Effect of a Crown Ferrule on the Fracture Resistance of Endodontically Treated Teeth Restored with Prefabricated Posts

Howard E. Strassler, DMD

Pereira JR, de Ornelas F, Conti PC, et al. J Prosthet Dent. 2006;95(1):50-54.

Abstract

STATEMENT OF PROBLEM: Root fracture is one of the most serious complications following restoration of endodontically treated teeth. PURPOSE: The purpose of this study was to compare the fracture strengths of endodontically treated teeth using posts and cores and variable quantities of coronal dentin located apical to core foundations with corresponding ferrule designs incorporated into cast restorations. MATERIALS AND METHODS: Fifty freshly extracted canines were endodontically treated. The teeth were randomly divided into groups of 10 and prepared according to 5 experimental protocols. Control group: teeth with custom cast post and core; 0-mm group: teeth without coronal structure (no ferrule); 1-mm, 2-mm, and 3-mm groups: teeth with 1 mm, 2 mm, and 3 mm of remaining coronal tooth structure (1-, 2-, and 3-mm ferrule), respectively. All specimens in 0-mm through 3-mm (noncontrol) groups were restored with a prefabricated post (Screw-Post) and composite resin (Z100™; 3M™ ESPE™, St. Paul, MN) core located superior to the different tooth structure heights. All teeth were restored with complete metal crowns. The fracture resistance (N) was measured in a universal testing machine at 45 degrees to the long axis of the tooth until failure. Data were analyzed by 1-way analysis of variance and Tukey test (alpha = 0.05). RESULTS: Significant differences (P<.001) were found among the mean fracture forces of the test groups (control group: 818.2 N; 0-mm, 1-mm, 2-mm, and 3-mm groups: 561.0 N, 627.6 N, 745.3 N, and 907.1 N, respectively). When the mode of failure was evaluated, all failures in the control group occurred due to root fracture, and all failures in the 0-mm group occurred due to core fracture. The majority of failures in the other groups occurred due to crown cementation failure. CONCLUSION: The results of this study showed that an increased amount of coronal dentin significantly increases the fracture resistance of endodontically treated teeth.

COMMENTARY

When restoring endodontically treated teeth, the concept of a ferrule (especially in the anterior region where most teeth have occlusion at 45 degrees from the long axis of the tooth) has been a benchmark. This study clearly demonstrates the importance of a ferrule when the preparation of an endodontically treated tooth extends beyond the margins of the tooth fracture. Increasing the length of the ferrule design in crowns had a significant effect on the fracture resistance of the endodontically treated teeth restored with a passively cemented, prefabricated post with a composite resin core.

In the past 5 years, there has been an increase in the use of fiber posts. I have seen many articles with an anterior tooth fractured at the gingival line that is then restored with a fiber post and a composite core with total disregard for ferrule design. These restorations will fail. Of more importance is that when these restorations fail, the blame will be on the post, not poor treatment planning. Planning a ferrule of ≥ 1.5 mm to 2 mm will contribute to clinical success when restoring endodontically treated teeth.

About the Author

Howard E. Strassler, DMD Professor and Director of Operative Dentistry Department of Endodontics, Prosthodontics and Operative Dentistry University of Maryland Dental School, Baltimore, Maryland