Caries and fluoride processes.

OBJECTIVES: The purpose of the work was to establish the level and source of salivary fluoride, whether it could interact with tooth mineral and whether it was able to effect calcium re-acquisition and remineralisation. METHODS: Fluoride in saliva and in solution was measured by electrode, calcium by complexometric titration and phosphate colourimetrically-to measure salivary fluoride, its uptake by mineral and the effects of such low levels on calcium and phosphate levels in solution in contact with suspensions of mineral hydroxyapatite. RESULTS: Fluoride levels in saliva were low but could interact with hydroxyapatite. Such levels caused apatite crystallite growth and preferential acquisition of calcium by calcium-deficient apatite. CONCLUSIONS: Salivary fluoride contents rose with increasing water fluoride levels. It was acquired by hydroxyapatite mineral. Topical fluoride was stored on oral tissues. Even these low fluoride contents could cause mineral crystallite growth with preferential calcium uptake. On a mineral area basis these effects were caused by quite low fluoride uptakes. These findings do not support reliance upon large fluoride uptakes by tooth enamel as evidence for commensurate caries reductions.

The use of fluorescein-enhanced quantitative light-induced fluorescence to monitor de- and re-mineralization of in vitro root caries.

The use of fluorescein-enhanced quantitative light-induced fluorescence (QLF) in the detection of in vitro root caries demineralization and reminerlization was investigated. Fourteen previously extracted human premolar roots were selected and determined to be caries-free. Cementum was removed and nail varnish applied leaving an exposed window. Positive and negative controls were selected. During a demineralizing regimen, roots were removed at regular intervals (12, 48, 72 and 120 h) and immersed in sodium fluorescein (0.2 mg L(-1)). Following gentle rinsing, each root was examined using QLF before being returned to the demineralizing solution. Following 120 h, each tooth was sectioned through the lesion and one-half retained for transverse micro radiography (TMR) analysis. The remaining half were subjected to a remineralizing regimen undergoing the same fluorescein and QLF examinations at 7, 28 and 36 days. Results showed that QLF effectively monitored demineralization/remineralization of root dentine as represented by fluorescein penetration. TMR analysis showed good correlations with QLF (DeltaZ/DeltaQ) after demineralization (r = 0.89) and remineralization (r = 0.84). The technique could represent an in vivo method for root caries detection and classification.

Visualization of root caries lesions by means of a diazonium dye.

A diazonium dye was used to visualize caries lesions in root tissue. Root caries lesions were created in vitro according to a variety of protocols based on methylcellulose gel (6% w/v) and/or lactic acid buffer (0.05 M, pH 4.5). Teeth containing lesions were soaked overnight in an alkaline solution of 2% (w/v) 2-naphthol or resorcinol, rinsed with distilled water, and immersed in a diazonium solution (prepared by titration of aniline with sodium nitrite in 1 M HCl at 5 degrees C) for up to 10 min, prior to being thoroughly rinsed with distilled water. The area of the caries lesion on the anatomical surface was clearly marked with a red/orange color following 5 minutes' incubation in the diazonium solution. The diazonium complex formed with 2-naphthol was found to be more resistant to leaching during rinsing and sectioning than that formed with resorcinol. Microscopic examination of sections taken in the apicalcoronal plane showed that the depth of area of the lesion was also marked by the red/orange coloration. Chemical changes in root mineral monitored during lesion formation showed some degree of correlation between lesion area and mineral dissolution. Visualization of coronal caries by this technique is currently under investigation. The visualization technique provides a simple means of determining the extent and severity of root caries lesions and may be a useful first step in their classification.

Interactions of fluoride and non-fluoride agents with the caries process.

Fundamental to the caries process and its inhibition is an understanding of the composition and structural relationships of dental mineral. These have received greater study in recent years, leading to a better understanding of the processes involved. Fluoride has been the most successful of the anti-caries agents to date, and many studies have concentrated on this ion. The anti-caries action of fluoride has been only partially explained by the early finding that fluoride-treated mineral was less soluble, and this criterion is now less widely accepted. The dissolutive process of caries is inhibited by fluoride, monofluorophosphate, trimetaphosphate, and zinc. However, only the first three of these show anti-caries activity. The presence of fluoride during in vivo and in vitro caries is conducive to the formation of an apparently intact surface zone. Current evidence is that this zone reforms during the caries process, thus acquiring fluoride and having larger crystallites compared with sound enamel. Trimetaphosphate also favors the formation of a surface zone. There is a clear beneficial involvement of fluoride, even at low levels, in the process of lesion remineralization. It is highly probable that this process results from re-growth of residual enamel crystallites rather than de novo precipitation of calcium phosphates. Levels of fluoride found in saliva can interact with dental mineral. Although zinc has been shown to adsorb upon apatite mineral and to restrict subsequent crystal growth, it does not appear to affect the action of fluoride, including remineralization, adversely. This may be due to the fact that the uptake of zinc is reversible.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of zinc with dental mineral.

As some currently available toothpastes contain zinc compounds, the reaction of zinc with dental mineral and its effect on crystal growth rates were studied using three synthetic calcium-deficient hydroxyapatites (HAP) as being representative of dental mineral. Zinc was readily acquired by all HAP samples in the absence of added calcium, the amount adsorbed being proportional to the HAP surface area; about 9 mumol Zn/m2 was adsorbed at high zinc concentrations. As zinc was acquired, calcium was released, consistent with 1:1 Ca:Zn exchange. Soluble calcium reduced zinc uptake and similarly, calcium post-treatment released zinc. Pretreatment of HAP with 0.5 mM zinc reduced its subsequent ability to undergo seeded crystal growth, as did extracts of a toothpaste containing 0.5% zinc citrate, even in the presence of saliva. The reverse reaction, i.e. displacement of adsorbed zinc by salivary levels of calcium, however, indicates the mechanism by which zinc can reduce calculus formation in vivo by inhibiting plaque mineralisation without adversely affecting the anti-caries effects of fluoride.

Chemical events during tooth dissolution.

Information on chemical changes during enamel dissolution has been collected from investigations on hydroxyapatite solubility, enamel solubility, artificial lesion formation, and natural caries. Although hydroxyapatite and enamel will ultimately dissolve in acid or during caries, compositional changes also occur. Most notably, there is a preferential dissolution of calcium, both from hydroxyapatite and from enamel, and of carbonate and magnesium from enamel. Root dentin yields substantial amounts of magnesium on acid attack. Fluoride may be involved in surface zone formation during attack, but an additional theory of coupled diffusion is described. Calcium-deficient mineral is produced during an acid attack, and this has lattice parameters and solubility behavior different from those of stoichiometric material. The interaction of fluoride produces a more stable lattice, resisting dissolution and favoring accretion, and tending to counteract the effects of carbonate and magnesium in forming mineral. The provision of fluoride, albeit at low levels, in plaque fluid is seen as being important in maintaining the net integrity of the tooth. More information is also needed on the role of the organic phase in tooth structures during caries and acid attack.

The antigravity suit in neurosurgery. Cardiovascular responses in seated neurosurgical patients.

The haemodynamic responses associated with inflation of the antigravity suit (G suit, aviation type) to 8.0 kPa were studied in a series of 40 patients who underwent neurosurgical operations in the sitting position. The study showed statistically significant increases in systolic arterial pressure (p less than 0.005) and mean central venous pressure (p less than 0.001) with inflation of the suit. The systolic arterial and mean central venous pressures remained significantly elevated immediately before deflation of the suit at the end of the operation (p less than 0.001 and p less than 0.005 respectively). The addition of 0.8-1.0 kPa positive end expiratory pressure during suit inflation was also investigated. A further increase in central venous pressure occurred but this did not achieve statistical significance.

The oral disposition of zinc following the use of an anticalculus toothpaste containing 0.5% zinc citrate.

Zinc is retained in the mouth after use of a toothpaste containing 0.5% zinc citrate. More than one third of the dose was found to be retained after normal brushing. Elevated zinc levels were also found in plaque. Saliva zinc levels were significantly above background for at least 2 h after brushing. In-vitro experiments demonstrated that zinc can bind to the pellicle-coated tooth surface and can subsequently adsorb into saliva. Plaque can calcify to form calculus containing appreciable levels of hydroxyapatite. Zinc adsorbs to hydroxyapatite inhibiting crystal growth. Levels of zinc in plaque were found to be considerably higher than those taken up by hydroxyapatite in an in-vitro test of crystal growth inhibition indicating the potential of zinc to inhibit calculus formation.

Occurrence of malignant hyperpyrexia in a patient with osteogenesis imperfecta.

Probable malignant hyperpyrexia (MH) developed and was successfully treated in a 20-yr-old man during anaesthesia for reduction of a fractured mandible. The sister of this patient had died after an anaesthetic at the age of 14 yr, but malignant hyperpyrexia was not suspected. Subsequent enquiries revealed that the patient and his sister both had osteogenesis imperfecta. This case illustrates the infrequently reported association of malignant hyperpyrexia with osteogenesis imperfecta, and the difficulties in obtaining an adequate personal and family history of previous anaesthetics.

Enamel crystal chemistry--where do we go from here?

This section of the meeting has been devoted to enamel crystal chemistry and its behavior during formation and demineralization. In dealing with calcified tissues of any type we are looking at a crystalline formation with the most diverse range of properties which one could choose for its purpose. The size, shape, and intercrystalline binding give mechanical strength, cutting ability, and flexibility where necessary.

Diagnosis of subdural haematoma by computed axial tomography: use of xenon inhalation for contrast enhancement.

A subdural haematoma is described in which a definite computed tomographic (CT) scan diagnosis was made only after contrast enhancement had been achieved by the inhalation of xenon. The different types of enhancement obtained with iodide containing contrast media and with xenon are discussed. The use of xenon to obtain further information in conditions which are inadequately elucidated by conventional CT must be balanced against its anaesthetic effects and relatively high cost.

Studies on dimethyl tubocurarine in anaesthetized man.

Intravenous doses of 0.3 mg/kg dimethyl tubocurarine were required for consistent and adequate surgical relaxation in patients during nitrous oxide anaesthesia and produced virtually complete neuromuscular paralysis (96-100%) of the tetanic and twitch responses of the adductor pollicis muscle. The duration of action of the drug was prolonged--more than 3 h was required to attain 50% recovery from full neuromuscular paralysis. At this degree of recovery neostigmine was an effective antagonist. Determination of the tetanic tension ratios showed that tetanic fade developed during onset of paralysis and remained maximal until about 25% recovery of the tetanic contractions, when it disappeared raidly as recovery progressed. These doses caused no significant changes in arterial pressure and heart rate and this absence of cardiovascular side-effects is a desirable property of dimethyl tubocurarine. However, for many surgical procedures, an agent with a similar pharmacological profile but with a shorter action is desirable.