Showing papers in "Dental Materials Journal in 1999"
TL;DR: It is concluded, therefore, that preparation of MAATY which absorbs less water may improve durability even when immersed in water.
Abstract: In order to understand the relationship between the durability of adhesive strength in the oral cavity and water absorption, a series of O-methacryloyl-N-acyl tyrosines (MAATY)-2-hydroxyethyl methacrylate (HEMA) bond system samples was prepared and their bonding strength to unetched human dentin was measured as a function of immersion period in water. Also, bulk polymerization was carried out to measure the amount of water absorption as a function of time. All specimens absorbed water suddenly when they were immersed into water. The amount of absorbed water was large when the carbon number in the acyl group was small or the number of carboxylic groups was large. The adhesive strength of the MAATY-HEMA system to unetched dentin decreased significantly when the MAATY-HEMA absorbed a larger amount of water. We concluded, therefore, that preparation of MAATY which absorbs less water may improve durability even when immersed in water.
87 citations
TL;DR: Results indicated that the higher filler content of the cement increased the wear resistance and this desirable influence appeared more remarkably in the wider horizontal gap dimension.
Abstract: We investigated the influence of filler content and gap dimension on the wear resistance of composite luting cement around CAD/CAM ceramic inlay restorations. Experimental hybrid dualcured composite luting cements containing 60, 70, 72, 74 and 80wt% of silanated barium-silica fillers were used for cementing CAD/CAM ceramic inlay into the cavity. The specimens involving inlay-cement-tooth interfaces were subjected to a three-body wear test. The relation between the interfacial gap dimension and wear loss was also investigated using 60, 70 and 80wt% filled cements. The cements containing more than 70wt% filler presented significantly higher wear resistance than 60wt% filled cement. There was a positive linear relationship between gap dimension and wear loss, and the inclination of the regression line decreased with increasing filler content. These results indicated that the higher filler content of the cement increased the wear resistance and this desirable influence appeared more remarkably in the wider horizontal gap dimension.
31 citations
TL;DR: The values of CSR for UDMA, Bis-MPEPP, EGDMA, TEGdMA, DMAEM, 4-META and HEMA exhibited a reduction in cytotoxicity in the presence of the S9 mix, but there were no significant differences between +S9 and -S9 for MMA.
Abstract: The purpose of the this study was to evaluate the cytotoxicity of dental resin monomers in the presence of a rat liver S9 mix containing cytochrome P 450 enzymes. JTC-12 cells derived from a monkey kidney were seeded on a 96-well multi-well-plate at 9×103 cells per well. After cultivation, the S9 mix was added to the wells as an S9 mix group (+S9), and PBS- was added to the other wells as a none-S9 mix group (-S9), then 7 different concentrations of various monomers were added to each well. All the specimens were cultured for another 24hrs. The cell survival ratios (CSR) were calculated by using a neutral red cytotoxicity assay.CSR for 50μg/mL of Bis-GMA/S9 mix was 92.6% while for none-S9 mix it was 6.6%. The values of CSR for UDMA, Bis-MPEPP, EGDMA, TEGDMA, DMAEM, 4-META and HEMA exhibited a reduction in cytotoxicity in the presence of the S9 mix. There were significant differences between +S9 and -S9 for respective monomers (p<0.05). However, there were no significant differences between +S9 and -S9 for MMA (p<0.05).
28 citations
TL;DR: It is indicated that Bis-GMA/TEGDMA resins showed the greatest water uptake at the ratio of 1/1, and the water sorption characteristic was not influenced by the degree of conversion but mainly by the hydrophobicity of the material.
Abstract: In this study, water sorption of resins and composites containing Bis-GMA and TEGDMA in various proportions were measured, and the influence of degree of conversion and the hydrophobicity of the material on the water sorption characteristics of Bis-GMA/TEGDMA resins were evaluated. Unfilled resins and composites containing Bis-GMA/TEGDMA, with a ratio of 1/1, 2/1, or 3/1 by weight, were prepared and cured. Water uptake and the degree of conversion of each specimen were determined, and the hydrophobicity was compared by measuring the contact angle of water. Both unfilled resins and composites containing Bis-GMA/TEGDMA in the ratio of 1/1 showed significantly greater water uptake than the others. The degree of conversion of the specimens increased as the proportion of TEGDMA was increased, and no inverse relationship was found between the water sorption and the degree of conversion. In contrast, the contact angle of the 1/1-specimen was less than the others, demonstrating significant correlation with the water uptake. These findings indicate that Bis-GMA/TEGDMA resins showed the greatest water uptake at the ratio of 1/1, and the water sorption characteristic was not influenced by the degree of conversion but mainly by the hydrophobicity of the material.
28 citations
TL;DR: A new glass ionomer cement using bioactive CaO-P2O5-SiO2(-MgO) glass was prepared and its setting process investigated using FT-IR and MAS NMR analyses, suggesting that Ca2+ was released from the glass powder to form carboxylate salt and that a degree of polymerization in the silicate network increased.
Abstract: We prepared a new glass ionomer cement using bioactive CaO-P2O5SiO2(-MgO) glass and investigated its setting process using FT-IR and MAS NMR analyses. The compressive strengths of the cements depended on the glass composition and a maximum strength of 33.3±4.7MPa was obtained using cement with the glass composition of MgO: 4.6, CaO: 44.9, SiO2: 34.2 and P2O5: 16.3% in weight. FT-IR analysis showed that the COOH group in the polyacrylic acid decreased and carboxylate ion (COO-Ca2+) increased after the setting reaction. A broad signal appeared around -82ppm in 29Si MAS-NMR spectra of the glass and a new signal corresponding to hydrated silica gel formation appeared around -102 and -111ppm after setting. This suggests that Ca2+ was released from the glass powder to form carboxylate salt and that a degree of polymerization in the silicate network increased. The setting mechanism of the cement was found to be essentially the same as in conventional glass ionomer cement.
27 citations
TL;DR: Calcium phosphates were formed on five kinds of substrate metals using a hydrothermal-electrochemical method in an autoclave with two electrodes and it seems that the incorporation of the metal ions released from the electrode decreased the Ca/P ratio of the deposit due to the formation of other compounds except hydroxyapatite.
Abstract: Calcium phosphates were formed on five kinds of substrate metals using a hydrothermal-electrochemical method in an autoclave with two electrodes. The electrolyte dissolving NaCl, K2HPO4, CaCl2.2H2O, tris (hydroxymethyl) aminomethane, and hydrochloric acid was maintained at 100 degrees C, 150 degrees C and 200 degrees C. The counter electrode, the anode, was platinum plate, 20 x 20 x 0.5 mm, and the working electrodes as cathode were pure titanium, pure zinc, pure nickel, pure iron, and stainless steel plates. A constant direct current at 12.5 mA/cm2 was loaded for 1 hr. Hydroxyapatite [Ca10(PO4)6(OH)2] only deposited at three temperatures on pure titanium plate. On pure zinc plate, both parascholzite [CaZn2(PO4)2.2H2O] and hydroxyapatite were formed at 150 degrees C and both parascholzite and ZnO were formed at 200 degrees C. Both hydroxyapatite and beta-TCP [beta-Ca3(PO4)2] were formed on pure nickel, pure iron, and stainless steel plates at 200 degrees C. It seems that the incorporation of the metal ions released from the electrode decreased the Ca/P ratio of the deposit due to the formation of other compounds except hydroxyapatite.
24 citations
TL;DR: Results suggested that resin infiltration into caries-infected dentin was not sufficient to allow perfect sealing of the restoration, and a new commercial self-etching/self-priming bonding resin (Unifil Bond, UB) was examined.
Abstract: We have examined the adhesive properties of a new commercial self-etching/self-priming bonding resin (Unifil Bond, UB) to normal and caries-infected dentin of human extracted molars using scanning electron microscopy (SEM) and a micto-tensile bonding strength (MTBS) test. In this study, 7 human extracted molars with moderate occlusal caries were used, and flat surfaces including occlusal dentin caries were prepared from the teeth. After the application of UB to the surfaces, a composite resin was built up, and subjected to the measurement of MTBS and SEM observation of the interfacial morphology between UB and dentin. The MTBS of UB to normal dentin was 33.4MPa, but that to caries-infected dentin was 11.0MPa. There was a significant difference between the MTBS to normal and carious dentin. SEM observation revealed that the typical hybrid layer was not formed in caries-infected dentin. These results suggested that resin infiltration into caries-infected dentin was not sufficient to allow perfect sealing of the restoration.
22 citations
TL;DR: The temperature-dependence of the mechanical properties of a new esthetic orthodontic wire with fiber-reinforced plastic (FRP) structure was investigated and a constant orthodentic force regarding temperature change would be advantageous from a clinical point of view.
Abstract: The temperature-dependence of the mechanical properties of a new esthetic orthodontic wire with fiber-reinforced plastic (FRP) structure was investigated. The new FRP wire, fabricated by a hot drawing method, is 0.5 mm in diameter and has a multiple fiber structure composed of biocompatible CaO-P2O5-SiO2-Al2O3 glass fibers of 20 microns in diameter and a polymethyl methacrylate matrix. The flexural load at a deflection of 1 mm and Young's modulus at 24, 37, and 50 degrees C under wet conditions showed similar fiber fraction dependence to those under dry conditions for a fiber fraction of 40-51%. The flexural load and Young's modulus tended to decrease slightly with increases in temperature. This tendency was larger for the lower fiber fraction. However, the difference in flexural load for a temperature difference of between 24 degrees C and 50 degrees C was at most 10 gf. This is negligibly small, and a constant orthodontic force regarding temperature change would be advantageous from a clinical point of view.
22 citations
TL;DR: The results suggested that the matrix of RGIs and PMCRs functioned as a reservoir of fluoride, but the functions were lost by acid attack.
Abstract: This study investigated the release and recharge of fluoride by restorative materials. Resinmodified glass ionomers (RGIs), polyacid-modified composite resins (PMCRs) and resin composite containing fluoride were used for comparison of fluoride release. Non-fluoride-releasing resin composite was used as a control. The amounts of fluoride release from RGIs and PMCRs remarkably increased in the citrate-phosphate acid buffer compared with distilled water. The amounts of fluoride recharged in RGIs increased with the concentration of NaF solution, but those of PMCRs exposed to all concentrations of NaF solutions were less than 1.5ppm. Neither resin composite containing fluoride and non-fluoride-releasing resin composite gave any evidence of recharge. RGIs and PMCRs affected by acid buffer solution could not recharge much fluoride even if they were immersed in the 1000ppmF NaF solution. The results suggested that the matrix of RGIs and PMCRs functioned as a reservoir of fluoride, but the functions were lost by acid attack.
21 citations
TL;DR: It was concluded that C-factor had no influence on the cavity adaptation for compomer restorations, which might be due to reduced stress generation at the bonding interface caused by relatively low mechanical properties immediately after curing, less elasticity, and water absorption in compomers.
Abstract: The effect of configuration factor (C-factor) on cavity adaptation was investigated in three compomer and one resin composite restorations. Eighty-four cylindrical dentin cavities (C-factor: approximately 2.5, 3.0 or 4.0) prepared on flat coronal dentin surfaces were filled with the materials in combination with their proprietary adhesive systems. Cavity adaptation was microscopically examined after 15 minutes storage in water at the top surface and at other four sites along the cavity walls. Additionally, indentation testing was performed for each material at 20 minutes and 24 hours after irradiation. Regression analysis revealed no relationship between C-factor and gap dimension in compomer restorations at any of the measuring sites, while a logarithmic relation was found only at the cavity floor of the composite fillings. All materials showed maturation of mechanical properties. The elastic component of the indentation was smaller in compomers than in the composite. It was concluded that C-factor had no influence on the cavity adaptation for compomer restorations. This might be due to reduced stress generation at the bonding interface caused by relatively low mechanical properties immediately after curing, less elasticity, and water absorption in compomers.
20 citations
TL;DR: Both the flexural and fatigue flexural strengths increased with improvement of surface profile, suggesting the importance of polishing of dental ceramics for not only the static strength but also the cyclic fatigue strength.
Abstract: The biaxial flexural strength and cyclic fatigue biaxial flexural strength of CAD/CAM ceramics polished with #220, 400, 600 and 1000 diamond pads were measured in an effort to determine the effect of surface roughness on fatigue behavior of dental ceramics. The surface roughness was improved after polishing with a smaller diamond grain pad. The flexural strengths of the specimens polished with #220, 400, 600 and 1000 diamond pad were 75.2, 76.6, 82.2, and 83.3 MPa, respectively; the fatigue flexural strength of those with #220, 400, 600 and 1000 were 53.0, 58.1, 60.0, and 61.5MPa, respectively. Both the flexural and fatigue flexural strengths increased with improvement of surface profile. These results suggest the importance of polishing of dental ceramics for not only the static strength but also the cyclic fatigue strength.
TL;DR: High-resolution proton-nuclear magnetic resonance (500 MHz) could be utilized for detection of ionic binding interaction of the 4-META resin system with calcium derived from hydroxyapatite to demonstrate an ionic interaction of 4-MET derived from 4- META with calcium.
Abstract: Our objective was to determine whether high-resolution proton-nuclear magnetic resonance (500 MHz) could be utilized for detection of ionic binding interaction of the 4-META resin system with calcium derived from hydroxyapatite. The stability of 4-META in aqueous medium was studied, findings indicated that 4-META was rapidly converted to 4-MET, a hydrate product of 4-META in 10% D2O/DMSO-d6. The 1H-NMR signals of the methacryloyloxyethoxy group of 4-MET remained intact following the addition of both monocalcium phosphate (MCP) and dicalcium phosphate dihydrate (brushite) solution, whereas those of its trimellitic portion were markedly shifted upfield depending on the phosphate concentration. The shielding effect followed by upfield shifts was due to the localization of electron density surrounding the carboxylate anions that were dissociated by the interaction with calcium counter cation. The shielding effect of 4-MET with brushite was larger than that with MCP. An ionic interaction of 4-MET derived from 4-META with calcium was demonstrated.
TL;DR: A high correlation was observed between the contraction gap width and the proportion of the free surface to the adhesive surface of the resin composite restoration.
Abstract: The effect of the cavosurface angle of dentin cavities prepared in extracted human molars on the cavity adaptation of a resin composite was evaluated by measuring the gap width between the resin composite and the dentin cavity wall. Cavities with cavosurface angles of 90 degrees, 120 degrees, 135 degrees, or 150 degrees were pretreated with one of two commercial dentin bonding systems or an experimental dentin bonding system. The contraction gap width was measured at both the cavity margin and the section cavity using a light microscope. Complete cavity adaptation was obtained with pretreatment of the experimental groups regardless of the cavosurface angle. The contraction gap observed at the cavity margin was prevented with the two commercial dentin bonding systems when the cavosurface angle was increased to 150 degrees. A high correlation was observed between the contraction gap width and the proportion of the free surface to the adhesive surface of the resin composite restoration.
TL;DR: It was concluded that the functional monomers were essential to obtaining the marginal integrity of the resin composite in the dentin cavities.
Abstract: The objective of the present study was to understand the role of the functional monomers in dentin bonding agents of an experimental dentin bonding system by measuring the wall-to-wall contraction gap and tensile bond strength measurement. The efficacy of three commercial dentin bonding agents after using EDTA for conditioning and GM for priming was evaluated by measuring the contraction gap of the resin composite in a cylindrical dentin cavity, and by measuring the tensile bond strength of the composite to a flat dentin surface. The effect of the functional monomers was demonstrated by the contraction gap measurement alone. The value of the contraction gap was significantly different between the commercial dentin bonding agents and these agents without functional monomers (p<0.05). It was concluded that the functional monomers were essential to obtaining the marginal integrity of the resin composite in the dentin cavities.
TL;DR: The effectiveness of the addition of a photoinitiator into self-etching primer was investigated by measuring the tensile bond strength between a resin composite and dentin or enamel.
Abstract: The effectiveness of the addition of a photoinitiator into self-etching primer was investigated by measuring the tensile bond strength between a resin composite and dentin or enamel. The addition of camphorquinone to 5 M (5 wt% MDP -35 wt% HEMA aqueous solution) or 30 M (30 wt% MDP -35 wt% HEMA aqueous solution) did not increase the bond strengths of resin composite to dentin or enamel. On the other hand, the bond strength to dentin was increased by the addition of a water-soluble photoinitiator, 2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-N,N, N-trimethyl-1- propanaminium chloride (QTX) to 5 M or 30 M. The bond strengths to enamel were not influenced by the addition of QTX to 5 M or 30 M.
TL;DR: This study describes research with a view to developing a new age-hardenable, high-carat dental gold alloy with better biocompatibility by addition of a small quantity of titanium to gold by means of hardness testing, X-ray diffraction study, scanning electron microscopic observation and energy dispersive spectroscopy.
Abstract: This study describes research with a view to developing a new age-hardenable, high-carat dental gold alloy with better biocompatibility by addition of a small quantity of titanium to gold. The relationship between isothermal age-hardening and phase transformation of the Au-1.6 wt% Ti alloy was investigated by means of hardness testing, X-ray diffraction study, scanning electron microscopic observation and energy dispersive spectroscopy. The hardening in the initial stage of ageing seemed to be attributable to the continuous precipitation of the Au4Ti ordered phase in the supersaturated alpha solid solution matrix. The overaging with softening was attributed mainly to the formation of precipitates at the grain boundaries, which grew to bright lamellae and seemed to be composed of the Au4Ti phase.
TL;DR: The major components contained in commercial Bis-GMA monomer were isolated by thin layer chromatography (TLC) and identified by NMR and high resolution mass spectroscopy and an unknown hydrophilic third major component was isolated and identified as 2,2-[4-(2-hydroxy-3- methacryloyloxy-1-propoxy)-4'-(2,3-dihydroxy- 1-propane)]dipheny lpropane.
Abstract: The major components contained in commercial Bis-GMA monomer were isolated by thin layer chromatography (TLC) and identified by NMR and high resolution mass spectroscopy In addition to the two major components already known (Bis-GMA and Iso-bis-GMA), an unknown hydrophilic third major component was isolated and identified as 2, 2-[4-(2-hydroxy-3-methacryloyloxy-1-propoxy)-4'-(2, 3-dihydroxy-1-propoxy)] diphenylpropane This compound was designated as BIS-GMA-H, because it has a structure of Bis-GMA with one of which methacrylic ester bond hydrolyzed
TL;DR: It was confirmed that the volumetric dimensional changes of RMGI in cavity were influenced primarily by the cavity C-value, and it was thought that greater contraction stress would remain in high C- Value cavities than low C- value cavities during the setting process.
Abstract: The effects of the C-value (bonded surface area/unbonded surface area) and the volume of the cavity on the volumetric dimensional changes [volumetric setting shrinkage (VSS) and volumetric hygroscopic expansion (VHE)] of a resin-modified glass-ionomer (RMGI) filled in experimental cylindrical cavities were evaluated. The VSS and the VHE rate decreased with increasing C-value. There was a high inverse regression between the cavity C-value and volumetric dimensional changes, but a low regression between cavity volume and volumetric dimensional changes. Therefore, it was thought that greater contraction stress would remain in high C-value cavities than low C-value cavities during the setting process. It was also confirmed that the volumetric dimensional changes of RMGI in cavity were influenced primarily by the cavity C-value.
TL;DR: Phase transformation behaviors in Au-Cu-Pd alloys were investigated by means of electrical resistivity measurements, hardness tests, X-ray diffraction and transmission electron microscopy, and two types of phase transformations were found, namely related to the single phase of Au3Cu and the coexistent phase of au3 Cu and AuCu I.
Abstract: Phase transformation behaviors in Au-Cu-Pd alloys were investigated by means of electrical resistivity measurements, hardness tests, X-ray diffraction and transmission electron microscopy. Anisothermal and isothermal annealing were performed. Two types of phase transformations were found, namely related to the single phase of Au3Cu and the coexistent phase of Au3Cu and AuCu I. The latter produced more remarkable hardening than the former. Hardening was brought about by the antiphase domain size effect of Au3Cu ordered phase in the single phase and by the formation of AuCu I ordered phase in the Au3Cu ordered matrix. There are three modes of phase transformation in the coexistent region depending on the composition. Each sequence is discussed.
TL;DR: Qualitative and quantitative analyses were conducted on four kinds of resin-modified glass ionomer (RMGI) cement liquids, LC, LC II, LC III (hereinafter referred to as LCs) and VM, using HPLC and laser Raman spectroscopic methods, and were able to identity the differences in form of the methacryloyloxy group.
Abstract: Qualitative and quantitative analyses were conducted on four kinds of resin-modified glass ionomer (RMGI) cement liquids, LC, LC II, LC III (hereinafter referred to as LCs) and VM, using HPLC and laser Raman spectroscopic methods. HPLC revealed that among the RMGI liquids LCs contain 31-32% HEMA (2-Hydroxyethyl methacrylate), and VM contains 18% of the same. The composition of RMGI cement liquids varied significantly between manufacturers. In Raman spectroscopic analyses, the spectra of liquids of various ratios of polyacrylic acid and HEMA were measured, and calculations were made on the peak intensity ratios of C=C stretch vibration to C=O stretch vibration, common in both HEMA and polyacrylic acid. The composition ratio of polycarboxylic acid to HEMA of commercial glass ionomer cements was assessed by the regression curve generated by a combination of peak intensity ratios and composition ratios. In addition, Raman spectroscopy was able to identity the differences in form of the methacryloyloxy group.
TL;DR: X-ray diffractometry was used to analyze the crystal phases of three commercial dentin and incisal porcelains prepared by normal cooling, quenching in water, and controlled slow annealing after normal firing, suggesting that the cooling condition has little effect on the microstructural changes of leucite crystals in the dental porcelain.
Abstract: X-ray diffractometry (XRD) was used to analyze the crystal phases of three commercial dentin and incisal porcelains prepared by normal cooling, quenching in water, and controlled slow annealing after normal firing. There were no remarkable differences in the contents of either tetragonal and cubic leucite in the fired porcelain discs prepared under the three cooling conditions. Furthermore, there were no significant differences in the parameters of the ƒ?-axis and c -axis of tetragonal leucite , and the ƒ?-axis of cubic leucite among them. These results suggest that the cooling condition has little effect on the microstructural changes of leucite crystals in the dental porcelains, since the leucite crystals were formed at a higher temperature range than the firing- and cooling-temperature range and were stabilized by incorporation of additives into the lattice.
TL;DR: The flexural strength of the prepared composites was significantly influenced by the surface condition of the filler particles, and increased significantly when the as atomized particles were acid-treated or acid- and heat-treated at 150 degrees C, but then significantly decreased as the heat treatment temperature increased.
Abstract: The effects of acid and heat treatments of silver-tin filler particles on the flexural properties of metal-resin composite restorative materials were investigated. Five metal-resin composite restorative materials containing different silver-tin filler particles treated under different conditions were experimentally prepared. The conditions of the alloy particles were; 1) as atomized (NT), 2) 1.8% HCl acid-treated (AT), 3) heat-treated at 150 degrees C for 5 min after AT (A15), 4) heat-treated at 200 degrees C for 5 min after AT (A20) and 5) heat-treated at 250 degrees C for 5 min after AT (A25). The flexural strength and the flexural modulus of elasticity were measured for the five metal-resin composites to evaluate the effects of the acid and heat treatments. The flexural strength of the prepared composites was significantly influenced by the surface condition of the filler particles (p < 0.01), and increased significantly when the as atomized particles (NT) were acid-treated (AT) or acid- and heat-treated at 150 degrees C (A15), but then significantly decreased as the heat treatment temperature increased (A20 and A25). The strength of the A15 composite was significantly higher than those of the other composites, and exceeded that (about 60 MPa) of the previous composite with no treatment. No significant difference was found in the flexural modulus of the composites.
TL;DR: A new non-contact measurement system employing of a line laser and CCD camera was developed to rapidly measure maloccluded dental casts with large depth and high accuracy.
Abstract: A new non-contact measurement system employing of a line laser and CCD camera was developed to rapidly measure maloccluded dental casts with large depth and high accuracy. In this system, the measuring interval along the line laser and the model scanning direction perpendicular to the line laser were both 0.2mm. By averaging the raw data through repetitious input and smoothing by local filtering, the noise was effectively decreased. Sub-pixel processing, which calculates the pixel position with the largest brightness within one pixel, improved the accuracy in the measurement to 22μm compared with 65μm before sub-pixel processing. Dental casts with malocclusion were measured with this system. The time and the depth for the measurement were about 10 minutes and 60mm, respectively. This was a vast improvement compared with our previous system employing a point laser. In the CG of the measured dental casts, smooth and detailed surface morphology were sufficiently reproduced, and recognition of the characteristic points in the cast could be accomplished with the accuracy of 30μm. This measurement system will be helpful to analyze the dental cast form with malocclusion in progress.
TL;DR: Metal-resin composites, using metal particles instead of inorganic particles as the filler and 4-META as the coupling agent, were experimentally prepared under 20 different conditions and the flexural strength was significantly influenced by the 4- META concentration, the metal particle content and their interaction.
Abstract: Metal-resin composites, using metal particles instead of inorganic particles as the filler and 4-META as the coupling agent, were experimentally prepared under 20 different conditions (five different concentrations of 4-META, and four different contents of metal particles) The flexural strength of the prepared metal-resin composites was in the range of about 145-613 MPa The flexural strength was significantly influenced by the 4-META concentration, the metal particle content and their interaction The highest strength was estimated at 2-3 mass% of 4-META concentration and 920-935 mass% metal filler content The flexural modulus of the metal resin composite ranged approximately from 78 GPa to 155 GPa The flexural modulus of the metal resin composite significantly increased with the metal particle content The effect of the 4-META concentration on the flexural modulus was not significant
TL;DR: This FTIR estimation method of residual monomers in cured resins using the NH absorbance peak as an internal standard could be an appropriate method when the resin monomer does not contain aromatic compounds.
Abstract: The purpose of this study was to establish a method using FTIR to evaluate the polymerization characteristics of UDMA-based resins. Three kinds of experimental UDMA-based resins were prepared with various molar fractions. IR spectra of the cured film specimens were measured with FTIR before and after extracting residual monomer from each specimen by MeOH. From the IR spectra, the changes in the number of double bonds were measured, with the NH absorbance peak as an internal standard, and the amounts of residual monomers (RM) were calculated. The MeOH-immersed specimens were analyzed by HPLC. The RM measured by FTIR were compared with those measured by HPLC. The RM measured by HPLC were more than those by FTIR. Since these differences could be due to the difference in the area measured, this FTIR estimation method of residual monomers in cured resins using the NH absorbance peak as an internal standard could be an appropriate method when the resin monomer does not contain aromatic compounds.
TL;DR: The isothermal age-hardening behaviour of a multi-purpose dental casting gold alloy was investigated by means of hardness testing, X-ray diffraction study, scanning electron microscopic observations and energy dispersive spectroscopy to attribute to the fine nodular precipitation resulting from the formation of the beta phase in the alpha 1 matrix.
Abstract: The isothermal age-hardening behaviour of a multi-purpose dental casting gold alloy was investigated by means of hardness testing, X-ray diffraction study, scanning electron microscopic observations and energy dispersive spectroscopy. By ageing of the solution-treated specimen at 400-500 degrees C, two phases of the Au-rich alpha 1 phase with an f.c.c. structure and the alpha 2 phase with an ordered f.c.c. structure based on Pt3In were transformed into three phases of the alpha 1 phase, the alpha 2 phase and the beta phase with an ordered f.c.t. structure based on PtZn. Hardening was attributed to the fine nodular precipitation resulting from the formation of the beta phase in the alpha 1 matrix. Softening was due to the coarsening of the fine nodular precipitates as the result of consumption of the alpha 2 phase.
TL;DR: The reinforcement mechanism of dentin mechanical properties by intracanal medicaments was investigated and it was found that eugenol immersion might have reinforced the dentin tensile strength by not only protein coagulation but also chelation with hydroxyapatite.
Abstract: The reinforcement mechanism of dentin mechanical properties by intracanal medicaments was investigated. The dumbbell-shaped specimens were prepared from a collagen sheet, demineralized dentin and organic dissolved dentin. After immersing the specimens in intracanal medicaments (eugenol and formocresol), the tensile test was carried out in 37 degrees C water and the Vickers hardness test was performed. The tensile strengths increased after eugenol and formocresol immersion, especially collagen and organic dissolved dentin after formocresol immersion and demineralized dentin after eugenol immersion. Thus, formocresol immersion might have reinforced the dentin tensile strength by protein coagulation, while eugenol immersion might have reinforced the dentin tensile strength by not only protein coagulation but also chelation with hydroxyapatite. However, the hardness values did not significantly change after intracanal medicament immersion.
TL;DR: Results indicate that the shape memory wire may be a reasonable material for a new concept of intermittent orthodontic treatment, in which mild force will be applied to the tooth for most of the daily hours and the tooth movement will be intermittently accelerated by larger forces generated only when the patient has hot foods or drinks.
Abstract: The characteristic temperature dependence of recovery force was evaluated for a Cu-containing Ni-Ti shape memory wire with the nominal Af point being 40°C. It exerted mild recovery force within the range of the proposed optimum force at the usual oral temperature. Larger forces were generated when it was heated to temperatures above Af: 40, 50 or 60°C. By subsequently cooling to temperatures below Af, the force decreased again, and vice versa. The excellent reversibility, reproducibility and durability of the recovery force were also confirmed. These results indicate that the shape memory wire may be a reasonable material for a new concept of intermittent orthodontic treatment, in which mild force will be applied to the tooth for most of the daily hours and the tooth movement will be intermittently accelerated by larger forces generated only when the patient has hot foods or drinks.
TL;DR: Three phase transformation modes occurred; ordering at grain boundaries and in the grain interior with nucleation and growth mechanism after incubation, and spinodal ordering without any incubation period, which increased according to Pd content and age-hardening of the alloys examined.
Abstract: Phase transformation mechanisms in the AuCu-Pd pseudobinary system were studied by means of electrical resistivity measurements, hardness tests, X-ray diffraction and transmission electron microscopy. A direct aging method was employed to eliminate the otherwise unavoidable ordering that takes place rapidly during quenching into ice brine, hence it is important to distinguish the ordering processes with and without an incubation period. Three phase transformation modes occurred, namely; ordering at grain boundaries and in the grain interior with nucleation and growth mechanism after incubation, and spinodal ordering without any incubation period. The age-hardening of the alloys examined was attributed to AuCu I ordering. Nucleation and growth mechanism followed by twinning occurred in the specimens aged at higher temperatures, while spinodal ordering was seen in specimens aged in lower temperature. The spinodal ordering temperature of AuCu-Pd alloys increased according to Pd content.
TL;DR: The results of the present study indicate that the powder-liquid system is effective to improve the properties of the metal-resin composite.
Abstract: In order to further improve the mechanical properties of a metal-resin composite and avoid the problems which were found in the previous metal-resin composite using a 2-paste system, another type of metal-resin composite using a powder-liquid system was developed. In the new system 4-META treatment was carried out at low temperature and DMPT was separated from the 4-META treated particles. The efficacy of this system as well as the effects of 4-META concentration, duration of 4-META treatment (immersion time) and filler content on the flexural properties, working time and setting time were investigated. The flexural strength of the powder-liquid composite was significantly affected by two main factors, immersion time and filler content, and the other properties (flexural modulus, working time and setting time) were by all three main factors. The highest flexural strength of the prepared composite was 91.8 MPa, which was higher than that of the 2-paste composite (64.0 MPa) by about 43%. This was achieved at a 0.1 ratio of 4-META concentration, 30 s immersion time and 94 mass% filler content. The working time and setting time ranged between 2.3-13.6 min and 4.2-20.1 min, respectively, and those of the highest strength composite were 3.0 and 5.2, respectively. The results of the present study indicate that the powder-liquid system is effective to improve the properties of the metal-resin composite.