In Situ Formation of Amorphous Calcium Phosphate to Remineralize Tooth Enamel

Objectives: To investigate the feasibility of remineralizing enamel using amorphous calcium phosphate in-situ formed during brushing from calcium ions released from chitosan microspheres and phosphate ions in water.
Methods: CaCl₂ was encapsulated in chitosan microspheres by water-in-oil emulsion/solvent-evaporation. The release of calcium ions from chitosan microspheres was studied at room temperature using double distilled (DD) water as the release medium. Hydroxyethyl cellulose dissolved in co-solvents of DD water and glycerin was lyophilized to remove water. The chitosan microspheres containing CaCl₂ were mixed with the above hydroxyethyl cellulose mixture to form Chitosan-Ca_P paste before use.
Sound teeth were cleaned and sectioned into halves using dental handpieces. The tooth halves were painted with nail varnish to expose 2mm x 5mm enamel. Acid cycles (6 hours of demineralization followed by 16.5 hours of remineralization per day) were used to evaluate the remineralization capability of Chitosan-Ca_P paste. The painted tooth halves were randomly divided into three groups, receiving no treatment (control group, n=9/group), MI paste plus (n=10/group), or Chitosan-Ca_P paste (n=10/group). In particular, enamel in Chitosan-Ca_P group was brushed using about 30 mg Chitosan-Ca_P paste in 150 µl Na₂HPO₄ solution. After 15 demineralization/remineralization cycles, the treated tooth halves were analyzed using scanning electron microscopes/ energy dispersive X-ray spectroscopy (SEM/EDX).
Results: The synthesized chitosan microspheres contained 14.0 ~ 16.6 wt% CaCl₂. The release of Ca²⁺ from chitosan microspheres was fast with about 97% of loaded Ca²⁺ released within 5 min. SEM/EDX results (Table 1) showed enamel receiving treatment of Chitosan-Ca_P paste or MI paste plus had statistically significant increase of both calcium contents and Ca/P weight ratios. However, there was no significant increase on the phosphorus contents.
Conclusions: Our results demonstrated that it is feasible to remineralize tooth enamel through in-situ formed amorphous calcium phosphate from the developed paste.