CHARACTERIZATION FRAMEWORK FOR BOND MECHANICS AT THE MINERALIZED TISSUE – ADHESIVE INTERFACE
University of Kansas
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The mechanical performance of the dentin-adhesive interface controls the overall failure of the dental restorations. This performance is evaluated by the bond strength tests, such as the micro-tensile test. The conventional bond strength tests suffer from large variations in the test results. They are also not capable of monitoring the local failure mechanisms. These challenges limit their ability to effectively support the design of dental restorative materials. Therefore, this present study focuses on a mechanical characterization framework to overcome these challenges. In this characterization framework, mechanical testing is complemented by mathematical modeling for a comprehensive understanding of the material behaviors. A granular micromechanics nonlinear material model was developed and implemented into a commercial finite element (FE) analysis software. This model captured the rate dependent nonlinear material behavior with damage and plasticity. The diametral compression test application overcame the challenges in the tensile and the interfacial mechanical tests. The mechanical behavior of the mineralized tissue, the adhesive polymer and the mineralized tissue – adhesive interface was obtained by using the diametral compression test. The dentin-adhesive interface consists of the dentin (the mineralized tissue), the adhesive polymer and the hybrid layer. The hybrid layer is composed of the demineralized dentin and the adhesive resin. Physical experiments can obtain the overall mechanical strength at the mineralized tissue – adhesive interface. However, it is critical to characterize the hybrid layer’s mechanical behavior locally. Therefore, the developed diametral compression test simulations enabled obtaining the mechanical behavior of the mineralized tissue, the adhesive polymer and the hybrid layer. Two different adhesive formulations were studied to investigate the self-strengthening property. Building on the learnings of the mechanical characterization and the design criteria, the simulations successfully captured the nonlinear rate dependent mechanical behavior of materials in the physical experiments. The self-strengthening property was shown to provide superior mechanical performance to the adhesive polymer and the mineralized tissue – adhesive interface. The results also indicated that a local failure might be initiated in the hybrid layer while the interface is still intact. This local failure was shown to affect stress distributions in the mineralized tissue and eventually lead to its failure.
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