Facile and Effective Approach Enabling the Prediction of the Dispersibility of Toothpastes With Rheological Parameters

摘要

The fast release kinetics of active ingredients and sensory characteristics such as the texture, flavor, and foam during tooth brushing are strongly related to the dispersibility of toothpastes. To this day, no standard method has been established to measure dispersibility of toothpastes. In this study, we demonstrate that the dispersibility can be estimated from the rheological properties. We measured various rheological properties, such as the shear viscosity (both low and high), slope of viscosities, yield stress, phase angle, complex modulus, shear strain, and recovery ratio, for eight toothpaste products using a rotational rheometer, along with the fluid viscosity using a Brookfield viscometer. To investigate the influence of each parameter on the dispersibility of the toothpastes, we performed linear regression analysis and extracted the correlation coefficients. Phase angle and shear strain exhibited significantly high correlation with the dispersibility. However, the other rheological properties and fluid viscosity had an insignificant effect on the dispersibility. Hence, it is reasonable to claim that the phase angle and shear strain could be the key indicators to assess the dispersibility of toothpastes on the basis of linear equations extracted from the regression analysis. Furthermore, the relation between the fluoride (F?) release kinetics and the toothpaste dispersibility was investigated. The linear regression and correlation analyses showed that the fluoride release kinetics is highly correlated with the dispersibility even though the formulations of the tested toothpastes vary. This suggests that the two key rheological parameters, phase angle and shear strain, can be used for the relative evaluation of the fluoride release kinetics of toothpastes. We believe that our novel, indirect method to predict dispersibility can be widely applied for the quality assurance and quality control of toothpastes manufactured in the private sector. This is because the measurements of such parameters using a rotational rheometer are commonly practiced, rapid, and highly reproducible.