Restoring endodontically treated teeth has been well investigated and the importance of ferrules in cast post designs has been shown to be significant. However, there are situations where including ferrules is difficult or impossible due to lack of natural tissue.
Objectives: to determine if absence of ferrules, with different post sizes, produced lower strength levels in cast post restorations.
Methods: Forty natural maxillary central incisor teeth were treated endodontically. Teeth were divided into four groups: (1) small post with ferrule, (2) small post without ferrule, (3) large post with ferrule, and (4) large post without ferrule. Post space was prepared for each group to 9mm with either size 4 or 6 patterns. Direct cast post and core resin patterns were made with corresponding plastic patterns. Crown preparation margins had buccal shoulder and lingual chamfer. Patterns were invested and cast in base alloy. The cast post and cores were cemented with resin-modified glass ionomer (RMGI). Impressions were made with PVS. PFM crowns were fabricated and cemented with RMGI. "Horizontal" force was applied to the teeth until catastrophic failure. ANOVA and Scheffe's tests were used to test the statistical significance of difference between means.
Results: Both presence and absence of ferrule and post size affected the force to fracture (p=0.004 and p=0.013 respectively). Highest fracture forces were found with the samples with ferrules and larger post size (mean=490N). Lowest values were found in samples without ferrules and with the small post size (mean=254N). There was not interaction between presence of ferrule and post size (p=0.937).
Conclusion: Both presence of ferrule and post size produced significant differences in "horizontal" fracture forces. Lack of ferrule and smaller post resulted in lower fracture forces; however, the lowest fracture forces may be above the levels required for the clinical applications.