1. Minimum of two central incisor teeth or all six anterior teeth may need to be crown lengthened
2. A shallow vestibule due to the attachment of buccinator and mentalis muscles limits the space available to accommodate the re-positioned muco-gingival flap which will in turn limit the amount of coronal extension possible.
3. When apically re-positioning a mucogingival flap after bone removal to partially expose the root of the tooth, the space available to accommodate the flap is determined by the muscle insertion.
4. Soft tissue — aesthetic considerations
4.1. To produce acceptable aesthetics:
4.2. If only one tooth requires crown lengthening, in order to gain even gingival heights:
4.2.1. Orthodontic eruption which is then followed by surgery.
4.3. If restorations are to be placed with their margins just sub-gingival, it is prudent to wait until :
5. A procedure that clinical height of the crown increased by removal of the coronal portion of periodontium with crestal bone. There must be at least 3 mm between most apical extension of restorative margin and crestal bone.
6. Anatomical factors to consider
6.1. Shape of single-rooted teeth
6.1.1. 6 months after surgery to be certain that no further change in after surgery and before the position of the gingival margin takes place.
6.1.1.1. where tooth tend to be cylindrical or if there is sufficient room at the level of the amelo-cemental junction(ACJ) to make the preparation, then extending the length of the clinical crown in an apical direction.
6.1.1.1.1. If there is insufficient room at the ACJ , or if the tooth tapers significfntly from that point,These require bevelled margins which need less tooth reduction in the marginal areas. The use of a metal collar has aesthetic implications if the patient has a high lip-line.
6.2. Molar root morphology
6.2.1. Deliberate bone removal my lead to exposure of the furcation entrance, leading to problems in plaque control and future loss of bone.
6.2.2. Single-rooted conical
6.2.2.1. same as anterior teeth.
6.2.3. Short root trunk
6.2.3.1. remove bone from the mesial and distal regions of a lower molar
6.2.3.1.1. less than ideal but may still be useful.
6.2.4. Long root trunk
6.2.4.1. bone may be removed around the circumference of the tooth.
6.2.4.2. Where the tooth root tapers from the amelocemental junction to the apex, after crown lengthening the post-surgical aesthetics may be poor because of the appearance of the very wide embrasure spaces that leave black triangles between the teeth. This effect can be partially reduced by either modifying the surgical technique in order to preserve the papilla or by over-building the neck of the crowns to reduce the size of the interdental area.
6.3. The width of interdental bone
6.3.1. If a pre operative RG shows very narrow interdental bone as a consequence of there being little space adjacent teeth.
6.3.1.1. In this situation consideration should be To whether extract the teeth and replacement with a pontic might be preferable