Abstract
Ammonium hexafluorosilicate [SiF: (NH 4 ) 2 SiF 6 ] was prepared in order to overcome the tooth discoloration caused by diamine silver fluoride [AgF: (NH 3 ) 2 AgF] application. We employed a single concentration of SiF solution in our previous study; therefore, it is still unclear how the concentration of SiF solution affects the occlusion of dentin tubules and composition of the precipitate.
Objective
The aim of this study was to evaluate the effects of changing the concentration of SiF on its clinical use as a dentin hypersensitivity treatment.
Methods
To simulate dentin tubules subject to dentin hypersensitivity, dentin disks were treated with EDTA for 2 min. Then, the disks were treated with several concentrations of SiF solution (from 100 to 19,400 ppm) for 3 min. The occlusion of dentin tubules was evaluated using scanning electron microscopy (SEM), and the composition of the precipitate formed in the tubules after SiF treatment was assessed using energy dispersive X-ray analysis (EDXA).
Results
SEM photographs demonstrated that dentin tubules after treatment with SiF were occluded homogeneously and fully regardless of the concentration of SiF solution. The Ca/P molar ratio of the precipitate formed in dentin tubules after SiF treatment was increased with the concentration of SiF solution.
Significance
It was concluded that the capacity to occlude dentin tubules was the same regardless of the concentration of SiF solution. However, the composition of the precipitate formed in the tubules was dependent on the concentration of SiF solution.
1
Introduction
Fluoride is effective for the prevention of dental caries, and sometimes it has also been used for the treatment of dentin hypersensitivity. The representative fluoride solution applicable for both treatments is diamine silver fluoride [AgF: (NH 3 ) 2 AgF] (Saforide ® , Beebland Medico Dental Inc., Osaka, Japan), which is widely used in dental clinics in Japan . However, AgF causes tooth discoloration, especially problematic with regard to permanent teeth. Ammonium hexafluorosilicate [SiF: (NH 4 ) 2 SiF 6 ] was subsequently prepared in order to overcome tooth discoloration caused by treatment with AgF . Acid resistance was significantly increased in both enamel and dentin after SiF treatment, similar to that following AgF treatment, being much more effective than NaF or acidulated phosphate fluoride (APF) . Also, open dentin tubules within simulated hypersensitive teeth were completely occluded with a silica–calcium phosphate precipitate to the depth of approximately 20 μm from the dentin surface immediately after SiF treatment, and induced apatitic precipitation on the dentin surface in the simulated oral environment when the dentin disk was immersed in synthetic saliva. Therefore, SiF solution shows a strong potential for use in dentin hypersensitivity treatment . The same concentration of SiF solution (9000 ppm) has been used throughout our study to compare its fluoridation effect with that of acidulated phosphate fluoride. Therefore, the effects of SiF concentration on the occlusion of dentin tubules and composition of the precipitate forming within tubules have not been studied up to now. The aim of this study was, therefore, to evaluate the effects of changing the SiF concentration and to identify an optimal concentration prior to its clinical use as a treatment for dentin hypersensitivity.
2
Materials and methods
2.1
Preparation of SiF solution
Several concentrations of SiF solution (from 100 to 19,400 ppm) were prepared from reagent grade chemicals (Kanto Chemical Co., Inc., Tokyo, Japan) following a previous study protocol . Then, the pH of each SiF solution was measured at room temperature with a pH meter (DKK·TOA Co., Tokyo, Japan).
2.2
Dentin disk treatment
Dentin disks were obtained from healthy adults with informed consent, through caries-free human molars extracted for periodontal reasons at the Tokushima University Hospital. Each tooth was sectioned horizontally below the cementoenamel junction. To prepare the disks from the middle of the coronal dentin, enamel was removed with a high-speed, water-cooled handpiece, followed by sectioning with a low-speed water-cooled diamond saw (Buehler Ltd., Evanston, IL, USA) to a thickness of approximately 1.5 and 0.5 mm for SEM observation and dentin permeability measurement, respectively . To remove the smear layer and prepare open dentin tubules to simulate dentin hypersensitivity, the disks were immersed in 0.5 mol/L EDTA (pH = 7.4) for 2 min . The disks were then washed with distilled water for 1 min and dried using a three-way syringe. These specimens served as a control. Several SiF solutions at different concentrations were applied to each pretreated dentin disk with a cotton swab for 3 min. After SiF treatment, the tooth was washed with distilled water for 1 min.
2.3
SEM observation
The occlusion of dentin tubules due to SiF treatment was evaluated through scanning electron microscope observation (Hitachi Co., Tokyo, Japan). The specimens obtained following the above procedures were dried with a critical point dryer (Hitachi Co., Tokyo, Japan). After the specimens were coated with gold, the surface and fractured surface were observed using SEM. Occlusion was evaluated in five specimens for each treatment concentration.
2.4
Dentin permeability
The ability of SiF to occlude dentin tubules was also evaluated from the dentin permeability measurements, made using an apparatus described by Pashley and Galloway . The rate of fluid flow through the dentin disk was measured with this apparatus. Fluid flow was measured by following the progress of an air bubble in a micropipette at a pressure of 98 kPa. Dentin permeability was measured after EDTA treatment (Control), just after SiF treatment. Dentin permeability was presented as a percentage value against the control (before SiF treatment) specimen. This permeability was taken as an averaged value from 10 specimens.
2.5
EDXA analysis
EDXA apparatus attached to a transmission electron microscope (H-500; Hitachi Co., Tokyo, Japan) was used to analyze the precipitate. The specimens after being treated with several concentrations of SiF solution were mounted on carbon holders and then carbon-coated. The carbon-coated specimens were analyzed with an accelerating voltage of 10 kV, a spot size of 100 nm, and a counting time of 100 s. The Ca/P molar ratio obtained with EDXA was the average value of ten specimens.
2.6
Statistical analysis
For statistical analysis, one-way factorial ANOVA and Fisher’s PLSD method, used as a post hoc test, were performed using the program “Stat View 4.02” (Abacus Concepts Inc., Berkeley, CA, USA). p -Values < 0.05 were considered to indicate significant differences.
2
Materials and methods
2.1
Preparation of SiF solution
Several concentrations of SiF solution (from 100 to 19,400 ppm) were prepared from reagent grade chemicals (Kanto Chemical Co., Inc., Tokyo, Japan) following a previous study protocol . Then, the pH of each SiF solution was measured at room temperature with a pH meter (DKK·TOA Co., Tokyo, Japan).
2.2
Dentin disk treatment
Dentin disks were obtained from healthy adults with informed consent, through caries-free human molars extracted for periodontal reasons at the Tokushima University Hospital. Each tooth was sectioned horizontally below the cementoenamel junction. To prepare the disks from the middle of the coronal dentin, enamel was removed with a high-speed, water-cooled handpiece, followed by sectioning with a low-speed water-cooled diamond saw (Buehler Ltd., Evanston, IL, USA) to a thickness of approximately 1.5 and 0.5 mm for SEM observation and dentin permeability measurement, respectively . To remove the smear layer and prepare open dentin tubules to simulate dentin hypersensitivity, the disks were immersed in 0.5 mol/L EDTA (pH = 7.4) for 2 min . The disks were then washed with distilled water for 1 min and dried using a three-way syringe. These specimens served as a control. Several SiF solutions at different concentrations were applied to each pretreated dentin disk with a cotton swab for 3 min. After SiF treatment, the tooth was washed with distilled water for 1 min.
2.3
SEM observation
The occlusion of dentin tubules due to SiF treatment was evaluated through scanning electron microscope observation (Hitachi Co., Tokyo, Japan). The specimens obtained following the above procedures were dried with a critical point dryer (Hitachi Co., Tokyo, Japan). After the specimens were coated with gold, the surface and fractured surface were observed using SEM. Occlusion was evaluated in five specimens for each treatment concentration.
2.4
Dentin permeability
The ability of SiF to occlude dentin tubules was also evaluated from the dentin permeability measurements, made using an apparatus described by Pashley and Galloway . The rate of fluid flow through the dentin disk was measured with this apparatus. Fluid flow was measured by following the progress of an air bubble in a micropipette at a pressure of 98 kPa. Dentin permeability was measured after EDTA treatment (Control), just after SiF treatment. Dentin permeability was presented as a percentage value against the control (before SiF treatment) specimen. This permeability was taken as an averaged value from 10 specimens.
2.5
EDXA analysis
EDXA apparatus attached to a transmission electron microscope (H-500; Hitachi Co., Tokyo, Japan) was used to analyze the precipitate. The specimens after being treated with several concentrations of SiF solution were mounted on carbon holders and then carbon-coated. The carbon-coated specimens were analyzed with an accelerating voltage of 10 kV, a spot size of 100 nm, and a counting time of 100 s. The Ca/P molar ratio obtained with EDXA was the average value of ten specimens.
2.6
Statistical analysis
For statistical analysis, one-way factorial ANOVA and Fisher’s PLSD method, used as a post hoc test, were performed using the program “Stat View 4.02” (Abacus Concepts Inc., Berkeley, CA, USA). p -Values < 0.05 were considered to indicate significant differences.
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