Fracture toughness of human dentin

Abstract

The purpose of this study was to determine the fracture toughness (K(IC)) of human dentin and to test the null hypothesis that K(IC) is not affected by the orientation of dentinal tubules relative to the plane of crack propagation. Triangular prisms (4 x 4 x 4 x 8 mm) were obtained from human molars and tested using the notchless triangular prism (NTP) specimen K(IC) 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 (PE), parallel aligned (PAA), and parallel transverse (PAT). 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 K(IC). There was no significant difference between the K(IC) of PAA specimens (1.97 +/- 0.17 MPa/m(1/2)) and PAT (2.02 +/- 0.18 MPa/m(1/2)). The K(IC) for the PE specimens (1.13 +/- 0.36 MPa/m(1/2)) was significantly lower. The SEM images of the fractured surfaces showed distinct differences that were correlated with the determined K(IC) values. The fractured surfaces of PAA and PAT specimens were rougher compared to PE specimens. Both the hyper mineralized peritubular dentin and the orientation of collagen fibrils surrounding the tubules could be responsible for the significant differences in K(IC). The results of this study identified a significant anisotropy of dentin with respect to its K(IC).

On the Mechanics of Fatigue and Fracture in Teeth

“…El Mowafy and Watts [113] obtained the first estimate for the plane strain fracture toughness (K Ic ) of human dentin using CT specimens. They reported an average value for K Ic of 3.08 MPaÁm 0.5 for crack growth parallel to the tubules; there is some concern with these results as the crack was started from a notch and not a precrack, which may have caused an overestimation [53,59].…”

“…[47][48][49]. Furthermore, Ruse et al [50] developed a novel notchless triangular prism (NTP) specimen for evaluating the fracture toughness of dental materials, adhesive interfaces and hard tissues [51][52][53]. Flexural loading of beams has been employed to measure [38] with permission from the publisher).…”

Effect of orientation on the in vitro fracture toughness of dentin: the role of toughening mechanisms

“…This highly oriented microstructure is believed to confer anisotropy to the mechanical properties, although the magnitude and orientation of the anisotropy is not well established. Indeed, after some five decades of research on the mechanical properties of dentin [e.g., [3][4][5][6][7][8][9][10][11][12][13][14][15], there is still little consistency in some of the basic questions that dictate its structural behavior.…”

Cross-sectional imaging of tooth bonding interface after thermal stresses and mechanical fracture

“…Indeed, the heat speeds up the hydrolysis of collagen fiber, weakening the dentin 25) . Due to the anisotropic fracture toughness of dentin, the fracture behavior is governed by both hyper mineralized peritubular dentin and orientation of collagen fibril the tubules 26) . The interface strength and critical separation of interface are the two key factors that influence the failure mechanism of dentin 27) .…”