Push-out bond strength of traditional and hollow fiber post cemented with a dual-curing self-adhesive resin

Aim: The purpose of this study was to evaluate the push-out bond strength of traditional glass fiber post and newly marketed glass fiber hollow post, both cemented using a dual-curing self-adhesive resin. Methods: Seven extracted human premolars with single canals were selected for the study. The crowns were removed using a size 701 high speed fissure bur. The root canals were mechanically prepared using ProTaper Universal until #F4 instrument and they were obturated using Thermafil Obturator #F4. A post space was obtained drilling a 7mm depth hole with a pre-calibrated 1.2mm diameter tip. Prepared teeth were randomly divided in two groups: a full post was luted in Group 1 (n=3), while a hollow post in Group 2 (n=4) by using a dual-curing self-adhesive resin cement. Treated tooth were mounted in resin blocks and sectioned perpendicular to the long axis of the root canal. Six 500 µm thick slices were obtained from each specimen. The push-out test was performed on each slice. Student’s t-test was used to compare push-out bond strength values between the two group. While comparisons of push out bond strength values among root region (cervical, middle and apical part), for each group, were performed with one-way ANOVA test. After the push-out test all specimens were analysed by scanning electron microscope (SEM) to determine the fracture patterns. The cross section of both the full and hollow posts were studied by SEM and EDS analysis to evaluate the amount and distribution of the glass fiber, as well as their chemical composition. The cross sections were prepared by embedding the samples into epoxy resin., The embedded samples were then grounded and polished on a plane orthogonal to the long axes of the sample until a complete exposure of the post cross section. Results: Push-out bond strength of Group 2 was significantly higher than that of group 1, respectively 6.38 MPa ±1.59 and 2.23 ± 3.64 MPa. No differences were observed between the three root regions (cervical, middle and apical part) in the same group. In both group the predominant failure mode, observed in 50% of the samples in Group 1 and in 44.4% of the samples in Group 2, was represented by mixed fracture, with resin cement covering 0-50% of the post diameter. In the hollow post, the glass fibers appeared of similar to each other and homogeneously arranged within the matrix. Differently, in the full post, fibers with different size with a lower homogenous arrangement where observed. Also, a different chemical composition of the glass fiber in the two posts was observed. The hollow post contain mainly SiO2, Al2O3 e CaO, whereas full post are predominantly composed of silica. Conclusion: The glass fiber hollow post showed significantly higher bond strength values compared to the glass fiber full post cemented using the same dual-curing self-adhesive resin.