Quantifying the demineralisation of enamel using a hyperspectral camera measuring fluorescence loss.

BACKGROUND: The gold standard for quantifying mineral loss of enamel is transverse microradiography (TMR) and is complimented by the non-destructive quantitative light induced fluorescence (QLF) which measures changes in autofluorescence. Fluorescence loss has been shown to correlate with mineral loss. Building upon the established method, the use of hyperspectral fluorescence imaging (HI) allows the capture of a broader range of wavelengths to quantify fluorescence changes more accurately. METHODS: Bovine Enamel was demineralised within the dual constant depth film fermenter over 14 days and analysed using TMR, QLF and HI. The mineral change values were compared using Pearson's Correlation Coefficient. RESULTS: The analysis showed a statistically significant correlation that was equal between TMR and HI (r = 0.844) and TMR and QLF (r = 0.844), but weaker between QLF and HI (r = 0.811). CONCLUSIONS: The correlations indicate that HI is a promising valid non-destructive method for quantifying mineral loss from bovine enamel that is as accurate as QLF and complements TMR.

The cariogenic effect of starch on oral microcosm grown within the dual constant depth film fermenter.

Evidence on the link between starch intake and caries incidence is conflicting, therefore the cariogenicity of starch compared with sucrose was explored using a dual Constant Depth Film Fermenter (dCDFF) biotic model system. Bovine enamel discs were used as a substrate and the dCDFF was inoculated using human saliva. CDFF units were supplemented with artificial saliva growth media at a constant rate to mimic resting salivary flow rate over 14 days. The CDFF units were exposed to different conditions, 2% sucrose or 2% starch 8 times daily and either no additional fluoride or 1450 ppm F- twice daily. Bovine enamel discs were removed at intervals (days 3, 7, 10 and 14) for bacterial enumeration and enamel analysis using Quantitative Light Induced Fluorescence (QLF) and Transverse Microradiography (TMR). Results showed that in the absence of fluoride there was generally no difference in mineral loss between enamel exposed to either sucrose or starch when analysed using TMR and QLF (P > 0.05). In the presence of fluoride by day 14 there was significantly more mineral loss under starch than sucrose when analysed with TMR (P < 0.05). It was confirmed that starch and sucrose are similarly cariogenic within the dCDFF in the absence of fluoride. With the aid of salivary amylase, the bacteria utilise starch to produce an acidic environment similar to that of bacteria exposed to sucrose only. In the presence of fluoride, starch was more cariogenic which may be due to the bacteria producing a more hydrophobic intercellular matrix lowering the penetration of fluoride through the biofilm. This is significant as it indicates that the focus on sugars being the primary cause of caries may need re-evaluating and an increase in focus on carbohydrates is needed as they may be similarly cariogenic as sugars if not more so.

A novel non-destructive technique for qualitative and quantitative measurement of dental erosion in its entirety by porosity and bulk tissue-loss.

OBJECTIVE: To explore the potential of combining non-contact profilometry (NCP) and confocal laser scanning microscopy (CLSM) data to measure the entire erosive process non-destructively and to validate findings using inductively coupled plasma-atomic emission spectroscopy (ICP-AES), scanning electron microscopy (SEM) and surface microhardness (SMH) using the same samples throughout. METHODS: Polished bovine enamel samples (n = 35) were divided into groups (7/group) with similar SMH values. Samples underwent individual erosive challenges (1 % citric acid, pH3.8) for 1, 5, 10, 15 or 30 min under stirring and aliquot extracts were analysed for Ca and P by ICP-AES. SMH was used to measure erosive softening. Profilometry was used to assess bulk volume loss (BVL). Images were captured by SEM. Samples were stained with rhodamine-B (0.1 mM, 24 h) and images captured by CLSM. Image processing was used to determine changes in fluorescent volume for the first 10 µm (ΔFV10) for each enamel sample which were combined with BVL to calculate total lesion volume (TLV). ANOVA, linear regression and Pearson correlation analysis were used where applicable. RESULTS: Surface softening, [Ca], [P], BVL and ΔFV10µm increased with acid erosion duration which were significant by 10 min (P < .01). The Ca:P ratio increased to 1.57 then decreased after 5 min erosion suggesting a sub/surface phase change, which was observed by SEM and CLSM showing significant changes to the enamel surface and subsurface morphology with time. Combination of BVL and ΔFV10 as TLV strengthened the significant correlations with [Ca], [P], and SMH (P < .01). CONCLUSION: This novel combination of CLSM and NCP allows for concurrent non-destructive quantification of the entire erosive process by mineral loss, and qualitatively characterise microstructural changes during dental erosion.

Characterisation of mineral loss as a function of depth using confocal laser scanning microscopy to study erosive lesions in enamel: A novel non-destructive image processing model.

OBJECTIVE: The aim was to develop a novel image processing protocol for confocal laser scanning microscopy (CLSM) to study mineral distribution within erosive lesions as a function of depth. METHODS: Polished bovine enamel samples (n = 80) were divided into groups (8/group) with similar mean surface microhardness (SMH) values. Samples underwent erosion (1 % citric acid pH3.8) for 1,5,10,15, or 30 min, with or without stirring giving 10 treatment groups in a 2*5 factorial design. SMH was used to measure erosive softening. Profilometry was used to measure bulk tissue loss. Samples were then stained with rhodamine-B (0.1 mM, 24 h) and imaged using CLSM. Image processing was used to measure fluorescence volume (FV) as a function of depth for each image. The data from reference images were subtracted from post-erosive data to determine changes in fluorescent volume (ΔFV) as a function of depth. 2-way ANOVA and linear regression analysis were used where applicable. RESULTS: Surface softening and bulk tissue loss increased with acid erosion duration with or without stirring. Stirring significantly increased net softening at each time point; specimens underwent significantly more bulk tissue loss (P < 0.05). CLSM showed the erosive lesion deepened as exposure to acid increased, and that at the near surface (0-10 µm) FV and ΔFV increased rapidly for stirred solutions. The increase in pore space translated to a softer surface as measured by SMH. CONCLUSION: This novel non-destructive method allows concurrent quantification of dental erosion by mineral loss as a function of depth, and qualitative characterisation of microstructural changes during early erosion.

Chapter 4: Microelements: Part I: Zn, Sn, Cu, Fe and I.

Microelements are essential components of the diet. This chapter describes the effect of several such elements: zinc, copper, iron, tin, and iodine, on oral health. As part of normal diets, these elements have limited associations with specific oral conditions. This is partly because of their presence at relatively low concentrations and partly because they are most often present as mixtures where the effect of any one element is confounded by others. Deficiencies in microelements can cause health problems. Hence supplements, often containing one or more microelements, are prescribed to combat such conditions. All these ions exhibit antibacterial properties. Such effects are invariably small at the concentrations found in conventional foods and drinks. However, at higher concentrations, these ions can inhibit acid production by plaque bacteria involved in dental caries. Of more importance, zinc and tin have potentially significant effects on the de- and remineralisation processes involved in dental caries. Indeed, both elements have been included in oral hygiene products such as toothpastes for many years. Zinc, in particular, has demonstrated not only the ability to reduce dissolution rates of enamel and hydroxyapatite but also to inhibit calculus formation. Tin can also markedly reduce the dissolution rates. Both Cu and Fe have demonstrated anti-caries effects in animal models, whilst Fe-containing drinks have been shown to reduce enamel erosion in situ. The broad spectrum antibacterial properties of iodine have been promoted for its potential use against both early childhood caries and chronic periodontitis. However, more convincing clinical research is required to validate efficacy.

Chitosan-bioglass complexes promote subsurface remineralisation of incipient human carious enamel lesions.

OBJECTIVES: To test the in vitro subsurface remineralisation efficacy of chitosan-bioglass complex on artificial white spot lesions. METHODS: 64 artificial enamel white spot lesions were created by acidic gel and equally separated for static and 7d pH-cycling models. In each model, samples were assigned to 4 groups: (1) bioglass application on chitosan pre-treated lesions (CB); (2) chitosan-bioglass slurry (CBS); (3) "standard" remineralisation solution (RS - positive control); (4) deionised water (NC - negative control). Before each treatment using remineralising agents, 3-minute pellicle was formed on lesions' surfaces. Mineral content changes, surface and subsurface microhardness and ultrastructure were evaluated by Raman intensity mapping, Knoop microhardness and scanning electron microscopy, respectively. Data were statistically analysed using one-way ANOVA with Tukey's test (p < 0.05 is considered as significant). RESULTS: Chitosan-bioglass complexing was found to exhibit greater mineral regain and recovery of surface and subsurface microhardness compared to "standard" remineralisation solution and control groups, after static and dynamic pH-cycling remineralisation for 7 days (p < 0.05). Specifically, dense precipitations with Ca/P ratios similar to that in pure hydroxyapatite (HA) were observed on surfaces and subsurfaces which filled the porosities in the dynamic pH-cycling group, leaving no prismatic enamel structure exposed. CONCLUSIONS: Chitosan-bioglass complex is positive in promoting subsurface mineral deposition in spite of the presence of a short-term salivary pellicle. Clinical significance chitosan-bioglass complexing may provide an alternative clinical strategy in remineralising early enamel carious lesions as well as desensitizing exposed porous vital dental tissues clinically.

In-vitro subsurface remineralisation of artificial enamel white spot lesions pre-treated with chitosan.

OBJECTIVE: To test the null hypothesis that chitosan application has no impact on the remineralisation of artificial incipient enamel white spot lesions (WSLs). METHODS: 66 artificial enamel WSLs were assigned to 6 experimental groups (n=11): (1) bioactive glass slurry, (2) bioactive glass containing polyacrylic acid (BG+PAA) slurry, (3) chitosan pre-treated WSLs with BG slurry (CS-BG), (4) chitosan pre-treated WSLs with BG+PAA slurry (CS-BG+PAA), (5) remineralisation solution (RS) and (6) de-ionised water (negative control, NC). Surface and cross-sectional Raman intensity mapping (960cm-1) were performed on 5 samples/group to assess mineral content. Raman spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) were used to identify the type of newly formed minerals. Surface and cross-sectional Knoop microhardness were implemented to evaluate the mechanical properties after remineralisation. Surface morphologies and Ca/P ratio were observed using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). Data were statistically analysed using one-way ANOVA with Tukey's test. RESULTS: BG+PAA, CS-BG, RS presented significantly higher mineral regain compared to NC on lesion surfaces, while CS-BG+PAA had higher subsurface mineral content. Newly mineralised crystals consist of type-B hydroxycarbonate apatite. CS-BG+PAA showed the greatest hardness recovery, followed by CS-BG, both significantly higher than other groups. SEM observations showed altered surface morphologies in all experimental groups except NC post-treatment. EDX suggested a higher content of carbon, oxygen and silicon in the precipitations in CS-BG+PAA group. There was no significant difference between each group in terms of Ca/P ratio. SIGNIFICANCE: The null hypothesis was rejected. Chitosan pre-treatment enhanced WSL remineralisation with either BG only or with BG-PAA complexes. A further investigation using dynamic remineralisation/demineralisation system is required with regards to clinical application.

Effect of phytate and zinc ions on fluoride toothpaste efficacy using an in situ caries model.

OBJECTIVES: To compare and explore the dose-response of phytate-containing 1150 ppm fluoride toothpastes on model caries lesions and to determine the impact of zinc ions. METHODS: This was a single-centre, randomised, blinded (examiner/laboratory analyst), six-treatment, four-period crossover, in situ study in adults with a removable bilateral maxillary partial denture. Study treatments were toothpastes containing: 0.425% phytate/F; 0.85% phytate/F; 0.85% phytate/Zn/F; F-only; Zn/F and a 0% F placebo. Where present, F was 1150 ppm as NaF; Zn was 0.3% as ZnCl2. Human enamel specimens containing early-stage, surface-softened (A-lesions) or more advanced, subsurface (B-lesions) caries lesions were placed into the buccal flanges of participants' modified partial denture (one of each lesion type per side). A-lesions were removed after 14 days of twice-daily treatment use; B-lesions were removed after a further 14 days. A-lesions were analysed for surface microhardness recovery. Both lesion types were analysed by transverse microradiography and for enamel fluoride uptake, with B-lesions additionally analysed by quantitative light-induced fluorescence. Comparison was carried out using an analysis of covariance model. RESULTS: Statistically significant differences between 1150 ppm F and the placebo toothpastes (p < 0.05) were shown for all measures, validating the model. No differences between fluoride toothpastes were observed for any measure with little evidence of a dose-response for phytate. Study treatments were generally well-tolerated. CONCLUSIONS: Results suggest phytate has little impact on fluoride's ability to promote early-stage lesion remineralisation or prevent more advanced lesion demineralisation in this in situ caries model. Similarly, results suggest zinc ions do not impair fluoride efficacy. CLINICAL SIGNIFICANCE: Toothpastes may contain therapeutic or cosmetic agents that could interfere with fluoride's caries prevention efficacy. The present in situ caries study has demonstrated that phytate, added to provide enhanced extrinsic stain removal/prevention, and zinc, added to inhibit malodour, do not impair fluoride efficacy.

Remineralisation of enamel white spot lesions pre-treated with chitosan in the presence of salivary pellicle.

OBJECTIVE: To investigate the remineralisation of chitosan pre-treated enamel white spot lesions (WSLs) by bioglass in the presence of the pellicle layer. METHODS: 50 artificial enamel white spot lesions were created by acidic gel. Two lesions were used to investigate the formation of the pellicle layer by treating with human whole saliva for 3 min. 48 lesions were assigned to 6 experimental groups (n = 8): (1) bioactive glass slurry, (2) bioactive glass containing polyacrylic acid (BG + PAA) slurry, (3) chitosan pre-treated WSLs with BG slurry (CS-BG), (4) chitosan pre-treated WSLs with BG + PAA slurry (CS-BG + PAA), (5) "standard" remineralisation solution (RS) and (6) de-ionised water (negative control, NC). Remineralisation was carried out using a pH-cycling model for 7 days. Before each treatment using remineralising agents, 3-min pellicle was formed on lesions' surfaces. Mineral content changes, surface and subsurface microhardness and ultrastructure were evaluated by Raman intensity mapping, Knoop microhardness and scanning electron microscopy, respectively. Data were statistically analysed using one-way ANOVA with Tukey's test (p < 0.05 is considered as significant). RESULTS: Despite the heterogeneously formed pellicle layer, all groups showed an increase in surface mineral content after pH-cycling. Chitosan pre-treatment enhanced the subsurface remineralisation of WSLs using bioglass as both pre-treated groups showed greater surface and subsurface microhardness compared to NC. CS-BG exhibited denser subsurface structure than BG, while in CS-BG + PAA the crystals were bigger in size but resemble more enamel-like compared to BG + PAA as shown in SEM observations. Remineralisation of RS was limited to the surface as no significant subsurface changes of mechanical properties and structure were found. CONCLUSIONS: Chitosan pre-treatment can enhance WSL remineralisation with bioglass biomaterials when a short-term salivary pellicle is present. A further investigation using a long-term pH-cycling model with mature pellicle is suggested with regards to clinical application. CLINICAL SIGNIFICANCE: Chitosan pre-treatment has the potential in clinical application to remineralise subsurface lesions to achieve lesion consolidation.

A Novel Kinetic Method to Measure Apparent Solubility Product of Bulk Human Enamel.

Introduction: Tooth enamel mineral loss is influenced by its solubility product value, which is fundamental to the understanding of de- and remineralization resulting from a carious or erosive challenge. Published pKsp values for human enamel and hydroxyapatite range from 110 to 126 suggesting a heterogeneous nature of enamel solubility. However, this range of values may also result from the variety of methods used, e.g., some authors reporting values for suspensions of enamel powder and others for bulk enamel. The aim of this study was to develop a method to measure the solubility of bulk human enamel under controlled in vitro conditions simulating demineralization behavior of enamel within the oral environment using scanning microradiography (SMR). SMR was used to monitor real-time changes in enamel demineralization rates at increasing calcium concentrations in a caries simulating demineralization solution until the concentration at which thermodynamic equilibrium between enamel and solution was achieved. Method: 2 mm thick caries free erupted human enamel slabs with the natural buccal surfaces exposed were placed in SMR cells exposed to circulating caries-simulating 2.0 L 0.1 M pH = 4.0 acetic acid, at 25°C. SMR was used to continuously measure in real-time the decrease in mineral mass during the demineralization at 5 different points from on each slab. Demineralization rates were calculated from a linear regression curve of projected mineral mass against demineralization time. Changes in the demineralization rates were monitored following a series of successive increases in calcium (and phosphate at hydroxyapatite stoichiometric ratios of Ca:P 1.67) were added to the demineralizing solution, until demineralization ceased. The pH was maintained constant throughout. Results: Demineralization halted when the calcium concentration was ~30 mM. At higher calcium concentrations, mineral deposition (remineralization) occurred. By comparison with results from speciation software calculations for the calcium phosphate ternary system, this result suggests that the bulk solubility product of enamel (pKspBEnamel) under the conditions used is 121. Discussion: The apparent pKspBEnamel under these conditions was higher than many previous reported values, and much closer to those previously reported for HAp. However, this is a bulk value, and does not reflect that enamel is a heterogeneous material, nor the influence of ionic inclusions.

Longitudinal correlation of 3D OCT to detect early stage erosion in bovine enamel.

Erosive tissue-loss in dental enamel is of significant clinical concern because the net loss of enamel is irreversible, however, initial erosion is reversible. Micro-hardness testing is a standard method for measuring initial erosion, but its invasive nature has led to the investigation of alternative measurement techniques. Optical coherence tomography (OCT) is an attractive alternative because of its ability to non-invasively image three-dimensional volumes. In this study, a four-dimensional OCT system is used to longitudinally measure bovine enamel undergoing a continuous erosive challenge. A new method of analyzing 3D OCT volumes is introduced that compares intensity projections of the specimen surface by calculating the slope of a linear regression line between corresponding pixel intensities and the associated correlation coefficient. The OCT correlation measurements are compared to micro-hardness data and found to exhibit a linear relationship. The results show that this method is a sensitive technique for the investigation of the formation of early stage erosive lesions.

Evidence of an in vitro Coupled Diffusion Mechanism of Lesion Formation within Microcosm Dental Plaque.

The purpose of this study was to determine whether or not the dual constant-depth film fermenter (dCDFF) is able to produce caries-like enamel lesions and to ascertain further information regarding the performance of this fully functional biological caries model. Conditions were defined by the continuation (CF) or cessation (FF) of a saliva-type growth medium supply during 50-mM sucrose exposures (8 times daily). Hydroxyapatite (n = 3) and bovine enamel (n = 3) substrata were included within each condition and samples extracted after 2, 4, 8, and 16 days. Community profiles were generated for fastidious anaerobes, Lactobacillus spp., Streptococcus spp., mutans streptococci (MS), and Veillonella spp. using selective culture techniques and enamel demineralisation assessed by transverse microradiography. Results demonstrated that the dCDFF model is able to produce caries-like enamel lesions with a high degree of sensitivity where reduced ionic strength within the FF condition increased surface layer mineral deposition. Between conditions, biofilm communities did not differ significantly, although MS in the biofilms extracted from the FF condition rose to a higher proportion (by 1.5 log10 units), and Veillonella spp. were initially greater within the CF condition (by 2.5 log10 units), indicating an enhanced ability for the clearance of low-pKa acids following exposures to sucrose. However, both conditions retained the ability for caries-like lesion formation.

Inhibitory Effects of Zinc Ions on Enamel Demineralisation Kinetics in vitro.

Metal ions including zinc have the ability to influence enamel demineralisation. However, there is a paucity of data regarding reductions in demineralisation effected by zinc ions (Zn2+) in the literature. Therefore the aim was to measure the effects of zinc ion concentration ([Zn2+]) on the real-time in vitro demineralisation of enamel, during exposure to caries-simulating conditions, using scanning microradiography (SMR). Human enamel blocks were fixed in SMR environmental cells, through which acidic solutions (0.1 M acetic acid, pH 4.0) were circulated for periods of 50 h. SMR was used to quantitatively measure continuous mineral mass loss. Subsequently, the effects of sequentially increasing [Zn2+] (0.1-3,565 ppm) in the acidic solutions were measured on the rate of enamel demineralisation. This study demonstrated that Zn2+ even at low concentrations significantly reduces enamel demineralisation. There was a log-linear relationship between the mean percentage reduction in demineralisation and increasing [Zn2+] up to 3,565 ppm, i.e. the change in the overall percentage reduction in demineralisation was greater at lower concentrations than at higher concentrations, with 60% reduction at 36 ppm increasing to 90% at 3,565 ppm. In conclusion, SMR demonstrated the ability of Zn2+ to reduce the rate of enamel demineralisation under real-time in vitro acid conditions simulating dental caries. The results suggest that Zn2+ in the oral fluids could protect against enamel demineralisation during an acidic challenge. The log-linear relationship between [Zn2+] and demineralisation suggests that the reduction in enamel dissolution is limited by the saturation of surface sites on the enamel surface.

Effects of fluoride concentration on enamel demineralization kinetics in vitro.

OBJECTIVES: The aim of the present study was to measure the effects of fluoride concentration on the real-time in vitro demineralization of enamel during exposure to caries-simulating conditions using Scanning Microradiography (SMR). METHODS: Enamel blocks obtained from non-carious human molars were fixed in SMR environmental cells, through which acidic solutions (0.1M acetic acid, pH 4.0) were circulated for periods of 48h. SMR was used to quantitatively measure continuous mineral mass loss. Subsequently, the effects of sequentially increasing fluoride concentration (0.1-4500mg/L [F(-)]) in the acidic solutions were measured on the rate of enamel demineralization. RESULTS: The data shows a log-linear relationship between [F(-)] and reduction in demineralization up to 135mg/L [F(-)]. Above 135mg/L, no further significant decrease in demineralization occurred. CONCLUSION: The optimum range of local fluoride concentration for reducing enamel demineralization was in the range 0.1-135mg/L [F(-)] under the conditions studied. CLINICAL SIGNIFICANCE: Relatively low [F(-)] can exhibit near-optimum protection. Increasing the fluoride concentrations above 135mg/L may not necessarily give an increased cariostatic benefit. Improving the means of delivery of relatively low fluoride concentrations to the oral fluids through slow releasing mechanisms, such as the oral fluoride reservoirs, is the more appropriate way forward for sustaining long-term clinical efficacy.

The primary and mixed dentition, post-eruptive enamel maturation and dental caries: a review.

The mouth is in flux from the time the primary teeth begin to erupt, in the first year of life, through to the end of the 'mixed dentition' (i.e. the concurrent eruption of the permanent teeth and exfoliation of the primary teeth), at around 12 years of age. Primary teeth facilitate the development of the facial muscles and speech. They act as 'guides' for erupting permanent teeth. If lost prematurely, subsequent misalignment of permanent teeth can make them difficult to clean and possibly more caries-prone. During the mixed dentition phase, teeth are at relatively high risk of caries. Erupting teeth are difficult to clean and cleaning may be avoided because of tender gums and behavioural factors in children. Permanent enamel (and possibly primary enamel) undergoes post-eruptive maturation, accumulating fluoride, becoming harder, less porous and less caries-prone. Overall, primary teeth are more vulnerable to caries than permanent teeth. Widespread use of fluoride toothpaste has effected marked reductions in caries. Some evidence exists that fluoride delivered from toothpastes may be somewhat more effective in reducing caries in primary than in permanent teeth. However, caries remains a public health concern globally. New fluoride toothpaste formulations, optimised using in vivo fluoride delivery and efficacy studies, may improve the caries resistance of mineral deposited during post-eruptive maturation. Behaviour should not be ignored; new formulations will be more effective if used according to professionally endorsed recommendations based on sound science. Establishing good oral hygiene behaviour early in life can lead to lasting anti-caries benefits.

Important considerations in the development of toothpaste formulations for children.

A number of factors should be taken into account when designing toothpaste formulations for use by children at the different stages of their development. While adult toothpaste formulations may provide caries prevention benefits for children at risk of caries, these formulations may also contain higher levels of abrasive in order to address the staining needs of the adult population owing to smoking and the consumption of dietary chromogens such as coffee and tea, which are not normally found in the diet of children. While toothpastes formulated for adults are also likely to contain higher concentrations of surfactant and flavour, many children prefer toothpastes with mild flavours and modest foaming characteristics. An ideal children's toothpaste formulation should therefore aim to maximise fluoride availability, with appropriate abrasivity, while still delivering effective cleaning, as well as levels and types of flavour and surfactant to provide an acceptable brushing experience. Selection of toothpaste flavour types for children of different ages should ideally be based directly upon preference data from children. Flavours perceived as pleasant during brushing studies have been linked to increased brushing time, which, in turn, can increase the delivery and efficacy of fluoride from toothpastes. Therefore, manufacturers select tested, child-friendly flavours to maximise compliance, providing a more pleasurable brushing experience and oral health benefits.

Diet and the microbial aetiology of dental caries: new paradigms.

The microbial and dietary factors that drive caries have been studied scientifically for 120 years. Frequent and/or excessive sugar (especially sucrose) consumption has been ascribed a central role in caries causation, while Streptococcus mutans appeared to play the key role in metabolising sucrose to produce lactic acid, which can demineralise enamel. Many authors described caries as a transmissible infectious disease. However, more recent data have shifted these paradigms. Streptococcus mutans does not fulfil Koch's postulates - presence of the organism leading to disease, and absence of the organism precluding disease. Furthermore, molecular microbiological methods have shown that, even with a sugar-rich diet, a much broader spectrum of acidogenic microbes is found in dental plaque. While simple sugars can be cariogenic, cooked starches are also now recognised to be a caries threat, especially because such starches, while not 'sticky in the hand', can be highly retentive in the mouth. Metabolism of starch particles can yield a prolonged acidic challenge, especially at retentive, caries-prone sites. These changes in the paradigms of caries aetiology have important implications for caries control strategies. Preventing the transmission of S. mutans will likely be inadequate to prevent caries if a sufficiently carbohydrate-rich diet continues. Similarly, restriction of sucrose intake, although welcome, would be unlikely to be a panacea for caries, especially if frequent starch intake persisted. Instead, approaches to optimise fluoride delivery, to target plaque acidogenicity or acidogenic microbes, to promote plaque alkali generation, to increase salivary flow or replace fermentable carbohydrates with non-fermentable alternatives may be more promising.

Role of gallium and silver from phosphate-based glasses on in vitro dual species oral biofilm models of Porphyromonas gingivalis and Streptococcus gordonii.

Phosphate-based glasses (PBGs) are excellent controlled delivery agents for antibacterial ions such as silver and gallium. The aim of this study was to assess the potential utility of novel PBGs combining both gallium and silver for use in periodontal therapy. To this end, an in vitro biofilm model with the putative periodontal pathogen, Porphyromonas gingivalis, and an initial colonizer, Streptococcus gordonii, was established. The effect of increasing calcium content in gallium-silver-doped PBG on the susceptibility of P. gingivalis was examined. A decrease in degradation rates (30.34, 25.19, 21.40 µg mm(-2) h(-1)) with increasing PBG calciumcontent (10, 11, 12 mol.% respectively) was observed, correlating well with gallium and silver ion release and antimicrobial activity against planktonic P. gingivalis (approximately 5.4log(10) colony-forming units (CFU) reduction after 24h by the C10 glass compared with controls) and S. gordonii (total growth inhibition after 32h by C10, C11 and C12 glasses compared with controls). The most potent PBG (C10) was evaluated for its ability to inhibit the biofilm growth of P. gingivalis in a newly established constant-depth film fermentor model. The simultaneous release of silver and gallium from the glass reduced P. gingivalis biofilm growth with a maximum effect (1.92log(10) CFU reduction) after 168 h. Given the emergence of antibiotic-resistant bacteria and dearth of new antibiotics in development, the glasses, especially C10, would offer effective alternatives to antibiotics or may complement current therapies through controlled, localized delivery of gallium and silver ions at infected sites in the oral cavity.

Zinc in the mouth, its interactions with dental enamel and possible effects on caries; a review of the literature.

Zinc is an essential trace element. In the mouth, it is present naturally in plaque, saliva and enamel. Zinc is formulated into oral health products to control plaque, reduce malodour and inhibit calculus formation. It has good oral substantivity, and elevated concentrations can persist for many hours in plaque and saliva following delivery from mouthrinses and toothpastes. Although low concentrations of zinc can both reduce enamel demineralisation and modify remineralisation, during caries clinical trials, the addition of zinc to fluoride toothpastes has not affected their ability to reduce caries. Mechanistic studies may help explain this apparent contradiction. Zinc is readily desorbed from hydroxyapatite by calcium, which is plentiful in plaque and saliva. Where crystal-growth sites remain occupied by zinc despite this, they may simply be 'over-grown' by remineralisation initiated at unoccupied sites. Further, under certain conditions, low concentrations of zinc can enhance remineralisation of enamel lesions, by retarding lesion arrestment. Although this may help to explain the apparent lack of an overall zinc effect on caries, it seems unlikely that any negative effects would be countered exactly by positive effects. Further mechanistic studies, complementing well-designed in vitro and in situ caries studies, should lead to further understanding of the zinc-enamel interactions relevant to demineralisation and remineralisation.

Protection against enamel demineralisation using toothpastes containing o-cymen-5-ol, zinc chloride and sodium fluoride.

AIM: To evaluate the ability of two experimental toothpastes containing 0.1%w/w o-cymen-5-ol, 0.6%w/w ZnCl2 and 0.320%w/w NaF to reduce demineralisation of sound human enamel compared with control toothpastes. METHODS: Study 1: Specimens were treated with toothpaste slurries, followed by alternating periods in demineralising and neutral solutions. Demineralisation was assessed using surface microhardness (SMH). Study 2: Specimens were subjected to a 14 day cycling regime of alternating demineralisation/remineralisation with two toothpaste treatments per day, before and after demineralisation. Demineralisation was assessed by cross-sectional microhardness and mineral loss (ΔZ) was calculated. Test toothpastes were a) 0%w/w or 0.002%w/w NaF placebo, b) 0.055%w/w or 0.149%w/w NaF (dose response), c) 0.320%w/w NaF marketed product, d & e) 0.1%w/w o-cymen-5-ol, 0.6%w/w ZnCl2 and 0.320%w/w NaF (experimental toothpastes). RESULTS: Study 1: Mean±SE % of baseline hardness values were a) 48.0±2.1a, b) 66.7±1.7b, c) 82.9±1.9c, d) 91.7±1.4d and e) 94.6±2.1d. Study 2: Mean±SE ΔZ values were a) 2114±187a, b) 1206±132b, c) 303±89c, d) 19±73c, and e) -10±55c. Letters represent different statistical groupings (P<0.05). CONCLUSION: In study 1, both experimental toothpastes were statistically superior to the marketed product and in study 2; they were at least as effective as the marketed product at reducing caries lesion development.