Mariana de Almeida Basílio1, Kátia Vieira Cardoso2, Selma Gutierrez Antonio3, Amin Sami Rizkalla4, Gildo Coelho Santos Junior5, João Neudenir Arioli Filho6. 1. Professor, Division of Prosthetic Dentistry, Metropolitan Union of Education and Culture, School of Dentistry, Bahia, Brazil. Electronic address: mariana_basilio@yahoo.com.br. 2. Doctoral student, Department of Dental Materials and Prosthodontics, São Paulo State University (UNESP), Araraquara School of Dentistry, São Paulo, Brazil. 3. Postdoctoral Researcher, Department of Physical Chemistry, São Paulo State University, Chemical Institute, São Paulo, Brazil. 4. Associate Professor, Department of Medical Biophysics, Western University, Schulich School of Medicine & Dentistry, London, Ontario, Canada. 5. Chair, Restorative Dentistry, Department of Dentistry, Western University, Schulich School of Medicine & Dentistry, London, Ontario, Canada. 6. Adjunct Professor. Department of Dental Materials and Prosthodontics, São Paulo State University, Araraquara School of Dentistry, São Paulo, Brazil.
Abstract
STATEMENT OF PROBLEM: Most ceramic abutments are fabricated from yttria-stabilized tetragonal zirconia (Y-TZP). However, Y-TZP undergoes hydrothermal degradation, a process that is not well understood. PURPOSE: The purpose of this in vitro study was to assess the effects of artificial aging conditions on the fracture load, phase stability, and surface microstructure of a Y-TZP abutment. MATERIAL AND METHODS: Thirty-two prefabricated Y-TZP abutments were screwed and tightened down to external hexagon implants and divided into 4 groups (n = 8): C, control; MC, mechanical cycling (1×10(6) cycles; 10 Hz); AUT, autoclaving (134°C; 5 hours; 0.2 MPa); and TC, thermal cycling (10(4) cycles; 5°/55°C). A single-load-to-fracture test was performed at a crosshead speed of 0.5 mm/min to assess the assembly's resistance to fracture (ISO Norm 14801). X-ray diffraction (XRD) analysis was applied to observe and quantify the tetragonal-monoclinic (t-m) phase transformation. Representative abutments were examined with high-resolution scanning electron microscopy (SEM) to observe the surface characteristics of the abutments. Load-to-fracture test results (N) were compared by ANOVA and Tukey test (α=.05). RESULTS: XRD measurements revealed the monoclinic phase in some abutments after each aging condition. All the aging conditions reduced the fracture load significantly (P<.001). Mechanical cycling reduced the fracture load more than autoclaving (P=.034). No differences were found in the process of surface degradation among the groups; however, the SEM detected grinding-induced surface flaws and microcracks. CONCLUSIONS: The resistance to fracture and the phase stability of Y-TZP implant abutments were susceptible to hydrothermal and mechanical conditions. The surface microstructure of Y-TZP abutments did not change after aging conditions.
STATEMENT OF PROBLEM: Most ceramic abutments are fabricated from yttria-stabilized tetragonal zirconia (Y-TZP). However, Y-TZP undergoes hydrothermal degradation, a process that is not well understood. PURPOSE: The purpose of this in vitro study was to assess the effects of artificial aging conditions on the fracture load, phase stability, and surface microstructure of a Y-TZP abutment. MATERIAL AND METHODS: Thirty-two prefabricated Y-TZP abutments were screwed and tightened down to external hexagon implants and divided into 4 groups (n = 8): C, control; MC, mechanical cycling (1×10(6) cycles; 10 Hz); AUT, autoclaving (134°C; 5 hours; 0.2 MPa); and TC, thermal cycling (10(4) cycles; 5°/55°C). A single-load-to-fracture test was performed at a crosshead speed of 0.5 mm/min to assess the assembly's resistance to fracture (ISO Norm 14801). X-ray diffraction (XRD) analysis was applied to observe and quantify the tetragonal-monoclinic (t-m) phase transformation. Representative abutments were examined with high-resolution scanning electron microscopy (SEM) to observe the surface characteristics of the abutments. Load-to-fracture test results (N) were compared by ANOVA and Tukey test (α=.05). RESULTS: XRD measurements revealed the monoclinic phase in some abutments after each aging condition. All the aging conditions reduced the fracture load significantly (P<.001). Mechanical cycling reduced the fracture load more than autoclaving (P=.034). No differences were found in the process of surface degradation among the groups; however, the SEM detected grinding-induced surface flaws and microcracks. CONCLUSIONS: The resistance to fracture and the phase stability of Y-TZP implant abutments were susceptible to hydrothermal and mechanical conditions. The surface microstructure of Y-TZP abutments did not change after aging conditions.