Interaction of Environmental Calcium/Phosphate with Glass Ionomers

Objectives: This study investigated the effect of environmental calcium (Ca) and phosphate (P) on the surface properties of highly viscous glass-ionomers (HVGICs). Methods: Fuji IX Fast (FN) (GC) and KetacMolar (KM) (ESPE) were mixed according to manufacturers'instructions, placed into customized molds (3mm long X 3mm wide X 2mm deep) and allowed to set. The specimens were kept in 100% humidity at 37~{!c~}C for 1 hour and stored in solutions with varying Ca and P levels at pH 3, 5 and 7. The levels of Ca and P varied as follows: Group1 - Ca: 0mM, P: 0mM; Group2 - Ca: 2.4mM, P: 0mM; Group3 - Ca: 1.5mM, P: 0.9mM; Group4 - Ca: 1.2mM, P: 1.2mM; Group5 - Ca: 0mM, P: 2.4mM. After 4 weeks of exposure to different solutions at pH 3, 5 and 7, surface hardness and elastic modulus were determined using depth-sensing micro-indentation (n=7) (Instron-5848). The sectioned surfaces were observed with scanning electron microscopy (SEM) (JSM-5600). Multiple comparisons of hardness and elastic modulus were performed using ANOVA/post-hoc Scheffe's test (p<0.05). Results: Mean hardness ranged from 34.54HV to 111.06HV (FN) and 11.20HV to 69.97HV (KM), while mean elastic modulus ranged from 9.87GPa to 20.21GPa (FN) and 5.36GPa to 14.71GPa (KM). At pH 7 and pH 5, different level of environmental Ca/P did not significantly affect hardness/modulus of HVGICs. At pH 3, higher levels of environmental phosphate resulted in higher hardness/modulus of HVGICs. Under SEM, a microscopic surface reaction layer was observed when HVGICs were exposed to storage solutions with pH 3. The surface reaction layer was thinner when level of environmental phosphate was higher. Conclusion: Interaction of environmental calcium/phosphate with glass ionomers was pH and phosphate dependent.