Purpose: To examine the fracture resistance and fracture modes of Prettau Highly Translucent Zirconia and Resin Nano Ceramic Lava Ultimate CAD/CAM endocrowns versus post and core supported CAD/CAM crowns in endodontically treated extremely damaged maxillary molars. Methods: Twenty maxillary first molars of similar size and shape were selected. The teeth were all decoronated and endodontically treated, then they were randomly divided equally into four groups (5 each) as follows; Group I: Five teeth restored by post and core supported Prettau Highly Translucent Zirconia (PZ) crowns. Group II: Five teeth restored by PZ endocrowns. Group III: Five teeth restored by post and core supported Resin Nano Ceramic Lava Ultimate (LU) crowns. Group IV: Five teeth restored by LU endocrowns. All specimens were scanned, designed and milled using ZirkonZahn CAD/CAM 5 Tec machine. After cementation, all specimens were thermocycled, then they were subjected to fracture resistance test and fracture mode analysis. The data were collected, tabulated and statistically analyzed. Results: Group I exhibited the highest fracture resistance followed by group IV then group III while group II exhibited the lowest fracture resistance. Groups I and II resulted in unfavorable unrestorable failures while Groups III and IV resulted in favorable restorable failures. Conclusions: Endocrowns can be used as a conservative clinical alternative for restoring severely damaged endodontically treated posterior teeth. Resin composites seem to be the material of choice to build-up endocrown restorations. Clinical Significance: Restoration of extremely damaged and endodontically treated teeth present a critical and time consuming clinical situation. Key words: Translucent Zirconia, Resin Nano Ceramic, Endocrowns, CAD/CAM Technology.

Objective: The purpose of this study was to evaluate the effect of two hydrogen peroxide concentrations, commonly used in In-Office bleaching, on the surface roughness and color change of different esthetic restorative materials. Materials and Methods: Sixty disc samples (10 mm in diameter and 2 mm in thickness) of the different restorative materials used were constructed following the manufacturers’ instructions. Samples were classified into three main groups (n=20) according to the type of restorative material: Group1: Microhybrid composite Filtek P90 Silorane, Group 2: IPS emax Press and Group 3: Vitadur Alpha porcelain. Each of the three groups was divided into two subgroups (n=10) (a and b) according to the type of bleaching agent used (Opalesence Xtra Boost 35% hydrogen peroxide (HP) and Zoom 2 25% HP respectively). Samples of subgroups were further divided into two equal divisions (n=5) according to the type of test performed (Roughness testing and Color assessment). Each sample was assessed for surface roughness and color change before bleaching so that each sample served as its own control. Surface roughness was examined using Environmental scanning electronic microscope (ESEM). Color measurements were made with spectrophotometer using CIELAB color scale. One sample from each subgroup was examined to confirm their crystalline phase before and after bleaching using X-Ray Diffraction. Results were statistically analyzed. Results: Significant differences in Ra values were observed between the unbleached and bleached samples, as well as between subgroups treated with Opalesence Xtra Boost and those treated with Zoom 2. The two bleaching agents had statistically significant effect on the color of restorative materials (P<0.05). Moreover, the color change was found to be significantly higher for the restorative materials treated with Opalesence Xtra Boost compared to Zoom 2, regarding their mean ΔE values. Conclusion: Highly concentrated in-office bleaching systems adversely affected the surface roughness and color of Filtek P90 Silorane, IPS e-max Press and Vitadur Alpha porcelain.