Low Thermal Degradation of monolithic zirconia dental prostheses: 1-yr results of a prospective clinical study with ex vivo analyses

Recent introduction of computer-aided design/computer-aided manufacturing (CAD/CAM) monolithic zirconia dental prostheses raises the issue of material low thermal degradation (LTD), a well-known problem with zirconia hip prostheses. This phenomenon could be accentuated by masticatory mechanical stress. Until now zirconia LTD process has only been studied in vitro. The main objective of this study was to evaluate the in vivo LTD of zirconia restorations on implants and natural teeth using an original protocol including ex vivo analyses of zirconia crystalline microstructure, focusing on the effect of occlusal stress and protection by a glaze layer. Secondary objectives included the investigation of the general behaviour of monolithic restorations and the study of material wear process.