Evaluating the effect of ferrule preparation and its length on fracture resistance of maxillary central incisors with cast post-core and PFM crowns

Background: Endodontically treated teeth are weaker than vital teeth and more prone to fracture. One of the special considerations in their restoration is the application of ferrule preparation. Objective: Evaluating the effect of ferrule and its length on fracture resistance of maxillary central incisors with cast post -core and PFM (porcelain fused to metal) crowns. Methods: This was an experimental study in which 30 extracted intact maxillary central incisors with similar dimensions were selected and randomly classified into three groups. Initially, the roots of teeth were treated after crown reduction and later, while considering the simulation of orthodontically crown lengthening, the teeth were fixed in acrylic blocks followed by making cast post and cores and luted with zinc phosphate cement. In first group (control group), ferrule wasn't prepared but in second and the third groups one millimeter- and two millimeters ferrule were prepared, respectively. Later, PFM crowns were made for all specimens and luted with Zinc Phosphate cement. Finally, the specimens were loaded under compressive static loading by Zwick testing machine, using a crosshead speed of 2.5 millimeter per minute with an angle of 135 degrees to the long axis from palatal aspect to fracture. The primary failure loads were recorded as fracture resistance in Newton. Data were subjected to Kruskal-Wallis at a significant level of 5. Findings: The average and standard deviation of fracture resistance in first group (without ferrule) was 581.37±141.12 N, in second group (with one millimeter ferrule) 606.37±114.38 N, and in third group (with two Millimeters ferrule) 569.44±61.69. No significant difference between three groups was found, statistically (p>0.05). Conclusion: Preparing one millimeter .ferrule and increasing its length to two millimeters- while orthodontically crown lengthening is required- makes no significant effect on fracture resistance of maxillary central incisors with cast post-core and PFM crowns.