Objectives: Bioactive glasses are used as remineralising additives for anti-sensitivity toothpastes. The objective is to design novel high phosphate compositions and incorporate fluoride in order to form fluorapatite as opposed to hydroxycarbonate apatite. The efficacy of the bioactive glass compositions to occlude dentine tubules was assessed using Focused Ion Beam - Scanning Electron Microscopy (FIB-SEM).
Methods: Two glasses were designed based on the commercial 45S5 glass composition. 45S5-P and 45S5-PF contained higher phosphate content (≈6mol% from 2.6mol%), with 5mol% of fluoride for glass 45S5-PF. The three compositions were left to sediment onto dentine in TRIS buffer (TB) for 9 hours and artificial saliva (AS) for 1 hour. Tubule occlusion was assessed using FIB-SEM.
Results: SEM images of dentine showed excellent coverage of the surface with glass particles and newly formed apatite-like growth. The 45S5 composition showed globular preferential growth on the peritubular dentine in TB, whereas it showed plate-like growth in AS, which can be indicative of octacalcium-phosphate, a recognised precursor phase in the formation of hydroxyapatite. Glasses 45S5-P and 45S5-PF showed plate-like growth and needle-like growth respectively in both TB and AS. The needle-like growth was expected to be fluorapatite, as previous 19F MAS-NMR studies confirmed fluorapatite formation from 45S5-PF. FIB-SEM images confirmed ‘deep' (>15 microns) occlusion of dentine tubules patent to the surface.
Conclusion: The glass composition and surrounding solution dictate the quantity and nature of apatite-like phases that form. Increasing the phosphate content increases the reactivity of the glass, whilst incorporating fluorine allows for the formation of fluorapatite, which may be more durable than conventional hydroxycarbonate apatite. Using the 45S5-PF composition appeared to show a greater level of occluded dentine tubules, which has the potential for more rapid and long-lasting relief from dentine hypersensitivity.
This project is co-funded by GSK and BBSRC.