Biomechanics of Single Unit Implant-supported Prostheses: Misfit, Stress and Detorque

Objectives: This study aimed to evaluate the influence of the casting procedure and cyclic loading of prosthetic frameworks on detorque of prosthetic screws, in the marginal misfit and stress of single unit implant-supported prostheses. Methods: Twenty specimens were obtained, each one consisting in a set of an implant (external hexagon 3.75 x 13mm), a prosthetic abutment (entirely calcinable or overcastted UCLA) and a prosthetic screw. After the specimens were obtained, the prosthetic screws were tightened with 30Ncm torque and released 24h later in order to evaluate initial detorque. The stress analysis was performed using strain gauges. The screws were retightened and marginal gaps and were assessed. All specimens were submitted to 10⁶ loading cycles, performed with 2Hz frequency and 130N load. The specimens were reevaluated for marginal misfit, detorque, and stress after the mechanical loading (final measurements). The results were submitted to analysis of variance for repeated measurements, followed by Tukey HSD test (α=0.05). Results: No differences were found on detorque values of the prosthetics screws for all groups and intervals evaluated (p=0.8922). The entirely calcinable abutments showed higher initial marginal misfit compared to the overcastted ones (p=0.0432). Mechanical loading did not affect the marginal misfit of both groups (p>0.05). There was no significant difference on stress of the abutments (p=0.2114). Stress decreased after mechanical loading on both groups (p<0.05). Conclusions: The overcastted abutments showed lower misfit when compared to the entirely casted abutments. The mechanical loading did not influence the marginal misfit and detorque of either groups. Nonetheless, it influenced the stress of single unit implant-supported prostheses.