ヒト歯の象牙エナメル質接合部における応力--有限要素法による検討

Stresses at the dentinoenamel junction of human teeth--a finite element investigation.

抄録

象牙エナメル質接合部（DEJ）に隣接するエナメル質と象牙質の応力変化を調べるために，上顎第一小臼歯の縦断面研削断面から3次元線形弾性有限要素モデルを作成した．DEJの輪郭の局所的な変化がエナメル質と象牙質の応力パターンに及ぼす影響も解析した．模型の咬合面全体に170Nの垂直荷重を作用させ、DEJの象牙質表面とエナメル質表面の法線応力（圧縮応力または引張応力）とせん断応力を計算した。象牙質とエナメル質の法線応力は模型の咬合面で最大となり、DEJの頬側および舌側表面に沿って減少した。しかし、法線応力の大きさは歯頸部エナメル質で増加し、せん断応力分布も増加した。法線応力と剪断応力は、DEJの輪郭と頬側および舌側の咬合面3分の1のエナメル質の厚さに著しく影響された。その結果、歯頸部のエナメル質と象牙質の機械的なかみ合わせは、DEJの他の部位よりも弱いため、この部位のエナメル質は遅発性のクラックを受けやすく、最終的に歯頸部う蝕の発生につながる可能性が示唆された。

A three-dimensional, linear, elastic finite element model of a maxillary first premolar from longitudinal ground sections was developed to investigate stress variation in the enamel and dentin adjacent to the dentinoenamel junction (DEJ). The effect of regional variation in the contour of the DEJ on the stress patterns for enamel and dentin was also analyzed. The normal (compressive or tensile) and shear stresses in the dentin and enamel surfaces of the DEJ were computed for a vertical load of 170 N acting on the entire occlusal surface of the model. The normal stresses in dentin and enamel were maximum on the occlusal surface of the model and diminished along the buccal and lingual surfaces of the DEJ. However, the magnitude of the normal stresses increased at the cervical enamel, which also showed increased values for shear stress distribution. The normal and shear stresses were markedly affected by the contour of the DEJ and the thickness of enamel in the occlusal third on the buccal and lingual surfaces. The results suggested that because the mechanical interlocking between enamel and dentin in the cervical region is weaker than in other regions of the DEJ, enamel in this region may be susceptible to belated cracking that could eventually contribute to the development of cervical caries.