Determination of the Properties of an Experimental Dental Composite with Addition of Hydroxyapatite with Varied Micro and Nano Particle Size: An Evaluation of Mechanical Properties, Ion Release, and Surface Characteristics

While resin-based dental composites (RBCs) are widely recognized as the golden standard in restorative dentistry, there is a need for improvement in their properties, including their potential biofunctional behavior. The aim of this study was to assess the impact of hydroxyapatite (HA) filler on the mechanical properties and provide preliminary evidence of biofunctional potential of prepared experimental RBCs. The effects of two forms of HA filler, mHA (2.5 μm) and nHA (<200 nm), in three concentrations (2.5, 5.0, and 7.5 wt.%) were tested in regard to hardness (HV), diametral tensile strength (DTS), flexural strength (TPB), flexural modulus, and calcium and phosphate ion release. Modification with HA improves the Vickers hardness and diametral tensile strength of RBCs, but has mixed effects on the flexural strength. The tested materials meet the minimum requirements for DTS and TPB for commercial composites, but their HV is closer to flowable materials. Calcium and phosphorus are detectable on the surface of HA-modified materials via SEM-EDS. There is also preliminary evidence of calcium and phosphate ion release in materials modified with HA, with the concentrations of 5 wt.% HA and above, providing the highest levels.