Yoshiharu Mukai

Remineralization of Advanced Root Dentin Lesions in vitro

The possibility for remineralization of advanced root dentin lesions was investigated in vitro. Lesions were produced in acidic buffer solution with 0.1 and 0.5 ppm fluoride, for 3 and 5 weeks, respectively, using a single-section model. Next, the sections were immersed in a remineralization solution containing 0.1 ppm F (as NaF) for 20 weeks. Microradiographs were made after each 4-week-period. The lesions were around 500 µm deep, with mineral loss values between 11,000 and 18,000 vol%·µm. After 20 weeks of remineralization, the absolute amounts of deposited mineral ranged from 7,500 to 10,000 vol%·µm, corresponding to a repair between 50 and 85%. Lesion depth was, on average, reduced by 199 µm. This was not significantly different (at p < 0.05) between the four experimental groups. This study showed that remineralization of advanced dentinal lesions is possible in spite of the virtual absence of mineral in the lesion body after demineralization. The surface layer of the lesion was the preferred site for mineral deposition until mineral content values reached those of sound dentine. The mineral content in the lesion body increased with time, at a rate reflecting the initial severity of the lesion. We conclude that a remineralized surface layer does not inhibit transport of mineral ions to the body and that the remineralization in the lesion body reflected the number of sites for crystal growth.

Effect of a Solution with High Fluoride Concentration on Remineralization of Shallow and Deep Root Surface Caries in vitro

A root dentin single–section model was developed to compare the efficacy of different fluoride treatments on the remineralization of lesions. Shallow (∼170 µm) and deep (∼400 µm) lesions were produced in acetic acid buffer solutions (pH 5.0) with 0.1– and 0.5–ppm fluoride for 3 days and 2 weeks, respectively. Next, the sections were pH–cycled for 4 weeks. Following the pH cycling, all sections were first remineralized for 5 weeks, then subjected to 10 days of demineralization. The treatments were (1) no treatment (control), (2) daily 1,450–ppm NaF toothpaste, (3) weekly 4,000–ppm fluoride solution, (4) a combination of treatments 2 and 3. In the shallow lesions, the 4,000–ppm fluoride solution and the combination treatment enhanced mineral deposition at the lesion front, producing a second, slightly hyperremineralized layer. Similarly, in the deep lesions a second remineralized layer was detected. In all lesions, the fluoride solution treatment showed significantly more remineralization compared to the control and the toothpaste treatment (p<0.05), most of which was formed during the pH cycling. In the demineralization period, the control showed significantly higher mineral loss than all other treatments. These results indicate that a 4,000–ppm fluoride solution might be effective for remineralization of root dentin lesions even over 400 µm depth.

Effect of denture base‐resin with prereacted glass‐ionomer filler on dentin demineralization

The demineralization of dentin was studied when placed adjacent to one of four experimental denture base-resins. These experimental resins contained polymethylmethacrylate (PMMA) and 0, 5, 10, 20 or 30 wt% surface reaction-type prereacted glass-ionomer (S-PRG) filler, respectively. A dentin thin-section was sandwiched between these resins and subjected to demineralization for 1 wk. Microradiographic analyses showed that the mineral vol% of the surface was increased, and lesion formation was inhibited, in a dose-response relationship with the amount of S-PRG filler. Moreover, the mineral loss decreased, by up to 60%, with an increasing amount of filler. These results indicate that denture base-resins containing S-PRG filler possess a substantial inhibition capability against demineralization, and this may thereby assist in preventing root caries of abutment teeth.

The caries-reducing benefit of fluoride-release from dental restorative materials continues after fluoride-release has ended

Abstract Objective. This study tested the hypothesis that the benefit of fluoride-releasing restorative materials continues even after their reserve of fluoride has been depleted. Materials and methods. Pits in perspex blocks simulating cavities were filled with either a fluoride-releasing or a non-fluoride-releasing restorative material and a dentin single-section was placed 1 mm from the edge of the filled pit. These combinations were exposed to an acid gel system. Each demineralized dentin section was separated from the adjacent material and immersed in fresh demineralizing solutions. Transversal microradiographs were taken following the two experimental periods. This study defined ΔΔZ as the increase of integrated mineral loss (ΔZ) during the second acid attack. Results. The first acid attack substantially demineralized the near-surface region (depth < 40 μm) in all samples. The second acid attack, however, did not cause further demineralization in this near-surface region. Instead, it demineralized dentin deeper than 40–60 μm. The ΔΔZ of the material that did not release fluoride was significantly greater than that of fluoride-releasing materials. Negative correlations were found between ΔΔZ and the mineral volume% of the near-surface region and lesion body of the initial lesions. These results indicate that the dentin mineral in the near-surface region is chemically altered to become acid-resistant fluorapatite. In addition, lesion progression during the second period of demineralization, which was fluoride-free, may have been affected for the materials that have high mineral content of the surface layer and lesion body. Conclusions. It is concluded that dentin surrounding fluoride-releasing materials is protected against demineralization even after the fluoride release has diminished.

Antibacterial Action of a Condensed Tannin Extracted from Astringent Persimmon as a Component of Food Addictive Pancil PS-M on Oral Polymicrobial Biofilms

The purpose of this study was to evaluate the antibacterial activity against polymicrobial (PM) biofilms of a condensed tannin extracted from astringent persimmon (PS-M), which is contained in refreshing beverages commercially available in Japan. Salivary PM biofilms were formed anaerobically on glass coverslips for 24 and 72 h and were treated for 5 min with sterilized deionized water (DW), 0.05 and 0.2 wt% chlorhexidine digluconate (CHX), and 0.5–4.0 wt% PS-M solution. The colony forming units (CFU/mL) were determined and morphological changes of the biofilms were observed by scanning electron microscopy (SEM). The CFUs were lower in all PS-M and CHX groups compared to the DW group. PS-M exerted a dose-dependent effect. PS-M (1.53 × 107) at a dose of 4.0 wt% had the same effect as 0.2 wt% CHX (2.03 × 107), regardless of the culture period. SEM revealed the biofilm structures were considerably destroyed in the 4.0 wt% PS-M and 0.2 wt% CHX. These findings indicate that the antibacterial effects of PS-M, a naturally derived substance, are comparable to those of CHX. PS-M may keep the oral cavity clean and prevent dental caries and periodontal disease related to dental plaque, as well as systemic disease such as aspiration pneumonitis.

Anti-demineralizing Potential of Bottled Sugar-free Green Tea Beverages in vitro

Abstract The purpose of this study was to evaluate the influence of a bottled green tea beverage on dentin demineralization with a demineralization gel system in vitro . Samples were cut from bovine root dentin. Each sample was immersed in 8% methylcellulose gel onto which a layer of green tea beverage was placed. For comparison, sugar-free coffee beverage, deionized water, and 0.8-ppm F solutions were used. After two weeks, the treatment solutions were replaced with demineralization solution. The mineral profiles and mineral loss values of the lesions were obtained by transversal microradiography (TMR) after one-week demineralization. The green tea, coffee, and fluoride solution treatments induced a significantly thicker surface layer when compared with the deionized water treatment. In particular, the mineral volume % of the demineralized dentin specimens treated with green tea was approximately seven times higher than that of the de-ionized water treatment. The green tea treatment showed significantly lower mineral loss than the other three treatments. TMR measurements clearly showed that the sugar-free bottled green tea beverage inhibited dentin lesion progression, presumably due to the effect of sub-ppm fluoride levels.

Relevance of surface characteristics in the adhesiveness of polymicrobial biofilms to crown restoration materials

We used a polymicrobial (PM) biofilm model to examine associations of bacterial adhesiveness with surface characteristics of various dental materials. Four types of dental materials (apatite pellet, zirconia, ceramic, and composite resin) with rough and mirror surfaces were used. Surface roughness, surface free energy, zeta potential, and colony-forming units (CFUs) of the biofilm formations were measured. Biofilms were cultured for 24 h under anaerobic conditions, plated onto blood agar medium, and anaerobically cultured for 4 days. After culturing, CFU per mm2 was calculated, and samples were observed under a scanning electron microscope. Means and standard deviations of the experimental data were estimated, and one-way ANOVA and Tukey multiple comparison assays were performed. Pearson correlation coefficients were obtained for the CFU and surface characteristics. Surface roughness and surface free energy appeared to affect generation of PM biofilms on oral materials, and zeta potential was involved in generation of PM biofilms on mirror-ground oral materials.

Influences of bicarbonate on processes of enamel subsurface remineralization and demineralization: assessment using micro‐Raman spectroscopy and transverse microradiography

In the present study, we investigated, using micro-Raman spectroscopy (Raman) and transverse microradiography, the influence of bicarbonate [sodium hydrogen carbonate (NaHCO3 )] on the effects of carbonate ions in the mineral phase during demineralization (acid resistance test) of subsurface lesions. Baseline lesions were created by demineralizing bovine enamel, and specimens were then exposed to remineralization solutions containing 0, 5, or 50 mM bicarbonate. Acid resistance tests were performed on remineralized and sound enamel specimens. Raman spectra showed that carbonate and phosphate were incorporated into both surface layers and lesion bodies during remineralization in the presence of bicarbonate. Moreover, the presence of bicarbonate did not affect the rates of remineralization, although the average mineral profiles of remineralized enamel differed from those of sound enamel after acid resistance tests. Raman analyses enabled close evaluation of site-specific characteristics of carbonate and phosphate in subsurface lesions. In conclusion, incorporation of carbonate and phosphate ions into enamel subsurface lesions during remineralization does not affect the magnitude of remineralization or acid resistance.

Effects of resin-based temporary filling materials against dentin demineralization.

This study investigated the in vitro anti-demineralization effects of resin-based temporary filling materials containing surface prereacted glass-ionomer (S-PRG) filler on dentin. Bovine root dentin specimens with a 3×3 mm experimental surface were divided into four treatment groups: DuraSeal (DU) as a control, S-PRG filler-free temporary material (S0), material containing 10% (S10) and 20% (S20) S-PRG filler. Each material was applied to 3×2 mm of the experimental surface, and the specimens were immersed in 8% methylcellulose gel demineralization system for one week at 37˚C. Mineral profiles and integrated mineral loss (IML) of lesions induced on the surface (3×1 mm) adjacent to the materials were computed by transversal microradiography. S10 and S20 yielded thick surface layers and shallow lesion bodies, with significantly lower IML than DU and S0 (p<0.05, Tukeys test). These findings indicate that temporary filling resin-based materials containing over 10% of S-PRG filler content have anti-demineralization effects on adjacent dentin.

Bond Strength and Water Resistance of a Resin Composite Bonded to Glass Plates Treated with Commercial Ceramic Primers

Background: Silane coupling agents are used as a bonding agent between ceramics and resins in dentistry. The effectiveness of these agents is often enhanced by the addition of acid or by heat treatment. Objective: This study aimed to evaluate, the clinical characteristics, TBS (tensile bond strength) and water resistance of eight commercial ceramic primers (seven silane coupling agents and one alumina zirconia primer). Method: Glass plates were used as the adherent. The TBS of the resin composite and the wettability of the resin monomer to glass surfaces treated with ceramic primers was investigated, with 3-MPS (methacryloxypropyltrimethoxysilane) used as a control. The values obtained from the experiments were analyzed using one-way ANOVA followed by Tukey’s multiple comparison tests (p < 0.05). Results: No significant differences in TBS were observed between the commercial products and MPS, except for the alumina zirconia primer. However, four products (three of the seven agents and the alumina zirconia primer) exhibited significantly lower TBS values after application of thermal stress when compared with those stored in water (p < 0.05). All but one of the eight primers displayed significantly higher contact angles between the treated glass and the resin monomer when compared with MPS (p < 0.05). These results suggest that some commercial ceramic primers may contribute to increased strength and durability.