Fracture of ceramic and metalloceramic cylinders

Abstract

untal porcelain combines esthetics with excellent biocompatibility and remains an important restorative material. Its major drawback is its low tensile strength, which results from the presence of surface and internal flaws and produces a brittleness characteristic of most ceramic materials. The porcelain-fused-to-metal (metalloceramic) and aluminous porcelain systems have been introduced to increase the fracture resistance to dental porcelain.’ Both systems are widely used in clinical dentistry. In recent years attempts have been made to reduce the technical complexity of the metalloceramic systems by bonding t:he porcelain directly to precious metal foils. With traditional metalloceramic complete veneer crowns, a minimum coping thickness of approximately 0.5 mm is necessary. The color of this metallic coping must then be masked with opaque porcelain, followed by dentin and enamel porcelains. As a result the final thickness of tlne crown is usually considerable if adequate esthetics is to be maintained. A deep preparation is needed to prevent the crown from being overcontoured, which can lead to gingival irritation. Bonding porcelain directly to a metal foil allows for the excellent esthetics of dental porcelain, without a need for an unreasonably thick restoration. The most widely known bonded foil system is the activated platinum (Pt) foil technique advocated by McLean and Sced.‘l* In this system, the standard Pt foil is tin-plated and then oxidized (activated) prior to the construction of the porcelain veneer crown with aluminous dental porcelain. Seed et a1.3 have reported that this system produces an 83% improvement in the tensile strength of the porcelain attributable to the presence of the activated Pt foil. Other bonded foil systems have used a gold coating to