types of finish line configurations have been advocated, each having some advantages and disadvantages (see the table below). Chamfer finish are normally advocated for full metal margins and shoulders are generally required to provide enough bulk for metal-ceramic crowns and full ceramic crown margins. Some evidence suggests adding a bevel to margins, especially where these are heavy, to decrease the distance between the crown and the tooth tissue. Preservation of the periodontium Linked to marginal integrity, placement of the finish line can directly affect the ease of manufacturing the crown and health of the periodontium. Best results are achieved where the finish line is above the gum line as this is fully cleanable. They should also be placed on enamel as this creates a better seal. Where circumstances require the margins to be below the gum line, caution is required as several problems can arise. First, there might be issues in terms of capturing the margin when making impressions during the manufacturing process leading to inaccuracies. Secondly, the biologic width, the mandatory distance (roughly 2 mm) to be left between the height of the alveolar bone and the margin of the restoration; if this distance is violated, it can result in gingival inflammation with pocket formation, gingival recession and loss of alveolar bone crest height. In these cases, crown lengthening surgery should be considered. Special considerations Ferrule effect Endodontically-treated teeth, especially those with little sound tooth tissue, are prone to fractures. The successful clinical outcome for these teeth relies not only on adequate root canal treatment, but also on the type of restorative treatment used, including the use of a post and core system and the type of extra-coronal restoration selected. Some evidence advocates the use of a ferrule to optimise the bio-mechanical behaviour of root-filled teeth, especially where a post and core system needs to be used. In dentistry, the ferrule effect is, as defined by Sorensen and Engelman (1990), a "360° metal collar of the crown surrounding the parallel walls of the dentine extending coronal to the shoulder of the preparation". Like the ferrule of a pencil which encircles the junction between the rubber and the pencil shaft, the ferrule effect is believed to minimise the concentration of stresses at the junction of post and core, ultimately providing a protective effect against fractures. It also reduces stress transmission to the root due to non-axial forces applied by the