オッセオインテグレーションの獲得は，インプラント治療成功のための決定的な要素のひとつである．「オッセオインテグレーション」とは元来，「荷重が加わっているインプラント表面と生体骨組織との構造的かつ機能的結合」と定義されている．しかしながら，ほとんどのインプラントに関する研究では，荷重の有無に関わらずにインプラント周囲の骨組織が評価されているため，インプラント歯学では，荷重の位置づけがきわめて曖昧だといわざるを得ない．
近年，アメリカ国立衛生研究所［National Institute of Health（NIH）］から，骨組織を完全に説明するためには，骨量や骨密度に加え，骨質の解析が必要であるとの提言がなされた．骨質とは，骨折への抵抗性を示す骨の総合的な特徴であると定義され，骨構造，骨代謝回転，石灰化ならびに損傷の蓄積などから構成される新しい概念である．骨質に関するいくつかの科学的根拠が基礎研究を通して明らかにされてきているが，インプラント歯学では骨質に関しての研究は行われておらず，このことは，荷重から捉えた「オッセオインテグレーション」や「骨質」に関する基礎研究が発展していないことを意味している．
本総説では，長崎大学が行っているインプラントに関する基礎研究から得られた結果を基盤として，骨質から捉えたオッセオインテグレーションの新しい知見を考察する．

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インプラント治療を行うにあたり，顎骨の形態や骨量を評価することは重要である．近年，術前診断の一環としてComputed Tomography（CT）を撮影し，これらを把握することが多い．しかし，臨床的に骨量が十分にあるにもかかわらず，治療経過が芳しくない症例を経験することがある．
一般的にCTを用いた画像診断で判別できるのは，骨密度や骨量である．したがってCTでは，骨の軟組織成分の状態は分かりにくい．整形外科領域では骨密度だけでなく，骨強度，骨質という概念を用いることで骨粗鬆症等の病態を説明している．しかしインプラント治療においては，骨量と骨質の概念は曖昧である．
インプラント治療は骨を基本とした治療法である．骨強度や骨密度，骨質という概念を用いることで，さまざまな臨床上の問題を解明する手がかりが得られるかもしれない．

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インプラントに関連し骨造成法を施行した場合，一本のインプラント体でも接触する骨の構造が既存骨部と移植骨部で異なる．一方，腫瘍などで生じた大きな欠損への顎骨再建では，インプラント体全体が移植骨と接触するため，その質的な検討は移植骨とインプラントの関係を検討する良いモデルとなる．
顎骨再建後の移植骨は，皮質骨はきわめて薄いが，海綿骨は既存骨と同等の構造と骨密度を有し，骨細胞を有する層板構造を呈していた．このような安定した骨質は術後1年以降に得られるが，術後長期でも既存骨と同等の皮質骨幅は得られなかった．すなわち，移植骨では海綿骨質が主にインプラントの長期安定性に関与する可能性が示唆された．しかし，骨造成施行の際には，全身の骨代謝，骨膜の状態，感染抵抗性等を配慮する必要があった．
臨床的に，既存骨，再建骨，造成骨へのインプラントの間で残存率に違いはなかったが，骨構造の観点からは移植骨が初期固定に関与することは困難で，さらに，咬合負荷後の力学的な挙動も既存骨と異なることに留意しなければならない．

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A chemical approach to the treatment of the implant surface is critical to promote bone formation around the implant. The aim of this study was to examine and compare the biological responses of a titanium surface treated with various chemical solutions. Titanium disks and cylindrical rods were prepared from commercially-pure titanium with machine turning. Titanium surfaces were treated with NaCl, KCl, CaCl₂, and MgCl₂ solutions for 3 h. The capacity for protein adsorption and cell attachment was tested on the titanium surface after solution treatment, in vitro, and was examined for its bone-to-implant strength in vivo. In addition, the wettability of each treated titanium surface was examined, and the cell survival rates were verified. In all solution conditions, no significant difference in cell viability and wettability was found. The control solution (pure water) showed no significant differences compared with the treatment groups of NaCl and KCl in protein adsorption and cell attachment capacity. After treatment with CaCl₂ or MgCl₂ solutions, protein adsorption and cell attachment were increased compared with those achieved with NaCl or KCl solutions. The solution containing Ca or Mg showed better boneimplant strength in vivo. The present results suggest that the titanium surface treated with a solution containing Ca or Mg ions enhanced protein adsorption and cell attachment capacity early and more dramatically for the process of bone formation and increased bone-implant strength in vivo. The solution treatment with divalent cations of Ca or Mg was effective for fabricating titanium implants with enhanced bioactivity and osteoconductivity. Therefore, this chemical treatment of titanium surfaces is a simple and convenient method for improving osseointegration.

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Because implants frequently comprise two or three types of pieces which are composed of small parts, fracture is apt to occur. Therefore, to increase strength, implants fabricated of both JIS type-4 titanium (G4) and Ti-6Al-4V alloy (G5) combined are currently being used. However, when different metals are used in combination, it is important to clarify the release of metal ions due to galvanic action, and the strength of the implants.
In this study, implant bodies and abutments were produced using G4 and G5 by machining, and two-piece implants of G4 and G5 combined were fabricated. The maximum bending load at an inclination of 30° and amounts of titanium and vanadium released in 1% lactic acid solution were measured.
The tensile strength, elongation, yield strength, and hardness of G4 and G5 wires were measured. As a result, the tensile strength, yield strength, and hardness were higher for G5 than G4, and the elongation of G4 was greater than that of G5. The maximum bending load of implants fabricated in combination at the inclination of 30° was the highest with G5G5, and lowest with G4G4. No significant difference in the maximum bending load was noted between G4G5 and G5G4. The strain showed a similar tendency. The amount of titanium release was the lowest with G4G4 and G4G5, and highest with G5G5. The amount of vanadium release was the lowest with G4G5, second lowest with G5G4, and highest with G5G5. Furthermore, because galvanic action does not readily occur with the combined use of titanium and titanium alloy and there was no problem regarding the strength, it was suggested that the combined implants would have no problems in clinical use.

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To evaluate one aspect of osteoclastic resorbabilities of calcium phosphate bone substitutes, their dissolution behaviors were compared in a weak acid solution without strong agitation to mimic the subosteoclastic zone. Of calcium phosphate bone substitutes, β-tricalcium phosphate (β-TCP)-associated material of CERASORB (CS) , ArrowBone-β-Dental (AB) , SynthoGraft (SG) and OSferion (OS) , apatite-associated material of Geistlich Bio-Oss (BO) and sintered carbonate apatite (CA) were used as particulates. Particle sizes of OS and CA were adjusted to those of CS, AB and SG; the latter three materials had essentially the same particle size ranging from 300 μm to 500 μm. Reaction kinetics were followed by measuring proton activity and by analyzing solution calcium and inorganic phosphate, and further analyzed by chemical potential plots obtained based on the solution composition. At one week of dissolution, CS, AB, SG, OS and CA reached quasi equilibrium with thermodynamic solubility of β-TCP, and BO reached quasi equilibrium with thermodynamic solubility of hydroxyapatite (HA). Estimation of Gibbs free energy of the degree of supersaturation or undersaturation with respect to HA at 1 h dissolution, which could be used to estimate dissolution rate, clearly showed that CA was much more soluble than β-TCP-associated materials of CS, AB, SG and OS, which were more soluble than BO, indicating that CA was easily dissolved by hydrogen ions secreted by osteoclasts. This finding strongly suggests that CA would be superior as an osteoclast-mediated bioresorbable bone substitute to any other calcium phosphate bone substitutes commercially in use today.

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When most of the upper jaw is lost by ablative surgery for a malignant tumor, a dento-maxillary prosthesis combined with an obturator is usually applied in order to rehabilitate the function of both mastication and speech and to improve the facial deformities. We present a case of a fabricated dento-maxillary prosthesis supported by dental implant following subtotal maxillectomy. The patient was a 51-year-old female. She was referred to our clinic by a dentist for examination of her upper palatal swelling. A biopsy was carried out and the histological diagnosis determined an adenoma. Surgical operation was done under general anesthesia. However, a pathologist found malignant cells by serial sectioning of the surgical specimen and finally diagnosed adenocarcinoma. Therefore, subtotal maxillectomy was performed immediately. After the radical surgery, the patient had no recurrence for seven years. She had used a dento-maxillary prosthesis combined with an obturator supported by her upper remaining teeth and alveolar bone. Unfortunately, the prosthesis became unstable due to loss of her hinge teeth caused by chronic periodontitis. We designed an implantsupported dento-maxillary prosthesis with dolder-bar type attachment. The dolder bar attachment was supported by three osseointegrated implants in her maxilla. After applying the implant-supported dento-maxillary prosthesis, her oral functions including mastication, deglutition and speech have been considerably improved for six years and seven months. The patient is highly satisfied with the prosthesis.

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