IADR Abstract Archives
Viscosity of Saliva as an Obstacle for Salivary Diagnostics
Objectives: Saliva is a promising tool to identify oral and systemic diseases using DNA and RNA based diagnostics. But the high viscosity of saliva prevents its wide usage in routine laboratories. We aimed to study the rheological properties of human saliva and tested various intervention methods to decrease its viscosity enabling automated pipettors and other diagnostic instruments to use this fluid.
Methods: We collected whole unstimulated saliva from 40 healthy individuals. Initially, we measured its viscosity (η) (unit: Pa×s) over a wide range of shear rate (unit: s-1) at room temperature using a Kinexus Pro+ rheometer (Malvern Instruments Ltd, UK). Then, fixed share rate was applied to test the effect of freezing/thawing at -80°C, 30 sec vortexing, 15 min enzymatic digestion with ProteinaseK (1,1mg/ml) and adding 0.1 ml 1% acetic acid to 1 ml saliva on viscosity. Mean ± SEM were given, non-parametric paired Wilcoxon tests were applied.
Results: We observed an extremely large variability in viscosity between samples ranging 0.2847 Pa×s – 4.167 Pa×s at shear rate 0.1 s-1 (n=20, mean= 1.174 Pa×s, 95% CI: 0.6636 – 1.683). The viscosity of saliva strongly depended on the applied shear rate, indicating non-Newtonian fluid characteristics (n=20, at 0.1 s-1, 1 s-1 and 10 s-1 viscosity was 1.35 Pa×s ±0.153, 0.13±0.022 Pa×s and 0.018±0.006 Pa×s, respectively). Freezing and thawing did not change sample viscosity at the same three shear rates (P=0.8695, P=0.4980, and P=0.6742, respectively). Vortexing did not change the viscosity either (P=0.8408). On the other hand, ProteinaseK exposure significantly decreased saliva viscosity (P=0.0002), similar to acidification of the samples by acetic acid (P=0.0121), used as a positive control.
Conclusions: Whole saliva has an extreme high variance in viscosity between subjects, an obstacle for using saliva in routine diagnostic procedures. But ProteinaseK application is a promising method to improve the rheological characteristics of saliva.
Methods: We collected whole unstimulated saliva from 40 healthy individuals. Initially, we measured its viscosity (η) (unit: Pa×s) over a wide range of shear rate (unit: s-1) at room temperature using a Kinexus Pro+ rheometer (Malvern Instruments Ltd, UK). Then, fixed share rate was applied to test the effect of freezing/thawing at -80°C, 30 sec vortexing, 15 min enzymatic digestion with ProteinaseK (1,1mg/ml) and adding 0.1 ml 1% acetic acid to 1 ml saliva on viscosity. Mean ± SEM were given, non-parametric paired Wilcoxon tests were applied.
Results: We observed an extremely large variability in viscosity between samples ranging 0.2847 Pa×s – 4.167 Pa×s at shear rate 0.1 s-1 (n=20, mean= 1.174 Pa×s, 95% CI: 0.6636 – 1.683). The viscosity of saliva strongly depended on the applied shear rate, indicating non-Newtonian fluid characteristics (n=20, at 0.1 s-1, 1 s-1 and 10 s-1 viscosity was 1.35 Pa×s ±0.153, 0.13±0.022 Pa×s and 0.018±0.006 Pa×s, respectively). Freezing and thawing did not change sample viscosity at the same three shear rates (P=0.8695, P=0.4980, and P=0.6742, respectively). Vortexing did not change the viscosity either (P=0.8408). On the other hand, ProteinaseK exposure significantly decreased saliva viscosity (P=0.0002), similar to acidification of the samples by acetic acid (P=0.0121), used as a positive control.
Conclusions: Whole saliva has an extreme high variance in viscosity between subjects, an obstacle for using saliva in routine diagnostic procedures. But ProteinaseK application is a promising method to improve the rheological characteristics of saliva.