الفهرس 
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Abstract
Colour stability and translucency of resin cements and flowable composites for ceramic veneer luting , is of prime importance for success of functional and esthetical veneer , ageing of luting materials cause changes in colour which directly affects the long term success of restoration.
Aim of study was to evaluate colour stability and translucency variations after aging for three luting agents that was luted to two different ceramic materials.
Glass ceramic slices (IPS Empress CAD) and (IPS Emax CAD) after been smoothed , polished and glazed were luted to composite bases with three different luting materials RelyX Ultimate, RelyX Veneer and Vertise flow flowable composite after been pressed with with glass slap and applying certain wait over them and the excess resin cement was removed and then cured from the free surface of the mould for 20 sec according to the manufacturer instructions.
Fourty two ceramic slices were used and subdivided into two groups every group with 21 ceramic slices and these two groups were further subdivided to three groups every group contains 7 ceramic slices according to the luting agent used for the sample.
After that by means of a spectrophotometer (Vita Easyshade compact) the L*,a* and b* values (according to the CIE Lab system) of each sample was recorded immediately after curing , then after 1500 cycles of thermal aging by means of thermocycling . Each cycle consisted of 30 sec Dwell time in a 5℃ water bath then 30 sec in a room temperature water bath and finally 30 sec in a 55℃ water bath. Between the aging stages the samples were placed in a 37℃ distilled water bath.
Then after aging the ΔE ( the change in color content ) of each resin was calculated for every sample by the following equation
∆E = [ ( ∆L^* )^2+ (∆a^* )^2+ (∆b^* )^2 ]^(1⁄2)
The general population can distinguish colour differences of value (ΔE<3.3) , which can be considered clinically significant , below that value it is regarded as clinical success.
The results showed that Vertise flow flowable composite had the least color change in all luting materials ( ΔE = 1.15±0.48 ) ,followed by RelyX veneer light cured resin cement ( ΔE = 1.53±0.38 ) and the highest value for colour change was for the RelyX ultimate dual cured resin cement ( ΔE = 2.94±0.42 ).
Also Contrast ratio results showed that Vertise Flow had the best translucency followed by Rely X Ultimate and Rely X Veneer .