Conversion Degree and Push-out Bond Strength of Two Composite Cements

Objectives: Aim of this study was to evaluate, by means of a non-destructive procedure, the degree of conversion (DC) of two different composite cements. Subsequently, the same samples underwent a push-out test to investigate the bond strength at the adhesive interface after DC microRaman evaluation. Methods: 24 single-rooted teeth were cut at the CEJ, endodontically treated and a 8mm post-space deep was made. Teeth were randomly divided in two groups (n=12) and RelyX Fiber Posts were luted using 2 composite cements: Multilink Automix (group A/control) and an experimental cement (group B/self-adhesive). Composites were cured (120s, 400mW/cm2) and each sample was cut, perpendicularly to the long axis, in 2mm-thick slices starting from the CEJ. The sections corresponding to 1mm, 3mm, 5mm were analysed with the microRaman spectrometer; then a push-out test evaluated the resistance to the displacement of the post. Finally the slices were analysed with an optical microscope to evaluate the nature of failure. Data were statistically evaluated (ANOVA, Tukey’s, p<0.05). Results: In group A we recorded higher strength at debonding (p<0.001) and higher DC (p<0.001) compared to group B. In both groups push-out strength was higher at 1mm than at 5mm (p=0.002). Most common failures (POF) are recorded at the cement-dentin interface. Group B didn’t show any POF at cement-post interface. Conclusions: an experimental cement self-adhesive showed a lower DC and a lower bond strength compared to the “traditional technique” composite (group A). Distance from the CEJ didn’t affect the DC, due to autopolymerizing component of both materials.