Fracture Properties of Human Enamel and Dentin

Abstract

Fracture in enamel is anisotropic with respect ot the orientation of the enamel rods, with Wf for fracture parallel to the rods being 0.3 X 10(2) J/meter2 but on the order of 2.0 X 10(2) J/meter2 for fracture perpendicular to the rods. Fractographs of enamel showed that the enamel rods behaved as integral units during controlled fracture. A model was proposed to explain the fracture properties of enamel involving the assumption that the hydroxyapatite crystals did not fracture but that their orientation determined the fracture properties. Dentin was also anisotropic, with fracture parallel to the dentinal tubules being the strong direction - Wf was 5.5 X 10(2) J/meter2 for fracture parallel to the tubules, but 2.7 X 10(2) J/meter2 for fracture perpendicular to the tubules. Wf for dentin was of the same magnitude as the high strain rate Wf found for bone (2.0 X 10(2) J/meter2 [ref 3]). The data obtained in this investigation indicated that dentin and enamel are brittle substances and that forces occasionally imposed during mastication or bruxism probably are capable of initiating fracture when the normal anatomy of the tooth has been altered by cavity preparation. As consequence, the design of cavity preparations should include considerations to reduce stress concentrations and thus improve the practical fracture strength of tooth structure.

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

“…Indeed, ref. [8] does indicate that crack propagation perpendicular to the tubules is more energetically favorable, consistent with the absence of fiber bridging in that direction. However, excessive scatter in their results makes such definitive conclusions difficult; moreover, no direct evidence of such bridging was presented.…”

“…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.…”

“…The earliest was by Rasmussen et al [8,9] who used a "work of fracture" (defined as the work per unit area to generate new crack surface) to quantify the fracture resistance. These authors reported an orientation effect on the toughness of dentin in that the work of fracture was found to be lower for cracking perpendicular to the dentinal tubular direction, i.e., in the plane of the mineralized collagen fibrils, compared to all other directions.…”

Sub-10-micrometer toughening and crack tip toughness of dental enamel

“…Previous studies of enamel fracture have observed cracks more commonly along rod boundaries than running through rods (Ramussen et al 1976). Bridges of 10-20µm wide in enamel have been observed in several previous experimental studies (Bajaj and Arola, 2009a, 2009b; Bechtle et al, 2010a;Bajaj et al, 2008); they span across multiple rods.…”

Australopithecus anamensis: A finite‐element approach to studying the functional adaptations of extinct hominins

“…Biomechanical tests are destructive and although they provide information about the bulk behavior of the tissue, they are unable to pinpoint areas of weaknesses within the tissue (Popowics et al, 2004). As these areas of weaknesses occur on a microstructural level (Rasmussen et al, 1976), they are inaccessible to traditional stress/ strain measurements (e.g., strain gauges). Here we present a new approach to overcome these difficulties.…”