Crown Lengthening and Crown-to-Root Ratio

The first steps in any treatment plan must include a proper diagnosis and an understanding of the patient’s concerns. Aesthetic perceptions between dentists and laypeople can vary.9 In this case, the patient’s chief concern was dark appearing teeth and the diastema between teeth Nos. 8 and 9.
From a restorative perspective, closing the diastema while maintaining ideal or golden tooth proportions was an important goal.10 Clinical crown lengthening would provide apical movement of the gingival margin to permit proper tooth preparation and creation of desired tooth height to width ratios.11 Detailed instructions, including diagnostic models, were given by the restorative dentist to indicate the amount of tooth exposure and gingival contours that were necessary to achieve his goals. The diagnostic wax-up model shows correction of the tooth shape, tooth rotations, and closing the diastema. The need for apical positioning of the gingival margin to permit creation of proper tooth proportion is evident. In cases like this, diagnostic models (including the diagnostic wax-up), are very useful in doctor-doctor, doctor-patient, and doctor-laboratory communication. They are also used to verify that the clinician’s and patient’s expectations are the same.
From a periodontal perspective, clinical crown lengthening involves removal of hard and soft periodontal tissues to gain supracrestal tooth length and the re-establishment of the biologic width.12 The histologic description of the dentogingival complex by Gargiulo, et al13 lead to the concept of biologic width. The mean sulcus depth was 0.69 mm. The epithelial attachment was 0.97 mm. The connective tissue attachment was 1.07 mm. The total of these mean lengths yields a 2.73 mm biologic width. With these dimensions in mind, the crestal bone was moved to position approximately 3 mm from the newly established gingival margin.14
Careful management of the interdental papillae area was also very important. Tarnow, et al15 found that the interdental papillae filled the embrasure space 98% of the time when the distance from the interproximal contact to the crestal bone was 5 mm or less. If this distance increased by only one mm, an interdental papillae that filled the embrasure space was present only 56% of the time. In order to minimize the risk of blunting of the interdental papillae, no bone supporting the interdental papillae was removed.
High quality provisional restorations are a critical element in the aesthetic results of clinical crown lengthening. Provisional restorations with proper margins and emergence profiles will help establish gingival health and aesthetics.1,2 If no surgical or prosthetic refinements are required, final impressions can be taken after 3 months of healing. Lanning, et al12 found the position of the free gingival margin, attachment, and bone levels remained stable between 3 and 6 months. They did note, however, healing must be closely monitored and that positional changes could occur beyond 6 months.