On dental anatomy and the fracture resistance of maxillary premolar teeth

Abstract

The fracture resistance of intact or restored posterior teeth has been evaluated in vitro in numerous works. However, only little or no considerations are generally given to the effects of dental anatomy and indenter dimensions on the failure conditions. This work explores these concerns for intact maxillary premolar teeth loaded by circular rods placed at the central fossa. The rod radius r varies from 1.57 to 4.8 mm. The evolution of damage is observed in situ from the tooth surface while the interior damage is examined from tooth sections prepared after unloading. The failure conclusively occurred by edge chipping in the shorter of the two tooth cusps. The chipping crack initiates at the contact site and grows along the DEJ or close to it in the dentin before deviating to the free surface. The chipping force is bounded from below by a virtually constant value termed P_ch. This interesting outcome is facilitated by a predetermined interrelationship between the inclination angles of the short and tall cusps in the tooth. An approximate fracture mechanics analysis is developed that yields P_ch = a₀d_c^3/2, where a₀ is a constant and d_c is a measure of enamel thickness at the tip of the short cusp. Finally, the significance of P_ch to tooth resilience, in vivo mastication failure, and maximum bite force delivered to the tooth is discussed.