Yamamoto Takatsugu, Ferracane Jack L, Sakaguchi Ronald L, Swain Michael V
Department of Operative Dentistry, Tsurumi University School of Dental Medicine, 2-1-3, Tsurumi, Tsurumi-ku, Yokohama, Kanagawa 230-8501, Japan.
Dent Mater. 2009 Apr;25(4):543-50. doi: 10.1016/j.dental.2008.10.008. Epub 2008 Dec 18.
Polymerization contraction of dental composite produces a stress field in the bonded surrounding substrate that may be capable of propagating cracks from pre-existing flaws. The objectives of this study were to assess the extent of crack propagation from flaws in the surrounding ceramic substrate caused by composite contraction stresses, and to propose a method to calculate the contraction stress in the ceramic using indentation fracture.
Initial cracks were introduced with a Vickers indenter near a cylindrical hole drilled into a glass-ceramic simulating enamel. Lengths of the radial indentation cracks were measured. Three composites having different contraction stresses were cured within the hole using one- or two-step light-activation methods and the crack lengths were measured. The contraction stress in the ceramic was calculated from the crack length and the fracture toughness of the glass-ceramic. Interfacial gaps between the composite and the ceramic were expressed as the ratio of the gap length to the hole perimeter, as well as the maximum gap width.
All groups revealed crack propagation and the formation of contraction gaps. The calculated contraction stresses ranged from 4.2 MPa to 7.0 MPa. There was no correlation between the stress values and the contraction gaps.
This method for calculating the stresses produced by composites is a relatively simple technique requiring a conventional hardness tester. The method can investigate two clinical phenomena that may occur during the placement of composite restorations, i.e. simulated enamel cracking near the margins and the formation of contraction gaps.
牙科复合材料的聚合收缩会在粘结的周围基底中产生应力场，该应力场可能会使预先存在的缺陷引发裂纹扩展。本研究的目的是评估由复合材料收缩应力导致的周围陶瓷基底中缺陷的裂纹扩展程度，并提出一种使用压痕断裂来计算陶瓷中收缩应力的方法。
在模拟牙釉质的玻璃陶瓷上钻出的圆柱孔附近，用维氏压头引入初始裂纹。测量径向压痕裂纹的长度。使用一步或两步光固化方法在孔内固化三种具有不同收缩应力的复合材料，并测量裂纹长度。根据裂纹长度和玻璃陶瓷的断裂韧性计算陶瓷中的收缩应力。复合材料与陶瓷之间的界面间隙用间隙长度与孔周长的比值以及最大间隙宽度表示。
所有组均显示出裂纹扩展和收缩间隙的形成。计算出的收缩应力范围为4.2MPa至7.0MPa。应力值与收缩间隙之间没有相关性。
这种计算复合材料产生的应力的方法是一种相对简单的技术，只需使用传统的硬度测试仪。该方法可以研究在复合修复体放置过程中可能出现的两种临床现象，即边缘附近模拟牙釉质开裂和收缩间隙的形成。
