J. Soc. Cosmet. Chem., 37, 211-223 (July/August 1986) Parameters for assessing the cleaning power of toothpastes H.-J. KLf3PPEL, W. PLOGER, F. FORG, and W. UMBACH Henkel KGaA, D-4000 Di•)seldorf, P.O. Box 1100, West Germany Received December 12,1985. Synopsis The cleaning effect of a dentifrice with respect to dental stain is usually regarded as dependent on the extent of its dentin abrasion. Accordingly, the use of products with high cleaning power is supposed to necessarily involve the risk of possible damage to dentin at the dentin-enamel junction. Our own tests, however, have shown that for nonscratching and polishing toothpastes this relationship only exists theoretically. Under given conditions, enamel abrasion is obviously the major factor in achieving a good cleaning effect. On the basis of this concept, marketable products can be developed with high cleaning power and low dentin abrasion. INTRODUCTION It goes without saying nowadays that the use of dentifrice in the form of a toothpaste or toothpowder is indispensable to maintaining good oral hygiene. Its purpose is to keep teeth free of bacterial plaque, extrinsic dental stain, and tartar. This is generally achieved by the tooth cleaning agents (synonyms: polishing agents, abrasives) and sur- factants contained in these dentifrices (1). The view may be correct that plaque removal is also possible merely with toothbrush and water given appropriate time and effort. Clinical tests conclusively prove, however, that the results of toothbrushing with a dentifrice are considerably more favorable and enduring (2,3). The polishing effect of the dentifrice may also be significant at least to some extent, as smooth surfaces become less quickly re-infested with bacteria than rough ones (4-8). After all, the removal of extrinsic dental stain is not possible without cleaning agents anyway (9-13). According to the current state of knowledge, dental stain arises due to pellicle discoloration. This may, for example, be due to the con- sumption of tea or coffee, the smoking of tobacco, or the use of prophylactic or medic- inal preparations such as chlorhexidine mouthwash solutions (14-18). As early as 1907, Miller (19) recognized that certain cleaning agents can cause unaccept- able abrasive damage to the tooth, especially at the sensitive enamel-cementum bor- derline (20). Since then, the question has been raised as to what properties cleaning Dedicated to Dr. Konrad Henkel on the occasion of his 70th birthday. 211

212 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS agents should have to fulfil their task of cleaning without causing significant damage to teeth. Dental requirements demand that a high cleaning effect is accompanied by as low a dentin abrasion as possible so that dentin at the dentin-enamel junction is not damaged. The fact that the enamel should also remain undamaged in the process appears obvious, even if a certain polishing effect seems desirable. A large number of methods have been developed for investigating the various param- eters. Special attention is naturally directed towards the measurement of clinically sig- nificant dentin abrasion. This is done today using the method developed by Graben- stetter (21), which involves measuring the abrasion of radiolabelled dentin (22-27) or by measuring surface profiles (25,28-31). Dentin abrasion has also been determined through weight loss (32). The same methods can be used in principle for measuring the degree of enamel abrasion (25,26,31,33). The roughness of enamel surfaces before and after treatment with dentifrices has been investigated in vitro and in vivo to discover whether products have a roughening or polishing effect. To this end, light reflection has frequently been employed as a mea- surement variable, in which case polychromatic light sources (34-40) and lasers (41,42) were used. Evaluations of the results have frequently been carried out using pictures taken with the aid of light or electron microscopes (38,39,43-45). There have, of course, also been attempts to determine the cleaning effect with in vitro methods. Initially substrates were coated with films such as paint coats (36,46,47). Today preference is given to the use of extracted human teeth with dental stain (48) or to synthetically discolored bovine teeth (49). The differences in light reflectance before and after treatment with the dentifrice serve as measurement variables. Numerous methods for examining these effects in clinical tests have been published (26,33,37,50-55). The publications by G. B. Winter eta/. (56) and W. B. Davis (57) supply valuable contributions to the cited complex of issues. Some of the methods quoted are also suitable for testing the effects of dentifrices on denture materials (58,59). AIM OF THE INVESTIGATION On the basis of currently available investigational results, it is assumed today that a dentifrice's cleaning effect improves with increasing dentin abrasion up to a limit not precisely specified (60). If there is, in fact, such a correlation, it clearly conflicts from a medical point of view with the already mentioned demands made of dentifrices, because products with high cleaning power for dental stain (discolored pellicle) would neces- sarily involve greater risk of damage to dentin at the dentin-enamel junction. Until now correlations between cleaning effect and enamel abrasion and between cleaning effect and scratching or polishing effects have been scarcely discussed. Since discolored pellicle is located on the enamel surface (61-65), the question arises as to why its removability is correlated with dentin abrasion and not with enamel abra- sion. This has been explained by the fact that the structure of pellicle consisting of proteins is more closely related to dentin than to enamel (66). This explanation is, however, somewhat unsatisfactory, as existing data from the literature also make a positive correlation between cleaning effect and enamel abrasion appear possible.