The effects of ferrule configuration on the anti-fracture ability of fiber post-restored teeth

To evaluate the fracture resistance of fibre post-restored teeth with various ferrule configurations by using fracture failure tests and extended finite element analysis (XFEM).

60 Maxillary central incisors were collected and divided into six groups (n=10) according to various ferrule configurations with different ferrule heights in the labial or palatal region. All of the teeth were endodontically treated and restored by using fibre posts, composite cores and metal crowns. Fracture failure tests were performed on the post retained restorations until fracture occurred. The ultimate load was recorded and analyzed by one way analysis of variance (ANOVA). The fractured specimens were longitudinal sectioned and investigated by micro-stereomicroscope and scanning electronic microscope. XFEM was used to model the fracture of the post-restored teeth and exhibit crack initiation and propagation in the cement layers.

Fracture failure tests indicated that the palatal ferrule significantly enhanced the fracture resistance of the post-restored teeth, regardless the height of the labial ferrule. The fractography investigation exhibited that the crack initiated at the palatal margin of the cement layer and propagated to the cervical region of the root. XFEM confirmed these findings and demonstrated that increasing of the palatal ferrule could effectively enhance the anti-fracture ability of the adhesive cement and protected the integrity of adhesive cement.

Adhesive interface was the susceptible structure of the post retained restorations. Increasing palatal ferrule height could effectively reduce the stress concentrated within the palatal adhesive cement.

"Ferrule effect" exhibits the protection of the interity of cement layer. Increasing the ferrule height, especially in the palatal side, can significantly enhance the anti-fracture ability of fibre post-restored teeth.