Fatigue of dental restorative materials

Abstract

Statement of problem: Dental restorative materials are subject to premature clinical failure under repetitive and constant occlusal loads. Exposure to aqueous environment has been found to degrade the strength of dental restorative materials. Purpose: The aim of this study is to compare the effect of static fatigue and moisture effect on the flexural strength of four dental restorative materials (Mack II feldspathic porcelain, resin infused AIpha III, resin infused In-Ceram, and Z1OO composite resin). Materials and Methods: Biaxial flexure strengths of the four dental restorative materials were determined under two environmental conditions (wet and ambient). The effect of static fatigue was determined by using a static fatigue machine, which was designed at Boston University and utilizes the biaxial flexure strength test. The restorative materials were tested under static load using 1OO%, 95%, 90%, and 85% of the minimal fracture load. Ten disc specimens were used for each category and the materials were tested under ambient and wet conditions. The biaxial flexure strength and the time to failure were determined. Results: The results of this study indicate that static fatigue and exposure to moisture have the potential to reduce the strength of the tested restorative materials. Application of loads less than the fracture loads can still cause failure in dental materials over a period of time. The mechanism of static fatigue was found to be similar for dental materials. The mechanism of static fatigue is also similar for the two different environmental conditions. The composite resin material (Z100) exhibited a higher resistance to static fatigue compared to the other materials. Conclusions: Dental restorative materials are subject to time dependent stress failure (static fatigue). Static fatigue and exposure to moisture reduces the biaxial strength of the dental restorative materials. Clinical significance: the results of this study suggest that dental restorative materials are susceptible to failure at smaller than short term strength loads when subjected to static fatigue, and exposure to moisture degrades the strength of restorative materials.