Browsing by Subject "Composite Resins -- Chemistry"

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    Curing Front Shape and Velocity in Cylindrical Bulk-Filled Light-Cured Resin Composite
    (2001) Wright, Chad M.; Katona, Thomas R.; Baldwin, James J.; Shanks, James C.; Chen, Jie; Moore, B. Keith
    Clinical failures of resin composite dental restorations are common phenomena. Such failures occur in part because of the polymerization shrinkage inherent to methacrylate-based materials. Numerous efforts have been attempted to reduce the deleterious effects of polymerization shrinkage. Despite such efforts, it appears that no simple solution to the problem exists. To effectively improve bonding methods, more information must be known about the polymerization process itself. By using the Finite Element Method (FEM), an accurate computer simulation model of the polymerization process may be created. Such a model may allow researchers to test the effects of alternative restorative and bonding techniques without actual in vitro experiments. To create an accurate computer model, much information about the transient events present during the curing process has yet to be obtained. In this non-clinical, data-gathering study, we: 1) verified that the shape of the curing front within a light-cured resin composite model is indeed convex, 2) determined that the curing front shape changes with depth of cure, and 3) measured the velocity of the curing front as it relates to curing light distance. Each of these observations and measurements has yielded information vital to the subsequent development of a resin composite polymerization model. It is anticipated that necessary data regarding other variables or aspects of the polymerization process will be obtained in subsequent research projects.
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    Generation of Transient Deformations and Strains by Light Polymerization
    (2002) Hamula, David W.; Katona, Thomas R.; Carlson, Timothy J.; Chen, Jie; Hohlt, William F.; Shanks, James C.
    A significant factor in the long term viability of resin composite dental restorations is minimizing the stress development along the wall of the cavity as the material shrinks during polymerization. The stress of polymerization shrinkage can lead to gap formation between the restoration and the walls of the cavity (microleakage). Clinical manifestations associated with material shrinkage include tooth sensitivity, discoloration, loss of restoration, secondary decay and tooth fracture. Recent research in resin composite polymerization has incorporated Finite Element (FE) stress analysis. An FE model predicted initial extrusion of the resin composite surface during light curing in a bulk-filled Class V restoration. The purpose of this project was to measure transient events during the polymerization of a light-cured resin composite. The hypothesis tested was that during light-activated polymerization of a Class V type restoration, the resin composite surface initially extrudes and measurable stresses occur along the cavity walls. In Experiment 1, initial surface movements were measured. A specifically configured test apparatus enabled surface resin movements to be recorded by a profilometer. Eight identical Class V preparations were drilled into a black acrylic block. The preparations were filled with Herculite and cured. For each of the eight trials, the profilometer recorded an initial extrusion of the resin composite surface. This experiment proved that during light activate polymerization of the resin composite, the FEM predicted counterintuitive initial surface extrusion does take place. In Experiment 2, initial strains were measured. For this pilot study a thin walled black acrylic tube was used as the Class V type restoration. Miniature strain gauge strips were placed along the wall of the cavity at right angles to measure circumferential and longitudinal strains along the cavity surface as the polymerization front advances. The preliminary data suggests the largest circumferential and longitudinal strains initially recorded were closest to the resin surface. The results of these experiments demonstrated initial resin composite surface extrusion and measurable strains along the cavity wall. This experimental data served as a partial validation of the FEM approach.