<i>Ex vivo</i> adsorption of proteins from salivas collected from different salivary glands.

<p>Example of the QCM-D response to salivary protein adsorption on hydroxyapatite crystals as a function of time, expressed in changes in third harmonic frequency (Δf3, thick line) and dissipation (ΔD3, thin line), together with AFM images of the topography of the adsorbed salivary conditioning films as observed at the end of an experiment. The QCM-D chamber is initially filled with buffer till a stable base-line is observed, after which saliva is introduced. After 30 min of salivary protein adsorption, the chamber is perfused again with buffer. (<b>A</b>) parotid saliva (PAR) from a single donor, (<b>B</b>) submandibular saliva (SM) from a single donor, (<b>C</b>) fresh whole saliva (WS) from a single donor, (<b>D</b>) reconstituted whole saliva (RWS) from a pool of donors.</p

Influence of detergents on desorption and adsorption of salivary proteins.

<p>Example of the QCM-D response to protein adsorption from reconstituted whole saliva (RWS) on hydroxyapatite crystal surfaces, perturbation and continued adsorption of salivary proteins as a function of time, expressed in changes in third harmonic frequency (Δf3, thick line) and dissipation (ΔD3, thin line), together with AFM images of the topography of the adsorbed films as observed at the end of an experiment. Perturbation was established by exposure to (<b>A</b>) buffer, (<b>B</b>) SLS, (<b>C</b>) NaHMP. The QCM-D chamber is initially filled with buffer till a stable base-line is observed, after which RWS is introduced for 2 h to allow salivary protein adsorption, after which a buffer rinse is applied, followed by 2 min perturbation by buffer or a detergent, intermediate buffer rinsing for 15 min and continued perfusion of the chamber with RWS and at the end there was a final buffer rinsing, as indicated in the figure.</p

Glycosylation, clinically registered intra-oral contact angles and sensory perception of tooth surfaces <i>in vivo</i>.

<p>(<b>A</b>) The %O_glyco of salivary films adsorbed on conditioning films exposed to buffer followed by reconstituted whole saliva (RWS), SLS (SLS+RWS) and NaHMP (NaHMP+RWS). Error bars represent the standard deviations over three independent XPS measurements on differently prepared samples. Statistically significant (p<0.05, two tailed Student t-test) differences of the SLS+RWS and NaHMP+RWS films with respect to RWS films is indicated by *sign. (<b>B</b>) Water contact angles <i>in vitro</i> for the films described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042600#pone-0042600-g005" target="_blank">Figure 5a</a> and clinically registered, water contact angles measured on the front incisors of human volunteers prior to and after brushing with a SLS or NaHMP containing formulation (represented by hatched columns). Error bars represent the standard deviations over twelve independent contact angle measurements. For the <i>in vitro</i> contact angles, statistically significant (p<0.05, two tailed Student t-test) differences with respect to RWS films are indicated by *signs, while #sign indicates significant differences of NaHMP+RWS films compared with SLS+RWS ones. Similarly, for the <i>in vivo</i> contact angles *signs are used to show the significant difference with respect to unbrushed films and #sign indicates significant differences of brushed films with NaHMP toothpaste compared with brushed films with SLS toothpaste. (<b>C</b>) Mouthfeel scores prior to and after brushing with an SLS or NaHMP containing toothpaste formulation. The mouthfeel questionnaire involved the following questions: 1. How do you like the smoothness of your teeth? 2. How do you like the clean feeling of your teeth? 3. How do you like the moist feeling of your teeth? 4. Overall, how do you like the feeling of your mouth? Scoring was done on a five point scale according to: −2 = extremely bad smoothness, −1 = bad smoothness, 0 = neutral, 1 = good smoothness, and 2 = extremely good smoothness. Error bars represent the standard deviations over the scores obtained from 64 volunteers after use of an SLS containing toothpaste and 12 volunteers after use of a NaHMP containing toothpaste. Statistically significant (p<0.1) differences with respect to pre-brushing are indicated by *signs for each formulation, while #sign indicates significant differences between the SLS and NaHMP containing toothpaste.</p

Schematic architecture of salivary conditioning films prior to and after chemical perturbation.

<p>(<b>A</b>) unperturbed salivary conditioning film, showing glycosylated mucins adsorbed in loops and trains over a layer of densely packed low-molecular weight proteins, including proline-rich proteins, histatins and lysozymes. (<b>B</b>) salivary conditioning film after exposure to detergents, showing removal of hydrophobic, smaller proteins and partial detachment of high molecular weight glycosylated mucins. Due to their larger size and multiple adsorption sites, larger proteins do not fully detach like the smaller ones. (<b>C</b>) salivary conditioning film after continued salivary flow over films exposed to detergents. Due to their smaller size, low molecular weight proteins adsorb faster than higher-molecular weight mucins, yielding a denser layer of adsorbed low-molecular weight proteins on the surface causing a greater structural softness and extended loops of glycosylated mucins, leaving the surface more hydrophilic. Smaller proteins have less chance to adsorb after exposure to SLS because more trains are left that occupy the substratum surface than after exposure to NaHMP.</p

Structural softness, lubricity and repulsive forces of <i>ex vivo</i> adsorbed salivary films from different volunteers.

<p>(<b>A</b>) Day-to-day and person-to-person variations in the structural softness of 30 min old adsorbed films on hydroxyapatite-coated quartz crystals from parotid (PAR), submandibular (SM), fresh whole (WS) and reconstituted whole saliva from a pool of donors (RWS), taken as the ratio of dissipation (ΔD3) and frequency shift (Δf3) of the third harmonic resonance frequency of the QCM crystal. (<b>B</b>) The coefficient of friction (COF) as a function of the normal force applied between a colloidal probe and films formed from salivas collected from different salivary glands and volunteers (see also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042600#pone.0042600.s001" target="_blank">Figure S1</a>). Data pertaining to salivas collected at different days are indicated by multiple lines, with colors corresponding with the labels in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042600#pone-0042600-g002" target="_blank">Figure 2A</a>. (<b>C</b>) Repulsive force as a function of the approach distance between a colloidal probe and films formed from salivas collected from different glands and volunteers. Data pertaining to salivas collected at different days are indicated by multiple lines, with colors corresponding with the labels in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042600#pone-0042600-g002" target="_blank">Figure 2A</a>. The distance D of the repulsive forces (inserts) is taken as the distance where the colloidal probe starts to experience a repulsive force >0.1 nN.</p