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

Ag-Pd binary alloys with various palladium contents were extracted in Eagle's minimum essential medium by dynamic extraction at 200 rpm at 37 degrees C. The extracts were filtered through a 0.22 microns cellulose acetate filter, and the silver and palladium amount of the extracts and filtrates as dissolved metallic elements was measured with atomic absorption spectroscopy. Extracts and filtrates were also used in cultivation of L-929 cells to study in vitro cytotoxicity. An increase in the palladium content of the alloy resulted in decreased silver dissolution and increased palladium dissolution. The amount of palladium in the filtrates increased as the extraction period was extended, but the amount of silver was negligible in all filtrates. Extracts which had been extracted for 1 day showed strong cytotoxicity in pure Ag. However, the addition of palladium at a weight percent of more than 40% decreased cytotoxicity almost to the control level. Filtrate which had been extracted for 1 or 3 days was noncytotoxic in all alloys. However, the filtrate which had been extracted for 5 or 7 days showed cytotoxicity, which was especially strong in high-palladium alloys. These results demonstrate that extraction using a dynamic method appears to be useful in the investigation of their corrosion and biocompatibility.

Adhesion durability between dentin pretreated with 10-3 and 4-META/MMA-TBB resin was studied. Reduction of etching periods with 10-3 was not so effective as expected. The weakening of bond strength during immersion in water at 37 degrees C to the dentin pretreated for 1 sec occurred faster than those for either 5 sec or 10 sec. The strength decreased from 12 MPa at 1 day to 9 MPa at 3 months, 3 MPa at 6 months and finally 2 MPa at 1 year in the case of 1 sec pretreated dentin. On the other hand, the strength became half after the storage in water for 1 year in the cases of 5 and 10 sec pretreated dentins. Combination of 10-3 pretreatment and subsequent glutaraldehyde treatment could stabilize the decrease but not completely. SEM and TEM examinations suggested that dentinal collagen exposed by the etching but not entangled and impregnated by poly (4-META-co-MMA) easily deteriorated by water during the longer immersion. Collagen modified with 10-3 and then with glutaraldehyde was also changed by the longer immersion.

An excellent durability of adhesion was obtained in the adhesion of 2% 4-META/MMA-TBB resin to dentin pretreated with EDTA 3-2 (NH4/Fe). Such high bond strength as 15 MPa did not change for up to one year even when they were immersed in water at 37 degrees C. The resin reinforced dentin, a hybrid, was identified between dentin and the cured resin by TEM. The collagen and hydroxyapatite were encapsulated with the copolymer and the crystals were not removed by the demineralization with either HCl or electronic staining. Tensile fracture between the hybrid and dentin like the adhered samples to 10-3 treated dentin did not occur and the cohesive failure in the resin was observed here after the storage in water for a year. EDTA 3-2 (NH4/Fe) could not completely demineralize the hydroxyapatite especially at the deeper portion and the width of the demineralized dentin became thinner than 1 micron. The encapsulated crystals with the resin could improve the resistance of collagen against deterioration in water and such good bonding durability could be obtained.

As a model experiment to understand the mechanism of adhesion of the 4-META-MMA/TBBO resin to dentin, 4-META-MMA/TBBO was polymerized in the presence of decalcified dentin sheet treated with citric acid (CA) aqueous solution containing ferric chloride (FC). Curing time of MMA/TBBO resin was reduced by the addition of 4-META to MMA. Addition of 4-META increased molecular weight of PMMA. PMMA polymerized inside the decalcified dentin sheet was insoluble in acetone. PMMA obtained from the monomer liquid used in commercial Super-Bond C & B was all insoluble and no soluble fraction was obtained. These results suggested that 4-META accelerated polymerization of MMA-TBBO resin in the presence of ferric ion and was effective to enhance molecular weight of PMMA. These effects seemed to be related to high bond strength of Super-Bond with dentin.

The zirconia investments with calcia were studied of the compressive strength, setting expansion, thermal expansion, total expansion, thermogravitometry, differential thermal analysis on fabrication method, concentration, particle size of zirconia, calcia and mixing liquid. Addition of calcia caused the change from contraction to expansion in setting expansion. The optimum concentration of calcia was determined to be 10 mol% as judged from total expansion, strength and operability.

The bending fatigue test of crown and bridge resin facing metal frame was carried out under a scanning electron microscope, and the fracture and propergation behavior of junction was studied. The resin facing metal frame with retention beads had a static breaking stress of about 100 kgf/mm2. The resin facing metal frame, when bonded with adhesive, had the stress of about 36 kgf/mm2. The specimens with retention beads and bonded with adhesive were not destroyed at cycles of 10(6) under the bending fatigue stress of below 40% and 50% of the static breaking stress, respectively. Marginal micro gaps between resin and metal frame with retention beads were observed before the fatigue test, and were increased with the number of cycles. Then fracture of the specimen occurred from the resin of the retention beads side. In the specimen bonded with adhesive, marginal micro gaps between resin and metal frame were observed during the fatigue test, and the partially cohesive fracture occurred.

Seven 2-thiobarbituric acid derivatives with methyl substituents were synthesized. Experimental visible-light curing resins were prepared using these compounds as a reducing agent in the dl-camphorquinone (CQ)-reducing agent initiator system. The effects of methyl substitution for thiobarbituric acid on initiation behavior of CQ-thiobarbituric acid initiator system were examined by analysis of polymerization of triethylene glycol dimethacrylate (3 G) in DSC and depth of cure. The solubility of thiobarbituric acid derivatives in 3 G was markedly changed by the introduction of the methyl group. Although the methyl group substitution at position 1 (3) in thiobarbituric acid improved the solubility of the acid in 3 G, it did not enhance the initiation ability. Maximum exothermic rate, time at maximum exothermic peak, amount of insufficiently polymerized layer and depth of cure were significantly improved by the introduction of one methyl group at the position 5. Thus the initiation ability was enhanced by the substitution. However, the introduction of two methyl groups at position 5 did not promote polymerization, but the inhibitory effect became apparent as the concentration of the reducing agent was increased.

A centrifugal barrel finishing apparatus with a variable turn table rotational speed (250-1,000 rpm) was newly developed and barrel finishing of Ni-Cr casting plates (10 x 10 x 2 mm) was performed using alumina base chips. When using the sample with a mirror face the amount of polishing and the surface roughness increased and the surface gloss decreased with the increase in rotation speed. A high rotational speed was useful for coarse polishing and low rotational speed was useful for fine polishing. The continuous barrel polishing was trially performed using the sample prepared by the carborundum wheel under variable rotational speed. Automatic polishing to fine polishing could be done using this apparatus.

Cell recovery of four cell lines [L-929 cells, HEp-2 cells, Gin-1 cells and the cells from human dental pulp tissues (Hp cells)] was examined after exposure to four zinc phosphate cements, five polycarboxylate cements, three glass ionomer cements, five resin based cements and one zinc oxide-eugenol.EBA cement. Phosphate cements, glass ionomer cements and zinc oxide-eugenol.EBA cement were markedly cytotoxic to the four cell lines 3 hours and 24 hours after mixing. Polycarboxylate cements considerably inhibited cell recovery of the three types of cells except Hp cells even 24 hours after mixing, compared to the gradual recovery of Hp cells after mixing. Two of the resin based cements inhibited cell recovery, while the three others allowed moderate cell recovery. The pH values of the medium used for the experiments was 6.6-6.8 for phosphate cements, glass ionomer cements and zinc oxide-eugenol.EBA cements. Polycarboxylate cements had no effect on the pH. On the other hand, in resin based cements the pH was shifted from acidic to basic. The solubility of the materials used was, in decreasing order: glass ionomer cements, zinc oxide-eugenol.EBA cement and one of the resin based cements, polycarboxylate cements, phosphate cements and another resin based cement, and the other three of resin based cements (lowest). The difference in cell recovery was considered to be due to composition and solubility of the materials.

Fe-containing hydroxyapatites and fluoridated hydroxyapatites were synthesized at 80 degrees C and pH 7.4. Fe-containing hydroxyapatites became poorly crystallized with the increase of Fe2+ ions in the solution and a- and c-axis dimensions seemed to decrease slightly. The apparent solubility of Fe-containing hydroxyapatites decreased greatly with the increase of iron content in spite of the decrease in crystallinity. Fe-containing fluoridated apatites were less well crystallized than Fe-free fluoridated apatites. The Fe2+ uptake of fluoridated apatites was independent of fluoride concentration in the solution. a-Axis dimensions of Fe-containing fluoridated apatites decreased with the degree of fluoridation in addition to the decrease related to the substitution of Fe2+ ions. The apparent solubility of Fe-containing fluoridated apatites decreased more than that of Fe-free fluoridated apatites especially at a low fluoride content.