On the ferrule effect and the biomechanical stability of teeth restored with cores, posts, and crowns

An abutment for a fixed partial denture may not contain enough tooth structure, such that the abutment does not provide an adequate ‘ferrule effect’. A crown or bridge dental prosthesis that is cemented onto such an abutment/s may undergo biomechanical failure. Here, the tooth, core, and post complex, on which the crown is cemented, may fracture off from the abutment, causing the crown to separate from the abutment, while the cement that bonds the crown to the tooth, core, and post complex remains intact, such that the tooth, core, and post complex remains inside the crown when the crown separates from the abutment. This article reviews the dentistry literature on the ferrule effect, and presents alternative definitions for terms such as ferrule, the ferrule effect, and the ferrule tooth structure. The article also explains how the use of a surgical operating microscope, or high magnification binocular surgical loupes of ×6-8, or greater magnification improve the ability of a dentist to assess how much ferrule tooth structure an abutment contains, compared to the use of unaided vision.