Effect of Thickness of CAD/CAM materials on Light Transmission

Objectives: This study evaluated light transmission (LT) through different thicknesses (0.5, 1.0, 1.5 and 2.0mm) of hybrid resin/ceramics and ceramics.
Methods: Hybrid resin/ceramics materials (shade A2HT) were tested: Enamic/Vita Zahnfabrik (EN), Lava Ultimate/3M ESPE (LU), HC Block/Shofu (HC) Cerasmart/GC Corp. (CE). An indirect conventional composite (Epricord/Kuraray - shade DA2) was used as a control. Ceramics (shade A1HT) tested were: Rosetta/Hass (RO), Suprinity/Vita Zahnfabrik (SU), e.max/Ivoclar Vivadent (EM), Celtra Duo/Dentsply (CD) and Real Life/Vita Zahnfabrik (RLO-Opaque, RLT-Translucent). For each material, five specimens were made 14 mm-wide X 14 mm-length at each thickness. They were wet-ground (600-grit) on both sides. The irradiance from a light-curing unit (LCU) (Elipar Deep Cure-S/3M) was measured with a laboratory-grade integrating sphere attached to a spectroradiometer. Samples of each restorative material were placed in between the opening of the sphere and the LCU tip. The LT through each sample was calculated as a percentage of the baseline. LT results were analyzed by two-way ANOVA and Tukey post-hoc test (α=0.05).
Results: For all materials, there was a significant difference in LT among the four thicknesses, except between 1.0 and 1.5mm thick RLO groups. 2mm of EP resulted in the lowest value (5.3%), while 0.5mm of CE allowed the greatest LT (55.3%). Among composites, the lowest values were through EP, followed by EN. HC and CE always allowed higher LT and did not differ from the thickest samples of LU. Regarding ceramics, LT was the lowest for RO, however for 1.0mm, RLO had the lowest value. No statistical difference was noted between SU and RLO, except for 1.0mm. EM and CD showed similar results, regardless of the thickness. For 1.5 and 2.0mm, RLT allowed the highest LT.
Conclusions: Light transmission through CAD/CAM materials tested is material dependent. Some transmit only 5.3% of the incident light. This might affect resin polymerization.