Shika zairyo, kikai = Journal of the Japanese Society for Dental Materials and Devices最新文献

The direct tensile test of composite resins using the specimen with the gauge length 10 mm has been developed by authors. In this study smaller specimens with the gauge length 5 mm and 2 mm were also investigated. As the gauge length became smaller, tensile properties such as the proportional limit, the proof stress, and the tensile strength showed the tendency to become higher. The effect of strain rate on the tensile properties appeared clearly when using the specimen with the gauge length 2 mm. The small specimen was found to have many advantages for the preparation, the cost of material and the handling during the tensile test.

Mechanical properties and curing depth of light-cured composite resins based on five types of urethane tetramethacrylate (UTeMA; IP-4 M, XY-4 M, MC-4 M, HM-4 M and TM-4 M) were investigated, and compared them with those of UDMA-based composite resins. Composites based on UTeMA monomers containing an aromatic or cyclohexane ring in their chemical structure (IP-4 M, XY-4 M and MC-4 M) showed a relatively rigid properties than those based on aliphatic UTeMA (HM-4 M and TM-4 M). The composite resins based on XY-4 M monomer showed a curing depth and transmission coefficient superior to the other composite resins. UTeMA-based composites showed a significantly higher rigid properties than UDMA-based composites, while their rigidity did not improve the flexural strength.

Chitosan, a naturally occurring high molecule or weight polymer which is stable in vivo like collagen, has proved a useful biomaterial in applications such as suture thread and artificial skin. A hydroxyapatite bone-filling material was developed with chitosan sol as a binder. Measurements were made of the solubility of chitosan, and of the setting time, compressive strength, and pH value of the material. X-ray microanalysis and diffraction analysis of the material were also conducted. Chitosan is freely soluble in malic acid and succinic acid, but insoluble in citric acid and oxalic acid. The setting time of the bone-filling material tended to decrease with increase in the amounts of its CaO and ZnO components. The setting time increased with increasing ratio of sol to other (powdered) ingredients. The pH value decreased with increasing ratios of chitosan sol to the powdered ingredients. High pH values resulted from increases in both CaO and ZnO. The time between the preparation of the chitosan sol and the onset of kneading significantly affected the compressive strength of the material when set. The strength measured roughly 50% more for times between 90 and 150 minutes than for times shorter or longer than that range. Greater compressive strength was generally observed for increases in both CaO and ZnO. The results of the X-ray microanalysis of the hardened paste showed calcium crystals other than hydroxyapatite.

Experimental gypsum-bonded investments containing 0.5-5.0 wt% NbC were prepared by mechanical mixing of each powder. Setting and thermal expansion measurement, compressive strength and casting accuracy for Ni-Cr alloy for metal-ceramic restoration were investigated. Analysis of NbC during heating was carried out by X-ray diffraction, TG-DTA and SEM. NbC was oxidized to Nb2O5 with a volume change between 300-600 degrees C, as in the following equation: 2NbC + 4 1/2O2----Nb2O5 + 2CO2 The theoretical volume of 1/2Nb2O5 calculated from the lattice constants according to JCPDS file was approximately 4 times larger than that of NbC. The experimental investments of 70 wt% cristobalite and 30 wt% gypsum containing 2.0, 3.0 and 5.0 wt% NbC showed large thermal expansion of 7.0, 10.0 and 13.0% respectively. The investment containing 2.0 wt% NbC showed nearly the same casting accuracy for Ni-Cr alloys for metal-ceramic restoration as the commercial phosphate-bonded investment.

The tracer element molten (TEM) method has been developed for flow visualization of molten Titanium in dental precision casting. The principle of this technique is as follows. When Titanium is cast, the tracer element wire inserted previously into the selective point of the sprue is molten little by little and distributed according to the molten Titanium flow in the mold cavity. After solidification, to observe the flow pattern, the tracer element needs to be analyzed on a section of the casting by EPMA equipped with the stage scan mapping system. This technique using Ag, Au, Pd or Pt as a tracer has been applied to some simple castings in shape and has been confirmed to be a very powerful technique for Titanium flow visualization in dental castings.

The adaptability of composite resin inlays was examined. CR Inlay and INLAY/ONLAY were used as materials. After the CR Inlay was polymerized in a U-form metal mold, the dimensional changes were measured before and after heating. Furthermore, the composite resin inlays made according to the manufacturer's instructions were cemented in an MOD type cavity and the film thickness of the cement was measured. The polymerization shrinkage of CR Inlay was 0.63% in the inside of the inlay and after heating it increased to 0.71%. The film thickness of the cement in the case of CR Inlay was more than 250 microns and that in the case of the INLAY/ONLAY was more than 750 microns in the MOD type cavity. Dentacolor XS (a box type photo generator) was better than Wite Lite (a handy type photo generator) for the polymerization of CR Inlay. Because of the poor adaptation of the inlays and the difficulty in removing a inlay from a stone model for CR Inlay, perhaps polymerization shrinkage of the inlay should be compensated in some way.

The thermal properties (thermal diffusivity and thermal conductivity) of human teeth and some dental cements were measured. The temperature change at the pulp cavity was also measured before and after the restoration with the full metal crown. The thermal insulating efficiency of dental cement was discussed. The thermal diffusivity of human dentin, enamel and dental cements was 2.04 x 10(-3), 3.22 x 10(-3), and 0.99-1.87 x 10(-3) cm2/sec, respectively. The thermal conductivity was 1.36 x 10(-3), 1.84 x 10(-3), and 0.50-1.51 x 10(-3) cal/cm.sec.degrees C, respectively. The dental cement beneath the crown insulated the thermal shock to dental pulp and the thermal insulating efficiency was increased with the decrease in the thermal diffusivity and thermal conductivity of dental cement.

The influences of the composition on abrasion resistance of composite resins were examined using various experimental composite resins which had various matrix resin, filler size and content. The abrasion test was conducted by the experimental toothbrush abrasion testing machine developed in our laboratory. Three series of heat-curing composite resins were tested. One series was made from a Bis-MPEPP or UDMA monomer, and a silica filler with an average particle size of 0.04, 1.9, 3.8, 4.3, 7.5, 13.8 and 14.1 microns. The filler content of this series was constant at 45 wt%. The second series contained a silica filler of 4.3 microns in a content ranging from 35 to 75 wt%. The third series contained a microfiller (0.04 microns) and macrofiller (4.3 microns) in total content of 45 wt%. In this series, the microfiller was gradually replaced by 5, 15, 25 and 45 wt% of the macrofiller. The results obtained for these three series indicated that the abrasion resistance of composite resins was controlled by the inorganic filler, mainly filler size and content. The abrasion loss did not vary with the difference of matrix resin. When the particle size of the filler was below about 5 microns, the abrasion resistance decreased markedly with the decrease in filler size. The composite resin which contained a 0.04 or 1.9 micron filler was less resistant to toothbrush wear than the unfilled matrix resin. However, the microfiller also contributed to abrasion resistance when used in combination with the macrofiller, although abrasion resistance decreased with the increase in the microfiller concentration. The increase of filler content clearly improved the abrasion resistance when used the macrofiller. The analysis of these results and SEM observations of the brushed surfaces of samples suggested that the toothbrush abrasion was three-body abrasion caused by the abrasive in the toothpaste, and affected by the difference in the particle size between abrasive and filler, and between the abrasive size and the interparticle distance of the filler.

A translucent aluminous porcelain was developed for dentistry. The effects of refractive indexes and sintering behaviors on transparency and strength of the aluminous porcelains consisting of high refractive germanate-glass (Na2O-TiO2-GeO2) and alumina crystal powders were examined. The various germanate-glass specimens with a high refractive index were made by fusion at about 1,300 degrees C. The refractive indexes of fused Na2O-TiO2-GeO2 glass specimens were 1.64-1.76, heightened with an increasing TiO2 content. The sintered aluminous porcelains were made from the mixed compacts consisting of 80 wt% germanate-glass and 20 wt% alumina at the densification temperature of 580-820 degrees C. Sintered aluminous porcelains prepared with high refractive germante-glass had a high transparency compared with the other aluminous porcelains, with almost the same transparency as a commercial feldspathic porcelain (body). Aluminous porcelains had lower transparency with different refractive index due to generation of crystals following the crystallization of glass matrix than that without crystallizing property. Bending strength value was 120 MPa, which is similar to that for the glass-alumina ceramics with the same content of alumina volume as germanate-glass aluminous porcelains. Non-crystallized aluminous porcelain had a higher strength compared with the crystallized one.

Light-cured opaque resins with excellent physical properties were prepared using five types of monomer liquid and titanium dioxide as the powder. The five opaque resin monomer liquid had the following monomer compositions. Methyl methacrylate (MMA)/di(methacryloxyethyl) trimethylhexamethylene diurethane (UDMA) = 70/30 (M-U), MMA/neopenthylglycol dimethacrylate (NPG)/UDMA = 45/45/10 (M-N-U), UDMA/MMA = 70/30 (U-M), 2,2-bis (4-methacryloxypolyethoxy phenyl) propane (2.6 E)/2,2-bis [4-(3-methacryloxy-2-hydroxy propoxy) phenyl] propane (Bis-GMA)/triethyleneglycol dimethacrylate (3 G) = 60/35/5(2.6-B-3) and 3 G/UDMA = 70/30 (3-U) by weight. The bond strength, photo-curability and handling properties of the opaque resin were improved. Three MMA-based opaque resins showed nearly the same values in Knoop hardness number, diametral tensile strength and shear bond strength. The depth of cure increased with the decrease in MMA content of monomer composition, while the amount of residual monomer decreased. The 2.6-B-3 opaque resin had nearly the same properties in depth of cure and Knoop hardness number as the 3-U opaque resin. However, the 2.6-B-3 and 3-U opaque resins had a diametral tensile strength more than twice as high as that of the U-M opaque resin. The bond strength of three MMA-based opaque resins showed 0MPa after 5,000 thermocycles, while the 2.6-B-3 opaque resin, about 16 MPa, and the 3-U opaque resin, about 25 MPa. Therefore, the bond strength of the opaque resin was influenced by monomer composition. 3G-UDMA opaque resin showed excellent physical properties and may be clinically acceptable to bond fixed prosthodontic composite.