Study on factors affecting the failure, deformation and adhesive durability of fluoride-releasing restorative materials

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The main goal of this study was to obtain the knowledge in the factors affecting the failure and deformation and the adhesive durability of fluoride-releasing materials under the various mechanical or chemical stress conditions, in order to develop more durable fluoride-releasing materials in the oral cavity. To achieve this goal the study mainly focused to characterize the failure and deformation behavior of commercially available fluoride-releasing restorative materials. Conventional glass ionomers increased strength with time; however, the ambient water and the acidic atmosphere deteriorate the surface texture. This would reduce the failure resistance of these materials. Resin-modified (light-cured) glass ionomers showed larger mechanical strength than the conventional ones because of incorporation of resin components into the matrix. The incorporated resin components notably enlarged elastic and residual deformation under static loading condition. The large deformation under stress, which exceeds the amount of deformation of tooth, would negatively influence the durability of materials when they were placed in the cavities. Glass ionomer-modified resin composites (compomers) or fluoride-releasable resin composite showed the greatest strength under any conditions employed among the fluoride-releasing materials examined in the study. This could be obtained from the strength and properties of the matrix made from resin. The adhesive strength to bovine dentin of compomers reduced after the repeated loading. As compared to other materials, these materials revealed the greatest resistance to fracture when the specimens were subjected to repeated shear loading condition. The durability of adhesion depended upon the bonding treatment used in these materials. Since the compomers have larger water sorption, the bonding strength between the compomer and the bonding agent would be a critical factor for durability. Further investigation will be made in future.