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Influence of zirconia (Y-TZP) substructure thickness on the bond strength, hardness and fracture toughness of veneer porcelain

Grant number: 13/13111-5
Support type:Scholarships in Brazil - Scientific Initiation
Effective date (Start): November 01, 2013
Effective date (End): October 31, 2015
Field of knowledge:Health Sciences - Dentistry - Dental Materials
Principal Investigator:Gelson Luis Adabo
Grantee:Giovanni Cunha
Home Institution: Faculdade de Odontologia (FOAr). Universidade Estadual Paulista (UNESP). Campus de Araraquara. Araraquara , SP, Brazil

Abstract

Zirconia has high biocompatibility, better esthetics and mechanical properties comparable to some alloys for porcelain fused to metal. However veneer delaminations and chipping in this kind of prosthesis are more common than in porcelain fused to metal. In contrast to metallic cores, zirconia and porcelain has low thermal conductivity. It delays the cooling rate which may potentially alter the porcelain coefficient of thermal expansion, and to induce to residual thermal stresses. The mechanical resistance of veneer porcelain depends on a suitable core support and on a controlled and homogeneous veneer thickness. Thus, it is recommendable anatomical core design to allow better veneer porcelain distribution. Nevertheless, anatomic frameworks can have thick parts which may lead to longer cooling time, increasing the possible effects on the veneer porcelain. The aim of this study is to evaluate the effect of zirconia thickness on mechanical properties and adhesion between veneer porcelain and zirconia substructure. Square samples of zirconia Ceramill ZI (Amann Girrbach - Austria) with 5 mm each side will be made in different thickness: 1 mm, 2 mm e 3 mm (n=15). A standardized thickness of veneer porcelain Vita VM9 (VitaZahnfabric - Germany) with 1.5 mm will be built in a the zirconia face. Thermal cycles for sintering the ceramic materials will be carried out according manufacturer's instructions. The shear bond strength between zirconia base and veneer porcelain will be performed in the universal testing machine MTS 810 (Material Test System, EUA) with 10 kN - load cell, and at a cross-head speed of 1 mm/min. The fractographic analysis will be made by optical and scanning electron microscopy. The Vickers hardness test will be carried out in microhardness (Buheler) and the fracture toughness will be calculated by indentation method. (AU)