Objective

It is known that after light-initiated free radical polymerization of a dimethacrylate monomer system, the curing continues for some period of time after the curing light emission has stopped (so-called delayed post-curing stage, DPCS). It is also known that during free radical polymerization, the presence of oxygen effectively inhibits polymerization of monomers. However, less is known of the influence of oxygen inhibition of light initiated polymerization during the DPCS. The aim of this study was to determine some polymerization related properties of a resin system during the DPCS.

Methods

Monomer systems of BisGMA-TEGDMA (60/40%) with light sensitive initiator-activator (camphorquinone-amine) system were polymerized by light-initiation (wavelength average 430–480 nm) with a radiation intensity of 1200 mW/mm² for 20 s on the ATR sensor of the fourier transform infrared (FTIR) spectrometer. After light curing, the samples were divided into two groups: the DPCS stage was allowed to continue in air (O₂-exposed group) or the samples were protected from the direct effect of air (O₂-protected group). The degree of monomer conversion (DC%) was monitored from the sample surface up to 360 min from both groups of samples (n = 6). Sample surfaces were additionally analyzed for surface microhardness (VHN) at four time-points corresponding to time-points of the DC% measurement (n = 6).

Results

After ending the light-curing of 20 s, i.e. during the DPCS, the DC% still increased from 50% to 65% in the O₂-protected group, whereas no increase was seen in the O₂-exposed group. Surface microhardness increased from 2.99 to 9.10 VHN of the O₂-protected samples and to 4.80 of the O₂-exposed samples during a 6-h period. Surface microhardness differed significantly between the groups (p < 0.005). There was significant correlation between the microhardness and DPCS (O₂-protected r = 0.950; O₂-exposed r = 0.940, p < 0.001). A correlation was also found between degree of conversion values and DPCS time (O₂-protected r = 0.941; for O₂-exposed r = 0.780, p < 0.001).

Significance

The results of this study suggested that O₂-inhibition of free radical polymerization of dimethacrylate resin occurred after ending the curing light emission. This correlated with a lower surface microhardness of the polymer when the DPCS continued under air-exposure.

中文翻译：

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二甲基丙烯酸酯树脂的延迟后固化阶段和自由基聚合的氧抑制作用

客观的

已知在二甲基丙烯酸酯单体体系的光引发的自由基聚合之后，在固化发光停止之后，固化持续一段时间（所谓的延迟后固化阶段，DPCS）。还已知在自由基聚合过程中，氧的存在有效地抑制了单体的聚合。然而，对于DPCS期间光引发的聚合的氧抑制的影响知之甚少。这项研究的目的是确定在DPCS期间树脂体系的一些与聚合相关的特性。

方法

BisGMA-TEGDMA（60/40％）的单体系统与光敏引发剂-活化剂（樟脑醌-胺）系统通过光引发（波长平均430-480 nm）聚合，辐射强度为1200 mW / mm ²，共20个在傅立叶变换红外（FTIR）光谱仪的ATR传感器上。光固化后，将样品分为两组：允许DPCS阶段在空气中继续（暴露于O _2的组）或保护样品免受空气的直接影响（O ₂-受保护的团体）。从两组样品（n = 6）直至360分钟的样品表面监测单体转化率（DC％）。另外在四个时间点分析样品表面的表面显微硬度（VHN），这四个时间点对应于DC％测量的时间点（n = 6）。

结果

在结束20秒的光固化之后，即在DPCS期间，在O ₂保护的组中DC％仍然从50％增加到65％，而在暴露于O _2的组中没有看到增加。在6小时内，表面显微硬度从O ₂保护的样品的2.99 VHN增加到9.10 VHN，在O ₂暴露的样品中增加到4.80 VHN 。两组之间的表面显微硬度差异显着（p <0.005）。显微硬度与DPCS之间存在显着相关性（O ₂保护的r = 0.950；暴露于O _2的r = 0.940，p <0.001）。还发现转化度值与DPCS时间之间存在相关性（O ₂保护的r = 0.941；对于O ₂暴露r = 0.780，p <0.001）。

意义

该研究结果表明，在结束固化发光之后，O ₂抑制了二甲基丙烯酸酯树脂的自由基聚合。当DPCS继续暴露在空气中时，这与聚合物的较低的表面显微硬度有关。