The sample of 5 patients for each group was based on the following formula: n = (Zα/2+Zβ)2 * (p1(1-p1)+p2(1-p2)) / (p1-p2)2, with a confidence level of 95%, power of 80% and the survival rates of 90% and 20% for composite and ceramic restorations, respectively (based on previous published data of in vitro fatigue tests).