The effects of polymerization mode and layer thickness on monomer released from bulk fill composite resins

Abstract

Background: Residual monomers released from composite resins have cytotoxic, mutagenic, and estrogenic effects. Mode of polymerization and application thickness are important for monomer release. Aims: The aim of this study was to investigate the effects of different modes of a third-generation light-curing unit (LCU) and layer thickness on residual monomer released from two different bulk-fill composite resins. A total of 80 samples were prepared for each bulk-fill composite using a mold. Each bulk-fill composite was divided into four groups according to polymerization mode (standard and extra power) and layer thickness (2 and 4 mm). In addition, four groups were divided into four subgroups according to time periods (1 h, 24 h, 3 days, and 7 days). Methods and Material: The samples were polymerized with VALO LED device. The amount of residual monomer was measured with High-Performance Liquid Chromatography (HPLC). All statistical analyses were processed using SPSS Version 23.0. The normal distribution of data was confirmed using Kolmogorov–Smirnov Normal Distribution Test and Shapiro-Wilk Normal Distribution Test. When the distribution was normal, parametric tests, Student's t test and one-way ANOVA, were used. When the distribution was not normal, non-parametric tests, Mann–Whitney U test, and Kruskal–Wallis testwere used. Results: It was found that the standard mode of LCU produced lower amounts of TEGDMA, Bis-GMA, and UDMA in both composite materials. In addition, when the layer thickness increased, TEGDMA, Bis-GMA, and UDMA releases increased, too. Conclusions: This study revealed that the amount of residual monomers released from bulk-fill composites was affected by layer thickness and polymerization time.

Influence of Layer Thickness and Shade on the Transmission of Light through Contemporary Resin Composites

“…To prevent the cytotoxic effects that can arise from unpolymerized monomers, irradiation time needs to be expanded in the case of thicker increments. In this regard, it was shown that from photopolymerized 2 mm-thick resin composite increments, fewer monomers, such as TEGDMA, Bis-GMA, and UDMA, were released compared to thicker layers that were identically cured [54].…”

The Effect of Layer Thickness and Light Intensity on the Degree of Conversion, Microhardness and Cytotoxicity of Bulk Fill Composite Resins

“…When composite resins are not sufficiently polymerized, their physical and mechanical properties weaken and residual monomer is released into the environment. These residual monomers can cause estrogenic, genotoxic and cytotoxic effects (7). Possible toxicological reactions are evaluated in vitro using cell cultures in cytotoxicity tests.…”