Abstract: Models of tooth with early stage caries were treated with suspension of toothpaste containing hydroxyapatite (HA).The effect of re-mineralization of tooth enamel surface was assessed by scanning electron microscopy and microhardness value measurement.Cadmium ion solutions with initial mass concentration of 0.2 mg·L^-1 were mixed with toothpaste suspensions with and without addition of HA respectively and then been kept still for 24 h.The residual cadmium ion mass concentration of the supernatant was measured by inductively coupled plasma emission spectrometer and the adsorption effect of cadmium ion was calculated.Results showed that the toothpaste containing HA could significantly re-mineralize and improve the microhardness of artificial enamel caries.The Vicker's hardness values were 253.87±5.66 and 291.90±10.37 in HA group,higher than that of 199.73±7.11 and 200.07±9.84 in control group (P<0.05).The adsorption rate of cadmium ion of toothpaste containing HA is higher than that of the control group.

Key words: toothpaste, hydroxyapatite, caries, heavy metal