Adaptação marginal e assentamento de cilindros calcináveis e sobrefundíveis fundidos em barras de Co-Cr / Vertical and passive fit of burnout plastic and pre-machined cylinders cast in Co-Cr frameworks

RESUMO

O objetivo desse estudo foi avaliar a adaptação marginal e a precisão do assentamento protético de cilindros plásticos e de cilindros plásticos com base usinada, fundidos em estruturas protéticas de liga de cobalto-cromo (Co-Cr). Em um modelo semicircular à base de poliuretano, quatro implantes de hexágono externo com conexões protéticas do tipo minipilar foram instalados, sendo oito sensores elétricos colados na superfície superior do bloco. A partir desse modelo foi realizado um índex sobre o qual foram confeccionadas dez barras segmentadas em acrílico, utilizando-se cilindros calcináveis e cilindros sobrefundíveis (n = 5). Depois de fundidas em centrífuga manual com liga de Co-Cr Biosil e soldadas convencionalmente, as estruturas tiveram os espaçamentos verticais entre cilindros e análogos avaliados sob microscopia de luz e as microdeformações determinadas por meio da extensometria. Os resultados foram analisados com o teste de análise de variância (p = 0,636) e teste t Student (p = 0,325), não apresentando diferenças estatísticas significantes. Concluiu-se que os cilindros sobrefundíveis não conferiram às barras nas quais foram fundidos maior adaptação marginal e passividade de assentamento que os cilindros plásticos calcináveis.

ABSTRACT

The aim of the present study was to evaluate the vertical and passive fit of plastic burnout cylinders and plastic cylinders with a pre-machined cobalt-chromium collar cast in implant-supported frameworks. Four external hex cylindrical implants and their respective conical abutments were placed in an experimental semicircular model on which eight-element strain gauges were attached in close proximity to the implants. The master model was duplicated originating an index that was used to wax-up ten standard bars segmented in four sections (n = 5) and to allow the measurements under an optical microscope. The segments were cast in Co-Cr alloy and soldered conventionally. Initially, the structures were submitted to optical measurements. An average misfit value was assigned for each group and the Analysis of Variance was applied (p = 0.636). Later, each structure was tightened to the master model and the stress generated was recorded. The mean strain developed at each group was calculated and the Student´s t test was applied (p = 0.325). No significant statistical differences were found. It can be concluded that pre-machined Co-Cr cylinders could not offer better vertical fit or passive fit when compared to plastic burnout cylinders.