Surgical crown lengthening
Under surgical crown extension is meant to engage in the dentistry , the aims, the remaining part of a tooth for subsequent recovery by means of a crown to extend. Despite the technical term of crown lengthening , the tooth is not actually lengthened, only the root portion of the tooth is exposed somewhat. The procedure is used when the tooth is completely or partially destroyed by caries up to the gingival margin and a crown restoration with a tight margin is not possible.
To avoid secondary caries , a crown must have a tight edge fit to the tooth. A razor-sharp edge of a crown is not sufficient for tightness, but the artificial crown must encircle the tooth in a width of 1.5 to 2 mm tightly and like a band. This ferrule effect (barrel hoop effect) also contributes to the stability and hold of the artificial crown on the tooth. A tight seal of the gingival margin is also necessary, which must seal the passage point of the tooth from the jawbone against penetrating germs from the oral cavity.
In 1961, Gargiulo determined the mean biological width to be 2.04 mm. Of this, 1.07 mm is occupied by the periodontium and about 0.97 mm by the marginal epithelium . If it is not possible to restore a tooth due to insufficient tooth substance, this procedure is used to remove some bone from the upper edge of the alveolus , ideally to create a 3 mm gap between the gum line and the upper edge of the alveolar bone. Without such a measure, the biological width would be undershot, which would result in chronic pain, chronic gingivitis and a breakdown of alveolar bones.
Apart from restoring a sufficient gum line, the ferrule effect contributes to the stability of the artificial tooth crown. If the future artificial tooth crown does not encompass the tooth in the form of a band, the risk of fracture of a root-treated tooth increases. In the upper X-ray you can see the tooth filling adjacent to the alveolar bone (white = radiopaque). On the lower X-ray you can see the crown restoration of the tooth after a surgical crown lengthening in the distal area, i.e. after the removal of the bone septum. (The lower X-ray is not an original image. It was digitally processed to show the principle of crown lengthening).
Crown / root ratio
The alveolar bone surrounding the tooth is also the alveolar bone of the adjacent tooth in the interdental space (interdental space). Surgical crown lengthening therefore also weakens the anchoring of the neighboring tooth in the jawbone. This is inevitable to some extent. At the same time, the crown / root ratio of the tooth and possibly the neighboring tooth is reduced, since the anchoring of the tooth in the jawbone is reduced at the same time. This has a direct influence on the abutment value of the tooth, i.e. the usability of the tooth in the context of prosthetic reconstructions.
Surgical crown lengthening involves the risk of exposing the bifurcation or trifurcation in multi-rooted teeth , which would make the periodontium more susceptible to infection . Furthermore, tooth loosening can result from this. Affected neighboring teeth can react with hypersensitivity to thermal stimuli. Aesthetic impairments can occur in the anterior region. Recessions of the papilla or the gingival margin cannot be ruled out.
As a rule, destroyed teeth must first undergo endodontic treatment . This is followed by the manufacture of a post abutment , with which an artificial tooth stump build-up is carried out, which is later supplied with an artificial tooth crown. In a further treatment step, the surgical crown lengthening is carried out. The respective procedure takes place under local anesthesia .
If bone loss is already evident on the tooth, the existing gingival pocket is shortened by a gingivectomy, thereby lengthening the visible part of the tooth.
Using the apical displacement flap - with or without bone resection - part of the gingiva is displaced towards the apical, thereby increasing the visible part of the crown.
Without bone loss, the gingiva on the tooth in question is carefully dissected and the exposed alveolar bone is removed to the required extent with a milling cutter ( round burr ). In order not to damage the roots of the neighboring teeth, the bone is removed there with hand instruments. The exposed part of the root is subjected to scaling in order to remove remnants of the periodontal bone so that reattachment (regrowth) is avoided. The gingival wound is treated with an atraumatic suture .
The final restoration of the tooth, for example with an artificial dental crown, can begin about six weeks after the procedure. In critical cases you should wait three months. Only after the gingival wound has healed can the tooth and the periodontium surrounding it be assessed to determine whether the desired biological width has been achieved.
The intervention is irreversible. Once the alveolar bone has been removed, it is almost impossible to rebuild the jawbone, i.e. bring it back to its previous level. This can have a negative effect on any implant restoration that may be required later . The patient must therefore be fully informed about the consequences of the operation. If the prognosis of the procedure is questionable, extraction of the tooth should be considered.
Orthodontic crown extension
In some cases, orthodontic crown lengthening is an alternative procedure, namely when there is still enough tooth substance that an orthodontic appliance can be attached to the tooth in order to pull the tooth slightly out of its socket. A distinction is made between slow and forced extrusion.
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