Effects of fluoride concentration on enamel demineralization kinetics in vitro

Objectives

The aim of the present study was to measure the effects of fluoride concentration on the real-time in vitro demineralization of enamel during exposure to caries-simulating conditions using Scanning Microradiography (SMR).

Methods

Enamel blocks obtained from non-carious human molars were fixed in SMR environmental cells, through which acidic solutions (0.1 M acetic acid, pH 4.0) were circulated for periods of 48 h. SMR was used to quantitatively measure continuous mineral mass loss. Subsequently, the effects of sequentially increasing fluoride concentration (0.1–4500 mg/L [F⁻]) in the acidic solutions were measured on the rate of enamel demineralization.

Results

The data shows a log-linear relationship between [F⁻] and reduction in demineralization up to 135 mg/L [F⁻]. Above 135 mg/L, no further significant decrease in demineralization occurred.

Conclusion

The optimum range of local fluoride concentration for reducing enamel demineralization was in the range 0.1–135 mg/L [F⁻] under the conditions studied.

Clinical significance

Relatively low [F⁻] can exhibit near-optimum protection. Increasing the fluoride concentrations above 135 mg/L may not necessarily give an increased cariostatic benefit. Improving the means of delivery of relatively low fluoride concentrations to the oral fluids through slow releasing mechanisms, such as the oral fluoride reservoirs, is the more appropriate way forward for sustaining long-term clinical efficacy.     

Does tin pre-treatment enhance the bond strength of adhesive systems to enamel?

Objectives

The study investigated the modification of composite-to-enamel bond strength by pre-treatment of enamel with a concentrated, acidic SnCl₂-solution.

Methods

Six groups of flat human enamel specimens (n = 44 per group) were treated as follows: OB-H: H₃PO₄ etching, Optibond FL application (primer + adhesive; manufacturer's instructions); OB-S: SnCl₂ pre-treatment, Optibond FL application (primer + adhesive); OB-HS: H₃PO₄ etching + SnCl₂ pre-treatment, Optibond FL application (primer + adhesive); CF-N: Clearfil SE application (primer + bond; manufacturer's instructions); CF-H: H₃PO₄ etching, Clearfil SE application (primer + bond); CF-S: SnCl₂ pre-treatment, Clearfil SE application (primer + bond). Enamel specimens were then built up with resin composite (Clearfil Majesty Esthetic) and stored (100% humidity, 37 °C, 1 week). μTBS-measurement and failure mode analysis of one-half of the specimens were performed immediately after storage, while the other half was analysed after a thermocycling procedure (8500 cycles; 5 °C and 55 °C; dwell time 30 s). Additional specimens were prepared for SEM- and EDX-analysis.

Results

Highest values were measured for OB-H before and after thermocycling, lowest values for CF-N. Compared to OB-H treatment, OB-S treatment reduced μTBS before/after thermocycling by 23%/28% and OB-HS treatment by 8%/24% (except for OB-SH before (n.s.), all p ≤ 0.001 compared to OB-H). In the Clearfil SE treated groups pre-treatment increased μTBS significantly compared to CF-N (before/after: CF-H: +46%/+70%; CF-S: +51%/42%; all p ≤ 0.001).

Conclusion

Pre-treatment with H₃PO₄ or SnCl₂ markedly increased the μTBS of Clearfil SE to enamel. However, thermocycling partly reduced the gain in μTBS obtained by SnCl₂ pre-treatment.

Clinical significance

The application of an acidic and highly concentrated SnCl₂ solution is a good option to increase the μTBS between enamel and a resin composite mediated by an adhesive system containing the multifunctional monomer MDP.     

Impact of two toothpastes on repairing enamel erosion produced by a soft drink: An AFM in vitro study

Objectives

The aim of the present in vitro study was the evaluation of two toothpastes (Sensodyne Pronamel and Biorepair Plus on repairing enamel erosion produced by a soft drink (Coca Cola), using Atomic Force Microscopy (AFM).

Methods

Fifty extracted human central incisors free of caries were selected and divided in a treatment and a control half; they were kept in artificial saliva during whole experimentation. The treatment halves were divided into five groups; group 1: demineralization with soft drink; group 2: demineralization with soft drink + Pronamel; group 3: demineralization with soft drink + Biorepair Plus; group 4: intact enamel + Pronamel; group 5: intact enamel + Biorepair Plus. Specimen demineralization was carried on in 4 intervals of 2 min. In groups 2, 3, 4, and 5 the toothpastes were applied for 3 min at 0, 8, 24 and 36 h. The surface of each specimen was imaged by AFM and R_rms, root-mean-square roughness, and Maximum Depth of the cavities were registered.

Results

Amongst treatment specimens of groups 1, 2, and 3 a statistically significant difference (P < 0.01) in R_rms and Maximum Depth values was registered: the toothpastes reduced enamel demineralization. No statistical differences in R_rms values were registered between the two toothpastes.

Conclusions

The toothpastes tested (Pronamel and BioRepair Plus) offer a degree of protection from erosive drinks.     

In vitro assessment of artificial saliva formulations on initial enamel erosion remineralization

Objectives

Various formulations of artificial saliva are present in the literature and little guidance is available on the standardization of type of saliva for use in in vitro protocols for erosive studies. The aim of this study was to evaluate the remineralizing capacity of different formulations of artificial saliva on initial enamel erosive lesion.

Methods

Bovine enamel blocks were subjected to short-term acidic exposure by immersion in citric acid 0.05 M (pH 2.5) for 15 s, resulting in surface softening without tissue loss. Then 90 selected eroded enamel blocks were randomly and equally divided into 6 groups according to saliva formulation (n = 15): Saliva 1 (contain mucin); Saliva 2 (Saliva 1 without mucin); Saliva 3; Saliva 4; Saliva 5 (contain sodium carboxymethyl cellulose) and control (C) (deionized water). After demineralization enamel blocks were subjected to remineralization by immersion in the saliva's formulations for 2 h. Enamel remineralization was measured by superficial hardness test (% superficial hardness change). The data were tested using ANOVA and Tukey's test (p < 0.05).

Results

All the tested formulations of artificial saliva resulted in significantly higher enamel remineralization compared to control (p < 0.001). Saliva 3 showed higher percentage of enamel remineralization than Saliva 5 (p < 0.05).

Conclusions

Besides the variety of artificial saliva for erosion in vitro protocols, all the formulations tested were able to partially remineralize initial erosive lesions.     

Effects of tooth whitening and orange juice on surface properties of dental enamel

Objective

To study the effects of 6% H₂O₂ activated with LED light on surface enamel as compared to orange juice challenges in vitro.

Methods

A total of 40 human enamel discs were incubated in saliva overnight to allow pellicle formation and then divided into three groups: 15 for whitening treatments, 15 for orange juice immersions and 10 for normal saline controls. Baseline microhardness was measured with a microhardness Knoop indenter (50 g, 10 s) and surface topography was evaluated with a focus-variation 3D scanning microscopy. Enamel discs were treated with H₂O₂ or orange juice for 20 min each cycle for five cycles to simulate daily treatment with the products for 5 days. The discs were stored in saliva between treatment cycles. Microhardness and surface topography were evaluated again after treatments. Changes in microhardness and in surface area roughness (Sa), mean maximum peak-to-valley distance (Sz) and the developed surface area ratio (Sdr) were compared before and after treatments (t-test) and among groups (ANOVA).

Results

Enamel surface hardness decreased by 84% after orange juice immersion but no statistically significant changes were observed in the whitening and control groups. Surface topography changed significantly only in the orange juice group as shown by increased Sa (1.2 μm vs. 2.0 μm), Sz (7.7 μm vs. 10.2 μm) and Sdr (2.8% vs. 6.0%). No such changes were observed in the whitening and control groups.

Conclusion

In comparison to orange juice challenges, the effects of 6% H₂O₂ on surface enamel are insignificant. Orange juice erosion markedly decreased hardness and increased roughness of enamel.     

Surface conditioning of natural enamel caries lesions in deciduous teeth in preparation for resin infiltration

Objectives

As a conditioning step for resin infiltration into caries lesions, the relatively impermeable surface layer should be removed using hydrochloric acid gel (15%) to achieve improved infiltration, as it could be shown for permanent teeth. It is unclear whether this etching regimen can be transferred to the deciduous dentition, where differences in surface structure have been reported. Thus, the aim of the present study was to evaluate the effect of phosphoric and hydrochloric acid gels on the surface layer reduction of natural lesions of primary teeth.

Methods

Thirty-two extracted or exfoliated primary molars with lesions confined to enamel were selected. Paired lesion halves were partially etched with either 37% phosphoric (H₃PO₄) or 15% hydrochloric acid gel (HCl) for 30 s, 60 s, 90 s, or 120 s, respectively.

Results

Etching with H₃PO₄ resulted in incomplete reduction of the surface layers in all groups [highest percentage reduction (SD) at 120 s: 54 (28)%] as observed with confocal microscopy. In contrast, surface layers could be eroded almost completely [99 (3)%] by etching with HCl for 120 s.

Conclusion

An effective erosion of the surface layer of natural enamel caries in deciduous teeth can be achieved by etching with 15% hydrochloric acid gel for 90–120 s.     

Comparison of Knoop and Vickers surface microhardness and transverse microradiography for the study of early caries lesion formation in human and bovine enamel

Objective

The aims of the present laboratory study were twofold: a) to investigate the suitability of Knoop and Vickers surface microhardness (SMH) in comparison to transverse microradiography (TMR) to investigate early enamel caries lesion formation; b) to compare the kinetics of caries lesion initiation and progression between human and bovine enamel.

Design

Specimens (90 × bovine and 90 × human enamel) were divided into six groups (demineralization times of 8/16/24/32/40/48 h) of 15 per enamel type and demineralized using a partially saturated lactic acid solution. SMH was measured before and after demineralization and changes in indentation length (ΔIL) calculated. Lesions were characterized using TMR. Data were analyzed (two-way ANOVA) and Pearson correlation coefficients calculated.

Results

ΔIL increased with increasing demineralization times but plateaued after 40 h, whereas lesion depth (L) and integrated mineral loss (ΔZ) increased almost linearly throughout. No differences between Knoop and Vickers SMH in their ability to measure enamel demineralization were observed as both correlated strongly. Overall, ΔIL correlated strongly with ΔZ and L but only moderately with the degree of surface zone mineralization, whereas ΔZ and L correlated strongly. Bovine demineralized faster than human enamel (all techniques).

Conclusions

Lesions in bovine formed faster than in human enamel, although the resulting lesions were almost indistinguishable in their mineral distribution characteristics. Early caries lesion demineralization can be sufficiently studied by SMH, but its limitations on the assessment of the mineral status of more demineralized lesions must be considered. Ideally, complementary techniques to assess changes in both physical and chemical lesion characteristics would be employed.     

Effect of tricalcium silicate (Ca3SiO5) bioactive material on reducing enamel demineralization: An in vitro pH-cycling study

Objectives

The aim of this study was to investigate the effect of Ca₃SiO₅ on reducing enamel demineralization under pH-cycling conditions.

Methods

Forty bovine enamel samples were treated under four conditions: group 1, double distilled water (negative control); group 2, 1000 ppm F (as NaF, positive control); group 3, Ca₃SiO₅ slurry; and group 4, Ca₃SiO₅–F slurry (Ca₃SiO₅ with 1000 ppm F aq.). All the specimens were treated with treatment materials 4 times each day. Samples in groups 1 and 2 were soaked in test solutions for 2 min and samples in groups 3 and 4 were painted in treatment slurry for 2 min. At times between treatments, they were immersed in citric acid solution 3 times a day and 15 s each time. All the procedures were repeated for 7 days. Knoop microhardness, scanning electron microscopy (SEM), X-ray diffraction (XRD) and atom force microscopy (AFM) were used to examine samples.

Results

After treatment for 7 days, enamels in all the groups were significantly softened. The extents of microhardness reduction were 52.3%, 28.5%, 28.5% and 20.2% for groups 1, 2, 3 and 4, respectively. Samples in the negative control group showed a typical acid etched pattern while enamels in other groups were relatively compact. There was no significant difference between samples treated with Ca₃SiO₅ and F. The combination of Ca₃SiO₅ with F showed the best effect on reducing enamel demineralization.

Conclusions

Ca₃SiO₅ is an effective material against enamel demineralization alone but in combination with F a better anti-demineralization effect may be obtained.     

Effect of experimental mouthrinses containing the combination of NaF and TiF4 on enamel erosive wear in vitro

Objective

This study analysed the anti-erosive effect of experimental solutions containing TiF₄ and NaF.

Methods

Bovine enamel samples (n = 15) were treated with: (1) commercial solution with SnCl₂/NaF (Erosion Protection^®); (2) experimental solution with 0.0815% TiF₄; (3) 0.105% NaF; (4) 0.042% NaF + 0.049% TiF₄; (5) 0.063% NaF + 0.036% TiF₄ or (6) control. The samples were submitted to pH cycles and daily fluoride applications for seven days. The enamel wear was measured using a contact profilometer and analysed by ANOVA (p < 0.05).

Results

The best anti-erosive effect was found for experimental solution with 0.0815% TiF₄ (99% reduction in enamel wear), followed by SnCl₂/NaF (78%) and 0.049% TiF₄ + 0.042% NaF solution (41%).

Conclusions

The experimental solution containing a specific combination of TiF₄ + NaF has the ability to partially reduce enamel erosion.     

Efficacy of the stannous ion and a biopolymer in toothpastes on enamel erosion/abrasion

Objectives

Sn²⁺ has promising erosion-inhibiting properties in solutions, but little is known about respective effects in toothpastes. In addition, biopolymers might have protecting potential. Aim of this study was to investigate the effects of Sn²⁺ in toothpastes and of a biopolymer (chitosan) added to a Sn²⁺ formulation on erosion/abrasion.

Methods

Enamel samples were subjected to cyclic erosion procedures (10 days; 0.50% citric acid, pH 2.5; 6× 2 min/day), and brushing (2× 15 s/day, load 200 g) during immersion in slurries (2 min). The toothpastes were NaF formulations (NaF/1, NaF/2, NaF/3) and Sn²⁺ formulations (NaF/SnCl₂, AmF/SnF₂, AmF/NaF/SnCl₂) and AmF/NaF/SnCl₂ + 0.5% chitosan.Declared concentrations of active ingredients in toothpastes were 1400–1450 μg/g F⁻ and 3280–3500 μg/g Sn²⁺. Negative controls were erosion only and placebo, positive control was a SnF₂ gel. Tissue loss was quantified profilometrically, Sn on enamel surfaces was measured by energy dispersive X-ray spectroscopy.

Results

Loss values (μm) for erosion only and placebo were 14.4 ± 4.5 and 20.2 ± 3.8, respectively, and 4.6 ± 1.9 for the positive control (p ≤ 0.001 each compared to erosion only). The other loss values were: NaF/1 16.5 ± 3.0, NaF/2 14.0 ± 2.7, NaF/3 12.6 ± 3.9, NaF/SnCl₂ 14.7 ± 5.1, AmF/SnF₂ 13.5 ± 4.8, AmF/NaF/SnCl₂ 12.4 ± 4.2, AmF/NaF/SnCl₂ + chitosan 6.6 ± 3.5 (except NaF/1 all p ≤ 0.01 compared to placebo). AmF/NaF/SnCl₂/chitosan was more effective than all other toothpastes (p ≤ 0.01 each). Sn on the enamel surface ranged between 1.3 ± 0.3 and 2.8 ± 0.04 wt.% with no obvious relationship with efficacy.

Conclusions

The NaF and Sn²⁺ toothpastes without chitosan exhibited similar anti-erosion and abrasion-prevention effects. The experimental Sn²⁺ formulation with chitosan revealed promising results similar to those of the positive control.

Clinical significance

NaF toothpastes offer a degree of protection against erosion/abrasion, which is likely sufficient for most subjects with average acid exposures. For patients with initial erosive lesions, however, more effective toothpaste is desirable. The combination of Sn²⁺ and a biopolymer appears promising in this context.     

Effect of open-sandwich vs. adhesive restorative techniques on enamel and dentine demineralization: An in situ study

Objectives

To assess in situ the effect of different restorative techniques used with fluoride-releasing materials on enamel and dentine demineralization in the presence of a cariogenic challenge.

Methods

Thirty human molars were prepared for 60 Class V cavities, with enamel and dentine margins. The teeth were divided into four groups (n = 15): L1 – open sandwich technique with a conventional glass ionomer cement (GIC), L2 – open sandwich technique with a resin-modified GIC, A1 – total-etch bonding with a fluoride-containing adhesive, A2 – total-etch bonding with a nonfluoride-containing adhesive. All the cavities were restored with a nanofilled composite. Fifteen volunteers used appliances containing one specimen from each group. The cariogenic challenge was carried out with a 20% sucrose solution 8×/day for 7 days. The specimens were sectioned for microhardness test and EDS analysis at different depths below the enamel and dentine margins (25, 50 and 100 μm) and distances from the tooth-restoration interfaces (25 and 75 μm). The data were analyzed by ANOVA and Games–Howell test (α = 5%).

Results

Both GICs produced higher hardness in enamel at all depth-and-distance combinations, but only L1 produced higher hardness in dentine (p < 0.05). L2 and A1 exhibited similar dentine hardness at 25 μm distance for all depths (p > 0.05). L1 demonstrated significantly higher amounts of calcium in dentine than the other groups, but had similar amounts in enamel to L2 and A1.

Conclusions

The open sandwich technique using conventional GIC proved more effective in reducing enamel and dentine demineralization at depths of up to 100 μm under a cariogenic challenge.

Clinical significance

Conventional GICs should be considered the materials of choice for lining of cavities not having all margins in enamel, particularly using the open sandwich technique.     

Randomised in situ trial on the effect of milk and CPP-ACP on dental erosion

Objectives

This randomised in situ study aimed to analyse the effect of milk (with or without 5 ppm F) and CPP-ACP pastes (with or without 900 ppm F) on dental erosion.

Methods

The study was a seven phase (5 days each) crossover design involving 15 participants wearing intraoral appliances with enamel and dentine specimens. Specimens were extraorally eroded (erosive soft drink, 6 × 90 s/day) and brushed (2 × 30 s/day, 2 N) using a non-fluoridated toothpaste (negative control). The test products were milk, milk + 5 ppm F (twice daily, each 100 ml/2 min), CPP-ACP paste, CPP-ACP paste + 900 ppm F (3 min/day) or a SnCl₂/AmF/NaF mouthrinse (positive control, 30 s/day), which were applied immediately after erosion with the appliances in the oral cavity. In an additional group, a fluoridated toothpaste was used without any additional test product. Tissue loss was determined profilometrically after 5 days and statistically analysed by linear mixed models methodologies (p < 0.05).

Results

Compared with the negative control (non-fluoridated toothpaste only, enamel: 2.2 ± 1.3 μm; dentine: 3.8 ± 2.2 μm), enamel and dentine loss was significantly reduced by the use of fluoridated toothpaste (enamel: 1.1 ± 1.0 μm; dentine: 2.4 ± 1.7 μm) and the SnCl₂/AmF/NaF mouthrinse (1.5 ± 1.5 μm; dentine: 1.8 ± 1.9 μm).

Conclusions

Milk and CPP-ACP were not effective in reducing enamel and dentine loss significantly, independently of the presence of fluoride.

Clinical significance

Enamel and dentine erosion were significantly reduced by the use of a fluoridated toothpaste or a SnCl₂/AmF/NaF mouthrinse, but not by milk or CPP-ACP under the conditions of the present study.

Clinical trials registration

NCT01566357.     

The erosive potential of some alcopops using bovine enamel: An in vitro study

Objectives

Alcoholic soft drinks have become increasingly popular and have high concentrations of citric acid and alcohol so might have the potential to cause dental erosion. This study aimed to investigate the erosive potential of alcopops on bovine enamel in vitro.

Methods

Six bovine upper incisors were prepared and sectioned to give six slabs per tooth, 4 mm × 4 mm each. Each slab was covered with nail varnish, leaving an exposed window (2 mm × 2 mm). Samples were immersed in 20 ml of each of the test solutions for 20 min, 1 h, and 24 h under gentle agitation (100 rpm). Enamel surface loss was determined using Quantitative Laser Fluorescence (QLF), Non-contact Profilometry (NCP) and Transverse Microradiography (TMR).

Results

Enamel loss occurred with all test drinks and the positive control (p < 0.05), and the depth of lesion correlated with pH and time. No significant difference was observed between 20 min and 1 h exposure, although both times had significantly (p < 0.05) greater erosion when compared with baseline. Within each alcopops group significant erosion had occurred at 24 h exposure compared with the baseline and previous times.

Conclusion

All the tested alcopops resulted in significant enamel loss at 24 h (p < 0.001) with direct correlation between degree of enamel loss and both pH and increasing exposure time.     

Effect of low-fluoride toothpastes combined with hexametaphosphate on in vitro enamel demineralization

Objectives

The aim of this study was to evaluate the anticaries effect of low-fluoride toothpastes combined with hexametaphosphate (HMP) on enamel demineralization.

Methods

Bovine enamel blocks were subjected to pH cycling and treatment with toothpaste's slurries (15 groups; 2×/day). Toothpaste mixtures contained the following: no fluoride (F) plus HMP (from 0 to 3.0%); 250 ppm F plus HMP (from 0 to 3.0%); 500 ppm F; 1100 ppm F; and a commercial toothpaste (1100 ppm F). After pH cycling, surface and cross-sectional hardness, as well as F present in the enamel were determined. The demineralization depth was analyzed using polarized light microscopy. The variables were subjected to 1-way ANOVA, followed by Student–Newman–Keuls’ test (p < 0.05).

Results

In the absence of fluoride, 0.5% HMP promoted the lowest mineral loss and its effect was similar to that of a 250 ppm F toothpaste (p > 0.05). The combination of 0.5% HMP and 250 ppm F resulted in lower mineral loss (p < 0.05) and similar lesion depth when compared to the 1100 ppm F toothpaste (p > 0.05).

Conclusion

To conclude, the combination of 0.5% HMP and 250 ppm fluoride in a toothpaste has a similar inhibitory effect on enamel demineralization in vitro when compared to a toothpaste containing 1100 ppm F.

Clinical significance

The anticaries effect of toothpaste containing 250 ppm F combined with 0.5% HMP was similar to that of a 1100 ppm F toothpaste, despite the 4-fold difference in F concentration. Although such effects still need to be demonstrated in clinical studies, it may be a viable alternative for preschool children.     

Effect of sodium,amine and stannous fluoride at the same concentration and different pH on in vitro erosion

Objective

This study aimed to compare the effects 0.5% and 1% sodium, amine and stannous fluoride at different pH on enamel erosion in vitro.

Methods

Bovine enamel samples were submitted to a cyclic de- and remineralisation for 3 days. Each day, the samples were exposed for 120 min to pooled human saliva and subsequently treated with one of the fluoride solutions for 3 min: amine fluoride (AmF, 0.5% and 1% F⁻), sodium fluoride (NaF, 0.5% and 1% F⁻), each at pH 3.9 and 7.0, and stannous fluoride (SnF₂, 0.5% and 1% F⁻), at pH: 3.9. Additionally, two groups were treated with fluoride-free placebo solutions (pH: 3.9 and 7.0) and one group served as control (no fluoridation). Ten specimens each group were inserted in a so-called artificial mouth and eroded six times daily with hydrochloric acid (pH 2.6) for 90 s each intermitted by exposure to artificial saliva (1 h). After 3 days, enamel loss was analyzed profilometrically and evaluated statistically by ANOVA.

Results

Only the acidic 0.5% and 1% SnF₂ and 1% AmF solutions were able to reduce erosive enamel loss significantly, while all other solutions and placebos did not differ significantly from the control. Between the acidic SnF₂ and the 1% AmF solutions no significant differences could be detected.

Conclusion

At the same concentrations, acidic SnF₂ and AmF may be more effective than NaF to protect enamel against erosion.     

Chitosan effect on dental enamel de-remineralization: An in vitro evaluation

Objectives

The aim of this work was to evaluate the in vitro effect of chitosan (concentration and time of action) treatment on enamel de-remineralization behavior upon a pH cycling assay.

Methods

Different group of human tooth samples were exposed to de-remineralizing solutions of controlled pH using a random experimental design. Microhardness and phosphorus chemical analysis were employed to evaluate the loss of phosphorus from the samples. Optical coherence tomography (OCT) images were obtained for selected specimens in order to evaluate the degree of penetration of chitosan into enamel.

Results

Vickers microhardness results were higher for samples treated with chitosan for concentration between 2.5 mg/mL and 5.0 mg/mL and time of action between 60 s and 90 s. A maximum inhibition of mineral loss of 81% was obtained. Chemical analysis indicated lower net pohosphorus loss (net P loss) for samples treated with chitosan. Best results were obtained in the same conditions found out with microhardness measurements. Chitosan had little effect on the remineralization process. OCT results indicated a correlation of chitosan penetration with chitosan concentration. For chitosan concentrations of 2.5 g/mL and 5.0 g/mL the penetration was up to the dentin–enamel junction.

Conclusions

Chitosan interferes with the process of demineralization of the tooth enamel inhibiting the release of phosphorus in this laboratory study. Demineralization is influenced by the concentration and exposure time of the biopolymer to the enamel. Microhardness measurements may be used as an indication of mineral loss from tooth enamel. Additionally, OCT images support the idea that chitosan may act as a barrier against acid penetration, contributing to its demineralization inhibition.     

Radiation therapy alters microhardness and microstructure of enamel and dentin of permanent human teeth

Objectives

To evaluate, in vitro, the effects of ionizing radiation on the mechanical and micro-morphological properties of enamel and dentin of permanent teeth.

Methods

Enamel and dentin microhardness (n = 12 hemi-sections) was evaluated at three depths (superficial, middle and deep) prior to (control) and after every 10 Gy radiation dose up to a cumulative dose of 60 Gy by means of longitudinal microhardness. Data were analyzed using two-way analysis of variance and Tukey's test at a significance level of 5%. Enamel and dentin morphology was assessed by scanning electron microscopy (SEM) for semi-quantitative analysis (n = 8 hemi-sections). Data were analyzed using Kruskal–Wallis and Dunn's or Fisher exact tests at a significance level of 5%.

Results

The application of ionizing radiation did not change the overall enamel microhardness, although an increase in superficial enamel microhardness was observed. The micro-morphological analysis of enamel revealed that irradiation did not influence rod structure but interprismatic structure became more evident. Dentin microhardness decreased after 10, 20, 30, 50 and 60 Gy cumulative doses (p < 0.05) compared with non-irradiated dentin, mainly in the middle portion of the tissue. The micro-morphological analysis revealed fissures in the dentin structure, obliterated dentinal tubules and fragmentation of collagen fibers after 30 and 60 Gy cumulative doses.

Conclusions

Although ionizing radiation did not affect the enamel microhardness of permanent teeth as a whole, an increase in superficial enamel microhardness was observed. Dentin microhardness decreased after almost all radiation doses compared with the control, with the greatest reduction of microhardness in the middle depth region. The morphological alterations on enamel and dentin structures increased with the increase of the radiation dose, with a more evident interprismatic portion, presence of fissures and obliterated dentinal tubules, and progressive fragmentation of the collagen fibers.

Clinical significance

This study shows that irradiation affects microhardness and micro-morphology of enamel and dentin of permanent teeth. The effects of gamma irradiation on dental substrate might contribute to increased risk of radiation tooth decay associated with salivary changes, microbiota shift and high soft and carbohydrate-rich food intake.     

The effect of increasing sodium fluoride concentrations on erosion and attrition of enamel and dentine in vitro

Objectives

To investigate the effect of an aqueous sodium fluoride solution of increasing concentration on erosion and attrition of enamel and dentine in vitro.

Methods

Enamel and dentine sections from caries-free human third molars were polished flat and taped (exposing a 3 mm × 3 mm area) before being randomly allocated to 1 of 5 groups per substrate (n = 10/gp): G1 (distilled water control); G2 (225 ppm NaF); G3 (1450 ppm NaF); G4 (5000 ppm NaF); G5 (19,000 ppm NaF). All specimens were subjected to 5, 10 and 15 cycles of experimental wear [1 cycle = artificial saliva (2 h, pH 7.0) + erosion (0.3% citric acid, pH 3.2, 5 min) + fluoride/control (5 min) + attrition (60 linear strokes in artificial saliva from enamel antagonists loaded to 300 g)]. Following tape removal, step height (SH) in μm was measured using optical profilometry.

Results

When the number of cycles increased the amount of tooth surface loss increased significantly in enamel and dentine after attrition and erosion and for dentine after attrition. Attrition and erosion resulted in greater surface loss than attrition alone after 15 cycles of experimental wear of enamel. 5000 ppm and 19,000 ppm sodium fluoride solutions had a protective effect on erosive and attritional enamel tooth wear in vitro, however no other groups showed significant differences.

Conclusions

The more intensive the fluoride regime the more protection was afforded to enamel from attrition and erosion. However, in this study no such protective effect was demonstrated for dentine.     

In vitro demineralization of human enamel natural and abraded surfaces: A micromechanical and SEM investigation

Objectives

To compare the demineralization pattern that occurs in abraded samples and unabraded ones quantitatively and microscopically using nanoindentation and SEM.

Methods

Using 12 human third molars, one half of each tooth was abraded to a depth approximately 200 μm below the outer surface enamel, and the other half was left untreated. All specimens were demineralized for 3 d, 5 d, 7 d and 14 d respectively. The cross sections of all lesions were evaluated with nanoindentation and SEM.

Results

Unabraded samples had least loss of mechanical properties and lesion depth compared to abraded samples, with most mechanical property loss occurring within a shallower layer of the lesion. The variation of mechanical properties in unabraded samples was wider than abraded samples. SEM images showed a characteristic “keyhole” structure for both samples after demineralization, with the rod core extensively demineralized while the interrod remained intact. Acid attack initiated at the rod sheath space then penetrated into the rod core before extending into neighbouring rods through the rod tail.

Conclusion

Abraded samples exposed to in vitro demineralization form deeper lesion depths and greater loss of mechanical properties than unabraded samples subjected to the same demineralization. Unabraded samples manifested characteristic subsurface demineralization with a shallow surface layer that remained intact, whereas no intact surface was found in abraded samples. The demineralization pattern of unabraded samples more closely resembled the pattern of natural white spot lesions and displayed wide inter-sample variation. Consideration should be given to experimental design with unabraded teeth specimens for future demineralization studies.     

Effect of fluoride varnish supplemented with sodium trimetaphosphate on enamel erosion and abrasion: An in situ/ex vivo study

Objective

To evaluate the effect of fluoride (F) varnishes supplemented or not with sodium trimetaphosphate (TMP) on enamel erosive wear followed or not by abrasion in situ.

Methods

Ten volunteers were selected and randomly divided into four groups, according to the varnishes tested: placebo (no F or TMP), 5% NaF (positive control), 2.5% NaF and 2.5% NaF/5% TMP. Enamel blocks (n = 4) were mounted in palatal devices and received an application of each test varnish, following a double-blind, crossover protocol. After 6 h, varnishes were completely removed and the blocks were subjected to erosive challenges by ex vivo immersion in citric acid (5 min, 4×/dia, 5 days). Following, half of the blocks were subjected to abrasion by brushing with a placebo dentifrice slurry for 15 s. Enamel wear (μm), surface hardness (SH_f) and cross-sectional hardness (ΔKHN) were assessed after each experimental period. Results were analyzed by ANOVA, Student–Newman–Keuls's test and Pearson correlation coefficient (p < 0.05).

Results

The fluoride varnish supplemented with TMP promoted significantly lower wear and ΔKHN when compared to the other groups after erosive challenges, followed or not by abrasion (p < 0.05). As for (SH_f) the fluoride varnish supplemented with TMP promoted similar results to the 5% NaF product, being significantly higher than the remaining groups after erosive and erosive + abrasive challenges (p < 0.05).

Conclusion

TMP significantly enhanced the effects of F on enamel wear after erosive challenges, followed or not by abrasion.