Dissolution of nickel from a pure nickel plate was studied in Ringer's and Hanks' solutions, a tissue culture medium, MEM, and artificial saliva to understand the corrosion behavior of alloys containing the metal under a physiological environment. Tissue culture medium containing serum and the artificial saliva containing either albumin or mucin were also prepared. Extraction was done under gyrating conditions for one week and then the extract was analyzed. The experimental process was repeated for ten weeks. 1. Dissolution of nickel in Ringer's and Hanks' solutions was less than 1ppm throughout the experimental period. 2. Dissolution of nickel in MEM was almost the same as that in saline solution at the 1st extraction, followed by gradual increase thereafter and reached 121.0ppm at the 10th extraction. On the other hand, addition of serum to MEM increased nickel dissolution at the 1st extraction, but the dissolution was similar to that in serum-free solution by the 10th extraction. 3. Dissolution of nickel in artificial saliva was 32.66ppm at the 1st extraction and then gradually increased up to the 4th extraction with a maximum dissolution of 107.6ppm. The dissolution level decreased with subsequent extraction.Addition of albumin to artificial saliva increased the dissolution at the 1st extraction. After the 2nd extraction, dissolution of nickel was similar to that without albumin. In the presence of mucin, dissolution of nickel was similar to that in artificial saliva at the 1st extraction, but, the level decreased markedly with subsequent extraction. 4. Ultrafiltration, which excluded molecules larger than 30, 000 MW, significantly reduced the level of nickel dissolution in artificial saliva containing albumin. The present results demonstrate that nickel dissolution is affected by the presence of either albumin or mucin, and also dependent upon the duration of extraction. The present findings may shed light on in vivo corrosion behavior and biocompatibility of the metal.

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Cell recovery from damage caused by dental materials was examined in vitro. Four kinds of tissue culture cells were cultured in petri dishes, onto which six metal elements (Co, Cr, Ni, Ti, Cu and Fe) for dental alloys had been vacuum-evaporated. The cells were then placed in a normal culture environment, and their growth evaluated. The pH and amount of dissolved metals were also measured. Cell morphology was observed by SEM. 1. Copper was the most soluble (over 100ppm) in either Eagle's MEM or Dulbecco's modified Eagle medium. This was followed by cobalt, nickel, iron and chromium in that order. Titanium was not soluble. 2. In cell growth tests with L-929 cells, HeLa S3 cells, HEp-2cells and Gin-1 cells, cytotoxicity was observed with copper, cobalt and nickel in that order. Chromium, iron and titanium showed little cytotoxicity. 3. The results of cell recovery tests with L-929cells, HeLa S3 cells and HEp-2 cells to the six metals were similar to the results of the cell growth tests. By contrast, cobalt and nickel showed strong cytotoxicity to Gin-1 cells. 4. Copper, cobalt and nickel caused extensive damage to the cells, whereas chromium, iron and titanium had little influence on cell morphology. The present results suggest that the cell recovery tests open a new field for testing cytotoxicity.

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The cytotoxic effect of composite resins were determined quantitatively by measuring the region of change in morphology of L cells produced in the monolayers. All materials tested were light-activated composite resins cured under the recommended condition; Pyrofil Bond (I), Pyrofil Light Bond (Anterior) U (II), the same with coating of bonding agent (III) and Pyrofil Light Bond (Anterior) G (IV). The specimen 5 mm in diameter and 1.5 mm in thickness, was set on the center of the established monolayer on a cover glass (24 mm×32 mm). After a 24-hour cell-material contact the cells were fixed and treated with Giemsa-stain. The degree of morphological degeneration of cells was estimated through a microscope on a scale ranging 1 (nonchange) through 4 (complete cytolysis). Then the distribution chart of scores was drawn, and the distribution area of each score was measured with a digitizing system on a personal computer. The cytotoxic effect could be determined quantitatively from the measured area, even in the case of some materials which produced a shapeless and complicated area of score distribution. The sum of areas scored 3 and 4 was regarded as an area of cell death, and its percentage was applied to the index of cytotoxic effect. According to the index values, cytoxicity order of the materials was expressed as IV>III>I>II. The method mentioned above was useful for the comparative study of a large number of specimens, because of the high sensitivity for detection and estimating procedure, within a lenient time limit.

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A three-dimensional shape measurement system for making teeth models was assembled by using a high precision laser displacement meter and computer controlled scanning machine (CAMM-3). From the data obtained, reconstruction of the teeth model by CG (computer graphics) was attempted by means of a wire frame model program. The 7 molar abutment tooth was measured, and detailed features such as finishing line of margin or groove of gum retraction were reproduced by CG drawings. The time required for measurement was about 40 minutes by using the automatic model scanning system. Further measurement with a larger region of model sucu as 4〜7 was accomplished, and details such as wing or margin of abutment and fissure of molar were repreduced by CG drawings. Some disadvantages were recognized. For instance, error data are formed when the reflected beam is shaded by the model itself, or measurement is impossible at the the undercut portion of the model where the laser beam can't reach. Some improvements such as rotation or tilting of model will be required.

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Effect of the addition of alkaline earth metal phosphate crystals to a dental stone (Fujirock) was investigated to improve the mechanical properties of gypsum model materials. Based on the observation of the surface profile of the dental stone set in contact with glass and SEM of the fractured surface of the hardened mixture, the surface roughness was markedly decreased by the addition of calcium hydrogen phosphate, tricalcium phosphate, calcium, hydroxyapatite and octacalcium phosphate crystals. The bending strength of the hardened mixture was improved by the addition of calcium hydrogen phosphate and octacalcium phosphate crystals, but markedly reduced in the case of barium hydrogen phosphate crystals.Addition of other alkaline earth metal phosphates did not affect the bending strength of the dental stone.

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Mg-containing fluoridated hydroxyapatites with various fluoride contents were synthesized (80℃ and pH 7.4) to examine the effect of Mg²⁺-F^- interrelation on their physicochemical properties, and compared with a corresponding Mg-free series. The a-Axis dimensions of Mg-containing fluoridated hydroxyapatites decreased with the increase of fluoride content and seemed to decreas emore with the increase of magnesium content. The c-axis dimensions decreased with the increase of magnesium content over the whole range of fluoride content. The Mg content of the apatites increased slightly with the degree of fluoridation despite the constant magnesium concentration in the feed solution. With the increase of fluoride content, the crystallinity varied differently in each series: Mg-free fluoridated hydroxyapatites showed a minium crystallinity at a low fluoride content; in those with a lower Mg content this was obliterated; and in the series with a higher Mg content, crystallinity rose to a maximum at about half of the maximum fluoride content, although crystallinity of F-free Mg-containing hydroxyapatites decreased monotonically with the increasing Mg content. Such a crystallinity behavior in each series was not analogous to the solubility behavior. A macroscopic mass transfer model for crysal growth has been proposed.

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The aim of this study is to improve the polymerization degree of visible light-cured resin. After preparing some kinds of trial visible light-cured resin by changing the amount of catalysts (a number of times), each set product was examined with regard to water sorption and solubility when set products were immersed in water and MeOH sorption, THF sorption and constituents of elution when set products were immersed in organic solvents. No clear relation between the varieties or amount of catalysts and water sorption or solubility was detected for set products immersed in water for a short period of sixty days or so. However, when MeOH was used as a solvent, there was an undeniable relation between the amount of catalysts and solubility, despite of the briefness of the immersion time. Finally the solubility of a trial visible light-cured resin that used the cyclophosphazene monomer 4PN-(TF)₁-(EMA)₇ was less than that of a resin which used commercially available Tri-EDMA. The amount of solubilized unreacted monomer was relatively small. In this case, the eluted amount of DMAB was most outstanding of all the catalysts. For the decrease of solubility, an effective method was found to be to increase the amount of photoinitiators, CQ and DB, to be mixed, while decreasing the amount of an auxiliary catalyst, DMAB.

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For the metal-ceramic composite implant, to make good use of the toughness of the metal, there is need to from a thin layer of ceramics. Alumina-coated stainless steel produced by the ion-plating method was investigated. The coated film on the stainless steel substrate was identified as α-Al₂O₃ by EPMA, XRD and XPS analysis. The proof stress and modulus of elasticity of alumina-coated stainless steel did not exchange by ion-plating. The residual strain on the first point observing cracks ranged from 0.5 to 1.6% by bending test. The composite material of 1〜5 μm thick film of alumina and 1 mm thick stainless steel was able to bend the radius ranging from 87.2 to 49.6 mm without cracking. The corrosion resistance was improved by coating 3 μm thick alumina on SUS 321 and the heat-treated SUS 321 stainless steel in 0.9% NaCl solution.

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The bond strength of the resins (MMA-TBB resin system) containing various methacrylates to dentin treated with a 10-3 solution was measured. The resin reinforced dentin was observed by SEM and the distribution of Ca, Fe and Br at resin (2 BEM)-dentin interface was analyzed by EPMA to determine the relationship between the bonding and the chemical structure of methacrylates as well as the formation of the resin reinforced dentin. There was no significant relationship between the monomer structure and the bond strength after immersion in 37℃ water for 1 day or 30 days. The resin reinforced dentin was about 3 μm thick at interface between all resins and dentin as observed by SEM. The presence of Fe in resin reinforced dentin was confirmed from the Fe X ray map and line profile. Br line analyses showed that the concentration of 2 BEM in resin reinforced dentin was higher than the original concentration in the resin monomer.

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One side welding of butt joint of pure titanium rods (JIS type II) was performed by the direct current TIG (tungsten innert gas arc) welding. Formation of fusion zone was influenced by the welding current, arc length, and arcing time. Welding time with full penetration and without burn through was set for each welding current. One or two pits were found in the surface of fusion zone when the welding was made, but they could easily be repaired. Welding could be done with little contamination when the welding part was sealed well by argon gas, and good mechanical properties were obtained with Hv 155, 428 MPa in tensile strength, 22 percents of elongation

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Factors affecting the machining properties of pure titanium with both ram and wire-type electric discharge machining were investigated. Surface texture and mechanical properties of the titanium specimen made by the electric discharge machine were also examined. The polarity of electrode and the electric conditions were found to affect the machining properties. For the electric discharge machine investigated in this study the conditions of pulse magnitude 16 A, pulse on time 100 μsec., pulse off time 60 μsec., and reversed polarity were found to be efficient in practice. The material of the electrode was also found to affect the machining properties. The copper electrode showed more sufficient machining properties than the other materials. Pure titanium was found to be machined easily by the wire-type electric discharge machine with the same electric conditions as stainless steel, and showed excellent machining properties. The electric discharge machining showed a matte finish with many small spots, and the wire-type electric discharge machining had smaller spots than the ram-type electric discharge machining. A hardening layer was found in the surface of the specimen made by the ram-type electric discharge machine and the thickness of the hardening layer was affected by the current conditions. No hardening layer was found in the surface of the specimen made by the wire-type electric discharge machine. The specimen made by the electric discharge machine showed sufficient tensile strength and elongation.

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Some trial models of titanium prosthesis were made by the electric discharge machine, and several investigations were made. The ram-type electric discharge machining was applied to the milling technic. Milling surface of titanium made by the electric discharge machine had a texture similar to that of precious metal. Titanium was efficiently drilled and grooved by the special electric discharge machine. The dimensional accuracy of model crown made by the ram-type electric discharge machine was investigated. Fittness between crown and abutment tooth was obtained when the reciprocation and the exchange of electrode were set. Male and female models of the telescope denture were made by the wire-type electric discharge machine, and the fittness between male and female could be controlled by numerical control.

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Resin cements consisting of hydroxyapatite and TMPT filler (2:3, by weight) as a powder and a mixture of HPPM and TEGDMA (2:3, by weight) as a liquid were prepared, and their physical properties and tensile bond strength to bovine teeth were investigated. The physical properties were measured: setting time 4 min 40 sec, film thickness 24.0 μm, compressive strength 1, 600 kgf/cm², diametral tensile strength 340 kgf/cm², and percentage of eluted monomer 1.51 wt%.The film thickness 24.0 μm was within the limit of JIS (30 μm) and was less than that of the resin cement previously reported. Tensile bond strength to enamel and dentin treated with 10-3 was 70 kgf/cm² and 22 kgf/cm² respectively, when the bonding agent consisting of a mixture of HPPM and TEGDMA (2:3, by weight) and BPO, DMPT, P-TSS as a catalyst were applied.

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Self-setting apatite cement which consists of an equimolar mixture of tetracalcium phosphate (Te-CP) and dicalcium phosphate dihydrate (DCPD) has been studied in vitro and in vivo to evaluate its potential as dental cement for clinical application. In synthetic saliva undersaturated with respect to DCPD but well supersaturated with respect to hydroxyapatite (HAp), no dissolution occurred even when the set cement still contained initial materials of Te-CP and DCPD, which eventially transformed into HAp about 4 hours after spatulation. On the contrary, the solution calcium and phosphate concentrations decreased once the set cement was introduced, which indicates that the set cement incorporated solution calcium and phosphate as solid phase of HAp. In oral environment where proteins and many inorganic ion species are expected to inhibit HAp formation, X-ray diffraction analysis suggested that the cement filled in monkey's tooth cavity for at least one day completely transformed into HAp. The crystallinity of the set cement as HAp increased with time even in oral environment as a result of remineralization. Under a scanning electron microscope, no apparent gap appeared between the hard tissues and the set cement which had been filled in monkey's tooth cavity for three months. Some portion of the cement at the interface suggested that the setting reaction took place by using HAp on hard tissues as seed nuclei. In this respect, direct chemical bonding exists between the set cement and hard tissues. Dye penetration test after thermal cycling of the same specimen indicated that the adaptation to the hard tissues is so superior that no significant amount of dye can penetrate, whereas for zincoxide-eugenol cement used as control cement, dye penetrates through the interface.

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Barrel finishing of cured base resin samples using the centrifugal barrel machine with alumina media (RK^®, UC^®, UP^®, and SA^®) and organic media(B^®) was performed and surface texture was examined. Crushed massive alumina media RK with a sharp edge showed the largest amount of polishing but the surface texture was found to be rough. Sintered globular media SA showed small amount of polishing and the surface texture could not be improved. Organic media B showed similar amount of polishing to sintered almina media UC and UP, and the surface texture was more efficiently improved than alumina media, and had a glossy surface. Barrel finishing with organic media was found useful to obtain a smooth and glossy surface of base resins.

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Surface tension of dental metals is important for the castability. A model for measuring surface tension of dental metal at solidification was devised and the equation was set up. Surface tension of silver copper, tin and zinc were obtained as an example. To the lower and part upper of the specimen in cylindrical shape, the Young-Laplace's formula was applied and the equation for measuring surface tension γ was obtained as follows. [numerical formula] With an argon arc furnace, metal was melted in a graphite crucible and after the metal was solidified, the curvature of the lower part of the specimen and others were measured. Then, surface tension was calculated. 1. To request the density of the metal was not necessary and the measuring was simple. 2. Only 0.4〜2.5 g of sample metal was necessary for measurement.

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To clarify the interface reaction between porcelain and a commercial Ni-Cr dental alloy (containing Be) during porcelainization, electron probe micro analyzer (EPMA) and X-ray diffraction method have been used to characterize the interface which emerged by selective dissolution of the alloy caused by the bromine-methanol solution. Elemental distribution maps across the reaction layer have been provided by alternating EPMA and etching the interface by 1 micron meter depth with Ar ion RF sputtering. At an early stage of porcelainization, a large amount of Ni oxide was generated. However, a long fusing interval resulted in the reduction of such a oxide and oxidation of Be became a dominant reaction. This is because porous porcelain particles change into airtight sintering glass and, as a result, oxygen partial pressure at the interface falls remarkably. Under this condition, oxidation depends upon the equilibrium dissociation pressure of each oxide rather than the alloy composition.

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A new functional monomer, 2-methacryloxyethyl hydrogen maleate (2 MEM), was prepared by the addtion of maleic anhydride to 2HEMA and its bond strength to polished and etched tooth surfaces under dry and wet conditions was measured and compared with that of 2-succinoxyethyl methacrylate [2SEM (control)]. The synthesized monomer was identified by elemental analysis, IR and NMR. The bond strength of 2 MEM to polished enamel was equivalent to or lower than that of the control under dry and wet conditions. However, the bond strength of 2 MEM to polished dentin and etched enamel and dentin under dry and wet conditions was higher than that of the control.

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