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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.

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Objectives:The aim of the current study was to evaluate the resin-dentin micro-tensile bond strength (μ-TBS) using 2 types of universal adhesives with etch-and-rinse and self-etch approaches after 24 hours and 6 months of water storage. Materials and Methods:A total of 20 extracted non-carious human molars were used in this study. Teeth were equally and randomly divided into 2 groups (N= 10 teeth) according to the type of adhesive used; Group I; Adhese® Universal and Group II; Single Bond Universal. Each group was further subdivided into 2 equal subgroups (n=5 teeth) according to the bonding approach used; Subgroup A; using the self-etch (SE) approach and Subgroup B; using the etch-and-rinse (ER) approach. After bonding, each tooth was built up by resin composite, cut into sticks (0.9 mm x 0.9 mm) and stored in distilled water at 37˚C for 24 hours and 6 months. Then, each stick was stressed under tension until failure using a simplified universal testing machine at a crosshead speed of 1 mm/min. Data were statistically analyzed using One-Way ANOVA, Two-Way ANOVA and Tukey HSD Tests. After μ-TBS testing, all debonded surfaces were observed using a stereomicroscope at 50X magnification to determine the modes of failure, which were categorized as adhesive, cohesive or mixed failure. Results:After 24 hours of water storage, there was no significant difference between the μ-TBS exhibited by Adhese Universal using both SE and ER approaches while both approaches differed significantly when using Single Bond Universal (P=0.0003). Furthermore, there was no significant difference when comparing the μ-TBS means of SE groups or ER groups of both adhesive systems. After 6 months of water storage at 37˚C, there was a significant decrease in the μ-TBS values of all groups (p<0.0001) except when Adhese Universal was used with SE approach, there was no difference between the 24 h and the 6 month-groups (p=0.1449). The failure mode analysis was consistent with the μ-TBS test results as the number of adhesive failures increased with decreased bond strength values. Conclusions:When bonding resin-based composite restoratives to dentin, a separate acidetching step is not required when using Adhese Universal, but it is preferred with Single Bond Universal adhesive. Aging markedly contributes to bond degradation of universal adhesives.