The relationship among the iodide permeability (Ip) test, the surface microhardness (SMH) test, and enamel demineralization chemically analyzed as mineral loss was investigated using bovine enamel blocks. Demineralization periods of 0 (control) and 5, 15, 30, and 45 min using 0.05 mol/l lactate (pH 4.75) were chosen to approximate the acid challenge occurring during the intraoral enamel demineralization test. Mineral loss (Ca and PO₄) was found to be directly proportional to dissolution time (r = 0.95). Changes (Δ) in Ip and SMH each increased linearly over time (r = 0.58 and 0.64, respectively) and were similarly related to mineral loss (r = 0.60 and 0.65, respectively). The correlation between ΔIp and ΔSMH was 0.55. When longer demineralization periods (60, 120, and 240 min) were included, the correlation between ΔIp and ΔSMH was 0.68. We conclude that both the Ip test and the SMH test can be used as measures of the early stages of enamel dissolution.

It is now well-accepted that the primary anti-caries activity of fluoride (F) is via topical action. The retention of F in the mouth after topical fluoride treatment is considered to be an important factor in the clinical efficacy of F. The purpose of this study was to evaluate F levels in ductal saliva, whole saliva, and pooled plaque after treatment with topical F agents intended for home use. Ten consenting adults, mean (SD) age 31.0 (8.2) years, participated in all aspects of the study. Two days before each test, subjects received a professional tooth cleaning and subsequently abstained from all oral hygiene procedures to permit plaque to accumulate, and from the use of F-containing dental products. Treatments consisted of a placebo dentifrice (PD), fluoride dentifrice (FD; 0.24% NaF), fluoride rinse (FR; 0.05% NaF), and fluoride gel (FG; 1.1% NaF). Unstimulated whole saliva and pooled plaque were sampled at multiple points over a 24-hour period. In a separate experimental series, stimulated parotid saliva was sampled over a two-hour period after treatment. Fluoride levels generally followed the same pattern in whole saliva and pooled plaque samples, with FG > FR > FD > PD. Night-time F application resulted in prolonged F retention in whole saliva but not in plaque. Fluoride levels in parotid saliva were only slightly higher after F treatment and returned to baseline levels within two h. The results of this study indicate that the method of F delivery, the F concentration of the agent, and the time of application (daytime vs. night-time) are important factors influencing F levels in the mouth.(ABSTRACT TRUNCATED AT 250 WORDS)

Recent evidence has suggested that the cariostatic effects of topical fluoride (F) are related to the presence of low concentrations of ionic F in the oral environment. The purpose of this study was to compare the retention of F in the oral environment over 24-hour periods after the use of a F dentifrice or a F rinse. Groups of ten consenting adult subjects (age 18-52 years) brushed and/or rinsed (B/R) in a standardized manner twice per day in the morning (AM) and before bed (PM) with either a placebo dentifrice (8 ppm F), NaF dentifrice (1100 ppm F), or NaF rinse (225 ppm F). Experiments were performed with placebo dentifrice only (PD); F dentifrice only (FD); F dentifrice followed by F rinse (FD/FR); placebo dentifrice followed by F rinse (PD/FR); and F rinse followed by placebo dentifrice (FR/PD). Unstimulated whole saliva samples were collected at baseline and then at 0, 15, 30, and 45 min, 1, 2, and 8 hr after B/R in the AM, after B/R in the PM and upon rising the following morning. Salivary flow rate and F were determined for each sampling interval. The results of this study suggest that: (1) F rinse may be a more effective way of delivering topical F than F dentifrice; (2) based on F retention, the combination of FD/FR was not more effective than FR only (PD/FR); (3) older individuals with gingival recession retained higher F levels; and (4) bedtime F application resulted in longer F retention than did daytime application, which may have important implications for enamel remineralization.

The intra-oral enamel demineralization test (IEDT) was introduced by Brudevold et al. (1984). This caries model involves human subjects wearing palatal appliances each holding eight bovine enamel blocks covered by a bacterial cell layer prepared by the harvesting of cultures of Streptococcus mutants (test plaque). The original model used the iodide permeability test for assessment of the extent of demineralization of bovine enamel blocks resulting from acid production by the test plaque after dietary substrate challenge. The IEDT model has been expanded and improved by us in the following ways: (1) Based on encouraging findings from an in vitro study (Zero et al., 1990), the surface microhardness test has been adopted to measure the extent of demineralization occurring at three sites on the enamel blocks corresponding to an area over which the effective plaque thickness is 0.5, 1.5, and 2.5 mm; (2) intra-oral pH of the test plaque is measured by means of a Beetrode miniature pH electrode at baseline, then at five, 10, 15, 30, and 45 min after the start of a test; (3) plaque samples are collected at the end of a test and analyzed for organic acid content by means of HPLC; (4) the bacterial test challenge has been expanded to include different cariogenic bacteria which are grown under various growth conditions. The improved model has the capability of studying fundamental aspects of the caries process, namely, the relationships among dietary substrate challenge, plaque pH change, plaque organic acid profiles, microbial virulence properties, and enamel demineralization. Furthermore, the model has the potential for use in more applied research on caries-preventive agents such as fluoride.

Previous studies have focused on enamel and plaque as the primary sites of fluoride (F) retention in the mouth. The present study was undertaken to evaluate the role of oral soft tissue as a site of F retention by comparing an edentulous subject panel (n = 9) with a fully dentate panel (n = 10). Unstimulated whole saliva samples were collected by having subjects pool saliva for two min. Samples were collected over a 24-hour period after application of a placebo dentifrice (PD; 0.4 ppm F), fluoride dentifrice (FD; 1100 ppm F), fluoride rinse (FR; 226 ppm F), or fluoride gel (FG; 5000 ppm F) delivered in custom trays. There was no statistically significant difference in salivary flow rate between the two panels for any of the treatments. The edentulous panel had higher salivary F levels than the dentate panel, which reached statistical significance (p less than 0.05) for the FD and FG treatments. In a separate study involving the same treatments, F levels at specific soft-tissue sites were measured over a one-hour period by use of absorbent discs placed in different soft-tissue areas of the mouth. The tongue and lower posterior vestibule retained the highest F levels, followed by the upper posterior buccal vestibule and upper anterior labial vestibule, with the lowest F levels retained in the lower anterior vestibule and the floor of the mouth. There was a strong-to-moderate correlation between whole saliva F concentration and F levels at specific soft-tissue sites. This study establishes the importance of oral soft tissue as the major site of F retention in the mouth.

Qualitative polarized light microscopy and crosssectional microhardness testing profiles were used to compare artificial root caries lesions with those naturally present in extracted human teeth. The artificial lesions were produced by immersion of roots with exposed windows in chemical buffers of acetate and lactate with no added enzymes or bacteria. The three buffer systems used produced lesions with the range of histological characteristics of natural lesions. These included a 'body' or 'surface' zone of the lesion when viewed in water, and a 'frontal' zone of reverse birefringence when viewed in quinoline. The 'frontal' zone was noted to first develop after three days of immersion in acetate buffer. Advanced natural lesions exhibited a wide, diffuse, advancing front, which was similar to that produced by 28-60 day lesions in acetate. Microhardness profiles of natural lesions could all be matched by one or more of the artificial lesions. The demineralizing process was seen to reduce mineral content across the lesion from 45 per cent in normal dentine to between 15 and 25 per cent.

The present study was undertaken to evaluate the effect of a twice-daily topical application of a 0.05% NaF mouthrinse on de- and remineralization in the oral cavities of subjects suffering from radiation-induced hyposalivation. Six subjects each wore a bonded intra-oral appliance containing a sound and a demineralized human enamel slab for four weeks. During that period, the subjects used 0.05% NaF rinses, twice daily, instead of the 1.1% NaF gel that had previously been a part of their preventive regimen. Salivary flow rates, plaque pH profiles following a 10% sucrose rinse, S. mutans and lactobacillus counts, fluoride clearance, and enamel microhardness were determined during the study. Sound enamel samples displayed no evidence of demineralization, and the previously demineralized enamel showed remineralization in the outer 50 microns in three of the six subjects. The results suggest that a twice-daily oral rinse with 0.05% NaF can prevent demineralization and enhance remineralization in subjects with radiation-induced hyposalivation.

The aim of the present study was to examine a sodium fluoride anticalculus dentifrice product containing soluble pyrophosphate for its ability to promote remineralization and/or inhibit demineralization of dental enamel in a pH cycling model in vitro. Enamel crowns with windows were subjected to 14 days of alternating demineralization and remineralization periods at 37 °C. Teeth were immersed 5 min daily in one of the test dentifrice systems (1:3 slurry in deionized water) between the demineralization and remineralization cycles. Test dentifrices included (1) sodium fluoride (NaF; 1,100 ppm F)/silica abrasive (Crest) and (2) NaF (1,100 ppm F) with 3.3% soluble pyrophosphate/silica abrasive (Crest Tartar Control). Controls included a placebo dentifrice (silica abrasive) with no added fluoride and a group which received no treatment at all, i.e., demineralization/remineralization only. Overall, both of the NaF dentifrices were very effective in limiting in vitro caries progression and were not significantly different from each other. Inclusion of pyrophosphate in the NaF dentifrice did not affect the net outcome of the cycling demineralization/remineralization processes which is in agreement with recent clinical and in situ studies of these products.