Understanding interface initiated fractures in glass-ceramic restorations

Ohio State University, Columbus OH

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Abstract

The long-range goals of this research proposal are to improve the clinical longevity of esthetic glass-ceramic restorations and potentially reduce the amount of tooth reduction required for successful clinical applications. In an ideal scenario, we would use these restoration types in much the same manner that we utilized cast metal in the previous century. The initial load bearing capacity of a well bonded, glass-ceramics restoration is well above the average maximum bite force applied by posterior teeth. Therefore, under service conditions, the survival of glass-ceramic restorations are likely to be influenced by degradation processes such as stress corrosion and cement degradation. Fractographic examination of failed glass-ceramic crowns indicates that interface initiated radial fractures are the predominant identified failure mode. To achieve our long range goals we need to minimize the probability of radial cracks. This will require a clear understanding of the relationship between the degradation processes and clinical survival. To improve our understanding we propose 3 specific aims. In aim 1 we hypothesize that the supporting cement type can influence stress corrosion effects in dental glass-ceramics. To evaluate our hypothesis we test ceramic plates with and without cement layers in a biaxial test mode using both the constant stress rate and constant stress methods of subcritical crack growth (SCG) parameter determination and statistically compare the resulting data. In aim 2 we hypothesize that the observed decrease in glass-ceramic restoration survival when used with conventional cement compared to resin cement is related to an increased stress state at the ceramic surface due to cement delaminations. To test our hypothesis we use a controlled laboratory fatigue model to generate predictable radial fractures in trilayer glass-ceramic [unreadable]restorations[unreadable]. We examine the [unreadable]restorations[unreadable] periodically to determine the presence of radial fractures and develop survival curves based on this assessment. Additionally we use non-invasive ultrasound scanning methods to gain additional spatial information about the cement interface state in terms of bond or no-bond (delamination). We combine this qualitative spatial information together with SCG parameters determined in aim 1 into a statistical fracture mechanics based model to explain and predict the resulting survival data. The actual and predicted survival curves are compared statistically to test the hypothesis. Finally in aim 3 we propose a novel non-invasive approach to evaluate the stress state at the cement interface beneath glass-ceramic restorations. We hypothesize that angle beam ultrasound scanning (ABUS) methods could be developed to detect small changes in the effective moduli of the supporting cement. To test our hypothesis we determine the accuracy and precision of the experimental ABUS device on [unreadable]calibrated[unreadable] restorations with varying cement moduli of [unreadable]known[unreadable] values.