インプラント治療は予知性が高いことから，歯の欠損補綴の第一選択肢と考えられるようになった．しかし，インプラント治療には種々の合併症があり，その中でもインプラト周囲炎が最も多く，その成因は単一のものでなく，宿主に関連する因子もあるが，インプラントシステムに関連する因子も含め，様々な因子が複雑に絡み合っていることから，治療に難渋するケースも多く，極度に進行した場合にはインプラント撤去を余儀なくされる．そのリカバリー処置としては，骨造成を含めたかなり高度なインプラント治療が必要となる．したがって，インプラント周囲炎は長期予後に最も関係することから，インプラントのオッセオインテグレーションのみを考慮するだけではなく，インプラント周囲骨の吸収防止や粘膜貫通部でのソフトティッシュ・シーリングの獲得によってインプラント周囲骨・軟組織の保全を図ることが，インプラント周囲炎の対策といえる．

具体的なインプラントシステムにおける工夫点としては，①インプラントカラーの表面加工・形状・性状は周囲骨の吸収が少なく，ソフトティッシュ・シーリングが期待できるように，②インプラントカラー部のデザイン（カラー部の形状だけでなく，マイクロスレッドやマイクログルーブも含め）を周囲骨の吸収が少なく，ソフトティッシュ・シーリングが期待できるように，③インプラントとアバットメントの界面に存在するマイクロギャップによる周囲骨吸収の影響をなくすか，マイクロギャップが存在しない連結様式にするなどが挙げられる．

本稿では，自験例であるmachinedインプラント（Nobel Biocare AB, Sweden），チタン表面を陽極酸化処理した粗面加工のTiUnite インプラント（Nobel Biocare AB, Switzwerland），レーザー・アブレージョンにて規則的な溝を有するLaser-Lok^®（以下L-Lと略す）インプラント（Biohorizons, USA）に関する臨床統計的観察も含め，前述の3項目について，インプラント周囲炎との関連性に関する現状と今後の展望について解説したい．

インプラント治療が補綴処置として広く一般的に行われるようになったが，インプラント周囲炎・周囲粘膜炎もまたインプラント埋入後の合併症として日常的に認められるものとなった．現段階でインプラント周囲炎に対する治療法の多くは臨床経験にもとづくものが多く，確固たるデータに欠け，不確実さを伴うものとなっている．それゆえインプラントのメインテナンスにおいては，可逆性の病変であるインプラント周囲粘膜炎の段階でトラブルを発見し，これが進行する前に治療を行う必要がある．さらに，これら疾患の発症リスクを理解し，予防につとめることも重要である．

インプラント周囲炎は歯周炎と同様，多因子性の疾患である．現在のところプラークやその沈着を可能にさせる上部構造の形態などの局所的因子は，インプラント周囲炎に対する真のリスクファクター・リスクインジケーターとして確実視されている．一方で本稿では，特に生体の感染に対する感受性に影響する全身的因子に着目して文献的考察を行った．その結果，現在，全身的リスクファクターとして挙げられている多くの疾患や遺伝形質などは，それをリスクと確定するには科学的根拠を欠いていることが明らかとなった．ただし，その中で糖尿病と喫煙についてはインプラント周囲炎との関連を示唆するデータが蓄積されつつあるといえる．

炎症の障害性刺激因子は物理的作用，科学的作用，病原微生物の作用に大別される．

一般的にインプラント周囲炎とは病原微生物の作用による炎症であり，対処法として汚染されたインプラント表面の除染にフォーカスが当てられているのが現状であろう．しかし，感染したからその部位のインプラント表面をレーザー照射，β-TCPの粉末の噴射，各種回転切削器具による機械的清掃等で除染するという短絡的な考えではインプラント周囲炎の問題は解決されないであろう．

筆者は何故その部位がインプラント周囲炎に罹患したのかが非常に大切であると考えている．そしてインプラント周囲炎は病原微生物の作用に物理的作用が深く関わっていることに気付いてくる．顎口腔系の力の歪が集中している部位が結果的に感染性のインプラント周囲炎になることが多い．天然歯で認められる感染から力の作用をともない発症する歯周炎とは逆で，力（物理的作用）が主導で後に感染するパターンがインプラント周囲炎には多く存在すると考えている．力の作用による炎症が起こす組織破壊が感染を誘発する可能性がある．

無論，病原微生物の作用に対しての対処は必須であり，局所的な部位のみの対処ではなく，宿主へのアプローチが重要になってくる．口腔内の歯周病菌のコントロールは必須であり，その対処とそして抗菌療法を詳しく解説したい．

Implant bodies and abutments produced using G4 and G5 were connected in combination. In each combined implant body and abutment, a strain gauge was attached to the most superior area of the test piece in the area of the collar. The strain in each strain gauge-attached test piece was measured in a universal testing machine at an inclination angle of 30°. The influence of the combination of test piece produced using G4 and G5 on the measured strain was evaluated, and the following conclusions were obtained. Although the maximum bending load for the abutment screw was larger with G5 than with G4, the amount of deflection of the abutment screw up to the maximum bending load showed no significant difference between G4 and G5. Up to loading of 450 N, no significant differences in the amount of strain were observed among any of the combinations of implant body and abutment. However, at a load of 500 N and above, the amount of strain in combined implant bodies and abutments showed that the amount of strain was lower with G5G5 than with G4G4 and G4G5. Therefore, it was suggested that the strain was reduced by improving the strength of the collar part of the implant.

Objectives : Proximal contact loss between posterior implant-supported fixed prostheses and adjacent teeth is frequently observed in clinical practice. The aim of this study was to evaluate potential factors of proximal contact loss using multivariate analysis.

Materials and Methods : One hundred thirty-five patients with 185 implant-supported fixed prostheses in the posterior region were included. At the follow-up visits, we examined proximal contact loss between 185 implant-supported prostheses and adjacent teeth with a 110-μm-thick contact gauge. We also evaluated age, monitoring period, region of implant (molar or premolar), crown-implant ratio, state of adjacent teeth (mobility, splinting and guidance) and Misch's bone density classification as potential factors. Statistical analyses were performed with the Mann-Whitney U test, Chi-squared test and logistic regression.

Results : One hundred seven of 185 proximal contacts (57.0%) were judged lost. The Mann-Whitney U test revealed that prostheses with proximal contact loss had greater crown-implant ratio than those without contact loss (p＜0.01). Bone density was associated with incidence of proximal contact loss. Cases with D1 and D2 classification more often showed contact loss than D3 and D4 (p = 0.01). With regard to adjacent teeth, with mobility (p = 0.02), non-splinting (p = 0.01) and participating in lateral guidance (p＜0.01) were related to proximal contact loss (Chi-squared test). In the logistic regression analyses, crown-implant ratio (OR = 7.17, p＜0.01), mobility of adjacent teeth (OR = 3.15, p = 0.03), splinting of adjacent teeth (OR = 0.35, p = 0.02) and bone density (OR = 0.44, p = 0.03) were significantly associated with proximal contact loss.

Conclusion : Proximal contact loss between implantsupported fixed prostheses was observed in 57% of prostheses in the present study. It was associated with greater crown-implant ratio, mobility of adjacent teeth, non-splinting of adjacent teeth and bone density.

Purpose : This study aimed to evaluate bone remodeling at the site of bone harvesting in the mandibular symphysis radiographically.

Materials and Methods : We assessed the sites where bone was harvested from the mandibular symphysis in 10 patients who required bone augmentation, over a period of 7 years from April 2005 to March 2012. The appropriate bone volume was harvested from the mandibular symphysis using a #701 fissure or trephine bur, under abundant saline irrigation. The lingual and inferior cortex bone was maintained where possible, and the wound underwent primary closure.

Observations and Measurements : We observed the bone surface before and after bone harvesting during the surgery, and measured the bone widths from the reference point on the lingual cortex bone to the labial bone surface at 0.5-mm intervals. For cases where more than 2 years had elapsed after surgery, the condition of the bone was evaluated from cone-beam computed tomography (CT) images, mainly obtained by cross-sectional cone-beam CT of the dental arch.

Results : The CT images revealed marked bone reformation at the concave bone harvesting sites by 6 months after bone harvesting surgery. Thereafter the volume of reformed bone volume gradually decreased, and the changes plateaued by approximately 1 to 2 years. The sites where bone was harvested developed a concave surface, sloping downward from the bone margin toward the center of the site. The labio-lingual bone width measured 5.5-11.5 mm (mean : 9.6 mm) before bone harvesting, 1.5-4.5 mm (mean : 3.0 mm) immediately after bone harvesting, and 4-10 mm (mean : 7.2 mm) more than 2 years after the surgery.

Conclusion : Up to 64% of the harvested bone volume was remodeled over a period of more than 2 years after bone harvesting surgery. The remodeled area formed a sloped concave surface within the margin of the bone harvesting area.

Dental implants have become a successful therapy for restoring the function of patients. Currently, computed tomography is essential for exploring bone quality and quantity and computer-guided surgery is often used for implant surgery. Computer-guided surgery can enhance the accuracy of implant positioning and angulation and facilitate minimally invasive surgery. In addition to diagnosing bone morphogenesis and bone quantity, it is essential to evaluate soft tissue for esthetic implant treatments. The purpose of this study was to evaluate initial mucosal thickness at the implant site by using cone-beam computed tomography (CBCT).

The subjects were 93 partially edentulous patients (39 males and 54 females, mean age 56.5 years). Initial mucosal thickness was measured by using CBCT with diagnostic templates and computer software. Differences in the mucosal thickness between jaws and sites were evaluated statistically.

The results were as follows :

1. The maxillary mucosal thickness (2.9±1.4 mm) was significantly higher than the mandibular mucosal thickness (1.9±1.0 mm).

2. The mucosal thickness was greater in the order of anterior region＞premolar region＞molar region

3. The ratio of thin mucosal thickness (≤2 mm) was 60.3% in the mandible.

Although the mandibular molar region is the area where dental implant therapy is performed most frequently, the width of the bone is narrow in many cases. The aim of this case report is to newly introduce the lateral ridge augmentation procedure using a modified lateral incision technique.

Guided bone regeneration combined with autologous bone graft for bone augmentation was performed on implant placement at the mandibular left molar area of a 55-year-old woman. Because the position of the mental foramen was comparatively high, a modified lateral incision technique designed to prevent neuronal damage was used. Buccal split-thickness incision was performed 4 mm below the mucogingival junction and was extended through the mesial aspect of the aftermost molar. The split-thickness incision was then extended with a vertical split-thickness incision at the location of the mesial line angle of the aftermost molar. Following supraperiosteal preparation, the periosteum was cut at the height of the alveolar crest. The full-thickness incision line was designed to leave the periosteum distal area of the aftermost molar of approximately 2 mm. The flaps of both split-thickness and full-thickness were then separated. Following perforation of the cortical bone to create the bleeding bone surface, two implants were placed into the planned positions. After autologous bone graft was performed, nonresorbable expanded polytetrafluoroethylene titanium-reinforced membrane was adjusted to the surgical site. Horizontal mattress sutures were used between the keratinized mucosa of the lingual flap and the periosteum of the buccal flap, and intermittent sutures were used between the mucosa of the lingual flap and the mucosa of the buccal flap, without excessive pressure and while ensuring closure of the membrane. At the time of the secondary operation, free gingival grafting was performed to increase the width of the keratinized tissue. Four years after surgery, the postoperative outcome is good.

Lateral ridge augmentation with the modified lateral incision technique may be a safe method of implant placement with bone graft in cases where the mental foramen is located at a higher position than usual.