Effect of ferrule and bonding on the compressive fracture resistance of post and core restorations.

AIM The purpose of this study was to compare the fracture resistance of endodontically treated teeth restored with different post and core systems in combination with complete metal crowns in teeth with no coronal structure. METHOD AND MATERIALS Fifty extracted mandibular premolars were divided into five groups. The coronal portion of each tooth was removed at the cementoenamel junction (CEJ) in all groups except Group 1. In this group the teeth were sectioned 1 mm above the CEJ to create a ferrule. After root canal preparations, cast posts were placed in the first four groups. Prefabricated glass fiber posts and composite cores were placed in the fifth group. An opaque porcelain layer was applied to the metal post surfaces in the third group and an alloy primer was applied to the posts in the fourth group before using Panavia F2 resin cement. No bonding agent or surface treatments were used for the first and second groups. A Ni-Cr full cast crown for each sample was prepared and cemented. A compressive load was applied at an angle of 45 degrees to the crown with a universal testing machine. After 500,000 mechanical cycles at 1.5Hz, the maximum load at fracture (N) was recorded. RESULTS Significantly higher fracture resistance values (216.87 N) and survival rates (75%) were demonstrated for non-ferrule teeth restored with opaque layered posts than for other non-ferrule groups. The prefabricated post group showed the most favorable fracture pattern in all test groups (P=0.04). CONCLUSION Either a ferrule preparation or bonding with the use of an opaque porcelain layer can increase the fracture resistance of teeth with little remaining tooth structure that are restored with cast crowns following endodontic therapy. CLINICAL SIGNIFICANCE Bonding cast posts to the tooth structure has a significant effect on compensating for the lack of a ferrule on endodontically treated teeth.