The purpose of this study was to investigate the deformation and flexural properties of acrylic and urethane polymers reinforced with glass fiber sheet. Four types of specimen —self-curing resin plate (R), light-curing oligomer plate containing a reinforcement (GO), and self-curing resin plate containing a reinforcement on one (GR) or both (GRG) sides— were prepared with three thicknesses: 1.5, 2.4, and 3.0mm. Gaps between polymerized test specimen and a standard metal plate were measured at the corner (C), middle of the long sides (LS), and middle of the short sides (SS). The gaps for R were 0-2.0μm. GO and GR markedly deformed at Points C, LS, and SS, and the degree of deformation increased as GO became thinner. Flexural strength was significantly increased by the reinforcement (p<0.05). The flexural moduli of 3.0-mm thick R, GO, and GR were significantly smaller than that of 1.5-mm thick specimens.

抄録全体を表示

The purpose of this study was to clarify the cytotoxicity of Ni²⁺ ions against murine peritoneal exudate cells (PEC) (macrophages). First, we examined the cell viability of PEC with and without lipopolysaccharide (LPS) stimulation in culture media containing Ni²⁺ ions up to 1000μmol/L. Results showed that the cytotoxicity of Ni²⁺ ions against PEC was dosedependent and accelerated by LPS stimulation, especially in media with Ni²⁺ ions exceeding 100μmol/L. Second, we measured the production of nitric oxide (NO) from PEC and found that LPS caused the PEC to produce abundant NO. However, high dose of Ni²⁺ ions at concentration more than 200μmol/L hindered and inhibited NO production. These results pointed out that the cytotoxicity of Ni²⁺ ions against macrophages depended on both the Ni²⁺ ion concentration and the presence of bacteria with LPS. Further, NO —a killer of bacteria— was lost when LPS-stimulated macrophages were exposed to high dose of Ni²⁺ ions.

抄録全体を表示

The purpose of this study was to examine if a modified direct relining method could result in excellent denture adaptation compared to a conventional method. Direct relining was done using heat-polymerizedacrylic resin base on a maxillary cast with two times of three seconds of cooling using dichloro-difluoro-methane coolant. Discrepancy between cast and intaglio surface at residual ridge and center of palate was measured at 12 minutes after mixing of resin (Time 0) and at 24 hours or seven days after water immersion (36°C). At Time 0 (with three seconds of cooling), the discrepancy at ridge (0.39±0.27) and palate (0.66±0.31) was significantly lower compared to that of control (ridge=0.93±0.51; palate=1.14±0.13, P<0.05); and the same observations occurred at 24 hours and seven days too. On intaglio side (with three seconds of cooling), the peak temperature was 5°C lower than that of control and it occurred at a delay of about 60 seconds. Based on the results of this study, we therefore suggested that this delayed and lowered temperature served to improve the adaptability of denture base.

抄録全体を表示

This study aimed to investigate the relationship between the radiopacity of an experimental light-cured composite resin and the amount and type of its radiopaque material: Ti, SrCO₃, ZrO₂, BaSO₄, or Bi₂O₃. Radiopacity of each material was evaluated in terms of aluminum equivalent thickness using an aluminum step wedge. Then, the half-value layer thickness of the experimental composite resin, which had an aluminium equivalent thickness of 1mm, was evaluated. It was found that the effects of elemental composition were not identical when evaluated in terms of aluminum equivalent thickness and by halfvalue layer. Nevertheless, both measurement methods indicated that radiopacity increased with increase in radiopaque material content as well as increase in atomic number of the element.

抄録全体を表示

This study evaluated the three-year clinical performance of Class V restorations made of a polyacid-modified resin composite, Dyract. Ninety-two Class V carious lesions in 28 patients were restored with Dyract. Restorations were clinically evaluated at baseline, first, second, and third year recall visits, according to the modified Ryge criteria by two experienced, calibrated examiners. Retention rate after three years in Class V carious restorations was 92.4%, with only seven failed restorations. Color change and marginal discoloration in restorations were found to be statistically significant (p=0.013 and p<0.001, respectively) at the end of third year, but none of the affected restorations required replacement. The results of this study revealed that at the end of three years, Dyract exhibited good clinical success rate but significant color change and marginal discoloration in Class V carious lesions.

抄録全体を表示

This study examined fracture toughness (K_IC) measurements obtained using the indentation fracture (IF) method with a view to improving their reliability. The K_IC values of five dental ceramics were measured using the IF method with five different formulas, and the single-edge precracked beam (SEPB) method was used as a control. The elastic moduli of the dental ceramics were evaluated by dynamic hardness test. Load conditions of the dental ceramics that produced a median/radial crack for the IF method formulas were investigated. Based on the resultant c/a and P/c^1.5 values, the indentation load (P) required for median/radial crack occurrence varied greatly from 29.4 to 196N depending on the ceramic used. Among the five formulas, none of the K_IC values obtained by the IF method with Miyoshi's formula differed significantly (p>0.05) from the values obtained using SEPB method. These results suggested that, after an appropriate indentation load is determined, reliable K_IC values for small dental ceramic specimens can be easily obtained using the IF method if Miyoshi's formula is used in combination with the dynamic hardness test.

抄録全体を表示

Adhesion promoting monomers—5-(4-vinylbenzyl)-2-thiobarbituric acid (5VS), 9, 10-epithiodecyl methacrylate (EP8MA), 9, 10-epithiodecyl 4-vinylbenzoate (EP8VB), and 3, 4-epithiobutyl 2, 2-bis (methacryloyloxymethyl) propionate (EP2BMA)—were added to the MMA liquid of a MMA-PMMA/TBBO resin. Three dental precious metal alloys were butt-jointed together with the MMA-PMMA/TBBO adhesive resin, and tensile bond strength was measured after 2, 000 thermocycles in water. Polymerization kinetics of MMA by 2, 2′-azobis (isobutyronitrile) at 70°C in the presence of 5VS, EP8MA, EP8VB, or EP2BMA were examined quantitatively using a DSC to clarify the relationship between the adhesive properties of MMA-PMMA/TBBO adhesive resin and the kinetic polymerization behavior thereof.
Obtained kinetic parameters indicated that 5VS was not suitable as an adhesive monomer for adhesive resin formulations and that EP2BMA possessed the latent potential as an adhesive monomer. Further, tensile test results revealed the applicability of EP8MA, EP8VB, and EP2BMA as an adhesive monomer component of adhesive resin formulations.

抄録全体を表示

Discoloration of provisional restorations can be an esthetic problem, especially when the treatment plan requires long-term provisionalization. In this study, therefore, we examined the effects of staining solution on the color stability of these provisional crown and bridge restoration materials: Structur, Temdent, and Tab 2000. Treatment solutions were namely carrot juice, tea, cola, light cola, and distilled water. Thirty samples were prepared for each type of provisional material, such that a total of 90 samples were prepared. The color value of each sample was measured with a colorimeter at baseline and after one day, one week, two weeks, and four weeks of immersion in various treatment solutions. Results were determined using the CIELAB system. Color change data were calculated and subjected to two-way analysis of variance. To examine significant interactions, one-way ANOVA and Tukey's multiple comparisons test were performed to identify differences between the solutions (p≤0.05).
After four weeks of treatment, color difference values were found to range from 0.20 to 3.99 ΔE* units. The highest color difference values were obtained in carrot juice, cola, and tea with Structur samples after four weeks, where these values were categorized as “noticeable” and “unacceptable” color change values. Based on the results of this study, we do not recommend amine-containing Structur to be used as a provisional crown and bridge restorative material for treatments of a longer duration.

抄録全体を表示

The purpose of this study was to evaluate how the different mechanical properties of two luting agents (acrylic resin cement and resin composite cement) influenced their bond strength to dentin, after cyclic loading that simulated chewing. Stainless steel rods were bonded to the flattened dentin surfaces with each luting agent. After immersion in water for 24 hours, half the specimens of each group were tested for tensile bond strength and the remaining half were subjected to a vertical load (75.6N, 1.2Hz) using an acrylic stylus—which upon contact with the specimen would rotate counterclockwise and then counter-rotate. Bond strength of the resin composite cement with self-etching was found to be significantly lower than the other adhesive systems. After 100, 000 cycles, the bond strength of resin composite cement was significantly decreased while acrylic resin cement showed no decrease in bond strength.

抄録全体を表示

The purpose of this study was to evaluate the bonding interface and bonding strength of electroformed coping when cast joining was used with a multi-purpose alloy. The multi-purpose alloy was cast at a mold temperature of 700, 750 or 800°C. A high noble alloy tab was also soldered onto an electroformed coping as a control. Sectioned surfaces of cast joining and soldered specimens were observed using a scanning electron microscope and analyzed using an electron probe micro analyzer. Shear bonding strength of specimens cast at 750°C and that of soldered specimens were determined. The edge of the cast joining alloy was round, but this improved as temperature increased. Diffusion of elements from the cast joining alloy and electroformed coping was detected at the interface, which contributed to a significantly higher bonding strength in the cast joining specimen than in the soldered specimen. These results suggested that the cast joining could be potentially employed for electroformed copings.

抄録全体を表示

The aim of this study was to evaluate the effectiveness of the microfocus radiograph CT system in examining the adaptation of all-ceramic crowns three-dimensionally and non-destructively. The computed tomograms of the crown and abutment model were filmed by microfocus radiograph CT. Using a volumetric rendering software, images of gaps were extracted and reconstructed three-dimensionally, and their volume data analyzed. In order to compare this method with the conventional method, fitness test silicone paste was sandwiched between the abutment and all-ceramic crown. Adaptation of the crown on the abutment model was then observed non-destructively and three-dimensionally. Furthermore, the gaps could be analyzed in any arbitrary position. Concerning mean gap thickness, there was significant differences between the two measurement methods. However, it was very slight. We therefore concluded that the microfocus radiograph CT system is well positioned to be an extremely effective method in examining the adaptation of all-ceramic crowns.

抄録全体を表示

The aim of this study was to investigate the effect of antagonist material and configuration on combined wear, which was produced by alternating toothbrush wear and simulated occlusal wear on one specimen. Worn volume and maximum worn depth comparisons were done using two antagonist materials (steel and ceramic) and two antagonist configurations (flat and round).
For the material factor, worn volume by the ceramic antagonist was greater than that by steel antagonist in the combined wear test. For the configuration factor, the round ceramic antagonist induced a greater volume loss of the resin composite. As for maximum worn depth, both the material and configuration of antagonist were influencing factors in the combined wear test—where the round ceramic antagonist induced a deeper wear of the resin composite. Based on the results of this study, we concluded that a round ceramic antagonist is suitable to be used for evaluating the wear behavior of resin composites.

抄録全体を表示

The purpose of the current study was to evaluate the performance of two laboratory light polymerization systems used to polymerize an indirect composite (Sinfony). A two-step polymerization system (Visio-Alfa and Beta) and a halogen-metal halide unit (Twinkle MIII) were assessed. The composite was polymerized either with the Visio units or with the MIII unit for different exposure periods. Knoop hardness, water sorption, and solubility in water of the composite polymerized with the following modes were determined: Visio, 15 minutes; MIII, 30, 60, 90, 120, and 180 seconds. Extension of light exposure time to the MIII unit improved the hardness of the composite from 30.5 (30s) to 40.7 (180s), whereas hardness obtained with the Visio units resulted in 24.8 (15 minutes). Water sorption and solubility of the composite were greater when it was polymerized with the Visio units than with the MIII unit.

抄録全体を表示

The purpose of this study was to determine the effects of staining solutions on the different shades of a dental composite, and to compare these effects with that of distilled water. Two shades of effect (ET1 and ET2), two shades of enamel (EL and EM), and two shades of dentin (DA1 and DA2) were used. Specimens were immersed in three staining solutions (chlorhexidine gluconate, filtered coffee, and orange juice) and distilled water. Color changes were characterized using the CIELAB color space. Since significant interactions occurred, the staining effect of each solution on each shade was determined using one-way ANOVA and the levels of factor in one-way ANOVA were compared using Tukey's method (p≤0.05). The staining solutions were found to be more chromogenic than distilled water, and EM and DA2 shades were found to be more color-stable. Based on the color change results in this study, chlorhexidine gluconate (1.45), filtered coffee (1.43), and orange juice (1.02) were determined as having “slight” staining effects on the tested shades. As for the tested shades in this study, they revealed acceptable color change results.

抄録全体を表示

This study investigated the effect of heat history on the corrosion of keepers used for dental magnetic attachments. Ferritic stainless steels of SUS 444 and 447J1 were prepared with heat treatments in the temperature range of 550-850°C for 1-5 hours. The stainless steels were electrochemically and metallurgically examined by anodic polarization curves in a 0.9% NaCl solution and by microstructural observation using an electron probe microanalyzer with WDS. Heating both kinds of stainless steel at 650-750°C for two hours or more led to the deterioration of their corrosion resistance. For example, there was evidence of a reduction in the breakdown potentials and an increase in the current densities of the anodic polarization curves. These phenomena were attributed mainly to the precipitation of the σ (FeCr) or Χ (Fe₁₈Cr₆Mo₅) phase, which sometimes resulted in intergranular corrosion. When dental alloys are cast in investment molds embedding the keepers, the heat time required for thermal expansion of the molds should be kept under one hour.

抄録全体を表示

Different types of calcium phosphate compounds are commercially available for medical and dental applications as bone substitute materials. Biological apatites contain several kinds of minor elements such as carbonate (CO₃), magnesium (Mg), and fluoride (F) in enamel, dentin, and bone. It has been shown that F ion and F-substituted apatite promoted osteoblast proliferation and inhibited osteoclast cell activity. The purpose of this study was to investigate the in vivo rat tibia activity on F-substituted apatite (FAp). Apatites of unsintered calcium deficient apatite (CDA), and FAps, with low, medium, and high F concentrations, were implanted in rat tibia for 1 and 2 weeks. Implanted tissues were embedded in paraffin blocks, stained with hematoxylin-eosin and histomorphometrically observed. Results showed that low F concentration induced better and faster new bone formation in vivo compared to CDA. Therefore the results suggested that F as a minor element in bone rendered a suitable effect on bone formation in vivo.

抄録全体を表示

In this study, we examined the effect of the transmitted amount of visible light through a resin composite on the curing depth and polymerization conversion. Transmitted amount of visible light was strongly dependent on the magnitude of refractive index difference that existed between the resin and silica filler. More specifically, the differences arose from the type of base monomer used. The transmitted amount of visible light exhibited a good correlation with the curing depth and Knoop hardness ratio of the bottom surface against the top surface of the resin composite. To improve the polymerization conversion of the cavity floor, it is important to reduce the refractive index difference that exists between the base resin and silica filler.

抄録全体を表示

CP titanium was polished with a colloidal silica suspension and chromic oxide slurry under low and high pressures. The polished surfaces were characterized by means of EPMA and XPS. Irrespective of polishing pressure, colloidal silica suspension successfully created a mirror-like surface that was clean at EPMA level. However, XPS detected a small amount of silicon on the outermost surface. On the other hand, chromic oxide slurry under high pressure yielded a very uneven surface with numerous scratches. The EPMA and XPS results suggested the presence of chromium-containing species in the polished surface, which might include hydroxides as well as oxides. In addition, the level of oxygen concentration was noticeably raised, which probably resulted from the increase of surface oxide film thickness or the extension of oxide-to-metal transition zone.

抄録全体を表示

We examined the effect of phosphate-buffered saline (PBS) solution with different pH values on the formation of porosity in the DNA/chitosan complexes, and evaluated the intercalation behavior of the complexes. Four different PBS solutions with pH=6.0, 7.0, 7.4, and 7.8 were used for rinsing water-insoluble DNA-chitosan complexes. All complexes showed high porosities ranging from 83 to 95%. Rinsing with PBS at pH 7.0, 7.4, and 7.8 reduced the porosity of the DNA-chitosan complexes. Re-rinsing with PBS at pH 7.4 reduced the porosity of the DNA-chitosan complex rinsed with PBS at pH 6.0. The appearances for porous formation were influenced by the differences in pH of PBS. Daunorubicin hydrochloride intercalated and bound in the grooves of DNA within all of the DNA-chitosan complexes, indicating that DNA in the complexes maintained its double-stranded helical structure. These results suggested that PBS-rinsed DNA-chitosan complex is promising as a scaffold material in tissue engineering.

抄録全体を表示

The corrosion and tarnish behaviors of three Ag-based alloys (Ag-Pd-Cu-Au alloy, Ag-In alloy, and Ag-Sn-Zn alloy) in polyvinylpyrrolidone iodine (povidone-iodine) solution were examined. The degree of tarnish was evaluated by visible-ray spectrocolorimetry. Corrosion potential measurements and analyses of corrosion products by X-ray diffractometry were carried out to elucidate the corrosion mechanism. The corrosion rate of the three Ag-based alloys in povidone-iodine solution at its practical concentration used as a gargle solution was so fast that the alloys tarnished within 10 seconds of immersion with the formation of AgI. Thermodynamic consideration and the results of surface analysis by X-ray diffractometry revealed that the main anodic and catholic reactions were Ag+I^-→AgI+e^- and I₂+2e^-→2I^- respectively.

抄録全体を表示

The purpose of this study was to evaluate the colors of resin composites used for the layering technique, as well as the translucency at various thickness. For the purpose of calculating the translucency parameter (TP), black and white backings were used to evaluate the CIELAB parameters of Filtek Supreme (3M) and Gradia Direct (GC) disks of various thicknesses (0.5, 1.0, 2.0, 3.0 and 4.0mm) and of three different shades (enamel-shade, body-shade, and opaque-shade). As for the color of each shade, it was evaluated using 4mm thick specimens on the white backing. Regarding TP, the opaqueshades were less translucent than the other shades. It was also found that translucency increased exponentially as thickness was reduced-regardless of shade. Regarding color, enamel-shades were more bluish (especially in GD) compared to the other shades, and the opaque-shades displayed a brighter and yellowish characteristic. In the layering technique, it is fundamental to have an accurate knowledge about the translucency and colors of the materials/shades used.

抄録全体を表示

The purpose of this study was to investigate the apparent viscosities and mechanical properties of two experimental lightcuring soft lining materials (SLM-1 and SLM-2) based on soft-type urethane oligomers, as well as the shear bond strength and dye penetration between the denture base resin and the polymerized SLMs after storage in water. The apparent viscosities of SLM-1 and SLM-2 were 144.0-146.9 and 1.9 Pa·s respectively. After storage in water for two prescribed periods (one day and three months), the mechanical properties of the SLMs on the overall were 10.6-20.6MPa for elastic modulus, 69.3-72.1 for hardness, and 3.8-4.0MPa for adhesive strength. Tensile strength was observed to decrease after three months' storage in water, when compared to that after one-day storage (p<0.01). Water sorption rates also differed significantly (p<0.05)—namely 3.0 and 2.8mg/cm² for SLM-1 after one day and three months respectively, and 2.0 and 2.2mg/cm² for SLM-2. As for dye penetration, no infiltration was observed at the denture base resin-SLM interface after three months' storage. Based on the results of this study, it seemed like the SLMs possess many suitable properties for use with a new technique that we recently developed for preparing denture base resin and soft lining material.

抄録全体を表示

This study evaluated the repair bond strength of Estenia composite. Disk specimens of a dentin material were conditioned with varying combinations of silane primer (Add-on Primer, Clearfil Porcelain Bond Activator, Clearfil Porcelain Bond Activator+Clearfil Mega Bond-Primer, Porcelain Liner M, and unprimed) and bonding agent (Clearfil Mega Bond-Bond, Modeling Liquid, Stain Diluent, and no bonding agent). After photopolymerization of the enamel material placed on each surface, the specimens were either wet- or dry-stored at 37°C for 24 hours. Average shear bond strength varied from 24.9 to 61.4 MPa, where the Clearfil Porcelain Bond Activator+Clearfil Mega Bond-Bond group and the Add-on Primer+Modeling Liquid group showed the greatest bond strength for dry and wet conditions respectively. To achieve reliable bond strength between layers of Estenia composite, it is highly recommended to use specific combinations of silane primer and bonding agent.

抄録全体を表示

The use of finite element analysis is becoming more widespread with rapid advancements in computer technology. However, the field of dentistry is not enjoying the spillover benefits of the expanded use of this design simulation and analysis tool. Finite element modeling requires measurement of the object. However, as the living body is morphologically very complex, this requires a great deal of both time and skill using CAD applications, thus preventing its widespread adoption in the dental field. Although there have been reports of finite element modeling from CT images, these methods require skilled programmers for software development—which is another factor that prevents its widespread adoption in dentistry. Therefore, establishing a finite element modeling method that is both accurate and practical will be of great benefit in clinical dentistry.
In the present study, a method using computer tomography and existing software was examined for finite element model construction based on computer tomography images. The results suggested that the method developed here is feasible and practical for clinical use.

抄録全体を表示

The purpose of this study was to evaluate the marginal and internal fit of all-ceramic crowns fabricated using the Decsy CAD/CAM system. A master die of maxillary first premolar was measured, and experimental crowns were fabricated. Four conditions were established by combining two convergence angles (4° and 12°) of the abutment with two different luting space settings (15μm and 55μm). The results showed that the experimental crowns had a marginal gap of 42 to 56μm. When the luting space setting was 15μm, the internal gap was 85-88μm; when the setting was 55μm, the internal gap was 126-138μm. The marginal gap for each experimental crown met the clinically acceptable criterion.

抄録全体を表示

The secretion of collagen by osteoblasts was observed by scanning electron microscopy (SEM). Osteoblast-like cells were cultured on a CO₃apatite-collagen sponge reinforced with a porous HAp frame. After three days' incubation, a number of newly created matrix fibrils, forming a network structure, were observed at the cell surface. SEM also showed that osteoblasts secreted collagen fibrils from their membrane, and that the collagen fibrils were twisted together. When collagen in an aqueous sol solution was sprayed onto the extremely smooth surface of a mica plate to support the secretion of osteoblasts, a collagen network structure could be clearly observed with atomic force microscopy (AFM). With this in vitro phenomenon, we could confirm the formation of collagen network structure without biological function. Therefore, it was suggested that the CO₃apatite-collagen sponge used in this study is a favorable scaffold biomaterial, on which osteoblasts could produce the unmistakable, characteristic extracellular matrix for mineralization. For therapeutic use of hard tissue biomaterials, collagen formation as an extracellular matrix (ECM) is very important because mineralization is subsequent to ECM.

抄録全体を表示