Flexural strength of hydroxyapatite-added glass ionomer cement

Objective:This study aimed to evaluate the effects of adding hydroxyapatite and water storage on the initial and long-term flexural strength of glass ionomer cement. Methods:Conventional glass ionomer cement (Fuji IX GP) was used as the control and was mixed according to the manufacturer`s instructions. The same material was used as the base material into which 8% hydroxyapatite granules was mixed (GIC + HAp) at P/L 3.6. All specimens (N=6/group) were fabricated using a 25 x 3 x 3 mm stainless steel split mold and stored in distilled water, dry and humid environment for a period of 15 min, 1h, 24h, 7d, 30d and 90d then subjected under a 3-point bending test. Analysis was done using Mann-Whitney test. Results: This study showed that adding hydroxyapatite to the glass ionomer cement yielded no significant difference in the long-term flexural strength (p>0.05) between the two cements in all three storage media. However, a significant increase in the initial strength of the cements added with hydroxyapatite was noted particularly after one h (28.9±6.8 MPa; p<0.05) and 24 h (32.1±4.9 MPa; p<0.05) in humid environment and after 24 h (25.9±1.4 MPa; p<0.01) in distilled water as compared to those of the control. Storage in both distilled water and humid environment yielded a significantly higher initial strength particularly after 15 min for both control (p<0.01) and GIC + HAp samples (p<0.05) compared to those in dry storage. Conclusion: Hydroxyapatite may hasten the increase in the initial flexural strength of the glass ionomer cement in an aqueous environment without significantly affecting its long-term maturation.