| Most of the all ceramic restoratins require the combination of two layers of ceramic material, such as a strong ceramic core and a veneering porcelain with better optical properties. The two materials must be chemically, thermally, mechanically and aestheticlly compatible. High-Strength Dental Cecamic (type A) (HSDC-A) is a glass-infiltrated alumina dental ceramic. Its three point flexure strength and fracture toghness are 389.60MPa and 3.2425MNm-2/3 respectively. Vintage AL vennering porcelain is developed exclusively for alumina coping due to its low coefficient of thermal expansion (CTE).In dentistry the most common method to predict thermal incompatibility between veneering and substrate materials is often characterized by their difference in thermal contraction coefficient (TCC) values . The method above is based on the assumption that dental ceramics contract linearly upon cooling. However, DeHoff and Isgro found that for many dental ceramics the expansion as function of temperature does not follow a linear expansion behavior but show a non-linear temperature-expansion relation. Unfortunately, they did not give any method to calculate the thermal mismatch value with their findings.In this study, we evaluated the compatibility between the two materials from the aspects such as bonding strength, SEM and EDS analysis of the bonding interface, thermal shock resistance, biaxial flexure strength of bilayered samples and Weibull analysis. In addition, a new method for taking into consideration of nonlinear contraction behavior of dental ceramics was proposed for calculating thermal mismatch value (Δα) between substrate and veneering materials. Finally, some results were drawn as following:1 The mean bonding strength between the HSCD-A and the veneering porcelain was 55.52±14.64MPa.2 SEM showed tight connection between the two materials. Element diffusion between the core ceramic and the veneering porcelain was also confirmed by EDS.3 The temperature of thermal shock resistance of this system was 179±15℃.4 The biaxial flexure strength of four groups MV, MC, BV, BC were 94MPa, 396 MPa, 118 MPa and 206 MPa respectively. The Weibull modulus and fracture mode the bilayered samples was influenced by the properties of the material subjected to tension.5 The new method proved to be a reliable one to predict thermal compatibility of multi-layer dental ceramic composites.Conclusion: Vintage AL veneering porcelain has good thermal and chemical compatibility with High Strength Dental Cecamic (type A). The modified thrmal mismatch values can be use to predict thermal compatibility... |
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