The role of chicken egg-shell nano- hydroxyapatite as fillers on the surface hardness of glass ionomer cement

Background: In the last years, glass ionomer cement (GIC) has become an adhesive restorative material used to treat dental caries. However, GIC has relatively low surface hardness compared to other restorative materials that limit its performance. This study aimed to investigate the role of nano-hydroxyapatite (nHA) as fillers produced from chicken-eggshells to improve the GIC surface hardness. Materials and methods: The study was a laboratory experiment employing a post-test-only control group design. Chicken-eggshell nHA was synthesized using the precipitation method. Surface hardness was investigated for 25 samples in five groups, four treatment groups and one control group, each with five samples. For each treatment sample, 3%, 5%, 7%, and 9% of chicken-eggshell nHA powders were added to the GIC powders. The GIC surface hardness was characterized using a Vickers Microhardness Tester. The obtained data were analyzed using a linear regression model. Results: The chicken-eggshell nHA had a mean size of 39.15 nm. Mean surface hardness after adding chicken-eggshell nHA was 70.21–79.27 HV, higher than that of GIC before the addition (61.86 HV). The treatment groups containing 7% and 9% chicken-eggshell nHA filler showed significant differences from control group (p < 0.01). Interestingly, mean GIC surface hardness increased significantly by 61% with an increasing concentration of chicken-eggshell nHA. Conclusion: The chicken-eggshell nHA filler increases GIC surface hardness