Ammonium hexafluorosilicate increased acid resistance of bovine enamel and dentine.

Although diamine silver fluoride (AgF: (NH3)2AgF) stains teeth black, it is known as a very effective agent to prevent the dental caries progress. In order to find another fluoride that has a similar anticariogenic effect without changing tooth color, we prepared ammonium hexafluorosilicate (SiF: (NH4)2SiF6), in which the silver of AgF is replaced with silicon. In this study, the anticariogenic effect of SiF was evaluated using bovine teeth. Fluoride solutions, SiF, AgF, acidulated phosphate fluoride (APF), and sodium fluoride (NaF), were applied to bovine enamel and dentine blocks, and the depth of demineralization was measured after exposure to a demineralizing solution for 24 h. Also, fluoride was applied to a simulated dentine caries specimen to evaluate the caries progress-preventing ability. For the dentine specimens, mineral loss (Delta Z) was also measured with microradiography. We found that SiF treated enamel showed better acid resistance than specimens treated with NaF or APF. AgF treated enamel also showed similar acid resistance, but was stained black. SiF and AgF treated caries-affected dentine showed reduced demineralization when exposed to a demineralization solution for 24 h. Mineral loss (Delta Z) was reduced to 85% and 75%, respectively. Although the acid resistance of the SiF treated teeth was inferior to that of the AgF treated teeth, we consider that SiF has good potential as anticariogenic agent, since it increased acid resistance without changing tooth color.

Effects of plaque control on the patency and occlusion of dentine tubules in situ.

To elucidate the nature of dentine hypersensitivity, the effects of plaque control on the patency and occlusion of dentinal tubules were investigated systematically in situ using human dentine slabs embedded in partial dentures. The dentine slabs were divided into three groups. In group I, the dentine slabs were kept in an oral cavity without plaque control. In group II, plaque was removed mechanically by brushing. Plaque control was carried out chemically using chlorhexidine in group III. After being kept in the oral cavities for 1, 2 and 3 weeks, the slabs were removed from the partial denture, followed by SEM observation to determine the morphological changes of the dentinal tubules. When no attempt was made to remove plaque, the diameter of tubule orifices increased to 390% of the original values within 3 weeks. In contrast, dentinal tubules were found to be occluded, i.e. the tubule orifices became <20% of the original value within 1 week when plaque control efforts were made, using either method of plaque control. We conclude that plaque control plays one of the key roles in the patency versus occlusion of dentinal tubules, and thus in the aetiology and natural reparative process of dentine hypersensitivity.

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.

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

OBJECTIVES: To improve the calcium phosphate precipitation (CPP) method for the occlusion of dentine tubules with calcium phosphate, the addition of calcium hexafluorosilicate (CaSiF6) to CPP solution was evaluated in vitro with respect to its occluding capacity and the composition of the precipitate. METHODS: The occlusion of dentine tubules was evaluated by SEM observations and by measurements of dentine permeability. The composition of the precipitate was determined by measuring the calcium to phosphorus (Ca/P) ratio of the precipitate in dentine tubules by energy dispersive X-ray spectroscopy (EDS). RESULTS: The addition of CaSiF6 to the CPP solution resulted in an increase of the Ca/P ratio in the precipitate not only on the dentine surface but also inside the dentine tubules; indicating that the precipitate became more apatitic in nature. The addition of CaSiF6 had no effect on occluding capacity in terms of measurements of dentine permeability or SEM observations. Dentine permeability decreased to approximately 4% of pretreatment values and the dentine tubules were occluded for approximately 10-15 microns from the dentine surface. CONCLUSION: It is concluded that the addition of CaSiF6 to CPP solution was desirable, since it provided a more apatitic precipitate in the dentine tubules, not only on the dentine surface but also inside the tubules, and there were no drawbacks with respect to its occluding capacity.

Morphological characterization of tube-like structures in hypersensitive human radicular dentine.

OBJECTIVES: The objective of this work was to determine if there were differences in the distribution of tube-like structures within the tubules of biopsies from hypersensitive versus non-sensitive human cervical radicular dentine. METHOD: Ten pairs of dentine were made from the exposed sensitive and non-sensitive radicular dentine of nine adult patients complaining of dentine sensitivity. The biopsies were made with a small hollow diamond bur. The specimens were submitted to HCl-collagenase treatment to partially digest the surface to permit visualization of subsurface structures. Half of the specimens were embedded in resin to facilitate longitudinal sectioning, and the other half were processed with embedding for SEM and EDS observation. RESULTS: Biopsies from hypersensitive regions exhibited hollow, tube-like structures within the lumina of dentinal tubules in 75.8 +/- 9.4%) ( mean +/- S.D.) of the tubules. In biopsies of non-sensitive areas of the same teeth, these tube-like structures were only seen in 20.4 +/- 8.5% of the tubules. In specimens that were embedded prior to treatment with HCl-collagenase, resin tags penetrated many of the tubules from hypersensitive dentine but few of the tubules from non-sensitive dentine. CONCLUSION: It is speculated that tube-like structures found in hypersensitive dentine play a role in maintaining the patency of the tubules which may prevent physicochemical processes from spontaneously occluding the tubules, thereby maintaining dentine sensitivity.

Duration of dentinal tubule occlusion formed by calcium phosphate precipitation method: in vitro evaluation using synthetic saliva.

The use of a calcium phosphate precipitation method occluded dentin tubules with apatitic mineral and, thus, showed good potential for the treatment of dentin hypersensitivity. The aim of this study was to elucidate the occluding behavior of the precipitate in the oral environment. Dentin disks treated by the calcium phosphate precipitation method, and disks treated with potassium oxalate, NaF, and SrCl2 solutions, were immersed in synthetic saliva, which was regularly replenished so that ionic concentration would be maintained. Treatment of dentin disks by the calcium phosphate precipitation method immediately reduced dentin permeability to 6 +/- 8%. When the disk was immersed in synthetic saliva, dentin permeability remained low, even seven days after immersion. Scanning electron microscopic observation showed no distinct boundary line between the precipitate and intertubular dentin; this indicated further mineralization on the precipitate. Potassium oxalate treatment also reduced the dentin permeability to 8 +/- 3%. However, the dentin permeability gradually but steadily increased with immersion time, reaching 39 +/- 14% at seven days. To elucidate the mechanism underlying dentin permeability changes in synthetic saliva, we immersed the precipitates, i.e., apatitic mineral and calcium oxalate, in a fixed volume of synthetic saliva. When calcium oxalate was immersed in synthetic saliva, there was a large concentration of oxalate ions, indicating dissolution of the calcium oxalate; this phenomenon was ascribed to the increase in dentin permeability. In contrast, calcium and phosphate ions decreased when apatitic powder, the precipitate formed by the calcium phosphate precipitation method, was immersed in synthetic salvia. The decrease in the calcium and phosphate ions in synthetic saliva indicated further precipitation of calcium phosphate on the apatitc precipitate.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of fluoride on the calcium phosphate precipitation method for dentinal tubule occlusion.

Use of the calcium phosphate precipitation (CPP) method makes possible the occlusion of dentinal tubules to approximately 10 to 15 microns from the dentinal surface, and thus shows good potential for the treatment of dentin hypersensitivity. The precipitate formed in the dentinal tubules by the CPP method is, however, not apatite [HAP; Ca10(PO4)6(OH)2], a component of tooth and bone, but dicalcium phosphate dihydrate (DCPD; CaHPO4.2H2O). Since fluoride enhances the conversion of DCPD to HAP, we evaluated the effects of fluoride on the texture of the precipitate formed by the CPP method and on its capacity to occlude dentinal tubules in this in vitro study. CPP solution (1.0 mol/L CaHPO4.2H2O dissolved in 2.0 mol/L H3PO4) was applied to a dentin disk and was subsequently neutralized with a post-treatment solution (1 mol/L NaOH, from 0 to 0.1 mol/L NaF). Scanning electron microscopy revealed that the precipitate occluded dentinal tubules to a depth of approximately 10 to 15 microns from the dentinal surface, regardless of the NaF concentration (from 0 to 0.1 mol/L) in the post-treatment solution. Also, dentin permeability was reduced to 15% by the CPP treatment regardless of the NaF concentration. The Ca/P molar ratio of the precipitate, measured by x-ray micro-analysis, was higher (1.25 +/- 0.04) in the presence of NaF than in its absence (1.03 +/- 0.01). For further identification of the precipitate formed in the dentinal tubules, the same procedure was used in glass tubes (diameter, 1 mm), so that a larger amount of precipitate would be obtained.(ABSTRACT TRUNCATED AT 250 WORDS)

Occlusion of dentinal tubules with calcium phosphate using acidic calcium phosphate solution followed by neutralization.

The occlusion of dentinal tubules with calcium phosphate, by a calcium phosphate precipitation method (CPP method), was investigated in vitro for evaluation of the potential value of this method for the treatment of dentin hypersensitivity. The method consists of treating the dentinal surface with a CPP solution, i.e., an acidic solution that contains both calcium and phosphate, followed by neutralization with basic post-treatment solution. The CPP solutions used in this study ([Ca] = 0.2 - 1.0 mol/L, [PO4] = 0.2 - 4.0 mol/L) were prepared by dissolving Ca(OH)2 or CaHPO4 x 2H2O in H3PO4 or HCl, and 1 mol/L NaOH solution was used for the post-treatment solution. Sections of human dentin disks treated by the CPP method were observed by scanning electron microscopy, and the precipitate in the dentinal tubules was subjected to x-ray micro-analysis. After treatment by the CPP method, dentinal tubules were occluded to a distance of approximately 15 microns from the surface, and the precipitate showed a Ca/P molar ratio of 1.03 +/- 0.01 To obtain a larger amount of precipitated mineral for further analysis, we used the same procedure with glass tubes (inside diameter, 1 mm). Powder x-ray diffraction analysis and FT-IR measurement revealed that the precipitate was dicalcium phosphate dihydrate (CaHPO4 x 2H2O). The instant precipitation of calcium phosphate mineral in the dentinal tubules demonstrated the potential value of the CPP method for the occlusion of dentinal tubules, this occlusion may be useful for the treatment of dentin hypersensitivity.