Influence of Oral Detergents and Chlorhexidine on Soft-Layer Electrokinetic Parameters of the Acquired Enamel Pellicle

Abstract

Electron microscopy has described the salivary pellicle as an ‘uneven, knotted structure’. This study describes a novel soft-layer model of salivary pellicles, based on measured electrophoretic mobilities and the influence of dentifrices and a chlorhexidine mouthwash on the parameters of the model. The enamel surface was found to possess a high number of fixed, negative charges (zN = –62 mM) and to be electrophoretically hard (1/λ = 0.6 nm), i.e. impenetrable to fluid flow. Adsorption of a salivary pellicle resulted in a fourfold reduction in the surface fixed charge density (zN = –15 mM) along with an increase in electrophoretic softness (1/λ = 2.3 nm). Exposure of pellicles to various dentifrices containing sodium fluoride as an active component and sodium lauryl sulfate as a detergent had little effect on the surface fixed charge densities (varying between –15 and –30 mM, depending on the dentifrice involved) and electrophoretic softnesses (varying between 2.3 and 3.4 nm). Exposure of pellicles to a dentifrice containing sodium fluoride and hexametaphosphate as an additional detergent yielded soft (8.0 nm) pellicles, penetrable to fluid flow, with few fixed, negative charges (1 mM). This is opposite to the effects of chlorhexidine, which created an electrophoretically hard pellicle (1.7 nm). This soft-layer electrokinetic model quantitatively shows that the degree to which pellicles are penetrable to fluid flow differs upon exposure to dentifrices, with relevance for plaque formation, de- and remineralization and staining processes.

In vitro studies on the effect of sodium tripolyphosphate on the interactions of stain and salivary protein with hydroxyapatite

“…32 Recently, Busscher et al 33 suggested, from electrophoretic data, that a polyphosphate-containing dentifrice caused pellicle adsorbed to enamel to have a more open structure that would allow 'flushout' of chromogens. The evidence presented here and in previous work, [9][10][11] that polyphosphates desorb protein from HA surfaces, suggests that this is not a complete explanation.…”

The Structure, Function and Properties of the Acquired Pellicle

“…It has been suggested recently by Busscher et al [91] that salivary pellicles are open structures allowing ion exchange at the enamel surface. This suggestion is in accordance with high-resolution SEM and AFM images of the pellicle layer [37,69,79], indicating a porous mesh-like surface pattern.…”

Potential benefits of chewing gum for the delivery of oral therapeutics and its possible role in oral healthcare

“…Stain prevention by polyphosphates has been attributed to adsorption of these highly negatively charged and hydrophilic molecules to the SCF, which makes incorporation of chromogens in superficial enamel layers more difficult. Administration of sodium hexametaphosphate through the chewing of gum produced a more hydrophilic tooth surface in vivo than a control gum [44], while sodium hexametaphosphate caused desorption of proteins from SCFs and created a more open film structure in vitro [45,46].…”

“…Chewing a gum containing polyphosphates made SCFs more hydrophilic and more negatively charged as compared with other gums. Since most oral bacterial strains are negatively charged [44,46], this implies weaker adhesion of oral bacteria and polyphosphates have been demonstrated to even promote detachment of bacteria from SCFs on enamel surfaces [99].…”