摘要:

The effect of low levels of fluoride on intracellular acid production and proton excretion in Streptococcus mutans NCTC 10449 at different growth and extracellular pH (pHo) levels was monitored under strictly anaerobic conditions. The sensitivity of S. mutans to fluoride increased as pHo decreased. Cells grown under acidic (pH 6.0 and 5.5) conditions were more resistant to fluoride than cells grown at a neutral pH. Under acidic extracellular conditions (pHo = 5.0), 0.025 mM fluoride inhibited proton excretion by approximately 50% in cells grown at pH 7.0. Slightly higher levels of fluoride (0.05–0.07 mM) were required for 50% or more inhibition in cells exposed to alkaline extracellular conditions or cells grown at acidic pH. Such levels of fluoride are about 10–20 times lower than that reported previously. Therefore, it is possible that as pH falls during initial bacterial glycolysis, sufficient amounts of anionic fluoride may be released, from its bound form in plaque, to cause significant inhibition of net proton movement out of the bacterial cell during further glycolysis, especially under the anaerobic environment of the deep layers of plaque. In addition to proton excretion, fluoride was also found to inhibit intracellular acid product

ISSN:0008-6568    

DOI:10.1159/000262421

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

The use of fluoride-releasing restoratives such as glass ionomer cements (GICs) has increased during the last decade. The antibacterial effect of released fluoride is thought to be a possible caries-preventive effect of these restorations. In this study fluoride concentrations in plaque on 1-year old resin-modified GIC, compomer and resin composite restorations were compared intraindividually and related to the occurrence of caries-associated bacteria. Plaque from class III restorations of the three restorative materials and from a proximal enamel surface in 18 individuals was analysed. Low fluoride levels were detected in all the samples, while the resin-modified GIC samples showed significantly higher amounts. The distribution of oral streptococci, mutans streptococci and lactobacilli did not differ significantly among the surfaces and did not correlate to the fluoride levels in the samples. A good correlation was found between the counts of mutans streptococci in saliva and their proportions in the plaque. The results indicate that the fluoride concentrations released in vivo from 1-year-old restoratives are not high enough to affect the plaque levels of the caries-associated bacteria mutans streptococci and lactobacilli.

ISSN:0008-6568    

DOI:10.1159/000262422

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

Fluoride-releasing materials have been reported to be bactericidal in vitro. This may be of benefit to modern dentistry, which is directed to the preservation of tooth tissue during restorative treatment. Little is known about in vivo effects. The aim is to investigate the influence of a resin-modified glass ionomer cement (RM-GIC) on carious dentine that remains under restorations, compared to amalgam. Using a split mouth design, 40 molar pairs in 40 patients (mean age 14.9 years) were selected, based on clinically and radiographically diagnosed occlusal dentine caries. Under aseptic conditions, the enamel was removed and the carious dentine was sampled just beneath the dentino-enamel junction using a round bur. Without further removal of carious dentine, the molars of a pair were alternately restored with RM-GIC or amalgam. The colour and the consistency of the carious dentine were assessed. The samples were processed for microbiological determination of total viable counts (TVC), mutans streptococci (MS), and lactobacilli (LB). After 6 months the molars were reopened, similarly sampled and evaluated, and then permanently restored after complete caries removal. For both materials a substantial decrease in the numbers of TVC, MS and LB was found after the 6-month period. Also a positive effect was observed on the colour and the consistency of the remaining carious dentine, which was comparable for the two materials. RM-GIC showed a significantly larger decrease in counts of MS and LB than amalgam, but not for TVC. Since in only few cavities the number of bacteria decreased under the level of detection, it is still considered essential to remove all carious dentine during restorative treatment.

ISSN:0008-6568    

DOI:10.1159/000262423

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

The aim of this work was to obtain further information about the origin of fluoride profiles in cementum. Fluoride was administered to rats at varying doses (0, 50,100 ppm F in drinking water) and for different durations (4,13 and 25 weeks). Fluoride distribution across the full thickness of molar cementum in rats was measured by means of an abrasive micro-sampling technique. The average fluoride concentrations in cementum increased significantly with increasing dose and duration of fluoride administration. The relative reduction of the average fluoride concentrations after cessation of fluoride administration was 94.2-36.5% at 50 ppm F and 62.2–49.2% at 100 ppm F in the outer layers (1–60 μm) and 91.5–24.1% at 50 ppm F and 74.1–7.6% at 100 ppm F in the middle (61–120 μm) layers of the cementum, respectively. The reduction rates were more closely related to the time intervals following cessation rather than fluoride concentrations in drinking water or specificity within the cementum. Two factors which may influence this are new cementum formation after withdrawal of fluoride and some fluoride release from cementum surfaces when the fluoride supply stopped. It was concluded that the cessation of fluoride administration reduced the fluoride concentration on the outer layers of cementum differing from bone where reduction occurs across the entir

ISSN:0008-6568    

DOI:10.1159/000262424

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

High-energy laser irradiation has been shown to cause crystalline transformations in apatites, which may lead to the formation of tricalcium phosphates with a resulting decrease in acid resistance. Depending on the nature and energy density of laser irradiation used, however, an increase of acid resistance of dental enamel has also been reported after laser irradiation. The aim of the present study was to investigate the phase transformation of hydroxyapatite (HA) to fluorapatite (FA) in a model system that incorporates sodium fluoride (NaF) into apatite structure by using laser irradiation. A CO2 laser was used at energy densities ranging from 21 to 500J/cm2. Synthetic HA mixed with NaF (10:1) was the target of laser irradiation. The crystalline structures were then investigated using X-ray diffraction analysis. The results showed that a phase transformation of HA to FA could be realized, and that the threshold energy density needed was 38 J/cm2. Not only is the finding crystallographically important, but it also opens new perspectives for future research regarding the development of laser technology for clinical purposes.

ISSN:0008-6568    

DOI:10.1159/000262425

出版商:S. Karger AG    

年代:1997

数据来源: Karger

ISSN:0008-6568    

DOI:10.1159/000262426

出版商:S. Karger AG    

年代:1997

数据来源: Karger

ISSN:0008-6568    

DOI:10.1159/000262427

出版商:S. Karger AG    

年代:1997

数据来源: Karger

ISSN:0008-6568    

DOI:10.1159/000262428

出版商:S. Karger AG    

年代:1997

数据来源: Karger