Friction and Wear Behavior of Human Teeth - Dental Biotribology - page 54

Fig. 3.11 SEM micrographs of wear scars on the surfaces of enamel subjected to different cycles
[ 35 ]: ( a ) 100 cycles; ( b ) 1,000 cycles; ( c ) 2,000 cycles; ( d ) 5,000 cycles

There were no obvious wear traces except for a few shallow scrapes on the
enamel surface after 10 cycles (Fig. 3.10a ). A zonary mark with a slight scratch was
observed on the worn surface after 100 cycles (Fig. 3.10b ). When a human tooth
enamel fl at specimen was pressed into contact with a 40-mm-diameter TC4 ball, the
Hertzian contact diameter was calculated to be 0.350 mm, as Johnson described
[ 28 ]. The associated mean contact pressure was 208.0 MPa, which was under the
yield stress of enamel [ 14 , 29 ]. The values of Young's modulus and Poisson's ratio
used in this calculation were 94 GPa and 0.28 for human enamel [ 14 , 29 ], and
113 GPa and 0.30 for TC4 [ 37 ], respectively. As shown in Fig. 3.13 , the width of the
wear scar on the enamel surface was about 345 m after 100 cycles. This value was

quite close to the Hertzian contact diameter (0.350 mm), suggesting that enamel
was in elastic contact with the TC4 ball under the normal load of 20 N at the early
stage of wear and that no obvious wear occurred. Therefore, few wear particles were
found on the worn surface of enamel after 100 cycles (Fig. 3.12a ); most of the
enamel rods on the contact surface arranged regularly, without signifi cant plastic
deformation (Fig. 3.14a ).

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