الفهرس 
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Abstract
This invitro study was designed to evaluate the color reproduction and translucency of two ceramic materials with different thickness, colored with different coloring techniques. A total of all ceramic specimens were constructed. Thirty monolithic zirconia (InCoris TZI ; Sirona, Bensheim, Germany) and fifteen lithium disilicate (IPS e.max CAD Impulse value ; Ivoclar vivadent, AG, liechtenstein) rectangular plate slices ( mm width × mm length) of approximately . mm, . mm and . mm thicknesses were cut using a CNC machine (Centroid USA). Thereafter, each thickness of Zirconia specimens was divided into two groups and colored using brush and dipping techniques (n= ). Uniform . mm-thickness rectangular specimens of light-polymerized material (IPS Natural Die Material; Ivoclar Vivadent AG) with shades ND and ND were fabricated to represent light and dark background respectively.
The color coordinates (CIE L*a*b*) were measured with a portable intraoral spectrophotometer (Vita easy shade; VITA, Zahnfabrik H, Rauter, GmbH & Co.KG). First the ceramic specimens were measured against light (ND ) and dark (ND ) substrates; with Spectrophotometer (Vita Easyshade), in ‗‗Tooth Single‘‘ mode. Thereafter, the vita easy shade was set to the restoration mode and the shade A was selected. In this mode the vita easy shade shows the difference between the selected shade and the measured shade (ΔE). Then the color coordinates (CIE L*a*b*) were measured specimen with the specimens placed on black and white backgrounds. Translucency parameters (TP) were calculated according to the following formula: TP= [(Lb* - Lw*) + (ab* aw*) + (bb* - bw*) ] . One-way ANOVA test was used for comparisons between ceramic thicknesses as well as overall comparisons between groups. Tukey‘s post-hoc test was used for pair-wise
comparisons when ANOVA test was significant. The results showed that . mm thickness lithium disilicate (IPS e.max CAD value ) provided the least color differences and hence more color reproduction. Dipping technique provided smaller Δ E values than brush technique. The TP values of the lithium disilicate ceramics ranged from . to . and the zirconia ceramics from . to . . There was an increase in the TP with a decrease in thickness, but the amount of change was material dependent.
Within the limitation of this study the following Conclusions can be drawn
-The translucency of dental ceramics was significantly influenced by the material type. Lithium disilicate glass ceramics provided greater translucency than monolithic zirconia.
-The translucency of all materials increased as the thickness decreased.
-Brush technique provided higher translucency than dipping technique in monolithic zirconia.
- Lithium disilicate (IPS e.max CAD value ) provided higher color match than monolithic zirconia.
-Dipping technique tends to provide better color match than brush technique in monolithic zirconia.
-The thickness of . mm in lithium disilicate (IPS e.max CAD value ) provided the least color differences and hence better shade match.
Clinical implications
-Translucency is not always desirable. Depending upon the clinical situation, a different need between greater translucency and masking ability will be identified according to the remaining tooth structure shade or core build up material. For this reason, it is important to be familiar with the translucency of different porcelain systems. The most appropriate porcelain system can be identified only according to a specific clinical situation.
-The tested monolithic zirconia, especially with brush technique may be recommended in case of dark substrate and/or when bleach brightness is required.
-Efficient masking without sacrificing translucency is best reached by lithium disilicate (IPS e.max CAD impulse value ) in minimum thickness.