Elsevier

Journal of Biomechanics

Volume 5, Issue 6, November 1972, Pages 557-564, IN1, 565-566
Journal of Biomechanics

Anisotropy in hard dental tissues

https://doi.org/10.1016/0021-9290(72)90027-9Get rights and content

Abstract

The critical angle reflection technique was used to determine longitudinal and shear sonic velocity components in the exposed surface of bovine incisors along the tooth axis and perpendicular to it. By grinding a flat on the tooth surface successive layers were exposed and the velocity components measured. Plots of the velocity variation with depth were prepared which show some variation in the enamel, much less in the dentine and a sharp drop at the dentino-enamel junction. Strong evidence of anisotropy is demonstrated, especially in enamel.

The longitudinal velocity component is larger than previous values for measurements through these hard tissues. Hydroxyapatite and bone models assuming hexagonal symmetry indicate that the surface velocity should be the smaller component. The Katz hexagonally symmetrical bone model shows a significant dip in the velocity along the 45° propagation direction. If it is assumed that prior measurements correspond to the 45° rather than the c-axis direction, a set of elastic constants can be calculated which are an estimate for enamel and dentine. These resemble the Katz bone model.

Enamel C11 115, C12 42·4, C13 30, 33 125, C44 22·8

Dentine C11 37, C12 16·6, C13 8·7, C33 39, C44 5·7

Katz bone model C11 31, C12 14·7, C13 11·3, C33 33, C44 6·2

(all × 109N/m2)

Poisson's ratio for enamel is estimated to be 0·28 and for dentine 0·32.

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