Impact of amino acid-regulated beta tricalcium phosphate hydroxyapatite on enamel: An updated perspective on hydroxyapatite crystal growth for adhesive bonding?

AIMS AND OBJECTIVES: To analyse development of hydroxyapatite (HAp) crystals doped with glutamic acid and phosphorine residue (Ser-OPO3) having self-remineralization, biocompatible and optimum bonding properties MATERIALS AND METHODS: β-tri calcium phosphate, ammonium phosphate dibasic HAp was dissolved with strontium Flouride Glu or Ser-OPO3 components and utilised in two 0.1% TCPCa3(PO4)2 Str/FL and 0.2% TCPCa3(PO4)2 Str/FL groups. HAp formulation was evaluated for particle-size analysis, crystal size and indices using FTIR. Demineralized enamel specimens were treated and characterized using transmission electron microscopy (TEM), Xray diffraction (XRD), solid state NMR, and mechanical properties. MC3T3 mouse fibroblastic cells were evaluated for alkaline-phosphate activity (ALP). Human gingival fibroblasts (PGF) were evaluated for morphology. After modifying Universal adhesives, tensile force was assessed at 24 hr and 3 months.

RESULT: Increasing concentrations of experimental solution exposure significantly affect mean diameter of HAp. The increasing FTIR intensity, were displayed; 0.2% TCPCa3(PO4)2 Str/FL > 0.1% TCPCa3(PO4)2 Str/FL> control. 0.2% TCPCa3(PO4)2 Str/FL revealed existence of distinct crystals, with planes orientated perpendicular to longer axis of tooth. XRD pattern indicated crystal growth with a rise in peak intensities in 0.2% TCPCa3(PO4)2 Str/FL group. The NMR spectra for Glu and Ser-OPO3 elucidated interactions between carbon atoms in amino acid and hydrogen atoms on HAp surfaces. Surface microhardness of 0.2% TCPCa3(PO4)2 Str/FL specimens showed significantly higher values on day 28 (p< 0.05). ALP density value of cells was significantly higher for 0.2% TCPCa3(PO4)2 Str/FL group on day 7 and 14. 0.1% TCPCa3(PO4)2 Str/FL and 0.2% TCPCa3(PO4)2 Str/FL enhanced migration of PGF cells in comparison to the control group (p<0.05). 0.1% TCPCa3(PO4)2 Str/FL and 0.2% TCPCa3(PO4)2 Str/FL groups showed significant differences in bond strength at different time points CONCLUSION: 0.1% TCPCa3(PO4)2 Str/FL and 0.2% TCPCa3(PO4)2 Str/FL were structurally integrated into the lattice demonstrating changes within the crystallite size and became conducive for adhesive bonding.

CLINICAL SIGNIFICANCE: The new amino acid-based hydroxyapatite formulation is chemically stable due to the substitution of OH- with F- and is crucial in the rehardening of caries and adhesive bonding.