Cell-free remineralization of enamel with biomineralizing peptide ADP5

Objectives: To develop cell-free remineralization of non-cavitated white spot lesions (WSL) of human enamel with ADP5, an amelogenin-derived peptide.
Methods: Cervical enamel of extracted human teeth were demineralized for 1.5 weeks in 0.2% acetic acid in 2.2mM CaCl₂ / 2.2mM K₂HPO₄ solution. Teeth were assigned to 6 groups (n=5 each) and treated either with ADP5 for 30minutes then 48mM Ca²⁺/28mM (PO₄)³⁻ for 2 hours (Group 1), or with ADP5 for 30minutes then 1100ppm F and 48mM Ca²⁺/28mM (PO₄)³⁻ for 2 hours (Group 2), or with 48mM Ca²⁺/28mM (PO₄)³⁻ for 2 hours (Group 3), or with 1100ppm F and 48mM Ca²⁺/28mM (PO₄)³⁻ for 2 hours (Group 4), or with 20,000 ppm F and 48mM Ca²⁺/28mM (PO₄)³⁻ for 2 hours (Group 5), or left with no treatment (Group 6) at 37^oC. Samples were prepared for scanning electron microscopy (SEM) for physical analysis of the structure and energy-dispersive X-ray-spectroscopy (EDS) for elemental compositions. The 2-sample t-test power analysis was used to determine sample size.
Results: ADP5 with Ca²⁺/PO₄³⁻ (Groups 1 & 2) showed a continuous layer of at least 10 μm-layer of mineral layer containing nanoscale plate-like calcium phosphate crystals growing from the surface of the underlying porous enamel. The new mineral layer was thick enough to mask the exposed enamel rods. At concentrations of 20,000 ppm F (Group 5), EDS data revealed a large fluoride peak that was twice the size as that of Ca²⁺, indicating the presence of CaF² particles. The cross-sectional morphology presented a 5 to 10-μm layer of spherical CaF₂ particles. No new mineral layer was observed in the groups 3 & 6. Group 4 displayed in some areas aggregates of discontinuous CaF₂ particles with exposed enamel rods.
Conclusions: A continuous layer of plate-like octacalcium phosphate (OCP) and hydroxyapatite (HAp) crystals was observed when ADP5 was applied on artificially induced WSLs on human teeth compared to the conditions, which lacked the biomineralizing peptide.