In Vitro Remineralization of Enamel Using Biomineralizing Peptide ADP5–pilot Study

Objectives: Develop a biomimetic approach to initiate cell-free re-mineralization of non-cavitated white spot lesions (WSL) of human enamel.
Methods: Extracted, caries-free permanent teeth were collected and stored in 70%ethanol (n=30). 4x4mm windows of cervical enamel were used for each experiment. Enamel surfaces were demineralized for 1.5 weeks in 1% acetic acid in 2.2mMCaCl₂/2.2mMK₂HPO₄ solution. Teeth were then assigned to 6 groups (n=5 each) and treated either with ADP5 for 30minutes then 4.08 mMCa²⁺/2.38mM(PO₄)³⁻ for 2hours (Group1), or with ADP5 for 30minutes then 1100ppmF and 4.08 mMCa²⁺/2.38mM(PO₄)³⁻ for 2hours (Group2), or with 4.08 mMCa²⁺/2.38mM (PO₄)³⁻ for 2hours (Group3), or with 1100ppmF and 4.08 mMCa²⁺/2.38 mM(PO₄)³⁻ for 2hours (Group4), or with 20,000ppmF and 4.08mMCa²⁺/2.38 mM(PO₄)³⁻ for 2hours (Group5), or left with no treatment (Group6) at 37^oC. Absorbance spectra were gathered before each experiment. Samples were prepared for scanning electron microscopy(SEM) and energy-dispersive X-ray-spectroscopy (EDS). 2-sample t-test power analysis was used to determine sample size.
Results: A continuous layer of Ca²⁺/PO₄³⁻ crystals was observed, possibly as a result of mineralizing effect of the peptide(Group1). The spherical particles formed island-aggregates when ADP5, fluoride, and (Ca)²⁺/(PO₄)³⁻ were present(Group2) as opposed to being widely disseminated in the absence of ADP5(Group 4). Ca²⁺/PO₄³⁻ treatment displayed no re-mineralization(Group3). 1100ppmF didn’t form any continuous layer on demineralized enamel(Group4). A continuous layer of spherical particles (CaF₂) was observed at concentrations of 20,000ppmF(Group5). Variations in the microstructure of etched enamel were observed among specimens(Group6). (Ca)²⁺/(PO₄)³⁻ ratios in the samples remained similar (mean=1.58±0.07) for all groups except Group5, displaying a F⁻/Ca²⁺ ratio of 2.06±0.09, possibly corresponding to CaF₂ stoichiometry.
Conclusions: Compared to conditions which lacked the biomineralizing peptide ADP5, a continuous layer of plate-like Ca²⁺/PO₄³⁻ crystals was observed when ADP5 was applied on artificially-induced WSLs on human enamel.