Enamel Softening Research Articles

Activity of Fluoride Varnishes Containing Micrometric or Nanosized Sodium Trimetaphosphate against Early Enamel Erosive Lesions In Vitro

This study aimed to assess the effects of fluoridated varnishes supplemented with micrometric or nanosized sodium trimetaphosphate (TMPmicro or TMPnano, respectively) against enamel softening in an early erosive model in vitro. Bovine enamel blocks (with mean surface hardness [SH] between 330.0 and 380.0 kgf/mm2) were selected and randomly assigned according to their SH (n = 8) into the following groups: Placebo (no fluoride/TMP; negative control), 5% NaF (positive control), 5% NaF + 5%TMPmicro, 5% NaF + 2.5%TMPnano and 5% NaF + 5%TMPnano. Blocks received a single application of the varnishes and were immersed in artificial saliva (6 h). Thereafter, the varnishes were removed and the blocks were subjected to four individual erosive challenges (1 min, citric acid, 0.75%, pH = 3.5, under agitation); SH was determined after each challenge. Data were subjected to ANOVA and Student–Newman–Keuls’ test (p < 0.05). Overall, the highest %SH loss was observed for the Placebo, followed by 5% NaF, 5% NaF + 5% TMPmicro, and both varnishes containing TMPnano, without significant differences between 2.5% and 5% TMPnano. It was concluded that TMP enhanced the effects of a 5% NaF varnish against enamel softening in an early erosive model in vitro, with an additional benefit from the use of nanoparticles over microparticles.

Influence of Viscosity and Thickener on the Effects of Bleaching Gels.

This study investigated the influence of the viscosity and kind of thickener of 35% hydrogen peroxide bleaching gels on the tooth (color change, demineralization of enamel, and permeation) and on the gel [reactive oxygen species (ROS), pH, and peroxide concentration]. Two hundred forty specimens were divided into groups of bleaching gels with different thickeners (CAR, carbomer; ASE, alkali swellable emulsion; MSA, modified sulfonic acid polymer; SSP, semisynthetic polysaccharide; PAC, particulate colloids) in three viscosities (low: 50,000 cP; medium: 250,000 cP; high: 1,000,000 cP). Color change (ΔEab), demineralization of enamel by Knoop microhardness (KHN) reduction analysis, and peroxide permeation (PP) were analyzed in the specimens, while pH, peroxide concentration (PC), and ROS were evaluated in the gels. Data were analyzed by two-way ANOVA (α=0.05). The higher viscosity gels reduced ΔEab, PP, enamel softening, and ROS in relation to the lower viscosity gels. However, the drop in pH and PC were higher in the more viscous gels. Gels with MSA produced higher ΔEab compared with SSP and ASE. The PP was higher for PAC, and smaller for SSP and CAR. The KHN reduction was higher for CAR and smaller for PAC. The higher pH reduction was seen for ASE and CAR, and the smaller for SSP. The PC reduction was higher for SSP and smaller for CAR. More ROS were observed for MSA and fewer for ASE. Increased gel viscosity was associated with reduced color change, permeation, demineralization of enamel, and ROS, and led to increased peroxide decomposition and pH alteration during the treatment. The kind of thickener significantly interfered with the treatment effects.

Enamel Softening Can Be Reduced by Rinsing with a Fluoride Mouthwash Before Dental Erosion but Not with a Calcium Solution.

This in-situ-study investigated if rinsing the oral cavity with a calcium containing solution or a fluoride containing mouthwash immediately before an erosive attack leads to reduced enamel softening. Bovine enamel samples (n = 240) with measured baseline surface microhardness (KHN) were assigned to five series (S1-5). Twelve participants carried out each series as follows: Four enamel samples of the associated test series were placed in an intraoral appliance and carried in each participants' mouth. After 30 min, the participants either rinsed the oral cavity for 60 s with 30 ml of a solution prepared from a 1,000 mg calcium effervescent tablet dissolved in 100 ml water (S2), an 800 mg calcium containing mineral supplement powder (5 g) dissolved in 200 ml water (S3), a fluoride (500 ppm) mouthwash (S4), a fluoride (500 ppm) and stannous chloride (800 ppm) containing mouthwash (S5), or did not rinse with any test solution before the erosive attack (S1, negative control). The participants subsequently rinsed the oral cavity with 100 ml of a soft drink (Sprite Zero) for 60 s to simulate the erosive attack and immediately afterwards with water to stop the erosive process. As final step, surface microhardness was measured a second time and hardness loss (∆KHN) calculated. Differences of ∆KHN between the series were investigated by fitting a mixed effect model to the data set. The highest loss of microhardness and thus softening of enamel (mean of ∆KHN; lower/upper confidence level) was observed in the negative control (S1: 60.2; 67.6/52.8). While no statistically significant difference (P > 0.05) compared to S1 could be found in S2 (50.0; 57.4/42.5) and S3 (54.6; 62.1/47.2), statistically significantly less softening of enamel (P < 0.001) was discovered in S5 (33.8; 41.2/26.4) and S4 (41.8.2; 49.3/34.4). S5 showed the overall lowest values for ∆KHN and thus best protection from enamel softening. Rinsing with a fluoride mouthwash or a fluoride and stannous chloride containing mouthwash immediately before an erosive attack reduces the softening of enamel. None of the investigated calcium-containing solutions was able to reduce erosion induced softening of enamel.

Prevention of Enamel Softening by Rinsing with a Calcium Solution before Dental Erosion

Objectives: This in situ study aimed to evaluate whether rinsing with a calcium-containing solution prior to an erosive attack reduces the softening of enamel. Materials and Methods: A total of 240 bovine enamel samples with determined baseline surface microhardness (KHN) were allocated to 5 runs in which each of the 12 volunteers performed the following experiment: 4 enamel samples were inserted in a custom-made intraoral appliance and carried in the mouth (upper jaw) for 30 min before each volunteer either rinsed his mouth for 60 s with a fluoride- and stannous ion-containing dental erosion protection mouth rinse as positive control (run 1), milk (run 2), a solution prepared from a 500-mg calcium effervescent tablet dissolved in 100 mL (run 3) or 200 mL (run 4) water, or did not perform any rinsing with a test solution before the erosive attack (run 5, negative control). To simulate the erosive attack, volunteers rinsed their mouth with a commercial soft drink (Sprite Zero) for 60 s and afterwards with water to stop the erosive process. Finally, surface microhardness was measured again and hardness loss (ΔKHN) calculated. A mixed effect model was fitted to the data set to investigate whether the different runs showed differences with respect to ΔKHN. Results: No significant difference in softening of enamel (mean of ΔKHN; lower confidence level/upper confidence level) was observed between the negative control run 5 (50.7; 60.8/40.6), run 2 (50.7; 60.8/40.6), run 3 (38.7; 48.8/28.6) and run 4 (40.7; 50.8/30.6) (p > 0.05, respectively). Enamel softening in the positive control run 1 (25.4; 35.6/15.3) was significantly lower compared to the softening in run 5 (p < 0.001). No significant difference was observed between run 1 and run 3 (p = 0.09). Conclusion: Other than the fluoride- and stannous ion-containing dental erosion protection mouth rinse, none of the investigated calcium-containing solutions is able to significantly reduce erosion-induced softening of enamel.

Efficacy of sodium and stannous fluoride mouthrinses when used before single and multiple erosive challenges.

Application of fluoride mouthrinse before an acidic challenge may decrease enamel erosion. This paper compares the efficacy of stannous (SnF2 ) and sodium (NaF) fluoride when facing single and multiple erosive cycles invitro. Human enamel samples (N=60) were randomly assigned to groups testing SnF2 and NaF mouthrinses (225p.p.m.) and a water control. Samples were allocated into subgroups testing one or five erosive cycles. Samples were immersed in test solution for 1min prior to citric acid immersion (0.3%, pH3.2, 10min), and the cycle repeated either one or five times. Analysis was done using profilometry and microhardness change. After one cycle, SnF2 resulted in least step height followed by NaF and water (1.3μm (0.63), 2.3μm (0.39), 4.3μm (0.41) respectively; P<0.0001). After five cycles SnF2 continued to reduce step height but pre-application of NaF was no different to water (4.6μm (0.7), 10.5μm (1.1) and 11.1μm (0.38) respectively; P<0.0001). There were no statistical differences in microhardness change between fluorides. After one erosive cycle, fluoride application resulted in statistically softer enamel compared with water. Both SnF2 and NaF reduced erosion after one cycle. After five cycles, SnF2 continued to offer protection whereas NaF was statistically comparable with water. Softening of enamel may not imply less erosion has occurred.

Erosive softening and erosive loss of enamel: Hardness and profilometry analysis

Objective – This study aimed to determine and differentiate erosive softening and enamel erosive loss induced by citric and hydrochloric acids. Material and Methods – Forty enamel specimens were divided into 2 groups: 1) 0.05 M citric acid (pH 2.5) simulating extrinsic erosion and 2) 0.01 M hydrochloric acid (pH 2.2) simulating intrinsic erosion. The enamel specimens were submitted to erosive challenges. Surface microhardness (softening) or contact profilometry (loss) was done after 30 s, after each 60 s up to 10 min, after each 5 min up to 30 min and after 60, 90 and 120 min. Results – Erosive softening (enamel hardness loss) was measurable up to 1 and 2 min for hydrochloric and citric acids, respectively. Erosive loss was significantly increased over time for both types of acids. After 8 min, citric acid was more aggressive than hydrochloric acid (p &lt; 0.001). Conclusion – The progression of enamel erosion from erosive softening to erosive loss is highly dependent on the type of acid, being citric acid more aggressive in later stages. Therefore, this finding should be considered when choosing the method of analysis for laboratory studies. Keywords: Enamel; Erosive wear; Microhardness; Profilometry; Tooth erosion.

In vitro re-hardening of artificial enamel caries lesions using enamel matrix proteins or self-assembling peptides.

ABSTRACTObjectives To assess the re-hardening potential of enamel matrix derivatives (EMD) and self-assembling peptides in vitro, hypothesizing that these materials may increase the mineralization of artificial carious lesions and improve hardness profiles.Material and Methods Forty-eight enamel samples were prepared from extracted bovine lower central incisors. After embedding and polishing, nail varnish was applied, leaving a defined test area. One third of this area was covered with a flowable composite (non-demineralized control). The remaining area was demineralized in an acidic buffer solution for 18 d to simulate a carious lesion. Half the demineralized area was then covered with composite (demineralized control), while the last third was left open for three test and one control treatments: (A) Application of enamel-matrix proteins (EMD - lyophilized protein fractions dissolved in acetic acid, Straumann), (B) self-assembling peptides (SAP, Curodont), or (C) amine fluoride solution (Am-F, GABA) for 5 min each. Untreated samples (D) served as control. After treatment, samples were immersed in artificial saliva for four weeks (remineralization phase) and microhardness (Knoop) depth profiles (25-300 µm) were obtained at sections. Two-way ANOVA was calculated to determine differences between the areas (re-hardening or softening).Results Decalcification resulted in significant softening of the subsurface enamel in all groups (A-D). A significant re-hardening up to 125 µm was observed in the EMD and SAP groups.Conclusions This study showed that EMD and SAP were able to improve the hardness profiles when applied to deep demineralized artificial lesions. However, further research is needed to verify and improve this observed effect.

Nanoscratch testing for the assessment of enamel demineralization under conditions simulating wine erosion.

Erosive tooth wear and dentinal hypersensitivity are common problems affecting professional wine tasters. By using nanoscratch testing, the aim of this in vitro study was to assess enamel softening under conditions simulating 10 one-minute episodes of wine erosion. Ten enamel specimens were bathed in artificial saliva for 2 hours before being eroded for 10 episodes, with each episode comprising one minute of wine erosion followed by one minute of remineralization in artificial saliva. Nanoscratches were placed with a spherical tip (20 μm radius) in a nanoindenter under a load of 100 mN at baseline (stage 1), after a one-erosion episode (stage 2) and after 10-erosion episodes (stage 3). There were significant effects of erosion stages on both scratch depth (p<0.001) and surface roughness (p<0.001). Post hoc tests showed significant differences in both scratch depths and surface roughness between stages 1 and 3 (p<0.001), and between stages 2 and 3 (p<0.01). Enamel softening occurs at an early stage of wine tasting, emphasizing the need to implement early preventive strategies in professional wine tasters. Further research elucidating the fundamental mechanisms involved in early stages of erosion has the potential to lead to development of more effective preventive strategies.

Experimental study of iron and multivitamin drops on enamel microhardness of primary tooth.

Objectives:Iron and multivitamin drops are being frequently prescribed in children less than 2 years of age. Due to their low pH levels, these drops may lead to the softening of enamel and accelerate the destructive process. The aim of the present study was to investigate the enamel microhardness of primary teeth after exposing them to iron and multivitamin drops.Materials and Methods:Forty healthy anterior teeth were randomly divided into four groups of 10 samples each. Samples were exposed to two iron drops of Kharazmi (Iran) and Ironorm (UK) and two multivitamin drops of Shahdarou (Iran) and Eurovit (Germany) for 5 min. The surface microhardness was measured before and after exposure and data processing was done using statistical paired t-test and analysis of variance (ANOVA) test. The surface structure of the teeth was examined by scanning electron microscope (SEM).Results:In all groups, microhardness was decreased, but it was not significant in Eurovit multivitamin group (P = 0.088). The reduction rate in Kharazmi iron group was significant compared to that in other groups (P < 0.005). Hardness reduction percent for Kharazmi iron drop was 28/12 ± 47/43. In SEM analysis, irregular granular appearance was observed in the enamel exposed to Kharazmi iron drop.Conclusion:The results showed that all the studied drugs have the potential to cause erosion; this potential is the most in Kharazmi iron drop and the least in Eurovit multivitamin drops. Therefore, after using these kinds of drops, preventive measures should be used in children.

A new optical detection method to assess the erosion inhibition by in vitro salivary pellicle layer

ObjectivesApplication of the recently developed optical method based on the monitoring of the specular reflection intensity to study the protective potential of the salivary pellicle layer against early enamel erosion. MethodsThe erosion progression was compared between two treatment groups: enamel samples coated by the 15h-in vitro-formed salivary pellicle layer (group P, n=90) and the non-coated enamel surfaces (control group C, n=90). Different severity of the erosive impact was modelled by the enamel incubation in 1% citric acid (pH=3.6) for 2, 4, 8, 10 or 15min. Erosion quantification was performed by the optical method as well as by the microhardness and calcium release analyses. ResultsOptical assessment of the erosion progression showed erosion inhibition by the in vitro salivary pellicle in short term acidic treatments (≤4min) which was also confirmed by microhardness measurements proving significantly less (p<0.05) enamel softening in the group P at 2 and 4min of erosion compared to the group C. SEM images demonstrated less etched enamel interfaces in the group P at short erosion durations as well. ConclusionsMonitoring of the specular reflection intensity can be successfully applied to quantify early erosion progression in comparative studies. In vitro salivary pellicle (2h) provides erosion inhibition but only in short term acidic exposures. Clinical significanceThe proposed optical technique is a promising tool for the fast and non-invasive erosion quantification in clinical studies.

Similar hematological and biochemical parameters among periodontitis and control group subjects

There are conflicting reports in the past literature documenting the tendency of anemia in patients with periodontitis. Hence, this study was undertaken to assess whether periodontitis may cause an anemic state, by evaluating and comparing the red blood cell count, levels of hemoglobin, hematocrit, erythrocyte sedimentation rate (ESR), serum iron and serum ferritin between subjects with and without periodontitis. In this cross-sectional study, 140 systemically healthy subjects of both sexes (mean age 46 years) were recruited as control group (50 subjects without periodontitis) and study groups comprising 30 patients each with mild, moderate and severe chronic generalized periodontitis. Periodontal parameters and orthopantamographs were taken for all the groups and then 5 mL venous blood samples were sent for complete blood count and biochemical analysis. Inter-group and intra-group comparisons were performed for all the assessed parameters. The periodontal parameters were significantly higher (P⩽.05) in periodontitis patients. Except for the ESR, which was significantly higher (P=.03) in the mild periodontitis group than the control group, hematological and biochemical parameters were not significantly different (P>.05) among the study groups or between the control and study groups. This difference was not evident even among the male and female subjects of both control and study groups (P>.05). Within the limits of this cross-sectional study, it can be concluded that the presence and severity of periodontitis may not affect the hematological and biochemical parameters of an individual. Further long term studies are however encouraged to validate these findings.

Evaluation of TEGDMA leaching from four resin cements by HPLC

The aim of this study was to evaluate the elution of TEGDMA from dual cured resin cements, used for bonding of ceramic restoration by high performance liquid chromatography (HPLC). Forty freshly extracted caries and restoration free molar teeth used in this study. Standardized Class I preparations were prepared in all teeth. Ceramic inlays were cemented with one of the dual cured resin cements (Variolink II, Rely X ARC, Rely X Unicem and Resilute). After cementation, specimens were stored in 75% ethanol solution. HPLC was used to analyze the amounts of TEGDMA in different time intervals. Two-way ANOVA and Tukey HSD tests were used to evaluate the results (P<.05). The amount of TEGDMA eluted from Resilute was the highest and the amount of TEG-DMA eluted from Rely X Unicem was the lowest (P<.05). The total amount of monomers was the highest after 21 days (P<.05). In the case of resin cements, elution of TEGDMA was the highest in Resilute and lowest in Rely X Unicem. The amount of TEGDMA eluted from resin cements was influenced by the time.

Counteractive effect of antacid suspensions on intrinsic dental erosion

This in vitro study aimed to investigate the anti-erosive effect of antacid suspensions applied to enamel after exposure to hydrochloric acid (HCl). Ninety bovine enamel slabs were embedded, flattened, and polished. Reference areas were created and specimens were divided into six groups. They were exposed to 0.01 M HCl (pH 2) for 2 min, followed by immersion for 1 min in one of the following test suspensions: magnesium hydroxide, aluminum hydroxide, magnesium hydroxide/aluminum hydroxide, sodium alginate/sodium bicarbonate/calcium carbonate, or hydrated magnesium aluminate. Artificial saliva was used as a negative control. Specimens were subjected to a total of five cycles of erosion/antacid treatment. Enamel surface loss was measured (in micrometers) by optical profilometry. In addition, baseline and final surface microhardness (SMH) values of enamel were obtained. It was found that antacid suspensions significantly reduced enamel loss, and that similar protection was afforded by all formulations. No differences were observed between the final enamel SMH values among groups. Antacid suspensions counteracted HCl-induced enamel loss, although they were not effective in reducing enamel softening. Mouth rinsing with antacid suspensions after vomiting can potentially represent a promising strategy to counteract enamel loss caused by erosion.

Erosive effects of beverages in the presence or absence of caries simulation by acidogenic challenge on human primary enamel: an in vitro study

To evaluate in vitro the erosive effects of beverages in the presence or absence of caries simulation (acidogenic challenge) on the microhardness of primary enamel. Forty human primary teeth were submitted to the erosive effects: 3 × 20-min-long daily immersion in fresh orange juice (orange group), strawberry yogurt drink (yog group), or cola soft drink (cola group) separately or in combination with acidogenic challenge (pH cycling for 10 days). Specimens were also submitted to acidogenic challenge alone, and in the negative control group specimens were not submitted to any treatment. Mineral loss was evaluated by cross-sectional microhardness determination. The data (Knoop hardness numbers, KHN) were subjected to 2-way analysis of variance and Tukey's post hoc test (α = 0.05%). All the test beverages significantly reduced the sample cross-sectional enamel hardness (KHN ± SD, 235.93 ± 18.15, 257.23 ± 21.79, and 253.23 ± 13.86 in the orange, yog, and cola groups, respectively) compared to samples in the negative control group (290.27 ± 3.92). In vitro acidogenic challenge exacerbated the mineral loss induced by all beverages (166.02 ± 4.28, 190.43 ± 17.55, and 198.39 ± 21.39 in the orange, yog, and cola groups combined to acidogenic challenge, respectively) compared to acidogenic challenge alone. All beverages exhibited erosive effects on primary enamel. Simulated caries challenge considerably exacerbated the enamel softening of primary teeth.

Acids with an equivalent taste lead to different erosion of human dental enamel

Objectives The consumption of acidic soft drinks may lead to demineralization and softening of human dental enamel, known as dental erosion. The aims of this in vitro study were to determine: (i) if different acids with a similar sensorial acidic taste lead to different hardness loss of enamel and (ii) if the fruit acids tartaric, malic, lactic or ascorbic acid lead to less hardness loss of enamel than citric or phosphoric acid when their concentration in solution is based on an equivalent sensorial acidic taste. Methods Enamel samples of non-erupted human third molars were treated with acidic solutions of tartaric (TA), malic (MA), lactic (LA), ascorbic (AA), phosphoric (PA) and citric (CA) acids with a concentration that gave an equivalent sensorial acidic taste. The acidic solutions were characterized by pH value and titratable acidity. Atomic force microscopy (AFM) based nanoindentation was used to study the nano mechanical properties and scanning electron microscopy (SEM) was used to study the morphology of the treated enamel samples and the untreated control areas, respectively. Results The investigated acids fell into two groups. The nano hardnesses of MA, TA and CA treated enamel samples (group I) were statistically significantly greater ( p < 0.05) than the nano hardnesses of PA, AA and LA treated enamel samples (group II). Within each group the nano hardness was not statistically significantly different ( p > 0.05). The SEM micrographs showed different etch prism morphologies depending on the acid used. Significance In vitro, the acids investigated led to different erosion effects on human dental enamel, despite their equivalent sensorial acidic taste. This has not been reported previously.

In vitro study on the wear behaviour of human tooth enamel in citric acid solution

Abstract With a worldwide increase in the ingestion of acidic soft drinks, the wear of human teeth in acidic oral environment is becoming normal, especially in young people. Previous studies mostly focused on the friction and wear behaviours of human teeth in the artificial saliva, and wear behaviours in acidic environment are still far from being well understood. In this paper, the wear behaviour of human tooth enamel against titanium alloy in 0.001 M citric acid solution (pH 3.20) has been investigated using a reciprocating wear machine. Three normal loads, 10 N, 20 N, and 40 N, were used. Results showed that in the citric acid solution, a honeycomb-like structure appeared on the surface of enamel as a result of severe dissolution of the enamel rods, and the surface hardness decreased. Under a low normal loading level, the surface softening of enamel caused by erosion dissolution played a significant role in its wear behaviour, and the wear mechanism of enamel was dominant by adhesion delamination. Hence, enamel wear in the citric acid solution was significantly higher than in the artificial saliva. With the load increasing, brittle fracture by the loading force aggravated, and obvious flake delamination happened. Enamel wear tended to be characterized mainly by mechanical removal. As a result, both the wear morphology and wear loss of enamel in the citric acid solution were similar to those in the artificial saliva at a high normal load of 40 N. These results indicated that there existed a competitive mechanism between the mechanical action and the chemical action when enamel wear occurred in the citric acid solution. The effect of erosion on the wear behaviour of enamel was more obvious under a low load than under a high load. The results would help extend understanding of the tooth wear process in acidic environment and provide a more rational explanation for the mechanism of tooth wear in the mouth.

Application of the specular and diffuse reflection analysis for in vitro diagnostics of dental erosion: correlation with enamel softening, roughness, and calcium release.

We present assembly and application of an optical reflectometer for the analysis of dental erosion. The erosive procedure involved acid-induced softening and initial substance loss phases, which are considered to be difficult for visual diagnosis in a clinic. Change of the specular reflection signal showed the highest sensitivity for the detection of the early softening phase of erosion among tested methods. The exponential decrease of the specular reflection intensity with erosive duration was compared to the increase of enamel roughness. Surface roughness was measured by optical analysis, and the observed tendency was correlated with scanning electron microscopy images of eroded enamel. A high correlation between specular reflection intensity and measurement of enamel softening (r(2) ≥ -0.86) as well as calcium release (r(2) ≥ -0.86) was found during erosion progression. Measurement of diffuse reflection revealed higher tooth-to-tooth deviation in contrast to the analysis of specular reflection intensity and lower correlation with other applied methods (r(2) = 0.42-0.48). The proposed optical method allows simple and fast surface analysis and could be used for further optimization and construction of the first noncontact and cost-effective diagnostic tool for early erosion assessment in vivo.

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.

Pectin, alginate and gum arabic polymers reduce citric acid erosion effects on human enamel

Objectives Consumption of acidic soft drinks may lead to the dissolution and softening of human enamel, known as erosion. The first aim of this in vitro study was to test the hypothesis that food-approved polymers added to citric acid solutions (CAS) decrease the erosion of human dental enamel compared to citric acid solutions without these polymers. The second aim was to test the hypothesis that these polymers added to CAS form a polymer layer directly on the eroded enamel surface. Methods Enamel samples were obtained by embedding pieces of non-erupted human third molars in resin, grinding, and polishing them. CAS with pH values (pH: 2.3, 3.3 and 4.0) of typical soft drinks were prepared and modified by adding one of the following food-approved polymers (1%, w/w): highly esterified pectin (HP), propylene glycol alginate (PGA) and gum arabic (GA). The enamel samples were exposed to these polymer-modified citric acid solutions (PMCAS) or CAS not containing polymers, respectively, for different time periods (30, 60 and 120 s). Atomic force microscopy (AFM)-based nanoindentation was used to analyze the nanomechanical properties of the treated enamel samples and the control samples. The enamel nanohardness and the reduced elastic modulus of the samples treated with PMCAS were statistically analyzed (ANOVA, t-test) and compared to the mechanical properties of the samples treated with unmodified CAS. Thus treated enamel samples were imaged by scanning electron microscopy (SEM) to investigate the surface morphology of the different enamel samples. Results Enamel samples treated with PMCAS containing GA or PGA showed statistically significantly higher nanohardness ( p < 0.05) compared to samples treated with CAS. PMCAS containing HP did not reduce the enamel nanohardness loss significantly compared to the CAS treated enamel samples. The enamel samples eroded with PMCAS show generally a smoother surface compared to the enamel surfaces of samples treated only with CAS as detected by SEM. Therefore, it is hypothesized that the polymers possibly adsorb on the eroded enamel surface. Significance The present in vitro erosion study shows that some of the polymers used in this study may possibly adsorb like a protective layer directly onto the human enamel surface. For GA and PGA this possibly formed polymer layer reduces the erosive effects of citric acid solutions as shown by nanoindentation measurements.

Degree of mineral loss in softened human enamel after acid erosion measured by chemical analysis

Objectives Erosive attack on enamel leads to a bulk material loss and a partial demineralisation at the lesion body. This zone of softened enamel has a reduced physical stability and large interprismatic porosities. The aim of the current study was to measure the degree of demineralisation with respect to the content of calcium and inorganic phosphorus in softened enamel using ultrasonication and chemical analysis. The erosive demineralisation was to be compared with demineralisation in caries. Methods Erosion of 10 polished human enamel samples was performed in 0.3% citric acid adjusted to pH 3.2 at 35 °C in a slowly stirred solution, each in a volume of 15 ml. After erosion the softened enamel was removed by ultrasonication in 2 ml of deionised water and enamel crystals were dissolved by adding 220 μl of 1 M HCl. Substance loss was measured profilometricaly after erosion and after ultrasonication. Surface size of eroded enamel was measured thus volume loss could be calculated. Calcium and phosphate ion concentration in the solutions were measured after ultrasonication. Results Citric acid erosion caused a mean substance loss of 16.0 μm (SD 2.5 μm) and further enamel softening of 2.4 μm (SD 1.5 μm). The degree of demineralisation of softened enamel, in comparison the original mineral content, was 62% for calcium and 64% for inorganic phosphorus was calculated. Conclusion The high degree of demineralisation shown in the current study explains the instability of softened enamel even against mild physical impact.