Ammonium hexafluorosilicate increased acid resistance of bovine enamel and dentine

Disinfection of caries affected dentin using Rose Bengal, Titanium Sapphire Laser; Ammonium Hexa-fluorosilicate, and ozonated water on resin dentin bond strength

AIM

The present study intended to evaluate the shear bond strength (SBS) of resin cement bonded to caries affected dentin (CAD) after disinfection with rose Bengal (RB), Ti-Sapphire Laser, Ammonium Hexafluorosilicate (NH₄)₂[SiF₆], and ozonated water (O₃) MATERIAL AND METHODS: A total of 100 extracted human mandibular molars were acquired using caries severity code, 6 of the ICDAS criteria. To achieve homogeneity and prevent size-biased distributions, the average cavity preparation of all specimens had a depth of 2 mm and a breadth of 3 mm. Specimens were divided into five groups (n = 20) at random according to type of disinfection. Group 1: control group, Group 2: RB, Group 3: O₃, Group 4: Ti-sapphire laser, and Group 5: (NH4)2[SiF₆]. All specimens were etch and rinsed, bonding agent was applied and restored with resin cement. Estimation of SBS was performed by placing samples (10/group) in universal testing machine. Stereomicroscope under 40 × magnification was employed for failure mode analysis (FMA). Statistical analysis was executed using the ANOVA and the Tukey multiple test (p<0.05).

RESULTS

The highest SBS was demonstrated in the control group when CAD bonded to resin cement without disinfection (18.22±1.14 MPa). Likewise, the lowest SBS values were unveiled by CAD disinfection with O₃ (12.44±1.36 MPa). Similarly, CAD when disinfected with RB (16.25±1.01 MPa) and Ti-sapphire laser (16.25±1.22 MPa) bonded to resin cement exhibited comparable bond results (p>0.05).

CONCLUSION

Caries affected dentin when treated with etch and rinse technique without the use of disinfectant displayed the highest SBS. However, it was seen that utilization of various disinfectants has altered the adhesion capacity or bonding efficacy of caries-affected dentin.

Effect of Fluoride Treatment on the Acid Resistance of Hydroxyapatite

The etching behavior of polycrystalline synthetic hydroxyapatite samples has been evaluated to explore the protective impact of fluoride on a tooth-like model system. Etching rates before and after fluoridation with a NaF solution at pH 6 were determined by atomic force microscopy. Despite a very low F concentration of ca. 0.2 atom % in the hydroxyapatite surface, a very strong effect on the acid resistance can be observed. Depending on the crystal orientation, etching in a NaAc buffer at pH 4.5 was completely inhibited for at least 5 min. The major part of the surface withstood etching even for more than 23 min. These results give new insights into how the amount of incorporated fluoride in hydroxyapatite correlates with its protective impact.

Arresting Dentine Caries with Silver Diamine Fluoride: What’s Behind It?

Unlike other fluoride-based caries preventive agents, silver diamine fluoride (SDF) can simultaneously prevent and arrest coronal and root dentine caries. The profound clinical success of SDF has drawn many clinicians and researchers to study the mechanism of SDF in arresting dentine caries. This critical review discusses how silver and fluoride contribute to caries arrest, in terms of their effects on bacteria as well as on the mineral and organic content of dentine. Silver interacts with bacterial cell membrane and bacterial enzymes, which can inhibit bacterial growth. Silver can also dope into hydroxyapatite and have an antibacterial effect on silver-doped hydroxyapatite. Furthermore, silver is also a strong inhibitor of cathepsins and inhibits dentine collagen degradation. Early studies proposed that silver hardened caries lesions by forming silver phosphate. However, recent studies found that little silver phosphate remained on the arrested dentine lesion. The principal silver precipitate was silver chloride, which could not contribute to the significant hardening of the arrested lesions. On the other hand, fluoride enhances mineral formation by forming fluorohydroxyapatite with reduced solubility. A significant increase in microhardness occurs with an elevated level of calcium and phosphorus but not silver on the surface layer of the arrested dentine caries lesion following SDF treatment. Fluoride also inhibits matrix metalloproteinases activities and therefore inhibits dentine collagen degradation. The combination of silver and fluoride in an alkaline solution has a synergistic effect in arresting dentine caries. The alkaline property of SDF provides an unfavorable environment for collagen enzyme activation. Understanding the mechanisms of SDF in arresting dentine caries helps clinicians to develop appropriate protocols for the use of SDF in clinical care.

Measuring the Remineralization Potential of Different Agents with Quantitative Light-Induced Fluorescence Digital Biluminator

Background

The aim of this study was to investigate the effectiveness of different remineralization agents by quantitative light-induced fluorescence digital Biluminator™ (QLF-D).

Methods

Artificial caries lesions were created, and the teeth were divided according to the tested materials: (i) distilled water, (ii) acidulated phosphate fluoride (APF), (iii) Curodont Repair (CR), (iv) ammonium hexafluorosilicate (SiF) and (v) ammonium hexafluorosilicate plus cetylpyridinium chloride (SiF + CPC). After treatment procedures, each of the samples was placed in artificial saliva. After demineralization and 1 and 4 weeks of remineralization procedures, fluorescence loss and lesion areas were measured with QLF-D. Data were statistically analyzed (α = 0.05).

Results

The fluorescence values of the demineralized enamel specimens treated with the various agents differed significantly compared with pretreatment values for both 1 and 4 weeks (p<0.05). At 4 weeks, the highest fluorescence gain was calculated in the CR, APF and SiF groups compared with the control (p<0.05).

Conclusions

APF, SiF and CR groups yielded greater remineralization ability than SiF + CPC and control groups.

Effect of silver diamine fluoride and ammonium hexafluorosilicate applications with and without Er:YAG laser irradiation on the microtensile bond strength in sound and caries-affected dentin

BACKGROUND AND OBJECTIVE

Cariostatic and preventive agents are applied to create caries-resistant dentin surfaces and may affect subsequent resin bonding. The aim of this study was to investigate the effect of different agents with and without Er:YAG laser irradiation on the microtensile bond strength (µTBS) of resin composite to sound dentin (SD) and caries-affected dentin (CAD), and to assess the morphological and chemical changes in the specimens.

MATERIALS AND METHODS

Ninety-six extracted molar teeth were divided into a control group (deionized water) and two experimental groups (ammonium hexafluorosilicate [SiF], silver diamine fluoride [SDF]), that subdivided according to different conditions (SD, CAD, SD+laser irradiation, CAD+laser irradiation). After treatment procedures, the teeth were restored and the µTBS was tested with a universal testing machine. Morover, 144 teeth were prepared and after treatment modalities; morphological changes of the surface were investigated and elemental analyses were performed using scanning electron microscope/energy dispersive spectroscopy (SEM-EDS). The data were analyzed using Kruskal-Wallis and Mann-Whitney U tests.

RESULTS

SDF and SiF applications reduced the µTBS values in both the SD and CAD subgroups (P < 0.05). Laser irradiation increased the µTBS values in the SiF group and the values were adversely affected in the SDF group (P < 0.05). Fluoride content of the specimens increased in all of the treatment groups, compared with the control group. Silver content was detected only in the SDF group, and silicon was detected only in the SiF group.

CONCLUSIONS

The µTBS values of resin composite, surface morphology and chemical characteristics of dentin were affected by the material type, dentin condition and laser irradiation and the use of SiF and SDF solutions under the resin restorations do not seem appropriate.

Effect on enamel shear bond strength of adding microsilver and nanosilver particles to the primer of an orthodontic adhesive

Background

The objective of this study was to determine whether the addition of microsilver or nanosilver particles to an orthodontic primer affects shear bond strength (SBS) and bracket/adhesive failure.

Methods

Bovine incisors were randomly divided into six groups with 16 specimens in each: In group 1 (control), brackets were bonded with Transbond™ XT primer. In the experimental groups, microsilver (groups 2 and 3) and nanosilver (groups 4–6) particles of different sizes were added to Transbond XT primer and light cured for 15 seconds [group 2: 0.1% (w/w) microsilver particle size 3.5–18 μm; group 3: 0.3% (w/w) microsilver particle size 3.5–18 μm; group 4: 0.11% (w/w) nanosilver particle size 12.6–18.5 nm; group 5: 0.18% (w/w) nanosilver particle size 12.6–18.5 nm; group 6: 0.33% (w/w) nanosilver particle size 12.6–18.5 nm]. Thereafter, brackets were bonded by light curing the adhesive for 20 seconds. After 24 hours of storage in distilled water at 37°C, SBS was measured with a Zwicki 1120 testing machine. The adhesive remnant index and the prevalence of silver spots on the specimen surface were determined under 10× magnification. Statistical two-way analysis of variance was performed to compare SBS, and a chi-square test was used to compare ARI scores and the prevalence of silver spots.

Results

No significant differences in SBS (control: 16.59 ± 6.82 MPa; group 2: 20.6 ± 4.19 MPa; group 3: 16.98 ± 4.84 MPa; group 4: 17.15 ± 5.92 MPa; group 5: 20.09 ± 3.35 MPa; group 6: 16.44 ± 4.51 MPa; p > 0.665) and ARI scores (p = 0.901) were found between the control group and any experimental group. Only experimental groups with nanosilver particles revealed statistically more silver spots on the remaining adhesive.

Conclusions

Addition of small concentrations of microsilver or nanosilver particles affects neither SBS nor ARI scores. Addition of nanosilver particles results in silver spots in the remaining primer visible under 10× magnification. Further studies are needed to investigate the anti-caries potential and clinical performance of conventional orthodontic primer with incorporated nanosilver or microsilver particles.

Effects of ammonium hexafluorosilicate application on demineralized enamel and dentin of primary teeth

Silver diamine fluoride (Ag(NH(3))(2)F) arrests caries but stains teeth black. To overcome this drawback, we applied ammonium hexafluorosilicate (AHF; (NH(4))(2)SiF(6)) and observed changes in the color and structure of demineralized enamel and dentin of extracted primary teeth. Enamel and dentin were demineralized in 10% EDTA solution for 90 s followed by 35% phosphoric acid gel for 60 s, then soaked in AHF solution for 60 s. Before analysis by scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS), enamel and dentin were demineralized in 10% EDTA for 90 s. Teeth were divided into 4 groups according to AHF application and artificial saliva immersion status and then examined. The data were statistically analyzed using one-way ANOVA and Fisher's PLSD test at a significance level of P < 0.05. AHF treatment did not cause visible discoloration. Enamel prisms and dental tubules appeared by demineralization were covered with precipitates by AHF application. A sphere-filled membranous structure was observed in the saliva immersion groups. EDS analysis showed that AHF application had no effect on enamel; however, F% and Ca/P ratio were significantly higher on dentin surfaces after AHF application without artificial saliva immersion. Further study on arresting caries treatment is required.

Cytotoxicity of ammonium hexafluorosilicate on human gingival fibroblasts

Ammonium hexafluorosilicate (SiF), which is claimed to significantly improve occlusion of dentinal tubules, was proposed as a novel desensitizer for dentine hypersensitivity (DH). However, the cytotoxicity of SiF on oral cells is lacking. The purpose of this study was to investigate the cytotoxicity of SiF on human gingival fibroblasts (hGFs) under different dosages (0.001%, 0.01%, 0.1%, and 1%) and treatment durations (1, 5, 10, and 30min). Cell proliferation, mitochondrial membrane potential (MMP) and cell cycle were tested by MTT assay, JC-1 staining and flow cytometry, respectively. Glutathione (GSH) depletion was analyzed to further investigate the underlying mechanism of SiF-induced cytotoxicity. MTT assay showed that there was significantly lower number of viable cells when the hGFs were treated with 0.01% (10min), 0.1% (10 and 30min) and 1% (5, 10, and 30min) SiF than the control group (p<0.05). MMP decreased and GSH depletion increased dramatically along with higher concentrations (0.1% and 1% SiF) and prolonged times (10 and 30min). DNA synthesis [S (%)] of cells treated with 0.1% and 1% SiF (5, 10, and 30min) was significantly lower than the control group (p<0.05). Our results indicate exposure to up to 0.01% SiF for less than 5min causes low or no cytotoxicity in vitro.

Effect of ammonium hexafluorosilicate application for arresting caries treatment on demineralized primary tooth enamel

Ammonium hexafluorosilicate (AHF) has been applied to arrest caries without discoloration. The purpose of this study was to observe structural and elemental changes of demineralized and AHF applied primary tooth enamel. Enamel from the labial surface of 20 primary canines was divided into an unground side and ground side at the center of the tooth, and demineralized with 35% phosphoric acid for 6 min. The teeth were divided into 4 groups according to a 3-min application of AHF and 1 week of soaking in artificial saliva, as follows: group A (neither AHF nor saliva), group B (only saliva), group C (only AHF), and group D (AHF and saliva), and then subdivided according to whether the enamel was ground or unground. Specimens were analyzed with scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). The data were statistically analyzed using ANOVA and Fisher's PLSD test at α = 0.05. In groups A and B, prism structures were seen, however, in groups C and D, enamel surfaces were covered with spherical particles. Ca/P ratio was significantly higher in groups C and D than in groups A and B. There was no significant difference between ground and unground enamel in the content of any element. The values for F, Na, Mg and Si persents and Ca/P ratio were significantly higher for the enamel surface than for points 10-30 µm beneath the surface. Results of this study suggest the possibility that AHF treatment arrests caries, although further study will be required to confirm this result.

Reinforcement of bond strength of self-etching orthodontic adhesive

OBJECTIVE

To determine the reinforcement of bond strength of a self-etching system by applying a pretreatment agent.

MATERIALS AND METHODS

Sixty extracted human premolars were used in this study. The enamel surfaces were treated with four pretreatment agents-phosphoric acid, polyacrylic acid, citric acid, and ammonium hexafluorosilicate (SiF)-and were examined under a scanning electron microscope. Afterward, orthodontic brackets were bonded with a self-etching adhesive system (n  =  10 for each agent), and shear bond strength was measured through a debonding process. The adhesive remnant index (ARI) was also assessed.

RESULTS

Enamel surfaces treated with polyacrylic acid seemed almost the same as intact enamel. Treatment with SiF induced slight shallow depressions compared with the intact enamel. On the other hand, enamel surfaces treated with citric acid and phosphoric acid showed severe etching patterns. All pretreatments increased the bond strength, but SiF-treated specimens revealed the greatest strength (12.201 ± 1.048 MPa), followed by polyacrylic acid (12.030 ± 2.103 MPa). The control group with no pretreatment showed the least strength (9.078 ± 1.678 MPa). All pretreatments increased ARI score compared with the control group.

CONCLUSIONS

Surface conditioning before bracket adhesion could reinforce the bond strength of the self-etching adhesive system, resulting in a more reliable bonding system.

Silver diamine fluoride: a caries "silver-fluoride bullet"

The antimicrobial use of silver compounds pivots on the 100-year-old application of silver nitrate, silver foil, and silver sutures for the prevention and treatment of ocular, surgical, and dental infections. Ag(+) kills pathogenic organisms at concentrations of <50 ppm, and current/potential anti-infective applications include: acute burn coverings, catheter linings, water purification systems, hospital gowns, and caries prevention. To distill the current best evidence relative to caries, this systematic review asked: Will silver diamine fluoride (SDF) more effectively prevent caries than fluoride varnish? A five-database search, reference review, and hand search identified 99 human clinical trials in three languages published between 1966 and 2006. Dual review for controlled clinical trials with the patient as the unit of observation, and excluding cross-sectional, animal, in vitro studies, and opinions, identified 2 studies meeting the inclusion criteria. The trials indicated that SDF's lowest prevented fractions for caries arrest and caries prevention were 96.1% and 70.3%, respectively. In contrast, fluoride varnish's highest prevented fractions for caries arrest and caries prevention were 21.3% and 55.7%, respectively. Similarly, SDF's highest numbers needed to treat for caries arrest and caries prevention were 0.8 (95% CI=0.5-1.0) and 0.9 (95% CI=0.4-1.1), respectively. For fluoride varnish, the lowest numbers needed to treat for caries arrest and prevention were 3.7 (95% CI=3.4-3.9) and 1.1 (95% CI=0.7-1.4), respectively. Adverse events were monitored, with no significant differences between control and experimental groups. These promising results suggest that SDF is more effective than fluoride varnish, and may be a valuable caries-preventive intervention. As well, the availability of a safe, effective, efficient, and equitable caries-preventive agent appears to meet the criteria of both the WHO Millennium Goals and the US Institute of Medicine's criteria for 21st century medical care.

Ammonium hexafluorosilicate elicits calcium phosphate precipitation and shows continuous dentin tubule occlusion

Diamine silver fluoride [AgF: (NH(3))(2)AgF] has been used clinically in Japan, as it reduces dental caries and dentin hypersensitivity. However, AgF stains the teeth black due to silver precipitation. To overcome this drawback, the authors prepared ammonium hexafluorosilicate [SiF: (NH(4))(2)SiF(6)], which does not stain the teeth, and SiF occluded open dentin tubules completely with silica-calcium phosphate precipitate.

OBJECTIVES

The aim of this study was to evaluate the duration of dentin tubule occlusion after SiF treatment in a simulated oral environment.

METHODS

To simulate dentin tubules subject to dentin hypersensitivity, dentin disks were treated with EDTA for 2 min. The disks were treated with 0.476 mol/L SiF for 3 min, and then the disks were immersed in synthetic saliva, which was regularly replenished to maintain its ionic concentration, for up to 7 days. The occluding ability of the dentin tubules was evaluated using scanning electron microscopy (SEM), and the hydraulic conductance was measured following Pashley's method at regular intervals.

RESULTS

SEM photographs demonstrated that dentin tubules were occluded homogeneously and completely with the precipitate at 7 days after treatment with SiF. In addition, newly formed calcium phosphate precipitate was present at the dentin surface. The dentin permeability showed a consistently low value throughout the experimental period. The values immediately after SiF treatment and 7 days after immersion were 11.9+/-3.7% and 7.9+/-2.9%, respectively.

SIGNIFICANCE

Ammonium hexafluorosilicate is useful for the treatment of dentin hypersensitivity, since ammonium hexafluorosilicate induced calcium phosphate precipitation from the saliva; therefore, it has a continuous effect on dentin tubules occlusion under a simulated oral environment.