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Edge chipping test in bars and crowns to predict the chipping on veneered zirconia

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Author(s):
Carina Baptiston Tanaka
Total Authors: 1
Document type: Doctoral Thesis
Press: São Paulo.
Institution: Universidade de São Paulo (USP). Faculdade de Odontologia (FO/SDO)
Defense date:
Examining board members:
Josete Barbosa Cruz Meira; Estevam Augusto Bonfante; Paulo Francisco Cesar; Rafael Ratto de Moraes
Advisor: Josete Barbosa Cruz Meira; Grace Mendonça Dias de Souza
Abstract

Aim: To deepen the investigation of the edge chipping method when using either bar or crown-shaped specimens, to verify whether the test is able to reproduce the well-known clinical outcome that veneered zirconia is more prone to chipping than porcelain-fused-to-metal when the fast cooling protocol is used. Materials and methods: edge chipping test was conducted with different shaped specimens: bars (monolithic: VM13, VM9 or zirconia; or bilayers: VM13-metal and VM9-zirconia) and bi-layer crowns. A microstructure analysis was performed on the monolithic bars (5 mm x 32 mm x 2.5 mm) to evaluate possible differences between VM13 and VM9, that could account for differences on bilayer specimens data. The bilayer bars (5 mm x 32 mm x 2.2 mm, 0.7 mm and 1.5 porcelain infrastructure) were subjected to two cooling protocols (slow and fast) and load was applied in two directions (parallel or perpendicular to the interface). For bilayer bars, residual thermal stresses were evaluated using finite element analysis. For crown-shaped specimens (corresponding to the first molar, with 0.7 mm framework thickness), the cooling protocol was the same employed for bilayer bars. The fractured surfaces of all specimens were examined utilizing a stereomicroscope at a magnification from 20x up to 50x. The edge chipping data were analyzed by several approaches presented in the literature, the ReA parameter (chipping resistance), corresponding to the average of force versus distance data collected over a broad range (N / mm), was chosen to compare the different experimental groups. Results: There was no significant difference between the veneers for chipping resistance, despite that VM13 presented the highest leucite content. On bilayer bars with slow cooling protocol and loading perpendicular to the interface, zirconia provided significantly higher chipping resistance than metal-based specimens. Edge chipping test was not able to detect differences between groups when fast cooling was used or loading was applied parallel to the interface. When crowns were subject to fast cooling, results revealed that metal framework has significantly higher veneer chipping resistance than zirconia. When the slow cooling protocol was used, differences between groups with different frameworks were not observed using edge chipping test. Conclusion: The chipping test on crowns reproduced the chipping resistance reported clinically better than bar-shaped specimens. Thus, efforts to improve the test using specimens more similar to the crown geometry are important. (AU)