الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
This study aimed to evaluate the effect of substrate, ceramic thickness and shade of resin cement on final color of multichromatic CADCAM blocks using digital shade matching software.
A metal mold (8×8×4) mm was constructed with a metallic rod. The metal mould was filled with composite resin material. 60 specimens were prepared 30 specimens A2 shade (group I) and 30 specimens A3.5 shade (group II) simulating teeth shades. Serial thin slices ceramic specimens were obtained from multilayered glass-ceramic blocks (IPS Empress CAD Multi C14 A1) using a IsoMet™ Low Speed Precision Cutter 30 ceramic specimens of (8×8×0.5 mm); and 30 ceramic specimens of (8×8×0.8 mm). Dimensions of the samples were measured using a digital caliper for accuracy.
Each group was subdivided according to the thickness of veneers into Subgroups IA and IIA (0.5mm thickness) and Subgroups IB and IIB (0.8mm thickness). Each subgroup was further subdivided according to the shade of resin cement used into Subgroups IAO, IAW, IAT, IBO, IBW, IBT, IIAO, IIAW, IIAT, IIBO, IIBW, IIBT where O denotes opaque cement, W white cement and T transparent cement.
Firstly, digital analysis was done by shadewave software to the veneers separately to obtain baseline data, then repeated after placement of the veneers 0.5mm and 0.8mm over substrate A2 and A3.5 without cementation to compare between different veneer thicknesses and substrate colors. Finally digital analysis of the ceramic specimens and its corresponding substrates will be done before and after bonding. The corrected images were then processed through adobe photoshop cc software and CIE L*, a* and b* values we recorded and color difference Delta E was then calculated. Results were recorded, tabulated and statistically analyzed.
Regarding effect of the multilayer ceramic chroma and its influence on color parameters, the results showed that for group 1 and group II the highest mean L* value was recorded in the upper third followed by the middle third and lowest mean L* value was recorded in lower third while the highest mean a* (redness) and b* (yellowish) values were recorded in the lower third followed by the middle third and lowest mean a* and b* values were recorded in the upper third. group 1 and group 2 showed highest mean Delta E in upper third followed by middle third and lowest mean Delta E was recorded in lower third.
Regarding effect of substrate, the results showed that in upper third, middle and lower thirds Subgroups IA and IB showed higher mean L* value (lightness), mean a* value (redness) and lower b* value (yellowish) than Subgroups IIA and IIB with no significant difference between them. In all Subgroups the upper third showed highest L * value followed by middle and lower third respectively. The lower third showed highest a*and b* values followed by middle and lower third. The results of this study showed that both substrates A2 and A3.5 in all subgroups greatly influenced the final shade of the veneers resulting in mean Delta E greater than ΔE 8.
Comparing between Subgroups IA and IIA and between Subgroups IB and IIB, the magnitude of mean delta E was higher for substrate A3.5 than substrate A2 in upper, middle and lower thirds with no Significant difference between them.
Regarding the influence of veneer thickness, comparing between Subgroup IA and IB and between Subgroup IIA and IIB, the results showed that in upper, middle and lower thirds increasing the thickness of veneers from 0.5mm to 0.8mm the higher the degree of L* value (lightness) with significant difference between them. Moreover, the values of a* (redness) decreases and b* value (yellowish) increase as thickness of the veneers increases from 0.5mm to 0.8mm with no significant difference between them regarding the a* and b* values in upper third middle and lower thirds. The mean Delta E recorded was higher in Subgroups IA, IIA than that of Subgroups IB, IIB with significance difference between 0.5mm veneer thickness and 0.8mm veneer thickness regardless of the substrate color in upper third, middle and lower thirds.
Regarding effect of resin cement on final shade of porcelain laminate veneers, three shades were evaluated in this study white, opaque and transparent cement. Comparing between Subgroups IAO, IAW, IAT, between Subgroups IBO, IBW, IBT, between Subgroups IIAO, IIAW, IIAT and between Subgroups IIBO, IIBW. IIBT the results showed that the use of opaque cement resulted in higher degree of L*values (lightness), higher b* values (yellowish) and lower a* values (redness) than white and transparent cement in upper, middle and lower thirds with significant difference between the three cements regarding the b* and L* values.
The highest mean Delta E was recorded in opaque cement, followed by white cement followed by transparent cement in upper, middle and lower thirds with significant difference between the three cements within Subgroup IA and Subgroup IIA (0.5mm veneer thickness) while there was No significant difference between the three cements within Subgroups IB and IIB (0.8mm veneer thickness).
It was concluded that ceramic chroma, substrate, ceramic thickness and shade of resin cement had a significant effect on final color of laminate veneers where they together play a detrimental role in changing the final color and should be considered carefully to obtain optimum results in daily practice.