Surface characterizations of glass-ionomers in acidic environments with calcium/phosphate supplement

Objectives: This study investigated the surface characteristics of highly viscous glass-ionomers (HVGICs) exposed to acidic conditions supplemented with calcium (Ca) and phosphate (P). Methods: Two capsulated HVGICs (Fuji IX Fast [FN], GC; KetacMolar [KM], ESPE) were mixed according to manufacturers' instructions. Specimens were fabricated, kept in 100% humidity at 37℃ for 1 hour and stored in acidic solutions (pH 3) with varying Ca & P levels: Group A - Ca: 2.4 mmol/l, P: 0 mmol/l; Group B - Ca: 1.5 mmol/l, P: 0.9 mmol/l; Group C - Ca: 1.2 mmol/l, P: 1.2 mmol/l; Group D - Ca: 0 mmol/l, P: 2.4 mmol/l. Acidic solution without Ca & P was used as control. After 4 weeks exposure to acidic solutions, the top surface of specimens was examined by SEM, EDS (JSM-5600, JEOL Ltd. Japan) & FTIR-ATR (Spectrum 2000, Perkin Elmer Instruments Inc.). Results: FN and KM showed similar trends in all conditions. Under SEM, Group A and Control specimens exhibited porous surface morphology, while many small particles were observed in Groups B, C and D. EDS X-ray microanalysis showed that the surface of conditioned specimens composed primarily of Al, Si, and Sr/Ca with P observed only in Groups B, C and D. FTIR-ATR spectra of Groups B, C and D displayed peaks around wavenumber of 1060 cm^-1 which may be assigned to P-O stretch band. Conclusions: Environmental phosphate present in acidic conditions may precipitate on the surface and improve acid resistance of HVGICs.