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歯内療法的に治療された歯根象牙質の破壊強度を試験するための新しい方法
A new method to test the fracture strength of endodontically-treated root dentin.
PMID: 33653597 DOI: 10.1016/j.dental.2021.02.001.
抄録
目的:
歯内療法的に治療した歯根象牙質の破壊強度を試験するための新しい方法を開発する。
OBJECTIVE: To develop a new method to test the fracture strength of endodontically-treated root dentin.
方法:
牛歯根を横方向に厚さ2mmの切片に切断し，根管を0.06のテーパで拡大した．各切片にレジンコンポジットの外層を接着し，根管と外半径の比が1/3以下になるようにした．得られた円板の内周面に灌水剤を塗布した後，万能試験装置に取り付けた同じテーパの鋼棒を中央から挿入して破壊した．破壊強度は厚肉円筒のラメの式を用いて計算した。灌漑の影響を受ける象牙質の深さを評価するためにマイクロインデンテーションを実施した．有限要素解析（FEA）を実施し，解析結果と同様に象牙質部の周囲にレジンコンポジットを使用することの妥当性を確認した．
METHOD: Bovine tooth roots were transversely cut into 2-mm thick sections and the root canals were enlarged with a taper of 0.06. An outer layer of resin composite was bonded to each section to make the root canal-to-outer radius ratio smaller than 1/3. The resulting discs were treated with irrigants at the inner surface and then fractured by inserting through the center a steel rod of the same taper attached to a universal test system. Fracture strength was calculated by using Lame's equations for thick-walled cylinders. Micro-indentation was performed to evaluate the depth of dentin affected by irrigation. Finite element analysis (FEA) was performed to verify the reasonableness of using resin composite to surround the dentin section as well as the analytical solution.
結果:
均質断面の解析液に基づく歯内療法処理根象牙質の破壊強度は139.69±32.59MPaであった．しかし，灌水剤による根管軟化を考慮したFEAでは，約33.5％過大評価された．治療した象牙質の補正破壊強度は114.58±26.74MPaであった．また，影響を受けた象牙質層を解析解に組み込むことで，解析解と数値解の間の破壊原因応力の差は約9.5%にまで低下した．
RESULTS: The fracture strength of endodontically-treated root dentin based on the analytical solution for a homogeneous section was 139.69 ± 32.59 MPa. However, FEA that took into account root canal softening caused by the irrigants showed that this was overestimated by about 33.5%. The corrected fracture strength of treated dentin was 114.58 ± 26.74 MPa. By incorporating the layer of affected dentin into the analytical solution, the difference in the fracture-causing stress between the analytical and numerical solutions dropped to around 9.5%.
重要性:
歯内療法で治療した歯根象牙質の破壊強度を測定するために、比較的簡単ではあるが臨床的に有用な方法が開発された。この方法は、従来の開管と灌漑によって治療された歯根象牙質にも適用可能である。
SIGNIFICANCE: A relatively simple but clinically relevant method has been developed for measuring the fracture strength of endodontically-treated root dentin. The method could be applied to root dentin that is treated by conventional canal opening and irrigation.
Copyright © 2021 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.