The Effect of Ferrule on the Fracture Resistance of Teeth Restored with Cast Dowel System

ABSTRACT

Cast post and cores have been advocated by some clinicians as preferable restorations for endodontically treated abutmant teeth. Preference for this post and core system derives, in part, from the incorporation of an encircling collar of metal (ferrule), which is hypothesized to protect the tooth from wedging stresses. This study determined the effectiveness of a metal collar in reducing stres concentrations when cast post and cores were loaded. Twenty freshly extracted canines free of cracks, caries, fractures, and restorations were selected for the study. The anatomic crowns of all teeth were removed perpendicular to the long axis of the tooth, from the most incisal point of the approximal cementoenamel junction. The teeth were assigned randomly to 2 groups 10 teeth each. The speciments were then endodontically treated. Core were modelled with sticky wax. Post and cores were cast in Ni-Cr alloy. Cast post and core restoration were then cemented in place with zinc polycarboxilate cement. The speciments were then embedded to acrilic resin block (42×42×26 mm). The compressive-shear stres was applied 152 degrees to the long axis of the teeth in a lingual dimple on the cores with a vertical loading apparatus on the Instron Testing Machine. Among the speciments groups, significantly higher fracture loads were observed in teeth restored with 2.0-mm ferrule compared with without ferrule (p<0.0003).