Acute exposure to mercury from amalgam: no short-time effect on the peripheral blood lymphocytes in healthy individuals

Mercury, released from dental amalgam, has been considered to adversely affect the human immune system. This study has been performed in order to evaluate if an acute low-dose mercury exposure, achieved by total amalgam removal in 10 healthy individuals, would affect the immunocompetent cells in human blood when the mercury level in blood and plasma was increasing. Induction of lymphocyte proliferation, measured as spontaneous de novo DNA synthesis, and total T cells, CD4+ T cells, CD8+ T cells, and B cells, was studied prior to and 7, 31, and 48 h after amalgam removal. In addition, the levels of interleukin-6 (IL-6) and C-reactive protein (CRP) in serum/plasma were measured. Despite a significant increase of the plasma mercury levels within 24 h after intervention, no significant influence on the peripheral blood lymphocytes could be detected during the first 48 h. The serum IL-6 levels increased significantly within 48 h after intervention, but were still low and within normal range. No influence on the CRP levels up to 7 d after amalgam removal was detected.

[New dental materials a health risk for dental staff. Acrylates can cause contact allergy and other problems]

The acrylic content of modern dental materials poses a risk of adverse reactions. Although the quantities of the substances released are normally too small to cause systemic reactions, local reactions may occur resulting in damage to the skin. A study, in which 81 dental workers referred to dermatologists for a variety of adverse reactions were patch tested, showed work-related dermatoses to represent a serious problem for dental staff, sometimes entailing occupational disability and re-schooling. Much of this could be avoided by observing special precautions to prevent direct contact with the sensitising substances in composite materials used in dental surgery. Since the use of dental amalgam has been reduced to about 10 per cent of all fillings in Sweden, the prevalence of adverse local reactions to the acrylic composite materials which are used instead may be expected to increase.

[The merit profile--an instrument for the evaluation of academic achievement]

The concept of a merit profile has been evolved at Karolinska Institute in Stockholm, whereby not only research achievements but also teaching, administrative and clinical skills and experience are each given merit ratings to produce an individual profile. This approach is based on the notion that all of these fields of activity constitute integregal facets of a scat of higher learning in medicine, and that a candidate's relative merits in each of these areas should be seen not only in relation to the overall academic goals but also to practical, professional considerations. The merit profile is intended to be used in selection for appointments and promotion, and as a basis for the continued enhancement of individual competence, and salary review.

The absorption, blood levels, and excretion of mercury after a single dose of mercury vapor in humans

Nine healthy volunteers without amalgam fillings were exposed to 400 micrograms/m3 mercury vapor (Hg0) for 15 min, corresponding to 5.5 nmol Hg0/kg body wt (median range: 4.4-7.2). Frequent sampling of blood, urine, and exhaled air was performed for 30 days after exposure. The median retention of Hg0 was 69% of the inhaled dose. During the first 3 days after exposure 7.5-12% of the absorbed dose was lost by exhalation, with the median half time of Hg0 in expired breath being 2.0 days. In blood and plasma, a rapid absorption phase of Hg was seen, followed by a biexponential decline of the curves in both media. A substantial interindividual variation was observed in the area under the concentration-time curves of Hg in blood and plasma. In plasma the median half time of the second phase was 10 days. About 1.0% of the absorbed Hg was excreted via urine during the first 3 days after exposure, whereas the estimated amount excreted during 30 days ranged from 8 to 40%. In order to evaluate the chronic exposure to mercury from dental amalgam in the general population, the daily Hg dose from the fillings were estimated based on the plasma Hg levels found in subjects with amalgam fillings and on the plasma Hg clearance obtained in the present study. The daily Hg dose was estimated to 5-9 micrograms/day in subjects with an ordinary number of amalgam fillings.

Toxicological aspects on the release and systemic uptake of mercury from dental amalgam

This paper summarizes some recent reports on mercury release from amalgam fillings and resulting concentrations in biological fluids, development of antibiotic resistance, and kidney function. In a series of studies of subjects with amalgam fillings, mercury (Hg) levels were followed in saliva, feces, blood, plasma, and urine before and until 60 d after removal of all of the fillings. The Hg concentrations in saliva remained elevated for at least 1 wk, suggesting that dissolved Hg vapor is not the major source of mercury in mixed saliva. An absorption phase of Hg was seen in plasma during 24 h after amalgam removal. After 60 d the plasma Hg concentration was reduced to 40%, of the baseline level. The decrease per amalgam surface was 0.11 nmol/l (range 0.02 0.40). The Hg level in feces increased two orders of magnitude two days after amalgam removal. At day 60, the median Hg concentration was still slightly higher than the median value of the amalgam free control group. The resistance patterns of the oral and intestinal microflora in these subjects were also studied. In the intestinal microflora, the relative amount of intestinal microorganisms resistant to 50 microM HgCl2 peaked 7 d after removal of the amalgam fillings, with a median value per sample of 6.1%, compared to 1.3% in samples collected prior to the Hg exposure. However, no statistical differences in the resistance pattern of the oral microflora were detected between the control and the experimental groups. A number of sensitive kidney function parameters were measured 1 wk before and 1, 2, and 60 d after amalgam removal. No effects on the various kidney parameters studied were recorded. According to the conclusions of independent evaluations from different state health agencies, the release of mercury from dental amalgam does not present any non-acceptable risk to the general population.

Mercury in biological fluids after amalgam removal

Dental amalgam is the major source of inorganic mercury (Hg) exposure in the general population. The objective of the present study was to obtain data on changes in Hg levels in blood, plasma, and urine following removal of all amalgam fillings during one dental session in 12 healthy subjects. The mean number of amalgam surfaces was 18 (range, 13 to 34). Frequent blood sampling and 24-hour urine collections were performed up to 115 days after amalgam removal, and in eight subjects additional samples of plasma and urine were collected up to three years after amalgam removal. A transient increase of Hg concentrations in blood and plasma was observed within 48 hours after amalgam removal. In plasma, the peak concentrations significantly exceeded the pre-removal plasma Hg levels by, on average, 32% (1.3 nmol/L; range, 0.1 to 4.2). No increase in the urinary Hg excretion rate was apparent after amalgam removal. An exponential decline of Hg was seen in all media. Sixty days after the amalgam removal, the Hg levels in blood, plasma, and urine had declined to approximately 60% of the pre-removal levels. In seven subjects, who were followed for up to three years, the half-lives of Hg in plasma and urine were calculated. In plasma, a bi-exponential model was applied, and the half-life was estimated at median 88 days (range, 21 to 121). The kinetics of Hg in urine (nmol/24 hrs) fit a mono-exponential model with a median half-life of 46 days (range, 35 to 67). It is concluded that the process of removing amalgam fillings can have a considerable impact on Hg levels in biological fluids. After removal, there was a considerable decline in the Hg levels of blood, plasma, and urine, which slowly approached those of subjects without any history of amalgam fillings.

In vitro effects of mercuric chloride (HgCl2) on human mononuclear cells

Due to the release of the toxic compounds of mercury from amalgam fillings, dental amalgam has been questioned as an adequate restoration material for tooth fillings. HgCl2 has been found to be mitogenic for human blood lymphocytes in vitro. However, activation required much higher concentrations than are ever found in vivo. This study has been initiated to evaluate further the influence of HgCl2 on human immunocompetent cells in vitro. It is found that HgCl2 in a narrow concentration range has the ability to preferentially stimulate the CD4+ T cell subset to blast transformation and DNA synthesis. The reaction, when monitored during days 2-6, is maximal at day 6, and most blasts express the IL-2 receptor (IL-2R), indicating in vitro activation. The CD8+ T cell subset is not affected to the same extent. In addition, HgCl2-induced lymphocyte reactivity is dependent on accessory cells, i.e. CD14+ cells.

Fluoride in plaque fluid and saliva after NaF or MFP rinses

A micro-analytic method, capable of measuring the fluoride concentration in 5 nl of plaque fluid, was used to follow changes in fluoride concentration in saliva and plaque fluid at 6 single tooth-sites in 6 subjects for 180 min after a 0.048 M fluoride rinse as a NaF or MFP (sodium monofluorophosphate) solution. The maximum fluoride concentrations in saliva after NaF was 13x higher than with MFP. About 5% of the total amount of fluoride following the 20 ml NaF rinse was retained in the oral cavity. The corresponding figure followig MFP was <1%. The saliva/plaque fluid fluoride ratios for upper molars and lower incisors were significantly higher than for the upper incisors and lower molars. There was a tendency for a decline in the ratios with respect to time for all sites. To characterize the plaque fluid fluoride intra-oral single-site distribution and clearance, fluoride concentration versus time (AUC) was calculated from 10 to 60 min after a rinse. The NaF AUC followed the order: upper incisor, lower molar, upper molar and lower incisors reflecting a different exposure and clearance pattern due to the different access of the plaque to saliva. The MFP AUC values varied more, but were all significantly lower than the NaF AUC values. Analysis of plaque fluid fluoride curves at various sites revealed an exponential decline in most cases. With NaF, the baseline plaque fluid fluoride levels were not reached within 3 h. It is concluded that NaF solutions result in a significantly higher intra-oral fluoride exposure than MFP solutions. The fluoride distribution and clearance of fluoride from different sites in the oral cavity are linked to salivary access to these sites. These site-specific differences may have clinical consequences with regard to the dynamics of fluoride in the de- and remineralization processes.

Combined inhibitory effect of fluoride and hypothiocyanite on the viability and glucose metabolism of Streptococcus mutans, serotype c

The separate and combined effects of peroxidase-generated hypothiocyanite (HOSCN/OSCN-) and F- ions on glucose uptake and growth of Streptococcus mutans ATCC 25175 were investigated. S. mutans cells were grown to late exponential or stationary growth phase, harvested, washed and suspended in 2.0 ml of sterilized human whole saliva supplemented with 10 mM D-glucose. This saliva-bacteria mixture was supplemented with 5-150 microM H2O2 at pH 5.0 or 6.5. At pH 5.0, up to 103 +/- 21 microM HOSCN/OSCN- was generated. After 20 h of incubation at 37 degrees C, the saliva-bacteria suspension exposed to HOSCN/OSCN- were plated on mitis salivarius agar plates and incubated anaerobically for 2 days. Identical experiments were made with F- ions (0.5, 1.0 and 5.0 mM). Both HOSCN/OSCN- and F- caused a significant dose-dependent growth inhibition at pH 5.0, whereas no inhibition was observed at pH 6.5. When F- and HOSCN/OSCN- were added simultaneously at pH 5.0, an additive effect of growth inhibition was observed. In glucose incorporation experiments the bacteria-saliva mixture was exposed to 1 microM HOSCN/OSCN-, 0.5 mM F- or both. F-, HOSCN/OSCN- or their combination in sterilized whole saliva at pH 5.0 caused 14.2, 67.8 and 74.2% inhibition, respectively. These observations indicate that F- and HOSCN/OSCN- ions have an additive inhibitory effect on S. mutans and therefore their combination is likely to be more antibacterial than either agent alone.

Glass ionomer materials as a rechargeable fluoride-release system

It is well established that glass ionomers (GI) release fluoride (F). The degree of F released depends on the physical and chemical properties of the product. In the present study the fluoride release and the capacity of the GI to be recharged with fluoride was tested for five different brands: XR Ionomer (Kerr), Vitrebond (3M), GC Fuji Lining (G.C. Dental Industries Corp.), Baseline VLC (Dentsply) and Zinomer (Dent. Mat.). Fifteen test specimens were prepared for each brand. The specimens were immersed in deionized water. The F released was measured once a day for 11 days. Refluoridation of the test specimens was done with solutions of 0.02%, 0.04% and 0.2% NaF for 5 minutes on days 11, 16, 21 and 26. The F released from recharged specimens was measured daily until day 32. There was a positive correlation between the amount of F in the GI and the ability to release F. The five materials became 'recharged' with F following repeated F exposure in solution, the 0.2% solution being the most effective. XR ionomer released significantly more fluoride than any other material and showed the greatest ability to be recharged. Zinomer released significantly less fluoride than any other material and showed the least ability to be recharged. The present results indicate that GI serves as a F reservoir and can act as a prolonged slow-release system for at least 32 days.

Mercury in saliva and feces after removal of amalgam fillings

The toxicological consequences of exposure to mercury (Hg) from dental amalgam fillings is a matter of debate in several countries. The purpose of this study was to obtain data on Hg concentrations in saliva and feces before and after removal of dental amalgam fillings. In addition Hg concentrations in urine, blood, and plasma were determined. Ten subjects had all amalgam fillings removed at one dental session. Before removal, the median Hg concentration in feces was more than 10 times higher than in samples from an amalgam free reference group consisting of 10 individuals (2.7 vs 0.23 mumol Hg/kg dry weight, p < 0.001). A considerable increase of the Hg concentration in feces 2 days after amalgam removal (median 280 mumol Hg/kg dry weight) was followed by a significant decrease. Sixty days after removal the median Hg concentration was still slightly higher than in samples from the reference group. In plasma, the median Hg concentration was 4 nmol/liter at baseline. Two days after removal the median Hg concentration in plasma was increased to 5 nmol/liter and declined subsequently to 1.3 nmol/liter by Day 60. In saliva, there was an exponential decline in the Hg concentration during the first 2 weeks after amalgam removal (t 1/2 = 1.8 days). It was concluded that amalgam fillings are a significant source of Hg in saliva and feces. Hg levels in all media decrease considerably after amalgam removal. The uptake of amalgam mercury in the GI tract in conjunction with removal of amalgam fillings seems to be low.

Exposure to hydrogen fluoride: an experimental study in humans of concentrations of fluoride in plasma, symptoms, and lung function

OBJECTIVES

To study the absorption of inhaled hydrogen fluoride (HF) by measuring plasma fluorides and HF concentrations in the breathing zone during exposure to HF. A possible dose-effect relation was investigated by following airway symptoms and lung function-that is, forced expiratory volume in one second (FEV1) and forced vital capacity (FVC)-during and after exposure to HF.

METHODS

20 healthy, male volunteers were exposed for one hour to constant HF concentrations that ranged from 0.2 to 5.2 mg/m3; these concentrations are known to occur among potroom workers in the primary aluminium industry. Plasma fluorides were analysed before, during, and after exposure. Symptoms from the eyes and the upper and lower airways were registered and graded from 1 to 5 with a standardised questionnaire.

RESULTS

The total symptom score was significantly increased at the end of exposure for all the subjects as a group (P < 0.01) and for the group exposed to HF below the present Norwegian standard for total fluorides 0.6 mg/m3 (P = 0.05). No change was detected in FEV15 although a significant decrease was found in FVC in the group exposed to fluorides below the hygienic standard (n = 9) and for the entire group (n = 23). Almost all the symptoms had disappeared four hours after the end of exposure. Symptom scores from the upper airways were significantly correlated with the HF concentration (r = 0.62, P = 0.002), the change in plasma fluoride concentration (delta C) (r = 0.51, P = 0.01), and the maximum plasma fluoride concentration (Cmax) (r = 0.42, P = 0.05). A significant correlation was also found between the total symptom score for airways and the HF concentration.

CONCLUSIONS

The present study showed a strong relation between inhaled HF and concentrations of fluoride in plasma. Upper airway and eye symptoms occurred after one hour of exposure to HF even when below the Norwegian hygienic standard for fluorides.

No evidence of renal toxicity from amalgam fillings

Dental amalgam continuously releases mercury. Studies of sheep [Boyd et al., Am. J. Physiol. 261 (Regulatory Integrative Comp. Physiol. 30): R1010-R1014, 1991] showed decreased renal function after placement of amalgam fillings. In this study, renal function was investigated in 10 healthy volunteers before and after amalgam removal. The subjects had an average of 18 tooth surfaces filled with amalgam, which was removed during one dental session. One week before and sixty days after removal, the glomerular filtration rate (GFR) was determined by 51Cr-EDTA clearance technique. Blood and urine samples were collected for analysis of mercury, creatinine, beta 2-microglobulin, N-acetyl-beta-glucosaminidase (NAG), and albumin 1 wk before and 1, 2, and 60 days after amalgam removal. The plasma mercury concentration increased significantly 1 day after removal. Sixty days later, significantly lower mercury levels were found in blood, plasma, and urine. The GFR values were similar before and after mercury exposure (mean 94 and 94 ml/min per 1.73 m2, respectively). No detectable effects occurred on excretion of NAG, beta 2-microglobulin, or albumin. It is concluded that no signs of renal toxicity could be found in conjunction with mercury released from amalgam fillings.

Resistance of the normal human microflora to mercury and antimicrobials after exposure to mercury from dental amalgam fillings

The concentrations of mercury in saliva and feces and the resistance pattern of the gastrointestinal microflora were investigated for 20 subjects. Ten patients, with a mean number of 19 amalgam surfaces, had all amalgam fillings removed during one dental session. Ten subjects without amalgam fillings served as a control group. Saliva and fecal samples were collected before amalgam removal and 2, 7, 14, and 60 days afterward. Mercury levels in saliva and feces correlated significantly with the number of amalgam surfaces. No differences in the resistance pattern of the oral microflora were detected between the two groups. In the amalgam group there was an increase in the relative number of intestinal microorganisms resistant to mercury, ampicillin, cefoxitin, erythromycin, and clindamycin on days 7-14. This was not statistically significant in light of the normal variations of the control group. A significant correlation between the prevalence of mercury resistance and multiple antimicrobial resistance in intestinal bacterial strains was observed.

Reovirus type 1 associated with meningitis

A previously healthy 3-month-old girl presented with symptoms of meningitis, diarrhoea, vomiting and fever. Green monkey kidney (GMK) cells inoculated with cerebrospinal fluid (CSF) revealed reovirus-like particles by electron microscopy. RNA-gel electrophoresis, immunofluorescence and virus neutralization identified the pathogen isolated from CSF as reovirus type 1. Antibody determination by immunofluorescence of paired sera showed a significant antibody titre rise to the CSF isolate and neutralization test revealed a greater than 4-fold antibody titre rise to the CSF isolate. The CSF isolate was also neutralized by reovirus type 1 antibodies. This report represents one of a few associating reovirus with CNS symptoms in humans.

Low concentrations of mercury induce changes in ion composition of cultured myoblasts

The effects of low concentrations (1 pM, 1 nM, 1 microM) of mercuric chloride on ion distribution in cultured myoblasts were analysed by energy dispersive X-ray microanalysis. An increase in intracellular sodium concentration was observed five minutes after addition of HgCl2 to the culture medium. This increase was dose dependent and accompanied by a transient decrease in potassium concentration. Exposure to 1 nM and 1 microM HgCl2 led to a two-fold increase in the cytoplasmic chlorine concentration. The higher HgCl2 concentration (1 microM) induced morphological alterations in the form of cell membrane blebs, perforations and shrinkage or flattening of the myoblasts. It was concluded that even low concentrations of mercuric chloride cause elemental and morphological changes in cultured myoblasts, which may reflect effects of the metal on membrane permeability.

Passive adsorption of immunologically active and inactive synthetic peptides to polystyrene is influenced by the proportion of non-polar residues in the peptide

A well-known drawback in the use of synthetic peptides as solid-phase antigens in immunoassays is that positive controls confirming the presence of the peptide on the solid phase are not always present. We therefore evaluated the applicability of a recently described enzyme immunoassay (EIA) method by which the presence of peptides is detected by biotinylation (BioEIA) of alpha- and/or epsilon-amino groups after passive adsorption. This approach allows the rapid screening of a large number of proteins and peptides in respect to passive adsorption to plastic surfaces. When using irradiated polystyrene microplates we found that 240 (94%) of 256 synthetic peptides, covering 85% of the complete hepatitis C virus (HCV) sequence, passively adsorbed to polystyrene. When comparing the results from the BioEIA to the peptide reactivity of human sera it was obvious that the absence of serum reactivities was not due to lack of peptide adsorption to the plates. Using 192 peptides the relation between the signal-to-cutoff ratio (S/CO) in the BioEIA and the amino acid content of the individual peptides was further analyzed. The S/CO ratio was related to the number of epsilon NH2 groups (Lys residues) present in the peptide (P < 0.001, Kruskal-Wallis). We separately related the amino acid content of 68 peptides with Lys and 124 peptides lacking Lys to the S/CO ratio in the BioEIA. In both cases it was found that an increasing amount of nonpolar residues such as Ala, Phe, Ile, Met, and Val (P < 0.05, respectively) in the peptides was related to a lower S/CO ratio in the BioEIA.(ABSTRACT TRUNCATED AT 250 WORDS)

Relation between exposure to fluoride and bronchial responsiveness in aluminium potroom workers with work-related asthma-like symptoms

BACKGROUND

The relation between plasma fluoride levels and bronchial responsiveness was investigated in a longitudinal study in aluminium potroom workers who reported work-related asthmatic symptoms.

METHODS

From a cross-sectional respiratory survey, 26 men who reported work-related asthmatic symptoms on a validated questionnaire were selected for repeated measurements of bronchial responsiveness to methacholine. Regular analyses of plasma fluoride levels were performed. Exposure to fluoride and total particulates was assessed from routine surveillance of the workplace. Bronchial responsiveness was expressed as the dose-response slope of the line through the origin and last data point.

RESULTS

A positive association was found between bronchial responsiveness and plasma fluoride levels, such that an increase in the plasma fluoride level of 10 ng/ml was associated with an increase in the dose-response slope by a factor of 1.11 (95% confidence interval 1.05 to 1.17). Plasma fluoride levels were associated with the total atmospheric fluoride concentration in mg/m3 (beta = 28.1), but not with total particulates in the environment.

CONCLUSIONS

Bronchial responsiveness in aluminium potroom workers reporting work-related asthmatic symptoms appears to be related to plasma levels of fluoride. The underlying mechanism is, however, unknown.

Absorption and retention of dietary and supplemental fluoride by infants

There is a widespread belief that an adequate intake of fluoride during the pre-eruptive stage of enamel formation (i.e., from the diet in frequent small doses throughout the day) will be protective against caries in later life. To obtain data on bio-availability and retention of fluoride in one age group (infants), we studied 3 treatment regimens: In Regimen A, small amounts of fluoride were obtained from the diet in frequent doses throughout the day; in Regimen B, a fluoride supplement (0.25 mg) was given once each day with a feeding; Regimen C was similar to regimen B except that the fluoride supplement was given 1 h before a feeding. For the 3 regimens, the respective mean absorptions of fluoride were 90.1, 88.9, and 96.0% of intake, and the respective retentions were 12.5, 47.1, and 52.3% of intake. Neither the difference in absorption nor the difference in retention between regimens B and C was statistically significant. By subtracting the background urinary excretion of fluoride (i.e., excretion of fluoride while diet was the sole source of fluoride) from the excretion after administration of the fluoride supplement, we calculated that 68.1% of the supplement was retained in Regimen B and 73.0% of the supplement in Regimen C. The difference was not significant.

Fluoride pharmacokinetics in infancy

Fluoride pharmacokinetic data are presented for infants given a fluoride supplement. Seventeen infants participated in a total of 20 studies. On one day, 0.013 mmol (0.25 mg) fluoride was given as a supplement (fluoride supplement study), and on another day a placebo was given (control study). Samples of plasma and urine were collected for 5 h and analyzed for fluoride. During control studies fluoride intake averaged 0.15 mumol/kg (2.9 micrograms/kg), and plasma fluoride concentrations ranged from 0.05 to 0.11 mumol/L (10 to 20 micrograms/L). In nine instances, the quantity of fluoride excreted in the urine was more than twice that consumed. When the fluoride supplement was given, total fluoride intake averaged 1.93 mumol/kg (36.6 micrograms/kg). Plasma peak concentration was reached by 30 min in 14 studies and by 60 min in six studies. Mean plasma peak fluoride concentration was 3.3 mumol/L (63 ng/mL). Area under the plasma concentration curve averaged 236 nmol.m-1 x min (4479 ng.mL-1 x min) and was not related to the dose of fluoride. The rate of urinary excretion was significantly correlated with rate of urinary flow. When the dose of fluoride was expressed per unit of body weight, fluoride retention was strongly related to the dose. Retention of the fluoride absorbed from the fluoride dose ranged from 75.4 to 87.6%. Plasma clearance averaged 6.8 mL.kg-1 x min-1 and decreased significantly with age. Net fractional clearance (renal clearance of the fluoride dose/GFR) averaged 56.7%, which was significantly greater than the 29% observed during the control studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluoride inhibits the antimicrobial peroxidase systems in human whole saliva

Fluoride (F-) ions at concentrations present in vivo at the plaque/enamel interface (0.05-10 mM) inhibited the activities of lactoperoxidase (LP), myeloperoxidase (MP) and total salivary peroxidase (TSP) in a pH- and dose-dependent way. The inhibition was observed only at pH < or = 6.5 and with F- concentrations > or = 0.1 mM. At pH 5.5 LP activity was inhibited by 85% and MP by 34% with 10 mM F-. TSP activity was also inhibited only at low pH (5.5) by approximately 25%. Furthermore, the generation of the actual antimicrobial agent in vivo, hypothiocyanite (HOSCN/OSCN-), of the oral peroxidase systems was inhibited by F-, again at low pH (5.0-5.5) both in buffer (by 45%) and in saliva (by 15%). This inhibition was observed only with the highest F- concentrations studied (5-10 mM). Fluoridated toothpaste (with 0.10 or 0.14% F) mixed with saliva did not inhibit TSP or HOSCN/OSCN- generation. This may have been due to the 'buffering' effect of toothpaste which did not allow salivary pH to drop below 5.9. We conclude that the F- ions in acidic fluoride products, e.g. in gels or varnishes (but not in toothpastes), may have the potential to locally inhibit the generation of a nonimmune host defense factor, HOSCN/OSCN/SCN-, produced by oral peroxidase systems. The possible clinical significance of this finding remains to be shown.

Effect of water rinsing after toothbrushing on fluoride ingestion and absorption

This investigation was done to determine the bioavailability of fluoride (F) after toothbrushing associated with different water rinsing procedures. Eight adult subjects participated in four experiments, conducted with a randomised, crossover design: (A) 2 min brushing with an F dentifrice, followed by three quick (3 x 2 s) rinses, each with 10 ml of water; (B) brushing as in A followed by one long-lasting (1 min) rinse with 5 ml of water combined with the toothpaste-saliva mixture; (C) brushing as in A followed by expectoration but without any water rinse afterwards; and (D) ingestion of the toothpaste as a slurry with 100 ml of de-ionized water. Blood samples were collected before and frequently for 6 h after each experiment and analyzed for F content. The area under the plasma F concentration vs. time curves (AUC) was calculated and the degree of F absorption estimated. AUC values obtained in experiment D were assumed to represent 100% F bioavailability. The plasma values recorded during experiment A were not significantly greater than the baseline values, indicating almost no F absorption when 3 quick water rinses were performed after toothbrushing. The degrees of F absorption after one long-lasting water rinse (B) were 7.6 +/- 4.2% and with no water rinse after toothbrushing (C) 23.8 +/- 13.5%, respectively. The results showed that the degree of F absorption after toothbrushing using an F toothpaste is strongly related to the mode of water rinsing.

Caries incidence, salivary flow rate and efficacy of fluoride gel treatment in irradiated patients

The caries-preventive effect of daily applications of a fluoride gel was studied in 55 patients receiving radiotherapy for tumors of the head and neck. The study was designed as a randomized, double-blind study with two parallel groups. From the start of radiotherapy one group received a 0.42% F gel once a day for 1 year. The other group received a daily application of a 1.23% F gel for 4 weeks followed by the use of the 0.42% F gel daily for 1 year. The results showed that in patients with an unstimulated saliva flow of > 0.1 ml/min daily fluoride gel treatment with a fluoride concentration of 0.42% F was sufficient to inhibit caries almost completely. The use of the 1.23% F gel was not superior to the 0.42% gel treatment program alone. In an attempt to evaluate the salivary flow rate as a diagnostic criterion for increased caries risk, sensitivity and specificity were evaluated. It was found that with an unstimulated saliva flow rate of < 0.1 ml/min the positive predictive value was 80%. The corresponding value for stimulated salivary flow rate of < 0.5 ml/min was 85%. One can therefore predict that 80% of patients with flow rates < 0.1 ml/min will develop at least one carious lesion per year. The corresponding negative predictive value for unstimulated saliva flow > 0.1 ml/min was 75%. That means that 75% of patients using the 0.42% F gel daily and with at least some saliva secretion will not develop any new carious lesions.

Maternal regulation of adrenocortical activity in the infant rat: effects of feeding

Basal and stress-induced corticosterone release in the infant rat has been shown to be inhibited by some aspect of maternal care. The following studies examined specific maternal cues that might be responsible for this regulation. In Experiments 1 and 2, 12-day-old pups remained with their dam but were either prevented or not from feeding; at the end of 24 hr, basal and stress-induced corticosterone levels were measured. Only those animals that were able to feed showed the hyporesponsiveness characteristic of nondeprived animals, suggesting that feeding rather than some other aspect of maternal care was the critical variable. In Experiment 3, all animals were maternally deprived, and some of them were fed via an intracheek cannula. Once again, feeding led to a pronounced diminution in both basal and stress-induced levels of corticosterone. Our results point to feeding as one of the critical features responsible for the inhibitory effect of the dam on the infant's adrenocortical activity.