الفهرس 
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Abstract
The present study was conducted to evaluate the stainability of a microhybrid (Te-Econom Plus), nanohybrid (Tetric Evo Ceram) and a nanohybrid ceramic based (IPS Empress Direct) resin composites on exposure to three indigenous stain beverages: tea, coffee and coke for a period of 3 hours per day after 7 days, 14 days, 21 days and 30 days.
A total of 120 disk specimens were prepared with 8mm in diameter and 2mm in thickness. Forty disk specimens were prepared for each type of resin composites tested (N=40), and thirty disks (N=30) were also prepared and kept in distilled water to be used as control throughout the whole period of time.
Preparation of the specimens and immersion media
The specimens were fabricated by packing the composite resin in a Teflon cylinderical mold using a custom made Teflon condenser. The specimens were covered by mylar strip and a glass plate placed on top with a 1kg weight for 30seconds and cured with a halogen light curing unit. All the specimens were stored in distilled water (control) at for 24 hours and baseline measurements were recorded followed by immersion in tea solution (a prefabricated tea bag in 250 ml of boiling water at 70°C for three minutes), coffee solution (5gm of instant coffee in 250 ml of boiling water at 70°C and stirred for one minute) and coke (250 ml of Pepsi soft drink at 10°C). The quantity and concentration of staining solution prepared, immersion time of 3 hours/day in staining solutions, and daily changing of staining solution were also strictly adhered to closely stimulate the in vivo conditions.
The 120 disk specimens prepared from all the resin based composite are divided into 3 groups (N=40) for each group which is further subdivided randomly into 3 subgroups (N=10) for each of the three immersion media prepared and a fourth control subgroup for each type of resin based composite material used (N=10) in which the specimen were kept in distilled water.
A- Group A Te-Econom Plus* which is further subdivided into 4sub groups according to the staining solutions that were used into:
Subgroup A1 tea±70°C (N=10)
Subgroup A2 coffee±70°C (N=10)
Subgroup A3 coke±10°C (N=10)
Subgroup A4 distilled water (N=10)
B- Group B Tetric Evo Ceram* subdivided into 4subgroups according to the staining solutions that were used into:
Subgroup B1 tea±70°C (N=10)
Subgroup B2 coffee±70°C (N=10)
Subgroup B3 coke±10°C (N=10)
Subgroup B4 distilled water (N=10)
C- Group C IPS Empress Direct* subdivided into 4sub groups according to the staining solutions were used into:
Subgroup C1 tea±70°C (N=10)
Subgroup C2 coffee±70°C (N=10)
Subgroup C3 coke±10° (N=10)
Subgroup C4 distilled water (N=10).
Color measurement
Color evaluation and differences ( for each specimen was measured using a digital spectrophotometer (VITA Easyshade@ Advance) for a period of 7days, 14 days,21 days and 30 days. The color was evaluated according to the color system CIE La*b*, commission international de l’ eclairage LAB. Statistical analysis was done using Mann Whitney test and Kruskal Wallis test.
The results of comparison between the different studied stages of mean ΔE for Tetric Evo Ceram material in different immersion media after 30 days of immersion, tea produced the worst color change (ΔE 11.73) which was rated according to NBS as very much color change & the color had” changed to other color ”followed by coffee (ΔE 10.16), water (ΔE 7.51) and coke (ΔE 6.84) which was rated as much color change& there was” extremely marked change” caused by coffee, water and coke respectively. Statistically significant difference (KWP1) was present at 1st week (<0.001*), 2nd week (<0.001*) and 4th week (0.016*) when comparing the different studied media. The results of comparison between the different studied stages of mean ΔE for Empress Direct composite material in different immersion media after 30 days of immersion, coffee produced the worst color change (ΔE 17.23) which was rated as very much change& that color” had changed to other color” followed by tea (ΔE 10.70), water (ΔE 10.53) and coke (ΔE 6.40) which was rated according to NBS as much change & that tea, water and coke produced ”extremely marked change” in color .statistically significant difference (KWp1) was present when comparing between the different studied media. The results of comparison between the different studied stages of mean ΔE for T-Econom composite resin based material in different immersion media after 30 days of immersion tea produced the worst color change (ΔE 12.64) which was rated as very much change& that ”color had changed to other color” followed by coffee (ΔE 8.98) which was rated according to NBS as much&” extremely marked” change in color, then water (ΔE 5.83) and coke (ΔE 5.47) which was rated as changes were appreciable &marked change in color. Statistically significant difference KWP1 was present at 1st week (<0.001*), 2nd week (<0.001*), 3rd week (<0.001*) and 4th week (0.001*) when comparing between different studied media. Thus, the comparison showed that the microhybrid Te-econom Plus was more stain resistant than nanohybrids Tetric Evo Ceram and IPS Empress Direct.