Nano-structural reinforcement of glass ionomer cement: unleashing the potential of hydroxyapatite and tetracalcium phosphate

Objective: To investigate the effects of hydroxyapatite (HAP) and tetracalcium phosphate (TTCP) addition into fabricated nano-sized GIC. Methods: Seven groups were evaluated in this study. Group A, consisting of commercially available GIC served as control group, while the remaining six groups (Groups B-G) comprised fabricated GIC associated with different ratio of HAP and TTCP. Chemical characterization was performed using FE-SEM, EDX, XRD, and FTIR. Physio-mechanical assessment included particle size distribution (PSD), initial setting time, ions release (F^-, Ca²⁺, PO₄^3-), pH measurement, and compressive strength. Statistical analyses were performed using one-way and repeated measures ANOVA, followed by post-hoc tests (p < 0.05). Results: The fabricated nano-sized GIC powder exhibited an amorphous phase, confirmed through XRD and FTIR analyses, and achieved a significantly reduced particle size of 92.2 ± 2.69 nm, compared to 769.3 nm in control group. Incorporating TTCP extended the setting time, particularly at 570 seconds longer than the control group, while HAP reduced it by up to 422 seconds. Calcium ion release was significantly enhanced in TTCP-modified GIC, with Group C (10 % TTCP; 0 % HAP) showing the highest release (2.4 ppm), while HAP-modified GICs demonstrated significantly improved compressive strength, reaching up to 112.25 ± 4.80 MPa in Group G (0 % TTCP; 10 % HAP). Fluoride ion release was consistent across all experimental groups, peaking on the first day and gradually decreasing over 28 days. The addition of TTCP and HAP shifted the pH of GICs from acidic (pH ∼1.0) to neutral (pH ∼6.9). Conclusions: The incorporation of TTCP and HAP into the fabricated GIC enhanced ion release and adjusted pH, showing potential advantages for dental applications. Further investigations are needed to explore their clinical relevance and long-term performance. Clinical significance: This study highlights that TTCP additions significantly enhance calcium/phosphate ion release and shift pH toward neutrality, whereas HAP-modified GICs improve compressive strength to levels meeting restorative standards. However, TTCP-modified GICs exhibit prolonged setting times and notably reduced compressive strength, limiting their suitability for load-bearing restorations; they are better positioned as liners/bases or for non–load-bearing, remineralization-oriented applications where bioactivity is prioritized over mechanical performance.