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The influence of two different curing regimens on light energy transmission through bulk-fill resin composites and Vickers hardness.

PURPOSE
To compare the total light energy transmission (J/cm2) through bulk-fill composite materials (BFMs) and Vickers hardness (VH) using a single-peak light curing unit (LCU) using two curing regimens.


METHODS
Samples (n= 5) of viscous BFMs, Tetric EvoCeram Bulk Fill (TBF), X-tra fil (XF), and flowable BFMs, SureFil SDR (SDR), and X-tra base (XB) were prepared in 4 mm deep rings. The control was Tetric EvoCeram (TEC), a conventional composite. Using MARC-RC, the irradiance delivered to the top surface of the samples was adjusted to either 800 mW/cm2 for 20 seconds (16 J/cm2) or 1,600 mW/cm2 for 10 seconds (16 J/cm2). Samples were stored post-irradiation at 22 ± 2°C for 24 hours. Top and bottom-surface VH were measured and Bottom/Top (B/T) VH ratios were calculated. Data were analyzed using one-way ANOVA (α= 0.05).


RESULTS
Total energy transmission for all materials ranged from 1.0 J/cm2 (6.1%) to 2.7 J/cm2 (16.9%). There was a statistically significant difference for total energy transmission to the bottom surface, more being transmitted at 800 mW/cm2 x 20 (P< 0.001). XB and TEC were significantly different, with higher B/T VH ratio when cured at 800 mW/cm2 x 20 seconds (P< 0.001). There was no statistically significant difference for TBF, XF and SDR (P> 0.05) with either curing regimen.


CLINICAL SIGNIFICANCE
The degree of cure was material-dependent and increasing curing time may be more important than LCU tip irradiation values. Manufacturer's recommended total energy regimen may not always be adequate for effective curing. Some bulk-fill materials, containing additional photo-sensitivity to lower wave lengths, may be adequately cured using a single-peak LCU.