الفهرس 
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Abstract
Objectives: This study was conducted to compare and evaluate in-vitro shear bond strength of resin composite bonded to two different dentin substitutes, resin-modified glass-ionomer cement and calcium silicate-based cement (Biodentine), using a universal adhesive in etch-and-rinse and self-etch adhesive modes, and characterizing their failure modes Materials and Methods: Forty discs of each dentin substitute, resin-modified glass-ionomer (group A) and Biodentine (group B) were constructed in a split Teflon mold (4mm diameter and 2mm thickness), with a total of 80 discs. A second split Teflon mold (6mm diameter and 2mm thickness) was used to bond resin composite to each specimen of dentin substitutes, using the same universal adhesive. Then each group was further equally subdivided into two subgroups. The first one was bonded with E&R adhesive mode and the second was bonded with SE adhesive mode. Shear bond strength test was performed at a cross-head speed of 1mm/min. Debonded specimens were examined under stereomicroscope at 20× magnification to evaluate the failure modes. Results: In general, high statistically significant difference was observed between the two dentin substitutes (P<0.001**). The shear bond strength of resin composite to RMGIC was significantly higher than that to Biodentine. It was also found that there was no significant difference between the E&R and SE adhesive modes, when were applied either with RMGIC or Biodentine. Modes of failure were predominately mixed failure modes in RMGIC specimens while in Biodentine specimens were predominately cohesive failure modes within Biodentine substrate. Conclusions: RMGIC achieved adequate SBS to withstand contraction forces from overlying resin composite. So, resin composite restoration can be placed immediately over RMGIC, completing the procedure in single appointment. However, Biodentine is a weak material in its early setting time. So, it is important to leave Biodentine to set and mature for longer time period before application of overlying resin composite restoration.