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The fracture resistance of wide root canals can be improved by using glass fiber-reinforced dowels relined with composite resin as an alternative to increasing the thickness of luting cement; however, the percentage nanoleakage would increase. On the other hand, the recently introduced prefabricated glass fiber-reinforced core can be considered a promising technique, but further investigations are necessary.

The amount of released ions is directly proportional to HP concentration and time of immersion. Specimens exposed to both HP and acetic acid showed increased weight loss and a higher corrosion rate than those exposed to acetic acid only. Surface roughness values were time and HP concentration dependent.

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Statement of the problem: Conservative esthetic restorative dentistry has become an essential component in modern clinical practice. However, the inlay retained fixed partial dentures (IRFPDs) have a higher risk of fracture and dislodgement due to minimal preparations. Purpose: to compare fracture resistance and retention of Lithium disilicate (IPS e.max) and Polyetheretherketone (BioHPP) IRFPDs fabricated with heat-press technique and CAD/CAM system. Materials and Methods: Forty models, each including extracted mandibular 2 nd premolar and 2 nd molar embedded in an epoxy resin block with 10 mm intra-abutment distance representing missing mandibular 1 st molar were constructed. The premolar and molar of each model received standardized class II inlay preparations. The constructed models were randomly divided into four groups; Group (1): IPS e.max Press IRFPDs, Group (2): IPS e.max CAD IRFPDs, Group (3): BioHPP Granulates IRFPDs, and Group (4): breCAM.BioHPP IRFPDs. All IRFPDs were cemented using RelyX Ultimate adhesive resin cement. Samples were stored for 24 hours in distilled water at 37°C, and then thermocycled for 5000 cycles. Universal testing machine was used to measure fracture and dislodging loads. Samples were examined for determination of failure mode using a magnifying lens. Results: The statistically significant highest mean dislodging load value was obtained in IPS e.max Press IRFPDs, followed by IPS e.max CAD, with the least value recorded in breCAM.BioHPP. In contrast, breCAM.BioHPP IRFPDs revealed the statistically significant highest mean fracture load value, followed by BioHPP Granulates, while the least mean fracture value was recorded in IPS e.max Press. Most failure occurred in IPS e.max groups was connector fracture, while in BioHPP groups was plastic deformation. Conclusions: Retention and fracture resistance of metal-free inlayretained bridges are significantly affected by both; material type and construction method. BioHPP has significant advantages for dental applications because of higher fracture resistance and better stress distribution. The bond strength at IPS e.max/ resin cement interface is considered a reliable bond presenting better retention to IRFPDs. Being a brittle material, connector fracture is the predominant failure mode of IPS e.max IRFPDs; however, BioHPP has low elastic modulus showing plastic deformation as a predominant failure mode.

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Purpose: The present study aimed to evaluate the effect of artificial aging on the optical properties and flexural strength of ultra-translucent tetragonal/cubic zirconia. Materials and Methods: A total of 30 (N=30) ultra-translucent cubic zirconia discs (DD cube X 2) were fabricated. Samples were divided into 3 equal groups (n=10) according to the aging protocol followed including Group (1): (control), samples were not subjected to hydrothermal aging protocol, (n=10), Group (2): Samples were subjected to one-hour hydrothermal aging protocol, (n=10), Group (3): Samples were subjected to 3 hours hydrothermal aging protocol, (n=10). Samples of each group were subjected to optical properties determination using spectrophotometer including (Translucency parameter TP, Contrast ratio CR, Change in color ΔE) and biaxial flexural strength determination using universal testing machine. Obtained values were statistically analyzed. Results: Statistical analysis using ANOVA test revealed no significant difference between the three tested groups. The highest mean value of translucency and biaxial flexural strength were recorded at the control group. While group (3) samples recorded the lowest mean values. Color change (ΔE) was performed for groups (2 and 3) to detect the amount of color change from control group. Group (3) samples recorded higher mean values than group (2) samples. Conclusions: Hydrothermal aging did not affect the optical properties and flexural strength of tetragonal / cubic zirconia (DD cube X 2).

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