Interactions between dodecyl phosphates and hydroxyapatite or tooth enamel: relevance to inhibition of dental erosion.

Tooth surface modification is a potential method of preventing dental erosion, a form of excessive tooth wear facilitated by softening of tooth surfaces through the direct action of acids, mainly of dietary origin. We have previously shown that dodecyl phosphates (DPs) effectively inhibit dissolution of native surfaces of hydroxyapatite (the type mineral for dental enamel) and show good substantivity. However, adsorbed saliva also inhibits dissolution and DPs did not augment this effect, which suggests that DPs and saliva interact at the hydroxyapatite surface. In the present study the adsorption and desorption of potassium and sodium dodecyl phosphates or sodium dodecyl sulphate (SDS) to hydroxyapatite and human tooth enamel powder, both native and pre-treated with saliva, were studied by high performance liquid chromatography-mass Spectrometry. Thermo gravimetric analysis was used to analyse residual saliva and surfactant on the substrates. Both DPs showed a higher affinity than SDS for both hydroxyapatite and enamel, and little DP was desorbed by washing with water. SDS was readily desorbed from hydroxyapatite, suggesting that the phosphate head group is essential for strong binding to this substrate. However, SDS was not desorbed from enamel, so that this substrate has surface properties different from those of hydroxyapatite. The presence of a salivary coating had little or no effect on adsorption of the DPs, but treatment with DPs partly desorbed saliva; this could account for the failure of DPs to increase the dissolution inhibition due to adsorbed saliva.

Chitosan microparticles for the controlled delivery of fluoride.

OBJECTIVES: To manufacture and characterise chitosan/fluoride microparticles prepared by spray drying and assess their utility as controlled release vehicles for fluoride. METHODS: Microparticles were manufactured from dispersions containing 1.0% and 2.0% (w/v) chitosan and 0.20% or 0.40% (w/v) NaF in the absence/presence of glutaraldehyde. Particle size distributions were determined using laser diffraction; fluoride loading and release were determined by ion-selective electrode. Release profiles were studied in isotonic media (pH 5.5) over 360 min; microparticles exhibiting greatest cumulative fluoride release were further evaluated at pH 4.0 and 7.0. Particle morphology was investigated using environmental scanning electron microscopy. Bioadhesion parameters were determined with a texture-probe analyser. RESULTS: Microparticles exhibited low polydispersity and volume mean diameters (VMDs) <6 µm. VMDs increased on doubling the chitosan/fluoride concentrations but were largely independent of glutaraldehyde concentration. Recovered yields were inversely proportional to dispersion viscosity due to compromised fluid atomisation; adding NaF reduced viscosity and improved yields. Best-case entrapment efficiency and NaF loading were 84.1% and 14%, respectively. Release profiles were biphasic, releasing 40-60% of the total fluoride during the first 600 s, followed by a prolonged release phase extending out to 6h. Incorporation of 0.40% NaF to the 2.0% chitosan dispersion yielded microparticles with reduced bioadhesive parameters (F(max) and WOA) versus the chitosan-only control whilst retaining significant bioadhesive potential. CONCLUSIONS: Bioadhesive chitosan/fluoride microparticles manufactured using a spray-drying protocol have been extensively characterised and further opportunity for optimisation identified. These microparticles may provide a means of increasing fluoride uptake from oral care products to provide increased protection against caries, however further work is required to demonstrate this principle in vivo. CLINICAL SIGNIFICANCE: Spray-drying is a low-cost route for the manufacture of bioadhesive chitosan/fluoride microparticles which can be exploited as controlled fluoride release agents to aid fluoride retention in the oral cavity. The potential exists to optimise release profiles to suit the delivery format thereby maximising the cariostatic benefits.

A comparative evaluation of the efficacy of two novel desensitising dentifrices.

A comparison of the desensitising efficacy of two commercially available dentifrices with different modes of action was conducted in a randomised, examiner-blind, two-arm, parallel group, 8-week, longitudinal clinical study. Dentifrice A, (Sensodyne Multi Action Iso-Active), contained 50000 ppm KNO(3) and 1450 ppm fluoride as NaF. Dentifrice B, Colgate Sensitive Pro-Relief, contained a combination of 80000 ppm arginine, bicarbonate, calcium carbonate, and 1450 ppm fluorine as NaMFP. Subjects (N = 110), stratified into two groups (N = 55), brushed twice-daily for 60 s, over an 8-week period. Sensitivity status, compliance, and safety were determined at 1, 2, 4, and 8 weeks. A fixed-effects ANCOVA statistical model was applied to the Intent-To-Treat population using a two-sided 5% significance level. After 8 weeks, the treatment groups using Dentifrice A and Dentifrice B exhibited mean reductions from baseline of 49% and 45% in air sensitivity visual analogue scale (VAS) score, 61% (both) in examiner-based Schiff Sensitivity score, and clinically significant reductions in tactile pain threshold; all reductions were statistically significant (P < 0.0001). Both treatment groups also exhibited significant reductions across all sensitivity measures at 1, 2, and 4 weeks (P ≤ 0.0059, Dentifrice A; P ≤ 0.0137, Dentifrice B).

Multifunctional poly(alkyl methacrylate) films for dental care.

Towards the evaluation of non-permanent dental coatings for their capacity to impart dental-care benefits, thin films of a homologous series of comb-like poly(alkyl methacrylate)s (ethyl to octadecyl) have been deposited, from aqueous latex formulations, onto dentally relevant substrates. AFM studies have shown that the thickness (40-300 nm) and surface roughness (8-12 nm) of coherent polymer films are influenced by the degree of polymerization and by the length of the pendant chain. Of the polymers under consideration, poly(butyl methacrylate) formed a close-packed film that conferred to dental substrates a high degree of inhibition to acid-mediated erosion (about 27%), as evaluated by released-phosphate determinations. The potential utility of the coatings to act as anti-sensitivity barriers has been evaluated by determining the hydraulic conductance of coated bovine-dentine substrates; single treatments of dentine discs with poly(butyl methacrylate) or with poly(ethyl methacrylate) effected mean respective reductions in fluid flow of about 23% with respect to water-treated controls; repeated applications of the poly(butyl methacrylate) latex led to mean reductions in fluid flow of about 80%. Chromometric measurements have shown that pellicle-coated hydroxyapatite discs treated with poly(butyl methacrylate), poly(hexyl methacrylate) or poly(lauryl methacrylate) exhibit significant resistance to staining by food chromogens.

Bioadhesion and retention of non-aqueous delivery systems in a dental hard tissue model.

OBJECTIVES: Effective delivery of active agents to dental hard tissues is critical to product performance and pertinent to biofilm control, caries, erosion, hypersensitivity and tooth bleaching. The aim of this study was to investigate in vitro the bioadhesion and retention behaviour of non-aqueous delivery systems (NADS) based on glycerol, PEG 400, Carbopol 974P and triclosan. METHODS: Tensile testing was employed to calculate the work of adhesion (WOA) and maximum force of detachment (F(max)) for formulations applied to hydroxyapatite (HA) and pellicle-coated HA surfaces (HAP). Formulation substantivity under conditions of dynamic flow was studied by monitoring the release of incorporated triclosan. The release data were fitted to a first-order model to generate a removal half-life (t(1/2)). RESULTS: Tensile testing showed a clear positive relationship between Carbopol concentration and bioadhesion. Increasing the PEG 400 concentration in formulations containing glycerol, 2% (w/w) Carbopol and 0.30% triclosan produced a local minimum for both WOA and F(max) at 10% (w/w). Values for WOA and F(max) decreased threefold in the presence of a salivary pellicle. Good correlations were obtained between (i) WOA and F(max) and (ii) WOA and t(1/2) and (iii) the elastic modulus of the formulations and t(1/2). CONCLUSION: The presence of a salivary pellicle markedly reduced the bioadhesive interaction between the NADS and the substrate. Increased Carbopol content appeared to be the dominant factor in promoting the WOA, elasticity and retention of NADS to HA surfaces. Such formulations might provide a suitable platform for developing systems suitable for promoting retention to hard surfaces within the oral cavity.

Initial stages of enamel erosion: An in situ atomic force microscopy study.

Time-resolved in situ atomic force microscopy has been employed to examine erosion progression in untreated and fluoride-treated enamel specimens during exposure to citric acid. Contact with the acidic reaction solution initiated the emergence and growth of dissolution pits in both the native and the fluoride-treated enamel. In native enamel, pits are first observed after 90 min exposure to the reaction solution, compared to 250 min in the case of the fluoride-treated enamel. These findings indicate that, within the constraints of this study, a single application of fluoride solution (1000 mg/L, 2 min) confers protection to the enamel surface against acid-mediated erosion. This paper also highlights the potential role intrinsic defects may have on the susceptibility of enamel to erosion and, in part, may explain why some people are more susceptible to acid erosion.

An in vitro evaluation of a novel high fluoride daily mouthrinse using a combination of microindentation, 3D profilometry and DSIMS.

OBJECTIVES: Firstly, to evaluate the in vitro anti-erosion efficacy of a new mouthrinse formulation containing 450 ppm fluoride using profilometry and microindentation. Secondly, to compare fluoride uptake by erosive lesions from two mouthrinses containing different fluoride sources using dynamic secondary ion mass spectrometry (DSIMS). METHODS: Sound human enamel was treated (60s) with mouthrinses containing different fluoride concentrations, then immersed in 1.0% citric acid pH 3.8 for either 300 s or 30 min (Studies 1 & 2 respectively). Surface roughness and erosion depth were determined profilometrically in Study 1, and surface microhardness monitored as a function of time in Study 2. Lesion rehardening was monitored following a 60 s rinse and immersion in artificial saliva for 48 h (Study 3), whilst Study 4 employed DSIMS to quantify fluoride uptake by lesions treated (60s) with rinses containing either sodium fluoride (NaF) or a NaF/Olaflur/stannous chloride combination. RESULTS: The test rinse (450 ppm fluoride) suppressed surface roughening and bulk tissue loss versus all comparators (p< 0.0001), except in the latter measure for the rinse containing 112 ppm fluoride. The test rinse significantly inhibited enamel surface softening versus the three rinses containing ≤112 ppm fluoride (as NaF) at 30 min (p<0.05), but was not statistically significantly different from the 225 ppm fluoride rinse. The test rinse conferred statistically superior lesion rehardening versus all comparators at both 24 and 48 h (p< 0.0001). DSIMS demonstrated statistically significantly higher fluoride uptake by incipient erosive lesions treated with the test rinse versus the NaF/Olaflur/stannous rinse. CONCLUSIONS: Anti-erosion efficacy was positively correlated with fluoride concentration. DSIMS showed significantly higher levels of fluoride uptake by incipient erosive lesions treated with the 450 ppm fluoride rinse versus the NaF/Olaflur/stannous rinse.

A comparative evaluation of fluoridated and non-fluoridated mouthrinses using a 5-day cycling enamel erosion model.

OBJECTIVES: To assess the relative protective effect of commercial mouthrinses containing 0-450 ppm fluoride on erosion progression in enamel using a simulated 5-day in vitro cycling model with concurrent monitoring of surface microhardness (SMH) and bulk tissue loss. METHODS: Specimens were randomly assigned to six treatment groups (n=6). The model mimicked morning and evening use with rinse times (30 or 60 s) reflecting those prescribed on pack, interspersed with three cycles of demineralisation/remineralisation per simulated day. The latter comprised 1.0% citric acid monohydrate pH 3.2 for 300 s, with subsequent remineralisation in mucin-free artificial saliva pH7.0 for 120 min. SMH was determined by Vickers microindentation and bulk tissue loss using white-light interferometry. RESULTS: From the end of day 1, fluoride-containing mouthrinses conferred statistically significant reductions in bulk tissue loss versus fluoride-free rinses (p<0.05), with lesion depth inversely proportional to fluoride concentration. From day 3, the mean lesion depth of specimens treated with the 450 ppm rinse were statistically significantly lower than all comparator treatment groups (p<0.05). Two distinct trends were apparent when comparing SMH changes in groups treated with fluoride-free versus fluoride-containing mouthrinses. In the latter, SMH levelled out over the final three simulated days in contrast to the former whose SMH continued to fall; differences were statistically significant at day 5 (p< 0.05). CONCLUSIONS: Bulk tissue loss is inversely proportional to fluoride concentration in this cycling model. The plateau in SMH reflects stabilisation of mineral density as the study progresses and the number of fluoride binding sites and consequently uptake increases, in turn leading to enhanced lesion remineralisation.

Evaluation of salivary fluoride retention from a new high fluoride mouthrinse.

OBJECTIVES: To evaluate salivary fluoride retention from a new high fluoride daily use mouthrinse over a 120 min period. METHODS: Sixteen subjects completed a randomised single-blind, four-treatment cross-over trial. Sensodyne® Pronamel® mouthrinse (A) contained 450 ppm fluoride; reference products were Colgate® Fluorigard® (B), Listerine® Total Care (C) and Listerine Softmint Sensation (D) containing 225, 100 and 0 ppm fluoride respectively. Salivary fluoride retention was monitored ex vivo after a single supervised use of test product (10 mL, 60 s). Samples were collected at 0, 1, 3, 5, 15, 30, 60 and 120 min post-rinse, generating fluoride clearance curves from which the area under the curve (AUC) was calculated. Differences in salivary fluoride concentrations for each product were analysed using ANCOVA at each time point using a 5% significance level, as well as lnAUC for the periods 0-120, 0-1, 1-15, 15-60 and 60-120 min. Pairwise comparisons between all treatment groups were performed. RESULTS: Salivary fluoride levels for A-C peaked immediately following use. Fluoride levels were statistically significantly higher for A versus B-D (p≤ 0.004), linear dose responses were apparent. AUC(0-120) was statistically significantly greater for A than for B (p = 0.035), C (p< 0.0001) and D (p< 0.0001). Post-hoc comparisons of lnAUC for the remaining time domains showed fluoride retention from A was statistically significantly greater versus B-D (p< 0.0001). CONCLUSIONS: Single-use treatment with the new mouthrinse containing 450 ppm fluoride resulted in statistically significantly higher salivary fluoride levels throughout the 120 min test period. Total fluoride retention (AUC(0-120)) was also statistically significantly greater versus comparator rinse treatments.

Studies on a novel combination polymer system: in vitro erosion prevention and promotion of fluoride uptake in human enamel.

OBJECTIVES: Firstly, determine the effect of pre-treating sound human enamel with a hydrosoluble combination polymer system (TriHydra™) comprising 0.20% carboxymethylcellulose, 0.010% xanthan gum and 0.75% copovidone, alone or in combination with fluoride, on in vitro erosion by citric acid. Secondly, investigate the effect of the polymers on fluoride uptake by incipient erosive lesions. METHODS: Study 1: Sound enamel specimens were treated (60s, 20°C, 150 rpm) with either (i) deionised water, (ii) polymers in deionised water, (iii) 300 mg/L fluoride or (iv) polymers in 300 mg/L fluoride. Specimen groups (n=5) were then immersed in 1.0% citric acid (pH 3.8, 300 s, 20°C, 50 rpm) and non-contact profilometry was used to determine surface roughness (Sa) and bulk tissue loss. Study 2: Incipient erosive lesions were similarly treated with (i)-(iv). Dynamic Secondary Ion Mass Spectrometry (DSIMS) was then used to determine the fluoride depth-distribution. RESULTS: Study 1: Mean±SD Sa and erosion depths for treatment groups (i)-(iv) were (a)657±243, (b)358±50, (c)206±72, (d)79±16 nm and (a)19.73±8.70, (b)2.52±1.34, (b)0.49±0.34 and (b)0.31±0.21 mm respectively (matching superscripts denote statistically equivalent groups). Study 2: Lesions treated with (iii) and (iv) exhibited similar fluoride penetration depths (∼ 60 µm). Mean fluoride intensity ratios based on F/(F+P) at 1 µm for treatment groups (i)-(iv) were (a)0.010±0.004, (a)0.011±0.004, (b)0.803±0.148 and (c)0.994±0.004 respectively. CONCLUSIONS: The combination polymer system exhibited anti-erosion efficacy in its own right. The polymer/fluoride admixture statistically significantly reduced Sa, however suppression of bulk tissue loss was not statistically significantly different versus either treatment alone. The presence of polymer appears to promote fluoride uptake by erosive lesions most noticeably in the first 6 µm.

Evaluation of mouthrinse and dentifrice regimens in an in situ erosion remineralisation model.

OBJECTIVES: To compare the effectiveness of dentifrice/mouthrinse regimens in a clinical in situ erosion remineralisation model. METHODS: Thirty-six subjects completed a randomised single-blind cross-over trial of five treatment regimens. R1: Dentifrice A [1450 ppm fluoride as the sodium salt (NaF), 50000 ppm potassium nitrate (KNO(3))] plus 450 ppm fluoride (NaF) rinse; R2: Dentifrice A plus sterile water rinse; R3: Dentifrice B (fluoride-free Dentifrice A) plus sterile water rinse; R4: Dentifrice B plus 450 ppm fluoride (NaF) rinse; R5: Dentifrice C (1000 ppm fluorine as sodium monofluorophosphate, 450 ppm fluoride as NaF) plus sterile water rinse. Subjects wore a palatal appliance holding eight pre-demineralised enamel blocks. A 60 min interval separated in vivo use of dentifrice and rinse with the appliance retained in situ for 4h. Efficacy endpoints were percentage surface microhardness recovery (%SMHR) following remineralisation, and percentage relative erosion resistance (%RER) of recovered specimens following a subsequent in vitro erosive challenge. Statistical analyses included ANOVA and selected twin-tailed t-tests. RESULTS: Mean %SMHR (±SE) was (a)42.14±1.39, (b)38.02±1.39, (c)30.57±1.39, (b)37.75±1.39 and (c)30.88±1.39 for regimens R1-R5 respectively (different superscripts denote statistically significant differences (p<0.05) between treatment regimens). Mean %RER (±SE) was (a)-2.88±2.16, (b)-14.54±2.16, (c)-40.05±2.16, (a)-3.76±2.16 and (d)-29.48±2.16 for regimens R1-R5 respectively. R1 elicited statistically significantly greater %SMHR versus all comparator regimens (p<0.01), and conferred statistically significantly greater %RER than comparator regimens (p<0.0001) except R4 (p=0.70). CONCLUSIONS: The combination treatment of dentifrice A containing 1450 ppm fluoride with the 450 ppm fluoride mouthrinse elicited significant enhancements in rehardening of incipient enamel erosive lesions, and significantly increased their subsequent resistance to a second erosive challenge.

Diffusive transport within dentinal tubules: an X-ray microtomographic study.

The hydrodynamic theory of dentine hypersensitivity proposes that external stimuli cause dentinal fluid movement within dentinal tubules thereby triggering mechanosensitive nerves and eliciting a pain response. The aim of this study was to employ X-ray microtomography (XMT) to monitor diffusion of caesium acetate through dentine to investigate the extent to which transport occurs within the primary tubules compared to that through branched microtubules believed to run perpendicular to the direction of the primary dentinal tubules. 2.0-mm thick coronal dentine disks masked to leave half of the upper surface exposed were imaged by XMT, initially in water, which was then replaced with an aqueous solution of 0.50 mol l(-1) caesium acetate. Further XMT images were acquired after 1 and 6 days immersion. The XMT images were used to measure the change in the X-ray linear attenuation coefficient resulting from caesium acetate ingress into dentine. There was clearly considerable ingress of caesium acetate into the dentine lying below the exposed surface, but considerably less beneath the sealed surface, suggesting that diffusive transport occurs predominantly in the direction of the primary dentinal tubules, with no significant lateral transport. Primary tubules are clearly the dominant transmission route for triggering the mechanosensitive nerves present at the dentine-pulp interface, and for delivery of nerve desensitising agents.

Mucoadhesion, hydration and rheological properties of non-aqueous delivery systems (NADS) for the oral cavity.

OBJECTIVES: Effective delivery of oral care actives from conventional hydrogel formulations is often compromised by poor retention associated with shear forces present in the mouth, salivary washout and over-hydration of the gel which can lead to structural breakdown and adhesive failure. Non-aqueous gels offer the opportunity to formulate rheologically acceptable vehicles with higher concentrations of bioadhesive polymer than is possible using water as the primary solvent. Accordingly, this study describes the formulation and characterisation of the rheology, hydration and bioadhesive properties of a range of non-aqueous delivery systems (NADS). METHODS: The formulations were composed principally of glycerol, with varying amounts of polyethylene glycol (PEG) 400 and Carbopol 974P being incorporated in the ranges 0-31.34% and 0-4% (w/w). Work of adhesion (WOA) and maximum force of detachment (Fmax) were determined using a Dartec tensile tester after application of a normal force. Rheology was assessed using a Bohlin CS CVO rheometer. RESULTS: WOA and Fmax increased with increasing compression time and Carbopol concentration. Addition of 30% (w/w) PEG 400 to the formulation containing 2% Carbopol in glycerol improved bioadhesive function. Formulation rheology was largely controlled by the Carbopol concentration, and to a lesser extent by the concentration of PEG 400 and these, in turn, largely determined the bioadhesion parameters and rates of hydration. CONCLUSION: The results of this in vitro study suggest that bioadhesion, and consequently potential drug bioavailability, would be enhanced by use of a water miscible non-aqueous delivery vehicle such as glycerol containing a bioadhesive polymer such as Carbopol with the addition of controlled amounts of PEG as plasticiser.

Novel quartz crystal microbalance based biosensor for detection of oral epithelial cell-microparticle interaction in real-time.

Recent applications of quartz crystal resonant sensor technology to monitor cell adhesion and specific ligand interaction processes has triggered the development of a new category of quartz crystal microbalance (QCM) based biosensors. In this study human oral epithelial cells (H376) were cultured on quartz sensors and their response to microspheres investigated in situ using the QCM technique. The results demonstrated that this novel biosensor was able to follow cell-microsphere interactions in real-time and under conditions of flow as would occur in the oral cavity. Unique frequency profiles generated in response to the microspheres were postulated to be due to phases of mass addition and altered cellular rigidity. Supporting microscopic evidence demonstrated that the unique frequency responses obtained to these interactions were in part due to binding between the cell surface and the microspheres. Furthermore, a cellular uptake process, in response to microsphere loading was identified and this, by influencing the rigidity of the cellular cytoskeleton, was also detectable through the frequency responses obtained.

Control of brushing variables for the in vitro assessment of toothpaste abrasivity using a novel laboratory model.

OBJECTIVES: Design and construct a tooth-brushing simulator incorporating control of brushing variables including brushing force, speed and temperature, thereby facilitating greater understanding of their importance in toothpaste abrasion testing methodologies. METHODS: A thermostable orbital shaker was selected as a base unit and 16- and 24-specimen brushing rigs were constructed to fit inside, consisting of: a square bath partitioned horizontally to provide brushing channels, specimen holders for 25 mm diameter mounted specimens to fit the brushing channels and individually weighted brushing arms, able to support four toothbrush holders suspended over the brushing channels. Brush head holders consisted of individually weighted blocks of Delrin, or PTFE onto which toothbrush heads were fixed. Investigating effects of key design criteria involved measuring abrasion depths of polished human enamel and dentine. RESULTS: The brushing simulator demonstrated good reproducibility of abrasion on enamel and dentine across consecutive brushing procedures. Varying brushing parameters had a significant impact on wear results: increased brushing force demonstrated a trend towards increased wear, with increased reproducibility for greater abrasion levels, highlighting the importance of achieving sufficient wear to optimise accuracy; increasing brushing temperature demonstrated increased enamel abrasion for silica and calcium carbonate systems, which may be related to slurry viscosities and particle suspension; varying brushing speed showed a small effect on abrasion of enamel at lower brushing speed, which may indicate the importance of maintenance of the abrasive in suspension. CONCLUSIONS: Adjusting key brushing variables significantly affected wear behaviour. The brushing simulator design provides a valuable model system for in vitro assessment of toothpaste abrasivity and the influence of variables in a controlled manner. Control of these variables will allow more reproducible study of in vitro tooth wear processes.

Fluoropolymers as low-surface-energy tooth coatings for oral care.

A range of low-surface-energy fluoropolymers has been synthesised and their effectiveness as dental-care coatings for plaque, stain and erosion prevention has been evaluated using a series of oral care models employing pressed discs of calcium hydroxyapatite or sections of human teeth. Since the blocking of dentinal tubules is a key mechanistic strategy in the treatment of dentine hypersensitivity, the capability of these non-permanent fluoropolymer coatings to occlude the pore structure of human dentine and to reduce the outward flow of simulated dentinal fluid has also been investigated. Several of the fluoropolymer coatings have been found to inhibit bacterial adhesion but no correlation has been established between anti-adhesion efficacy and fluorine content or surface energy. All the fluoropolymers have been seen to reduce stain uptake by pellicle-coated HA discs, with homopolymers being considerably more effective than copolymers. Some fluoropolymer coatings have also been shown to inhibit the acid demineralisation of hydroxyapatite discs and to reduce dentine permeability. Coatings of the 2:1 copolymer of 1H,1H,2H,2H-perfluorodecyl acrylate and 2-hydroxyethyl acrylate are most promising, exhibiting significant anti-adhesion and anti-erosion efficacy and reducing dentine permeability to a level that is comparable with that achieved with the standard treatment employed in commercial anti-sensitivity formulations.

Synthesis and characterization of low surface energy fluoropolymers as potential barrier coatings in oral care.

A series of low surface energy fluorinated homopolymers and copolymers has been synthesized and characterized using thermal, optical, spectroscopic, and chromatographic techniques. Their utility as barrier technologies in oral care has been considered, and aqueous nanosuspensions of the materials have been deposited as films on model dental hard surfaces in the presence and absence of a salivary pellicle. Calcium hydroxyapatite has been used as a model for enamel, as has PMMA due to its widespread use in denture fabrication. Surface energy determinations, combined with XPS studies, have provided insights into the molecular-level organization at the surface of the film structures. Studies of solubility in supercritical carbon dioxide have identified the polymers that are suitable for processing in this medium.

The role of erosion, abrasion and attrition in tooth wear.

There is increasing clinical awareness of erosion of enamel and dentine by dietary acids and the consequent increased susceptibility to physical wear. Enamel erosion is characterized by acid-mediated surface softening that, if unchecked, will progress to irreversible loss of surface tissue, potentially exposing the underlying dentine. In comparison, dentine erosion is less well understood as the composition and microstructure are more heterogeneous. Factors which affect the erosive potential of a solution include pH, titratable acidity, common ion concentrations, and frequency and method of exposure. Abrasion and attrition are sources of physical wear and are commonly associated with tooth brushing and tooth-to-tooth contact, respectively. A combination of erosion and abrasion or attrition exacerbates wear; however, further research is required to understand the role of fluoride in protecting mineralized tissues from such processes. Abrasive wear may be seen in a wide range of patients, whereas attritive loss is usually seen in individuals with bruxism. Wear processes are implicated in the development of dentine hypersensitivity. Saliva confers the major protective function against wear due to its role in pellicle formation, buffering, acid clearance, and hard tissue remineralization. This review focuses on the physiochemical factors impacting tooth wear.

Surface microhardness changes, enamel fluoride uptake, and fluoride availability from commercial toothpastes.

OBJECTIVE: The aim of the present study was to evaluate the ability of a new fluoride-containing dentifrice to protect surface-softened enamel against further erosive challenges in an in vitro cycling model, and to relate any effects to enamel fluoride uptake (EFU) and free fluoride. METHODOLOGY: Human enamel specimens were subjected to a daily cycling regimen comprising: three two-minute treatments; five two-minute challenges using 1% citric acid pH 3.8; and remineralization in a mixture of human saliva and mucin-containing artificial saliva. Surface microhardness (SMH) was measured at baseline, 10, and 20 days, and the fluoride content of biopsied specimens determined at 20 days. EFU studies were based on method #40 described in the United States Food and Drug Administration (FDA) testing procedures. Free-fluoride availability was determined from slurries of one part toothpaste plus three parts deionized water. RESULTS: SMH showed that a 1150 ppm NaF test dentifrice protected enamel specimens greater than Crest Cavity Protection (1100 ppm NaF) and a fluoride-free placebo at both 10 days and 20 days (p < 0.05). The fluoride content of specimens treated with this prototype was higher than either Crest or the placebo. SMH for a 1450 ppm NaF test dentifrice was greater than for Elmex Sensitive (1450 ppm amine F) and placebo at 10 days, while both products were greater than the placebo at 20 days. The fluoride content of specimens treated with this test dentifrice was higher than Elmex Sensitive, which was higher than placebo. The fluoride uptake seen in the cycling model correlated for the NaF dentifrices with a standard EFU procedure. Different EFU results for a series of commercial dentifrices demonstrated that EFU is not necessarily a function of free-fluoride availability. CONCLUSION: This study demonstrated that fluoride dentifrices can increase the protection of enamel against an erosive challenge in vitro, and that the increased protection correlated with fluoride uptake. The fluoride uptake seen in the cycling model correlated with a standard FDA EFU procedure for the NaF dentifrices. The present studies demonstrate the importance of formulation effects on driving performance in in vitro models.

In vitro microhardness studies on a new anti-erosion desensitizing toothpaste.

OBJECTIVE: To evaluate in vitro the efficacy of a new anti-erosion desensitizing toothpaste to inhibit enamel surface softening by a dietary acid, and promote re-hardening of artificial erosive lesions. METHODOLOGY: The ability of the toothpaste to inhibit formation and promote repair of erosive lesions in human enamel has been investigated. In an enamel surface softening study, sound human enamel was pre-treated with one of four toothpaste slurries for two minutes, before exposure to 1.0% citric acid, pH 3.8, for a total of 30 minutes. The surface microhardness (SMH) of the specimens was determined at baseline and at 10-minute intervals using a Struers Duramin-1 microindentor. In an enamel re-hardening study, the erosive lesions were prepared by exposure of the specimens to 1.0% citric acid, pH 3.8, for 30 minutes. After two minutes treatment with a toothpaste slurry, lesion repair was monitored by SMH after 4, 24, and 48 hours incubation in artificial saliva. This remineralizing phase was modified by the addition of an aliquot of the relevant toothpaste slurry, to mimic in vivo carryover of the formulation. RESULTS: The new test formulation, Elmex Sensitive, and Colgate Sensitive exhibited statistically significant inhibition of citric acid-mediated enamel surface softening versus a fluoride-free placebo at all time points. The test toothpaste gave statistically superior protection against the erosive challenge compared to Elmex Sensitive and Colgate Sensitive after 20- and 30-minute exposures. In the remineralization studies, erosive lesions treated with the test toothpaste exhibited statistically superior re-hardening versus lesions treated with Elmex Sensitive and Colgate Sensitive after 24- and 48-hour incubation in the artificial saliva. Lesions treated with Elmex Sensitive re-hardened to a statistically significant extent versus the fluoride-free placebo toothpaste. A re-hardening study, in which a series of the new toothpaste-base formulations containing increasing concentrations of NaF were evaluated, showed a clear fluoride dose response. CONCLUSION: The present microhardness studies show that treatment with fluoride-containing toothpastes helps protect sound enamel from acid-mediated surface softening, and promotes re-hardening of erosive lesions. The new test toothpaste exhibited statistically superior efficacy to Elmex Sensitive and Colgate Sensitive in both in vitro models.