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. Author manuscript; available in PMC: 2009 Dec 1.

Published in final edited form as: Biomaterials. 2008 Sep 18;29(36):4847–4854. doi: 10.1016/j.biomaterials.2008.08.019

Observations of crack extension in enamel.

(a) an optical micrograph of crack extension in enamel. Cyclic crack growth resulted in the formation of several unbroken ligaments of tissue that bridge the crack (black arrowheads). The direction of crack growth is from left to right

(b) variation in the fracture plane across the specimen thickness. Notice the larger amplitude and frequency of the waviness towards the inner enamel. Such features are formed due to crossing of bundles of prisms (also known as decussation). Notice the presence of a small portion of dentin and the DEJ at the end of the inset (the data reported in the study does not include the response where the crack reaches the DEJ as the crack becomes unstable prior to reaching the end of the inset)

(c) a view of smaller broken ligaments (white arrowheads) spread across the specimen thickness from (b). The image was taken at the surface corresponding to steady state growth (ΔK~ 0.6 MPa·m^0.5)

(d) crack extension in decussated enamel and fracture of individual prisms (indicated by white arrowheads). Note the individual and small groups of nano crystalline rods that also served as ligaments in the fracture process (circled region)

Observations of crack extension in enamel.

(a) an optical micrograph of crack extension in enamel. Cyclic crack growth resulted in the formation of several unbroken ligaments of tissue that bridge the crack (black arrowheads). The direction of crack growth is from left to right

(b) variation in the fracture plane across the specimen thickness. Notice the larger amplitude and frequency of the waviness towards the inner enamel. Such features are formed due to crossing of bundles of prisms (also known as decussation). Notice the presence of a small portion of dentin and the DEJ at the end of the inset (the data reported in the study does not include the response where the crack reaches the DEJ as the crack becomes unstable prior to reaching the end of the inset)

(c) a view of smaller broken ligaments (white arrowheads) spread across the specimen thickness from (b). The image was taken at the surface corresponding to steady state growth (ΔK~ 0.6 MPa·m^0.5)

(d) crack extension in decussated enamel and fracture of individual prisms (indicated by white arrowheads). Note the individual and small groups of nano crystalline rods that also served as ligaments in the fracture process (circled region)