A method has been developed for testing dentifrice abrasiveness which is based on a commercial toothbrush motor that operates a brush with only one or two tufts and on the application of dentifrice to a disk of neutron-irradiated dentin. Greater precision was found when only one tuft was used. The wear by two commercial dentifrices depended on the force on the brush and on the concentration during testing.

Demineralization of bovine tooth enamel was assessed by various physical means, and results were compared to measured changes in penetrability to iodide ions (delta Ip). Blocks of bovine enamel were exposed in vitro to lactate buffer (pH 4.3) containing 25 mMCaCl₂ and 10mM KH₂PO₄ for up to 4days. Delta Ip increased over a wide range with time. A plot with respect to microhardness exhibited a pronounced inflection, with delta Ip rising rapidly at indentation depths greater than 2.5 μm. Microradiography and polarized light microscopy demonstrated subsurface lesions coincident only with the higher delta Ip values. The limited demineralization during the early time periods, therefore, was associated with only minimal changes at or near the enamel surface, yet could be detected readily with the delta Ip system. Demineralization produced intraorally in subjects rinsing with 5 % sucrose was accompanied by increases in delta Ip, but no changes in surface microhardness or microscopic appearance of the enamel. It appeared that, under these conditions, demineralization was limited to the surface and corresponded to the very early phases of lesion formation.

Fluoride acquisition by human enamel from topical application of either fluoride solutions or self-gelling fluoride systems with tetraethoxysilane (TES) was studied in vitro. Also studied was fluoride deposition from self-gelling systems incorporating certain positively charged polymers (Jaguar C-15 or DEAE dextran) to reduce the rate of fluoride release from the gels. The systems tested were all 0.65 M with respect to fluoride and of neutral pH. Sodium fluoride with 2% cetylpyridinium chloride (CPC) and ammonium fluoride with 1% sodium lauryl sulfate (SLS) were tested either as solutions or as self-gelling preparations with 20% TES. Additional studies involved gels with (1) sodium fluoride, 0.5 M sodium phosphate and 1% SLS; (2) sodium fluoride with 5% Jaguar C-15 and 1% CPC; (3) ammonium fluoride, 0.5 M ammonium phosphate and 1% SLS, and (4) ammonium fluoride with 5% DEAE dextran and 1% Tergitol 15-S-12. The findings showed that self-gelling systems deliver more fluoride to the enamel than their solution counterparts. The amount of firmly bound fluoride resulting from topical interaction was also greater from the self-gelling sodium fluoride system than from the application of an analogous sodium fluoride solution throughout the outer 20 μm of the enamel. The ammonium fluoride self-gelling system was only superior to the solution in this respect at the very enamel surface (i.e. depth of 2.5 μm). Incorporation of positively charged polymers in the gel systems resulted in decreased deposition of total fluoride and also of firmly bound fluoride.