Braga Roberto R, Hilton Thomas J, Ferracane Jack L
Depto. de Materiais Dentarios da FOUSP, São Paulo, SP, Brazil.
J Am Dent Assoc. 2003 Jun;134(6):721-8. doi: 10.14219/jada.archive.2003.0258.
The authors compared the polymerization contraction stress produced by flowable resin-based composites with stress values produced by nonflowable composites. They also measured the stress reduction produced by placing a precured layer of flowable composite under a nonflowable composite.
The authors first tested four flowable and six nonflowable composite materials for contraction stress in a tensiometer. In the second part of the study, they applied a 1.4-millimeter-thick layer of flowable composite or unfilled resin and precured it in the test apparatus to assess the stress relief produced by a low-modulus material during light curing of a subsequent layer of highly filled composite. Flexural moduli of the precured materials were determined via a three-point bending test.
The stress values ranged between 6.04 and 9.10 megapascals. The authors found no significant differences in stress between flowable and nonflowable composites. Microfilled composites produced lower contraction stress than did hybrids. The flexural modulus of the flowable composites varied between 4.1 and 8.2 GPa. Regarding the effect of a precured layer of composite on contraction stress, the authors observed significant reductions with only one of the flowable materials and with the unfilled resin.
The flowable composites produced stress levels similar to those of nonflowable materials. Most of the flowable materials tested did not produce significant stress reductions when used under a nonflowable composite.
Using a flowable resin-based composite as a restorative material is not likely to reduce the effects of polymerization stress. When used in a thin layer under a nonflowable composite, the stress reduction depended on the elastic modulus of the lining material.
作者比较了可流动树脂基复合材料产生的聚合收缩应力与非可流动复合材料产生的应力值。他们还测量了在非可流动复合材料下方放置一层预固化的可流动复合材料所产生的应力降低情况。
作者首先在张力计中测试了四种可流动和六种非可流动复合材料的收缩应力。在研究的第二部分，他们施加了一层1.4毫米厚的可流动复合材料或未填充树脂，并在测试装置中对其进行预固化，以评估低模量材料在随后的高填充复合材料层光固化过程中产生的应力释放。通过三点弯曲试验确定预固化材料的弯曲模量。
应力值在6.04至9.10兆帕之间。作者发现可流动和非可流动复合材料之间的应力没有显著差异。微填充复合材料产生的收缩应力低于混合复合材料。可流动复合材料的弯曲模量在4.1至8.2吉帕之间变化。关于预固化复合材料层对收缩应力的影响，作者仅观察到一种可流动材料和未填充树脂的应力有显著降低。
可流动复合材料产生的应力水平与非可流动材料相似。测试的大多数可流动材料在非可流动复合材料下方使用时不会产生显著的应力降低。
使用可流动树脂基复合材料作为修复材料不太可能降低聚合应力的影响。当在非可流动复合材料下方以薄层使用时，应力降低取决于衬层材料的弹性模量。
