| Dental ceramics are desirable restorative materials due to their biocompatibility, chemical durability, thermal insulation, and superior esthetic qualities. The clinical success of metal-ceramic restorations has been proven. However, the lifetimes of all-ceramic restorations are less predictable due to the brittle nature of ceramics. Recently, manufacturers have developed new dental ceramic systems that are less susceptible to fracturing, resulting in increased lifetime expectancy. The goal of this project is to determine ceramic material properties and relate these findings to help predict the lifetime survival of an all ceramic prosthesis. A four-point flexure test was performed on bilayered and multilayered rectangular beam ceramic specimens. Bilayered specimens were made using a densely sintered zirconia ceramic and a fluorapatite glass-ceramic with bonding of the two layers mediated by a liner ceramic. Two experimental groups both had a bilayered veneer-core construction but differed in thermal history. Group BT was tempered, and Group BA was annealed. Comparing these groups allowed for determination of residual stress at the veneer surface by difference in rapid and slow cooling. The third group of specimens (Group MA) was made using only veneer ceramic, and comparing Group BA and Group MA allowed for determination of stress caused by difference in coefficient of thermal expansion of the veneer and core ceramics. The significance of this investigation is to develop a method for evaluating the thermally induced residual stress between two different ceramic materials. This will allow future researchers to construct more accurate stress-lifetime-failure probability models for dental ceramics. With this information, the lifetime of prostheses can be predicted using finite element and time-dependent reliability software. |
