DISTRIBUIÇÃO DE TENSÕES EM MOLAR RESTAURADO PELA TÉCNICA ENDOCROWN

Abstract

Endodontically treated molars generally present reduced crown structure, with a greater risk of biomechanical failure when compared with living teeth, restoration technique thereof being a challenge for dental profession. The aim of this paper was to analyze, using the finite elements method (FEM), the stresses distribution in a first molar restored with the Endocrown technique, after simulating functional forces. A lithium disilicate ceramic (IPSe.max Press) and a second generation indirect resin composite (SR Adoro) were used as restorative materials, adhesively cemented to the tooth with a dual polymerization luting agent (Variolink II). In order to obtain their mechanical properties, specimens of these materials were subjected to compressive and diametral tensile strength tests 24 h after manipulation. Based on a CAT scan of the lower third of the face, a 3D model of tooth 36 endodontically treated was simulated. Tooth was sectioned nearly 1 mm above the enamel margin, inner angles were rounded, a layer of 0.05 mm of luting agent was manufactured and the remnant of the original tooth was modeled with both restorative materials. The following models were obtained: Model 1, Endocrown in SR Adoro under axial load; Model 2, Endocrown in IPSe.max Press under axial load; Model 3, Endocrown in SR Adoro under oblique load; Model 4, Endocrown in IPS e.max Press under oblique load. Each model was subjected to a force of 100 N. The strength of the luting and restorative materials and of tooth tissues was evaluated using the Mohr Coulomb (MC) failure criterion, and tensile and compressive contact stresses and shear stresses at the adhesive interface were analyzed. As a result of simulations, according to the MC criterion, Model 2 proved to be 17% better than Model 1, and Models 3 and 4 showed failures in the restorative material. In the adhesive cement and enamel, both for axial and oblique loads, it was found that distribution of stresses was more homogeneous for models with more rigid restorative material, behavior which is repeated in the analysis of tensile and compressive contact stresses and shear stresses. Based on the results obtained, it was possible to conclude that Endocrown restorations, when perfectly cemented and made of ceramic are more resistant to fracture than composite Endocrown. Loads of the oblique direction represent a critical point in the success of the restoration, integrity of the margin and conservation of the tooth remaining.