It must be remembered that any dental implant has the possibility to fail, because the implant is one of the artificial materials in dentistry. However, it is well-known that the treatment for the unsuccessful implants are not easy, because the excision of the implant from the jaw bone is sometimes very difficult and the postoperative bone resorption is often so severe that the implant can't be installed and that the conventional removable prosthesis can not be applied.
In this article we completely reported that the four implant failure patients were treated satisfactorily by the application of the removable prostheses with tapered telescopic crowns (Konuskronen) after excision of the unsuccessful implants, and then we discussed the interface between the implant and bone tissue, the excision method and postoperative bone resorption, the reconstruction with removable prosthesis and the indication for the implant therapy from the view of pathology, oral surgery, and prostihodontics.
The results obtained are below;
1. After the excision of the implants: If the patient had partial edentulism, the removable prosthesis with tapered telescopic crowns (Konuskronen) was very beneficial.
2. The soft tissue was unfavorable for the interface between the endosseous implant and the bone tissue.
3. According to the failure implant: The excision method should be selected to remove the implant simply and to minimize the postoperative bone resorption.
4. The degree of the bone resorption after excision: The screw-type endosseous implant and the pin-shaped endodontic-endosseous implant were slight in degree, but the plate-type endosseous implant, the blade-vent endosseous implant, and the periosteal implant were prominent in degree.
In conclusion at the present time we feel that the screw-type endosseous implant with direct bone anchoring might be most favorable.

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Synthetic apatites differ in forms and compositions due to the different sintering method, and precipitation of nitrogenous species is often noted.In this study, we make further investigations on the precipitation of nitrogenous species in commercial synthetic apatite using diffuse reflectional spectrophotometry to determine IR absorptions for the analization of spectral difference, etc.
The result is that the absorption of nitrogenous species which is considered as CN₂^2-, OCN^- shown at 2,010 cm^-1 and 2,200 cm^-1 of all samples except CO₃-Ap and the recognization of these IR absorption in synthetic apatites of different types suggests the neccesity of further detailed investigations on the biocompatibility of synthetic apatite.

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Due to the research from many angles, dental implants have been widely used in practice.
From the aspect of material science, they are generally categorized as metallic implants and ceramic implants. Among them, implants utilizing pure titanium or hydroxyapatite have gained a high reputation for their superior biocompatibility and comparable stability in bones when applied in practice. Taking advantage of these characteristics, endosseous implants of titanium blade which are coated with HAP alumina by plasma sprayed technique, have been developed.
This study, through biological testing, aims to compare changes and reactions of bone in case of pure titanium blade and HAP alumina coated blade-vent implants.
We made the implant material free standing and adjusted the implants head in order to avoid occlusal stress and other functional pressures inside the mouth. One month after the blade insert,the bone in contact with the blade was cut out and analyzed by diffuse reflectional infrared spectrophotometry using on FT/IR-7000 infrared spectrophotometer (Japan Spectroscopic, Co.,Ltd.). The study results including spectral differences with the osseous bone are described in this paper.

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Hydroxyapatite is the main component of inorganic materials of bone and tooth, and has been many reported for basic examination and clinical application as medical materials. But commercial synthetic apatite component differ between companies because of its sintering or synthetic method, and its components differ from biological apatite at that.
Then, we compared apatite compositions in order to test differences between bone apatite and commercial synthetic apatite or not. The analysis of composition examined by Infrared Fourier Transform spectrometer 7000 type (made by Japan Spectroscopic Co.,Ltd.) and measured spectra subtracted from commercial synthetic apatite (Bonetite, Apaceram)to bone apatite.
As the results, 1)The composition differs from synthetic and bone apatite. 2)Furthermore, there was different compositions of commercial synthetic apatites with each other.
Accordingly, it became necessary that we should consider the differences of apatite composition in living tissue.

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　ジルコニアセラミック（ZC）をラット下顎切歯のエナメル質側歯根膜に埋入してその組織反応を観察し，エナメル質側歯根膜を構成する間葉系細胞の生物学的特徴を検討した．ZC埋入6，8週後，ZC－エナメル質側歯根膜界面に無細胞性セメント質様層が認められ，セメント質様層直下には立方形のセメント芽細胞様細胞が配列していた．電顕的にセメント質様層は非線維性セメント質と線維性セメント質で構成されていた．また，セメント芽細胞はゴルジ装置，少量の粗面小胞体，ミトコンドリアなどを有し，線維性セメント質に垂直に侵入したシャーピー線維束に密接していた．ZC埋入後16，32週間では無細胞性セメント質の厚さが増加し，シャーピー線維間にセメント芽細胞が規則的に配列していた．本研究結果から，ラット切歯エナメル質側歯根膜を構成する間葉系細胞はZCなどの埋入による組織治癒過程でセメント芽細胞に分化し，無細胞性セメント質を形成することが示された．

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As one of the types of endodontic endosseous implants, taper pins are often employed. In implanting taper pins, reamers or drills are used for enlarging the root canal exteriorly and preparing the canal taper. In this study, four operative techniques (methods A to D) are assessed from the viewpoint of the compatibility of taper pins with the canal walls.
Method A: Drills are primarily used.
Method B: Hand reamers
Method C: General method (KYOCERA method)
Method D: Engine reamers
Materials used in this experiment include acrylic resin plates and extracted upper incisors. The compatibility was examined by use of Indian ink.
The resalts are as follows:
1. The compatibility between the taper pins and the canal walls created through the acrylic resin plates was not always satisfactory. The penetration of Indian ink was observed in the taper portions prepared by any of the four methods to a depth of 3 mm above the canal apices and in the straight portions further above.
However, method A was significant in that the penetration of ink was almost limited within the 3 mm taper portion.
2. As regards the damage to the root apices, in every method cracks and/or splinters occurred during the processes of perforating the root,enlarging the root canal and preparing the canal taper. The number of cracks and splinters was significantly smaller in methods A and D than in method C. The lengths of the cracks found after using methods A, B,and D were 0.2～2.39 mm shorter than those found after using method C. The lengths of the splinters found after using method D were significantly smaller by 0.08～0.25 mm than those found after using methods A, B, and C.
3. The damage occurred frequently when a 13 P drill (35%), an A-reamer (22.3%) and a hand reamer (17.6%) were used.A modified A-reamer and a B-reamer caused damage frequently……4.1% and 2.0%, respectively. No damage was wrought by a 17 P drill.
In conclusion, these results indicate that much improvement should be made on the instruments used for taper pin implantation.

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　6種類の市販のチタン製骨内インプラントを用いて，微細な表面形態を比較するために走査電子顕微鏡による表面観察を行った．これらのインプラントは肉眼的にはブレード状，らせん形状，ねじ状，円筒状そして中空円筒状などの特徴のある形状を有していた．走査電子顕微鏡による高倍率の観察の結果，いずれのインプラントも特徴のある微細な表面形態を有していることが判明した．この表面形態は平滑な面あるいは粗い面，そして規則正しい面あるいは不規則な面として特徴づけられた．これらの微細な表面形態は，各インプラントシステムに用いられている製作方法や表面仕上げ方法の違いにより決定されると考えられた．

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　6種類の市販のチタン製骨内インプラント，および純チタン板材からワイヤ放電加工で製作された試作のブレードインプラントを実験に用いた．インプラントの切断面を金属組織学的手法を用いて研磨，エッチングを行い，金属顕微鏡で組織の観察を行った．また切断面のマイクロビッカース硬さを測定した．3種類のブレードタイプのインプラントの引張試験を行った．金属組織の観察結果，焼鈍組織が観察されたインプラントと加工により変形させられた結晶組織が観察されたインプラントが認められた．また各インプラントで結晶の大きさも異なっていた．各種インプラントのマイクロビッカース硬さは，155から287の範囲で製品間に有意差が認められた．引張試験の結果，試験したブレードインプラントは，すべて十分な塑性変形ののちに破断した．各種インプラントに認められた金属組織や機械的性質の違いは，原材料の選択および各システムに用いられている製作方法により決定されたと考えられる．

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　4種類の市販チタン製骨内インプラントおよび1種類の試作チタン製インプラントを用いて，インプラント表面の酸化物について，オージェ電子分光分析を行い検討した．各試料のオージェスペクトルを測定し，さらにアルゴンイオンでスパッタを行いながら，スパッタ時間とともにスペクトルのピーク高さを計測して，深さ方向の構造について検討した．いずれの試料のオージェスペクトルからも酸素，チタン，炭素のピークが検出された．酸素とチタンのピーク高さを考慮すると，すべての試料の最表層は酸化チタン（TiO₂）でおおわれていると考えられた，深さ方向の構造の様相から，実験に用いたチタン製インプラントの表層には，175～455 Åの厚さの酸化物被膜があると考えられた．このように各種インプラントにより酸化物被膜の厚さが大きく異なっていることが判明したが，これは各種インプラントで製作方法や表面仕上げの方法が異なっているためであると考えられた．

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Last year, we reported about mobility of implants by PERIO TEST(Part.1). We took many measurements of SUMICIKON implants with PERIO TEST (PT) by the same method. PT revealed us a relation between in implant and a bone, which had many objective and quantitative results for us at chairside. We had some interesting results that distinguished of sex and age.
Those results were as follows:
1. The distinction of sex(male; n=20, female; n=19)Before this examination, we felt better results on the male in clinical situation. But the result was proved not to be distinction of sex. SUMICIKON is a“ Bio-integrated implant type”, has a transmit ability of a bone by HAP. That fact was, the distinction of sex＜“Bio-integrated effect.
2. The distinction of age(a.35～44 years old;n=9,b.45～54 years old;n=16, 55 years old～;n=14) We classed 3 generations of age. We researched about PT value influences of genontology, specially about the aged of females who became osteoporosis after amemorrhea. But the result proved not to be a distinction of age.

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It has been known that contacts of dis-similar metals in an oral cavity cause galvanic pain, corrosion or discoloration of metals. These unfavorable phenomena have been considered in the dental field for a long time. As the electrochemical aspects,the corrosion is explained by an intersection of the polarization curves when two dis-similar metals have contacted each other.
The purpose of this study is to investigate the electrochemical behavior of dis-similar metal contacts by developing the analysis of polarization curves.
Polarization curves of constituent metals and the curve obtained from the relation between an electrode potential and current were measured.In this circuit,the value of current was altered with changing resistance.
Commercially pure gold, pure titanium,cobalt-chromium alloys, and nickel-titanium alloys were provided as the electrodes.
The electrolyte solution was 0.1 N NaCl.
The electrochemical reaction on the contact of dis-similar metals has been discussed on the experimental results obtained.
The results are as follows:
1. The polarization curve with a constant potentionstatic method corresponded to a potention-current curve which was obtained in the electric circuit constructed with two dis-similar metals and a resistance in a series. The same value of the short-circuit potention and current was obtained from different two curves described above.
2. As a tendency, the short-circuit current decreased quickly with time when a polarization potention strongly depended on a polarization current.
3. Since the polarity of the open-circuit potention did not change,it is explained that the same kind of redox reactions between dis-similar metals take place even after a long process time proceed.

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Porous implants are dental implants provided with porous alumina ceramic roots having a porosity of 35% and an average pore diameter of 130μm were placed in the mandible of Japanese Monkeys(Macaca fuscata). After sacrificing animals periodically, at 4 and 12 months, new bone formation in the pore spaces was investigated by scanning electron microscope.
Results
All the implants showed a high degree of stability, throughout the experimental periods under occlusal stress. Bone ingrowth into the ceramic pores was observed in all the specimens.Scanning electron micrographs of porous layer were characterized by interconnecting three dimensional pore structures and micropores of poly-crystalline alumina. As a results of this experiment, interlocking effect divided into two regions, bone ingrowth to root pore spaces and the micro anchoring with bone to micropore structures.

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