Ferrule effect: a literature review

Preserving intact coronal and radicular tooth structure, especially maintaining cervical tissue to create a ferrule effect, is considered to be crucial for the optimal biomechanical behavior of restored teeth. The ferrule effect has been extensively studied and still remains controversial from many perspectives. The purpose of this study was to summarize the results of research conducted on different issues related to the ferrule effect and published in peer-reviewed journals listed in PubMed.

The search was conducted using the following key words: "ferrule" and "ferrule effect" alone or in combination with "literature review," "fracture resistance," "fatigue," "finite element analysis," and "clinical trials."

The findings from reviewed articles were categorized into three main categories: laboratory studies, computer simulation, and clinical trials. Laboratory studies were further classified into subchapters based on the main aspect investigated in relation to the ferrule effect.

The presence of a 1.5- to 2-mm ferrule has a positive effect on fracture resistance of endodontically treated teeth. If the clinical situation does not permit a circumferential ferrule, an incomplete ferrule is considered a better option than a complete lack of ferrule. Including a ferrule in preparation design could lead to more favorable fracture patters. Providing an adequate ferrule lowers the impact of the post and core system, luting agents, and the final restoration on tooth performance. In teeth with no coronal structure, in order to provide a ferrule, orthodontic extrusion should be considered rather than surgical crown lengthening. If neither of the alternative methods for providing a ferrule can be performed, available evidence suggests that a poor clinical outcome is very likely.