Failure characteristics of endodontically treated premolars restored with a post and direct restorative material

Ninety-one extracted maxillary premolar teeth were restored with a prefabricated post and amalgam, composite resin or glass-cermet core. Each group was again divided into three groups of 9-13 teeth to be subjected to an increasing load in one of three standardized directions (10, 45 and 90 degrees to the long axis of the tooth). Failure load and characteristics of failure were recorded. The glass-cermet-restored teeth had a lower strength than the other groups for every load direction (Student's t-test: P less than 0.01). Amalgam and composite resin groups showed a significant difference only for the 10 degrees loading condition (Student's t-test: P less than 0.02). Teeth restored with amalgam cores displayed a higher mean failure load, in combination with a 46% occurrence of root fracture.