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

Summary 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° 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 < 0.01). Amalgam and composite resin groups showed a significant difference only for the 10% loading condition (Student's test: P < 0.02). Teeth restored with amalgam cores displayed a higher mean failure load, in combination with a 46% occurrence of root fracture.