Objectives

Polymerization shrinkage of resin composite restorations can cause debonding at the tooth–restoration interface. Theory based on the mechanics of materials predicts that debonding at the pulpal floor would half the shrinkage displacement at the occlusal surface. The aim of this study is to test this theory and to examine the possibility of detecting subsurface resin composite restoration debonding by measuring the superficial shrinkage displacements.

Methods

A commercial dental resin composite with linear shrinkage strain of 0.8% was used to restore 2 groups of 5 model Class-II cavities (8-mm long, 4-mm wide and 4-mm deep) in aluminum blocks (8-mm thick, 10-mm wide and 14-mm tall). Group I had the restorations bonded to all cavity surfaces, while Group II had the restorations not bonded to the cavity floor to simulate debonding. One of the proximal surfaces of each specimen was sprayed with fine carbon powder to allow surface displacement measurement by Digital Image Correlation. Images of the speckled surface were taken before and after cure for displacement calculation. The experiment was simulated using finite element analysis (FEA) for comparison.

Results

Group I showed a maximum occlusal displacement of 34.7 ± 6.7 μm and a center of contraction (COC) near the pulpal floor. Group II had a COC coinciding with the geometric center and showed a maximum occlusal displacement of 17.4 ± 3.8 μm. The difference between the two groups was statistically significant (p-value = 0.0007). Similar results were obtained by FEA. The theoretical shrinkage displacement was 44.6 and 22.3 μm for Group I and II, respectively. The lower experimental displacements were probably caused by slumping of the resin composite before cure and deformation of the adhesive layer.

Significance

The results confirmed that the occlusal shrinkage displacement of a resin composite restoration was reduced significantly by pulpal floor debonding. Recent in vitro studies seem to indicate that this reduction in shrinkage displacement could be detected by using the most accurate intraoral scanners currently available. Thus, subject to clinical validation, the occlusal displacement of a resin composite restoration may be used to assess its interfacial integrity.

中文翻译：

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是否可以从复合修复体的咬合面位移中检测出牙髓地板脱粘？

目标

树脂复合材料修复体的聚合收缩会导致牙齿-修复界面脱胶。基于材料力学的理论预测，牙髓底部的脱胶将使牙合面的收缩位移减半。这项研究的目的是检验这一理论，并检验通过测量表面收缩位移来检测地下树脂复合材料修复体脱粘的可能性。

方法

使用线性收缩应变为0.8％的商用牙科树脂复合材料，在铝块（8毫米厚，宽10毫米，高14毫米）。第一组具有与所有型腔表面粘合的修复体，而第二组具有未与型腔底板粘合的修复体，以模拟脱胶。每个样品的近侧表面之一喷有细碳粉，以允许通过Digital Image Correlation（数字图像关联）测量表面位移。在固化之前和之后拍摄斑点表面的图像以进行位移计算。为了进行比较，使用有限元分析（FEA）对实验进行了模拟。

结果

第一组显示最大咬合位移为34.7±6.7μm，并且牙髓底部附近有收缩中心（COC）。第二组的COC与几何中心重合，最大咬合位移为17.4±3.8μm。两组之间的差异具有统计学意义（p值= 0.0007）。FEA获得了类似的结果。第一组和第二组的理论收缩位移分别为44.6和22.3μm。较低的实验位移可能是由于固化前树脂复合材料的塌陷和粘合剂层变形所引起的。

意义

结果证实，通过牙髓地板剥离，树脂复合材料修复体的咬合收缩位移显着降低。最近的体外研究似乎表明，可以通过使用目前可用的最精确的口腔内扫描仪检测到收缩位移的减少。因此，经过临床验证，树脂复合材料修复体的咬合位移可用于评估其界面完整性。