Influence of different prosthetic screws and framework material in the compensation of misfit in ill-fitted overdenture retaining bars with two implants.

Abstract

Passive fit of implant frameworks is an important factor for the longevity of this type of rehabilitation. Ill-fitted frameworks generate stresses that are transmitted to the retention system, implants and peri-implant bone tissue. This study aims to verify the role of screw type (conventional (CS) or coated with a carbon layer (LS)) and bar material (Co-Cr, Ni-Cr, Ti cp) in misfit compensation after torque application; the axial force applied by the screw on the framework; and to verify the stress transmission in such situations through finite element analysis. Sixty frameworks for lower overdentures retained by two implants will be made and distributed into six experimental groups (n = 10): G1-Co-Cr alloy and CS; G2-Co-Cr alloy and LS; G3 - Ni-Cr alloy and CS; G4-Ni-Cr alloy and LS; G5 - Ti cp and CS; G6 - Ti cp and LS. A master cast will also be made with 100 ¼m misfit in one component, and using a linear optical microscope the values of misfit will be verified before and after the torque application. Experimental test will be made to evaluate the axial force exerted on the framework by the different screws. The obtained values will be submitted to statistical analysis to check for associations between the variables. The results obtained in such evaluations will be used in the construction of three-dimensional models and in the finite element analysis. For the analysis of the stresses, (1) a displacement will be made in the ill-fitted region of the framework in order to present the same misfit compensation for each group in the linear optical microscopic analysis; and (2) the average forces verified in the experimental test will be applied to the ill-fitted region of the framework. The finite element analyses will be performed aiming to verify the Maximum Principal Stress and von Mises, in MPa.