Protective effect on enamel demineralization of a CPP–ACP paste: an AFM in vitro study

Objectives

The aim of the present in vitro study was the evaluation of a CPP–ACP paste (Tooth Mousse) on preventing dental erosion produced by a soft drink (Coca Cola), using Atomic Force Microscopy (AFM).

Methods

Thirty extracted human central incisors free of caries were selected and divided in a treatment and a control half. The treatment halves were divided in three groups—group 1: demineralization with soft drink (4 intervals of 2 min); group 2: demineralization with soft drink (4 intervals of 2 min) plus Tooth Mousse; group 3: intact enamel plus Tooth Mousse. In groups 2 and 3 Tooth Mousse was applied for 3 min at 0, 8, 24 and 36 h. The surface of each specimen was imaged by AFM and R_rms values were registered.

Results

Among treatment specimens of groups 1 and 2, a statistically significant difference (P < 0.01) in R_rms values was registered: treatment of the specimens with CPP–ACP paste had a protective effect on enamel demineralization. In group 3 no statistically significant difference was registered between exposed and not exposed halves of the specimens.

Conclusions

The use of a CPP–ACP paste had a protective effect on enamel demineralization in an in vitro model.     

Prevention of dentine erosion by brushing with anti-erosive toothpastes

Objective

This in vitro study aimed to investigate the preventive effect of brushing with anti-erosive toothpastes compared to a conventional fluoride toothpaste on dentine erosion.

Materials and methods

Bovine dentine specimens (n = 12 per subgroup) were eroded in an artificial mouth (6 days, 6 × 30 s/day) using either citric acid (pH:2.5) or a hydrochloric acid/pepsin solution (pH:1.6), simulating extrinsic or intrinsic erosive conditions, respectively. In between, the specimens were rinsed with artificial saliva. Twice daily, the specimens were brushed for 15 s in an automatic brushing machine at 2.5 N with a conventional fluoride toothpaste slurry (elmex, AmF) or toothpaste slurries with anti-erosive formulations: Apacare (NaF/1% nHAP), Biorepair (ZnCO₃-HAP), Chitodent (Chitosan), elmex Erosionsschutz (NaF/AmF/SnCl₂/Chitosan), mirasensitive hap (NaF/30% HAP), Sensodyne Proschmelz (NaF/KNO₃). Unbrushed specimens served as control. Dentine loss was measured profilometrically and statistically analysed using two-way and one-way ANOVA followed by Scheffe‘s post hoc tests. RDA-values of all toothpastes were determined, and linear mixed models were applied to analyse the influence of toothpaste abrasivity on dentine wear (p < 0.05).

Results

Dentine erosion of unbrushed specimens amounted to 5.1 ± 1.0 μm (extrinsic conditions) and 12.9 ± 1.4 μm (intrinsic conditions). All toothpastes significantly reduced dentine erosion by 24–67% (extrinsic conditions) and 21–40% (intrinsic conditions). Biorepair was least effective, while all other toothpastes were not significantly different from each other. Linear mixed models did not show a significant effect of the RDA-value of the respective toothpaste on dentine loss.

Conclusion

Toothpastes with anti-erosive formulations reduced dentine erosion, especially under simulated extrinsic erosive conditions, but were not superior to a conventional fluoride toothpaste.     

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 desensitising toothpastes on dentinal tubule occlusion: A dentine permeability measurement and SEM in vitro study

Objectives

The purpose of this study was to evaluate the in vitro effectiveness of a new bioglass-containing and two commercial desensitising toothpastes on dentinal tubule occlusion after citric acid challenge or artificial saliva (AS) immersion.

Methods

One hundred dentin discs from human third molars were used. Specimens were randomly divided into five groups (n = 20), Group 1: EDTA-treated dentin; Group 2: brushing with distilled water; Group 3: brushing with Novamin; Group 4: brushing with Sensodyne Freshmint; Group 5: brushing with Colgate Sensitive. In each group, samples were then equally split into two subgroups (n = 10) to test two post-treatments: 6% citric acid challenge or 24 h immersion in artificial saliva. Dentine permeability of each specimen was measured before and after each treatment using a hydrostatic device working at 20 cm H₂O pressure. Data were analysed by two-way repeated measures ANOVA to determine if there were any significant differences within or between groups. Dentine morphology and surface deposits were observed by SEM.

Results

All three desensitising toothpastes significantly reduced dentine permeability and created precipitates on the treated dentine surfaces. Moreover, the reductions in dentine permeability showed partial recovery after a citric acid and artificial saliva immersion. Sensodyne showed significant resistant to acid attack and Novamin exhibited the lowest permeability after artificial saliva immersion for 24 h.

Conclusions

The application of the three toothpastes resulted in effective dentinal tubule occlusion. However, the new bioglass-containing toothpaste (Novamin) represented excellent occlusion effects after brushing treatment and AS immersion, while Sensodyne demonstrated more reduction in permeability when citric acid challenged.     

Wettability of root canal sealers on intraradicular dentine treated with different irrigating solutions

Objectives

The aim of this in vitro study was to evaluate the wettability of AH Plus and ThermaSeal Plus sealers on intraradicular dentine treated with different irrigating solutions.

Methods

Fifty anterior teeth were decoronated and split longitudinally. Each root half was divided into 5 groups (n = 10). Group I: 5 mL of 2.5% NaOCl + QMix. Group II: 5 mL of 2.5% NaOCl + 17% EDTA. Group III: 5 mL of 2.5% NaOCl + 7% maleic acid. Group IV: 5 mL of 2.5% NaOCl. Group V: 5 mL of distilled water. Irrigation regimens were performed for 1 min. Each specimen was placed inside a Dynamic Contact Angle Analyser. A controlled-volume droplet of sealer was placed on each specimen and the static contact angle was analysed.

Results

The contact angle made by both sealers with EDTA-irrigated dentine was significantly larger when compared to the other irrigants (P < 0.05). For ThermaSeal Plus, contact angles produced on maleic acid-, NaOCl- and distilled water-irrigated dentine were not significantly different, but were all significantly larger than the contact angle produced on QMix-irrigated dentine (P < 0.05). For AH Plus, contact angles produced on NaOCl- and distilled water-irrigated dentine were not significantly different, but were significantly larger than those made by maleic acid and QMix.

Conclusion

When used as a final irrigant, QMix favours the wetting of root canal dentine by both AH Plus and ThermaSeal Plus sealers. Maleic acid shows a promising result when compared to EDTA and NaOCl. Wettability of both sealers is the worst on EDTA-irrigated dentine.

Clinical significance

The present study highlights the effect of newer endodontic irrigating solutions on the wettability of sealers on to the root canal dentine, which is required for obtaining good obturation seal.     

Physical chemical effects of zinc on in vitro enamel demineralization

Objectives

Zinc salts are formulated into oral health products as antibacterial agents, yet their interaction with enamel is not clearly understood. The aim was to investigate the effect of zinc concentration [Zn²⁺] on the in vitro demineralization of enamel during exposure to caries-simulating conditions. Furthermore, the possible mechanism of zinc's action for reducing demineralization was determined.

Methods

Enamel blocks and synthetic hydroxyapatite (HAp) were demineralized in a range of zinc-containing acidic solutions (0–3565 ppm [Zn²⁺]) at pH 4.0 and 37 °C. Inductively coupled-plasma optical emission spectroscopy (ICP-OES) was used to measure ion release into solution. Enamel blocks were analysed by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), and HAp by X-ray diffraction (XRD) and neutron diffraction (ND).

Results

ICP-OES analysis of the acidic solutions showed a decrease in [Ca²⁺] and [PO₄³⁻] release with increasing [Zn²⁺]. FTIR revealed a α-hopeite (α-Zn₃(PO₄)₂.4H₂O)-like phase on the enamel surfaces at >107 ppm [Zn²⁺]. XRD and ND analysis confirmed a zinc-phosphate phase present alongside the HAp.

Conclusions

This study confirms that zinc reduces enamel demineralization. Under the conditions studied, zinc acts predominantly on enamel surfaces at PO₄³⁻ sites in the HAp lattice to possibly form an α-hopeite-like phase.

Clinical significance

These results have a significant implication on the understanding of the fundamental chemistry of zinc in toothpastes and demonstrate its therapeutic potential in preventing tooth mineral loss.     

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.     

In vivo spectrophotometric evaluation of pure enamel and enamel–dentine complex in relationship with different age groups

Objective

The aim of this in vivo study was to investigate the influence of age on optical properties of pure enamel and enamel–dentine complex.

Methods

A spectrophotometric study was performed on two different age groups: young (10–35 years old) and adult (36–60 years old). In both groups, the tooth's total area of the upper right central incisor was recorded. Areas of 2 mm thick pure enamel and 3 mm enamel–dentine complex were detected and their L*a*b* and CR evaluated.

Results

For 2 mm pure enamel medians in the young group were L*74.8, a*3.1, b*15.1, against white background; and L*65.5, a*0.9, b*10.3 against black background. The correspondent opacity was 75%. In the adult group medians were L*70.0, a*4.1, b*15.4 against white background; and L*61.2, a*1.6, b*9.6, against black background. The correspondent opacity was 75%. For 3 mm enamel–dentine complex medians in the young group were L*77.8, a*3.0, b*19.8 against white background; and L*74.2, a*1.1, b*15.9, against black background. The correspondent opacity was 89%. In the adult group medians were L*73.4, a*4.0, b*18.5 against white background; and L*71.0, a*2.0, and b*15.3 against black background. The correspondent opacity was 90%.

Discussion

The application of this method on a larger group of subjects of different ages may serve as a database for a more exact characterization of optical properties of natural enamel and dentine.

Conclusions

L* values in enamel, as well as a* value of 3 mm thick enamel–dentine complex and 2 mm pure enamel were significantly higher in the young age group.

Clinical significance

L* and a* values of enamel over white and black backgrounds were statistically different within the 2 age groups considered. L* values over white background and a* values over black background of the enamel dentine complex seem to change with age. The opacity (CR) for enamel nor for enamel dentine complex does not change within the two age groups considered in this study.     

Shear bond strength of porcelain laminate veneers to enamel,dentine and enamel–dentine complex bonded with different adhesive luting systems

Objectives

The aim of this study was to evaluate the shear bond strength of porcelain laminate veneers to 3 different surfaces by means of enamel, dentine, and enamel–dentine complex.

Methods

One hundred thirty-five extracted human maxillary central teeth were used, and the teeth were randomly divided into 9 groups (n = 15). The teeth were prepared with 3 different levels for bonding surfaces of enamel (E), dentine (D), and enamel–dentine complex (E–D). Porcelain discs (IPS e.max Press, Ivoclar Vivadent) of 2 mm in thickness and 4 mm in diameter were luted to the tooth surfaces by using 2 light-curing (RelyX Veneer [RV], 3M ESPE; Variolink Veneer [VV], Ivoclar Vivadent) and a dual-curing (Variolink II [V2], Ivoclar Vivadent) adhesive systems according to the manufacturers’ instructions. Shear bond strength test was performed in a universal testing machine at 0.5 mm/min until bonding failure. Failure modes were determined under a stereomicroscope, and fracture surfaces were evaluated with a scanning electron microscope. The data were statistically analysed (SPSS 17.0) (p = 0.05).

Results

Group RV-D exhibited the lowest bond strength value (5.42 ± 6.6 MPa). There was statistically no difference among RV-D, V2-D (13.78 ± 8.8 MPa) and VV-D (13.84 ± 6.2 MPa) groups (p > 0.05). Group VV-E exhibited the highest bond strength value (24.76 ± 8.8 MPa).

Conclusions

The type of tooth structure affected the shear bond strength of the porcelain laminate veneers to the 3 different types of tooth structures (enamel, dentine, and enamel–dentine complex).

Clinical significance

When dentine exposure is necessary during preparation, enough sound enamel must be protected as much as possible to maintain a good bonding; to obtain maximum bond strength, preparation margins should be on sound enamel.     

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.     

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.     

In vitro evaluation of fluoride and calcium sodium phosphosilicate toothpastes, on root dentine caries lesions

Objectives

The aim of this in vitro study was to assess the effect of toothpastes containing three different sodium fluoride concentrations and a calcium sodium phosphosilicate system, on root dentine demineralization and remineralization.

Methods

During a fourteen-day pH-cycling protocol, pre-softened bovine root dentine specimens were immersed twice daily, before and after the demineralization periods, for 2 min, in the following toothpaste slurries: (a) non-fluoridated (control), (b) 7.5% calcium sodium phosphosilicate, (c) 1450 ppm F, (d) 2800 ppm F, and (e) 5000 ppm F. Subsequently, the slabs were subjected to a fifty-hour acid resistance test. Knoop microhardness at different lesion depths was assessed in specimen cross-sections and KHN values were converted to vol.% mineral. Comparisons between the groups were performed at each lesion depth through ANOVA-based tests and furthermore, regression analysis of the derived statistic of “integrated vol.% mineral loss” was carried out. Also, lesions were evaluated qualitatively using transmission and polarized light microscopy.

Results

The 5000 ppm F toothpaste group, during pH-cycling, presented significantly less total vol.% mineral loss and subsequently exhibited considerably increased surface acid resistance, compared to all the other tested groups. The calcium sodium phosphosilicate toothpaste, during pH-cycling, inhibited demineralization and/or promoted remineralization of the surface layers significantly more effectively than the control group nevertheless, subsequently, the acid resistance of the calcium sodium phosphosilicate dentifrice group was similar to that of the control group. These observations were confirmed by microscopic examination of the lesions.

Conclusions

Under the present experimental conditions, the 5000 ppm F toothpaste, promoted remineralization and inhibited demineralization more effectively, than the other tested toothpastes.     

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.     

Human gingival fibroblasts function is stimulated on machined hydrided titanium zirconium dental implants

Objectives

The aim of this study was to evaluate the influence of different titanium zirconium (TiZr) alloy surfaces on primary human gingival fibroblasts (HGF) for improved soft tissue integration of dental implants.

Methods

TiZr polished, machined and machined + HCl/H₂SO₄ acid-etched surfaces were modified by cathodic polarization and/or HNO₃/HF acid etching. Contact angle of surfaces was measured. The influence of modified TiZr surfaces on HGF was evaluated through the analysis of cell number, morphology, recovery after a wound (wound healing assay) and the expression of several genes, including matrix metalloproteinase-1 (MMP1) and metallopeptidase inhibitor-1 (TIMP1).

Results

Modification of TiZr surfaces decreased its hydrophilicity. Hydride implementation on TiZr surfaces via cathodic polarization increased TIMP1 expression and decreased MMP1/TIMP1 mRNA ratio. Cathodic polarization of machined surfaces promoted cell attachment. Cells on machined and machined + cathodic polarization surfaces grew aligned to the microgrooves whereas on all polished surfaces they grew randomly. Acid etching of polished and machined surfaces did not improve HGF function.

Conclusions

Hydride implementation on TiZr machined surfaces may be used as new dental implant material for improved soft tissue integration.

Clinical significance

Enhancing dental implant surfaces’ bioactivity by hydride implementation may promote soft tissue attachment and sealing around the implant and reduce peri-implantitis related to ECM-destruction compared with conventional machined surfaces.     

Marginal leakage of two newer glass-ionomer-based sealant materials assessed using micro-CT

Objectives

To test newer glass-ionomer-based materials as sealant materials. One glass-ionomer sealant was light-cured to obtain an early setting reaction. The null-hypothesis tested was: there is no difference in marginal leakage of sealants produced with high-viscosity glass-ionomer, with and without energy supplied, and that of glass-carbomer, in comparison with resin composite sealants in vitro.

Methods

Materials used were Clinpro^®, Ketac Molar Easymix^® and Glass-Carbomer^®. Sealants were placed in the occlusal surface of 89 molar teeth, thermocycled for 5000 cycles and evaluated using micro-CT for silver nitrate penetration depth at the enamel–sealant interface by two trained evaluators. Data were analysed, using ANOVA and Scheffe's test.

Results

Glass-carbomer sealants showed one or more ‘fracture lines’ in the material and at the enamel–material interface, filled with a kind of transparent, but not black coloured, material. High-viscosity glass-ionomer sealants with and without energy supplied had statistically significantly lower mean marginal leakage scores than sealants produced by composite resin (p < 0.01). No marginal leakage was found in the high-viscosity glass-ionomer group without energy supplied.

Conclusions

The high-viscosity glass-ionomer (Ketac Molar Easymix^®) sealants had lower marginal leakage than resin composite sealants, and should be tested in vivo. Glass-carbomer sealants were non-interpretable.     

Impairment of nasal airway under intermittent hypoxia during growth period in rats

Objective

To clarify the influences of intermittent hypoxia (IH) on the growth and development of the midfacial area, including the nasal cavity, in growing rats.

Design

Seven-week-old male Sprague–Dawley rats were divided into two groups: the experimental group (n = 5), which was exposed to IH for 8 h during light periods at a rate of 20 cycles/h (nadir, 4% O₂ to peak, 21% O₂ with 0% CO₂), and the control group (n = 5), which was exposed to room air. After 3 weeks, the maxillofacial structures in both groups were evaluated with respect to the height, width, length, surface area, cross-sectional area, and volume of the nasal cavity using soft X-ray and micro-CT.

Results

The experimental group showed a significantly smaller cross-sectional area and volume than did the control group. The surface area exhibited no significant differences between the two groups, although it tended to be smaller in the experimental group than in the control group. The nasal volume divided by the length of the tibia (for comparison with whole-body growth) was significantly smaller in the experimental group than in the control group.

Conclusions

These data suggest that IH exposure suppresses growth and development of the nasal cavity and may result in nasal breathing disturbance.     

Effect of pretreatments on the metal–ceramic bonding strength of a Pd–Ag alloy

Objectives

The purpose of this study was to evaluate the efficacy of surface treatments on the bonding properties between a metal and ceramic.

Methods

Sixty metal specimens were divided equally into four groups of 15 samples each. These groups received different treatments (Gr1: 250 μm Al₂O₃ + preoxidation; Gr2: 250 μm Al₂O₃ + degassing; Gr3: 120 μm Al₂O₃ + preoxidation; Gr4: 120 μm Al₂O₃ + degassing). Bond strengths were evaluated using a three-point bending test. The results were analyzed using 2-way ANOVA and Tukey's test. Scanning electron microscopy and energy dispersive spectroscopy were used to observe the microscopic features, elemental compositions and distributions, and diffusion in the specimens. Mechanical profiler was used to measure the roughness of metal surface.

Results

The bond strengths of the four groups ranged from 45.00 ± 3.63 MPa to 51.61 ± 5.91 MPa, with significant differences (P < .05). The specimen that received the pretreatment of 250 μm Al₂O₃ air-particle abrasion + degassing had the highest bond strength. Heating under different oxygen partial pressures caused the final Pd–Ag alloys to have varying degrees of internal oxidation and different quantities of metallic nodules. None of the elements in either the ceramic or the Pd–Ag alloy layer diffused into the other layer.

Conclusions

The metal–ceramic specimen subjected to air-particle abrasion with 250 μm Al₂O₃ and degassed before porcelain firing had significantly higher bond strength than specimens treated differently.     

Longitudinal monitoring of demineralization peripheral to orthodontic brackets using cross polarization optical coherence tomography

Objectives

The aim of this study was to test the hypothesis that cross-polarization optical coherence tomography (CP-OCT) can be used to longitudinally monitor demineralization peripheral to orthodontic brackets in an extended clinical study.

Methods

A high-speed CP-OCT system was used to acquire 3D volumetric images of the area at the base of orthodontic brackets over a period of 12 months after placement. The reflectivity was measured at 3-month intervals for 12 months to determine if there was increased demineralization. Two teeth were monitored on 20 test subjects and the brackets were bonded using two types of adhesives. This was a randomized controlled clinical study with a split mouth design such that each subject served as his or her own control. On one side, the control premolar was bonded with a bonding agent (Adper Scotchbond from 3 M ESPE, St. Paul, MN) and composite (Transbond XT from 3 M Unitek, Monrovia, CA) that lacked fluoride. On the other side, the experimental premolar was bonded with a fluoride releasing glass ionomer cement (GC Fuji Ortho LC from GC America, Alsip, IL).

Results

There was a small but significant increase in the calculated lesion depth and integrated reflectivity over that depth (ΔR) for both adhesive types (p < 0.0001) indicating increasing demineralization with time. There was no significant difference in the lesion depth (p = 0.22) and ΔR (p = 0.91) between the groups with the fluoride releasing glass ionomer cement and the conventional composite.

Conclusions

CP-OCT was able to measure a significant increase in demineralization (p < 0.0001) at the base of orthodontic brackets over a period of 12 months.     

Influence of the irradiation distance and the use of cooling to increase enamel-acid resistance with Er:YAG laser

Objectives

The aim of this study was to assess the influence of irradiation distance and the use of cooling in the Er:YAG laser efficacy in preventing enamel demineralization.

Methods

84 enamel blocks were randomly assigned to seven groups (n = 12): G1: control group – no treatment, G2–G7: experimental groups treated with Er:YAG laser (80 mJ/2 Hz) at different irradiation distances with or without cooling: G2: 4 mm/2 mL; G3: 4 mm/no cooling; G4: 8 mm/2 mL; G5: 8 mm/no cooling; G6: 16 mm/2 mL; G7: 16 mm/no cooling. The samples were submitted to an in vitro pH cycles for 14 days. Next, the specimens were sectioned in sections of 80–100 μm in thickness and the demineralization patterns of prepared slices were assessed using a polarized light microscope. Three samples from each group were analyzed with scanning electronic microscopy. Analysis of variance and the Fisher test were performed for the statistical analysis of the data obtained from the caries-lesion-depth measurements (CLDM) (alpha = 5%).

Results

The control group (CLDM = 0.67 mm) was statistically different from group 2 (CLDM = 0.42 mm), which presented a smaller lesion depth, and group 6 (0.91 mm), which presented a greater lesion depth. The results of groups 3 (CLDM = 0.74 mm), 4 (CLDM = 0.70 mm), 5 (CLDM = 0.67 mm) and 7 (CLDM = 0.89 mm) presented statistical similarity. The scanning electronic microscopy analysis showed ablation areas in the samples from groups 4, 5, 6 and 7, and a slightly demineralized area in group 2.

Conclusions

It was possible to conclude that Er:YAG laser was efficient in preventing enamel demineralization at a 4-mm irradiation distance using cooling.     

Monitoring bacterial-demineralization of human dentine by electrochemical impedance spectroscopy

Objective

The purpose of this study was two-fold: (1) to monitor bacterial biofilm formation and bacteria-induced demineralization of dentine in situ by using electrochemical impedance spectrum (EIS); (2) to examine the relationship between EIS findings and changes in the chemical composition and ultrastructure of dentine during bacteria-induced demineralization.

Methods

In this study, dentine demineralization was induced by Streptococcusmutans (ATCC 25175) in the presence of sucrose in culture medium and was monitored using two EIS measurement systems (Type A with a working electrode and Type B without a working electrode). Scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) were employed to examine the morphology, element contents and crystallinity of hydroxyapatite (HAP) on the dentine surface. Transverse microradiography (TMR) was used to characterize the lesion depth and degree of mineral loss during demineralization.

Results

The resistance of the bulk dentine (R_d) and the apparent resistance of dentine (R_a) measured from the Type A and Type B EIS systems, respectively, decreased gradually with demineralization. The resistance of the biofilm formed on dentine surface was determined by fitting the EIS data with equivalent circuits. The presence of biofilm slightly increased R_a of dentine before demineralization. However, the electrochemical behavior of biofilm did not affect the decreasing impedance of dentine with demineralization. The SEM, EDX, XRD and TMR results demonstrated that the surface and bulk dentine gradually became more porous due to the loss of minerals during demineralization, which in turn resulted in the decrease in R_d and R_a values obtained from EIS systems.

Conclusions

This investigation highlighted EIS as a potential technique to monitor biofilm formation and bacterial-induced demineralization in situ.