NiTi alloys are well known for its unique properties, such as shape memory effect and super-elasticity.They also possess good corrosion resistance and mechanical properties in high temperature phase.In this paper, the dental castings of NiTi alloys were examined by using an argon arc pressure casting machine, and mechanical properties and microstructures were studied.Good mechanical properties were obtained by using Alumina or Magnesia coated phosphate-bonded investiment mold.The properties of NiTi alloys were changed by composition and the conditions of heat treatment.Shape memory effect and super-elasticity were showed even after dental castings.From the results of this study, NiTi alloys are considered to be promissing dental casting alloys and new development of dental techniques are expected by using these unique properties.

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Commercially available tannin fluoride preparations, which are used to prevent caries by strengthening both inorganic and organic components of teeth, were added to dental cements for luting.New cements containing tannin fluoride preparations were compared with conventional type cements based on Japanese Industrial Standard(JIS)T-6602 and ADA Specification No.8.From our observations, the following results were obtained:1.The mechanical properties of cements containing tannin fluoride preparations were superior to those lacking them.2.The solubility of HY-BOND(glasionomer-c)was markedly lower than that of Fuji-Ionomer Type1, but the addition of Tannin Fluoride preparations to the latter resulted in even higher solubility in our laboratory's experiment.3.The film thickness of glass ionomer cement, which has been a problem until now, was decreased by using modified, smaller powder particles, and so forth.

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Studying on the corrosion of a conventional type spherical alloy and a high-copper type spherical alloy, the amount of dissolved elements, Ag, Sn, Cu and Hg was measured by means of an atomic absorption analyzer.Three factors, A)solution, B)time and C)temperature and levels were selected.Both amalgams showed a same tendency on dissolution of Ag and Hg.The ratio of Hg to Ag dissolved from both amalgams was slightly less than that of γ₁phase.Although a large amouunt of Sn was released from the conventional amalgam, no Hg as a component for γ₂phase was detected.An approximate amount of Sn and Cu to the ratio of η'phase was released from the high-copper amalgam.The ratio of corrosion is estimated as γ₂:γ₁ is about 8.5 and η':γ₁ is about 2.2 by calculation based upon the amount of dissolved Ag, Sn and Cu.As for the factors influencing the amalgam corrosion, factors B and C to γ₁phase, factors A and C to γ₂phase, and all factors to η'phase were respectively significant.

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Various commercially available amalgams were metallographically investigated using SEM/EDX.As a result, amalgam alloys were divided into two types, low copper-content alloys containing at most 6wt% copper and high copper-content alloys containing more than 6wt% copper.Furthermore, high copper-content alloys were classified into admixed and single compositions by the type of copper-addition.Amalgams made from these alloys showed the characteristic structure respectively.The low copper amalgams showed three types, namely, lathe-cut, spherical and admixed types.On the other hard, the admixed high copper amalgams were divided into non γ₂ type and γ₂ containing type, then subdivided into several types by the alloy particle form and composition.And the high copper single comosition amalgams showed three types, namely, spherical, spheroidal and lathe-cut types.

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Improvement of the physical properties of dental restorative resin was made with incorporation of crosslinked polymethacrylate derivatives as the filler of composites.However, these polymer fillers had poor solubility to monomer and unfavourable physical properties of resultant specimens.In this study, surface treatments were made on the praticles of crosslinked polymethacrylate and its effect on the Rockwell hardness, transverse strength and abrasion resistance was observed.Filler[Poly 2, 2-bis(4'-methacryloxy ethoxy phenyl)propane]and triethylene glycol dimethacrylate-bis MEPP(50:50mol%)were mixed together, poured into the metallic mold and heated to 130℃ for 15minutes, thus prepared the test specimens.Transverse strength of polymerized specimens were 769 kg/cm² for non-treated, 1205 kg/cm² for MACl-treated, 1144 kg/cm² for γ-MPTS-treated and 1400 kg/cm² for the specimens prepared from sulfuric aicd-MACl-treated polymer filler.On the other hand, with Rockwell hardness and abrasion resistance, little differences were observed between specimens prepared from surface treated and untreated polymer fillers.

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Summary The purpose of this paper was to study the effect of vibration for the fluidity of slurry such as dental stones and investments.The fluidity was defined by the speed of slurry flowing down the semicircular trough of diameter20 mm with inclination angle 20°.Other parameters were frequency(20〜200Hz), peak-to-peak amplitude(150〜3000μm)and wave shape(sine or rectangular).Results were as follows.1)Frequency and amplitude of vibration were closely related to the fluidity.As these were respectively increased, the fluidity was increased.But, there was limitation of increase, and beyond the limitation, the fluidity was rather decreased.In case of rectangular wave, the fluidity increased a little.2)As the water-powder ratio was decreased, the fluidity of slurry was decreased.Using the same kind of powder, the effect of vibration for the fluidity showed almost same tendency.3)There were various forms of fluidity curve caused by the difference of powder under the same vibration.4)The fluidity of slurry mixed with colloidal silica was decreased, especially fluidity showed more decrease between 15 and 30wt% SiO₂.5)Under stronger vibration, some kinds of slurry didn't flow but slid down in a mass, in this condition bubbles were easily produced.

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The purpose of this study was to investigate the clinical applicability of the combined cast restorations made by connecting the different types of dental alloys by using a new technique:the technique for connecting different types of alloys without soldering.In this technique the different types of alloys were cast into the mold separated by platinum foil simultaneously.The image of structures around the connected area was observed under the LM and SEM.In cases when 20K gold alloy or platinum gold alloy were used, their contact to platinum foil was observed to be readily fused without segregation.In case of Au-Ag-Pd alloy the connection was observed to be also excellent.In this case, however, the structural image observed under the LM and SEM showed that diffusions of some elements occurred between the platinum foil and the alloy.In all cases, porocities, oxide membrane or any other structural image which indicates the weakness of the connection were not observed.In addition this technique is very simple, therefore, this technique may be recommended for clinical applications.

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In order to examine the solubility of porcelain, three kinds of porcelain were prepared.Then, author steeped it either in alkali or acid solution and a quantitative analysis of dissolved element from porcilain was taken out and then surface roughness with dissolving was experimented.As a result, these are as follows:1)The dissolved quantities of various commercial enamel veneering porclain showed approximate values in each solutions that is acid(pH4.0:I-S), nearly-neutral(pH6.4:II-S)and alkali(pH10.0:III-S).On the other hand, differences in dissolution were recognized according to the kind of dissolved solution.Therefore, the dissolution was the largest in III-S, next in I-S and II-S.2)Much dissolved elements are Si, Na and K.On the other hand, less are B and Al.Ti was not detectable.3)From the measurement of roughness and the observation of SEM, surface roughness of porcelain was apt to be large according to the increase of dissolution.

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NiTi alloy has been given much attention in recent years.It possesses unique properties, such as“shape memory effect”and“outstanding elasticity”.Recently, the new NiTi alloy wire which possesses superelastic property was developed.The author has reported its tensile and three points bending properties before.In this study, bend and successive 90degrees bends tests were performed in accordance with The ADA Specification No.32 for Orthodontic Wires to evaluate the properties of the new superelastic NiTi alloy wire and compare them to those of stainless steel, Co-Cr alloy and work hardened NiTi alloy wire.In bend test, the new superelastic NiTi alloy wire produced low and almost constant bending moment between 50 and 80degrees of deflection angle as the wire returned to a rest position.The angle of permanent bend of it was zero even after 90degrees bend.In successive 90degrees bends test, the new superelastic NiTi alloy wire stood over 2000times, which were remarkably higher than those of stainless steel and Co-Cr alloy wire, and 4times over than that of work hardened NiTi alloy wire.These properties of the new superelastic NiTi alloy wire seem to be very useful for orthodontics.Fractured surfaces of the NiTi alloy wires by SEM after successive bends test showed dimple rupture pattern which were much different from those of stainless steel and Co-Cr alloy wires.

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A new composite resin“TC”has recently developed by joint efforts of Tani and Fujisawa Research Laboratory, Tokuyama Soda Co.Ltd..One of special features of TC is to be filled with submicronsized spherical silica particles which lie between conventional composites and microfilled resins in size of fillers.The ability to take a good polish and to maintain the polish are important clinical properties of dental restorative materials.The purpose of the present study was to evaluate the surface characteristics of TC in comparison with a conventional composite resin(Clearfil F II)and a microfilled resin(Superlux).Six specimens(11×11×1.5mm)in each material were cured at room temperature for 20minutes sandwiching with strips and stored in 37℃ water for 24hours.One group of specimens were polished with silicon carbide papers(#320 and #600)and buffed with alumina suspension using a polishing machine.Another group of specimens were polished with Sof-lex Discs(Medium, Fine and Super Fine)under dry condition by hands.On each step, the surface gloss and the surface roughness of the specimen were measured with a gloss meter(Nippon Denshoku Co.)and a surface roughness analyzer(Surfcom 304B, Tokyo Seimitsu Co.).The surface gloss was expressed as a percentage(GS)relative to the standard black board(GS 89%).1.With all materials, the value of the gloss of the unpolished surface, i.e.the matrixed surface, was best(GS 82〜90%).The gloss diminished steeply after coarse polishing and recovered in some degree as polishing progressed.However, it was impossible that the conventional composite could recover the surface smoothness lost by polishing.2.Both the gloss and the surface roughness of TC showed higher than those of the microfilled resin and much higher than those of the conventional composite resin in every polishing stage.

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Chemical composition and crystalline structure of enamel fused by YAG laser irradiation were studied by means of microradiography, electron microprobe, and microfocus-laue analysis.Compared with unlased enamel, a decrease in soft X-ray transmittance and an increase in Ca-K_α and P-K_α X-ray intensities were observed in fused enamel.Preferential evaporation of organic components by laser irradiation and density increase in enamel by fusion and resolidification are supposed to take place.By means of microfocus-laue analysis, a certain ordering in crystal orientation upon resolidification of fused enamel was verified by the spotty reflection rings in photographs.Besides, unknown reflection appeared at reflection angle 2θ≈31.0°in addition to the ordinary hydroxyapatite peaks of enamel, and it was identified as a reflection from α-or β-calcium orthophosphate which is the high temperature phases of hydroxyapatite.The improvement in acid-resistance of laser-exposed enamel was assured by the microprobe analysis of Ca and P, while in the extremely thin surface layer, slight decrease in concentration relative to unexposed one was observed.

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An unique automatic sterilizer for dental handpieces was devised to eliminate cross-contamination or cross-infection in dental practice.The features are as follows.1.Almost every type of high-speed dental handpieces are generally applicable.The air-bearing hand-piece is particularly relevant to the new sterilizer.2.The dental handpieces are cleansed and sterilized internally as well as externally with detergent or disinfectant discharged through the internal tubes of handpieces and kept in an ultrasonic bath.3.This sterilizer is believed to be easier and more efficient in sterilization than the conventional ones.4.This system would be effective to hepatitis B virus if a 2% glutaraldehyde solution is used as disinfectant.

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Newly developed posterior composite resins were compared with anterior composite resins and a dental amalgam by determining bond strength to tooth substance and some physical properties.Findings obtained were as follows:1.Bond strength of posterior composite resins was generally inferior to that of anterior adhesive composites.But, Pyrofil Radioopaque resin showed the bond srength nearly equal to that of anterior adhesive composites.2.Applying the new type of bonding agents increased in bond strength of the resins to both enamel and dentin.3.Physical properties of the composite resins at the early stage were superior to those of the amalgam.4.Compressive strength, tensile strength and bending strength of the posterior composites were higher than those of the anterior composites.Particularly, the compressive strength was remarkable.5.Maximum bending deformation was greatest with Microrest Jar Type resin and smallest with Pyrofil Radioopaque resin.

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The quantitative analysis of the casting porosity did not progress well as compared with that of the mechanical properties.The purpose of this study was to quantitatively determine the casting porosity and to investigate which parameter was useful in case of this quantitative analysis.Casting porosity of Au-Pd-Ag-Cu alloy was determined quantitatively by use of a system for quantitative image analysis.After taking a photograph of the casted specimen which was subdivided into equal sized pieces, the casting porosity was determined.The size and the form of each porosity, and the distribution of porosities were measured.The main results were summarized as follows The porosity ratio was influenced by the distance from the sprue.There was a clear difference between the porosity ratio of the central part and that of the marginal part.There was a definite correlation between the porosity ratio and the maximum area of the porosity.The perimeter of a porosity, the convex perimeter of a porosity and the lower positive tangent count of a porosity were useful parameters to determine the form of a porosity.From the facts described above, it was clear that the quantitative image analysis was very useful to determine the casting porosity.

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An optical microscopic observation, an electron microscopic observation and a measurement of weight change were performed on the dental base alloy with the composition of Ag-8wt.% Cu which were immersed in the Hanks' solution and in the Eagle's MEM.In the Hanks' solution AgCl was precipitated on the surface and an weight of the specimen was increased.For the specimen immersed in the Eagle's MEM, on the other hand, the weight was decreased and the precipitation was determined to be Ag₅P₂O₆N.Structural feature of each specimen did affected both on the amount of weight change and on the morphology of the precipitation.

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Dental base Ag-8wt.% Cu alloy were immersed in the Hanks' solution and in the Eagle's MEM and an electrochemical measurements were performed on the alloys.It was found that the rest-potential of the alloy in the Hanks' solution was rather noble than in the Eagle's MEM and that a arising point of an anodic polarization curve which corresponds to dissolving of silver was shifted into higher potential side in the Eagle's MEM.Structural feature of the alloy affected on its every electrochemical behavior.

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