Boaro Letícia Cristina Cidreira, Brandt William Cunha, Meira Josete Barbosa Cruz, Rodrigues Flávia Pires, Palin William M, Braga Roberto Ruggiero
University of Santo Amaro, Department of Dentistry, Implantology Unit, São Paulo, SP, Brazil.
University of Santo Amaro, Department of Dentistry, Implantology Unit, São Paulo, SP, Brazil.
J Dent. 2014 Feb;42(2):140-8. doi: 10.1016/j.jdent.2013.11.016. Epub 2013 Dec 1.
To determine the free surface displacement of resin-composite restorations as a function of the C-Factor, volume and substrate stiffness, and to compare the results with interfacial stress values evaluated by finite element analysis (FEA).
Surface displacement was determined by an extensometer using restorations with 4 or 6mm diameter and 1 or 2mm depth, prepared in either bovine teeth or glass. The maximum displacement of the free surface was monitored for 5 min from the start of photoactivation, at an acquisition rate of 1s(-1). Axisymmetric cavity models were performed by FEA. Structural stiffness and maximum stresses were investigated.
For glass, displacement showed a stronger correlation with volume (r=0.771) than with C-Factor (r=0.395, p<0.001 for both). For teeth, a stronger correlation was found with C-Factor (r=0.709; p<0.001) than with volume (r=0.546, p<0.001). For similar dimensions, stress and displacement were defined by stiffness. Simultaneous increases in volume and C-Factor led to increases in stress and surface displacement. Maximum stresses were located at the cavosurface angle, internal angle (glass) and at the dentine-enamel junction (teeth). The displacement of the restoration's free surface was related to interfacial stress development.
Structural stiffness seems to affect the shrinkage stress at the tooth/resin-composite interface in bonded restorations. Deep restorations are always problematic because they showed high shear stress, regardless of their width. FEA is the only tool capable of detecting shear stress due to polymerization as there is still no reliable experimental alternative.
确定树脂复合材料修复体的自由表面位移与C因子、体积和基底刚度之间的函数关系，并将结果与通过有限元分析（FEA）评估的界面应力值进行比较。
使用直径为4或6mm、深度为1或2mm的修复体，在牛牙或玻璃中制备，通过引伸计确定表面位移。从光固化开始起，以1秒^(-1)的采集速率监测自由表面的最大位移5分钟。通过有限元分析建立轴对称腔模型。研究结构刚度和最大应力。
对于玻璃，位移与体积的相关性更强（r = 0.771），而与C因子的相关性较弱（r = 0.395，两者p < 0.001）。对于牙齿，与C因子的相关性更强（r = 0.709；p < 0.001），而与体积的相关性较弱（r = 0.546，p < 0.001）。对于相似尺寸，应力和位移由刚度定义。体积和C因子同时增加会导致应力和表面位移增加。最大应力位于洞缘角、内角（玻璃）和牙本质-釉质交界处（牙齿）。修复体自由表面的位移与界面应力发展有关。
结构刚度似乎会影响粘结修复体中牙齿/树脂复合材料界面处的收缩应力。深修复体总是存在问题，因为无论其宽度如何，它们都表现出高剪切应力。由于目前仍没有可靠的实验替代方法，有限元分析是唯一能够检测聚合引起的剪切应力的工具。
