Improving mechanical properties of glass ionomer cements with fluorhydroxyapatite nanoparticles

Glass ionomer cements show great potential as low cost, minimally invasive dental restorative materials. However, their use is limited by relatively poor mechanical properties, especially fracture toughness. One possibility for improving their fracture toughness is through the addition of fluorhydroxyapatite nanoparticles, which resemble the crystals found in tooth enamel. Hydroxyapatite and fluorhydroxyapatite nanoparticles with fluoride substitution levels ranging from 0 to ∼95% and a small amount of AB-type carbonate substitution have been prepared and added to commercially available Fuji IX glass ionomer cement to examine the effect of the nanoparticles on the cement mechanical properties. The fluoride substitution level and other nanoparticle properties were accurately determined using a combined approach of XRD, XPS, TEM and FTIR. The material was in the form of agglomerated single crystal nanorods with volume average dimensions of approximately 30 × 30 × 60–80 nm. This combination of chemistry and morphology closely resembles the crystals in enamel and makes these particles perfect candidates for producing reinforced glass ionomer dental restorative materials. Preliminary tests have been carried to assess the affect of these particles on the compressive strength, hardness, and fracture toughness of Fuji IX hand mixed cement. A significant increase was found for hardness, but no significant change was found for fracture toughness or compressive strength, although there appeared to be a slight trend of increasing compressive strength with wt% nanoparticle addition. The results indicate that the mixing procedure must be carefully controlled to obtain the desired mechanical effect without degrading the working properties of the cement.