Fracture toughness of human dentin

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<jats:title>Abstract</jats:title><jats:p>The purpose of this study was to determine the fracture toughness (<jats:italic>K</jats:italic><jats:sub>IC</jats:sub>) of human dentin and to test the null hypothesis that <jats:italic>K</jats:italic><jats:sub>IC</jats:sub> is not affected by the orientation of dentinal tubules relative to the plane of crack propagation. Triangular prisms (4 × 4 × 4 × 8 mm) were obtained from human molars and tested using the notchless triangular prism (NTP) specimen <jats:italic>K</jats:italic><jats:sub>IC</jats:sub> test. Dentin prisms were prepared so that the plane of crack propagation would have three different orientations relative to the orientation of dentinal tubules: perpendicular (<jats:bold>PE</jats:bold>), parallel aligned (<jats:bold>PAA</jats:bold>), and parallel transverse (<jats:bold>PAT</jats:bold>). The prepared specimens were secured in the specimen holder and loaded in tension until fracture or crack arrest. The maximum load recorded was used to calculate <jats:italic>K</jats:italic><jats:sub>IC</jats:sub>. There was no significant difference between the <jats:italic>K</jats:italic><jats:sub>IC</jats:sub> of <jats:bold>PAA</jats:bold> specimens (1.97 ± 0.17 MPa/m<jats:sup>1/2</jats:sup>) and <jats:bold>PAT</jats:bold> (2.02 ± 0.18 MPa/m<jats:sup>1/2</jats:sup>). The <jats:italic>K</jats:italic><jats:sub>IC</jats:sub> for the <jats:bold>PE</jats:bold> specimens (1.13 ± 0.36 MPa/m<jats:sup>1/2</jats:sup>) was significantly lower. The SEM images of the fractured surfaces showed distinct differences that were correlated with the determined <jats:italic>K</jats:italic><jats:sub>IC</jats:sub> values. The fractured surfaces of <jats:bold>PAA</jats:bold> and <jats:bold>PAT</jats:bold> specimens were rougher compared to <jats:bold>PE</jats:bold> specimens. Both the hyper mineralized peritubular dentin and the orientation of collagen fibrils surrounding the tubules could be responsible for the significant differences in <jats:italic>K</jats:italic><jats:sub>IC</jats:sub>. The results of this study identified a significant anisotropy of dentin with respect to its <jats:italic>K</jats:italic><jats:sub>IC</jats:sub>. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 66A: 507–512, 2003</jats:p>

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