Effect of cyclic loading and casting technique over marginal fit, strain and loosening torque on frameworks of multi-unit implant-supported prostheses

Author(s)

Cláudia Lopes Brilhante Bhering

• Document type: Master's Dissertation
• Press: Piracicaba, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Odontologia de Piracicaba
• Defense date: 2013-06-21

Examining board members

Marcelo Ferraz Mesquita; José Maurício dos Santos Nunes Reis; Rafael Leonardo Xediek Consani

• Advisor: Marcelo Ferraz Mesquita; Jessica Mie Ferreira Koyama Takahashi

Abstract

This study aimed to evaluate the influence of casting and cyclic loading on marginal misfit, strain and loosening torque of multiple implant-supported prostheses. Fixed partial dentures (FPD) frameworks supported by two implants and fixed full-arch dentures (FAD) frameworks supported by five implants were waxed using overcasted or calcinable mini abutment cylinders (n=10). The models were obtained with external hexagon implant analogs and mini abutments fixed to waxed frameworks. A plaster index was obtained using mini abutment modified analogs for strain gauge analysis. Four groups were obtained according to prosthesis (FPD or FAD) and cylinder (calcinable or overcasted) type. The frameworks were casted in CoCr alloy. The abutment and prosthetic screws were tightened with 20Ncm and 10Ncm, respectively, using digital torque meter. After 24 hours, initial loosening torque and marginal misfit were evaluated. The misfit readings were performed following the single screw test protocol. The prosthetic screws were tightened with 10Ncm and strain analysis performed by strain gauges bonded at the mini abutment analogs surface forming a ¼ of Wheatstone bridge. The screws were retightened and the samples submitted to 106 mechanical cycles (2Hz/280N). The final measurements were performed and the results submitted to 2 way - Anova/Tukey's HSD Test and Pearson Correlation Test (?=0.05). No difference was found in marginal misfit on all time intervals and groups on the plaster index (p>0.05). The frameworks manufactured with overcasted cylinders presented higher strain than calcinables ones, regardless of prosthesis type and time evaluated (FPD: Initial p=0.0047; Final p=0.0004; FAD: Initial p=0.0476; Final p=0.0115). No difference was observed in strain before and after cyclic loading (p>0.05). Considering the resin model, the calcinable FPD groups presented higher marginal misfit than overcasted ones (Initial: p=0.0005; Final: p=0.0007). Similar marginal misfit was noted among FAD groups (p>0.05). The cyclic loading did not affect the marginal misfit (p>0.05) in both evaluated models. The overcasted FADs abutment screws showed lower loosening torque than calcinable ones after cyclic loading (p=0.0024). The prosthetic screws of calcinable frameworks presented lower loosening torque than the overcasted at final measurement (FPD: p=0.0013; FAD: p=0.0064). After cyclic loading, the prosthetic screw loosening torque of calcinable FPDs decreased (p=0.0044). Negative correlation was observed between marginal misfit and loosening torque of prosthetic screws (FPD: r=-0.49523 p=0.0012; FAD: r=-0.31423 p=0.0483). No correlation was observed between misfit and strain (FPD: r=0.24 p>0.05; FAD: r=0.21 p>0.05). It is concluded for marginal fit, the benefit of the cylinder type depends on prosthesis design and component evaluated. Overcasted components generate higher strain and screw stability than totally calcinable ones. The cyclic loading did not influence misfit and strain of multiple-unit prostheses, but decreased the screw loosening torque in poorly fitted frameworks. There was no correlation between marginal misfit resulted from casting and strain induced on the system. There was correlation between marginal misfit and prosthetic screw loosening torque when submitted to cyclic loading (AU)

• FAPESP's process: 11/02841-7 - Effect of cyclic loading and casting technique over marginal fit, stress and detorque in multi-unit implant-supported prostheses
• Grantee: Cláudia Lopes Brilhante Bhering
• Support Opportunities: Scholarships in Brazil - Master