Halloysite Nanotubes as Nanofillers to Reinforce Glass Ionomer Cements

Glass ionomer cements (GICs) have many clinically favourable properties such as adhesion to tooth tissues and moisture tolerance, but have low strength compared with other direct dental restorative materials, and this limits their applications. Nanomaterials have shown promise in reinforcing biomaterials, including cements. The aim of this study was to explore whether the compressive strength of a GIC could be enhanced using halloysite nanotubes (HNTs), a naturally occurring hollow tubular material derived from clays. 1-15% by mass HNT was incorporated into GICs, coupled with adjustments to the powder:liquid ratio to account for the lubricating properties of HNTs. Compressive strength was measured, and the most promising formulation further investigated with respect to other mechanical and physical properties. 5% HNTs with 5:1 powder:liquid increased compressive strength by 34% with respect to unmodified GIC (187 and 140 MPa respectively; p=0.0004). Hardness and wear resistance also increased by 11% (p=0.0006) and 22% (p=0.0139) respectively. Diametral tensile strength was unchanged (p=0.795) and fluoride release from HNT-GICs was reduced by an average of 14% over 28 days. In conclusion, these nano-reinforced cement materials with improved mechanical properties could ultimately provide GICs for a wider range of uses in restorative dentistry.