The aim of this in vitro study was to evaluate the effect of adding nano-crystalline fluorine hydroxyapatite (FHAp) bioceramic into dental adhesive on the mechanical properties and bonding strength to dentin substrate. FHAp was synthesized using a sol–gel method and characterized using x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Citric acid was used as the coupling agent. The fillers were added to an ethanol-based experimental dental adhesive containing Bis-GMA, TEGDMA, and HEMA (weight ratio 2:1:1). Camphorquinone (0.1%w) and ethyl-4-dimethylaminobenzoat (0.1%w) were used as photo-initiator and co-initiator for photo-polymerization at the weight ratios of 0, 0.2, 0.5, 1, and 2%. Flexural strength and modulus of photo-polymerized specimens were measured using a three-point bending test (n = 10 for each group). Degree of conversion (DC) was measured using FTIR. Microtensile bond strength test (μTBS) to bovine dentin was measured (n = 10 for each group). The data were analyzed using one-way ANOVA and Tukey post hoc tests (α = 0.05). Results showed that the maximum flexural strength and modulus were obtained by adding 0.2 and 1% FHAp, respectively. Therefore, the FHAp fillers made the adhesive stiffer but more brittle up to 1% w/w. Adding 2% fillers decreased the mechanical properties and precipitation of some fractions of fillers was observed. The SEM imaging showed an integrated interface between fillers and the resin matrix. Moreover, the DC was not affected by the filler content and all samples showed more than 98% of conversion. Maximum μTBS was obtained in 1%-filled specimen. In conclusion, adding 1% w/w FHAp bioceramic fillers may improve the bonding strength to the dentin substrate. More studies are needed to evaluate the bioactivity of FHAp-filled dental adhesives.
Journal of the Australian Ceramic Society – Springer Journals
Published: May 26, 2018