The present study aimed to formulate an experimental adhesive (EA) and reinforce it with 5 wt.% titanium dioxide (TiO2) or zirconium oxide (ZrO2) to yield 5% TiO2 and 5% ZrO2 adhesives, respectively, and then analyze the impact of this reinforcement on various mechanical properties of the adhesives. The EA contained a blend of monomers such as bisphenol A glycol dimethacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA), 2-hydroxyethyl methacrylate (HEMA), and ethyl 4-dimethylamino benzoate and camphorquinone. The EA included ethyl 4-dimethylamino benzoate and camphorquinone photo-initiators, and diphenyliodonium hexafluorophosphate (DPIHP) was also included to act as an electron initiator. The TiO2 and ZrO2 nanoparticles were incorporated into the EA post-synthesis. To characterize the filler nanoparticles, scanning electron microscopy (SEM) and line-energy dispersive X-ray (EDX) spectroscopy were performed. The adhesives were characterized by analyzing their rheological properties, shear-bond strength (SBS), and interfacial failure types. Further, the resin–dentin interface was also analyzed via SEM. The TiO2 nanoparticles were spherically shaped on the SEM micrographs, while the ZrO2 nanoparticles were seen as non-uniformly shaped agglomerates. The EDX mapping demonstrated the presence of Ti and oxygen for TiO2 and Zr and oxygen for the ZrO2 nanoparticles. Both 5% TiO2 and 5% ZrO2 adhesives revealed decreased viscosity as compared with the EA. The 5% TiO2 adhesive demonstrated higher SBS values for both non-thermocycled (NTC) and thermocycled samples (NTC: 25.35 ± 1.53, TC: 23.89 ± 1.95 MPa), followed by the 5% ZrO2 adhesive group (NTC: 23.10 ± 2.22, TC: 20.72 ± 1.32 MPa). The bulk of the failures (>70%) were of adhesive type in all groups. The SEM analysis of the resin–dentin interface revealed the development of a hybrid layer and resin tags (of variable depth) for the EA and 5% TiO2 groups. However, for the 5% ZrO2 group, the hybrid layer and resin tag establishment appeared compromised. Reinforcement of the EA with TiO2 or ZrO2 caused an increase in the adhesive’s SBS (with the 5% TiO2 group demonstrating the highest values) in comparison with the EA (without nanoparticles). However, both nanoparticle-containing adhesives revealed decreased viscosity compared with the EA (without nanoparticles). Further studies investigating the impact of diverse filler concentrations on the properties of adhesives are suggested.

The present study aimed to prepare experimental adhesives (EAs): 5 wt.% titanium dioxide (TiO2) adhesive; and 5 wt.% zirconium oxide (ZrO2) adhesive; and analyze their impact on bond integrity of fiber posts to root dentin, and viscosity. The EA was composed of: bisphenol A glycol dimethacrylate (BisGMA); triethylene glycol dimethacrylate (TEGDMA); 2-hydroxyethyl methacrylate (HEMA); and ethyl 4-dimethylamino benzoate and camphorquinone. TiO2 and ZrO2 particles were individually incorporated into the EA at 5 wt.%, to form two groups (5% TiO2 and 5% ZrO2). The adhesives, with particles, were characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy. The bonded interface was evaluated for adhesive–dentin penetration at the interface, using SEM. The study adhesive groups (EA, 5% TiO2 and 5% ZrO2) were analyzed for rheology and push-out bond strength of the fiber post to root dentin. Data were analyzed using analysis of variance and post hoc comparison. Both TiO2 and ZrO2 particles had irregular, non-uniform shapes. The EDX mapping showed the elemental presence of Ti (TiO2), Zr (ZrO2) and oxygen in formulated adhesives. The 5% TiO2 and 5% ZrO2 adhesives showed a decrease in viscosity, compared with the EA. Bond strength among the 5% TiO2 and 5% ZrO2 adhesives was statistically comparable (p > 0.05), but higher than the control group (10.57 ± 1.45 MPa) (p < 0.05). Reinforcement of the experimental dentin adhesive with 5% TiO2 or 5% ZrO2 increased the push-out bond strength of the fiber post to root dentin, in comparison with the EA. Particle-incorporated adhesives (5% TiO2 and 5% ZrO2) displayed decreased viscosity, compared with the EA (without particles).