Physicomechanical and thermal analysis of bulk-fill and conventional composites

Abstract The aim of this study was to evaluate the degree of conversion (DC) and the thermal stability of bulk-fill and conventional composite resins. Eleven composite resin samples were prepared to evaluate the DC, Vickers microhardness (VMH), mass and residue/particle loss, glass transition temperature (Tg), enthalpy, and linear coefficient of thermal expansion (CTE) using infrared spectroscopy (FTIR), microdurometer analyses, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dilatometry (DIL). The data were subjected to statistical analysis, with a significance level of 95%. DC and VMH were not influenced by the polymerized side of the sample, and statistical differences were recorded only among the materials. Decomposition temperature, melting, and mass and residue loss were dependent on the material and on the evaluation condition (polymerized and non-polymerized). Tg values were similar between the composites, without statistically significant difference, and CTE ranged from 10.5 to 37.1 (10-6/°C), with no statistical difference between the materials. There was a moderate negative correlation between CTE and the % of load particles, by weight. Most resins had a DC above that which is reported in the literature. TGA, Tg, and CTE analyses showed the thermal behavior of the evaluated composites, providing data for future research, assisting with the choice of material for direct or semidirect restorations, and helping choose the appropriate temperature for increasing the DC of such materials.

摘要
本研究旨在评估大块充填复合树脂（bulk-fill）与传统复合树脂的转化率（degree of conversion, DC）及热稳定性。我们制备了11组复合树脂样品，通过红外光谱法（infrared spectroscopy, FTIR）、显微硬度计分析、热重分析（thermogravimetric analysis, TGA）、差示扫描量热法（differential scanning calorimetry, DSC）及热膨胀分析法（dilatometry, DIL），对其DC、维氏显微硬度（Vickers microhardness, VMH）、质量与残渣/颗粒流失量、玻璃化转变温度（glass transition temperature, Tg）、焓及线性热膨胀系数（linear coefficient of thermal expansion, CTE）开展检测。所得数据采用统计学分析，显著性水平设定为95%。
结果显示，DC与VMH不受样品聚合面的影响，仅在不同材料间存在统计学差异；分解温度、熔融行为以及质量与残渣流失量均受材料类型及检测状态（聚合与未聚合）的影响。两类复合树脂的Tg值相近，无统计学显著性差异；CTE范围为10.5~37.1（10^-6/℃），不同材料间无统计学差异。CTE与填料颗粒的质量占比呈中度负相关。多数树脂的DC高于文献报道值。TGA、Tg及CTE分析明确了受试复合树脂的热行为，可为后续研究提供数据支持，辅助直接或半直接修复体的材料选择，并为提升此类材料DC的适宜温度选择提供参考。