Methods: Thirty-two human maxillary central incisors were randomly divided into 4 experimental groups; group 1: ferrule+post fit, group 2: ferrule+smaller post, group 3: no ferrule+post fit and group 4: no ferrule+smaller post. Root canal treatment was performed and post space was prepared using DT light drill no.2. In groups 1 and 3, teeth were restored using DT light post no.2, while in groups 2 and 4, using post no.1. Posts were cemented with Panavia F 2.0, then composite core build-up and Ni-Cr crowns were fabricated. The teeth were embedded in acrylic resin blocks with simulated PDL. The specimens were loaded on a universal testing machine with crosshead speed of 1 mm/min on the palatal surface at 135๐ to long axis of tooth until failure. The failure modes were evaluated by visual inspection under stereomicroscope.
Results: Fracture force of group 1, 2, 3 and 4 were 1476.9± 252.1 N, 1350.4± 110.7 N, 803.9± 148.9 N and 675.5± 165.7 N, respectively. Two-way ANOVA and Tukey HSD revealed that fracture force in group 1 and 2 were significantly higher than group 3 and 4 (p<0.05). No significant difference was found between groups 1 and 2 and between groups 3 and 4. From the failure analysis in group 1, the failure occurred around cervical third of root. In group 2, bending of root that cause horizontal root fracture was mostly observed. In groups 3, horizontal fracture at crown margin was mostly observed. In group 4, bending of root and horizontal fracture at crown margin were both observed.
Conclusion: Restoring RCT-teeth with no ferrule tend to failed with horizontal fracture at crown margin while restoring with small post tends to failed by bending of root.