摘要:

Mg-containing calcium phosphate crystals including pseudocuboidal, rhombo-hedral shapes and groupings of quadrangular blades cubically arranged were found in human tooth enamel by scanning electron microscopy and by electron probe microanalysis. In caries-free old enamel, these hexahedrally based crystals measuring 0.5–2.5 μm in length were observed in some crevices of tufts and lamellae. The crystals were rarely seen in the inner crevices of caries-free exfoliated deciduous enamel and none could be seen in sound young enamel. In brown-coloured old enamel possessing arrested caries with lamellae, some of the lamellae contained crystals measuring 0.1–1.5 μ in length adjacent to half-dissolved prisms. These crystals, identified as Mg-containing whitlockite, will grow during a long period after eruption of the tooth or during the enamel caries pr

ISSN:0008-6568    

DOI:10.1159/000261432

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

The aim of this study was to determine the crystalline structure and chemical alterations of synthetic hydroxyapatite after irradiation with either CO2, Nd:YAG or CO2-Nd:YAG combination lasers at high energy densities of 500-3,230 J·cm2. Further, dissolution kinetics of the lased material were analysed and compared with those of unlased apatite. Electron microscopy showed that the lased material consisted of two kinds of crystals. From the micrographs their diameters varied from 600 to 1,200 Å and from 3,000 to 6,000 A, respectively. The larger crystals showed 6.9-Angström periodic lattice fringes in the transmission electron microscope. α-Tricalcium phosphate (TCP) was identified by X-ray diffraction. Selective-area electron diffraction identified the large crystals to consist of tricalcium phosphate while the smaller crystals were probably hydroxyapatite. Assays of dissolution kinetics showed that at these high energy densities lased material dissolved more rapidly than unlased synthetic hydroxyapatite due to the higher solubility of

ISSN:0008-6568    

DOI:10.1159/000261433

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Some newly designed surface-active phosphates were investigated with respect to their capacity to inhibit caries lesion formation in vitro. On the labial or buccal surfaces of sound human third molars, windows were prepared for investigation. One half of each window was treated with the test compound at pH values of 7.5, 5.5, or 3.5. The other half served as a control. Both halves were de-mineralized and the generated caries lesions in both parts were compared by means of quantitative microradiography. Mono-, bis- and trisphosphates differed only marginally in their effect on the demineralization. The compounds diminished the demineralization down to 30% of that of untreated enamel. Per molecule at least one long alkyl chain (more than 12 C atoms) was required for achieving decreased demineralization, indicating the importance of a low surface tension. The results suggest that some of the tested compounds have promising properties for their use as anticaries agents, especially when applied in combination with fluoride.

ISSN:0008-6568    

DOI:10.1159/000261434

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Many clinicians take for granted that occlusal caries which is just visible as a cavity is extended (deep) into the dentine. This study was aimed at quantifying this opinion. The study was carried out with 60 molars containing small but visible occlusal cavities. After taking bite-wing radiographs the crowns were separated from the roots and embedded. 700-μm sections were cut and glued on plastic sheets. X-ray pictures were taken of the sections which were scored by independent examiners. The bite-wings provided inaccurate estimates of the extent of caries. Radiographs of the sections revealed that about 25% of the molars had caries which reached just to the dentino-enamel junction, while the remaining 75% showed caries extending far into the dentine

ISSN:0008-6568    

DOI:10.1159/000261435

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

A dilution technique, with fluoride as a marker, has been developed to measure the volume of saliva and other fluids in the mouth. Immediately after swallowing, a small amount of fluoride solution is placed in the mouth, mixed with the oral fluids, and expelled from the mouth. The fluoride concentration of the expelled oral fluid is measured and the volume of fluid in the mouth at the time of spitting calculated from the fluoride dilution. Mean values of 0.75 ± (SD) 0.28 ml for males and 0.72 ± (SD) 0.16 ml for females were recorded. The accuracy of the volume determination is about ± 0.10 ml in vivo. This technique has provided a convenient and rapid means of determining saliva volumes. It could also be used to determine rates of secretion and may prove useful in the clinic for assessing a patient’s salivary compet

ISSN:0008-6568    

DOI:10.1159/000261491

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

A model system was used to examine the relation between the duration of plaque pH fall and enamel demineralization following the intake of dietary carbohydrate in humans. Subjects wore palatal appliances containing blocks of bovine enamel covered with Streptococcus mutans IB 1600, and rinsed with 5 or 10% sucrose. Changes in iodide penetrability (delta Ip) of the enamel, and the pH and extracellular calcium and inorganic phosphate (Pi) concentrations of the streptococcal plaque were determined. Following rinses with 5% sucrose, delta Ip increased with time and reached a maximum (11.2 ± 2.2 units) at 45-60 min although the S. mutans plaque remained acidic (pH = 4.8 ± 0.6). After 10% sucrose, the maximum (14.7 ± 3.1 units) was reached while the plaque pH was 4.0 ± 0.3. Second rinses with sucrose increased delta Ip at most by 30%. Thus, demineralization did not persist throughout the period of low plaque pH, but occurred primarily during the early phase of plaque acidogenesis. Enamel demineralization appeared to be limited by factors other than the pH of the streptococcal plaque. Calcium concentrations in the S. mutans plaque rose to a maximum of 10.9 ± 2.8 mEq/1 at 30 min after the 5% sucrose rinses, then fell; Pi reached a stable level of 12.2 ± 2.3 mEq/1 by 60 min. Calculations showed that conditions approached saturation with respect to enamel and dicalcium phosphate dihydrate as demineralization reached a maximum. Demineralization appeared to be limited at low plaque pH, therefore, by the accumulation of high levels of mineral ions in the streptococcal plaque. These findings suggest that the effects on the natural dentition will be limited when consuming a number of carbohydrate-containing foods during a

ISSN:0008-6568    

DOI:10.1159/000261492

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Intra-oral remineralisation of experimental caries-like lesions in human enamel, as determined by polarised light microscopy and quantitative microradiography, was promoted to a similar extent (% fall in ΔZ, 18.6 and 19.0) by chewing a sorbitol or sorbitol/xylitol (3:l)-sweetened gum for 20 min after each of three meals and two sugary snacks daily. The results suggest that reported differences in the properties of the two sweeteners do not affect their ability to enhance remineralisation due to salivary stimulation

ISSN:0008-6568    

DOI:10.1159/000261493

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Enolase from Streptococcus mutans has been purified to homogeneity by a three-step procedure. As shown by analytical ultracentrifugation and poly-acrylamide gel electrophoresis under denaturing conditions, the purified enzyme is an octamer with molecular weight Mr = 360 kDa, composed of eight identical subunits with Mr = 45 kDa. The kinetic parameters of S. mutans enolase in the presence of 1 mM Mg2+ are Aspec = 130IU × mg-1 and KM = 0.44 mM as determined by steady-state experiments in the D-glycerate 2-phosphate to enolpyruvate phosphate reaction. Enzymatic activity is inhibited noncompetitively by fluoride in the range between 0 and 10 mM NaF yielding Ki = Ki = 1.39 mM, but inhibition characteristics become competitive when tested above 10 mM. In the presence of only small amounts of phosphate (0.5 mM) the inhibitory effect of fluoride is enhanced dramatically yielding Ki = 0.26 mM. Inhibition by NaPO3F is competitive with Ki = 0.9 mM, indicating that free fluoride ions in combination with phosphate are more effective in inhibiting S. mutans enolase. It can be concluded that inhibition of enolase by fluoride in combination with phosphate can influence glycolysis in S. mutans and so reduce acid production or even growth rate, thereby leading to potential anticariogenic effects

ISSN:0008-6568    

DOI:10.1159/000261494

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Increased salivary viscosity may be associated with an increase in dental caries. In order to examine this relationship, the caries level in rats was monitored following gastric intubation with tung oil which has been shown to significantly increase salivary viscosity. Tung oil intubation over an 8-week period significantly increased the salivary viscosity in rats as compared with deoinized water and corn oil intubation. The total number of carious lesions was significantly increased (p < 0.05) in the tung oil intubated rats as compared with the two other groups. This increase in carious lesions was primarily associated with the smooth surfaces of the teeth. There was also a significant increase (p < 0.05) in the extent of enamel and dentin involvement of the tung oil intubated rats as compared with the other two groups. Histologic examination of the submandibular glands revealed an increase in the amount of glycoprotein material in the convoluted granular tubules of the tung oil intubated rats as compared with the deionized water and corn oil intubated animals. Collectively, these results suggest that tung oil intubation is correlated with both increased salivary viscosity and increased smooth-surface dental caries, suggesting that the viscosity may be related to dental caries progression.

ISSN:0008-6568    

DOI:10.1159/000261495

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

The effects of hyposalivation on the induction of dental caries and on the composition of the oral microflora were examined in specific pathogen-free Sprague-Dawley rats fed either a sucrose or a wheat flour diet with or without inoculation of Streptococcus mutans. Significant dental caries was induced in hyposalivated rats fed diet 2000 containing 56% sucrose, irrespective of infection by S. mutans. Diets containing 56% wheat flour did not induce dental caries in either hyposalivated or sham-operated rats, irrespective of infection by S. mutans. Bacteriological examinations at the end of the experiment demonstrated that the total numbers of lactobacilli and staphylococci increased in hyposalivated rats irrespective of the diet given, while the inoculated stain of S. mutans decreased significantly in hyposalivated rats. These findings suggest that some acidogenic microorganisms such as lactobacilli and staphylococci that can utilize sucrose or glucose but not wheat flour may also promote dental caries in hyposalivated rats.

ISSN:0008-6568    

DOI:10.1159/000261496

出版商:S. Karger AG    

年代:1992

数据来源: Karger