Evaluation of in vitro properties of films of saliva substitutes in contact with different surfaces. A comparative study with instruments for measurements of friction and rheologic properties.

An instrument based on friction measurement has been developed to evaluate oral mucosal dryness objectively. The purpose of this study was to compare the friction instrument with instruments measuring in vitro rheologic properties. Measurements were performed against steel and irreversible hydrocolloid after application of different concentrations of aqueous solutions of carboxymethylcellulose and chitosan lactate. The results of the measurements were logical, with inversely proportional values for the friction instrument as compared with values obtained using the instrument measuring rheologic properties; that is, increased viscosity led to decreased friction values.