Development and characterisation of novel fluorapatite containing dental composite materials

Objectives: The objectives of this study were to develop model dental composites incorporating fluorapatite (FA) as secondary filler and to characterise their physical and mechanical properties and fluoride ion release. Methods: Experimental composites were formulated containing BisGMA/TEGDMA/BisEMA and barium aluminium silicate glass as the primary filler. FA rod-like crystals and bundles were synthesised using a hydrothermal method and incorporated at 0 (0FA), 10 (10FA), 20 (20FA), 30 (30FA) and 40% (40FA) by mass into the previously identified optimum experimental composite, maintaining an overall filler content of 80%wt. 0FA and TetricEvoCeram (TC) were used for comparison as the experimental and the commercial controls, respectively. Two-body wear, Vickers Hardness (HV), Degree of Conversion (DC), Flexural strength (FS), Flexural modulus (FM), Fracture Toughness (K1C) and fluoride ion release were measured for each composition. Quantitative analysis of wear volume was carried out using a noncontact profilometer. Qualitative imaging of wear and fracture surfaces was undertaken using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). Statistical analysis was conducted using SPSS version 21. Results: All experimental composites showed similar wear resistance (p > 0.05) and enhanced microhardness compared to TC (p < 0.05). DC for all composites ranged between 56-60% at 20s polymerisation (p > 0.05). FA composites showed higher FM (p < 0.05) and similar FS (p > 0.05) to TC but lower FM and FS when compared to 0FA. 30FA and 40FA showed similar K1C to TC and 0FA (p > 0.05), whereas 10FA and 20FA showed lower K1C when compared to the other groups (p < 0.05). Under neutral pH, no fluoride release was detected from FA containing composites. However, under acidic conditions (pH 4), FA containing composites released fluoride when compared to the controls (p < 0.05), the amount of which was proportional to the amount of FA incorporated within the samples, i.e. 40FA> 30FA > 20FA > 10FA (p < 0.05). Conclusions: Experimental dental composites were successfully produced incorporating FA as secondary filler. The addition of FA did not affect the key physical and mechanical properties when compared to the commercial control. FA composites showed short and long term fluoride release under acidic conditions showing a promising step towards a potential “smart” fluoride releasing dental composite.