Numerical modelling of tooth enamel subsurface lesion formation induced by dental plaque.

Using a one-dimensional mathematical model that couples tooth demineralisation and remineralisation with metabolic processes occurring in the dental plaque, two mechanisms for subsurface lesion formation were evaluated. It was found that a subsurface lesion can develop only as the result of alternating periods of demineralisation (acid attack during sugar consumption) and remineralisation (resting period) in tooth enamel with uniform mineral composition. It was also shown that a minimum plaque thickness that can induce an enamel lesion exists. The subsurface lesion formation can also be explained by assuming the existence of a fluoride-containing layer at the tooth surface that decreases enamel solubility. A nearly constant thickness of the surface layer was obtained with both proposed mechanisms. Sensitivity analysis showed that surface layer formation is strongly dependent on the length of remineralisation and demineralisation cycles. The restoration period is very important and the numerical simulations support the observation that often consumption of sugars is a key factor in caries formation. The calculated profiles of mineral content in enamel are similar to those observed experimentally. Most probably, both studied mechanisms interact in vivo in the process of caries development, but the simplest explanation for subsurface lesion formation remains the alternation between demineralisation and remineralisation cycles without any pre-imposed gradients.

Comparison of the enamel solubility reduction from Various prescription and OTC fluoride toothpastes and gels.

OBJECTIVE: The purpose of this in vitro study was to determine if a novel 970 ppm F ion SnF2OTC gel (Enamelon Preventive Treatment Gel) and a 1150 ppm F- ion SnF2OTC Enamelon Toothpaste, each delivering amorphous calcium phosphate (ACP), can significantly reduce the effect of an acid challenge to enamel as compared to two prescription (Rx) strength 5000 ppm F- ion (NaF) dentifrices containing tri-calcium phosphate (TCP), and an Rx 900 ppm F- ion (NaF) paste with casein phosphopeptide-amorphous calcium phosphate (CPP-ACP). The effect will be determined by measuring the resistance of enamel specimens to an acid challenge before and after treatment with the test dentifrices. METHODS: The procedure used in this study was the FDA Test Method #33 for the determination of the effect of different test dentifrices on enamel solubility reduction. Twelve sets of three extracted human teeth were unprotected and etched prior to treatment with 0.1 M lactic acid buffer solution. The amount of phosphate dissolved from the teeth was quantified via measuring the phosphate in the retained lactate buffer solution with phosphorous analysis (pre-treatment phosphorous levels). The teeth sets were then exposed to the following treatments (diluted 1:3 parts in preheated [37 degrees C] distilled water): 5000 ppm F- ion, sodium fluoride (NaF) Rx dentifrice containing TCP; 5000 ppm F- ion, NaF Rx dentifrice; 900 ppm F- ion, NaF Rx paste with CPP-ACP; 1150 ppm F- ion, stannous fluoride (SnF2) OTC toothpaste delivering ACP Enamelon Toothpaste; and 970 ppm F- ion, SnF2 OTC gel delivering ACP (Enamelon Preventive Treatment Gel). The teeth sets were rinsed with distilled water and then exposed to 0.1 M buffered lactic acid solution. The amount of phosphate in the lactic acid buffer was determined for a second time (post-treatment phosphorous levels). The percent of enamel solubility reduction was then computed as the difference between the amount of phosphorous in the pre- and post-treatment lactic acid solutions divided by the amount of phosphorous in the pre-treatment solution, and multiplied by 100. RESULTS: The percent reduction in enamel solubility recorded in this study was as follows: 60.14 ± 0.79 for the Enamelon Toothpaste; 56.91 ± 1.05 for the Enamelon Preventive Treatment Gel; 18.78 ± 3.20 for the 5000 ppm F- ion, NaF prescription dentifrice "A' with TCP; 6.84 ± 1.20 for the 900 ppm F- ion, NaF paste with CPP-ACP; 5.82 ± 3.10 for the 5000 ppm F- ion, NaF prescription dentifrice "B" with TCP; and -5.45 ± 1.86 for the negative control. The differences between all the products tested were statistically significant (p < 0.05), except for the Enamelon products that were not statistically different. The 900 ppm F- ion, NaF paste with CPP-ACP and the 5000 ppm F- ion, NaF toothpaste results were also not statistically different. CONCLUSION: The Enamelon products (970 ppm and 1150 ppm F- ion, SnF2 OTC dentifrices) delivering ACP were statistically significantly more effective in reducing enamel solubility than two Rx strength 5000 ppm F- ion NaF toothpastes containing TCP and the Rx 900 ppm F- ion NaF paste containing CPP-ACP.

Effects of buffering properties and undissociated acid concentration on dissolution of dental enamel in relation to pH and acid type.

To quantify the relationships between buffering properties and acid erosion and hence improve models of erosive potential of acidic drinks, a pH-stat was used to measure the rate of enamel dissolution in solutions of citric, malic and lactic acids, with pH 2.4-3.6 and with acid concentrations adjusted to give buffer capacities (ß) of 2-40 (mmol·l(-1))·pH(-1) for each pH. The corresponding undissociated acid concentrations, [HA], and titratable acidity to pH 5.5 (TA5.5) were calculated. In relation to ß, the dissolution rate and the strength of response to ß varied with acid type (lactic > malic ≥ citric) and decreased as pH increased. The patterns of variation of the dissolution rate with TA5.5 were qualitatively similar to those for ß, except that increasing pH above 2.8 had less effect on dissolution in citric and malic acids and none on dissolution in lactic acid. Variations of the dissolution rate with [HA] showed no systematic dependence on acid type but some dependence on pH. The results suggest that [HA], rather than buffering per se, is a major rate-controlling factor, probably owing to the importance of undissociated acid as a readily diffusible source of H(+) ions in maintaining near-surface dissolution within the softened layer of enamel. TA5.5 was more closely correlated with [HA] than was ß, and seems to be the preferred practical measure of buffering. The relationship between [HA] and TA5.5 differs between mono- and polybasic acids, so a separate analysis of products according to predominant acid type could improve multivariate models of erosive potential.

Effects of a novel fluoride-containing aluminocalciumsilicate-based tooth coating material (Nanoseal) on enamel and dentin.

PURPOSE: To investigate the effect of a fluoride-containing aluminocalciumsilicate nanoparticle glass dispersed aqueous solution (Nanoseal) on enamel and dentin, under the hypothesis that this material can form insoluble mineral deposits that confer acid resistance to the tooth structure and occlude open dentin tubules. METHODS: Labial enamel and dentin of human extracted incisors were used. Morphology of the enamel and dentin artificially demineralized with a lactic acid solution that before and/or after coated with the test material were analyzed with a wavelength-dispersive X-ray spectroscopy electron probe microanalyzer with an image observation function (SEM-EPMA). Moreover, incorporation of the calcium and silicon by enamel and dentin were also detected with SEM-EPMA. RESULTS: Application of the fluoroaluminocalciumsilicate-based tooth coating material resulted in the deposition of substances (nanoparticles) onto the enamel surface porosities and open dentin tubules on the artificial lesions. Prior coating with the test material reduced the demineralization-induced loss of enamel and dentin. Moreover, Ca and Si incorporation into superficial enamel and dentin was detected.

Enamel protection from acid challenge--benefits of marketed fluoride dentifrices.

OBJECTIVE: To determine the ability of various marketed dentifrices containing stabilized stannous fluoride (SnF2), sodium fluoride (NaF), or sodium monofluorophosphate (SMFP) to protect enamel against the earliest stages of erosive dietary acid damage using an in vitro enamel protection model. METHODS: Acid-challenged, extracted human teeth were treated with a 1:3 dilution of dentifrice, rinsed, and then challenged in a controlled series of tests using four dietary acids considered potentially erosive to teeth. Each acid was collected and analyzed to determine the level of mineral (phosphorous) removed from the teeth during the challenge. Post-treatment results were compared to baseline values for each acid. Results for the four acids were averaged and reported as an average percent protection value for each of the dentifrices tested, with higher values representing greater acid protection. The study included six dentifrices formulated with (A) sodium fluoride (NaF), (B) stabilized stannous fluoride (SnF2), (C,D) NaF plus 5% potassium nitrate (KNO3), (E) sodium monofluorophosphate (SMFP), or (F) SMFP plus 8% arginine bicarbonate. RESULTS: The stabilized SnF2 dentifrice demonstrated an average protection score of 39.3%, while products formulated with NaF resulted in protection scores between 11 and 13%. The SMFP dentifrice was rated at -3.5%, and the SMFP + arginine bicarbonate dentifrice resulted in a net average score of -5.0%. Results of this test were statistically significant (p < 0.05, ANOVA: B > A = C = D > E = F), in favor of the stabilized SnF2 dentifrice. CONCLUSIONS: These results suggest the stabilized SnF2 dentifrice has the potential to provide significantly better overall acid protection versus any of the other dentifrices included in the study.

A new model for demonstrating enamel protection benefits relative to acid challenge.

OBJECTIVE: To determine the applicability of a modified US FDA Caries Monograph test method for measuring the protective benefits of fluoride (F) against erosive, dietary acids. METHODS: Acid-challenged teeth were treated in two studies with a dentifrice, rinsed, and then re-challenged in a series of tests using three dietary acids. Study 1 included dentifrices containing 1450 ppm F as sodium fluoride (NaF) + triclosan [A], 1450 ppm F (NaF) + potassium nitrate (KNO3) [B], 1000 ppm F as sodium monofluorophosphate (SMFP) [C], and 0 ppm F (placebo) [D]. Study 2 included dentifrices containing 1450 ppm F (NaF) [A]; and 0 ppm F (placebo) [B]. Acids were analyzed for phosphate removed during tooth challenges, with post-treatment results compared to baseline. Results were averaged and reported as a % protection value for each product, with higher values indicating greater protection. RESULTS: Study 1: % protection for A = 16.4; B = 13.0; C = 7.1; and D = -5.2. Study 2: A = 15.2; B = -10.5, with A = B > C > D: Study 1; and A > B: Study 2. In each study, p < 0.05, ANOVA. CONCLUSIONS: The model provides a viable tool for initially assessing the potential for fluoride-containing oral care products to protect teeth against erosive, dietary acids. This can then lead to further and more elaborate testing with reasonable expectations for outcomes.

Mineral ions in the fluid of biofilms formed on enamel and dentine shortly after sugar challenge.

To test the effect of distinct solubilities of dentine and enamel on mineral ion concentration in the biofilm fluid during a sugar-induced pH drop, dental biofilms were formed in situ for 4 days on acrylic (control), dentine or enamel. On the 5th day, they were treated with water (control) or 20% glucose and collected 5 min later. Significantly lower pH values and higher calcium concentrations were found in the biofilm fluid after glucose exposure, without significant differences among the three substrates. During pH drop, biofilm reservoirs release calcium to the fluid, masking the differential solubility between enamel and dentine.

Dose-response effects of zinc and fluoride on caries lesion remineralization.

The present mechanistic in vitro study aimed to investigate dose-response effects of zinc and fluoride on caries lesion remineralization and subsequent protection from demineralization. Artificial caries lesions were created using a methylcellulose acid gel system. Lesions were remineralized for 2 weeks using citrate-containing artificial saliva which was supplemented with zinc (0-153 µmol/l) and fluoride (1.1 or 52.6 µmol/l) in a 7 × 2 factorial design. Lesions were also remineralized in the absence of zinc and citrate, but in the presence of fluoride. After remineralization, all lesions were demineralized for 1 day under identical conditions. Changes in mineral distribution characteristics of caries lesions after remineralization and secondary demineralization were studied using transverse microradiography. At 1.1 µmol/l fluoride, zinc exhibited detrimental effects on remineralization in a dose-response manner and mainly by preventing remineralization near the lesion surface. At 52.6 µmol/l fluoride, zinc retarded remineralization only at the highest concentration tested. Zinc enhanced overall remineralization at 3.8-15.3 µmol/l. At 76.5 and less so at 153 µmol/l, zinc showed extensive remineralization of deeper parts within the lesions at the expense of remineralization near the surface. Citrate did not interfere with remineralization at 1.1 µmol/l fluoride, but enhanced remineralization at 52.6 µmol/l fluoride. Lesions exhibiting preferential remineralization in deeper parts showed higher mineral loss after secondary demineralization, suggesting the formation of more soluble mineral phases during remineralization. In summary, zinc and fluoride showed synergistic effects in enhancing lesion remineralization, however only at elevated fluoride concentrations.

SEM investigation on casein phosphopeptides capability in contrasting cola drinks enamel erosion: an in vitro preliminary study.

AIM: Erosion of dental hard tissues induced by acidic dietary components is a high-prevalence finding, especially among children and adolescents. Acidic soft drinks are frequently implicated in dental erosion. The aim of this in vitro study was to assess if CPP-ACP preparation is capable of reducing enamel erosion caused by a cola-type drink. MATERIALS AND METHODS: Twenty-five sound human permanent premolars, extracted for orthodontic reasons in patients of 12-16 years old, were used. The roots were removed and the crowns were sectioned in order to obtain 3 enamel sections from each tooth. The specimens were immersed in: (A) cola-type drink; (B) cola-type drink plus CPP-ACP; (C) deionised water (control) for: 48 h, 24 h, 12 h, 6 h and 3 h, respectively. pH values were constantly monitored. Statistical analysis was performed using ANOVA. The enamel samples were evaluated for surface changes using scanning electron microscopy (SEM). RESULTS: Specimens subjected to cola-type drink (treatment A) showed wide areas of enamel dissolution, while the treatment B specimens showed a few areas of little enamel erosion, different from control samples. Adding CPP-ACP to the cola-type drinks influenced pH levels of the solutions, but always in the acidity range. CONCLUSION: CPP-ACP provides protection against dental erosion from cola-type drinks in vitro. Therefore, further studies are necessary to evaluate if adding casein phosphopeptide-stabilised amorphous calcium phosphate complex to acidic cola drinks could reduce their erosive potential in vivo as well.

A comparison of sports and energy drinks--Physiochemical properties and enamel dissolution.

The consumption of sports and energy drinks by children and adolescents has increased at an alarming rate in recent years. It is essential for dental professionals to be informed about the physiochemical properties of these drinks and their effects on enamel. The present study measured the fluoride levels, pH, and titratable acidity of multiple popular, commercially available brands of sports and energy drinks. Enamel dissolution was measured as weight loss using an in vitro multiple exposure model consisting of repeated short exposures to these drinks, alternating with exposure to artificial saliva. The relationship between enamel dissolution and fluoride levels, pH, and titratable acidity was also examined. There was a statistically significant difference between the fluoride levels (p = 0.034) and pH (p = 0.04) of the sports and energy drinks studied. The titratable acidity of energy drinks (11.78) was found to be significantly higher than that of sports drinks (3.58) (p < 0.001). Five of the energy drinks (Red Bull Sugar Free, Monster Assault, Von Dutch, Rockstar, and 5-Hour Energy) were found to have the highest titratable acidity values among the brands studied. Enamel weight loss after exposure to energy drinks was significantly higher than it was after exposure to sports drinks. The effect of titratable acidity on enamel weight loss was found to vary inversely with the pH of the drinks. The findings indicated that energy drinks have significantly higher titratable acidity and enamel dissolution associated with them than sports drinks. Enamel weight loss after exposure to energy drinks was more than two times higher than it was after exposure to sports drinks. Titratable acidity is a significant predictor of enamel dissolution, and its effect on enamel weight loss varies inversely with the pH of the drink. The data from the current study can be used to educate patients about the differences between sports and energy drinks and the effects of these drinks on tooth enamel.

Influence of five home whitening gels and a remineralizing gel on the enamel and dentin ultrastructure and hardness.

PURPOSE: To investigate the influence of calcium phosphate enhanced home whitening agents on human enamel and dentin surface microhardness and ultramorphology. METHODS: Five intact molars crowns were used for ultrastructural analysis and five for microhardness test. Each resulting coronal structure was cut in slices. After measuring baseline Knoop Hardness Number (KHN) of the enamel and dentin, the slices were divided into six experimental groups and one control (n= 5). G1= 15% carbamide peroxide (CP); G2= 16% CP; G3= Ca and PO4 (remineralizing agent); G4= 16% CP with Ca and PO4; G5= 7.5% hydrogen peroxide (HP) with Ca and PO4; G6=7.5% HP with Ca. After each daily session of treatment, specimens were stored in distilled water (37 degrees C) until the next session. Products were applied for 2 weeks, according to manufacturers' instructions. Additional KHN weredetermined. RESULTS: Conventional whitening agents (G1; G2) and the gel with Ca (G6), caused KHN decrease (P< 0.05).The remineralizing and whitening agents with Ca and PO4 (G3; G4; G5) did not change KHN. A change of morphology was observed on enamel and dentin surfaces in G1; G2; G5.

Human and bovine enamel erosion under 'single-drink' conditions.

Tooth-surface pH is lowered, during drinking, to a value close to the pH of the drink itself. After the drink is swallowed, the pH rises to baseline values but this process can take several minutes. Few techniques can quantify enamel erosion at timescales representative of single drinks. The objective of this study was to compare human and bovine erosion over acid-exposure times of 2 s to 1 h. Human and bovine enamel softening was compared in vitro using nanoindentation (2-60 s of exposure to acid) and tissue loss was compared using optical profilometry (1-60 min of exposure to acid). Nanoindentation revealed statistically significant softening after 2 s (human) and 5 s (bovine); there were no significant differences in hardness reduction for the two tissues at any time-point. Profilometry demonstrated statistically significant tissue loss after 20 min (human) and 10 min (bovine); bovine tissue loss progressed 30% faster than human tissue loss. These results support the use of bovine enamel as a substitute for human enamel in erosion studies, with the understanding that for moderate exposure times bovine enamel erodes 30% faster than human enamel. Nanoindentation can be used to detect enamel dissolution at timescales comparable to the oral dwell-time of a single 'mouthful' of a beverage.

Tin-containing fluoride solutions as anti-erosive agents in enamel: an in vitro tin-uptake, tissue-loss, and scanning electron micrograph study.

Tin-containing fluoride solutions can reduce erosive tissue loss, but the effects of the reaction between tin and enamel are still not clear. During a 10-d period, enamel specimens were cyclically demineralized (0.05 M citric acid, pH 2.3, 6 x 5 min d(-1)) and remineralized (between the demineralization cycles and overnight). In the negative-control group, no further treatment was performed. Three groups were treated (2 x 2 min d(-1)) with tin-containing fluoride solutions (400, 1,400 or 2,100 ppm Sn2+, all 1,500 ppm F-, pH 4.5). Three additional groups were treated with test solutions twice daily, but without demineralization. Tissue loss was determined profilometrically. Energy-dispersive X-ray spectroscopy was used to measure the tin content on and within three layers (10 mum each) beneath the surface. In addition, scanning electron microscopy was conducted. All test preparations significantly reduced tissue loss. Deposition of tin on surfaces was higher without erosion than with erosion, but no incorporation of tin into enamel was found without demineralization. Under erosive conditions, both highly concentrated solutions led to the incorporation of tin up to a depth of 20 mum; the less-concentrated solution led to small amounts of tin in the outer 10 mum. The efficacy of tin-containing solutions seems to depend mainly on the incorporation of tin into enamel.

Effect of stannous fluoride and dilute hydrofluoric acid on early enamel erosion over time in vivo.

Recent experimental in vivo studies have shown that aqueous solutions of stannous fluoride (SnF(2)) and hydrofluoric acid (HF) can reduce enamel solubility after 5 min. The aim of this study was to evaluate the longer-term protective effect of SnF(2) (0.78%, pH 2.9) and HF (0.2%, pH 2.0) (both approximately 0.1 mol/l F) using the same experimental model. Labial surfaces of healthy anterior teeth (all four surfaces when possible, otherwise a pair of surfaces) in 103 subjects (n = 399 teeth) were exposed to citric acid (0.01 mol/l, pH 2.7). The acid was applied using a peristaltic pump (5 ml, 6 ml/min) and was collected in coded test tubes (etch I). The test solutions were then applied to the same surfaces of the teeth (1 min, 6 ml/min). After either 1, 7, 14 or 28 days, citric acid was again applied to the same surfaces and subsequently collected (etch II). Enamel solubility was examined by assessment of calcium concentration in etch I and etch II solutions using atom absorption spectroscopy. Median values were calculated for all time periods and statistical analysis was carried out using the Wilcoxon signed-ranks test. Results showed that HF reduced enamel solubility by 54 and 36% after 1 and 7 days, respectively. After 14 and 28 days, there was no longer any effect. SnF(2) showed no protective effect after the first day. Given these results, repeated application of HF and especially SnF(2) may be necessary to improve the protective effect of these fluorides, and this requires further testing.

Comparison of the effects of TiF4 and NaF solutions at pH 1.2 and 3.5 on enamel erosion in vitro.

This study aimed to analyse and compare the protective effect of buffered (pH 3.5) and native (pH 1.2) TiF(4) in comparison with NaF solutions on enamel erosion. Bovine samples were pretreated with 1.50% TiF(4) or 2.02% NaF (both 0.48 M F) solutions, each at a pH of 1.2 and 3.5. The control group received no fluoride pretreatment. Twenty samples per group were eroded with HCl (pH 2.6) for 10 x 60 s. Erosion was either investigated by profilometry (n = 10) or by determination of calcium release into the acid (n = 10). Additionally, the elemental surface composition was quantified by X-ray energy-dispersive spectroscopy in fluoridated but not eroded samples (6 samples per group). Scanning electron microscopy was performed prior and after erosion (2 samples per group). Cumulative enamel loss (mum) and calcium release (nmol/mm(2)) were analysed by repeated-measures ANOVA. The Ti and F surface composition was analysed by one-way ANOVA separately for each element. Only TiF(4) at pH 1.2 reduced enamel surface loss significantly. Calcium release was significantly reduced by TiF(4) and NaF at pH 1.2, but not by the solutions at pH 3.5. Samples pretreated with TiF(4) at pH 1.2 showed a significant increase in Ti, while NaF increased F concentration significantly. Only TiF(4) at pH 1.2 induced the formation of a glaze-like layer, which was still present after erosion. Enamel erosion can be significantly reduced by TiF(4) at pH 1.2 but not at pH 3.5. TiF(4) at pH 1.2 was more effective in protecting against enamel erosion than NaF.

The effects of acidic fluoride solutions on early enamel erosion in vivo.

Acidic fluoride solutions may reduce dental erosion. The aim of this study was to compare the effect of different acidic fluoride solutions on enamel dissolution using an established in vivo model. When possible 4 anterior teeth (255 teeth in a total of 67 subjects) were isolated and exposed to 0.01 M citric acid. The acid was collected in test tubes before (etch I) and 5 min after (etch II) application of test fluoride preparations. Acidic fluoride solutions (pH range 1.5-2.9), i.e. SnF(2), TiF(4) and hydrogen fluoride (HF) (all approx. 0.1 M F), HF (0.027, 0.055, 0.082 M F) and neutral NaF solution (0.1 M F) as control were applied to the labial surfaces of the teeth for 1 min (6 ml/min). Enamel dissolution was examined by chemical analysis of calcium content in the citric acid etch solutions using atom absorption spectrometry. The change in calcium concentration (DeltaCa) and the percentage of mean calcium reduction were calculated from the difference in calcium loss between etch I and etch II. Statistical analysis was carried out using the Wilcoxon signed rank test and Kruskal-Wallis tests with Dunn's multiple comparison. Results showed a mean DeltaCa of 0.671 mg/l (SD 0.625) for SnF(2), and ranged from 0.233 mg/l (SD 0.248) for the weakest HF solution to 0.373 mg/l (SD 0.310) for the strongest HF solution. This represented a 67% reduction in enamel dissolution for SnF(2) and a 40-76% reduction for the HF solutions. No reduction was observed for TiF(4) or NaF. The types of metal, pH and fluoride concentration are all important for the in vivo effect.

Preventive effect of an iron varnish on bovine enamel erosion in vitro.

OBJECTIVE: The aim of this study was to evaluate, in vitro, the effect of an experimental varnish containing iron on the dissolution of bovine enamel by carbonated beverage. METHODS: Eighty specimens were randomly allocated to four groups (n=20 per group), according to the following treatments: Fe varnish (FeV, 10 mmol/L Fe), F varnish (FV, 2.71% F), placebo varnish (PV) and control (not treated, NT). The varnishes were applied in a thin layer and removed after 6h. Then, the samples were submitted to six cycles, alternating re- and demineralisation (only 1 day). Demineralisation was performed with the beverage Coca-Cola (10 min, 30 mL/block) and remineralisation with artificial saliva for 1h. In order to determine the amount of enamel dissolved, the wear was analysed by profilometry. Data were analysed by ANOVA and Tukey's test (p<0.05). RESULTS: The mean wear (+/-S.E.) was significantly lesser for the FeV (0.451+/-0.018 microm) when compared to the other treatments. The FV caused significantly less wear (0.554+/-0.022 microm) when compared to PV (0.991+/-0.039 microm) and NT (1.014+/-0.033), which did not significantly differ from each other. CONCLUSIONS: The results suggest that the iron varnish can interfere with the dissolution of dental enamel in the presence of acidic beverages.

Effects of ER,Cr:YSGG laser irradiation and fluoride treatment on acid resistance of the enamel.

PURPOSE: The purpose of this study was to evaluate the effect of the Er,Cr:YSGG loser on the enamel's acid resistance when irradiated alone, prior to or after acidulated phosphate fluoride (APF) treatment. METHODS: Eighty-five enamel surfaces were prepared from 17 extracted human premolars and randomly assigned to 5 groups: (1) untreated (control); (2) irradiated with a Er,Cr:YSGG loser; (3) exposed to a 1.23% APF gel; (4) loser-irradiated followed by APF treatment; and (5) APF-treated followed by loser irradiation. The specimens were individually demineralized in 0.2 M acetate buffer solution for 10 days, and the acid resistance was evaluated by determining the calcium ion using atomic absorption spectrometry. RESULTS: Significant differences were found between group 1 and groups 2 through 5 (P < 0.001). There were no signifIcant differences between groups 2 and 3 (P = 1.000). Compared to groups 2 and 3, a lower calcium content was detected in the demineralization solution for groups 4 and 5. The difference between groups 4 and 5, however, was not statistically significant (P = 0.289). CONCLUSIONS: Combining ocidulated phosphate fluoride with the Er,Cr:YSGG loser decreased the enamel demineralization more than either fluoride treatment or laser treatment alone.

Influence of peroxide treatment on bovine enamel surface--cross-sectional analysis.

Carbamide peroxide and hydrogen peroxide are used as the main agents in vital tooth bleaching. In this study, the influence of peroxide treatment on cross-sectional morphology and mechanical property was investigated. A 3 x 5-mm window of enamel on the labial surface of a bovine tooth was exposed to immersion in 10% or 30% carbamide peroxide or hydrogen peroxide for 30 or 180 min. After immersion, the cross-sectional structure of each specimen was examined by nanoindentation and SEM. Nanohardness in the enamel showed a decrease at 2 microm below the surface, but none at 50 microm. High concentrations of peroxide caused erosion to a depth of 5 microm below the surface. In conclusion, decrease in nanohardness and change in morphology were limited to an area less than 50 microm below the surface, regardless of either concentration of peroxide or period of immersion.

Inhibition of hydroxyapatite dissolution by whole casein: the effects of pH, protein concentration, calcium, and ionic strength.

Formulating drinks with reduced erosive potential is one approach for reducing dental erosion. In this study, whole casein was added to citric acid solutions representative of soft drinks, and the hydroxyapatite dissolution rate was assessed. Adding 0.02% (w/v) casein to acid solutions significantly reduced the hydroxyapatite dissolution rate by 51 +/- 4% at pH values of 2.80, 3.00, 3.20, 3.40, and 3.60, although the baseline dissolution rates of course varied as a function of pH. The protein concentration [0.002, 0.02, and 0.2% (w/v) casein] had no significant effect on dissolution inhibition. Adding both casein and calcium to citric acid resulted in a further reduction in the dissolution rate at low and intermediate calcium concentrations (5 and 10 mM) but not at higher calcium concentrations (20 and 50 mM). Ionic strength had no significant impact on the efficacy of casein. Casein also significantly reduced the hydroxyapatite dissolution rate when the hydroxyapatite was coated with a salivary pellicle. The reduction in dissolution rate is ascribed to firmly adsorbed casein on the hydroxyapatite surface, which stabilizes the crystal surface and inhibits ion detachment.