Modified Microparticles for Enhanced Dentine Occlusion

Methods: Microparticles of titanium dioxide, aluminium oxide and silica were coated with a number of cationic and anionic polymers using one of two methodologies: (i) a ‘double coating' methodology whereby the microparticle was first electrostatically coated with a cationic polymer and then subsequently coated with the desired anionic polymer, or (ii) via a ‘single-layer' deposition method whereby an anionic polymer is electrostatically deposited onto a positively charged substrate. Following coating, the microparticles were purified by cross-filtration. Polymer coating was monitored by polymer loss from solution, thermogravimetric analysis and light microscopy. Polymer-coated microparticles were evaluated using a hydraulic conductance model to determine both the extent of suppression of fluid flow and persistence of effect. Scanning electron microscopy (SEM) was used to interrogate the dentine specimens pre- and post treatment.

Results: Polyethyleneimine-coated silica further modified using polyacrylic acid (PAA), polyvinylpyrrolidone and alginate all elicited significant reductions in dentine permeability relative to the uncoated silica control. PAA-coated TiO₂ elicited the greatest reduction in dentine permeability; SEM confirmed the presence of a uniform homogeneous occlusive coating. All modified particles were observed to be substantive against rinsing and brushing challenges.

Conclusion: Surface modification of common toothpaste microparticulates with bioadhesive polymers has been successfully employed to deliver significant in-vitro reductions in dentine permeability. Concomitant enhancement of dentine and tubule occlusion versus the control parent microparticles were confirmed by SEM.