Effects of hexafluorosilicate on the precipitate composition and dentine tubule occlusion by calcium phosphate

Crystal structure of CaSiF6·2H2O(mP2) and reevaluation of the SiIV-F bond-valence parameter R0

The structure of a second polymorph of CaSiF6·2H2O [calcium hexafluorido-silicate dihydrate; space group P2/c (No. 13), Pearson symbol mP2] was elucidated by single-crystal X-ray diffraction. It arose as an unexpected product when soda-lime glass was attacked by HF. Its crystal structure consists of infinite ∞ 2[Ca(H2O)2/1(SiF6)4/4] layers oriented parallel to the bc-crystallographic plane, a unique motif among structurally characterized hydrated hexa-fluorido-silicates. The crystal structure also exhibits inter- and intra-layer hydrogen bonds, with the inter-layer O-H⋯O hydrogen bonds involving a disordered hydrogen atom. The large deviation between the calculated bond-valence sum for Si and the expected value prompted a redetermination of the empirical SiIV-F bond-valence parameter R 0. Based on a data set of 42 high-quality crystal structures containing 49 independent SiIV coordination environments, a revised value of 1.534 Å was derived for R 0.

Duration of dentin tubule occlusion by the calcium phosphate precipitation method: An in vivo study in beagle dogs

The aim of the present study was to assess the duration of dentin tubule occlusion by the calcium phosphate precipitation (CPP) method in the vital teeth of beagle dogs. Vital teeth were treated using the CPP method, potassium oxalate, or a bonding agent (Liner bond II) after cavity preparation and acid etching. The dentin tubules of all groups, except for the bonding agent, opened more widely with time in the absence of plaque control. Dentin tubules treated with the CPP method were open and no precipitate remained in the absence of plaque control. Differences were observed in dentin tubule occlusion when plaque control was achieved by daily tooth brushing. The majority of dentin tubules were occluded with an apatitic precipitate seven days after the CPP method with plaque control. The present results demonstrated that the CPP method is useful with proper plaque control.

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.

Evaluation of post-treatment solutions for clinical use with the calcium phosphate precipitation method

OBJECTIVE

We have proposed a calcium phosphate precipitation (CPP) method that occludes dentine tubules with apatitic minerals for the treatment of dentine hypersensitivity. The current CPP method uses 1 mol/l NaOH as the post-treatment solution. However, its high pH is not desirable for clinical use. The aim of this study was to evaluate several solutions, especially buffer solutions, as post-treatment solutions for the CPP method.

METHODS

The CPP solution was mixed with several post-treatment solutions at various mixing ratios in test tubes. The precipitates were collected, and freeze-dried in a vacuum. Their weights were measured to evaluate the feasibility of buffer solution for the post-treatment solutions. Among the solutions, we selected one buffer solution and have done further evaluation using human dentine disks. The degree of occlusion of dentine tubules was evaluated by scanning electron microscopic observation and measurement of dentine permeability. Also, the composition of the precipitate was analyzed using energy-dispersive X-ray microanalysis and powder X-ray diffraction.

RESULTS

Among the solutions, 1 mol/l NaHCO3 gave sufficient amounts of precipitate at a relatively mild pH, and thus was considered to be a good candidate for a post-treatment solution. Scanning electron microscopic observation showed that dentine tubules were occluded with the precipitate to a depth of approximately 10 microns from the surface when the CPP treatment was done twice, and dentine permeability was reduced to 98.8%. The precipitate was dicalcium phosphate dihydrate (DCPD; CaHPO4-2H2O) when the post-treatment solution was free of NaF. In contrast, the precipitate was an apatitic mineral with CaF2 as a by-product when the post-treatment solution contained NaF.

CONCLUSIONS

We concluded that 1 mol/l NaHCO3 containing 0.3 mol/l NaF would be suitable as the post-treatment solution for the CPP method as it has a relatively mild pH and occludes dentinal tubules well.