Mechanical and biological enhancement of glass ionomer cement through nanofiller integration: a preliminary study for improved restorative applications.
TL;DR
The optimized formulation was G4 at 5 wt% total nanoparticle loading, which improved the mechanical performance of Fuji IX GIC while maintaining acceptable cytocompatibility and color stability.
Abstract
Glass ionomer cements (GICs) are widely used in restorative dentistry because of their chemical adhesion to dental tissues and fluoride release. However, their clinical performance may be limited by insufficient mechanical strength, reduced durability under occlusal loading, and aesthetic concerns. Nanoparticle reinforcement may help address these limitations. This study screened hybrid tri-nanofiller formulations containing nano-hydroxyapatite (nHA), nano-zirconium oxide (nZrO₂), and nano-aluminum oxide (nAl₂O₃) in Fuji IX GIC to identify an optimized formulation using a sequential screening approach. Surface characteristics, structural features, cytocompatibility, and color stability were also evaluated. One unmodified Fuji IX control and sixteen experimental subgroups were prepared in a 4 × 4 comparative screening matrix using four tri-nanofiller formulations and four total nanoparticle loadings: 3, 5, 7, and 9 wt%. In the first stage, all subgroups were screened using compressive strength (CS) and diametral tensile strength (DTS). Mechanical data were analyzed using within-loading one-way ANOVA with Tukey's HSD post hoc test, and two-way ANOVA was additionally performed to assess the effects of formulation, loading concentration, and their interaction. Based on mechanical screening, the G4 formulation was selected for further evaluation using atomic force microscopy (AFM), cell counting kit-8 (CCK-8) cytotoxicity testing on human dental pulp stem cells (hDPSCs), color stability assessment, scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). G4 at 5 wt% total nanoparticle loading showed the most favorable mechanical performance, with CS = 160.4 ± 7.64 MPa and DTS = 15.66 ± 0.92 MPa. This subgroup corresponded to 95 wt% Fuji IX, 3.5 wt% nZrO₂, 1.0 wt% nHA, and 0.5 wt% nAl₂O₃. SEM/EDS supported nanoparticle incorporation and homogeneous elemental distribution. AFM analysis showed lower surface roughness at 3% and 5% than at higher loadings. The CCK-8 assay showed no significant cytotoxicity for G4 at 3, 5, 7, or 9 wt% compared with the unmodified control. Color stability remained clinically acceptable at 3 and 5 wt%, whereas 7 and 9 wt% showed greater discoloration. The optimized formulation was G4 at 5 wt% total nanoparticle loading, which improved the mechanical performance of Fuji IX GIC while maintaining acceptable cytocompatibility and color stability.