Ohlmann Brigitte, Gruber Rudolf, Eickemeyer Grit, Rammelsberg Peter
Department of Prosthodontics, University of Heidelberg. Heidelberg, Germany.
J Prosthet Dent. 2008 Sep;100(3):211-9. doi: 10.1016/S0022-3913(08)60180-8.
Although composite resin materials are used for posterior crown restorations, the influence of preparation design, material thickness, convergence angle, and method of cementation on fracture resistance remains unclear.
The purpose of this in vitro study was to test the hypothesis that minimal preparation designs provide an acceptable level of fracture resistance for posterior composite resin crowns.
Nonreinforced Artglass composite resin crowns (n=128) were fabricated on human molars in 16 test groups (n=8). Axial tooth preparation included a 1-mm-deep shoulder or a 0.5-mm chamfer preparation, whereas occlusal reduction was either 0.5 mm or 1.3 mm. The total angle of convergence was 4 or 11 degrees and the crowns were cemented either with glass ionomer cement (Ketac Cem) or resin cement (2bond2). After 10,000 thermal cycles, crowns were vertically loaded until failure occurred; load was measured in newtons. Statistical analysis was performed by a 4-way ANOVA (alpha=.05).
Statistical analysis revealed significant effects of occlusal thickness (P<.001), cement (P<.001), preparation design (P=.011), and convergence angle (P=.001) on the fracture resistance of the composite crowns. For composite resin crowns with an occlusal thickness of 0.5 mm, the resistance to fracture was lower than for crowns with a 1.3-mm thickness. Fracture resistance was greater when resin cement was used, and greater for the chamfer finish line than for the shoulder finish line. Use of a greater total convergence angle reduced fracture resistance.
Fracture resistance of composite resin crowns was significantly improved by increasing the occlusal thickness of the crowns, by using resin cement, and by reducing the total convergence angle.
尽管复合树脂材料用于后牙冠修复，但预备设计、材料厚度、聚合角和粘结方法对抗折性的影响仍不明确。
本体外研究的目的是检验以下假设，即最小化预备设计可为后牙复合树脂冠提供可接受的抗折水平。
在16个试验组（每组n = 8）的人类磨牙上制作128个非增强型Artglass复合树脂冠。轴向牙体预备包括1mm深的肩台或0.5mm的倒角预备，而咬合面磨除量为0.5mm或1.3mm。总聚合角为4度或11度，冠用玻璃离子水门汀（Ketac Cem）或树脂水门汀（2bond2）粘结。经过10000次热循环后，垂直加载冠直至发生破坏；以牛顿为单位测量载荷。采用四因素方差分析进行统计分析（α = 0.05）。
统计分析显示，咬合面厚度（P < 0.001）、粘结剂（P < 0.001）、预备设计（P = 0.011）和聚合角（P = 0.001）对复合树脂冠的抗折性有显著影响。对于咬合面厚度为0.5mm的复合树脂冠，其抗折性低于厚度为1.3mm的冠。使用树脂水门汀时抗折性更高，且倒角边缘线的抗折性大于肩台边缘线。总聚合角越大，抗折性越低。
通过增加冠的咬合面厚度、使用树脂水门汀和减小总聚合角，可显著提高复合树脂冠的抗折性。
