Effect of aging, thermocycling, laboratory procedures and cycling loading on the mechanical properties of partially stabilized zirconia & Bond strength of pressable and conventional veneering porcelain to partially stabilized zirconia
Date
2008
DOI
Authors
Abu-alnasar, Hiba A.
Version
OA Version
Citation
Abstract
Objectives: This in-vitro study is designed to evaluate the effect of aging, thermocycling, laboratory procedures and cycling loading on the mechanical properties and the phase composition of yttria stabilized zirconia presently used commercially as a framework for crowns and bridges.
Methods: Vita YZ, Lava and Tosoh blocks were sectioned into discs, sintered and divided into two groups with and without cycling loading. In the first part of this study, the no cycling loading groups were divided into seven groups: control (1), thermal cycle (2), aging (3), simulated veneer firing (4), polished (5), ground (7). Group one is the control group consisted of as sintered discs. Group two includes specimens subjected to 3,000 thermal cycles with a dwell time of 30 seconds at 5C0 and at 55C0 with a transfer time of about five seconds. Group three includes sintered specimens aged in water at 36 c0 for 18 month in an incubator. Group four consisted of sintered specimens that were subjected to four repeated firing cycles according to the veneering system's firing chart. The last groups tested are the sixth and seventh groups that include sintered specimens treated with two different polishing wheels 15µ and 90µ size, under a specific load and time. In the second part of this study, Vita YZ, Lava and Tosoh specimens were subjected to cycling loading and were divided into 6 groups: as sintered then cycling loading (1), thermal cycle then cycling loading (2), simulated veneer firing then cycling loading (4), polished then cycling loading (5), ground then cycling loading (7) and last group all: ground, simulated veneer firing, thermal cycle and finally subjected to cycling loading.
Results: Zirconia showed no significant differences in flexural strength compared to as sintered when subjected to thermocycling, aging and stimulating veneer firing, the flexural strength of each material with different treatments were (870.0 ± 87.68, 971.0 ±109.61, 939.2 ±113.49 MPa) for Vita YZ, (961.3 ± 98.4, 942.9 ±139.1, 822.5 ±78.2 MPa) for Lava and (1029.1 ±126.2, 1031.3 ±163.4, 881.6 ±171.0 MPa) for Tosoh respectively. After polishing and grinding the biaxial strength were (1091.4 ±96.3, 1289.8 ±156 MPa) for Vita YZ. (1172.3±105.3 ,1191.8 ±183.61 MPa) for Lava, and (1142.5 ±89.0,1179.8 ±74.9 MPa) for Tosoh. Cycling loading has no significant effect on the biaxial strength. There was no significant difference in the biaxial strength after cycling loading.
Conclusions: There were statistically significant differences in the mean flexural strengths of the tested materials after grinding and polishing compared to as sintered. Except Vita YZ did not show significant differences in strength after polishing. Thermocycling and simulated veneer firing did not result in a significant change in the biaxial strength of tested materials. There was no significant difference in the biaxial strength after cycle loading after different surface treatments. Except Vita YZ ground was significantly higher than ground then cycling load group. There was no significant difference in the biaxial strength of the materials subjected to aging in water.
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Thesis (D.Sc.D.)--Boston University, Goldman School of Dental Medicine, 2008 (Dept. of Restorative Sciences and Biomaterials).
Includes bibliographical references: leaves 105-110 (Ch. 1); leaves 174-176 (Ch. 2).
Thesis (D.Sc.D.)--Boston University, Goldman School of Dental Medicine, 2008 (Dept. of Restorative Sciences and Biomaterials).
Includes bibliographical references: leaves 105-110 (Ch. 1); leaves 174-176 (Ch. 2).
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This work is protected by copyright. Downloading is restricted to the BU community. If you are the author of this work and would like to make it publicly available, please contact open-help@bu.edu.