The optical properties of aesthetic dental restorations transcend color and their restoration remains a challenge in clinical dentistry. They can be obtained by optimal selection of the material, and appropriate processing technology, but the oral environment can influence the stability of the obtained optical properties. However, clinicians and dental technicians have the control over the manufacturing process, and they should choose proper products and use them as instructed by the manufacturers. On the other hand, different laboratory procedures may affect the restoration’s optical properties and the final color. These laboratory procedures, from beginning till end, include: pressing of the ceramic, polishing, and glazing. Spectrophotometers allow the measurement of different values, in order to evaluate optical properties, not only the color of a restoration.
The purpose of this study was to evaluate the effects of surface processing on the optical properties stability of hot pressed glass ceramics in various beverages, with different pH values and temperatures. Hot-pressed ceramic specimens (1.5 mm diameter, 1.5 mm thickness) from feldspar (Vita PM 9, Vita Zahnfabrik) and Lithium disilicate (e.max press, Ivoclar Vivadent AG) translucent glass ceramics were fabricated using manufacturer's instructions for each material. The specimens were ground and polished, under water, to final dimensions. They were finished using medium and fine abrasives and pastes on bristle brushes. Half of them were coated on 1 side with an uniform layer of glazing agent. Baseline color measurements were carried out according to the CIELab color system. L, a, b values were obtained by using a spectrophotometer (Vita Easyshade Advance 4.0; VITA Zahnfabrik). After baseline colors were measured, the specimens were divided in three groups and immersed in water, Cola, and tea. Color measurements were repeated after immersion, after 24, 48, and 72 hours. Translucency parameter (TP), and opalescence (OP) were determined by calculating. Regarding the TP, the significant changes occur after 24 hours of immersion for feldspar samples. The values decrease, both for glazed and polished samples. After 48 hours the values tend to be similar to the initial values, still maintaining relatively constant after 72 hours. Similar to the TP parameter, the OP parameter changes significantly for the feldspar ceramic, for both polished and glazed samples, after 24 hours of immersion in all beverages. For the lithium disilicate ceramic there are no significant variations during the tested period. Within the limitations of this study, results suggest that the major difference in terms of optical properties depends on the type of ceramic. Lithium disilicate ceramic has superior optical properties than the feldspar one, in terms of translucency and opalescence, and the values remain stable in various beverages, independent of pH and temperature.