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An investigation by electron diffraction, transmission and scanning electron microscopy, and energy-dispersive X-ray analysis has shown that Ta additions to a 40-30-30 Co-Cr-Ni-base alloy strengthen by ordering and by formation of coherent α-Co3Ta precipitate. However, increasing Ta content increases the proportion of the hexagonal phase and decreases ductility.

Heat treatment caused an increase in ductility. Aging caused an increase in strength and hardness with a decrease in ductility. Overaging caused decreases in strength and ductility. Solution treating resulted in a single phase. The precipitation of coherent intermetallic compounds caused maximum strengthening with minimum loss of ductility.

The σ phase is rich in Ta. When the Ta concentration is less than 14%, σ does not interfere with the slip mechanism; when the Ta concentration is more than 15%, σ interferes with the slip mechanism. The coherent α-Co 3Ta phase forms at Ta concentrations of less than 15%, whereas incoherent γ-Co 2Ta forms only at higher Ta concentrations. The interface between σ and the matrix is an important factor in the failure mechanism.

Strength, dimensional change during setting, and corrosion resistance have been measured for amalgams prepared from splat-cooled alloys of different compositions in the Ag-Sn-Cu system. The amalgam with optimum values of these properties was made from the alloy containing 60 at. % Ag, 25 at. % Sn, and 15 at. % Cu. Tensile strengths for amalgams from this alloy were about 8000 psi, dimensional change during setting near zero, and corrosion resistance was good. X-Ray diffraction showed that the γ1 and γ2 phases formed during the early stages of setting but that the γ2 phase had essentially disappeared after about 24 hr. At the latter time Cu6Sn5 was present.

The hypothesis that the cavity preparation design for proximal-occlusal Class 2 amalgam restorations influences the plastic deformation characteristics of the amalgam was investigated. The parameters involved the use of retentive grooves and bevels as well as different alloy systems. A machine was designed for subjecting the specimens to dynamic loading, and the deformation of the restorations was measured. The results Indicate that the alloy formulation plays a greater role in mesiodistal deformation than does the presence of a cervical retention groove or a cavosurface margin bevel. In particular, this study provides additional evidence that the creep properties of the alloy may be related in some manner to deformation, or marginal breakdown, or both.

An amalgam that is based on a cadmium-10% nickel alloy is capable of Plastic deformation and it offers a substantial increase in resistance to cracking and tarnishing with some loss in corrosion resistance in saline solution and in hardness. The amalgam has not yet been tested for biologic safety.

Eight distinct types of wires were compared for the property of each wire's working range. Specifically, the two types of cobalt nitinol wires were compared with three typical 18-8 stainless steel leveling wires (0.014, 0.016, and 0.018 inch) and three typical Twist-Flex leveling wires (0.0175, 0.0195, and 0.0215 inch). The parameter measured was per cent elastic return of the deflected wire back to an original undeflected undeformed parabolic preformed arch shape. Double determinations of 480 measurements by two independent observers, abstracted and statistically quantified, are reported in two tables in addition to being graphically illustrated. Ten replications of each of the eight wire types were made in order to determine and quantify the following four variables: 1. 1. Millimeter return of the wire after being deflected and tied into the bracket slot. 2. 2. Millimeter distance of the undeflected undeformed “standard” preformed arch wire form from the bracket slot. 3. 3. Standard deviation of the millimeter return after the wire was cut loose from the bracket slot and had some degree of permanent deformation remaining in the wire. 4. 4. Per cent return of the permanently deformed test wire expressed as a ratio of the “standard” undeformed preformed wire's distance to the deepest part of the bracket slot. Measurements were achieved by the investigators' use of vernier calipers (Helios) with a dial read out to 1 20 mm., on standardized photographs of each wire's deformation compared to its standard.

T In a previous laboratory study designed to analyze features of Class II amalgam cavity design,l it was found that restorations placed in cavities having inter-proximal axial retention grooves demonstrated the highest resistance to bulk fracture when compared with restorations of other designs. To test the significance of these results, a subsequent clinical evaluation of two cavity designs was conducted .* One design had no retentive features, whereas the other differed only with respect to the addition of two inter-proximal axial retention grooves placed with a 69L bur. Restorations in this clinical study were placed only in mandibular second premolar where incipient lesions indicated conservative or narrow-width cavity designs. The results showed no evidence of bulk fracture for either of the two designs tested. At the completion of this study, several questions were raised: Would the absence of bulk fracture prevail for restorations in molar teeth, in wide as well as narrow cavity designs, and what would be the influence of different amalgam alloys? In addition, what would be the effect of inter-proximal axial retention grooves on the proximal extrusion of the amalgam restoration out of the cavity preparation? This is a phenomenon commonly attributed to clinically placed amalgam restorations that have been in service a considerable time. The purpose of this study was to resolve these questions by introducing into the experimental design the additional factors of restoring molar teeth, including all cavity preparations regardless of proximal widths, and varying the amalgam alloys. In addition to the recording of the incidence of bulk fracture, proximal extrusion was measured.

Electric phenomen of dental metal in mouth have been described and discussed in many papers, and the E. M. F. of dissimilar metals have been determined. On the other hand, it is well known that when a metal is immersed in electrite solution, electric current does occur between the tissues of high potential and those of low potential and corrosion of the metal is increased. We have determined the electric potential of similar dental metals and alloys in various condition of them as follows :(1) Potential in physiological salt solution1) Between polished and unpolished metals2) Between polished and rough polished surfaces of metals3) Between polished and corrosive surfaces of metals(2) Potential in oral saliva1) Between polished and rough polished surfaces of metals2) Between polished and corrosive surfaces of metalsThe results are as follows:1) Our experiments appear to demonstrate conclusively that electric current will exist in the mouth even if the mouth contains similar dental metals alone.2) The phenomen of polarization undoubtly reduces the current somewhat, but not to zero.3) The potential difference is higher in physiological salt solution than in oral saliva.4) The value of potential difference is due to the difference of surface fineness and the condition of corrosive substances.

Silver amalgam restorations have been placed for more than a century, with excellent and with unsatisfactory results. The appearance of an amalgam restoration is dependent on cavity design and preparation, selection of alloy, manipulation of alloy and mercury, contouring and finishing procedures, and age and environment of the restoration. Changes have occurred in amalgam during the years. A recent available dental alloy addition is a dispersion strengthened system. Another system being studied experimentally substitutes about 10 weight percent of gold for silver in the alloy. It is hoped that these new systems will provide dental amalgam with improved clinical quality

A 30-month study was made of the deleterious effects of saliva contamination during condensation of amalgam specimens. No expansion attributable to saliva contamination was seen in specimens made with zinc-free alloys, but all contaminated specimens from alloys containing zinc showed excessive expansion. In most contaminated specimens prepared with zinc and nonzinc alloys, gross reduction in strength was seen.

The polarographic behaviour of complexes of the noble metals was studied by oscillographic polarography. A method was developed for the polarographic determination of copper, gold and palladium; silver and nickel do not interfere. Applications to the analysis of dental alloys proved successful.

The selection and properties of materials for dental practice. 6. Dental alloys and associated materials

真空埋没が鋳造修復物の膨縮変化と鋳肌アラサへ及ぼす影響を検討すべく, 真空および常圧下でType IIIの金合金および市販銅合金を用いて, 帽冠形鋳造体の原型への適合度を測定した。また板状鋳造体の面アラサを触針法にて測定し, さらに万能拡大投影機にて肌アレの分布状態を観察した。また鋳造体面および鋳型壁の, 加熱前および加熱後の状態を走査型電子顕微鏡を用いて直接観察した。真空埋没にはVacuum Minaを用い, 埋没材には松風クリストバライト埋没材を使用した。また鋳造に際して, 鋳型の予熱温度は, 金合金は700℃, 銅合金は600℃とした。その結果次のような知見を得た。1) 真空埋没を行うことによる埋没材の凝結膨張量の増加は, 粗面の影響でカバーされる程度のものであって, 鋳造体の適合試験による膨縮変化量に統計学的有意差を生じなかった。2) 真空埋没法によれば, 鋳造体表面に気泡が生じなかったのみならず, より滑沢で面アレ部の少ない鋳造体が得られた。3) 金合金の面アレ部は鋳造体全面に均等に散在していたが, 銅合金では主としてスプルー線の裏側に特に集中する傾向がみられた。4) 埋没材鋳型壁の結晶の配列や形には加熱前後では著しい差が認められたが, 真空埋没と常圧埋没との間には明かな差が認められなかった。5) 実際の臨床で真空埋没を行なう際には, 埋没材を常圧埋没と同様の混水比を用いて差支えなく, これによって表面の滑沢な適合度のよい鋳造修復物が容易に得られるものと考えられる。

The reaction of tissue to 55-nitinol wire suture placed subcutaneously in forty-five rats was followed for 9 weeks. The tissue reaction was minimal at all time periods. The reparative process was initiated within 1 to 2 weeks and formed a dense, relatively avascular fibrous connective tissue capsule by 5 to 6 weeks, with little change beyond this time. When compared to stainless steel in previous experiments, the nitinol was indistinguishable from the stainless steel at similar time periods. Therefore, on the basis of the results of this experiment, it appears that 55-nitinol compares favorably with stainless steel and could be used in the deep tissues.

Mechanical and heat treatment characteristics of two nickel-chromium-based dental casting alloys were investigated. Both alloys showed rapid response to heat treatment. In their softened state the alloys lost 25 to 50% of their as-cast hardness. Elongation was 20 to 45%. Rehardening nearly restored as-cast strength, whereas elongation values remained at 10 to 17%.

A tooth must be harnessed in such a manner as to have the tooth do its own work and do, or help to do, the work of a missing adjacent tooth or teeth. For esthetic reasons the tooth should have its labial or buccal surface left uncovered. Since a thin layer of a material placed over a surface is called a veneer, and since only part of the crown of the tooth is to be covered, it seems logical that the term “partial veneer crown” would be appropriate. If the plan or design of the preparation and casting is based on the rules and principles of science, which is knowledge gained and verified by exact observation and correct thinking as distinguished from empiricism, it should be called, “the scientifically designed partial veneer crown.”

The corrosion of some gold base alloys was studied in artificial saliva through the use of electrochemical methods, primarily potentiokinetic curves. The effects of various alloying elements were investigated.

No other material is so universally and successfully employed in restoring carious teeth to a state of usefulness as is dental amalgam. Besides forming such a large proportion of the fillings, the number of amalgam restorations made annually is tremendous. The office of the Surgeon General stated that 68,170,326 permanent fillings were inserted by Army dentists from December 7, 1941, to September 1, 1945, and most of them were of amal­ gam.1 Historically, amalgams were first intro­ duced in Europe in 1826 (under the name of “ silver pastes” ) and in America in 1833. Partly because of their inferior and undependable performance, but largely because they were first used by charlatans, the adoption of amalgams by the dental profession was slow. What has been called an “ amalgam war” raged, beginning in 1845. The American Society of Dental Surgeons passed a resolution in 1845 which reads: Resolved, That any member of the Society who shall hereafter refuse to sign a certificate pledging himself not to use any amalgam, and, moreover, protesting against its use, under any circumstance, in dental practice, shall be ex­ pelled from the Society.

— Twenty-six amalgam restorations were performed using the conventional amalgam technique, and 26 using the wet amalgam technique on the same Class II cavity model. For the marginal proximal areas the mean difference in residual mercury content between the two techniques was 5.0% and for the remainder of the restoration 3.6%. The wet technique required, on an average, 58% more amalgam than did the conventional technique. The differences between the two techniques were statistically significant (P

Petrographic study of the refractory performance of silica-bonded investments revealed that recrystallized silica bonds consisting of tridymite and cristobalite are formed during burnout. The major reaction product created during casting is eskolaite. Liquefaction and sintering in the investment at and near its interface with the casting plugs pores and may lower permeability.

Waterstratの処方に従って, ガリウム・パラジウム・スズ合金を試作し, この合金の硬化24時間後の歯質に対する接着力および窩洞に填塞した充填物の辺縁封鎖性について, 従来のアマルガムとの比較検討を行った。また硬化したガリウム合金表面, 接着力試験後のエナメル質被接着面および充填物の窩洞接触面を走査電顕で観察し, またガリウム合金の凝結膨張量を測定して, 次のような知見を得た。1) アマルガムは歯質に対して接着力を全くもたなかったが, ガリウム合金は接着性を有し, 特に象牙質よりもエナメル質に強く接着した。2) ガリウム合金のエナメル質に対する接着力は室温より口腔温の方が低く, また湿度が増加すると低下し, 水中ではさらに低下した。粉に対する液量が減ると接着力は低下した。3) ガリウム合金の象牙質に対する接着力は室温より口腔温の方が低く, また液量が少ないほど低く, この点ではエナメル質の場合と同様の傾向を示した。湿度に関しては室温のときには乾燥空気中が一番強く, 口腔温のときには乾燥空気中と水中で接着力がほとんどなかったのに対して, 飽和湿気中のみ若干の接着力を示した。4) 充填物の辺縁封鎖性はガリウム合金が最も良く, 削片型アマルガムがこれに次ぎ, 球状アマルガムが最も悪かった。5) 硬化したガリウム合金表面は細かいほぼ均一な凹凸面を示し, 未研磨面では合金粒子とマトリックスが区別できなかったが, 研磨面では両者が明瞭に区別できた。6) 引張り試験後のエナメル質被接着面にはガリウム合金がちぎれて斑点状に付着していた。7) 球状アマルガム充填の窩洞接触面は海綿状の残留合金粒子と粒状構造の結晶の集合からなるマトリックスがみられ, 凹凸が多かった。削片型アマルガム充填では接触面の形は不規則で, 凹凸はやや少なかった。ガリウム合金充填では合金粒子とマトリックスの区別がつかず, 軽石状の細かい凹凸による粗造面を呈していた。8) ガリウム合金の凝結膨張量は粉に対する液量が減るほど大きくなり, 24時間後では1: 0.5のとき21μm/cm (0.21%) , 1: 0.43のとき35.7μm/cm (0.36%) , 1: 0.4のとき40.7μm/cm (0.41%) であった。

Cobalt-base alloys strengthened by intermetallic compounds of tantalum were prepared and tested. Some of the alloys were stronger and more ductile than conventional base-metal alloys.

The purpose of our studies was to determine the corrosive behavior of dental restorative alloys in the mouth and, at the same time, to examine them from a dental health point of view. The conclusions are as follows : 1. Even the copper alloy which is commonly supposed to have a high degree of corrosion actually has as small weight loss in the mouth as 0.022 to 0.034 mg/cm2 for a day.2. The type of amalgam which is widely used in many countries today has the weight loss in vivo as little as 0.0063 mg/cm2 a day.3. The basic reason why these alloys are not corroded as is generally supposed is that the salivary secretion has the benefit of keeping the mouth clean. It is also due to the fact that the saliva works to inhibit the corrosion of alloys.4. As it became clear by our testing that 1950 Ministry of Welfare corrosion test was not realistic as a means of expressing the corrosive behavior of dental alloys, it was removed from the specifications.5. Within the same oral cavity, the degree of corrosion varies from area to area, that is, anterior teeth, posterior teeth, occlusal, buccal to lingual or proximal surface. By observing the copper alloy restorations after they were removed, the corrosion is most pronounced on the proximal surface.

Numerous laboratory studies have been conducted in an effort to determine the susceptibility of dental alloys to tarnish and corrosion.1–8 These investigations have embodied a variety of storage media, storage times and the influence of variables such as the presence of dissimilar metals. However, there is little in vivo data to establish the validity of the various in vitro tests with respect to their efficacy in predicting the susceptibility of the respective alloys to tarnish in the oral environment. It was the purpose of this research to compare the tarnish of three gold alloys as assessed by an in vitro test with the in vivo tarnish of the same alloys.

25. Flag, J . F . Metallic pastes for filling teeth. Am. J . D. Sc. 4:210, 1844. 26. Sweeney, J . T. Amalgam manipulation: manual vs. mechanical aids. Part II . Comparison of clinical applications. J .A .D .A . 27:1940 Dec. 1940. 27. Swartz, M. L., and Phillips, R. W . Study of am al­ gam condensation procedures with emphasis on the residual mercury content of the increments. I. Strenqth, flow, and dimensional change. J . D. Res. 33:12 Feb. 1954. 28. Skinner, E. W ., and Phillips, R. W . Science of dental materials, ed. 5. Philadelphia, W . B. Saunders Co ., I960, chapter 21. 29. Swartz, M. L .; Phillips, R. W ., and El Tannir, M. D. Tarnish of certain dental alloys. J . D. Res. 37:837 Sept.-Oct. 1958. 30. Roper, L. H . Restorations with amalgam in the army: an evaluation and analysis. J .A .D .A . 34:443 April I, 1947. 31. Moss, R. P. Amalgam failures. U. S. Armed Forces M. J . 4:735 May 1953.

X-ray diffraction analysis of the alloy system Co-Ni-Cr-Ta showed that the ternary alloy base consisted of three phases (a, β, and σ). Addition of Ta caused a decrease in the intensity of the β lines. Further Ta additions caused diffraction lines characteristic of the intermetallic compound α-Co3Ta. At higher Ta concentrations, the intensity of the lines characteristic of the σ phase increased and lines characteristic of Co2Ta appeared.

現在歯科用合金として各種の合金が使用されているが, 更に優れた新合金が待望されている。歯科用合金に於てPdは, AgやAu等への添加元素として広く用いられ, その有効な事が知られているが, 純Pdに対し諸元素添加による機械的性質の変化等については, 未だ良く知られていない。そこで本研究は, 純Pdに個々の元素を添加した各種のPd基2元合金を作製し, その種々な性質を調べる事を目的として, 硬さ試験や引張試験を行って, 機械的性質を調べ, あわせて変色試験及び顕微鏡組織観察を行った。これらの結果を検討し, 次の様な知見が得られた。(1) Pd基2元合金に於て, 各元素の添加量と硬度に関して, Pdと全率固溶を示す元素ではNi, Co, Cu, Ag, Auの順で比較的ゆるやかな勾配で硬度を増加させる。固溶限のあるものでは, Sn, In, Mnが, 急激に微少の添加量で硬度を増加させる。Znも同様だが, その度合はSn, Inよりも少い。Cdは固溶限のあるものでは, 一番少い増加を示した。(2) 引張り強さに関しては (1) と同様, 全率固溶を示すものは, ゆるやかな上昇を示した。そして20wt%～40wt%添加量の範囲でピークを示し, それ以上の添加量では, Auを除き減少していく。Cuが最も大きな引張強さの増加量を示した。固溶限のあるものは, いずれも微少の添加量で引張強さを増加させる。Cu添加合金は, 引張強さに関しては良好な値を示したが, 弾性率及び比例限は, その割には低く弾性エネルギーの増加量は他の合金元素と比較して少い。Ni添加合金は, 弾性エネルギーでCu添加合金の2倍近い値を示し, 他の合金元素と比較して, 弾性特性を増加させるのに有効である。(3) JIS規格に沿った変色試験では, 本研究のPd基2元合金は, いずれも満足し得る耐硫化性を示した。JIS規格に沿った変色試験よりも苛酷な変色試験に於ては, Ag系, Cu系, Ni系に変色しやすい傾向が認められた。(4) 鋳造性に関して, Mn系, Cu系, Co系にしばしば鋳巣や湯流れの悪さ等が認められたが, 他のものは比較的良好であった。顕微鏡組織観察では, Au系, Mn系に偏析が多くみられた。他のものでは等軸結晶やDendrite或いはDendriteが崩れつつあるか, 形成されつつある組織像を示した。

歯科用ニッケルクローム合金において, いかなる条件下で最もよい鋳造面が得られるかを検討するために, 3種の市販合金を石膏系, リン酸塩系の各種埋没材を用いて鋳造し, それぞれの鋳造体面を比較した。得られた鋳造体面の清掃法を検討した後, 清掃後の鋳造体面を, 肉眼ならびに光学顕微鏡, 万能拡大投影機, 触針式アラサ計で観察あるいは測定し, ざらに走査電顕にて鋳造体面と鋳型壁の細部を観察比較した。また, 鋳造体の断面標本を作り表面性状と結晶粒との関係を検討した。これにより次のような知見を得た。1) ニッケルクローム合金の鋳造体から付着物のみを除いて鋳造面をそのまま正確に露出するための清掃法としては, 50%NaOH溶液中で30分間沸騰させ, 純水中で沸騰後超音波洗溝する方法が最適であった。 (但し若干の合金面の削磨が許される臨床的な清掃のためにはサンドブラストが有効と思われた。)2) タイコンおよびウィロンは鋳造時に埋没材の粒度が大きいほど荒くなった。従ってタイコンおよびヴィロンの鋳造のためには, 粒子の疎大なセラミゴールド埋没材は不適であって, それ以外の埋没材では石膏系でもリン酸塩系でも大体同様に滑沢な鋳造面が得られた。3) サンコリゥムは著しく酸化されやすく, そのために溶湯は鋳型壁から部分的にあるいは全面的に離れて凝固し, 部分的に離れた所では斑点状に特に肌アレの著しい部分を生じた。サンコリゥムの鋳造のためには, 試験された埋没材の中, 酸化の少ないコロイダルシリカを加えたリン酸塩系のセラミゴールド埋没材が最も滑沢な鋳造面を作った。

The purpose of this study was to investigate the influence of changing the precondensation mercury content (initial mercury content) on the final strength of amalgams when the condensation was delayed. Another purpose was to study the effect on the transverse strength of mulling the amalgam mix after the delay. The material consisted of ten different brands of alloy. Three different alloy-mercury ratios were used with each alloy brand; Mix I about 50% Hg, Mix II about 54% Hg and Mix III about 59% Hg. Rectangular amalgam test pieces, measuring 2 × 2 × 12 mm, were condensed after a 5 minutes delay by hand using a load of about 17 kg/cm2. The transverse strength test was performed after one week using three point loading. The five minutes delay of the condensation reduced the strength of the amalgams by 1 to 42 per cent depending on the brand of alloy and precondensation mercury content. The three preamalgamated amalgams were affected less by the delay than the other amalgams. Increasing the precondensation ...

The static creep properties of 14 commercially available amalgam alloys were determined. The creep properties of 14 commercially available amalgam alloys were measured, and the compressive strengths and residual mercury content of the alloys were also tested. Creep values ranged from 4.6% to 0.35%. No relationship was found between creep and the compressive strength of the alloy or its residual mercury content.