An in vitro study of the fracture resistance and the incidence of vertical root fracture of pulpless teeth restored with six post-and-core systems

Statement of problem. Posts and cores are often required with pulpless teeth to provide retention and resistance form for complete crowns. Nevertheless, conventional posts may increase the potential for root fracture. Purpose. This study compared the resistance to vertical root fracture of extracted teeth treated with postcore systems that were modified with polyethylene woven fibers (Ribbond) with those treated with conventional post-and-core systems. Material and methods. Canal instrumentation was performed for 60 maxillary central incisors, and complete crown preparations were made. The coronal portion of each tooth was amputated, and 6 post-and- core systems were studied. Specimens were mounted in acrylic resin blocks with a layer of polyvinyl siloxane covering the roots. Loads were applied at an angle of 130 degrees and measured with a universal testing machine. Results were analyzed statistically with 1-way analysis of variance with Student-Newman-Keuls grouping and chi-square analysis. Results. Cast posts and cores resulted in significantly higher failure thresholds than all others, except for prefabricated, comparably sized, parallel-sided posts with composite cores. All failures in the group with fast posts involved fracture of the teeth, whereas 70% of the teeth with comparably sized parallel-sided posts and composite cores failed as a result of tooth fractures and 30% experienced core fractures. The woven fiber post-core system was significantly lower in strength than all others, and exhibited significantly fewer vertical root fractures. Conclusions. Polyethylene woven fiber and composite resin without a prefabricated post resulted in significantly fea er vertical root fractures, but mean failure load was the lowest. Smaller diameter prefabricated posts combined with the polyethylene woven fiber and composite cores improved resistance to failure. Traditional cast posts and cores were the strongest of the 6 post-core systems.