Effect of Different Ferrule Length on Fracture Resistance of Endodontically Treated Teeth: An In vitro Study

A ferrule has been described as a key element of tooth preparation when using a post and a core. It is a vertical band of tooth structure at the gingival aspect of crown preparation. It lessens the stress transmission to the root which is due to forces from posts or bending during seating of the post. The incorporation of a ferrule can help to withstand the forces of occlusion, preserve the hermetic seal of the luting cement, and minimize the concentration of stresses at the junction of post and core.

To evaluate and compare the effect of ferrule length on fracture resistance of endodontically treated mandibular premolar teeth, restored with prefabricated glass fiber post luted with resin cement, composite core and a full coverage metal crown.

Forty freshly extracted mandibular premolars were treated endodontically. They were randomly divided into four groups according to their ferrule height: 3 mm, 2 mm, 1 mm and 0 mm (no ferrule). All specimens were restored with prefabricated glass fibre posts (Reforpost, Angelus) and composite resin (Filtek™ Z250XT). Standardized preparation was done on each specimen to receive a cast metal crown. The specimens were thermocycled and compressive static load at a crosshead speed of 1 mm/min was applied at an angle of 30° on lingual incline of buccal cusp of the crown until failure occurred. The load (N) at failure and mode of failure were recorded. Statistical analysis was performed with Kruskal Wallis test.

Fracture resistance values among the groups was found to be statistically significant (p<0.001). The 3 mm ferrule group had significantly higher failure load (971.99±133.07) compared to 2 mm (848.84±109.60), 1 mm (714.64±133.89) and 0 mm ferrule groups (529.36±119.95). More favourable failure modes were observed in almost all groups.

The results of this study showed that fracture resistance of endodontically treated teeth increases as ferrule length increases.