Fig. 3

ATR–FTIR spectra of dentin slices surface. Spectrum 1, a natural dentin slice; Spectrum 2, a demineralized dentin slice; Spectrum 3, a demineralized dentin slice after TPP treatment; Spectrum 4, a demineralized dentin slice after remineralization with CPP–ACP combined with TPP for 21 days. The peak value at 1018 cm⁻¹ indicated the anti-symmetric stretching vibration peak of PO4³⁻. The peak at 1647 cm⁻¹ was the characteristic peak of amide I band, and 1550 cm⁻¹ was the characteristic peak of amide II band. The characteristic peak at 1239 cm⁻¹ was amide III band