| Summary: | 碩士 === 國立臺灣大學 === 臨床牙醫學研究所 === 100 === Mineral trioxide aggregate (MTA), a type of calcium silicate cement, is widely used in endodontic repair therapies due to its good sealing ability, surface bioactivity and biocompability. However, several disadvantages of MTA have been reported such as long setting time, difficulty in handling, expensive and the releasing of heavy metal ions. Tricalcium silicate (C3S), the main constituent of MTA, has been proved to govern the properties of MTA including the physicochemical, biocompatible and bioactive properties. Therefore, our research team developed new tricalcium silicate cements with high purity, porous structure, and short setting time, named sn200 and so400, via sol-gel process by modification of mixing order (r ratio) and concentration of catalyst. Moreover, their physicochemical properties were tested and confirmed to be comparable with MTA. However, their surface bioactivity and biocompability were unknown and needed further evaluation. The purpose of this study is to evaluate the surface bioactivity and biocompability of sol-gel tricalcium silicate cements (so400 and sn200) in comparison with melt-quench method C3S (mC3S), commercial gray MTA (GMTA) and white MTA (WMTA). To study the surface bioactivity, the test materials were immersed in simulated body fluid (SBF) and distilled water, respectively and the behaviors of bioactive layer formation of test materials were analyzed via SEM-EDS, XRD and SS-NMR. The ions exchange between material and environment were measured by ICP-MS and the environmental pH was recorded. To study the biocompability, mineralizing rat pulpal cell line (MRPC-1) was used to evaluate the cell adhesion and the cytotoxicity of tested materials using the direct and indirect contact models, respectively. Utilizing SEM-EDS, we found the calcium-phosphate contenting precipitates in granular appearance with acicular surface formed on the surface of all test materials of SBF group, in comparison to those samples of distilled water group. After hydration, the peaks corresponding to Ca(OH)2 were identified by XRD either in SBF or distilled water groups and those peaks decreased in intensity or even disappeared as immersion time increased. When hydrated in SBF for 28 days, some small and broad peaks at 2θ=29.4⁰ and 2θ=25.9⁰, 31.8⁰ were observed in XRD pattern, which may corresponding to CaCO3 and poor crystallized hydroxyapatite (HAP). Different to the environmental pH increased rapidly to 11~12 in the first day of hydration in distilled water, lower pH value (8.5~10) was found in SBF group, which is favorable for the calcium ions releasing into environment. Consistently, the Ca+2 concentration of SBF group was 1.5~2 times of distilled water group although both groups demonstrated the similar trend of the change of Ca+2 ions as the time increased. In addition, we found the silicon ions increased rapidly in the first day of hydration and then decreased gradually as the time increased in all materials of SBF group, except WMTA. Meanwhile, no silicon ions were detected in distilled water group. For all of test materials, the phosphate ions of SBF decreased rapidly and became undetectable within 1~4 days, which may imply the formation of bioactive layer starts in the early stage of hydration. Besides, the signal at 2.6ppm was obtained in all test materials hydrated in SBF using 31P MAS SS-NMR analysis, which confirmed the HAP formed on the surface. Furthermore, good cell adhered to all test materials was observed in 24-hour culture, although the scores for cell adhered to mC3S and so400 were slightly lower in 4-hour culture. Using Transwell indirect contact model, we found there were no significant difference of cell viabilities among the test materials, but WMTA demonstrated the significant lower cell viability than that of control group without material treatment. Based on these findings, we proved the sol-gel tricalcium silicate cements (so400, sn200) have surface bioactive property with a HAP layer formed on their surface and the good biocompatibility in vitro. Moreover, take the advantages of its short setting time and the comparable physical properties of MTA, the sol-gel C3S of sn200 is considered as a potential material in endodontic applications.
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