Role of salivary film structure in biolubrication

Conditioning film is a mixture of proteins that facilitate the articulation of the body parts through lubrication. Compared to other body parts, oral cavity is a unique system where the lubrication is changed not only because of the diseases but also due to perturbation. By using the oral cavity as the model system we examine the changes in the lubrication due to chemical perturbation, for example, after treatment with tooth paste with sodium fluoride - sodium lauryl sulfate combination and only sodium lauryl sulfate. In general, salivary protein films after chemical perturbation is revived with a different structural configuration that is comprised of a rigid basal and a soft over layer, as shown by using quartz crystal microbalance with dissipation monitoring and water contact angle measurements. Perturbed salivary protein films has better wear resistant property compared with unperturbed salivary protein films (no chemical treatment). And, the stable coefficient of friction values for perturbed salivary protein films is 2 times lower than unperturbed salivary protein film at physiologically relevant contact pressures (72 to 250 kPa), as determined by the nanotribometer. In vivo smoothness scores also indicated a significant improvement in the smoothness feeling immediately after perturbation by toothpastes. Smooth feeling after using the toothpastes as a routine to manage oral hygeine is attributed to the re-structuring of interfacial salivary protein film into rigid and hydrophilic layers that provides sustained lubrication and simultaneously triggering the smooth experience by the tongue in the oral cavity.