Evaluation Of Some Optical Properties and Color Reproduction Of Translucent Zirconium Oxide Ceramic Before and After Aging Using Three Different Shades Of Resin Cement.

Abstract

One of the most difficult challenges in esthetic dentistry is obtaining an exact color match between natural teeth and an artificial restoration making the visual recognition of the inserted restoration a difficult task even for well-trained eyes. The achievement of an all-ceramic esthetic restoration that matches perfectly with adjacent teeth is the result of the interplay several optical factors. Recent developments in ceramic technology and evolutionary treatment methods had led to the introduction monolithic zirconia as a restorative solution with the clinical advantage of reduced thickness. Fabrication of monolithic restorations with an appropriate shade, translucency and opalescence is critical for matching to the neighboring teeth and for a natural-looking appearance. The study was performed to evaluate color reproduction and translucency of Translucent zirconium oxide ceramic in comparison with Leucite reinforced ceramic (IPS Empress CAD) by using different thicknesses of ceramic materials and different shades of underlying resin cement before and after aging using spectrophotometric analysis. A total of 180 all-ceramic slices were constructed from translucent zirconia (InCoris TZI) and leucite reinforced ceramics (IPS Empress CAD High Translucency and Low Translucency) with shade corresponding to A2 in the vita shade guide. A tooth colored substrate was constructed from natural die material of shade ND2. The ceramic blocks were cut in thicknesses of 0.5 mm, 0.8 mm, 1mm, and 1.2 mm using percision cutting saw, Translucent zirconia specimen were sintered in Sirona HTC furnace. All specimens were the finished and polished. Three different values of resin cement (Variolink Veneer low value -2, medium value 0 and high value +2) were applied to the specially designed cement space in the natural die material substrate. The color coordinates of ceramic slices (CIE L*a*b*) were measured with intraoral spectrophotometer (Vita Easy Shade) using three different values of resin cement. Color differences were measured before and after aging. Then the color coordinates (CIE L*a*b*) were measured on black and white backgrounds and translucency parameters (TP) and Opalescence parameter (OP) were calculated before and after aging. The results of color measurements showed significantly higher ΔE for all Translucent Zirconia specimens regardless of cement value and aging process than Empress CAD LT and Empress CAD HT. The value of resin cement had statistically significant effect on ∆E but still within clinically acceptable range. Aging had significant effect on ∆E with Translucent Zirconia showing highest values that were beyond the clinically acceptable range. Results of translucency and opalescence showed that: Empress CAD LT and Empress CAD HT have higher translucency than Translucent Zirconia. The material thickness have significant effect on translucency irrespective of the type of the material as the thickness increase translucency decrease. Aging, regardless type of material and thickness , decreased (TP) values and led to a less translucent material significantly. Regarding opalescence none of the tested materials showed enough opalescence (<9) to give the restoration the vitality appearance. Aging has no significant effect on opalescence