目的: キャスタブルセラミックスクラウンは審美性に優れているが, 強度に問題があることが指摘されている. そこで, 下顎第一大臼歯部における天然歯およびキャスタブルセラミックスクラウンとして知られるキャスミック^®クラウンのモデルに生じる内部応力の差異について比較検討した.
方法: 天然歯モデルとキャスミック^®を作製し, 荷重点および荷重方向を変化させて, クラウン, 支台歯, 周囲組織に生ずる内部応力の差異を, 三次元有限要素法により比較検討を行った.
結果: 中心咬合位では相当応力, 引張応力および圧縮応力のすべてにおいて, キャスミック^®が天然歯モデルと比較して大きな値を示した. 偏心位では, 相当応力と圧縮応力は天然歯モデルの咬頭頂歯軸方向荷重において最も大きな値を示し, 引張応力はキャスミック^®が外斜面歯軸方向荷重において最も大きな値を示した. 引張応力分布は天然歯モデルでは荷重点下周囲表層, キャスミック^®では荷重点下周囲表層とクラウン内側面に大きく認められた.
結論: キャスミック^®は外斜面歯軸方向荷重で最も大きな引張応力値を示し, その応力分布の様相は, 荷重点下周囲クラウン表層からクラウン内側面にかけて認められた. したがって, この荷重条件で破折が起こる可能性が最も高いことが示唆された.

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歯科修復物としてのクラウンを、身体形状に合わせて個別生産する必要性が高まっている。我々は、ラピッドプロトタイピングの一種である光造形法を用いて、アルミナ40vol.%-アクリル樹脂のスラリーを紫外線レーザーにより硬化させ、3次元のを積層造形することに成功した。さらに、このコンポジット造形物をフルセラミックス化するために、脱脂及び焼結処理を施した。その後、この焼結体表面の観察、及び収縮率と密度の計測を行った。

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This paper introduces a dental crown production system. The crown designed in this system not only had nointerference at intercuspal position but also given functional occlusal surfaces. The functional occlusal surface was createdwith virtual articulator which reproduces the movement of subject's mandible on a computer system. Finally, validity of theprocesses in this crown production system, errors which were caused in each process and the necessity of dental CAE (Computer-Aided Engineering) system were discussed.

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Newly developed plate shape control system, using attached shape meter, was put in service in Mizushima Works, Kawasaki Steel Corp. This system consists of (1)Sensors ; attached shape meter, multi head γ ray thickness meter (crown meter) (2)Actuator ; oil pressure type work roll bending device and (3)Models : shape prediction model, plate crown prediction model.
The closed loop, comprising attached shape meter and work roll bending system based on the shape prediction model, characterizes this system.
Introduction of this system, enables the improvement of flatness and plate crown accuracy, which meets ever upgrading customer's demand and also yields improvement and chance free rolling.
This report describes the following terms ;
(1)Specification of shape meter and work roll bending device.
(2)Algorithm of shape control system.
(3)Results.

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In order to determine the clinical assessment of the polycarboxylate cements, some test were made on four commercially available polycarboxylate cements and one zinc phosphate cement as control.
The findings are as follows:
1. Tensile strength of the polycarboxylate cements obtained with the crown model was similar or stronger than that of zinc phosphate cement. Tensile strength with taper 1/10 crown model was significantly stronger than that with taper 2/10 crown model.
2. In case of the shear strength at dentine-polycarboxylate interface on smooth surface was stronger than on rough surface, and the result showed that adhesion was due to chelate bond. While the shear strength at dentinecement interface obtained with polycarboxylate cements was variable, it was certainly superior to that obtained with zinc phosphate cement.
3. The shear strength of polycarboxylate cements was more than twice that of zinc phosphate cement.
4. The polycarboxylate cements were not irritant to dental pulp.
5. The properties obtained with these test made the polycarboxylate cement the material of choice for cementing full crown restorations and bridge work on vital teeth.

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The purpose of this study was to examine how various designs of coping affect the strength and stress distribution of the porcelain fused to castable ceramic (PFC) crowns. Four different coping designs and three types of crown were made:(Model 1) 1/3 of the labial cervical to the incisal;(Model 2) the labial to incisal;(Model 3) the labial to incisal, and 1/3 of the lingual;(Model 4) covering the entire labiolingual region.(Model 5) a castable ceramics crown; and (Model 6) a porcelain-fused-to-metal (PFM) crown.
All the models were subjected to destructive strength test and stress analysis using the finite element method (FEM), and the results were as follows:
1. When stress was applied to PFC crowns at 45° to the incisal region, the destructive strength tended to decrease as the porcelain-fused area increased. The destructive strength of Model 4 significantly decreased compared with the others when stress was applied to the center of the lingual at 45°.
2. FEM analysis showed that, in vital abutment teeth under four stress conditions, there were no marked differences in the tensile stress distribution and values among the different coping designs.
3. From the viewpoint of dynamics, Models 1 and 2 were considered to have the most desirable coping designs for PFC crowns.

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単純化された歯科フルクラウン鋳造体の, 凝固時における温度変化を有限要素法によりシミュレーションした結果, 以下の結論を得た.1)鋳造体におけるニッケルクロム合金と, 金銀パラジウム合金の凝固過程には大きな違いが存在する.2)ニッケルクロム合金の凝固時には, その部位により大きな温度差がある.この温度差は, ニッケルクロム合金の凝固区間における熱伝導率が低いことに原因している.3)凝固時における, 金銀パラジウム合金鋳造体の温度は, 部位によらずほぼ一様である.4)薄いニッケルクロム鋳造体の場合には, 部位による温度差は極端に増大する.5)有限要素法による歯科鋳造の凝固過程に対するシミュレーションは有効である.

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The construction of the new hot strip mill of 1 840 mm in width was started to replace the old one in June, 1982 and was completed on its commercial operation on August 1, 1984, in Nippon Steel's Hirohata Works. The computer control systems of the mill have enabled us to achieve high-accuracy quality controls.
First, we have developed absolute mode AGC system which gives the high accuracy of strip thickness for full strip length. The system is composed of four main functions as described below.
(1) Quick-response AGC with hydraulic screw down system
(2) Compensating control for mass flow balance
(3) Decoupling control of bender and screw down systems for gauge, crown and shape of strip
(4) Set up function for control parameters
Secondly, we have developed crown and shape control system which has high capability by adopting "pair cross roll system" for the first time in the world and work roll bender system of servo-valve drive type. The main functions are described below.
(1) Pre-set function of roll cross angles corresponding to crown schedule for each strip
(2) Feedback crown and shape control of work roll bender system within each strip

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Tetragonal zirconia polycrystals stabilized with 3 mol-% yttria (TZP) exhibit good mechanical properties, favorable esthetic appearance and translucency. Despite this, zirconia has not been widely used for all-ceramic restorations due to the difficulty of shaping it. A new process called the cercon smart ceramics^® system overcomes this limitation by milling ceramic blanks in a porous, presintered and yet easily machinable state which are afterwards sintered to full density. The sintering shrinkage is compensated for by enlarging the shape prior to machining. Not only the fracture resistance but also the marginal fitness are important for all-ceramic restorations to produce satisfactory results.
In this comparative in vitro study, the marginal fitness of TZP all-ceramic crowns and fixed partial dentures (FPDs) were examined.
The marginal discrepancies of the FPDs (29.3μm) were not significantly different from those of the crowns (31.3μm) .
The results of this work suggest that
1) The marginal fitness of all-ceramic restorations fabricated by the Cercon^® system was satisfactory for clinical use.
2) The dimensional stability of the Cercon^® substructure was maintained during firing of the porcelain and successive glazing.

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The titanium crown is rapidly replacing other metallic crowns today. However, it has a crucial problem; the crown worked in a conventional way is less adaptable. To solve that problem, a new technique employing CAD/CAM with a laser measuring system has been developed to produce an accurate and desirable inner surface of the titanium crown. Then a coordinate measuring machine was set to measure and contrast two of the candidates:
1. The inner surface of the titanium crown worked in the conventional way:
Laser beams were applied to the titanium crown at 90°to the long axis of the tooth and the inner surface was finished with the ball-end-mill of a 2.0-mm diameter.
2. The inner surface of the titanium crown worked in the new technique:
The model abutment was set at a 10°angle to apply the laser beams effectively to the cervical part of the titanium crown for measuring the accuracy. The same ball-end-mill was used to rough-finish it, and then the 1.0-mm diameter one was used to elaborate it.
The result showed remarkable contrasts to reveal the superiority of the new technique: the conventional way produced a significant tolerance from the occlusal area to the cervical; the new technique produced a fine marginal form and a high adaptability in the working accuracy.

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In order to achieve schedule matching between the continuous casting and hot rolling operations, thus ensuring the maximum benefits of "Hot charge rolling, "we have established the schedule-free hot rolling technology that frees the continuous casting operation from various restrictions of the downstream hot rolling operation. Starting from the Kimitsu-developed crown control process ("NBCM rolling method"), we have developed the rolling-mill arrangement, which combines the NBCM (New Back up roll Crowning Mill), the high-strength work roll bender, and the work roll shifting device and has functions nearly equal to those of the 6-high rolling mill. In addition, we have also developed and successfully put into practice the high precision preset control model, the hot-rolling dynamic control model and the automatic scheduling function, aimed at the maximum utilization of the above rolling-mill arrangement, resulting in substantial achievements in energy conservation and yield improvement.

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本年の保険改定により大臼歯部チタン鋳造冠が保険収載された．本総説では，チタン鋳造の研究について，鋳造法や固定性補綴装置への応用など30年以上にわたる研究成果をもとに紹介する．

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CAD/CAMによる間接修復用コンポジットレジン冠の適応が大臼歯まで拡大されているが，特に歯科用金属アレルギー患者における第二大臼歯への適応では歯冠高径が十分に得られない症例が多く，脱離，破損の懸念がある．このような症例における代替技術として，日本歯科理工学会では，高い機械的性質と耐食性を有し，生体安全性に優れたチタンおよびチタン合金の鋳造法による歯冠修復物について検討し，日本補綴歯科学会とともに医療技術評価提案書を申請した結果，大臼歯における純チタン第2種の全部鋳造冠が令和2年6月に保険収載された．また，チタンの歯科鋳造には特殊な鋳造機や専用の埋没材を用いる必要があることから，新技術として承認された．また，健康保険適用の金属材料として広く用いられてきた金銀パラジウム合金の価格は高騰を続けており，その代替材料としても期待される．

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　歯科用CAD/CAMシステムにより製作したコンポジットレジンクラウンの辺縁適合性を検討した，8本の歯型に対して，それぞれ歯科用CAD/CAMシステムによりコンポジットレジンクラウンを製作し，内面の調整を行わずにクラウンを歯型へ合着した．そして，樹脂包埋後に8分割 し，1つの試料に対して16断面のクラウン辺縁のセメント厚さを測定した．また，製作 したクラウンの辺縁部を走査型電子顕微鏡で観察した．その結果，コンポジットレジンクラウン辺縁におけるセメント厚さの平均値は45μmであった．また，コンポジットレジンクラウンの辺縁にはわずかにチッピングが観察されたが，セラミッククラウンの辺縁と比較してチッピングは非常に少なく，切削加工に対する優れた加工特性を示していた．

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本研究では，歯科精密鋳造にて修復装置を作製する工程のワックスアップに際して，ワックスCAD/CAMテクニックを用いて作製するワックスCAD/CAMクラウン（ワックスクラウンと略）の加工精度に及ぼすセメント層の設計値の影響について検討した．ワックスクラウン内面の寸法を，咬合面内面から2.0，3.0，4.0，5.0 mmの部位およびフィニッシュライン部で測定し，加工精度を評価した．ワックスクラウン内面の寸法は，セメント層の厚さの設計値が0 μmの場合は，フィニッシュライン部を除くすべての測定部位で支台歯原型より小さくなり，浮き上がりを示した．セメント層の厚さの設計値が50，100および150 μmでは，すべての測定部位で支台歯原型より大きくなり，入らなくなるものはなかったが，作製したワックスクラウンが18〜38 μmほど小さめに加工されることが認められた．CAD/CAMシステムでは，この加工誤差を把握してセメント層の厚さの設計を行う必要性が示唆された．

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