Effect of mechanical cycling, material and retorque screws, in stability of complete implant-suported prosthesis with two fit levels

Author(s)

Ana Paula Farina

• Document type: Doctoral Thesis
• Press: Piracicaba, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Odontologia de Piracicaba
• Defense date: 2011-01-03

Examining board members

Marcelo Ferraz Mesquita; Monica Nogueira Pigozzo; Mauro Antonio de Arruda Nóbilo; Rafael Leonardo Xediek Consani; Ricardo Faria Ribeiro

• Advisor: Marcelo Ferraz Mesquita

Abstract

The prosthesis screw loosening is often found at routine examinations and may cause complications. Therefore, methods to prevent them must be developed. The objective of this study was to evaluate the influence of retorque application on joint stability of prosthetic screws (titanium or gold) in implant-supported dentures under different fit levels (passive or misfit), after masticatory function simulated by means of mechanical cycling (6 months, loosening torque, screws retightening and another 6 months of simulation; or 1 year of simulation). In the first chapter, 10 mandibular implant-supported dentures and 20 cast models were fabricated to two fit levels: passive fit and misfit. Two tightening techniques were also evaluated according to the retorque application and screws material: 1) without retorque + titanium screws; 2) without retorque + gold screws; 3) retorque + titanium screws; and 4) retorque + gold screws. The screws were tightened 10 Ncm and retightened to 10 Ncm after 10 min. The screw joint stability was measured after a one-year clinical function simulation using a digital torque meter. Data were analyzed statistically by ANOVA/Tukey's test (?=0.05). The factors of fit level and tightening technique and the interaction between the factors were statistically significant. The misfit decreases the loosening torque. The retorque application increased joint stability independent of fit level or screw material. In the chapter 2, passive and misfit dentures were fabricated as in chapter 1. The loosening torque was measured after two conditions of clinical use simulating: six months / torque loosening / retightening / further six months / loosening torque; and one year of simulation / loosening torque. Titanium and gold screws were used. The statistical analysis was similar to the first chapter. Therefore, the factor cycling time and condition use (fit level and screw type) as well the interaction between the factors influenced the loosening torque values (p<0.05). After six months another six months of masticatory function simulated, the titanium screws showed higher loosening torque than did gold screws for the same fit level. After one year of clinical use simulation, both material screws in passive dentures showed higher loosening torque values than did misfit dentures. Thus we can conclude that the misfit decreases the loosening torque and retorque application increased joint stability. The stability of titanium screws was higher than gold screws after 6 months of simulation, due to its lower plastic deformation. When the cycling time was analyzed, titanium screws were less stable after 1 year of simulation due to loss of torque in misfit presence, requiring more careful monitoring to maintain stability (AU)

• FAPESP's process: 09/02306-4 - Effect of mechanical cycling, material and screw retorque, on stability in multiple implant supported prosthesis with two misfit levels.
• Grantee: Ana Paula Farina
• Support Opportunities: Scholarships in Brazil - Doctorate