College of Dentistry, University of Tennessee Health Science Center, Memphis, TN, USA.
Dent Mater. 2013 May;29(5):573-9. doi: 10.1016/j.dental.2013.03.006. Epub 2013 Mar 26.
Polymerization of composite restorations causes shrinkage, which deforms and thus stresses restored teeth. This shrinkage deformation, however, has been shown to decrease over time. The objective was to investigate whether this reduction was caused by hygroscopic expansion or stress relaxation of the composite/tooth complex.
Extracted molars were mounted in rigid stainless steel rings with four spherical reference areas. Twelve molars were prepared with large mesioocclusodistal slots, etched, bonded, and restored with a composite material (Filtek Supreme, 3M ESPE) in two horizontal layers. Ten intact molars were the controls. The teeth were stored either in deionized water or silicone oil. They were scanned after preparation (baseline), restoration (0-week), and after 1, 2, and 4 weeks storage. Scanned tooth surfaces were aligned with the baseline using the unchanged reference areas. Cuspal flexure was calculated from lingual and buccal surface deformation. To verify that the restorations had remained bonded, dye penetration at the interfaces was assessed using basic fuchsin dye. Statistical assessment was done by ANOVA followed by Student-Newman-Keuls post hoc test (p=0.05).
Substantial cuspal contraction was found for restored teeth after the composite was cured (13-14 μm cuspal flexure). After 4 weeks cuspal contraction decreased significantly for restored teeth stored in water (7.3 ± 3.2) but not for those stored in silicone oil (11.4 ± 5.0). Dye penetration of the occlusal interface was minimal in both groups (106 ± 87 and 21 ± 28 μm in water and silicone oil, respectively).
The results suggest that hygroscopic expansion was the main mechanism for shrinkage stress compensation.
复合材料的聚合会导致收缩，从而使修复的牙齿变形并产生应力。然而，这种收缩变形会随着时间的推移而减小。本研究旨在探讨这种减少是由于复合材料/牙齿复合物的吸湿膨胀还是应力松弛引起的。
将提取的磨牙用带有四个球形参考区域的刚性不锈钢环固定。12 颗磨牙制备有大的近远中向槽，酸蚀、粘结，并用复合材料（Filtek Supreme，3M ESPE）在两个水平层中修复。10 颗完整的磨牙作为对照。牙齿分别储存在去离子水或硅油中。在制备后（基线）、修复后（0 周）以及储存 1、2 和 4 周后进行扫描。使用未改变的参考区域对扫描后的牙面与基线进行对齐。从颊舌面的变形计算牙尖的挠曲。为了验证修复体仍然粘结，使用碱性品红染料评估界面处的染料渗透。使用方差分析（ANOVA） followed by Student-Newman-Keuls 事后检验（p=0.05）进行统计评估。
在复合材料固化后，修复后的牙齿发现有明显的牙尖收缩（13-14 μm 牙尖挠曲）。在水储存 4 周后，修复后的牙齿牙尖收缩显著减少（7.3 ± 3.2），而在硅油储存中则没有减少（11.4 ± 5.0）。在两组中，牙合面界面的染料渗透都很小（水和硅油中分别为 106 ± 87 μm 和 21 ± 28 μm）。
结果表明，吸湿膨胀是收缩应力补偿的主要机制。
