Crown Lengthening with Osseous Reduction
Jorge André Cardoso
According to the principles outlined in Chapters 4.1 and 4.2, osseous reduction is needed when there is an altered active eruption, where the bone level is coronally positioned too close to the cemento-enamel junction (CEJ), making the soft tissue excessively cover the crown. In these cases, once the correct amount of bone and soft tissue is repositioned in a more coronal position, the appearance of the tooth will be more aesthetic, with a more pleasant length/width ratio, and no root exposure will result. The fundamental notion that clinicians must have is that, in an average dentogingival complex, the gingival margin will be established 3 mm apical from the bone margin after healing from an osseous reduction – 2 mm of biologic width plus 1 mm of gingival sulcus.1, 2 This is critical for predictable results.
In other situations when aesthetic crown lengthening is desired, the clinician has to consider the possibility of root exposure after healing. This means that the CEJ should always be the most apical limit of the final gingival margin. Again, the critical rule that the gingival margin will heal, on average, 3 mm apical to the bone level needs to be remembered. So the final bone position should never be more than 3 mm of the CEJ if the tooth is not to be restored. However, root exposure after healing from osseous reduction can be acceptable if restorations such as crowns are planned to cover the exposed root.
There are limits to the amount of crown lengthening with bone reduction that can be performed:
- The final crown/root ratio should not be unfavourable bio-mechanically.3
- The root diameter gets smaller in an apical position. If excessively performed, crown lengthening can result in a rectangular-shaped tooth and papillae loss.
- While a crown has a retentive form and can be cemented, veneers need to be bonded. If veneers are planned, root exposure is not recommended, as the apical limit of the veneer should be kept in enamel and avoid bonding to the cementum/dentin of the root, which is less predictable in the long term.4–6
Once the bone-reduction level is chosen, the second decision will be whether the soft tissue should simply be removed or placed in a more apical position. As stated in Chapter 4.2, a minimum amount of 2 mm of keratinised tissue height will be left at the site to provide an efficient biological seal that is more stable to potential aggression such as subgingival margins or excessive brushing.7 Therefore, a gingivectomy can be performed only if the remaining keratinised tissue will be at least 2 mm. If this is not the case, then the keratinised tissue must be kept and, ideally, repositioned apically.8
There are five essential factors to be considered in the process: final incisal edge position, final desired gingival margin, bone level, CEJ and attached gingiva.
These factors are concerned with treatment planning and smile design. Once the incisal edge is determined, the final gingival position is established according to the desired length of the teeth involved. The key is to understand that a gummy smile look is a proportion between white and pink.9 Sometimes only lengthening the incisal edges may have a significant impact and solve the aesthetic problems without changing the soft tissues. In other cases, combined incisal edge lengthening with soft-tissue removal can allow a more conservative alteration at the gingival margins. The desired final outcome should be previewed with a mock-up, as suggested in Chapter 4.1, and recorded in photographs (Figure 4.3.1). Impressions and models should be made of the original situation and the mock-up in place. This way references will be kept during surgery and a template can be used to guide the necessary reduction (Figure 4.3.2).