Influência do desajuste marginal na força de destorque de parafusos protéticos
Influence of marginal misfit on the loosening torque of prosthetic screws
Cardoso, L.; Daroz, L.G.D.; Fragoso, W.S.; Consani, R.L.X.; Mesquita, M.F.; Henriques, G.E.P.
Rev. odontol. UNESP, vol.36, n4, p.371-377, 2007
Resumo
A manutenção da estabilidade da conexão parafusada é fundamental para sucesso a longo prazo das reabilitações implanto-retidas. Contudo, em estruturas protéticas envolvendo múltiplos implantes, a presença de desajustes marginais pode afetar negativamente esta estabilidade. O objetivo deste estudo foi avaliar a força imediata necessária para o destorque de parafusos protéticos em estruturas implanto-retidas com diferentes níveis de desajuste marginal. A partir de matriz metálica contendo 3 réplicas de pilares cônicos dispostos 10 mm de centro a centro, foram confeccionadas 10 estruturas fundidas em monobloco utilizando-se titânio comercialmente puro. Para cada estrutura, foi quantificada a força imediata necessária para o destorque dos parafusos protéticos utilizando-se torquímetro digital de precisão. Ainda, através do teste do parafuso único e visualização direta em microscópio de medição (120x), foi calculado o valor médio de desajuste marginal. A força de destorque imediata e os desajustes marginais foram verificados em duas situações experimentais distintas: Situação (MM) – com as peças parafusadas diretamente sobre a matriz metálica; e Situação (MI) – com as peças parafusadas sobre um modelo index simulando desajuste mínimo. O valor médio de desajuste marginal para a situação MM foi de 188 μm (DP ± 61,5) e para a MI, de 66 μm (DP±18,5). A média de força de destorque dos parafusos protéticos para a situação MM (5,81 ± 0,77 N.cm) foi significativamente inferior à situação MI (7,42 ± 0,93 N.cm) (p < 0,05). O maior nível do desajuste marginal reduziu significantemente a força imediata necessária para o destorque dos parafusos protéticos.
Palavras-chave
Implantes dentários, prótese dentária, torque, passividade
Abstract
The maintenance of the screw-joint stability is crucial for the long-term success in implant-supported rehabilitations. However, in multi-unit implant frameworks, the occurrence of marginal misfits could affect negatively this stability. The purpose of this study was to evaluate the loosening torque of prosthetic screws in implant-retained frameworks with different levels of marginal misfit. A metallic master cast containing 3 conical abutment analogs disposed 10 mm center to center was used to manufacture 10 one-piece casting frameworks made from cast titanium. Using a digital torque meter, it was quantified the immediate loosening torque necessary to loose the prosthetic screws for each framework. Also, using the one-screw test protocol associated with direct visualization by means of a light microscope (x120), the marginal misfit for each structure was calculated. Both immediate loosening torque and marginal misfit were evaluated under two different conditions: (MM) with the frameworks tightened over the metallic master cast; and (MI) with the frameworks tightened over an index cast that simulated a minimum misfit condition. The mean marginal misfit value for situation (MM) was 188 μm (DP ± 61.5) and for (MI) 66 μm (DP ± 18.5). The immediate loosening torque value necessary to loose the prosthetic screws was significantly lower for the situation MM (5.78 ± 1.03 N.cm) than the situation MI (7.06 ± 0,62 N.cm) (P < 0.01). For higher marginal misfit values, a lower loosening torque force is necessary to loose the prosthetic screws in implant-retained frameworks.
Keywords
Dental implants, dental prosthesis, torque, passivity
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