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S. Nares (ed.)Advances in Periodontal Surgeryhttps://doi.org/10.1007/978-3-030-12310-9_12
12. Crown Lengthening and Prosthodontic Considerations
Crown lengtheningFunctionalEstheticBiologic widthSurgery
12.1.1 Biologic Width
Of critical importance is understanding the risks involved if the biologic width is violated. If crown lengthening is not performed when indicated, the oral tissues will aim to correct for this invasion in an unpredictable and uncontrolled manner. Chronic tissue inflammation can occur, as well as recession and bone resorption, possibly leading to intrabony defects .
12.1.2 Mucogingival Considerations
The term mucogingival condition refers to “deviations from the normal anatomic relationship between the gingival margin and the mucogingival junction (MGJ).” Examples include recession, absence or decreased keratinized tissue, and lack of attached tissue . As discussed by Zadeh and Gil in this volume, the etiology of these mucogingival conditions is multifactorial. Factors can include tooth position, orthodontic treatment, gingival biotype, frenum position, vestibular depth, and mechanical insult. A thin gingival biotype is more likely to result in gingival recession versus a thick biotype. Buccally positioned dentition has been associated with thinner labial bone and gingiva and therefore at greater risk of gingival recession as well. Similarly, orthodontic movement in the buccal direction is more likely to cause mucogingival conditions versus that in a lingual direction . Further evidence shows that some toothbrushing factors can be associated with gingival recession, especially in more prone sites (i.e., those with other contributable factors for mucogingival deformities) [8, 9].
Crown lengthening may include gingivectomy, and therefore it is important to understand the gingival condition prior to any surgical intervention. Additionally, the quality and quantity of tissue can contribute to the overall gingival health, especially around restorations.
The need for keratinized and/or attached gingiva for periodontal health is somewhat controversial in the literature. It is well-documented that areas of little to no keratinized tissue are able to be maintained and provide support over long periods of time. Nonetheless, this outcome is only possible with excellent oral hygiene and regular professional maintenance [8, 9]. This is highlighted in a split mouth long-term study . Areas of little to no attached gingiva were either augmented with a free gingival autogenous graft or left alone, and not all of the patients received professional maintenance. Over time, patients who followed good oral hygiene and received maintenance showed adequate health in treated sites, as well as those that were not treated. In patients who did not follow maintenance protocols, the non-augmented sites resulted in increased inflammation and recession compared to augmented sites. Overall, the general consensus is that keratinized tissue deficiency predisposes to the development of gingival recession and inflammation . It is suggested that 2 mm of keratinized gingiva, with 1 mm being attached, is needed for optimal health [9, 11]. Therefore, the keratinized and attached tissue should be assessed prior to crown lengthening procedures.
12.1.3 Functional Crown Lengthening
At its essence, functional crown lengthening is a resective procedure undertaken to so that sound tooth structure can be exposed to support a new restoration and to re-establish a biologic width at a more apical position than prior to the surgical intervention. Initially proposed by D.W. Cohen in 1962, current protocol involves judicious removal of surrounding hard and soft tissue structures, so that the resulting tooth exposure is approximately 4 mm superior to the osseous crest. This amount of tooth exposure is required to allow re-establishment of the biologic width and to facilitate the ideal preparation of the tooth, ferrule, and marginal seal [3, 18–20].
Tooth decay which compromises the gingival sulcus and connective tissue attachment and/or is invading the biologic width
Tooth fracture which compromises the gingival sulcus and connective tissue attachment and/or is invading the biologic width, with adequate remaining tooth structure, periodontal attachment, and supporting alveolar bone
Teeth with excessive retrograde wear where crown lengthening is required for adequate seating and retention of a full coverage restoration
Teeth, due to super-eruption, which have insufficient interocclusal space for requisite restorative dentistry
Altered passive eruption, where the gingival margin is coronal to the CEJ and the osseous crest is approximate to or at the CEJ (Fig. 12.4a, b)
External root resorption involving the dental structures adjacent to the gingival margins and/or the osseous crest
An adjunctive or ancillary treatment modality to functional crown lengthening is the use of orthodontics for forced eruption. Orthodontic forces may be utilized to either slowly or rapidly erupt the tooth in an occlusal or incisal direction in an attempt to bring either the osseous crest and underlying periodontal structures more coronally  or to extrude the tooth from the dentoalveolar complex so that the fracture or caries is exposed. Subsequent surgical re-establishment in an apical direction of the periodontal complex may or may not be required. Further discussion of this treatment modality can be found in the chapter by Schmerman and Obando in this volume.
Caries or dental fracture extending significantly apical to the osseous crest requiring excessing alveolar bone removal.
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