Spectral Transmittance and Colour of Dentine Porcelains for All-Ceramic Restorations

Objectives: The aim of the research was to observe spectral transmittance in the visible spectrum and compare the Total (TT), Diffuse (DT) and Direct (DirT) Transmittance of fired VM7® (VITA, Germany) dentine porcelains for all-ceramic restorations in the 3D-master shade system. Methods: Three disc samples with the size of 13 mm in diameter and 1.4 mm in thickness from each shade were fired following the manufacturer's instructions. Both faces of the fired disks were ground and polished down to the thickness of 1.0 mm. Spectral transmittance data for TT, DT in the visible spectrum were collected at 1 nm intervals using a computer-controlled spectrophotometer. DirT was calculated. Results: Principal results are summarized as follows:(1)The contribution of DirT decreases at <500nm and the contribution of DT increases at <500nm (2) With increasing value TT, Dt, and DirT decrease and the maximum slope of the transmittance curves (near 620nm) for TT, DT and DirT increase.(3)With increasing chroma TT decreases significantly in the short wavelength range. The maximum slope of the TT, DT and DirT curve increases and moves towards the longer wavelengths. The contribution of Dt to TT increases in wavelengths shorter than 500nm. Conclusion: When comparing value, a decrease in long and short wavelengths is observed with an increase in the differential coeffiecent, therefore suggesting a possible 2nd phase of 620nm grain size is related to value. When comparing chroma, a decrease in the short wavelength (<500nm) is observed whereas long wavelength is unchanged. When comparing a constant value but different chroma, a phase 500nm grain size is strongly suggested to be increased.