Abstract : Cohesive fracture of the veneering ceramic (chipping) is the first cause of failure of zirconia-based prostheses on natural teeth and implants. Besides risk factors related to the material (thermal stresses generated during the manufacturing process, framework inappropriate design), there are some clinical risk factors, which can influence the restoration prognosis. Indeed, unfavorable occlusal relationships and/or the presence of parafunctions such as bruxism and clenching, which are frequent pathologies, engender significant overloading. A retrospective study was performed at the University Hospital Center (CHU) of Liege on 147 dental and implants prostheses, placed between May 2003 and January 2012. This study highlighted a significant correlation between chipping and the absence of an occlusal nightguard (p = 0.0048), the presence of a ceramic restoration as an antagonist (p = 0.013), the presence of occlusal parafunctions (p = 0.018), and the presence of implants as support of the restorations (p = 0.026). These results underline the importance of external stress and occlusal risk factors diagnosis, as the need to perform an occlusal nightguard to patients with parafunctions.