Abstract
The main complications of zirconia-based laminated systems are chipping and delamination of veneering porcelain, which has been found to be directly associated with the development of residual thermal stresses in the porcelain layer. This study investigates the effects of cooling rate and specimen geometry on the residual stress states in porcelain-veneered zirconia structures. Bilayers of three different shapes (bars, semi-cylindrical shells, and arch-cubic structures) with 1.5mm and 0.7mm thickness of dentin porcelain and zirconia framework, respectively, were subjected to two cooling protocols: slow cooling (SC) at 32°C/min and extremely-slow cooling (XSC) at 2°C/min. The residual thermal stresses were determined using the Vickers indentation method and validated by finite element analysis. The residual stress profiles were similar among geometries in the same cooling protocol. XSC groups presented significantly higher tensile stresses (p=0.000), especially for curved interfaces. XSC is a time-consuming process that showed no beneficial effect regarding residual stresses compared to the manufacturer recommended slow cooling rate.
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