The effect of implant-abutment connection fit and proximal contact tightness on screw loosening

PURPOSE: This study aims to evaluate how the fit between implant-abutment connection surfaces and the proximal contact tightness of crowns affect abutment screw loosening. MATERIALS AND METHODS: Forty implants with internal hex connections were placed in stainless steel models in the maxillary right first molar region. Monolithic zirconia crowns with standard and 15 µm reduced proximal contacts were used with abutments with standard and 25 µm horizontally reduced hex connections. After cementation, four groups of specimens-standard abutment/standard proximal contact (control), reduced fit abutment/standard proximal contact (RS), standard abutment/reduced proximal contact (SR), and reduced fit abutment/reduced proximal contact (RR)-were subjected to simultaneous thermocycling (± 5 - 55℃) and chewing cycles (100 N, 1.6 Hz, 40 mm/sec lateral and vertical speed, lateral movement: 6 mm, vertical movement: 0.5 mm). Removal torque values (RTVs) were measured using a digital torque meter. Data were analyzed using two-way ANOVA and the Bonferroni test (α = .05). RESULTS: < .05). The RR group had the lowest removal torque values (RTVs) (21.70 ± 0.99 N·cm), while the control group had the highest (26.82 ± 0.70 N·cm). The RS group (24.78 ± 0.89 N·cm) had lower RTVs than the SR group (25.51 ± 0.52 N·cm). CONCLUSION: The findings indicate that inadequate proximal contacts and horizontal misfit of the implant-abutment connection may lead to torque loss and screw loosening.