Rehabilitating endodontically treated teeth (ETT) that have suffered significant structural compromise remains a complex challenge for dental professionals. It demands precise planning and careful consideration of various restorative options. These treatment modalities include direct composite restorations, post-and-core restorations, and full-coverage crowns. Among these, the post-and-core method stands out as the traditional gold standard, particularly when substantial coronal dentin is lost. Custom-fabricated metallic posts and cast post-and-core systems have been widely used over time due to their excellent compatibility with the prepared post space, significant retention capabilities, and resistance to fracture. However, these systems also come with limitations, such as excessive rigidity, stress concentration at the junction between the post and dentin, and an increased risk of severe root fractures, often necessitating tooth extraction.
To address these concerns, prefabricated glass fiber posts have risen in popularity. These posts offer superior biomechanical compatibility, enhanced flexural strength, and a more even distribution of occlusal forces across the root structure. Unlike metal posts, glass fiber posts have an elastic modulus similar to dentin, which helps reduce stress concentrations and the likelihood of vertical root fractures. Furthermore, they provide aesthetic advantages, ease of placement, and the ability to bond securely with adhesive resin cement, thus improving retention. Despite their benefits, the long-term success of glass fiber posts is influenced by multiple factors, including post design, cementation techniques, bonding efficacy, core material selection, and most crucially, the presence of a ferrule.
One of the most pressing concerns for ETT restored with post-and-core systems is their heightened vulnerability to fractures. This is primarily due to the altered mechanical properties and the loss of vital dentin, which reduces fracture resistance and increases susceptibility to failure under occlusal forces. Root morphology, post adaptability, bonding quality, occlusal forces, and the design of the restoration all contribute to fracture resistance in ETT. However, the presence of a ferrule has been identified as one of the most critical factors in preventing root fractures in post-restored teeth.
The ferrule effect refers to the circumferential band of remaining tooth structure that surrounds the post-and-core restoration and extends coronally beyond the margin of the prepared tooth. A well-designed ferrule enhances fracture resistance by acting as a supportive barrier, dissipating functional stresses that would otherwise be concentrated at the post-dentin interface. This effect significantly reduces the likelihood of post debonding, vertical root fractures, and core failures, ultimately improving the long-term success of ETT. Research indicates that a minimum ferrule height of 1.5 to 2 mm substantially enhances fracture resistance, with even greater resistance observed at higher ferrule heights. The mechanism behind this effect lies in the reinforcement of the remaining coronal dentin, which prevents leverage forces from causing post dislodgement or root fractures.
Despite the well-established importance of the ferrule, there is a notable gap in the literature regarding the quantitative impact of varying ferrule heights on the fracture resistance of ETT restored with glass fiber posts. This study thus aims to evaluate and compare the influence of different crown ferrules on the fracture resistance of ETT restored with glass fiber posts, as well as to assess the failure patterns associated with each configuration.
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