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.

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. 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 cemented. Third GROUP, CAD-CAM post group n=10 Post space was prepared in the same way like negative control group but CAD –CAM post was used. All root with the posts were sectioned transversely in to 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.

Objectives: the aim of this study was to compare fracture resistance of endodontically treated premolars restored with fiber reinforced post and different resin composite restorative materials. Materials and Methods: Eighty sound extracted premolar teeth were divided in to 3 groups; A (10 teeth kept sound as +ve control), B (10 teeth prepared only as –ve control), C (60 teeth divided into subgroup a as prepared and restored without post, and subgroup b as prepared and restored with prefabricated fiber-reinforced post (Glassix plus, Harald Nordin SA, Switzerland)). Each subgroup was divided into 3 divisions (n=10); 1 (coronal restoration with Tetric EvoCeram), 2 (coronal restoration with Tetric N-ceram), and 3 (coronal restoration with Tetric N-ceram Bulk-fill). All the teeth in group C were prepared for MOD cavities, root canal cleaned, shaped and obturated. All the teeth were subjected to thermo-mechanical aging and the universal testing machine by applying vertical compressive force at a crosshead speed of 0.5 mm/ min. All the data were collected to be subjected to quantitative statistical analysis. Results: Group A showed the highest fracture resistance values, and Group B showed the lowest values. Two-way ANOVA showed a significant difference among all groups. Conclusions: Bulk-fill resin composite restorations supported with prefabricated fiber-reinforced post improved fracture resistance of endodontically treated maxillary premolars.

Objectives: To assess the impact of intra-coronal preparation depth and restorative material on the fracture resistance of molar restored by endo-crown restoration. Materials and Methods: Forty root canal treated maxillary first molars were prepared for endo-crown restorations. Specimens were divided according to the pulpal extension depth and material type into four groups (n=10): teeth prepared with 3 mm pulpal extension and restored by PEEK (TP); teeth prepared with 3 mm pulpal extension and restored by zirconia (TZ); teeth prepared with 5 mm pulpal extension and restored by PEEK (FP); and teeth prepared with 5 mm pulpal extension and restored by zirconia (FZ). After fabrication of the restorations, each endo-crown was cemented to its corresponding tooth. All specimens were thermo-cycled (5,000 cycles - 5°C and 55°C). Each specimen was loaded till failure using universal testing machine, then the mode of failure was recorded. Two-way ANOVA and Tukey’s post-hoc tests were employed for data analysis (P< .05). Results: The highest fracture load was recorded with FP group (2578.3± 337 N) and the lowest value was recorded with TZ group (1511.42± 168 N). Two-way ANOVA test showed a significant difference among studied groups. Post hoc test showed significant differences between each pair of groups, except a non-significant difference (P = .787) between TZ and FZ groups. Conclusions: The fracture strength of molars restored with endo-crowns can enhanced by increasing the extension depth into pulp chamber. Moreover, PEEK is considered a promising material for endo-crowns.