Evaluation of fracture toughness of human dentin using elastic–plastic fracture mechanics

Abstract

Dentin, the mineralized tissue forming the bulk of the tooth, lies between the enamel and the pulp chamber. It is a rich source of inspiration for designing novel synthetic materials due to its unique microstructure. Most of the previous studies investigating the fracture toughness of dentin have used linear-elastic fracture mechanics (LEFM) that ignores plastic deformation and could underestimate the toughness of dentin. With the presence of collagen (approximately 30% by volume) aiding the toughening mechanisms in dentin, we hypothesize that there is a significant difference between the fracture toughness estimated using LEFM ( K c) and elastic–plastic fracture mechanics (EPFM) ( K J c). Single-edge notched beam specimens with in-plane ( n=10) and anti-plane ( n=10) parallel fractures were prepared following ASTM standard E1820 and tested in three-point flexure. K J c of the in-plane parallel and anti-plane parallel specimens were found to be 3.1 and 3.4 MPa m 1/2 and K c were 2.4 and 2.5 MPa m 1/2, respectively. The fracture toughness estimated based on K J c is significantly greater than that estimated based on K c (32.5% on average; p<0.001). In addition, K Jc of anti-plane parallel specimens is significantly greater than that of in-plane parallel specimens. We suggest that, in order to critically evaluate the fracture toughness of human dentin, EPFM should be employed.