Ferrule effect: Need for Ferrule, Advantages, Design & Classification of Ferrule

A Ferrule is a 360 degree collar of the crown surrounding the parallel walls of the dentin extending coronal to the shoulder of the preparation. When properly placed, it reduces the incidence of fracture in endodontically treated teeth. Ferrule combines a shoulder preparation with parallel coronal dentin walls and improves overall resistance of restoration. Ferrule design incorporates nearly parallel walls, a minimum height of 2mm, width of atleast 1mm and preferably placed circumferential. Another important aspect to be considered while placing a ferrule is the biologic width. In severely damaged tooth with no clinical crown available, surgical crown lengthening or orthodontic  extrusion can be considered.