Optical properties and microstructure of CAD/CAM silicate glass-ceramics with different levels of translucency

The aim of this study was to analyze the optical properties of current CAD/CAM silicate glass-ceramics and the context of their structural properties.

Different glass-ceramics (VITABLOCS Mark II, Nice, Celtra Duo, IPS e.max CAD) were prepared at the manufacturer-specific translucency level (LT/MT/HT/O2/O1) in disc form (0.5/1.0/1.5 mm thickness) and examined via a benchtop spectrophotometer (X-Rite Ci76000). TP_ab, TP₀₀ (translucency), the CR (contrast ratio), ΔE₀₀ (masking ability), OP_RT (opalescence) and FL (fluorescence) were calculated. The microstructure was analyzed via powder X-ray diffraction (XRD) with Rietveld refinement and scanning electron microscopy (SEM).

With increasing sample thickness, TP_ab and TP₀₀ decreased, and the CR increased. IPS e.max CAD showed the highest (Emax_O1) and lowest (Emax_LT) translucencies. Thickness had no clear effect on ΔE₀₀, OP_RT or FL. Emax_O1/O2 generally presented very high OP_RT and FL values. All the ceramics had different phase components and glass contents. The glass content of MarkII was the highest, and that of Nice_LT/HT was the lowest. The translucency increased within a particular product line (Nice, Celtra or Emax) with increasing glass content. No correlation between the glass content and optical properties was observed between the different glass-ceramics MarkII, Nice, Celtra and Emax. Furthermore, no correlation was found between the crystallite shape/size and optical properties.

To match dental restorations with the aesthetics of natural teeth, knowledge of the optical properties of glass-ceramics is important.