الفهرس 
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Abstract
Composite resins are widely used as an esthetic restorative material, however the difficulty of restoring proper shade is a common challenge during fabrication of composite restorations. OMNICHROMA (Tokuyama Dental America) is recently introduced, as the first shade matching composite which poses a unique property based on “smart chromatic technology”. On the other hand, maintaining color matching between restoration and tooth is among the important criteria of successful esthetic restoration as color changes with time due to either intrinsic or extrinsic factors. So, the aim of the current invitro study was to evaluate the effect of artificial aging through storage of the specimens for 6 months in artificial saliva on the stability of color match between the teeth and Omnichroma composite resin compared to that in the teeth restored with Tetric EvoCeram nanohybrid composite resin. Twenty sound, freshly extracted human maxillary premolars were collected, cleaned from debris, and soft tissue and stored in saline until the experiment time scheduled within three months after extraction. Teeth were mounted in acrylic resin blocks (only roots were embedded below CEJ by 2mm). The baseline shade of the selected teeth was A2 as measured from the middle third of the buccal surface by spectrophotometer (Vita Easyshade Advance). Trapezoidal Class V cavity was prepared on the buccal surface of each tooth 0.5 mm coronal to CEJ. Cavity dimensions were width of 4 mm occlusally and 3mm gingivally ,2 mm occluso-gingival length and 1.5mm depth. Cavities were prepared by No.56 fissure carbide bur in a high-speed hand piece with air water spray, that was replaced by a new one after every 4 cavities. A 45-degree bevel was placed on the occlusal margin of the cavity by a flame shaped diamond bur. Specimens were randomly divided into two equal groups (n= 10) representing the materials used to restore the cavities; group I: Tetric EvoCeram while group II: Omnichroma. Cavities were restored with their respective adhesives and the special dispensers following the manufacturer’s instructions. A transparent cervical matrix was used to get smooth and polished surface. Specimens were then stored in saline for 24 h at 37 °C and 100% humidity in an incubator. They were artificially aged by storage in artificial neutral saliva in an incubator at 37±5°C for 6 months during which the saliva was replaced daily. Color measurements and ΔE values were recorded before cavity preparation representing the baseline tooth color to be used for detection of the initial color match between the tooth and that of the restoration that was measured after storage in saline for 24 hours. At the end of the storage period, the color of both the teeth and the restorations was remeasured to detect the stability of color match between the restoration and the tooth after storage. All the recorded data was collected, tabulated, and statistically analyzed using SPSS version 26. Results: At baseline, group I (restored with Tetric EvoCeram) composite resin, nearly comparable mean ΔE values was recorded for the teeth (5.03±2.09) and restoration (5.33±2.0). While in group II restored with Omnichroma composite resin a lower value was recorded for the teeth (5.55±2.1) compared to that of the restoration (6.05±2.1). Independent t-test revealed no statistically significant difference between the values of the teeth and restoration in both group I (p=0.75) and group II (p=0.6). This denotes the initial color match between teeth and restoration. Regarding the effect of storage on the color match between the teeth and restoration, in group I (restored with Tetric EvoCeram) a higher mean ΔE value (6.43±2.15) was recorded for the restoration compared to that of the teeth (5.03±2.09), however no statistically significant difference was found between both values (p=0.15). Similar finding was found regarding group II (restored with Omnichroma) where higher mean ΔE value was recorded for the restoration (6.71±2.14) than that of the teeth (5.55±2.10) with no statistically significant difference between both values (p=0.23). This denotes the stability of color match between the teeth and restoration in both groups after storage in artificial saliva for 6 months. In addition, the effect of storage on the color change of teeth revealed that teeth used in group I had similar mean ΔE value (5.03 ±2.09) before and after storage with no statistically significant difference between both values (p=1.00). The same was found regarding teeth used in group II recording mean ΔE value (5.55±2.10) before and after storage with no statistically significant difference between both values (p=1.00), denoting that 6-month storage in artificial saliva had no effect on the teeth color. While the effect of storage on the color change of the tested restorative materials revealed that, in group I (restored with Tetric EvoCeram) a lower mean ΔΕ values (5.33±2.09) was recorded at the base line compared to that (6.43±2.15) after 6 months storage with no statistically significant difference between both values (p=0.26). Similarly in group II (restored with Omnichroma), a lower mean ΔΕ values (6.43 ±2.1) was recorded at the baseline compared to (6.71±2.14) after 6 months storage with no statistically significant difference between both values (p=0.49). This denotes that the utilized aging protocol did not significantly change the color of the tested composites materials.