各種アマルガムの圧縮強さにおよぼす腐食の影響を調べた.含亜鉛ならびに無亜鉛の従来型削片状アマルガム, 球状アマルガムおよび高銅型アマルガム11種を用い, 37℃水中あるいは0.5%食塩水中に1週間, 3カ月, 6カ月浸漬した後, 圧縮強さを測定した.水中に1週間浸漬しても圧縮強さの低下はみられなかったが, 食塩水中に浸漬すると, 従来型削片状アマルガムにおいて, 空気中に1週間保存した対照群に比して7∿10%の低下が認められた.3カ月経過すると, 水中, 食塩水中いずれにおいても使用したアマルガムすべてに圧縮強さの増加がみられた.その後6カ月目までの3カ月間に強さは低下したが, その減少量はアマルガムのタイプによって異なっていた.従来型削片状アマルガムが比較的大きな低下を示した.削片状γ合金に球状Ag-Cu共晶合金を加えた高銅型アマルガムには, 食塩水中においても有意な低下は認められなかった.圧縮強さに関する限り, これらの合金は最も腐食の影響が少ないといえる.Inを含むAg-Sn-Cu三元合金から成る高銅型アマルガムは3カ月まで他のいずれのアマルガムより高い圧縮強さを示したが, 6カ月経過すると強さは著しく低下し, 最も弱いものとなった.無亜鉛アマルガムは同じ商品名の含亜鉛アマルガムに比して, わずかに食塩水の影響による強さの低下が少ないという傾向が認められた.

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各種アマルガムを37℃, 0.5%食塩水中に6カ月間浸漬した後, 走査型電顕ならびにエネルギ分散型X線マイクロアナライザを用いて, 組織変化および腐食生成物を調べた.アマルガムには, 含亜鉛ならびに無亜鉛の従来型削片状, 球状アマルガム, 削片状Ag_3Sn合金にAg-Cuを添加した高銅型アマルガム, およびAg-Sn-Cu三元合金に少量のInを含む高銅型アマルガム, 計11種を選んだ.従来型アマルガムにおいては, γ_2相が選択的に腐食し, その跡からSnとClが検出された.試験片表面は隆起状の厚い腐食生成物におおわれており, その生成物は主としてSnとClを含む内層とSnに富む外層の2層から成っていた.またγ_2相ほどではないが残留γ合金粒子にも腐食のあとがみられた.Ag-Cu合金を添加した高銅型アマルガムにおいては, γ_2相がほとんど存在しないために著しい腐食は認められなかった.表面はCuに富む小さな結晶におおわれていた.Cu_3Sn相の跡ならびにγ相近傍からSnとClが検出されたことから, これらの相が比較的腐食されやすいことがわかった.Ag-Sn-Cu三元合金を用いた高銅型アマルガムは, 3カ月まではすぐれた性質を示すが, 3カ月から6カ月にかけて異常な圧縮強さの低下, 多量のCuならびにHgの溶出, および著しい組織変化がみられ, 試験片表面にはロクショウの生成が認められた.これらはInの影響によるものと考えられる.また, すべてのアマルガムの腐食生成物中あるいは表面に, 腐食の結果新たに成長したと思われるγ_1相が観察された.腐食相(Clの侵入)は, 従来型, 高銅型いずれにおいても含亜鉛アマルガムに比して無亜鉛アマルガムで一般に深部まで認められ, 4mmφの試験片の中心部にまで達しているものもあった.

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It seems that conventional heat-curing resins for crown and bridge are not necessarily satisfactory in respect to their thermal and mechanical properties. In order to improve these properties, not a few attempts have already been made for many years. But the results are not so successful so far as polymethylmethacrylate is used as the initiating polymer powder for further polymerization with a suitable monomer liquid. In this study, therefore, other polymer powders than polymethylmethacrylate were used to improve the inferior properties of the conventional heat-curing resins. Eight polyfunctional methacrylates, namely, ethyleneglycol dimethacrylate (EDMA), diethyleneglycol dimethacrylate (Di-EDMA), triethyleneglycol dimethacrylate (Tri-EDMA), neopenthylglycol dimethacrylate (NPG), trimethylol propane trimethacrylate (TMPT), bisphenol-A dimethacrylate (BPDMA), 2, 2-bis (4-methacryloxyethoxyphenyl) propane (Bis-MEPP), and bisphenol-A diglycidylmethacrylate (Bis-GMA), were selected and polymerized by the powder-liquid method as in dental use. Then the physical and mechanical properties of the polymers obtained, such as polymerization shrinkage, knoop hardness, abrasion loss, coefficient of thermal expansion, and others were measured as well as their cytotoxicity to Hela cells. The properties of the eight experimental resins were compared with those of a commercial resin, SR-pyroplast. From the results, four polyfunctional methacrylates (EDMA, NPG, BPDMA, Bis-MEPP) were selected as hopeful out of eight ones. Then four kinds of polymer powder were prepared out of the selected four methacrylate monomers, respectively, and these were further polymerized with each one out of the selected four monomers or all the combinations of two-component copolymers of them. The kinds of resulting polymers numbered (_4II_4+4_4C_2=) 40. From these forty combinations the most superior ones were selected in view of the properties mentioned above. At the same time, the most preferable mol fraction (%) of components of the comonomer was also determined. As the conclusion, it was found that the copolymer which was prepared by polymerization of NPG (60mol%)-Bis-MEPP (40mol%) comonomer with Bis-MEPP polymer, possessed many excellent physical and mechanical properties, such as high resistance to water sorption, high values of Knoop hardness number and abrasion resistance. These were highest among those of the specimens prepared in this study and higher than those of a commercial 'hard type' resin, SR-pyroplast.

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In preventive dentistry the fluoride treatment is used for decreasing the caries susceptibility which depends upon the fluoride contents in the surface enamel. It is necessary to clarify these problems that the susceptibility to the fluoride is related with the post-eruptive maturation of the surface. A window was opened for the control and fluoride application on the surface enamel in each four layers. The volume of the calcium and fluoride between the unerupted (horizontally impacted) teeth and the erupted (lower first molar) teeth was determined. The results of this research were as follows : 1. the calcium content increased along with the inner layers. 2. The fluoride content in each group showed the maximum in the first layer and decreased along with the inner layers. The fluoride concentration in the erupted group was higher than the unerupted group in each layer. 3. The calcium and fluoride contents were in inverse relation. 4. The fluoride concentration in the unerupted and erupted teeth increased more on the outer surface layer than that of the inner layer. 5. The fluoride concentration in each erupted tooth was significantly higher than in the unerupted teeth. 6. The fluoride uptake on the unerupted enamel surface exposed to APF solution was almost the same (100 ppm) in each layer. But, in the erupted teeth, the uptake was more than ten times that in the unerupted teeth at the level 3 μm from the surface and seemed to be similar at levels below 50μm as compared with the unerupted teeth. It was concluded that the post-eruptive maturation progressed in the layer up to 20μm from the enamel surface within which the fluoride exchanges.

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Extracellular glucans produced by Streptococcus mutans contains α-1, 6 and α-1, 3 glucosidic linkages and are closely connected in the pathogenesis of dental caries. In this study, dextranase (EC 3.2.1.11) was detected in the culture supernatant of S. mutans AHT and partially characterized. 1. The cultivation of S. mutans AHT with a complex medium supplemented with glucose resulted in the appearance of the constitutive dextranase in the culture supernatant. 2. The extracellular dextranase was partially purified from the culture supernatant of S. mutans AHT by the fractionation and Bio-Gel A-5m gel filtration. The dextranase fraction (β-fraction) with GTF action and the GTF fraction (α-fraction) without dextranase were separated by the gel filtration ; A 560-fold purification was obtained for dextranase with a yield of 19% over the culture supernatant and a 75-fold purification for GTF with a yield of 9%. The purified dextranase had a pH optimum of ca.5.5, a temperature optimum of ca.37℃ and did not degrade insoluble glucan derived from S. mutans AHT.

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To clarify possible reasons of discoloration and recesson of the gingiva upon application of porcelain-fused-to precious metal crown, changes in the metal surface caused by heat treatment or firing as well as changes before and after immersion in an etching fluid of the porcelain-fused-to precious metal crown were analyzed by erectron-probe microanalyses. Furthermore, through vital tissue reactions using test animals and upon application tests of the porcelain-fused-to precious metal crown, influences on the gingiva were studied by histological observations and erectron-probe microanalyses. The results obtained are as follows : 1. Upon heat treatment a coarse oxide layer of tin (Sn) and indium (In) was formed on the metal surface. Upon microscopical observations it was found that microparticles consisting of precious metal components were solid dissolved on the surface of the oxide layer and Sn and In are segregated around grain boundaries and polish scratches. 2. Regardless of covering with fused porcelain, the oxide layer appeared on the metal surface by firing as seen in the case of heat-treated samples. Microparticles observed in heat treatment fused together on the surface and Sn and In were deposited mainly in grooves between those fused microparticles and the part jointed to porcelain. Furthermore, it was also known that the oxide layer was eliminated by polishing, thus segregation of the respective element disappeared. 3. The immersion test in an etching fluid revealed no change on the surface structure of polished specimes, however, heat-treated specimens showed reduction of Sn and In, the oxide layer being fallen off from the surface. Also, microparticles isolated on the surface were observed to be smallar in size and less in quantity. 4. The tissue reaction test using rabbit revealed that fine deposits were seen on connective tissue just below fibroserous membrane covering the heat-treated specimens, and around such deposits granulation tissue mainly consisting of histiocytes and eosinocytes was formed. Upon x-ray microanalyses the deposits proved to be oxides of Sn and In. In addition, from a part of the deposits gold (Au) was detected. 5. Upon crown application test using monkey, dull purple discoloration was recognized on cervical margin of the gingiva in contact with crown, and fine dark brown deposits were found in connective tissue around the blood vessels, fibroblasts, as well as in intravascular endothelia. Upon x-ray analyses the deposits were confirmed to be oxidized Sn and In.

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Although glass ionomer cement has been successfully used in clinical treatments, it has two properties which may handicap its clinical use. First, the syneresis from cement is marked for a few hours after setting. Second, the fine cracks considerably grow up on the surface of set cement. To minimize these undesirable properties, the clinicians must be aware of the correct handling method of materials. The purpose of this experiment was to make clear the relationship between the syneresis of cement and the surface cracks. The results obtained were as follows : 1) A rapid local syneresis, which came from the surface of set cement, caused of the occurrence of surface crack. 2) Coating (varnish or cacao-butter) on cement had considerably effects in prevent of syneresis.

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Design of partial denture constructions is a primarily important factor for the preservation of the remaining natural teeth and supporting structures, edentulous ridges, surrounding muscles, temporomandibular joints and so on, as well as for the improvement of aesthetics and mastication. In order to assure the design most appropriate for the case of interest, it is necessary to refer to many clinical cases of which longterm prognoses have been observed. One of partial dentures attached with buccal bur has satisfactorily worked on the patient after excision of haemangioma who had never been satisfied by other dentures.

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The control of tooth hypersensitivity presents a problem to the dental profession. This clinical study was undertaken to estimate the effectiveness of Mostellon, a corticosteroid solution, in the treatment of tooth hypersensitivity. One hundred and seventeen hypersensitive teeth in 34 patinents were treated topically with Mostellon for 1 to 3 days by a single application daily. Cold water and a sharp explorer were applied to the teeth in order to verify the sensitivity and to evaluate the effectiveness of the treatment. The degree of sensitivity, as well as the stimulus causing sensitivity, was recorded for each subject at Day 0, 1, 2, 3, 7, 14, 21, 28, 56 and 84. The results were as follows : 1) Mostellon was effective in 53% of 108 subjects with a relief from the cold stimulus and in 65% of 111 subjects with a relief from the tactile stimulus. 2) Mostellon was effective in 100% of 37 slight subjects, 69% of 67 moderate subjects and 0% of 13 severe subjects. 3) A complaint of clinical side effect was bad taste in 50% of all patients.

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