الفهرس 
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Abstract
The purpose of this in-vitro study was to investigate the effect of bleaching agent (ZOOM, Discus Dental, USA) on color, surface roughness and shear bond strength of two ceramic materials; feldspathic porcelain and lithium disilicate. Thirty recently extracted maxillary central incisors were collected, amputated below the cemento-enamel junction and were mounted in PVR tubes. A total of thirty ceramic discs were fabricated; fifteen discs were fabricated of feldspathic porcelain VITA VMK (VITA Zahnfabrik, Bad Sackingen, Germany) and the other fifteen discs were fabricated of lithium disilicate IPS e.max CAD (Ivoclar Vivadent, Liechtenstein) ceramic. Variolink veneer (Ivoclar Vivadent, Liechtenstein) was used in this study to cement the ceramics discs to the flattened enamel surface of the central incisors. Using the universal testing machine, Stereomicroscope and VITA Easyshade the shear bond strength, surface roughness and color change were tested. The discs were bleached with ZOOM bleaching gel and underwent three bleaching cycles of fifteen minutes each. Post-bleaching assessment of shear bond strength, surface roughness and color were evaluated. All data were collected and statistically tabulated. Multiple analyses of variance were used. Shear bond strength and surface roughness results revealed insignificant difference. The results of the color assessment were statistically insignificant with a slight change in lightness.
CONCLUSION
Within the limitations of this in vitro study, the following conclusions were drawn:
1. Although there was no significant difference in color change, a slight increase in lightness was observed in feldspathic porcelain after bleaching.
Summary and conclusion
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2. A slight increase in surface roughness was observed in both ceramic materials used after bleaching though it was statistically insignificant.
3. There was no significant difference in shear bond strength upon bleaching, a slight increase in shear bond strength in both ceramic materials used was observed.
Clinical recommendation:
It is safe to use In-office bleaching agent with existing ceramic restorations. Bleaching did not significantly affect the color, surface roughness or the shear bond strength of the two types of ceramics used.