Objective

This study aims to assess the validity of a recent theory which proposes that (1) the magnitude of the shrinkage stress of resin composites depends on the thickness of the boundary layer under triaxial constraints relative to the total thickness of the specimen and (2) the boundary-layer thickness is proportional to the diameter of the specimen.

Methods

Cylindrical specimens of three commercially available resin composites, three diameters (4, 5 and 6.3 mm) and four thicknesses (2, 3, 5 and 6.5 mm) were tested. Curing was applied using a LED light for 40 s. Microscopic images (32×) of the specimens before and after curing were analyzed to determine the lateral shrinkage profile along the vertical axis. Boundary-layer thickness was determined from the point where lateral shrinkage displacement first reached the maximum value found at mid-thickness.

Results

Lateral shrinkage displacement at mid-thickness was close to the theoretical value based on published shrinkage-strain data, with the ratio between experimental and theoretical values being 1.04 ± 0.06. The boundary-layer thickness was found to be proportional to specimen diameter only, independent of material, C-factor, and specimen thickness. The proportionality constant was 0.64 ± 0.07, which was approximately 3 times that of the effective value indicated by shrinkage strain/stress calculations.

Significance

This study validates the assumption made in the shrinkage-stress theory recently proposed and provides a more precise and mechanistic interpretation for the C-factor, i.e. the C-factor, as a measure of a specimen's constraint, is the ratio between the boundary-layer thickness and the total thickness of the specimen.

中文翻译：

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与牙科树脂复合材料光聚合有关的C因子的机械表现。

目的

这项研究旨在评估最新理论的有效性，该理论提出：（1）树脂复合材料的收缩应力的大小取决于三轴约束下边界层的厚度相对于试样的总厚度，（2）边界层厚度与样品直径成正比。

方法

测试了三种市售树脂复合材料，三个直径（4、5和6.3毫米）和四个厚度（2、3、5和6.5毫米）的圆柱试样。使用LED灯进行固化40秒。分析样品在固化之前和之后的显微图像（32倍），以确定沿垂直轴的横向收缩曲线。从横向收缩位移首先达到在中厚度处发现的最大值的点确定边界层厚度。

结果

根据公开的收缩应变数据，中厚度的横向收缩位移接近理论值，实验值与理论值之比为1.04±0.06。发现边界层厚度仅与样品直径成正比，与材料，C因子和样品厚度无关。比例常数为0.64±0.07，约为收缩应变/应力计算所表示有效值的3倍。

意义

这项研究验证了最近提出的收缩应力理论中的假设，并为C因子提供了更精确和机械的解释，即C因子作为试样约束的度量，是边界层之间的比率。厚度和样品的总厚度。