistically significant difference. A statistically significant trend was seen in the RTV over the number of insertion cycles with each insertion cycle showing an increase by 0.252Ncm. Conclusion: Implant screw tightening protocols do not influence the reverse torque values. Multiple insertions of an implant screw may increase the reverse torque value.