Objective

Resin-Composites are now available designed for polymerization using 3 s of intense light irradiation. The aim was to develop an experimental method to probe their surface viscoelastic integrity immediately following such rapid photo-cure via macroscopic surface indentation under constant stress as a function of time.

Methods

Two bulk-fill composites (Ivoclar AG) were studied: Tetric PowerFill (PFill) and PowerFlow (PFlow). Split molds were used to fabricate cylindrical {4 mm (dia) × 4 mm} paste specimens, irradiated at 23 °C at 0 mm from the top surface with a BluephasePowerCure LED-LCU, with 3 s or 5 s modes, emitting 3 and 2 W/cm², respectively. Post-irradiation specimens were immediately transferred to an apparatus equipped with a flat-ended indentor of 1.5 mm diameter. 14 MPa compressive stress at the indentor tip was applied centrally in < 2 min and maintained constant for 2 h. Indentation (I) magnitudes were recorded in real-time (t), with I(t) data re-expressed as % indentation relative to the 4 mm specimen height. After 2 h, the indentor was unloaded and indentation recovery was monitored for a further 2 h. Parallel sets of measurements were made where indentation was delayed for 24 h. Further measurements were made with more conventional composites: EvoCeram Bulk Fill (ECeram) and Tetric EvoFlow Bulk Fill (EFlow). These were irradiated for 20 s at 1.2 W/cm². Kinetic data were curve-fitted to exponential growth functions and key parameters analyzed by ANOVA and post-hoc tests (α = 0.05).

Results

I(t) plots looked initially similar to bulk creep/recovery: rapid deformation plus viscoelastic response; then, upon unloading: rapid (elastic) recovery followed by partial viscoelastic recovery. However, unlike multiply irradiated and stored bulk-creep specimens, the present specimens were exposed to only 3 or 5 s “occlusal” irradiation; generating “hard” surfaces. Subsequently, during the 2 h indentation, the polymer matrix network continued to harden and consolidate. Upon initial loading, I(t) reached 2–3% indentation, depending upon the formulation. Upon unloading at 2 h, elastic recovery was only ca. 1 %. Delayed loading for 24 h, generated I(t) plots of significantly reduced magnitude. Most importantly, however, the I(t) plots for ECeram and EFlow, after 20 s irradiation, showed I(t) magnitudes quite comparable to the PFill and PFlow rapid-cure composites.

Significance

Macroscopic indentation creep has been shown to be a workable procedure that can be applied to rapid-cure materials to assess their immediate surface integrity and developing viscoelastic characteristics. The applied stress of 14 MPa was relatively severe and the indentation/recovery profiles of PowerFill materials with only 3 or 5 s irradiation demonstrated comparability with their established 20 s cure siblings, evidencing the suitability of the PowerCure system for clinical application.

中文翻译：

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超快速光聚合复合材料的表面粘弹性完整性表征：方法开发。

目的

现在可以使用树脂复合材料，设计用于使用3 s的强光照射进行聚合。目的是开发一种实验方法，以通过在恒定应力下随时间变化的宏观表面压痕，在如此快速的光固化后立即探测其表面粘弹性的完整性。

方法

研究了两种散装填充复合材料（Ivoclar AG）：Tetric PowerFill（PFill）和PowerFlow（PFlow）。使用分体模具制造圆柱状{4 mm（直径）×4 mm}的糊状样品，用Bluephase PowerCure LED-LCU在3 °C或5 s模式下于23°C从顶表面照射3 s或5 s模式，发出3和2 W / cm ²， 分别。辐照后的样品立即转移到装有直径为1.5 mm的平头压头的设备中。在小于2分钟的时间内，在压头尖端施加14 MPa的压缩应力，并保持恒定2 h。压痕（I）的大小实时（t）记录，I（t）数据以相对于4 mm样品高度的压痕百分比重新表示。2小时后，卸载压头，并继续监测压痕恢复2小时。进行平行测量，压痕延迟24小时。使用更常规的复合材料进行了进一步的测量：EvoCeram填充料（ECeram）和Tetric EvoFlow填充料（EFlow）。这些以1.2 W / cm ²照射20 s。通过ANOVA和事后检验（α= 0.05）将动力学数据曲线拟合至指数增长函数和关键参数。

结果

I（t）图最初看起来与体积蠕变/恢复相似：快速变形加上粘弹性响应；然后，在卸货时：快速（弹性）恢复，然后进行部分粘弹性恢复。但是，与多次辐照和储存的蠕变试样不同，本试样仅暴露于3或5 s的“咬合”辐照。产生“硬”表面。随后，在2小时的压痕过程中，聚合物基质网络继续硬化并固结。初始加载时，I（t）的压痕达到2-3％，具体取决于配方。在2 h卸货后，弹性回复率仅为约。1％。延迟加载24小时，生成的I（t）图的幅度明显减小。然而，最重要的是，在20 s辐照后，ECeram和EFlow的I（t）图显示了与PFill和PFlow快速固化复合材料相当的I（t）幅值。

意义

宏观的压痕蠕变已被证明是一种可行的方法，可用于快速固化的材料，以评估其直接的表面完整性和发展的粘弹性特征。14 MPa的施加应力相对较重，仅用3或5 s辐照的PowerFill材料的压痕/恢复曲线证明与已确立的20 s固化同级材料具有可比性，证明PowerCure系统适合临床应用。