Department of Restorative Dentistry, Division of Dental Materials, Piracicaba Dental School, State University of Campinas, UNICAMP, Piracicaba, SP, Brazil.
J Dent. 2012 Oct;40(10):802-9. doi: 10.1016/j.jdent.2012.05.014. Epub 2012 Jun 9.
To evaluate the effects of four different light-curing protocols on the microtensile bond strength (μTBS), ultimate tensile strength (UTS), Knoop micro-hardness (KH) and cross-link density (CLD) of a nano-filled resin composite.
Filtek Supreme XT (3M-ESPE) was used for the entire experiments following four light-curing approaches: ST, standard irradiance; HI, high irradiance; PD, pulse delay; SS, soft start. The specimens were submitted to different storage periods (24h or 6 months), cut into match-sticks and subsequently submitted to μTBS testing. Hourglass specimens were also prepared for UTS and KH. Cylindrical specimens were prepared for the CLD evaluation after absolute ethanol challenge. The results were statistically analyzed with a two-way ANOVA and Tukey's test (α=0.05).
For UTS and KH, continuous irradiance (PD and SS) induced statistically higher results (p<0.05) both after 24h and 6 months of water storage compared to ST and HI groups. However, a drop in UTS and KH was obtained after 6 months in all groups. The μTBS was not affected by the different light-curing approaches and, no statistical differences (p>0.05) were observed between 24h and 6 months storage. The CLD evaluation showed a statistical drop in KH after 24h of ethanol storage for PD and SS (step-curing protocols) compared to those attained in continuous mode (ST and HI).
The soft-start mode may improve the UTS and KH of nano-filled resin composites without compromising the resin-dentine μTBS. However, both the step-curing protocols may reduce the cross-link density of the composite polymeric network.
High irradiances photo-polymerization may be adequate for direct aesthetic restorations such as veneers and onlays. Meanwhile, the soft start protocol would seem more appropriate for the photo-polymerization of high c-factors class I and II restorations.
评估四种不同光固化方案对纳米填充树脂复合材料的微拉伸结合强度（μTBS）、极限拉伸强度（UTS）、努普微硬度（KH）和交联密度（CLD）的影响。
采用 Filtek Supreme XT（3M-ESPE）进行整个实验，采用四种光固化方法：ST，标准照度；HI，高照度；PD，脉冲延迟；SS，软启动。将试件分别进行 24h 或 6 个月的不同储存期，切割成火柴棒，然后进行 μTBS 测试。也制备了沙漏试件进行 UTS 和 KH 测试。在绝对乙醇挑战后，制备圆柱形试件进行 CLD 评估。采用双向方差分析和 Tukey 检验（α=0.05）对结果进行统计学分析。
对于 UTS 和 KH，连续光照（PD 和 SS）在 24h 和 6 个月水储存后，与 ST 和 HI 组相比，统计学上均产生更高的结果（p<0.05）。然而，所有组在 6 个月后 UTS 和 KH 均有所下降。不同光固化方法对 μTBS 没有影响，在 24h 和 6 个月储存之间未观察到统计学差异（p>0.05）。CLD 评估显示，与连续模式（ST 和 HI）相比，PD 和 SS（分步固化方案）在 24h 乙醇储存后 KH 的硬度明显下降。
软启动模式可以提高纳米填充树脂复合材料的 UTS 和 KH，而不会影响树脂-牙本质的 μTBS。然而，两种分步固化方案可能会降低复合材料聚合网络的交联密度。
高照度光聚合对于贴面和嵌体等直接美学修复可能是足够的。同时，软启动方案对于高 c 因素 I 类和 II 类修复的光聚合似乎更为合适。
