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Objectives This pilot study aimed to compare the in-mouth retention of an oil-based saliva substitute (emulsion, consisting of rice bran oil, soy lecithin and water) with water and a 1% w/v methylcellulose suspension (polymer) in healthy volunteers. Methods Each formulation was tagged with 1 mmol/L lithium and participants (n = 30) rinsed their mouth with one randomly assigned formulation (emulsion, polymer or water) for 30 s, before expectorating into a cup. Concentration of lithium expectorated was measured and amount of each formulation remaining in the mouth was estimated. Patient acceptability was investigated using questionnaires, and Fourier-Transform Infrared spectroscopy (FTIR) was used to determine the presence of oil in expectorated samples. Results Immediately after rinsing, taste was rated lower in the emulsion group compared to the polymer or water groups (p > 0.05), although variability was high. Mean retention was highest in the emulsion group, with a difference of 8.34 ± 2.71% (p = 0.003) and 4.57 ± 2.71% (p = 0.06) compared with the water and polymer groups, respectively. FTIR confirmed the presence of oil in all expectorated emulsion samples. Conclusion The emulsion was not inferior to the polymer in terms of retention immediately after rinsing. The next step is to conduct larger clinical studies over longer time periods in participants with salivary hypofunction. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of the present study was to investigate lecithin-rice bran oil rheological properties with the view to consider these as potential saliva substitutes in patients with severe xerostomia and salivary hypofunction. Pseudo-ternary phase diagrams of rice bran oil, lecithin and water mixtures were constructed and characterised using polarising light microscopy. Viscoelastic properties, which we hypothesise are important determinants in product performance, were analysed using both flow and oscillatory rheology. Rheological properties were influenced by composition, frequency and shear stress. Frequency-dependent viscoelasticity was observed in some formulations where viscosity dominated (tan δ >1) at frequencies under 5Hz and elasticity dominated (tan δ <1) at higher frequencies. Threshold frequencies were determined for each formulation, where a peak in loss tangent was observed, coinciding with a reduction in the storage modulus and increase in loss modulus. The frequency-dependent behaviour of emulsions are of interest because these combinations exhibit viscous behaviour at low frequencies, which may improve lubrication of the oral cavity at rest, whereas increased elasticity at higher frequencies may improve retention during higher-shear tasks such as swallowing and speaking. [Copyright &y& Elsevier]

In recent years, there has been a particular interest in bioadhesive formulations for oromucosal drug delivery as this may promote prolonged local therapy and enhanced systemic effect. Saliva plays a vital role in oromucosal drug absorption by dissolving the drug and presenting it to the mucosal surface. However, the rheological, chemical, and interfacial properties of this complex biological fluid may strongly affect the adhesion of bioadhesive formulations. There is a need for well characterized in vitro models to assess the bioadhesive properties of oral dosage forms for administration in the oral cavity. Thus we aimed at developing an advanced ex vivo buccal retention model, with focus on choosing a physiologically relevant irrigation media closely resembling human saliva. Spray dried chitosan microparticles containing metformin hydrochloride as an example of a small hydrophilic drug, were employed as bioadhesive formulations. Chewing-stimulated human whole saliva was collected and characterized for use in retention studies in comparison with four artificial irrigation media; phosphate buffer, Saliva Orthana®, porcine gastric mucin base media (PGM3), and xanthan gum based media (XG2). Retention of metformin, applied as spray dried microparticles on porcine buccal mucosa, greatly depended on the characteristics of the irrigation media. When rheology of the irrigation media was examined, changes in retention profiles could be interpreted, as irrigation media containing mucin and xanthan gum possessed a higher viscosity than phosphate buffer, which led to longer retention of the drug due to better hydration of the mucosa and the spray dried microparticles. Metformin retention profiles were comparable when human saliva, Saliva Orthana®, or PGM3 were used as irrigation media. Moreover, PGM3 displayed physico-chemical properties closest to those of human saliva with regard to pH, protein content and surface tension. Saliva Orthana® and PGM3 are therefore considered as suitable irrigation media for further retention studies. [ABSTRACT FROM AUTHOR]

Xerostomia is commonly known as ‘dry mouth’ and is characterised by a reduction or loss in salivary production. A bioadhesive gel for its localised treatment was formulated to help enhance the residence time of the product, based on the polymer Carbopol 974P. The bioadhesion of various formulations was evaluated on different mucosal substrates, as simulations of the oral mucosa of xerostomic patients. Depending on the type of model substrate used, the mechanism of bioadhesion could alter. When the rheology of various formulations was examined, changes in bioadhesion were more easily interpreted, as the presence of other excipients caused an alteration in the rheological profile, with a change from a fully expanded and partially cross-linked system to an entangled system. Improving the lubricity of the product was considered important, with optimum incorporation of vegetable oil causing a desirable lowering of the observed friction of the product. The final complex formulation developed also contained salivary levels of electrolytes to help remineralisation of teeth, fluoride to prevent caries, zinc to enhance taste sensation, triclosan as the main anti-microbial/anti-inflammatory agent and non-cariogenic sweeteners with lemon flavour to increase the palatability of the product while stimulating any residual salivary function. [Copyright &y& Elsevier]

The sensation of dry mouth also referred to as xerostomia is becoming increasingly common worldwide. Current treatment strategies include topical agents, sialagogues and saliva substitutes. The latter have been reported to be ineffective as special physicochemical features of natural saliva have so far been ignored (e.g., buffer capacity, osmolality, etc.). The aim of this study was to comprehensively investigate the most relevant physicochemical properties of three products frequently used in the clinics and compare them to unstimulated whole saliva (UWS). Sialin-Sigma®, Glandomed® and Xylitol CVS HealthTM Dry Mouth Spray were characterized regarding their pH, osmolality, electrical conductivity, buffer capacity, rheological behaviour, microstructure, surface tension and wettability and compared to UWS. The influence of residual saliva was examined under consideration of the conditions of xerostomia to assess whether the quantity given in the instruction for use is appropriate. All three products showed significant differences to UWS regarding the values received. Only Xylitol CVS HealthTM Dry Mouth Spray showed a comparable wettability. It could be further determined that the recommended doses were too low. These data can not only be used for an improved understanding of saliva, but also for the development of a replacement fluid to successfully alleviate xerostomia. [ABSTRACT FROM AUTHOR]