Is there correlation between polymerization shrinkage, gap formation, and void in bulk fill composites? A μCT study

Abstract: This in vitro study aimed to evaluate the volume of polymerization shrinkage (VS), gap (VG), and void (VV) using computerized microtomography (μCT) in bulk fill resin composites and conventional class I restorations, and to establish a correlation between these factors. Class I cavities (4 x 5 x 4 mm), C-factor = 4.2, were performed on caries-free human third molars and randomly divided into five groups (n = 6): FSI (Filtek Supreme XTE incremental insertion); FSS [(Filtek Supreme XTE single insertion(SI)]; TBF [(Tetric Bulk Fill: SI and manual filling (MF)]; SFM (Sonic Fill: SI/MF); and SFS (SonicFill: SI and sonic filling). The teeth were scanned and analyzed by μCT at T0, after filling the cavity with resin, and at T1, after polymerization for VG and VV, and for VS (T1-T0). There was statistically significant difference in VS in μCT for the FSI and FSS groups and between SFS and FSS as well as some difference in VV for FSI and bulk fill resin composites and no difference in VG between the conventional technique and bulk fill composites. Bulk fill resin composites presented similar VS and gap formation to those of incrementally inserted conventional resin composites. There is a moderate and weak positive correlation between polymerization shrinkage and gap formation and void, respectively. The final gap formation was more dependent on the initial gap than on polymerization shrinkage or void volume.

摘要：本体外研究旨在通过显微计算机断层扫描（computerized microtomography，μCT）评估大块充填树脂复合材料（bulk fill resin composites）与传统I类洞修复体的聚合收缩体积（volume of polymerization shrinkage, VS）、间隙体积（volume of gap, VG）及孔隙体积（volume of void, VV），并明确上述指标间的相关性。我们于无龋人类第三磨牙上制备窝洞系数（C-factor）为4.2的I类洞（4×5×4 mm），并随机分为5组（每组n=6）：FSI组（Filtek Supreme XTE分层充填）、FSS组（Filtek Supreme XTE单次充填（SI））、TBF组（Tetric Bulk Fill：单次充填（SI）与手动充填（MF））、SFM组（Sonic Fill：单次充填/手动充填）及SFS组（SonicFill：单次充填与超声充填）。分别于树脂充填完成即刻（T0）及聚合固化完成后（T1）通过μCT扫描分析VG与VV，并通过T1与T0的差值计算VS。μCT分析结果显示，FSI组与FSS组的VS存在统计学差异，SFS组与FSS组的VS亦存在显著差异；FSI组与大块充填树脂复合材料的VV存在一定差异，而传统技术与大块充填复合材料的VG无显著差异。大块充填树脂复合材料的VS与间隙形成量与分层充填的传统树脂复合材料相近。聚合收缩与间隙形成、聚合收缩与孔隙分别呈中等强度及弱强度正相关。最终间隙形成量更依赖于初始间隙，而非聚合收缩或孔隙体积。