Evaluation of reliability and failure modes of ceramic crown systems depending on framework design and marginal ridge load application

Author(s)

Vinícius Pavesi Fardin

• Document type: Master's Dissertation
• Press: Bauru.
• Institution: Universidade de São Paulo (USP). Faculdade de Odontologia de Bauru (FOB/SDB)
• Defense date: 2013-05-29

Examining board members

Gerson Bonfante; Paulo Francisco Cesar; Pedro Cesar Garcia de Oliveira

• Advisor: Gerson Bonfante

Abstract

The excellent mechanical properties of zirconia make it to be the material of choice for ceramic crowns and posterior fixed prostheses. However, problems still exist related to the chippings. The lack of framework support to ceramic veneer is indicated as a possible cause. This study aimed to evaluate through laboratory tests if metallic and ceramic framework with conventional or modified design show statistical difference in reducing mechanical complications, such as chipping or fracture of the ceramic veneer on receiving axial loads in marginal ridges of the first molar inferior crowns through the following null hypotheses: 1) the response to fatigue in marginal ridges will not increase the presence of damage to the crowns; 2) framework`s design will not modify the presence of damage to the crowns, regardless of the material used. Forty crowns were manufactured on standardized preparations and divided into four groups: group I (conventional framework Cobalt-Chromium), group II (modified framework Cobalt-chromium), group III (conventional framework Zirconia - ZirCAD IPS Emax) and group IV (modified framework Zirconia - IPS Emax ZirCAD). These crowns were subjected to cyclic loading in a fatigue machine and submerged in water (1.000.000 cycles or until the fracture - load range at 30-300 N). The initial load was applied on the mesial marginal ridge with indenter ceramic Lithium disilicate (IPS Emax Press), and after the end of the cycle, the distal alternatively. The cycling was interrupted at a prescribed number of loading cycles (125.000) and crowns were inspected for damage accumulation under a stereomicroscope. In the end, fractured crowns were submitted to scanning electron microscopy and crowns without fractures were embedded in epoxy resin and sequentially polished for the analysis of the damage. Each sample received scores according to the type of failure presented. Statistical analysis was carried out with Kruskal-Wallis test and multiple conparisons between groups were carried out with Dunn wed significant differences between groups, however there was no difference between the groups of the same ceramic systems. It was concluded that the first hypothesis was accepted and the second hypothesis was rejected. (AU)

• FAPESP's process: 11/16377-0 - Evaluation of reliability and failure modes of ceramic crown systems depending on framework design and location of load application
• Grantee: Vinicius Pavesi Fardin
• Support Opportunities: Scholarships in Brazil - Master