The Relationship of Particle Size and other Properties of Dentifrice Ingredients to Toothbrush-Abrasion of Enamel

Abstract

We have been engaged for several years in the study of the abrasive properties of dentifrices and their individual ingredients, with the broad aim of establishing the basic factors controlling toothbrush-abrasion. In the first phase of this study, a mechanical brushing device was built through which controlled abrasion of teeth or other materials could be produced. A procedure for using this device on teeth was described in some detail in the first report (1), including factors which must be controlled, such as swelling of teeth, concentration of slurry, variability of teeth, etc. In a second paper (2), the problem of determining the size of particles in powders was considered at some length. From the many such procedures suggested by others, for special purposes, there were selected the microscope visual method, and the Klein surface-increment scale hydrometer technic, for characterizing the powders used in this study. The particle size distributions of a considerable number of powders were measured by these two technics, and the mean and median particle sizes and specific surface areas calculated. This paper presents results on the correlation of the sizes of the particles in these powders with their abrasive power for teeth. There are also considered the influence of hydrogen ion concentration and of hardness on abrasion. In subsequent papers, the correlation between the abrasion of these powders for teeth and various metal plates and glass will be presented to determine whether the use of these test objects will provide a less variable material for such studies, which can be relied on to predict the abrasion which would be caused by the powders on teeth. As a part of the general program, the abrasive power of some 60 commercial dentifrices has also been reported (3), including some consideration of the newer types of liquid preparations. W. D. Miller (4) first forcefully attracted attention to the need for studies of this type when he showed that most dentifrices in use in 1907 cut the teeth rather badly when used under conditions not unlike those of their everyday application. He demonstrated that acidic materials enhanced the process of toothbrush wasting by extracting the calcium salts from the enamel. He also pointed out, many years in advance of the recent releases on the subject, that anyone brushing