Polymerization shrinkage behaviors of class V dental composite restorations

摘要

One cause of dental composite restoration failure is the polymerization shrinkage The contraction stress counteracts with the tooth-composite bonding and causes marginal microleakage and debonding In dental class V restorations the non-retentive cavity geometry and complicated margin locations on enamel or dentin are especially unfavorable for bonding This study is aimed to measure the shrinkage behaviors of class V composite restorations during polymerization and its possible relaxation after polymerization using an experimental-numerical analysis In addition the effects of cavity form and composite materials on the shrinkage behaviors were investigated Sixty premolars were prepared with two cavity designs: a box-cavity and a V- cavity; and were further divided into three restorations: a nanocomposite Z350 filling (Z350); Z350 filling with a flowable composite lining (Z350/F); and a low-shrinkage composite filling (LS) After restorations the specimens were irradiated for 40 seconds and their images were captured during- and post-irradiation for 1 hour A digital-image-correlation (DIC) program Vic-2009 was used to calculate the full-field deformation A corresponding finite element analysis (FEA) simulated the polymerization shrinkage by a thermal expansion module and accordingly to analyze the stress on tooth and restorations Finally the microleakage of these restorations was examined From the shrinkage measurements the displacements and strain increased with time The displacements were greater in Box-cavities than in V-cavities and greater on the bottom than on the top margins For all locations Z350 presented the greatest displacements and strains Z350/F reduced the displacements on the bottoms LS presented the least displacement and strain except on the bottom of V-cavities Z350 and Z350/F showed tensile strain on the lateral margin while LS showed a compressive strain FEA showed that the stresses of box-cavities were greater than those in V-cavities The maximum stress existed on the top enamel margin The stress of LS in V-cavity was greater on the bottom than that on the top margin which may increase the debonding For the microleakage observation there was difference among three restorations on the top margins and box-restorations revealed more microleakage than those in V-restorations especially for Z350/F LS did not improve marginal adaptations With these results the effect of composite material and cavity form should be considered A box-cavity is more retentive but shows a great shrinkage LS reduced the shrinkage and stress but did not present an improved which may be due to the low bond strength

獎項日期	2014 8月 27
原文	English
監督員	Terry Yuan-Fang Chen (Supervisor)