Development and characterisation of dental composites containing anisotropic fluorapatite bundles and rods

Objectives. To develop dental composites incorporating fluorapatite (FA) crystals as a secondary filler and to characterise degree of conversion, key mechanical properties and fluoride release. Methods. FA rod -like crystals and bundles were hydrothermally synthesised and characterised by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), X-ray diffraction (XRD) and 19F MAS-NMR. Composites were formulated containing BisGMA/TEGDMA/BisEMA and barium-aluminium-silicate glass (OFA). FA crystals were incorporated at 10 (10FA), 20 (20FA), 30 (30FA) and 40 wt% (40FA) maintaining a filler content of 80 wt% (63-67 vol%). Degree of conversion (DC), flexural strength (FS), flexural modulus (FM), fracture toughness (K1c), Vickers hardness (HV) and 2 -body wear were measured. Fluoride release was measured in neutral and acidic buffers. Results. XRD and 19F MAS-NMR confirmed that only FA was formed, whilst SEM revealed the presence of single rods and bundles of nano -rods. DC ranged between 56-60% (p > 0.05). FA composites showed lower FM and lower FS (p < 0.05), but comparable wear resistance and HV (p > 0.05) to OFA. 30FA and 40FA showed similar K1c to OFA (p > 0.05), with SEM showing evidence of toughening mechanisms, whereas 10FA and 20FA showed lower Kic (p <0.05). FA containing composites released fluoride that was proportional to the amount of FA incorporated (p <0.05) but only under acidic conditions. Significance. The addition of FA to the experimental composites reduced strength and stiffness but not the DC, hardness or wear rate. 30FA and 40FA had a higher Kic compared to other FA groups. Fluoride release occurred under an accelerated acidic regime, suggesting potential as a bioactive 'smart' composite. (c) 2020 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.