Crown lengthening

Crown lengthening is a surgical procedure performed by a dentist, or more frequently a periodontist, where more tooth is exposed by removing some of the gingival margin (gum) and supporting bone. Crown lengthening can also be achieved orthodontically (using braces) by extruding the tooth. Crown lengthening is done for functional and/or esthetic reasons. Functionally, crown lengthening is used to: 1) increase retention and resistance when placing a fabricated dental crown, 2) provide access to subgingival caries, 3) access accidental tooth perforations, and 4) access external root resorption. Esthetically, crown lengthening is used to alter gum and tooth proportions, such as in a gummy smile. There are a number of procedures used to achieve an increase in crown length. The remaining crown of the natural tooth needs to be sufficiently long to have adequate retention and resistance to withstand occlusal (biting) forces. Without adequate retention and resistance, a prosthetic crown can be dislodged and/or damaged. Suggested characteristics are: 1) 10-20° of occlusal convergence, 2) minimum height of 4 mm for molars and 3 mm for other teeth, 3) a height:width ratio of 0.4 or greater, and 4) proximal line angles should be conserved. When these characteristics are lacking, auxiliary retention (e.g. axial grooves) are needed. Previously known as biologic width, supracrestal tissue attachment (STA) consists of the junctional epithelium and connective tissue attachment above the alveolar crest. On average, STA is 2.04 mm, with the junctional epithelium and connective tissue constituting 0.97 and 1.07 mm, respectively. However, the STA has been observed to vary between 0.75 - 4.33 mm. It is important to avoid invading the STA when fabricating dental restorations. If a dental restoration invades the STA, chronic inflammation is likely to occur which then causes pain, gum recession, and unpredictable loss of alveolar bone.