M. Larsen

Fluoride Is Unable to Reduce Dental Erosion from Soft Drinks

The main aim of the present study was to compare the erosive capabilities of some fruit-flavoured drinks, fresh or saturated with CaF2, with their content of acids and with previous results from some carbonated soft drinks. The other aim was to measure and compare the rates of dissolution of CaF2 in some carbonated and non-carbonated drinks and water. Seven commercially available fruit-flavoured drinks were diluted for drinking. Two human molars, each with two approximately 4 × 4 mm windows, were exposed continuously to 500 ml of each drink with or without prior equilibration with CaF2 under gentle agitation for 48 h. The depths of the erosions were then measured on microradiographs made from sections. Dissolution rate of CaF2 was measured by suspending 0.5 g of the salt in 0.5 litre of the drinks for 2, 10 and 60 min followed by solution analysis. The pH of the drinks was 2.83–3.51. The amount of NaOH required to bring pH to 5.5 ranged from 12–42 mmol/l, which is more than the amount necessary for most carbonated soft drinks. Equilibration with CaF2 gave total fluoride concentrations of 3–8 ppm. The depths of the lesions induced by the drinks without added fluoride were 450–625 µm whilst those developed by the drinks equilibrated with CaF2 were 350–625 µm. The dissolution of CaF2 was faster in the carbonated drinks and in distilled water than in the non-carbonated drinks. In conclusion, non-carbonated fruit-flavoured drinks contain considerable amounts of acids which, in vitro, induce erosions in teeth similar to those induced by carbonated soft drinks. Saturation with CaF2 reduced the in vitro development of erosions by 28% induced by drinks with pH above 3; in drinks with pH below 3, erosions were not affected by pH, despite total fluoride concentrations of up to 20 ppm.

Development of Dental Fluorosis according to Age at Start of Fluoride Administration

The aim was to determine at what ages the different types of human permanent teeth are susceptible to development of fluorosis. The prevalence of disturbances of enamel mineralization was recorded blindly in 70 children who had previously participated in a fluoride tablet program (0.5 mg F–– per day) and 40 other children who had never received fluoride tablets. Comparison of the prevalence of enamel lesions between these two groups and between the ages at which children began to take the tablets revealed the ages at which there was an increased risk of fluorosis. The data showed that fluoride can affect teeth late in their development when enamel is in a stage of late secretion or early maturation. It was concluded that this finding, which is in accordance with experimental animal studies, calls for a fundamental change in thinking not only with respect to the mechanisms involved in human enamel fluorosis, but also in relation to timing of fluoride programs.

Individual variations of pH, buffer capacity, and concentrations of calcium and phosphate in unstimulated whole saliva

In order to evaluate the risk of development of dental caries and/or of formation of dental calculus, salivary variables have often been used, but not with particular success. A reason for the apparent lack of association could be that the individual temporal variation of a characteristic was so substantial relative to the overall variation that it is not possible to characterize an individual by a single salivary measurement. The aim here was to examine the individual variation of pH, buffer capacity, and concentrations of calcium and phosphate and to compare it with the overall variation of the characteristics in order to shed light on the above problem. Eight weekly samples of up to 4 ml of unstimulated whole saliva were collected from 11 dental students before tooth brushing on their arrival at 8 a.m. in the dental school. Calcium was determined by atomic absorption spectroscopy, phosphate colorimetrically, and pH electrometrically. The buffer capacity was assessed by titration of the saliva sample from the pH initially observed to pH 3. It was found that within each individual the concentration of calcium and of phosphate, pH, the hydroxyapatite ion product and the buffer capacity varied considerably over the 7 weeks. The individual range frequently covered more than a third of the total range. Further, within each of the variables, single individuals could be found whose samples covered 60% or more of the overall range, whilst others covered less than 10% of the range. It was therefore concluded that, although collected at the same time of the day, pH, buffer capacity and concentrations of calcium and phosphate in unstimulated whole saliva in the single individual vary so much that characterization of individuals and of their saliva based on a single salivary analysis is unreliable and hazardous.

Effects of Fluoride on the Initial Colonization of Teeth in vivo

The effects of fluoride on the initial adherence of bacteria to smooth surface enamel were evaluated in an in vivo model system. Both quantitative and qualitative changes in the col

A computer program for correlating dental plaque ph values, cH+, plaque titration, critical ph, resting ph and the solubility of enamel apatite

A computer program was written in Visual Basic (Microsoft) to calculate (a) the area between a plaque pH curve (as seen after a sucrose rinse) and either a resting pH (around pH 7) or a critical pH value (around 5.5) above at least parts of the pH curve; (b) the solubility of apatite at the pH values in plaque; (c) the area between the plaque pH solubility curve and the apatite solubility at the resting pH/critical pH; (d) the area between plaque cH+ curve and the cH+ value at resting pH/ critical pH; and (e) the area between a plaque pH curve and a cut-off pH value below the curve, e.g. pH 3. It was found that because both the cH+ and the solubility of apatite increased logarithmically with a pH drop, the two latter area functions (d, e) were basically different from those based directly on pH curves. Thus, pH changes around the resting pH value had little effect on areas calculated from concentrations of H+ and solubility. In contrast, a small pH change around pH 4 had a strong impact on both demineralization potential and areas based on cH+. Also, because of the logarithmic nature, demineralization potentials were generally large in comparison to remineralization potentials, a point that has hitherto received little attention.

Effect of dietary nitrogen content and intravenous urea infusion on ruminal and portal-drained visceral extraction of arterial urea in lactating Holstein cows

Urea extraction across ruminal and portal-drained visceral (PDV) tissues were investigated using 9 rumen-cannulated and multi-catheterized lactating dairy cows adapted to low-N (12.9% crude protein) and high-N (17.1% crude protein) diets in a crossover design. The interaction between adaptation to dietary treatments and blood plasma concentrations of urea was studied by dividing samplings into a 2.5-h period without urea infusion followed by a 2.5-h period with primed continuous intravenous infusion of urea (0.493+/-0.012 mmol/kg of BW per h). Cows were sampled at 66+/-14 and 68+/-12 d in milk and produced 42+/-1 and 36+/-1 kg of milk/d with the high-N and low-N diets, respectively. The arterial blood urea concentration before urea infusion was 1.37 and 4.09+/-0.18 mmol/L with low-N and high-N, respectively. Dietary treatment did not affect the urea infusion-induced increase in arterial urea concentration (1.91+/-0.13 mmol/L). Arterial urea extraction across the PDV and rumen increased from 2.7 to 5.4+/-0.5% and from 7.1 to 23.8+/-2.1% when cows were changed from high-N to low-N, respectively. Urea infusion did not decrease urea extractions, implying that urea transport rates were proportional to arterial urea concentrations. Urea extraction increased more across the rumen wall than across the total PDV for low-N compared with high-N, which implies that a larger proportion of total PDV uptake of arterial urea is directed toward the rumen with decreasing N intake. The ruminal vein - arterial (RA) concentration difference for ammonia increased instantly (first sampling 15 min after initiation of infusion) to the primed intravenous infusion when cows were adapted to the low-N diet. The RA difference for ammonia correlated poorly to the ventral ruminal concentration of ammonia (r=0.55). Relating the RA difference for ammonia to a function of both ruminal ammonia concentration and the RA difference for urea markedly improved the fit (r=0.85), indicating that a large fraction of ammonia released to the ruminal vein is absorbed from an epithelial ammonia pool not in equilibrium with the ventral ruminal ammonia pool. Changing cows from high-N to low-N affected the relative blood urea clearance by kidneys and PDV. The clearance by the kidneys decreased from 41 to 27+/-2 L/h and the clearance by the PDV increased from 52 to 105+/-12 L/h when the diet was changed from high-N to low-N. In conclusion, urea transport across gut epithelia in cattle is adapting to N status and driven by mass action. Data are commensurable with a model for urea transport across gut epithelia based on regulated expression or activity of facilitative urea transporters.

Effect of abomasal glucose infusion on splanchnic and whole-body glucose metabolism in periparturient dairy cows

Six periparturient Holstein cows fitted with ruminal cannulas and permanent indwelling catheters in the hepatic portal vein, hepatic vein, mesenteric vein, and an artery were used to study the effects of abomasal glucose infusion on splanchnic and whole-body glucose metabolism. The experimental design was a split plot, with cow as the whole plot, treatment as the whole-plot factor, and days in milk (DIM) as the subplot factor. Cows were assigned to 1 of 2 treatments: the control (no infusion) or infusion (1,500 g/d of glucose infused into the abomasum from the day of calving). Cows were sampled at 12 d prepartum and at 4, 15, and 29 DIM. To study portal-drained visceral uptake of arterial glucose, [U-(13)C]glucose was continuously infused into the jugular vein on sampling days. Postpartum, voluntary dry matter intake and milk yield increased at a lower rate with the infusion compared with the control. The net portal flux of glucose increased with the infusion compared with the control, and 67 +/- 5% of the infused glucose was recovered as increased portal flux of glucose. The net hepatic flux of glucose was lower with the infusion compared with the control; however, the net hepatic flux of glucose per kilogram of dry matter intake was not affected by treatment. The arterial concentrations of glucose and insulin decreased and concentrations of nonesterified fatty acids increased from prepartum to 4 DIM with the control, but these effects were not observed with the infusion. The arterial concentration of beta-hydroxybutyrate decreased more from prepartum to 4 DIM with the infusion, compared with the control. Uptake of arterial [U-(13)C]glucose in the portal-drained viscera was affected neither by the infusion nor by the DIM and averaged 2.5 +/- 0.2%. The whole-body glucose supply changed to be less dependent on the recycling of lactate (Cori cycle) with the infusion. It was concluded that small intestinal glucose absorption is an efficient source of glucose to the peripheral tissues of dairy cows in very early lactation. At least 67% of the available glucose was recovered in the portal vein without affecting hepatic gluconeogenesis. Infused cows produced less milk and had a lower feed intake, indicating that an improved glucogenic status in very early lactation impaired metabolic adaptations to lactation.

Precursors for liver gluconeogenesis in periparturient dairy cows

The review is based on a compiled data set from studies quantifying liver release of glucose concomitant with uptake of amino acids (AA) and other glucogenic precursors in periparturient dairy cows. It has become dogma that AAs are significant contributors to liver gluconeogenesis in early lactation, presumably accounting for the observed lack of glucogenic precursors to balance estimated glucose need. Until recently, there has been paucity in quantitative data on liver nutrient metabolism in the periparturient period. Propionate is the quantitatively most important glucogenic precursor throughout the periparturient period. However, the immediate post partum increment in liver release of glucose is not followed by an equivalent increment in propionate uptake, because of the lower rate of increment in feed intake compared with the rate of increment in requirements for milk synthesis. The quantitative data on liver metabolism of AA do not support the hypothesis that the rapid post partum increase in net liver release of glucose is supported by increased utilisation of AA for gluconeogenesis. Only alanine is likely to contribute to liver release of glucose through its role in the inter-organ transfer of nitrogen from catabolised AA. AAs seem to be prioritised for anabolic purposes, indicating the relevance of investigating effects of supplying additional protein to post partum dairy cows. Combining data from quantitative and qualitative experimental techniques on L-lactate metabolism point to the conclusion that the quantitatively most important adaptation of metabolism to support the increased glucose demand in the immediate post partum period is endogenous recycling of glucogenic carbon through lactate. This is mediated by a dual site of adaptation of metabolism in the liver and in the peripheral tissues, where the liver affinity for L-lactate is increased and glucose metabolism in peripheral tissues is shifted towards L-lactate formation over complete oxidation.

Effect of abomasal glucose infusion on splanchnic amino acid metabolism in periparturient dairy cows

Six Holstein cows fitted with ruminal cannulas and permanent indwelling catheters in the portal vein, hepatic vein, mesenteric vein, and an artery were used to study the effects of abomasal glucose infusion on splanchnic AA metabolism. The experimental design was a split plot, with cow as the whole plot, treatment as the whole-plot factor and days in milk (DIM) as the subplot factor. Cows were assigned to 1 of 2 treatments: control or infusion of 1,500 g/d of glucose into the abomasum from the day of calving to 29 DIM. Cows were sampled prepartum and at 4, 15, and 29 DIM. Postpartum dry matter intake increased at a lower rate with infusion compared with the control. Arterial concentrations of all essential AA (EAA) were lower with infusion compared with the control. Net portal fluxes of His, Ile, Leu, Lys, Met, Phe, Thr, Val, Ala, Pro, Ser, and Tyr were lower with infusion compared with the control and the net portal fluxes of these AA showed positive correlations with dry matter intake, whereas the net portal fluxes of Asp, Glu, and Gln were unaffected by treatment. Net hepatic fluxes of EAA were not affected by treatment but increased as lactation progressed with both treatments. On a net basis, all EAA were removed by the liver prepartum and at 4 DIM, whereas Met, Phe, and Thr were the only EAA being removed at 29 DIM. Except for Ala, AA removed by the liver might be used primarily for noncatabolic processes, as exemplified by the 16% of hepatic Gly uptake accounted for as urinary hippurate. The measured hepatic uptake of glucogenic precursors (glucogenic AA, volatile fatty acids, lactate, and glycerol) accounted for 50 to 90% of the hepatic release of glucose. The hepatic urea output accounted for more than 100% of the hepatic ureagenic precursor uptake, indicating that the glucogenic precursors unaccounted for are nonnitrogen-containing compounds. In conclusion, an increased exogenous glucose supply to the small intestine did not seem to affect the amount of EAA and non-EAA available for peripheral tissues in early lactation, and the study did not indicate an AA-sparing effect of small intestinal glucose absorption. In periparturient dairy cows, hepatic catabolism of AA was not driven by the increased whole-body demand for glucose, and Ala was the only AA that contributed substantially to hepatic gluconeogenesis. In very early lactation, the supply of EAA might be of greater concern than the supply of glucogenic substrates.

Experiments on the initiation of calcium fluoride formation with reference to the solubility of dental enamel and brushite

As calcium fluoride formation following topical application of fluoride may be responsible for at least some of the caries-reducing effect of fluoride, the concentration of fluoride necessary to induce its formation were examined. The aim was to determine the degree of supersaturation with respect to calcium fluoride necessary for inducing its spontaneous precipitation, with close reference to its possible formation and retention on dental hard tissue when topical fluoride solutions are used clinically. Powdered enamel or brushite were suspended for 4 h in aqueous solutions buffered at pH 7.2 and 5.0. After the equilibration, ion concentrations were determined and degrees of saturation with respect to apatite and brushite were calculated. In aqueous solutions at pH 7.2 and 5.0 with similar concentrations as those found in the equilibrated suspensions the fluoride concentration was adjusted to from 5 to 500 parts/10(6). After 2 h of gentle agitation the supernatant was analysed, the precipitate (if any) isolated and examined by X-ray diffraction. Initiation of spontaneous calcium fluoride formation required a calcium fluoride ion-activity product of 10(-7.6) or more, 300 parts/10(6) fluoride were necessary to initiate calcium fluoride formation in neutral solution saturated with enamel, and the increased solubility of enamel apatite at low pH allowed calcium fluoride formation from solutions with as low as 100 parts/10(6) fluoride. When phosphate was present in the solution a competing apatite formation could mask the calcium fluoride formation. In neutral solutions saturated with respect to brushite, spontaneous fluorapatite formation was initiated by 100 pats/10(6) fluoride. With 200 parts/10(6) fluoride a further competing formation of calcium fluoride occurred.