Impact fracture characteristics of intact and crowned human central incisors.

Dynamic fracture energies and patterns of fracture in extracted human central incisors were determined for groups of intact controls, groups with Vita Dur N crowns, Vita Hi Ceram crowns, Dicor crowns and porcelain veneers. Teeth were struck on their middle labial surfaces by a pendulum impact device. The mean fracture energy for teeth with Dicor crowns was significantly lower than for all other groups (P < 0.05). Control tooth crowns fractured obliquely in an apical-direction. Vita Dur N and Dicor crowns shattered, the underlying tooth usually fracturing in the plane of the impact force. Vita Hi Ceram crowns chipped at the site of impact and some fractures were located in the roots. Gold crowns remained cemented and fracture occurred at the crown/root junction, or in the root. Porcelain veneers fractured at the site of impact but remained cemented. Dicor crowns were less fracture resistant than other restoration types tested. Porcelain veneers and full gold crowns stiffened teeth which led to more root fractures than the porcelain crowns.