Effect of Thickness and Substrate on Color Matching with Translucent Tetragonal Zirconia
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STATEMENT OF PROBLEM: It has been reported that the color of the substrate can influence the final shade of translucent restorations. Such effect is dependent on the thickness and translucency of the restorative ceramic material. While studies have explored the effect of substrate on the final shade of silica-based ceramics, there is limited researches on such effect on translucent zirconia. PURPOSE: The purpose of this research was to evaluate the effect of restoration thickness and underlying substrates on the final shade of translucent tetragonal zirconia. MATERIALS AND METHODS: Forty discs of Y-TZP were prepared from Zenostar zirconia blocks (Ivoclar Vivadent). Ten discs were distributed into one of four groups (n=10/group), each group of different thickness as following; 0.6, 1, 1.5, 2 mm. Color measurements were done using spectrophotometer for the control and each of the zirconia specimen against four different substrates: titanium, gold hue, dark shade resin composite (ND8) and white opaque zirconia. Mean ΔE and ΔL were calculated between the control and test groups. The clinical significance thresholds were set as following; perceptible threshold ΔE=1; acceptable thresholds ΔE=3.7, ΔL= |±2|. RESULTS: Mean ΔE for all test groups were clinically perceptible (ΔE>1). Clinically unacceptable results (ΔE>3.7, ΔL > |±2|) were observed with the titanium substrate (0.6, 1 and 1.5mm) and for dark resin and zirconia substrates with 0.6mm of the tested zirconia. Unacceptable ΔL (ΔL > |±2|) were also observed with gold hue and dark resin with 0.6 and 1mm specimens. Titanium substrate resulted in the highest ΔE and ΔL; while the lowest ΔE values were measured with the gold hue and white opaque zirconia substrates. As zirconia thickness increased, ΔL and ΔE fell within the acceptability threshold for all substrates (ΔL < |±2|, ΔE < 3.7). CONCLUSIONS: Achieving clinically acceptable shade matching with titanium substrates was challenging with translucent zirconia. Increasing the thickness of translucent restorations was necessary for shade matching with discolored substrates. Opaque zirconia and gold hue abutments could be considered most predictable implant abutments in the esthetic zone. The minimum thickness recommended to achieve a clinically- acceptable color match exceeded the minimum thickness recommended by the manufacturer for sufficient fracture resistance of the restoration.