Objective

To determine the post-curing in six commercial contemporary resin-based composites (RBCs) using axial shrinkage, the degree of conversion, and Vickers hardness.

Methods

Five Bulk Fill and one conventional RBCs from three companies were selected with a wide range of filler volume content. The axial shrinkage of samples that were 1.00 mm thick by 9–10 mm diameter was measured using a modified bonded disk method over a time between 15 h and 19 h at temperatures of 26 °C and 34 °C (mouth temperature). The degree of conversion (DC) was collected continuously for 10 min using mid-infrared spectroscopy in the attenuated total reflectance geometry. Vickers hardness was measured at 1 h post-irradiation using a load of 300 gf. For all three tests, the samples were irradiated at five exposure times, 20, 5, 3, 1.5 and 1 s with a light curing unit radiant exitance of 1.1 W/cm². Three samples (n = 3) were used for each experimental condition.

Results

After light exposure, the axial shrinkage and degree of conversion exhibited a functional time dependence that was proportional to the logarithm of time. This suggests an out-of-equilibrium polymer composite glass that is transitioning to thermal equilibrium. At a sufficiently long time and among the RBCs investigated, the shrinkage related physical aging rate was found to vary between 1.34 and 2.00 μm/log(t). The rate was a function of the filler content. Furthermore, 15 h after light exposure, the post-curing shrinkage was estimated to be an additional 22.5% relative to the shrinkage at 100 s for one RBC at T = 34 °C. The hardness in the photo-cured RBC was varied by using different light exposure times. The first two experimental techniques show that the higher the initial DC 10 min after light exposure, the smaller is the post-curing shrinkage related and DC related physical aging rates. A direct correlation was observed between the shrinkage related and the DC related physical aging rates.

Significance

Post-curing shrinkage should be evaluated for longer than 1 h. The post-curing shrinkage 15 h after light exposure in dental RBCs can be appreciable. The long-term development of built-in stress within the tooth wall structure may shorten the restoration’s lifespan.

中文翻译：

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牙科树脂基复合材料的后固化

客观的

为了确定使用轴向收缩率，转化度和维氏硬度的六种现代当代树脂基复合材料（RBC）的后固化。

方法

选择了三家公司的五种散装填充料和一种传统的RBC，它们具有广泛的填充物体积含量。使用改良的粘合盘方法，在26°C和34°C（口温）的温度下，在15 h至19 h的时间内，测量了1.00 mm厚，直径9-10 mm的样品的轴向收缩率。使用中红外光谱法在衰减的总反射率几何结构中连续收集转化度（DC），持续10分钟。在辐射后1小时使用300gf的载荷测量维氏硬度。对于所有三个测试，分别在20、5、3、1.5和1 s的五个曝光时间照射样品，光固化单元的辐射出射率为1.1 W / cm ²。每个实验条件使用三个样本（n = 3）。

结果

曝光后，轴向收缩率和转化率表现出与时间的对数成比例的功能时间依赖性。这表明正在转变为热平衡的不平衡聚合物复合玻璃。在足够长的时间内，在所研究的RBC中，发现与收缩有关的物理老化速率在1.34和2.00μm/ log（t）之间变化。该速率是填料含量的函数。此外，在曝光后15小时，相对于T = 34°C的一个RBC在100 s时的收缩率，估计固化后的收缩率是22.5％。通过使用不同的曝光时间来改变光固化的RBC中的硬度。前两项实验技术表明，曝光10分钟后的初始DC越高，固化后收缩率和直流相关物理老化率越小。观察到与收缩相关的和与DC相关的物理老化率之间的直接相关。

意义

固化后收缩应评估超过1小时。牙科RBC暴露15 h后的固化后收缩率是可观的。牙齿壁结构内的内置应力的长期发展可能会缩短修复体的寿命。