歯内療法によりエンドクラウンで修復された上顎小臼歯の応力分布に及ぼす基材の影響

[Influence of base materials on stress distribution in endodontically treated maxillary premolars restored with endocrowns].

抄録

目的:

歯内療法によりエンドクラウンで修復した上顎前歯の応力分布に及ぼす基材の影響を3次元有限要素解析により評価する．

OBJECTIVE: To evaluate the influence of base materials on stress distribution in endodontically treated maxillary premolars restored with endocrowns using three-dimensional finite element analysis.

方法:

上顎第二小臼歯をMicro-CTでスキャンし，厚さ1mmのセラミックエンドクラウンの3次元有限要素モデルを作成した．また，ネガティブコントロールとして，土台のないモデルも作成した．基材は，光重合型グラスアイオノマー（3M Vitrebond，3657MPa），流動性コンポジットレジン（3M Filtek Z350XT Flowable Restorative，7300MPa），高強度グラスアイオノマー（GC Fuji Ⅸ，13 130MPa），ポストコンポジットレジン（3M Filtek P60，19700MPa）と弾性率が異なる4種類の従来基材を用いています．200Nの力を垂直方向と斜め方向に負荷し，歯組織と接着層の応力分布と大きさを3次元有限要素解析により検討した．

METHODS: A maxillary second premolar was scanned by Micro-CT and a three-dimensional finite element model of ceramic endocrown with 1 mm thickness of base was established. A model without base was also established as a negative control. Four kinds of conventional base materials with different elastic modulus were adopted: light cure glass ionomer(3M Vitrebond, 3 657 MPa), flowable composite resin(3M Filtek Z350XT Flowable Restorative, 7 300 MPa), high strength glass ionomer(GC Fuji Ⅸ, 13 130 MPa), and posterior composite resin(3M Filtek P60, 19 700 MPa). With a 200 N force loaded vertically and obliquely, the distribution and magnitude of stress in the tooth tissue and adhesive layer were investigated by three-dimensional finite element analysis.

結果:

象牙質および接着層の最大フォンミーゼス応力値（垂直/斜め）は以下のように測定された．(1)基材なし．象牙質19.39/70.49MPa，接着層6.97/17.97MPa，（2）光重合型グラスアイオノマー．象牙質で 19.00/69.75 MPa，接着剤層で 6.87/16.30 MPa，(3) 流動性コンポジットレジン．象牙質で 18.78/69.33 MPa，接着層で 6.79/16.17 MPa；(4) 高強度グラスアイオノマー．象牙質で 18.71/69.20 MPa，接着層で 6.74/16.07 MPa，(5) 後方コンポジットレジン．(5)後方コンポジットレジン：象牙質で18.61/69.03 MPa，接着剤層で6.70/16.01 MPa．同じ荷重条件下で，基材の弾性率が異なるモデルでも，ほぼ同様の応力分布パターンを示した．歯組織のフォンミーゼス応力は，主に歯頸部に集中した．斜め荷重では，von Mises応力が集中する領域は，垂直荷重の場合と同様であったが，その値は増加した。歯頸部への応力集中は，基材を用いたモデルでは，基材を用いないモデルに比べて緩和された．歯組織および接着層の最大von Mises応力は，基材の弾性率が高くなると減少し，象牙質の弾性率に近づいた．

RESULTS: The maximum von Mises stress values(vertical/oblique) in dentin and adhesive layer were measured as follows: (1) no base material: 19.39/70.49 MPa in dentin and 6.97/17.97 MPa in adhesive layer; (2) light cure glass ionomer: 19.00/69.75 MPa in dentin and 6.87/16.30 MPa in adhesive layer; (3) flowable composite resin: 18.78/69.33 MPa in dentin and 6.79/16.17 MPa in adhesive layer; (4) high strength glass ionomer: 18.71/69.20 MPa in dentin and 6.74/16.07 MPa in adhesive layer; (5) posterior composite resin: 18.61/69.03 MPa in dentin and 6.70/16.01 MPa in adhesive layer. Under the same loading condition, models with different elastic moduli of base materials had similar stress distribution patterns. The von Mises stress of tooth tissue was mainly concentrated in the tooth cervix. Under oblique load, the regions where von Mises stress concentrated in were similar to those under a vertical load, but the values increased. The stress concentration in the tooth cervix was alleviated in models with base materials compared with the model without base material. The maximum von Mises stress in the tooth tissue and adhesive layer decreased when the elastic modulus of base materials increased and got close to that of dentin.

結論:

小臼歯部エンドクラウンの基材として，弾性率が高く象牙質に近いコンポジットレジンを用いることで，歯頸部および接着層への応力集中を緩和できることが示唆された．

CONCLUSION: The posterior composite resin of which the elastic moduli is high and close to that of dentin is recommended as base material for premolar endocrowns to alleviate the concentration of stress in tooth cervix and adhesive layer.