Contact damage of dental multilayers

The growing market drives the high demand for artificial dental crowns. (Rekow and Thompson, 2007) However, all-ceramic dental crowns continue to fail at a rate of approximately 3% each year (Burke et al., 2002). These stimulate recent research efforts to develop crack-resistant dental crowns in recent decades.;This dissertation presents the results of combined experimental, analytical and computational studies of contact-induced deformation and cracking in ceramic/adhesive/composite dental multilayer structures. A dental multilayer is an engineering idealization of a dental crown. It mimics the layered structure of the crown on a real tooth and simplifies the complex curvatures and loading conditions into flat layers subjected to normal compressive Hertzian loading. (Kelly, 1997; Lee et al., 2002; Rekow and Thompson, 2007; Shrotriya et al., 2003).;In this dissertation, the initial efforts focus on the experiments and modeling of the rate dependent effects of critical load (which corresponds to the onset of sub-surface radial cracking) in dental multilayer structures. Focused ion beam and scanning electron microscopy (FIB/SEM) are used to reveal high resolution images of sub-surface inter/intragranular cracking modes that have not been reported before. A mechanistically-based rate dependent environmentally-assisted slow crack growth (RDEASGG) model is developed. This is shown to be good for predictions of critical loads determined in experiments at different loading rates. A study of the fatigue life behavior of the same dental multilayer structures is then presented. The results show that the fatigue failure of the multilayers is also associated with the pop-in of sub-surface radial cracks in the top ceramic layer. The results also suggest that the appropriate fatigue life prediction models will depend strongly on the magnitude of the relaxation times with respect to the periods of the fatigue cycles. Finally, the dissertation explored the bio-inspired design of dental multilayers. A micron-scale, bio-inspired functionally graded material (FGM) is developed to bond the top ceramic layer to the dentin-like composite substrate. The FGM is shown to exhibit higher critical loads over a wide range of loading rates. The implications of the results are then discussed for the design of bio-inspired dental crowns.