This study assesses the effect of the material type (lithium disilicate, zirconia, and polymer-infiltrated ceramic) and dental bonding substrates (dentin, dentin with intra-coronal cavity, and dentin with composite filling) on the fracture resistance and failure mode of molars restored by occlusal veneers. Methods: Ninety occlusal veneers, fabricated from either lithium disilicate, zirconia, or polymer-infiltrated ceramic, were adhesively bonded to teeth prepared with either dentin, dentin with intra-coronal cavity, or dentin with composite filling. All specimens were thermally aged (5000 cycles), then load cycled (120,000 cycles). Each specimen was subjected to a compressive load through fracture, then was examined (×20) to identify the fracture type. Data were statistically analyzed. Results: Material type and dental substrate had no significant effect on the fracture resistance of adhesively retained occlusal veneer restorations. For each material, no significant differences were found between veneers bonded to dentin, dentin with intra-coronal cavity, and dentin with composite filling. Additionally, within each bonding substrate, there were no significant differences between lithium disilicate, zirconia, and polymer-infiltrated ceramic veneers. The adhesive failure was recorded mainly with zirconia occlusal veneer restorations. Conclusions: Considering the fracture results, lithium disilicate, zirconia, and polymer-infiltrated ceramic occlusal veneers perform well whatever the type of dental bonding surface. When the dental bonding surface varies, different occlusal veneer materials should be considered. Occlusal veneers bonded to dentin, dentin with composite filling, or dentin with an intra-coronal cavity exhibited a fracture resistance exceeding the average human masticatory forces in the molar area.

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Objectives:The aim of this study was to evaluate the effect of adaptation of glass fiber post on Push-out bond strength to root canal dentin. Materials and Methods:Thirty human single-rooted premolar teeth were endodontically treated. The specimens were divided into 3 groups: First group, positive control group n=10 the post space was prepared with the #0.8 drill to receive a #0.8 prefabricated glass fiber post. The second group, Negative control group n=10 post space were prepared to simulate an oversized root canal and then #0.8 prefabricated glass fiber post was used. Third group, CAD-CAM glass fiber post group n=10 Post space was prepared in the same way like negative control group but CAD -CAM post was used. All posts were cemented to their corresponding roots using self adhesive resin cement. All root with the posts were sectioned transversely into 2.0 mm thick slices and the push-out test was done. Results were analyzed by two-way ANOVA followed by a Tukey's post hoc test, p= 0.05.Results: Push out bond strength was significantly higher in CAD-CAM post group in comparison with Negative control group and positive control group. No significant differences was observed in Push out bond strength between positive control and negative control groups. The bond strength was higher for coronal third than middle and apical third.Conclusions: CAD-CAM post is an effective treatment for flared root canals. The bonding strength of the coronal third of the root dentin was significantly greater than the middle and apical third.