Objective: To investigate the effect of thickness, translucency and surface finish of prosthetic materials on the transmission of curing-light irradiance.
Methods: Slabs of material with various thicknesses (t; 0.5~3.0mm) were sliced from one CAD/CAM block of each material with a diamond saw. Blocks of materials included Celtra™ Duo (Dentsply; HT-A1, LT-A3), Enamic® (Vita; HT-1M1, HT-3M2, T-3M2), Lava™ Ultimate (3M/ESPE; HT-A1, LT-A1, HT-A3, LT-A3) and e.max® CAD (ceramed) (Ivoclar Vivadent; HT-A1, HT-A4, LT-A1) as control. Irradiance (It, 380~540nm) of Valo® Cordless curing light (Ultradent, South Jordan, USA) transmitting through individual as-sliced slab was measured with MARC® Resin Calibrator (BlueLight Analytics, Halifax, Canada) at a 3-mm distance from the light source. The measurement was repeated after the side of slabs facing curing-light was polished to 0.3µm-finish. Measurement of each slab was repeated five times and the mean It values were fit into an exponential decaying function, It=Iₒ•exp(-λ•t), for each material-polish condition. The regression yielded values of Iₒ, irradiance when the slab thickness is 0mm, and λ, attenuation coefficient. The goodness-of-fit (r²) of each regression was >99%.
Results: Three-way ANOVA shows that Iₒ is significantly affected by polishing (p=0.0409), but not by translucency (p=0.0893) or shade (p=0.5546), and λ is significantly affected by translucency (p=0.0002) or shade (p=0.0007), but not polishing (p=0.8345). The order of λ was Enamic=Lava (p=0.2815) > e.max=Celtra (p=0.1812) for high-translucent HT-A1 and HT-1M1, and Enamic > Celtra=Lava (p=0.1388) for low-translucent LT-A3 and T-3M2. No irradiance was detected with 3.0mm-thick Celtra LT-A3 or Enamic T-3M2. Polishing increased total irradiance transmitted by 2~9% (p<0.0001), but the increase was independent of the shade (p=0.3869) or translucency (p=0.5801).
Conclusion: Light transmission through CAD/CAM prosthetic materials was significantly reduced by opacity, darker shade, increasing thickness and surface roughness of the material.
Materials were graciously provided by 3M/ESPE, Dentsply, Ivoclar Vivadent and Vita.