title: Fracture resistance of monolithic zirconia crowns with different occlusal thicknesses in implant prostheses.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  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.
  
  
  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.
authors.affiliation: 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.
authors.forename: Ting-Hsun
authors.initials: TH
authors.lastname: Lan
authors.affiliation: Assistant Professor, Department of Biomedical Engineering, I-Shou University, Kaohsiung, Taiwan.
authors.forename: Pao-Hsin
authors.initials: PH
authors.lastname: Liu
authors.affiliation: Professor, Department of Materials & Opto-electronic Science, National Sun Yat-Sen University, Kaohsiung, Taiwan.
authors.forename: Mitch M C
authors.initials: MM
authors.lastname: Chou
authors.affiliation: Professor, School of Dentistry, College of Dental Medicine, Kaohsiung, Taiwan.
authors.forename: Huey-Er
authors.initials: HE
authors.lastname: Lee
mesh_terms: D017076:Computer-Aided Design; D003442:Crowns; D003776:Dental Porcelain; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D008422:Materials Testing; D013314:Stress, Mechanical; D013499:Surface Properties; D015040:Zirconium
chemical_list: D003776:Dental Porcelain; D015040:Zirconium