Light Transmittance and Depth of Cure of a Bulk Fill Composite Based on the Exposure Reciprocity Law

Abstract The objective of this study was to evaluate the effect of the exposure reciprocity law of a multi-wave light-emitting diode (LED) on the light transmittance (LT), depth of cure (DOC) and degree of conversion in-depth (DC) of a bulk fill composite. A bulk fill composite (EvoCeram® bulk fill, Ivoclar Vivadent) was photoactivated using the multi-wave LED (VALO™ Cordless, Ultradent). The LED was previously characterized using a spectrophotometer to standardize the time of exposure when using the Standard or Xtra-Power modes with the same radiant exposure of 20J/cm2. LT was evaluated through samples of the bulk fill composite every millimeter till 4 mm in-depth. DOC was evaluated according to the ISO 4049. DC of the central longitudinal cross-section from each sample of the DOC test was mapped using FT-NIR microscopy. Data were statistically analyzed according to the experimental design (α=0.05; ß=0.2). The radiant exposure in the violet wavelength range for Standard and Xtra-Power was 4.5 and 5.0 J/cm2, respectively; for the blue wavelength range the radiant exposure for Standard and Xtra-Power was 15.5 and 15.0 J/cm2, respectively. There was no statistical difference in the DOC using Standard or Xtra-Power light-curing modes, but the DOC was lower than the claimed by the manufacturer (4 mm). The DC was not significantly affected by the light-curing mode up to 4 mm in depth (p>0.05). According to exposure reciprocity law, the reduction in exposure time using the same radiant exposure did not affect the depth of cure of the bulk fill composite.

摘要 本研究旨在评估多波长发光二极管（multi-wave light-emitting diode, LED）的曝光互易律对大块充填复合树脂的透光率（light transmittance, LT）、固化深度（depth of cure, DOC）及深层转化率（degree of conversion in-depth, DC）的影响。实验选用Ivoclar Vivadent公司的EvoCeram®大块充填复合树脂，采用Ultradent公司的VALO™无绳多波长LED进行光活化处理。此前已通过分光光度计对该LED进行表征，以标准化标准模式与Xtra-Power模式下的曝光时间，确保两种模式的辐射曝光量均为20J/cm²。透光率检测通过对深度每间隔1mm的大块充填复合树脂样本进行测试，直至4mm深度。固化深度依据ISO 4049标准开展评估。针对固化深度测试的每个样本的中央纵向切面，采用傅里叶变换近红外显微术（FT-NIR microscopy）绘制其转化率分布图谱。数据按照实验设计进行统计学分析（α=0.05；β=0.2）。标准模式与Xtra-Power模式下，紫光波段的辐射曝光量分别为4.5 J/cm²与5.0 J/cm²；蓝光波段的辐射曝光量则分别为15.5 J/cm²与15.0 J/cm²。采用两种光固化模式时，固化深度无统计学差异，但实测固化深度低于制造商宣称的4mm。在0~4mm深度范围内，光固化模式对深层转化率无显著影响（p>0.05）。根据曝光互易律，在相同辐射曝光量下缩短曝光时间，不会对大块充填复合树脂的固化深度产生影响。