Demineralization is the process of removing calcium and phosphate ions from hydroxyapatite crystals in hard tissues of the teeth. The lost calcium and phosphate ions can be replaced by application of a remineralization agent ie hydroxyapatite. Hydroxyapatite can be synthesized from natural ingredients such as fish bones. In this study was to determine the effect of hydroxyapatite from bone waste of tilapia fish (Oreochromis niloticus) on hardness of enamel surface. Thirty-two premolar teeth

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... mounted on self cured acrylic resin and were divided into 4 groups and demineralized. Enamel hardness (pre-test) was measured by Vickers Hardness Tester and followed by a process of remineralization using a hydroxyapatite paste (HA) that synthesized from the tilapia bone by precipitation method. The paste was applied to group A (5% HA), B (10% HA), C (15% HA) then was immersed in artificial saliva while group D (control) was only immersed in artificial saliva. The surface hardness of enamel was measured again (posttest) after 7 days of treatment. The surface hardness of enamel for group A (424,19±14,50); B (456,58±9,82); C (482,64±9,90); D (418,44±8,23). Statistical tests showed that there were significant differences between the treatment group and the control group except group A. Application of hydroxyapatite paste from bone waste of the tilapia (Oreochromis niloticus) could increase the surface hardness of the enamel.