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 restorations . We examine the restorations 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 calibrated restorations with varying cement moduli of known values.
There is evidence that the cement can influence the clinical survival of glass-ceramic crowns. The overall goal of this application is to understand the factors that lead to fracture and the influence that the cement has on the fracture process. We propose to answer 3 questions. Does the cement influence the stress corrosion process in dental glass-ceramics? How can information about the interface state and computer simulations be used to explain difference in observed survival rates of glass-ceramics attached to teeth with different cements? And finally can non-invasive ultrasound methods be developed to measure small changes in the effective elastic properties of the underlying cement? The proposed methods could have a significant impact on the way we evaluate the stability of adhesives for various restoration types.
| Nasrin, Sadia; Katsube, Noriko; Seghi, Robert R et al. (2018) Approximate relative fatigue life estimation methods for thin-walled monolithic ceramic crowns. Dent Mater 34:726-736 |
| Nasrin, S; Katsube, N; Seghi, R R et al. (2017) Survival Predictions of Ceramic Crowns Using Statistical Fracture Mechanics. J Dent Res 96:509-515 |
| Nasrin, Sadia; Katsube, Noriko; Seghi, Robert R et al. (2016) 3D statistical failure analysis of monolithic dental ceramic crowns. J Biomech 49:2038-2046 |
| Lekesiz, Huseyin; Katsube, Noriko; Rokhlin, Stanislav I et al. (2013) Effective spring stiffness for a periodic array of interacting coplanar penny-shaped cracks at an interface between two dissimilar isotropic materials. Int J Solids Struct 50:2817-2828 |
