Effects of porcelain-metal junction angulation on porcelain fracture

The different porcelain-metal junction angulations from 45 to 135 degrees have no effect on the amount of compressive force required to fracture the porcelain. The compressive force required to fracture the samples was reduced by half when the contacts were placed 1 or 2 mm from the porcelain-metal junction. Nevertheless, even at 2 mm from the porcelain-metal junction, the compressive strength was approximately six times that of the average biting force. Therefore, clinical fractures are not the result of biting force but possibly the burnishing effect on the metal as the patient slides through the junction. An experiment designed to study a sliding force on the porcelain-metal junction is needed to understand the causes of fracture that originate there and to determine an optimum distance for the placement of occlusal contacts.