Ting-Hsun Lan1, Pao-Hsin Liu2, Mitch M C Chou3, Huey-Er Lee4. 1. Attending Dentist, Department of Dentistry, Kaohsiung Medical University Hospital, Kaohsiung Taiwan; Assistant Professor, School of Dentistry, College of Dental Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan. Electronic address: tinghsun.lan@gmail.com. 2. Assistant Professor, Department of Biomedical Engineering, I-Shou University, Kaohsiung, Taiwan. 3. Professor, Department of Materials & Opto-electronic Science, National Sun Yat-Sen University, Kaohsiung, Taiwan. 4. Professor, School of Dentistry, College of Dental Medicine, Kaohsiung, Taiwan.
Abstract
STATEMENT OF PROBLEM: The use of monolithic zirconia crowns in implant prostheses is increasing, especially when the interdental space is insufficient. However, fractures have been reported in clinical practice. PURPOSE: The purpose of this study was to determine the minimal thickness of a complete zirconia crown used for an implant prosthesis in the posterior dental region. MATERIAL AND METHODS: Fifty complete zirconia crowns were produced using a computer-aided design/computer-aided manufacturing technique. In each group, 5 crowns of varying thicknesses (0.4, 0.5, 0.6, 0.7, and 0.8 mm) were subjected to cycles of vertical and 10-degree oblique compressive loading at 5 Hz and 300 N in a servohydraulic testing machine. Five finite element models comprising 5 different occlusal thicknesses (0.4, 0.5, 0.6, 0.7, and 0.8 mm) were simulated at 2 loading angles (0 and 10 degrees) and 3 loading forces (300, 500, and 800 N). Data were statistically analyzed, and fracture patterns were observed with a scanning electron microscope. RESULTS: Cyclic loading tests revealed that the fracture resistance of the specimens was positively associated with prosthesis thickness (P<.01). Low von Mises stress values were obtained for prostheses with a minimal thickness of 0.7 mm under varying loading directions and forces. CONCLUSIONS: Zirconia prostheses with a minimal thickness of 0.7 mm had a high fracture resistance and the lowest stress values. Therefore, dentists and laboratory technicians should carefully choose the optimum thickness of zirconia prostheses.
STATEMENT OF PROBLEM: The use of monolithic zirconia crowns in implant prostheses is increasing, especially when the interdental space is insufficient. However, fractures have been reported in clinical practice. PURPOSE: The purpose of this study was to determine the minimal thickness of a complete zirconia crown used for an implant prosthesis in the posterior dental region. MATERIAL AND METHODS: Fifty complete zirconia crowns were produced using a computer-aided design/computer-aided manufacturing technique. In each group, 5 crowns of varying thicknesses (0.4, 0.5, 0.6, 0.7, and 0.8 mm) were subjected to cycles of vertical and 10-degree oblique compressive loading at 5 Hz and 300 N in a servohydraulic testing machine. Five finite element models comprising 5 different occlusal thicknesses (0.4, 0.5, 0.6, 0.7, and 0.8 mm) were simulated at 2 loading angles (0 and 10 degrees) and 3 loading forces (300, 500, and 800 N). Data were statistically analyzed, and fracture patterns were observed with a scanning electron microscope. RESULTS: Cyclic loading tests revealed that the fracture resistance of the specimens was positively associated with prosthesis thickness (P<.01). Low von Mises stress values were obtained for prostheses with a minimal thickness of 0.7 mm under varying loading directions and forces. CONCLUSIONS:Zirconia prostheses with a minimal thickness of 0.7 mm had a high fracture resistance and the lowest stress values. Therefore, dentists and laboratory technicians should carefully choose the optimum thickness of zirconia prostheses.
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