Soluble Phosphate-Based Glass for The Potential Treatment of Periodontitis

Abstract

Bioactive glasses are one of the most important bioactive materials that can produce substantial effects in the field of tissue engineering. In the field of periodontology, PerioGlas® is a silicate- based bioactive glass which has been used commonly for the treatment of periodontal diseases. However, during glass dissolution, this glass generates an alkaline pH which is likely to induce the growth of P. gingivalis bacteria (periodontopathic bacteria). Furthermore, the large particle size of this material was clinically shown to substantially reduce the degradation rate of the silicate glasses. Phosphate glasses (near metaphosphate composition) generate an acidic pH on dissolution as a result of breakdown of phosphate chains creating an acidic-type phosphate species. Additionally, in the presence of alkaline phosphatase enzyme (ALP), phosphate glasses generate orthophosphate species PO43- upon degradation of metaphosphate species, which would enhance hydroxyapatite formation and mineralization. The aim of this project was to investigate the potential of degradable phosphate glasses for use as a grafting material for the treatment of periodontitis. Several series of simple binary phosphate glass systems were prepared, xR2O-P2O5 or xRO- P2O5, where R = Na, K, Ca, Sr and Zn, and x = 45, 50 and 55 mol%. The structure of the glasses was characterized using several techniques. These included Phosphorus-31 Magic Angle Spinning- Nuclear Magnetic Resonance (31P MAS-NMR) as the main technique. Additionally, X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), Particle size Analysis (PSA), Energy Dispersive X-ray Spectroscopy (EDX), and Scanning Electron Microscopy (SEM). Glasses were dissolved individually in tris buffer solution mimicking the pH of oral environment and the changes were tested at different time points. The dissolution products were investigated by solution-state of Phosphorus-31 Nuclear Magnetic Resonance (31P NMR) spectroscopy and 2D 31P gradient Correlated spectroscopy (COSY) experiment. ALP was added to selected compositions to enzymatically hydrolyse the phosphate compounds in solution to release orthophosphate species. The solutions were characterized by 31P solution-state NMR and 2D 31P gradient COSY experiment. 31P MAS-NMR spectra showed that Q2 species were the dominant species with small amount of Q0 and Q1 species. The solubility of the glass was affected by modifier cation. The pH values were influenced by phosphate content in the glasses. The 31P solution-state NMR exhibited different peaks of the Q0, Q1, and Q2 species. In the presence of ALP enzyme, the phosphate species further degraded into orthophosphates which can promote remineralising environment. Compared to calcium phosphate glasses, zinc phosphate glasses of all three formulations showed substantial difference in dissolution also revealing additional interaction with ALP enzyme, which can be most beneficial. Phosphate glasses can be used for potential treatment of periodontal defects for pH modulating and delivering plenitude of phosphate in addition to cations. If added to a periodontal bone graft formulation, soluble phosphate glass would dissolve generating lower pH values, which will inhibit the growth of P. gingivalis and subsequently create stimulating mineralising environment.