W.A. van der Reijden

Shear rate dependent viscoelastic behavior of human glandular salivas

Rheological properties of unstimulated human whole saliva (CHWS) and human glandular salivas (parotid, submandibular, sublingual, and palatal) of 7 healthy persons were investigated. The viscosity eta and elasticity eta of these salivas were measured as a function of oscillating shear rate gamma on an oscillating capillary viscoelasticity analyzer (Vilastic 3). Viscosity eta and elasticity eta of total and glandular salivas decreased in the following order: SL > Pal approximately CHWS approximately SM > Par. Rheological behavior of submandibular, palatal and sublingual saliva displayed a comparable pattern, although sublingual saliva showed significantly higher absolute values. The difference in viscoelasticity between submandibular and sublingual saliva was not due to differences in mucin concentration between SM and SL saliva. Flow curves of a range of SL saliva dilutions and flow curves of concentrated SM saliva showed that sublingual saliva was intrinsically more elastic than submandibular saliva.

Influence of Polymers for Use in Saliva Substitutes on De- and Remineralization of Enamel in vitro

A number of polymers which have previously been tested for their applicability as thickening agents in saliva substitutes were studied in vitro for their caries-protective properties. These were: polyacrylic acid, carboxymethylcellulose, xanthan gum, guar gum, hydroxyethylcellulose and porcine gastric mucin. The polymers were tested for their effects on: (1) growth of hydroxyapatite crystals in a supersaturated calcium phosphate solution, (2) dissolution of hydroxyapatite crystals in 50 mM acetic acid, pH 5.2 and (3) demineralization and remineralization of bovine enamel in a pH-cycling model. Growth of hydroxyapatite crystals was strongly inhibited by polyacrylic acid and carboxymethylcellulose at very low concentrations (0.005% w/v). Other polymers displayed lower inhibition of hydroxyapatite crystal growth. Hydroxyapatite dissolution was inhibited by all polymers except by hydroxymethylcellulose and xanthan gum. This occurred both in the presence of the polymers as well as after a 30-min preincubation. In the pH-cycling experiment, bovine enamel specimens with preformed lesions were alternately exposed to a demineralization buffer and a remineralization buffer containing the polymers hydroxyethylcellulose, carboxymethylcellulose, xanthan gum, polyacrylic acid, or porcine gastric mucin. A remineralization buffer containing 1 ppm NaF was used as a positive control. Under the experimental conditions, the control experiment without additives resulted in a net mineral loss (30.6 mumol Ca/cm2 after 14 days of pH cycling). In the presence of 1 ppm NaF, a small mineral gain was observed (8.6 mumol/cm2). All polymers largely inhibited further demineralization (1.2-12.3 mumol/cm2) except polyacrylic acid which, inhibited of its high calcium-binding capacity, caused demineralization, especially in the remineralization buffer (17.1 mumol/cm2). In conclusion, polymers tested in this study, except the polyacrylic acid, reduced the demineralization of enamel in vitro. The precise mechanism of the protective effect is not clear but it is speculated that formation of an absorbed polymer layer on the hydroxyapatite or enamel surface may provide protection against acidic attacks.

Treatment of oral dryness related complaints (xerostomia) in Sjögren’s syndrome

Primary Sjogren’s syndrome (SS) is a systemic autoimmune disorder characterised by a chronic, progressive loss of salivary and lacrimal function resulting in symptoms of oral and ocular dryness. The involvement of exocrine glands is the result of a focal, periductal mononuclear cell infiltrate and the subsequent loss of secretory epithelial cells.1 As a consequence, major changes occur in both the salivary flow rate and salivary composition.2-9 In the case of secondary SS a second autoimmune disease is involved, mostly rheumatoid arthritis.nnThe role of saliva in maintaining oral health and even quality of life is obvious in people who are lacking sufficient saliva.10-12 The effects of the reduced salivary flow rate (xerostomia) and changed salivary composition in SS are apparent (tableu20091): there are problems in eating, speaking, and swallowing12-15 and frequently disturbances in taste perception.16 In addition, reduced clearance of food, changes in microbial ecology and a reduced buffer capacity have their effects on oral health: an increased susceptibility to dental caries and oral infections are important clinical manifestations of the oral component of SS.17 18 When the systemic disease advances, salivary secretion declines further.7nnView this table:nnTable 1 nConsequences of xerostomiannnnA reduction of the salivary flow rate below physiological values can be induced by several other causes as well.19 Dry mouth symptoms are known as a side effect of more than 400 drugs.20 21 In most of these cases the level of reduction of the salivary flow is slight and can be compensated for by mechanical or gustatory stimulation. Other common causes of prolonged hyposalivation include other autoimmune disorders such as systemic lupus erythematosus,22 23 uncontrolled diabetes mellitus24 25 and salivary gland injury as a result of radiotherapy in the head and neck region.26 nnThis review describes the current …

Rheological properties of commercially available polysaccharides with potential use in saliva substitutes.

The rheological properties of a number of natural and synthetic polysaccharides have been compared with porcine gastric mucin (PGM), a mucin-containing saliva substitute (Saliva Orthana) and with clarified human whole saliva (CHWS). The effects of ionic strength, pH and calcium and fluoride ions on the viscoelastic properties of these polymers have been investigated. Of the polysaccharides tested, xanthan gum and scleroglucan appeared to resemble CHWS most in viscoelastic behavior and may be potential candidates for use in artificial saliva. Both PGM and Saliva Orthana, however, did not show any elastic behavior, whereas a viscosity comparable to human saliva was only observed in highly concentrated solutions. Of the polysaccharides tested, scleroglucan also had mucin-adhesive properties resulting in rheological synergism. This may be the first step in mucoadhesion which may protect underlying oral surfaces in vivo.

Evaluation of the use of xanthan as vehicle for cationic antifungal peptides.

Oral candidiasis frequently occurs in individuals with dry mouth syndrome (xerostomia), in immunocompromised patients and in denture wearers. The aim of this study was to develop a formulation which will prolong the retention time of antimicrobial agents at the site of application. The activity against Candida albicans of a synthetic cationic peptide dhvar 1, based on the human fungicidal salivary peptide histatin 5, was tested either in a mixture with the bioadhesive polymer xanthan, or after covalent coupling to this polymer. The presence of xanthan resulted in an increase of the LC50 value of the peptide from 2.6 (S.D.=0.6) to 5.8 (S.D.=4.0). Covalent coupling caused an additional increase of the LC50 value to 18.4 (S. D.=6.7). Coupling caused a reduction of the viscosity and elasticity of the xanthan solution related to the applied concentration of the coupling agent. Incubation of the peptide with clarified human whole saliva resulted in proteolytic degradation of the peptide. In the presence of xanthan the degradation occurred more slowly. It was concluded that xanthan is an appropriate vehicle for antimicrobial peptides in a retention increasing formulation.