Fracture Toughness of Two Types of All-ceramic Restoration after Repeated Firing

Abstract

Background The ability to measure and describe changes in the mechanical properties of ceramics due to various thermal handling protocols will provide a better understanding of the mechanical performance and application of dental ceramic materials. Objectives To evaluate and compare the fracture toughness of two types of all-ceramic restoration (Zirconia and IPS e. max (Lithium disilicate) CAD) after repeated firing.Materials and Methods Sixty all ceramic samples (in final dimensions of 18 mm Length, 4 mm Width, and 3 mm Thickness) were prepared and divided into two main groups according to the used materials; Group (Z) for Zirconia and Group (E) for IPS e. max CAD. Each main group subdivided into three subgroups according to firing cycles. The (Z) group subdivided into ZF3, ZF5 and ZF7; And group (E ) also subdivided into EF3, EF5 and EF7 for three, five and seven firing cycles respectively. Then, the samples were subjected to the indentation strength using a Micro-Vickers Hardness Tester device. After completing of the firing process, the samples were subjected to the fracture toughness test for each specimen. Scanning electron microscope (SEM) images were taken for one random specimen for each subgroup. Results The data showed the highest fracture toughness were obtained with EF5 and the lowest fracture toughness with ZF7 and the P-value of (P≤ 0.05). LSD test done and revealed a highly significant difference between the groups. Conclusion generally, E. Max. CAD material may verify best results of fracture toughness test compared with Zirconia material after repeated firing cycles.