BackgroundThis study aimed to evaluate the bond strength and the penetration depth of two adhesive systems to a new experimental semi-IPN fiber post versus a commercial post.Material and MethodsExperimental Kevlar fiber (KF) and control everStick®POST (ES) posts (n=20/ group) with a diameter of 1.5 mm were used, 10 posts coated with StickResin (SR) and the other 10 posts coated with Scotch bond multipurpose (SBMP) adhesives. Composite resin buildup was performed over each post, using a cylindrical plastic mold (10 mm × 6 mm). Four discs of 2 mm thickness were prepared from each post/composite buildup and underwent pushout bond strength test at a crosshead speed of 0.5 mm/min accompanied by failure mode analysis. A further three specimens from each subgroup were bonded with adhesives labeled with 0.1 wt% Rhodamine B and embedded in acrylic resin, sectioned and examined under a confocal Laser-scanning microscope (CLSM) to measure the depth of resin penetration. Statistical analysis included ANOVA and Tukey test, the significance level was assumed at a p-value less than 0.05.ResultsThe push-out bond strength of KF was comparable to that of ES with both SBMP and SR adhesives (P >0.05). Bond strength value for SBMP was higher than SR adhesive in either ES and KF posts with no significant difference (P > 0.05). ES exhibited higher adhesive penetration depth compared with KF (p<0.05).ConclusionsThe bond strength of Kevlar post was comparable with the everStick post and the semi-interpenetrating structure of Kevlar post displayed some adhesive monomers diffusion indicating its usefulness as a new intracanal post. Key words:Kevlar fiber post, Bond strength, Penetration depth, Confocal, Semi-IPN polymer system.

The aim of this study was to assess the effect of preheating on the surface microhardness of different commercially available composite resins .Materials and Methods: Tubes of the composite resins were either kept at room temperature (24 ±1 0 C) or preheated for 40 min in a commercially preheating device to 40 0 C, 50 0 C and 60 0 C, respectively. From composite resin tubes, a total of 120 disk-shaped specimens (40 specimens of each composite resin, 10 disks from each temperature setting) were prepared by inserting uncured preheated composite resin into cylindrical nylon moulds (5 mm diameter × 2 mm height); before light polymerized for 40s with a lightemitting diode curing unit. The Vicker's microhardness number (VHN) of each specimen was measured. Two-way ANOVA and Tukey test were used to analyze the collected data at a significance level of 0.05. Results:In comparison to the room temperature, there was a significant increase in the mean VHNs of each composite resin by preheating to 40 0 C, 50 0 C and 60 0 C, respectively (p<0.05). For G-aenial posterior, Filtek Z350XT and Tetric-N-Ceram, at room temperature, the mean VHNs were 51± 4.3, 60.6± 3.7 and 76.6±1.4, respectively with significant difference between G-aenial posterior and Tetric-N-Ceram (p<0.05), while at 40 0 C, the mean VHNs were 65.7±2.5, 86.8±2.3 and 88.4±1.8, respectively with significant differences (p<0.05) between G-aenial posterior and the other two composites. At 50 0 C, the mean VHNs were 109.4±0.9, 104.4±3.4 and 114±0.71, respectively with no significant difference between composite resins. At 60 0 C, the mean VHNs were 122±3.2, 129±3.4 and 136±2, respectively with significant difference between G-aenial posterior and Tetric-N-Ceram (p<0.05). Conclusions:Preheating significantly increased the surface microhardness of all tested composite resins with the highest value observed for Tetric N-Ceram at 60 0 C preheating temperature.