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FRACTOGRAPHIC ANALYSIS OF MONOLITHIC AND BILAYERED ZIRCONIA AFTER THERMO-MECHANICAL FATIGUE AND FRACTURE STRENGTH TEST

Objective: To study the fracture origin of different zirconia restorations. Materials and Methods: A first upper premolar sound natural tooth was prepared and duplicated into epoxy resin die. Twenty-one full coverage crowns were fabricated and divided into three groups according to type of ceramic material; super high translucent monolithic zirconia (Zolid fx) group (A), super translucent monolithic zirconia (STML Katana) group (B), and zirconia core (Ceramill zi) with hand-layered veneering porcelain (Vita VM9) group (C). Crowns were cemented with selfadhesive resin cement. All samples were first subjected to thermal cycling (5o-55oC/10,000 cycle) and then to chewing simulator (240,000 cycles, 50N). After fracture resistance test, fractographic method was used to analyze the fractured samples. Results: The fracture origin of all studied groups was similar with crack origin located at occlusal surface (cone crack). Crack origins were indicated with mirror regions with appearing lines of hackle. Conclusion: The fracture origin was found to be dependent on the fracture resistance technique rather than the material itself.