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A pH cycling model which incorporated a severe demineralization component was used to evaluate fluoride uptake and lesion progression for each of a NaF-based dentifrice, NaF-based mouthrinse and a monofluorophosphate (MFP)-based dentifrice. Simultaneous transverse fluoride and calcium profiles across the resulting artificial lesions were obtained using a proton microprobe technique with a resolution of approximately 10 microns. Longitudinal microhardness testing and proton microprobe calcium profiles were used to determine the extent of lesion progression (delta Z) with respect to untreated controls. Under the pH cycling conditions of the present study, the NaF dentifrice and mouthwash were observed to have a considerably higher uptake of fluoride in the lesion than the MFP dentifrice. Although the mineral content profiles of the lesions differed for treatments with each of the fluoride products, the differences were not significantly different in this model.

Modern techniques in dental research continue to assist in the study of the mode of (anticaries) action of topical fluorides. The Plaque Glycolysis and Regrowth Model (PGRM) facilitates the standardized assessments of antimicrobial effects on plaque following use of test formulations in vivo without complications arising from coincident mineral reactivity. In vivo plaque glycolysis testing demonstrates that topically applied fluoride, at conventional levels found in dentifrices, has only modest effects on the metabolic (acid-producing) activity of dental plaque. Any 'plaque' contribution to fluoride efficacy must come from more subtle effects on plaque acidogenicity than those measured in PGRM. The 19-F MAS NMR (Magic Angle Spinning Nuclear Magnetic Resonance) technique provides unambiguous measures of the reaction products of F-enamel interactions. Studies have revealed a new 'reaction product' of fluoride-enamel interactions-designated as Non-Specifically-Adsorbed Fluoride, NSAF. This species, along with FAP (fluoroapatite), FHAP (fluorohydroxyapatite), and CaF2 (calcium fluoride), contributes to the remineralization/ demineralization benefits of fluoride. pH cycling and in situ denture chip studies permit quantitative assessments to be made of the relative benefits of fluoride in promoting remineralization and in inhibiting demineralization. Results from pH cycling/ in situ experiments are strongly supportive of Koulourides' 'Acquired Acid Resistance' concept, describing fluoride's decay-preventive effects. The continued application of new analytical/physical techniques and testing regimens to the study of fluoride anticaries mechanisms may lead to the development of improved fluoride agents/treatment modalities for the prevention of dental caries.

Six subjects wore lower-arch intra-oral appliances supporting plaque-covered enamel units in the left and right buccal sulci. Units on both sides received identical cariogenic challenges by intermittent immersion in 0.28 M glucose. When one side was treated, in addition, with a mouthrinse designed to enrich plaque with Ca, P, and F, there was a 76% reduction in the softening and a 96% reduction in the porosity, created in enamel by the glucose exposures. F dentifrice extract, used similarly, caused a 67% reduction in enamel softening and a 93% reduction in porosity. When the two treatments were compared in the same experiment, the mouthrinse had a significantly greater effect in limiting enamel softening, but the porosity measurement technique was not sensitive enough to confirm this finding. Use of the mouthrinse caused variable deposition of fluorhydroxyapatite in plaque, and scanning electron microscopy examination of enamel showed small adherent hard deposits in some subjects. The polished enamel surface enabled backscattered electron imaging which revealed preferential dissolution of the core and tail regions of the prism. The results suggest that plaque mineral enrichment may be even more effective than F dentifrice in preventing dental caries.

The surface morphology of human enamel treated with pulsed, infrared laser radiation was examined using reflected light and scanning electron microscopy. Thin (

The hypothesis that diffuse opacities in enamel result from a chronic, mild disturbance to ameloblast activities was tested using fluoride. Three sheep (HF) were dosed orally with 0.5, and 3 (LF) with 0.2 mg fluoride/kg body weight daily for 6 months. A control sheep (C) received no additional fluoride. The 7 sheep were killed at or close to the time of emergence of their permanent central incisors. One tooth from each sheep was sectioned longitudinally. The enamel related to the secretory (S) and maturation (M) phases of ameloblast activity at the start of fluoride dosing was determined from a tetracycline marker. The pattern of mineralization of the outer 150 micron of the cut labial enamel was assessed using microhardness testing. The SEM appearance of the acid-etched outer enamel was compared in S and M zones in 5 teeth. The enamel of the C tooth was translucent. Diffuse opacities, similar in appearance to human fluorosis, were present in all fluoride-treated teeth. Hardness values in the outer 70 micron of the enamel decreased as the fluoride dose increased and, in the HF teeth, were lower in the S zone than in the M zone. Fluoride given during the M phase induced a surface hypomineralization which increased in degree and depth when fluoride was also given during the S phase. The SEM appearance of M and S enamel was similar in 2 LF and 1 HF teeth but, in the other HF tooth, S enamel but not M enamel had a disordered prism structure and loosely-packed crystals in an abnormal organic matrix. Histological examination revealed that ameloblasts remained in only 4 of the 7 teeth and that their regression and the formation of the cementum adjacent only to the labial enamel were progressing abnormally.

Initial lesions in bovine enamel were remineralized in vitro for periods lasting from one hour to two weeks; in some cases, remineralization was interrupted daily for a ten-minute APF application. After two weeks, surface coatings appeared on APF-treated specimens; SEM and TEM observations, including selected area and micro-electron diffraction, indicated both a layered structure within these coatings, and the predominance of calcium fluoride single crystals, ranging from 0.1 to 1.0 micrometer in size. Using double (45 Ca and 32 P) labeled remineralizing solutions, we obtained depth profiles of deposited labeled calcium and phosphate; these indicated that repeated APF applications prevented inward penetration of calcium and phosphate and limited the deposition of these ions to an outer surface region corresponding to the surface coating. These phenomena are explained in terms of the composition and apparent reactivity of the coating.

Defects present in 12 human permanent teeth were classified on the basis of their macroscopic appearance as hypoplasia (three teeth), diffuse opacities (three teeth), white demarcated opacities (one tooth but two defects), or yellow demarcated opacities (five teeth but six defects). The hardness values and SEM appearance of the defective enamel were determined after the teeth were sectioned through the lesion(s) and were distinctive for each type of defect. The thin enamel of the hypoplastic lesions was either opaque (with reduced hardness values) or translucent (with near-normal hardness values and sometimes a change in prism orientation external to an incremental line). The enamel of the diffuse and demarcated opacities was of normal thickness. The changes in the macroscopic and SEM appearance, and the reduced hardness values of the diffuse patchy opacities, were restricted to the outer 150 μm of the enamel. The demarcated opacities varied in position and depth, and in places had a clearly marked boundary with the adjacent normal enamel. Hardness values were related to color change, with yellow lesions being softer than white. Although prism direction was normal within demarcated opacities, prism outlines were less distinct. The findings suggest that temporary and permanent dysfunction of ameloblasts can occur in both secretory and maturation phases, influencing the final appearance of the lesion.

Octacalcium phosphate (OCP) and apatite overgrowths were studied using scanning and transmission electron microscopy (SEM and TEM). Precipitates containing overgrowths were prepared using constant composition methods with either OCP or dental enamel apatite seeds. In some cases the OCP-apatite interface was imaged using high-resolution TEM at an approximate 2.5-A resolution. Chemical analysis showed that OCP could be grown on apatite seeds under constant composition conditions, but that apatite growth on OCP although not kept at constant composition, indicated the growth of a phase more basic than OCP with a Ca P molar ratio of 1.50 ± 0.04. High-resolution TEM confirmed that this phase was “apatite-like.” The data show that it is possible to grow apatite on OCP and vice versa near physiological pH. Overgrowths of apatite and OCP are of biological interest as both phases appear to precipitate during hard tissue mineralization.

Developmental defects in incisors were induced by daily oral ingestion of sodium fluoride solutions. Teeth extracted at eruption from sheep that had been subjected to four different fluoride regimens—0.2 or 0.5 mg F/kg body weight daily for 6 months, 2 or 6 mg F/kg body weight daily for 21 days—were analysed for fluorine by gamma emission using a proton microprobe. Calcium and zinc profiles were also measured using proton-induced X-ray emission. Diffuse opacities, similar in appearance to mild human fluorosis, were produced by the first two regimens, whereas the last two produced hypoplastic lesions. Different distributions of fluoride were found in the unerupted enamel and dentine, and these patterns reflected variations in both the duration and concentration of the fluoride dose used to induce the fluorotic lesions.

Three topical fluoride agents deposited surface coatings of different morphology and thickness on intact human enamel surfaces. The agents studied were an acidic silane fluoride lacquer, a neutral NaF lacquer, and an APF gel. Each agent reacted with the enamel surface differently, producing its own distinctive etching pattern. The smallest particles observed in the surface coatings were from 20 to 30 nm in diameter and appeared to have indistinct morphologies. They often agglomerated into spherical globules ranging from 1-3 μ m in diameter.

High-resolution transmission electron microscopy is one of the few techniques where it is possible to investigate dental enamel at the individual crystallite level. By measuring interfringe spacings i

The effect on structural defects of carbonate, zinc, strontium, fluoride and lead inclusions in synthetic apatites has been studied by high resolution transmission electron microscopy. Treatment of dental enamel by zinc and strontium solutions has been similarly investigated. Electron beam damage to crystal surfaces was always seen in unerupted enamel and short-term refluxed aqueous apatites, and occasionally in mature enamel, but was not observed in high temperature synthetic apatites or long-term refluxed aqueous apatites. Concentrated areas of calcium deficiency (15–40 A in diameter), probably related to screw dislocations, were observed in untreated normal dental enamel and all synthetic apatites except high temperature carbonate-free stoichiometric preparations. These deficient regions are related to carbonate inclusion and are important in the susceptibility or resistance of enamel crystals to acid attack during the dental caries process.

The mineral profiles of artificial caries-like lesions formed in intact human dental enamel and pretreated with pulsed, infrared laser radiation were determined using a longitudinal microhardness tech

The crystallographic structure of surface coatings produced by three topical fluoride agents deposited by a single application on intact human enamel surfaces was investigated by light- and dark-field transmission electron microscopy, as well as by electron and x-ray diffraction. The agents studied were an acidic silane fluoride lacquer, a neutral NaF lacquer, and an APF gel. The smallest coherently diffracting particles were CaF2 microcrystallites 4-15 nm in diameter. Large apatite-like crystals, approximately I μm in length, were also observed in the outer surface coating produced by the silane fluoride lacquer.

Three patients with a partial natural dentition in one jaw and a full denture in the other participated in this study. Enamel treated with APF gel, Duraphat or Fluor Protector and untreated controls were positioned in a full denture for periods up to 3 months. Plaque accumulation on the enamel blocks was evaluated by scanning electron microscopy. The results show that in all 3 patients studied the formation of CaF2 inhibited dental plaque accumulation.