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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.

1. 1. Teleost otoliths when viewed with transmitted light microscopy have patterns of microincrement width variation arranged in reasonably periodic layers with less periodic streaking, perpendicular to the microincrement, associated with variation in crystal bundle widths. 2. 2. Digitized transmitted light micrographs of otolith sections were converted into two dimensional Fourier transforms and finally into power spectra. Analysis of the power spectra showed that orthogonal periodicities exist in otoliths of different species. A general relationship between increase in lateral microincrement width and crystal bundle width was observed. 3. 3. Direct measurement of microincrement width and crystal width along the growth axes of otoliths was used to argue that otolith growth was continuous even at the edges of large otoliths.

1. 1. The sagittal otoliths of teleosts rest in a groove in the base of the otic cleft resulting in restriction of growth along part of the ventral edge of the otolith. 2. 2. The rate of crystalline deposition of the otolith is low at the sulcus, increasingly higher along the sulcul surface rising to a maximum at the growing edge of the otolith. 3. 3. It is proposed that the gradient in growth of crystalline deposition between sulcus and otolith edge is maintained by a pH gradient resulting from high to low levels of metabolic activity. 4. 4. Decreasing crystal widths along sulcus to edge surface are in accordance with those predicted by the Ostwald-Lussac law of crystal size changes along solubility gradients. 5. 5. The metabolic basis driving the pH gradient makes it probable that check rings in the sulcul part of the otolith are caused by surges in metabolic activity, not age.

Triclosan monophosphate is a phosphorylated derivative of the antimicrobial agent, triclosan. In comparison with triclosan, it is highly soluble in aqueous solutions. It is hypothesized that, within the oral environment, triclosan monophosphate (which may be devoid of antimicrobial activity) will be hydrolyzed into triclosan by the action of microbial phosphatases. The liberated triclosan may then exert antimicrobial activity. To test this hypothesis, we designed experiments to measure the phosphatase activity of plaque and selected species of oral micro-organisms and to demonstrate hydrolysis of triclosan monophosphate. Tests comparing the minimal inhibitory concentration and minimal bactericidal concentration of triclosan and triclosan monophosphate were also undertaken. Dental plaque and the majority of the bacterial strains tested showed phosphatase activity against p-nitrophenyl phosphate which peaked below neutral pH (acid phosphatases) or above neutral pH (alkaline phosphatases). Dental plaque showed the highest levels of alkaline phosphatase (optimum at pH 9.0) and relatively high levels of acid phosphatase (optimum at pH 6.0 to 6.5). Dental plaque and selected species of micro-organisms were all capable of hydrolyzing triclosan monophosphate, albeit at different rates. The minimal inhibitory concentration and minimal bactericidal concentration values for triclosan monophosphate against eight bacterial strains were always considerably higher than the corresponding values for triclosan. Addition of triclosan monophosphate to an established culture (ca. 109 cfu/mL) of Capnocytophaga gingivalis growing continuously showed that triclosan monophosphate was rapidly hydrolyzed into triclosan with concomitant loss of total bacterial viability. It is therefore likely that triclosan monophosphate will be broken down into triclosan within the oral environment with concomitant antimicrobial activity.

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.

In examining the microstructure of TEM specimens prepared from D + -implanted Cu for the presence of bubbles it was found that cuprous oxide (Cu 2 O) layers had formed over large areas of the specimen surfaces. The Cu was irradiated at normal incidence with 200 keV D + ions at a temperature of 120 K to a dose of ~2 × 10 21 D + / m 2 . Ar + ion milling at 330 K was used to erode irradiated surfaces to various depths prior to chemical back-thinning in a jet electropolishing bath. There was no evidence for the formation in the Cu of bubbles of either deuterium or argon, but dislocations at high density and planar defects were evident. Lattice fringes from {110}, {111} and {200} planes in Cu 2 O and moire patterns formed by double diffraction in the Cu and overlaid Cu 2 O film were obvious features in bright-field micrographs. The moire patterns include examples of magnified images of lattice defects.

1. 1. Teleost otoliths were shown to be composed of twinned aragonite crystals laid down as a series of protein-rich and protein-deficient bands consisting of bundles of crystals orthogonal to the band orientation. 2. 2. The cycle of protein-rich, protein-deficient mineral was correlated to diurnal rhythms in the amount of haemotoxylin eosin staining protein vesicles within the kinocilia cells of the macula. 3. 3. The hypothesis is presented that twinning leads to rapid growth of the otolith and that crystal increments are laid down under central neural control, leading to obligatory daily growth rings in teleost otoliths growing under normal physiological conditions.

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.

The initial rates of dissolution of synthetic apatites were determined using the rotating disc method. The reactivities of carbonated apatites in acidic media were directly related to their carbonate

A series of synthetic carbonated and non-carbonated apatites was investigated using high resolution transmission electron microscopy, and their dissolution behavior was tested under sink conditions, using the rotating disc method. n-Beam lattice images of the apatite samples were of a resolution greater than has been previously reported, and revealed an increase in crystalline disorder with the incorporation of carbonate in the apatite structure. This resulted in an increased rate of dissolution and a decreased activation energy for dissolution for the carbonated apatites. Thus, carbonate increased the reactivity of hydroxyapatite.

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

Experimental high-resolution lattice images of synthetic hydroxyapatite which contain image detail of a 0.20–0.25 nm resolution, are reported in two zone axis directions, 〈010〈 and 〈001〈. Good matches with computed images over a range of crystal thicknesses, defocus conditions and aperture variations were obtained in the 〈010〈 direction, although contrast reversals occurred every 20–30 nm change in defocus conditions. However, the image contrast was very sensitive to the experimental conditions and was difficult to computer-match in the 〈001〈 direction. Images with trigonal symmetry in this direction were observed under certain conditions even though projection of the hydroxyapatite structure, as determined by X-ray structure analysis, should result in hexagonal symmetry. This may be due to surface effects, local crystal-structural defects or to structural transformation arising from electron beam damage.

A range of carbonated apatites was prepared by aqueous precipitation at 37, 60, and 85°C and at controlled pH values varying from 6.00–9.50 in 0.25 increments. The products were analyzed for Ca, P, Sr, Mg, Na, F, and carbonate. Their initial dissolution rates were measured in a pH 4.5, 0.01 mol · liter−1 acetate buffer. Information about crystal morphologies and crystal defects was obtained by x-ray diffraction and high-resolution transmission electron microscopy (TEM). The CaP molar ratios of the products, together with their Sr and Mg contents, increased with increasing pH. Initial dissolution rates of the products, when adjusted for carbonate content, were in the order 37 > 60 > 85°C whereas apparent particle sizes determined by TEM and x-ray diffraction were ordered 37 < 60 < 85°C. Carbonated apatites precipitated at pHs of 7.0 or less were observed to have planar defects parallel to (100) that were identified as unit-cell-thick intergrowths of octacalcium phosphate. Carbonated apatites precipitated at higher pHs and noncarbonated apatites did not have these defects. A crystal growth mechanism is proposed to account for the presence of the (100) defects.

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

Planar defects parallel to (100) with an approximate [1/400] displacement vector have been identified by high resolution transmission electron microscopy and by micro-electron diffraction in the center of synthetic carbonated apatite crystallites. Similar intergrowths, 0.8-1.5 nm in width, have been observed in dental enamel, dentin and bone apatite crystallites. Four possible structural models of the defect core are proposed to explain these experimental features, and computer-simulated lattice images of the models are compared with the experimental images. Typical defects were consistent with a two-dimensional octacalcium phosphate inclusion, one unit cell thick, embedded in an apatite matrix.

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.