Chemical events during tooth dissolution

Self-assembly of dental surface nanofilaments and remineralisation by SnF2 and CPP-ACP nanocomplexes

Dental caries, erosion and hypersensitivity are major public health problems. SnF₂ is used widely in oral care products to help prevent/treat these conditions. Casein phosphopeptide-stabilised amorphous calcium phosphate nanocomplexes (CPP-ACP) are a biomimetic nanotechnology of salivary phosphopeptide-ACP complexes that deliver bioavailable calcium and phosphate ions to promote dental remineralisation (repair). We show here using in vitro studies and a double-blind, randomised controlled, cross-over design in situ clinical trial that SnF₂ and CPP-ACP interact to form a nanofilament coating on the tooth surface and that together they are superior in their ability to promote dental remineralisation. Sn(II) by cross-linking the CPP-ACP helps to stabilise the complexes which improves delivery to the tooth surface and enhances binding and ion incorporation into tooth mineral. The combination of SnF₂ and CPP-ACP in oral care products may significantly improve their efficacy in prevention/treatment of dental caries/erosion and hypersensitivity.

The effect of various model parameters on enamel caries lesions in a dose-response model in situ

OBJECTIVES

The aim of this exploratory double-blinded, randomized, cross-over, in situ study was to compare the effects of various model parameters ('intervention', 'brushing', 'position') on enamel caries lesions in a dose-response model.

METHODS

In each of four experimental legs of four weeks 16 participants wore intraoral mandibular appliances with four 'plaque-retaining' and four 'easily cleanable' positioned pre-demineralized bovine enamel specimens in the vestibular flanges mimicking proximal and buccal surfaces, respectively (n=512). The four randomly allocated interventions (either application only or brushing) included the following dentifrices: AlF3 1360ppmF(-)+chlorhexidine 0.05% (Lacalut aktiv, LA1360), NaF 1,450ppmF(-)(Blend-a-Med ProExpert), NaF 500ppm F(-) and 0ppm F(-) as negative control (NC) (both experimental, based on Blend-a-Med ProExpert).

RESULTS

Differences in integrated mineral loss (ΔΔZ) and lesion depth (ΔLD) were calculated between values before and after the in situ period using transversal microradiography. Significant differences for ΔΔZ [adjusted mean (95% CI))] were found between NC, NaF500 and LA1360for both 'plaque-retaining' [-1830 (-2371;1289); -986 (-1530;442); -2 (-548;544)vol%×μm] as well as 'easily cleanable' specimens [-399 (-682; -116); -391 (-672; -110); -16 (-302;270)vol%×μm]. Values for NaF1450 revealed a similar dose-response as LA1360.Values for LA1360 and NaF1450 did not differ significantly (p>0.05; ANCOVA).

CONCLUSION/CLINICAL SIGNIFICANCE

The design of the present in situ study was able to reveal a fluoride dose-response to hamper further demineralization of enamel specimens for 'easily cleanable' and 'plaque-retaining' sites being brushed or not. Particularly 'plaque-retaining' sites seem to be recommendable for measuring potential anticaries efficacy in situ.

An in vitro study of the effect of aluminum and the combined effect of strontium, aluminum, and fluoride elements on early enamel carious lesions

The purpose of this in vitro study was to evaluate the effect of aluminum and of combined strontium, aluminum, and fluoride treatments on enamel demineralization and remineralization. During a 6-day pH-cycling protocol, pre-softened bovine enamel slabs were immersed twice daily for 1 min in the following experimental solutions: (a) distilled water [W] (negative control); (b) 1,000 ppm F [F] (positive control); (c) 1,000 ppm Al [Al]; (d) 1,000 ppm Al,1,000 ppm F applied interchangeably [Al-F]; (e) 1,000 ppm Al, 1,000 ppm F, applied in sequential order [Al+F]; (f) combined 1,000 ppm Al and 150 ppm Sr [Al+Sr]; and (g) combined 150 ppm Sr and 1,000 ppm F [Sr+F]. Subsequently, the specimens were subjected to a 5-day acid resistance test. Lesions were evaluated quantitatively by performing surface microhardness and qualitatively by using polarized light microscopy. According to the results, solutions [Sr+F] and [Al-F] enhanced remineralization and inhibited demineralization as effectively as the [F] solution and significantly superiorly compared to [Al+Sr] and [Al] solutions. All tested solution groups, except for the [Al+Sr] group, presented significantly increased resistance to acidic attack, compared to [W]. PLM examination revealed that all solution groups, except for the [W] group, developed an acid-resistant zone at lesion surfaces. In conclusion, under the present experimental conditions, the combined strontium-fluoride and aluminum-fluoride treatments presented similar anti-caries efficacy compared to fluoride treatment alone, but they did not show evidence of synergistic activity on pre-softened enamel.

Salivary monitoring related to major surgery

BACKGROUND

Prolonged surgical procedures involving stress, extended general anaesthesia and a long pre-surgical fasting period may have systemic effects such as alterations in saliva flow rate and composition. These may compromise the patient's electrolytes and fluid balance and cause dehydration, systemic stress and oxidative changes.

PATIENTS AND METHODS

Saliva was collected prior and following surgery from 20 patients and 20 control subjects. The saliva samples were analysed for flow rates and levels of the following: calcium (Ca), magnesium (Mg), total protein, albumin and lactate dehydrogenase (LDH), total antioxidant status (TAS), uric acid (UA), superoxide dismutase (SOD), carbonyls, matrix metalloproteinases (MMPs) -2, -3 and -9 and heat shock proteins (HSPs) 70 and 90.

RESULTS

Salivary levels of Ca, Mg, protein, albumin and LDH were higher in post-surgical patients by 70% (P = 0·002), 88% (P = 0·0001), 120% (P = 0·13), 111% (P = 0·039) and 492% (P = 0·006) respectively than that in healthy controls. Salivary antioxidants in the surgical patients were higher while salivary carbonyls remained unchanged. Salivary TAS levels in pre- and post-surgical patients were higher by 63% (P = 0·001) and 85% (P = 0·0001) respectively, UA concentrations by 92% (P = 0·014) and 81% (P = 0·036) respectively and SOD values by 47% (P = 0·61) and 112% (P = 0·049) respectively. Salivary concentrations of MMP3 were higher in pre- and post-surgical patients by 23% (P = 0·067) and 30% (P = 0·044) respectively.

CONCLUSIONS

Local salivary, oral and systemic-induced alterations should be prevented. Moreover, salivary collection and analysis may be a new, efficient tool in the monitoring of patients undergoing major surgery. Further related research is necessary.

The Effect of Lesion Characteristics at Baseline on Subsequent De- and Remineralisation Behaviour

The aim was to study the effect of lesion characteristics at baseline on subsequent de- and remineralisation behaviour. Artificial lesions used during in vitro and intra-oral studies exhibit an increasing tendency toward net remineralisation with increasing integrated mineral loss at baseline (DeltaZ(base)). Proposed explanations include: (i) small lesions may be more vulnerable to demineralisation, and (ii) large lesions may be more difficult to remineralise. To evaluate these hypotheses, subsurface lesions were created in numerous blocks of human and bovine enamel, with a range of depths and DeltaZ(base), measured by microradiography. One group of lesions was further demineralised, a second group remineralised, and subsequently, both groups re-analysed. Under demineralising conditions, there was a marked decrease in further mineral loss with increasing DeltaZ(base). Under remineralising conditions lesions gained mineral in proportion to DeltaZ(base). The decrease in demineralisation of lesions with larger DeltaZ(base) may be partially a result of decreased intrinsic solubility through modified chemical composition, e.g. loss of magnesium, carbonate etc. The results may explain the tendency toward net remineralisation with increasing DeltaZ(base) in pH-cycling regimes.

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.

Treating root-surface caries

This article summarizes the effectiveness of restorative materials used to restore root surfaces, the mechanisms by which these materials reduce caries, and placement techniques for restoring root-surface lesions. Patients may be classified into low, medium, and high caries risk groups for root caries, and specific dental restorative material recommendations are made for each category. Effective plaque control, xylitol-containing chewing gums, antimicrobial agents, fluoride-releasing restorative materials, topically applied fluoride, and fluoride-containing toothpastes provide maximum protection for the high caries risk patient.

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.

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)

Dental tissue effects of fluoride

It is now well-established that a linear relationship exists between fluoride dose and enamel fluorosis in human populations. With increasing severity, the subsurface enamel all along the tooth becomes increasingly porous (hypomineralized), and the lesion extends toward the inner enamel. In dentin, hypomineralization results in an enhancement of the incremental lines. After eruption, the more severe forms are subject to extensive mechanical breakdown of the surface. The continuum of fluoride-induced changes can best be classified by the TF index, which reflects, on an ordinal scale, the histopathological features and increases in enamel fluoride concentrations. Human and animal studies have shown that it is possible to develop dental fluorosis by exposure during enamel maturation alone. It is less apparent whether an effect of fluoride on the stage of enamel matrix secretion, alone, is able to produce changes in enamel similar to those described as dental fluorosis in man. The clinical concept of post-eruptive maturation of erupting sound human enamel, resulting in fluoride uptake, most likely reflects subclinical caries. Incorporation of fluoride into enamel is principally possible only as a result of concomitant enamel dissolution (caries lesion development). At higher fluoride concentrations, calcium-fluoride-like material may form, although the formation, identification, and dissolution of this compound are far from resolved. It is concluded that dental fluorosis is a sensitive way of recording past fluoride exposure because, so far, no other agent or condition in man is known to create changes within the dentition similar to those induced by fluoride. Since the predominant cariostatic effect of fluoride is not due to its uptake by the enamel during tooth development, it is possible to obtain extensive caries reductions without a concomitant risk of dental fluorosis.