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Crack depth measured from top of tallest cusp to maximum penetration, for nominal tooth of base radius R = 5 mm and enamel thickness d = 1.5 mm. Data for tooth with symmetrical quadrate cusps, three at height H = 7.5 mm (as in figure 3), but one higher cusp (cusp 1) at H = 8.5 mm. L denotes longitudinal crack in enamel side wall. Higher load is required to drive crack in taller cusp. (Online version in colour.)
