Pfeifer Carmem Silvia Costa, Braga Roberto Ruggiero, Ferracane Jack Liborio
Carmem Silvia Costa Pfeifer, graduate student, University of São Paulo, School of Dentistry, Department of Dental Materials, São Paulo, Brazil.
Oper Dent. 2006 Sep-Oct;31(5):610-5. doi: 10.2341/05-118.
Evaluate the influence of pulse-delay curing on shrinkage stress and microhardness of 2 restorative composites (Herculite XRV and Tetric Ceram).
Two pulse irradiances (500 and 100 mW/cm2) were applied for 1 or 5 seconds, respectively (radiant exposure = 0.5 J/cm2). In both cases, photoactivation was completed applying 500 mW/cm2 for 39 seconds after a delay time of 0, 1 or 3 minutes. Shrinkage stress was monitored for 10 minutes in specimens 5-mm in diameter by 1-mm in height. Knoop hardness (KHN) was used to estimate the degree of conversion 10 minutes after photoactivation and after 48 hours of storage in distilled water (37 degrees C) in specimens with similar geometry and dimensions. Additional KHN readings after 4 8 hoursof storage in ethanol (37 degrees C) were used to estimate polymer structure. The results were evaluated using ANOVA/Tukey test and Student t-test (a=0.05).
For Tetric Ceram, 3-minute delay led to stress reduction compared to continuous curing at 500 mW/cm2 (4.7+/-0.6 MPa and 7.0+/-1.3 MPa, respectively). At 100 mW/cm2, 1 minute delay was enough to cause significant stress reduction (5.2+/-0.5 MPa). For Herculite, the pulse with 3 minute delay led to stress reduction compared to no delay for both irradiances (100 mW/cm2: 6.3+/-0.5 MPa and 7.8+/-0.8 MPa, respectively; 500 mW/cm2: 6.4+/-0.3 MPa and 7.8+/-0.7 MPa, respectively). At 10 minutes, only small differences in microhardness were observed for both materials. No differences were found after water and ethanol storage (p>0.05).
The composites behaved differently when subjected to pulse curing. Stress reduction was influenced by delay time but not by pulse irradiance. KHN results suggest that similar degrees of conversion and polymer structure were achieved with the photoactivation methods tested.
评估脉冲延迟固化对两种修复性复合材料（Herculite XRV和Tetric Ceram）收缩应力和显微硬度的影响。
分别以两种脉冲辐照度（500和100 mW/cm²）施加1秒或5秒（辐射暴露量=0.5 J/cm²）。在这两种情况下，在延迟0、1或3分钟后，再以500 mW/cm²照射39秒以完成光活化。对直径5毫米、高1毫米的试样监测10分钟的收缩应力。用努氏硬度（KHN）评估光活化10分钟后以及在37℃蒸馏水中储存48小时后，具有相似几何形状和尺寸的试样的固化程度。在37℃乙醇中储存48小时后的额外KHN读数用于评估聚合物结构。结果采用方差分析/图基检验和学生t检验进行评估（α=0.05）。
对于Tetric Ceram，与500 mW/cm²连续固化相比，3分钟延迟导致应力降低（分别为4.7±0.6 MPa和7.0±1.3 MPa）。在100 mW/cm²时，1分钟延迟足以显著降低应力（5.2±0.5 MPa）。对于Herculite，与无延迟相比，3分钟延迟脉冲导致两种辐照度下的应力均降低（100 mW/cm²时分别为6.3±0.5 MPa和7.8±0.8 MPa；500 mW/cm²时分别为6.4±0.3 MPa和7.8±0.7 MPa）。10分钟时，两种材料仅观察到显微硬度的微小差异。在水和乙醇储存后未发现差异（p>0.05）。
复合材料在脉冲固化时表现不同。应力降低受延迟时间影响，但不受脉冲辐照度影响。KHN结果表明，所测试的光活化方法实现了相似的固化程度和聚合物结构。
