The effect of zirconia coping design and surface roughness on the fracture strength of the veneering pressed ceramic.
Abstract: ABSTRACT Statement of the problem: With the increased use of zirconium core material in fixed prosthodontic and the superior physical properties of zirconium, the main problem in zirconium supported prostheses is the chipping and fracturing of the veneering porcelain. Purpose of the study: This study aimed to find a method to improve the interface between the zirconia core and the veneering ... read morepressed porcelain by providing a mechanical support in the shape of a zirconia core and/or by roughening the surface of the zirconia core with sandblasting. Materials and Methods: The samples were prepared by utilizing a metal die, with the following preparation criteria: 6-degree axial taper, 1.5-mm shoulder finish line placed 0.5 mm occlusal to the cemento-enamel junction, 1.5-mm axial reduction, 2-mm occlusal reduction, and 5-mm occluso-gingival height. A master metal die was used for all groups. Four groups were prepared with ten samples per group. In group "A" (control group), the abutment was scanned, the zirconia coping was milled, and the veneering porcelain was pressed per manufacture recommendations. In group "B" (mechanical support group), the design of the core received a mechanical support design in the proximal surface of the zirconia coping. In group "C" (sandblasting group), the coping was milled as in the control group; then the coping was sandblasted. In group "D" (sandblast & mechanical support group), the coping received both the mechanical support design and sandblasting as in group "B" & group "D". The samples were then loaded with a controlled load profile utilizing a cyclic loading machine for 100,000 cycles under wet conditions. At the end of cyclic loading, each specimen was loaded statically until fracture to determine the ultimate strength of the porcelain by utilizing the Instron machine. Descriptive statistics (e.g. means, frequency, standard deviation and variance) were calculated, and comparisons between the groups were performed. Statistical analysis was done using two-way analysis of variance (ANOVA) to evaluate the effect of mechanical support and sandblasting, Pairwise t-tests were used to test between groups significance. Statistical tests were performed at 95% confidence level, (alpha=0.05). All the data was entered and analyzed using the SPSS statistical software package. Results: The average fracture load was 525.8 N (72.63 Standard Deviation) for the control group (Group "A"), 549.3 N (70.17 SD) for the sandblast group (Group "B"), 982.8 N (81.23 SD) for the support group (Group "C") and 941.639 N (94.25 SD) for the support and the sandblast group (Group "D"). None of the samples failed during the cyclic loading. Conclusion: Based on this study, modifying the design of the zirconia coping by adding mechanical support in the proximal area will increase the fracture strength of the pressed veneering ceramic. On the other hand, sandblasting the zirconia coping has no effect on the fracture strength of the pressed veneering ceramic.
Thesis (M.S.)--Tufts University, 2012.
Submitted to the Dept. of Posthodontics.
Advisor: Hiroshi Hirayama.
Committee: Ki-Ho Kang, Luis Del Castillo, and Paul Stark.
Keyword: Dentistry.read less
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