Calheiros Fernanda C, Braga Roberto R, Kawano Yoshio, Ballester Rafael Y
Department of Dental Materials, School of Dentistry, University of São Paulo, Av. Prof. Lineu Prestes, 2227, São Paulo, SP 05508-900, Brazil.
Dent Mater. 2004 Dec;20(10):939-46. doi: 10.1016/j.dental.2004.03.003.
To verify the relationship between contraction stress and degree of conversion (DC) in different composites (Filtek Z250, Filtek A110, Tetric Ceram and Heliomolar).
For the contraction stress test, composite (2 mm thick) was applied between two 5-mm diameter glass rods, mounted in a tensilometer. DC was determined by Infrared Photoacoustic spectroscopy in specimens with similar dimensions and geometry, submitted to identical curing conditions. Specimens were exposed to different energy densities (4.5, 13.5, 27.0, 54.0 and 108.0 J/cm2) by varying exposure time. Contraction stress and DC were recorded 10 min after the beginning of photoactivation. Results were analyzed by ANOVA/Tukey's test and regression analysis.
For contraction stress, the interaction between composite and energy density was significant. Stress values ranged between 0.6+/-0.2 and 2.0+/-0.3 MPa at 4.5 J/cm2, 2.3+/-0.5 and 4.3+/-0.4 MPa at 13.5 J/cm2, 3.8+/-0.5 and 5.8+/-0.9 MPa at 27.0 J/cm2, 4.2+/-0.8 and 7.9+/-0.9 MPa at 54.0 J/cm2 and 6.6+/-0.8 and 8.1+/-0.9 MPa at 108.0 J/cm2. Tetric Ceram (39+/-5.8%) showed a higher average DC than the other materials. Heliomolar (28+/-5.2%) showed an average DC similar to Filtek Z250 (32+/-6.6%) and to Filtek A110 (24+/-7.5%) regardless of the energy density level. No significant increase in DC was observed above 27 J/cm2.
At high energy levels, DC had a tendency to level off earlier than contraction stress values.
Using high energy densities may cause a significant increase in stress values, without producing a significant increase in conversion.
验证不同复合材料（Filtek Z250、Filtek A110、Tetric Ceram和Heliomolar）的收缩应力与固化程度（DC）之间的关系。
进行收缩应力测试时，将2毫米厚的复合材料置于两根直径5毫米的玻璃棒之间，安装在拉力计上。通过红外光声光谱法在尺寸和几何形状相似、处于相同固化条件的试样中测定DC。通过改变曝光时间使试样暴露于不同的能量密度（4.5、13.5、27.0、54.0和108.0 J/cm²）下。在光活化开始10分钟后记录收缩应力和DC。结果通过方差分析/ Tukey检验和回归分析进行分析。
对于收缩应力，复合材料与能量密度之间的相互作用显著。在4.5 J/cm²时，应力值范围为0.6±0.2至2.0±0.3 MPa；在13.5 J/cm²时，为2.3±0.5至4.3±0.4 MPa；在27.0 J/cm²时，为3.8±0.5至5.8±0.9 MPa；在54.0 J/cm²时，为4.2±0.8至7.9±0.9 MPa；在108.0 J/cm²时，为6.6±0.8至8.1±0.9 MPa。Tetric Ceram（39±5.8%）显示出比其他材料更高的平均DC。无论能量密度水平如何，Heliomolar（28±5.2%）显示出与Filtek Z250（32±6.6%）和Filtek A110（24±7.5%）相似的平均DC。在27 J/cm²以上未观察到DC有显著增加。
在高能量水平下，DC比收缩应力值更早趋于平稳。
使用高能量密度可能会导致应力值显著增加，而不会使固化程度显著提高。
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