Salivary Pellicle Structural Changes after Exposure to SDS and STP

Objective:  The enamel pellicle is juxtaposed between protecting enamel from acidic and abrasive damage, whilst concomitantly aiding the adsorption of plaque forming bacteria close to the tooth surface. This study investigates how dentifrice products (STP and SDS) impact the salivary pellicle; by measuring changes in surface mass, density, thickness and viscoelasticity of the pellicle. This will improve our understanding of the way SDS and STP not only remove the pellicle from enamel, but also what effect that exposure to these chemicals has on the structure of the remaining pellicle.

Method: Saliva was obtained from 14 apparently healthy, non-smoking, male and female volunteers, ranging in age from 20 to 50 years. We measured salivary pellicle adsorption and displacement via Quartz Crystal Microbalance and a Dual Polarisation Interferometer.

Result: After exposure to 10mM SDS the pellicle adsorbed onto hydroxyapatite sensor was reduced from 1215±289ng/cm² to 663±297ng/cm² ; and to 491±293ng/cm²  after exposure to 10mM STP. This showed that the remaining pellicle adsorbed onto the hydroxyapatite substrate was larger in mean mass when exposed to 10mM SDS as opposed to 10mM STP.  However, this was not the case with the pellicle adsorbed onto silica sensors, where 10mM SDS removed 4 times as much pellicle (897±214ng/cm²) when compared to the amount of pellicle removed by 10mM STP (204±101ng/cm²).

Conclusion: The interaction of the polyanion STP with the salivary pellicle is strongly influenced by electrical charge of the surface that the pellicle has adsorbed to. For example, STP removes pellicle from a hydroxyapatite surface via competitive adsorption for the cationic calcium ions within hydroxyapatite, and by sequestering calcium ions that cross link proteins within the pellicle. However, when the pellicle is adsorbed onto the negatively charged silica surface, removal of pellicle via competitive adsorption no longer takes place.