Effect of Restoration Design on the Removal Torque Loss of Implant-supported Crowns after Cyclic Loading

Aim: To compare the removal torque loss (RTL) percentage of screw-retained, cement-retained, and combined screw-and cement-retained implant-supported crowns after cyclic loading and measure the impact of cyclic loading on removal torque.Materials and methods: Thirty-two dental implants (4.0 × 10 mm) in resin blocks and abutments were divided into four groups (n = 8) based on restoration design: combined screw-and cement-retained group (SC), two cement-retained groups: cemented with adhesive resin cement (AR) (Panavia V5) or provisional cement (PR) (RelyX Temp NE), and screw-retained one-piece titanium group (TI).Removal torques were measured in Newton-centimeter (Ncm) before and after 500,000-cycle cyclic loading with forces ranging from 20 to 200 N at 15 Hz.The RTL percentage in each group was calculated.The paired t-test was used to detect the difference between pre-loading (RT1) and post-loading removal torque (RT2) in each group and 1-way ANOVA was used to detect the difference of RTL percentage between groups.Results: The post-loading removal torques in all groups were significantly lower than their pre-loading removal torques (p < 0.001).The 1-way ANOVA test found no significant difference in the RTL% between the study groups.The PR group exhibited the lower RTL% (30.74 ± 7.3%), followed by the TI (30.78 ± 5.6%), AR (32.12 ± 2.5%), and SC (35.71 ± 5.1%) groups.Conclusion: Combined screw-and cement-retained restorations exhibited similar RTL compared with other restoration designs, and cyclic loading significantly affected the removal torque.Clinical significance: Combined screw-and cement-retained restorations can be utilized in single-tooth situations, offering a comparable impact on screw joint stability while providing benefit of retrievability.Cyclic loading significantly influences joint stability, periodic checkup for screw loosening is recommended.