Kaolin Clay as a Polishing Agent for Toothpaste

by Steve Wilson

Humans have used clay since before recorded history to make bricks for constructing buildings, to make pottery and mold figures, and to decorate themselves and their artifacts. Moreover, when people did begin to record their activities, they did so by making marks in clay. Today, a fine white clay, called kaolin, is used in making artistic and functional ceramics, in paints, paper and inks … and now, in toothpaste.

The need for abrasive agents in teeth cleaning has been recognized since ancient times, and various materials (e.g., pumice, bone ash and powdered marble, shells and coral) have been used for the mechanical removal of tooth debris and stains.¹ In modern times, the application of a toothpaste with a toothbrush has been the primary method for cleaning the teeth. A key function of toothpaste is to control stain accumulations, which are attributable mainly to the chemical bonding of dietary chromagens with proteinaceous compounds in the salivary pellicle that coats the tooth surfaces.²  Extrinsic (surface) stain is tenacious, and its prevention or removal requires toothpaste that contains abrasive agents since tooth brushing without such is ineffective.³  Traditionally, to achieve mechanical cleaning a toothpaste needs three formulation components:  1) an abrasive agent 2) a thickening agent to hold the abrasive in suspension during brushing 3) a surface-active agent to facilitate the removal of oral debris.⁴ Abrasives, which are the principal component contributing to the physical removal of stains, are insoluble substances comprising silicas (e.g., hydrated silica), metal oxides (e.g. alumina), phosphates (e.g., calcium pyrophosphate), carbonates (e.g., calcium carbonate) and silicates (e.g., aluminum silicate or kaolin clay).

Extensive research and development have been conducted during the past half century in an effort to optimize the cleaning efficiency of toothpaste abrasives while minimizing any deleterious wear effects to the teeth. Although this might appear to be easily accomplished, the practice of designing effective toothpaste abrasive systems is actually quite complex,⁵ and is dependent on a variety of properties of the agent, including chemical composition, crystal structure, cleavage, friability and hardness, as well as concentration, shape, size distribution and surface features of the particles. In addition to balancing these characteristics to optimize stain removal without causing harmful abrasion to the teeth, abrasives must be compatible with other toothpaste ingredients, particularly therapeutic agents (e.g., fluoride), and must demonstrate acceptable formulation properties (e.g., viscosity and flow) without compromising important consumer attributes (e.g., taste and appearance).

Significant advances by toothpaste manufacturers during this period have resulted in currently available multi-functional toothpastes that deliver various therapeutic and cosmetic benefits, including treatment of bad breath, caries, gingivitis, dental plaque, dental calculus, demineralization and dentinal hypersensitivity.^6,7 Nevertheless, in spite of this progress, the primary reason people use toothpastes is to improve tooth appearance by cleaning the teeth and reducing unsightly stains.⁸

Another characteristic of toothpaste that has not received as much attention is polishing ability. Like stain removal and abrasivity, the polishing ability of toothpaste is a physical phenomenon associated with the abrasive system. The concept of high enamel luster is important for two reasons. First, from a cosmetic viewpoint, an increase in luster contributes to the aesthetics of the dentition, and improved surface smoothness is conducive to a feeling of oral cleanliness.  Also, more highly polished enamel appears whiter than duller enamel.^9,10 Second, and more importantly, smooth highly polished tooth surfaces are less receptive to accumulation and retention of dental plaque, calculus, extrinsic stain and the concomitant oral disease processes. Many studies have demonstrated that rough, unpolished tooth surfaces facilitate the formation and retention of dental plaque, oral debris, calculus and extrinsic stain.^11,12,13,14 For example, initial bacterial colonization of enamel surfaces starts in surface irregularities (e.g., pits, scratches, defects) and preferential retention occurs on rough surfaces where bacteria are more protected from shear forces.^15,16

The superb cleaning and polishing properties of kaolin are attributable, at least in part, to the shape and configuration of its particles. Kaolin particles are thin, flat platelets that are about 10 times as wide as they are thick with microscopic ridges on their surfaces. When suspended in a medium and pressed (e.g., by toothbrush bristles) up against a surface (e.g., a tooth) to be polished, the platelets have a natural tendency to orient themselves flat against the surface. When moved across this surface, the tiny ridges on the kaolin particles work together like miniature files to produce a microsmooth surface on the teeth, with maximum gloss and luster. In contrast, other abrasives have more irregular, spherical shapes that depend on particle edges, only a few per particle, to scrape, scratch or gouge the surface. 

In summary, a toothpaste should have the ability to remove extrinsic stains effectively without resulting in unnecessary deleterious abrasion to the teeth.  Additionally, as a means of inhibiting dental accumulations (i.e., stains, plaque and calculus), a toothpaste should impart a smooth, highly polished surface to the teeth, thereby contributing not only to oral aesthetics, but also to a concomitant improvement in oral health. An ideal toothpaste should provide optimum cleaning (i.e., extrinsic stain removal) and polishing with minimum abrasion to the dental hard tissues (viz. cementum, dentin and enamel).  Maximum stain removal ability and low abrasivity are diametric opposites, as are high cleaning and high polishing.  Thus, it is inevitable that some concessions must be made in order to achieve a suitable compromise, a fact that accounts for the large differences in stain removal, polishing, and abrasion properties of the various abrasive agents used in commercial toothpastes currently available to the public.  The benefits of using kaolin clay (available in Dentisse® Natural Reflection™ Toothpaste) over other abrasive systems are its gentleness in combination with high polishing and stain removal properties.

Steve Wilson is the director of sales and marketing of Dentisse®, a brand of oral care products, including Dentisse Natural Reflection toothpaste made with refined kaolin; an alcohol-free oral rinse with aloe vera and xylitol called Natural Solution;  and an all-natural lip balm named Natural Protection. 

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