Objective

The aim of the study was to determine the effects of ultra-fast (3 s) light-curing on the viscoelastic behaviour at clinically relevant frequencies, and cell toxicity, in a resin-based composite (RBC) with reversible addition-fragmentation-chain transfer (RAFT) mediated polymerization.

Methods

Three different protocols were used to cure cylindrical samples (height = 4 mm, ϴ = 5 mm), including ultra-fast (3s) cure with high radiant emittance, 10 s and 20 s cure with moderate radiant emittance. The properties of the light curing device were evaluated in all curing protocols by spectrophotometry up to an exposure distance of 10 mm. The light transmission through the samples was determined in real-time with the same spectrophotometer. Absorbance was calculated as a function of wavelength. The quasi-static (indentation hardness/H_IT, indentation modulus/E_IT) and viscoelastic (storage modulus/E′, loss modulus/E″, loss factor/tan δ) material behavior was determined in an instrumented indentation test with a DMA (Dynamic Mechanical Analysis) module for 10 frequencies (0.5–5 Hz) by profiling the center of the samples in 330 μm steps from top to bottom. Cellular toxicity on human gingival fibroblast (HGF-1) was assessed using a WST-1 colorimetric assay after incubation time of up to 3 months. One and multiple-way analysis of variance (ANOVA) with Tukey honestly significant difference (HSD) post-hoc tests (α = 0.05) were applied.

Results

The irradiance transmitted through a 4 mm high sample was less than 7% of the incident irradiance, and the absorbance was similar for all curing protocols, showing a decrease with wavelength. Similar quasi-static and viscoelastic parameters were observed regardless of the curing protocol. H_IT increased slightly and E_IT, E′, E″ and tan δ decreased with frequency. Occasionally, slightly higher confidence intervals were observed for the ultra-fast curing group, which were related to a potential accumulation of stress. The curing protocol had no effect on cell viability (p = 0.326) but the eluate age (p < 0.001, η_P² = 0.879) did. None of the groups showed cell toxicity at any point in time with respect to the corresponding negative control.

Conclusions

The ultra-fast curing with high irradiance induced no cell toxicity and an equivalent viscoelastic behavior as with conventional curing protocols in a RAFT-modified RBC.

中文翻译：

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超快（3 秒）光固化对具有 RAFT 介导聚合的牙科树脂基复合材料中细胞毒性和粘弹性行为的影响

客观的

该研究的目的是在具有可逆加成断裂链的树脂基复合材料 (RBC) 中确定超快 (3 s) 光固化对临床相关频率下的粘弹性行为和细胞毒性的影响转移（RAFT）介导的聚合。

方法

使用三种不同的协议来固化圆柱形样品（高度 = 4 mm，ϴ = 5 mm），包括具有高辐射发射率的超快速 (3s) 固化、具有中等辐射发射率的 10 秒和 20 秒固化。光固化装置的性能在所有固化方案中通过分光光度法进行评估，曝光距离可达 10 毫米。使用相同的分光光度计实时测定通过样品的透光率。吸光度计算为波长的函数。准静态（压痕硬度/H _IT，压痕模量/E _IT) 和粘弹性（储能模量/E'、损耗模量/E”、损耗因子/tanδ）材料行为是在仪器压痕测试中用 DMA（动态机械分析）模块在 10 个频率（0.5-5Hz）下确定的从上到下以 330 μm 的步长对样品中心进行轮廓分析。在长达 3 个月的孵育时间后，使用 WST-1 比色法评估对人牙龈成纤维细胞 (HGF-1) 的细胞毒性。应用了具有 Tukey 诚实显着差异 (HSD) 事后检验 (α = 0.05) 的单因素和多因素方差分析 (ANOVA)。

结果

透射过 4 毫米高样品的辐照度小于入射辐照度的 7%，所有固化方案的吸光度都相似，显示出随波长的降低。无论固化方案如何，都观察到类似的准静态和粘弹性参数。H _IT略有增加，E _IT、E'、E" 和 tan δ 随频率降低。有时，观察到超快速固化组的置信区间略高，这与潜在的压力积累有关。固化方案对细胞活力没有影响 (p = 0.326)，但洗脱液年龄 (p < 0.001, η _P ²  = 0.879) 有影响。相对于相应的阴性对照，没有任何组在任何时间点显示出细胞毒性。

结论

高辐照度下的超快速固化不会引起细胞毒性，并且与 RAFT 修饰的 RBC 中的常规固化方案具有相同的粘弹性行为。