الفهرس 
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Abstract
evaluate the effect of two MMPs inhibitors namely: Chlorhexidine based and doxycycline based on the color stability of two shades of resin composite. Methods: Sound human molar teeth were used in this study. Flat dentin surfaces were obtained by grinding the occlusal surfaces. Teeth were divided into three equal groups each according to the MMP inhibitor used: Group I1: no pretreatment (control group), Group I2: chlorhexidine digluconate; Group I3: MTAD. For each specimen Adper™ Single Bond Adhesive was applied to the treated surface and light cured. Each group was then subdivided into two equal subgroups of ten teeth each (S1, S2) according to the shade of resin composite used. A specially fabricated metallic holder was used to pack resin composite. For each subgroup the color was assessed three times. After baseline measurements, specimens were aged for 50 hours with a total energy of 600kJ/m2 with accelerated aging chamber using xenon long arc 1400 watts with a sophisticated controlled irradiance system insuring uniform specimen exposure. After aging, each specimen was removed and subjected to color measurement in the same way as the baseline. The specimens were then re-aged for another 50 hours representing 2 years aging. The color change was calculated twice from the following equation: ΔE*= [(ΔL*) 2 + (Δa*) 2 + (Δb*) 2] 1/2. Results: shade B1 had a higher mean ΔE value (7.37±0.47) than shade A3 (4.60±0.42). It was also observed that MTAD induced the highest significant color change (ΔE 6.59±0.44), followed by CHX (ΔE 6.08±0.39) in all tested groups with a ΔE ≥3.3. While the control groups showed the least change (ΔE 5.28±00.36). Conclusion: MMPs inhibitors jeopardize the color stability of resinous restorations. Doxycycline based inhibitors induced a higher perceptible color change compared to their chlorhexidine based alternative. Color stability of resin composite is shade dependent.