Microtribology of Human Teeth - Dental Biotribology - page 128

Fig. 5.17 SEM images showing the orientation of the HA crystals on the axial section of a
human tooth
Fig. 5.18 Schematic illustration showing the anisotropic wear behavior of tooth enamel while
scratching along the directions ( a ) parallel and ( b ) vertical to the enamel rod's axis
modulus of the interrod enamel were reported to be about 73.6 % and 52.7 % lower
than those of the enamel rod, respectively [ 5 ]. Therefore, the interrod enamel may
play the role of a “buffer” during the scratching process. As shown in Fig. 5.18a ,
when the scratching tests were performed along the parallel direction to the axis of
the enamel rod, the enamel rod was squeezed by the diamond tip and the adjacent
interrod enamel was apt to play a buffer role against the applied stress [ 18 ]. As a
result, no evident debris was found on the scratches parallel to the enamel rod's axis
even at a high load of 80 mN. However, when the scratching tests were performed
along the vertical direction to the axis of the enamel rod, the buffer effect of the
interrod enamel was extremely limited, and the brittle debris was generated beside
the scratches [ 14 ]. In fact, such anisotropic wear behavior based on the orientation
of the fiber was also reported in other materials, such as bamboo and fluorapatite
single crystals [ 21 , 22 ].