Guided surgical crown lengthening

Surgical crown lengthening is broadly indicated for aesthetic and functional reasons.^{1, 2} Aesthetic indications include altered passive eruption, gingival asymmetry, excess gingival show and correcting the height to width ratio of teeth.³ Functional indications are mostly concerned with increasing the quantity of supragingival tooth tissue for a ferrule.^{4, 5}

When assessing a patient for surgical crown lengthening the clinician must consider the endodontic and prosthodontic status of the teeth, as well as the periodontal factors described elsewhere.^{5, 6} An important periodontal factor to consider when planning a stable, healthy, post-surgery gingival position is the dento-gingval complex. The dento-gingival complex dimension can vary from individual to individual and tooth to tooth, though is widely accepted to be 3 mm on the labial surface.^{7, 8} This dimension includes what was formerly known as the biological width, now replaced with ‘supracrestal tissue attachment’ (STA) following the World Workshop on the Classification of Periodontal and Peri-implant Diseases and Conditions.⁹ Therefore, to produce a predictable harmonious outcome, the clinician must respect this dimension when considering bone height reduction.⁶

Historically, one surgical guide would be made for the soft tissues and another for the hard tissues, or the clinician would measure 3 mm from the soft tissue guide during surgery. Both of these techniques can be time consuming and introduce error. The surgical guide described here incorporates both the soft and hard tissue contour and can be precisely measured pre-operatively.

To create this surgical crown lengthening guide, pre operative study casts of the case are required (Figure 1); if it is a particularly difficult case the casts may require mounting with a diagnostic wax-up. Depending on the desired tissue resection, a Chu's aesthetic gauge (HuFriedy) can be helpful to ensure the most pleasing height-to-width ratio (Figure 2). The bone contour is then designed to follow apical to the gingival contour with calipers set to 3 mm working from each tooth's gingival zenith point to create a smooth, harmonious outline (Figure 3). In the laboratory, the guide is vacuum-formed from a 1 mm Erkodur hard disc (Erkodent) (Figure 4). The guide is then cut along the pencil lines to leave an inner window for the gingival contour and an outer edge contour for the osseous resection (Figure 5).

After appropriate surgical preparation and anaesthesia, the guide is placed over the teeth and gingiva. A periodontal probe is used to pierce the gingiva along the contoured inner window of the guide (Figure 6). This creates the proposed gingival contour and flap outline. Following reflection of the soft tissue, the surgical guide's outer edge contour is the reference for the osseous resection (Figure 7). The osseous resection must be a gentle harmonious contour for a predictable and aesthetically pleasing outcome. In instances where a split thickness flap is required due to less than 2 mm of keratinized tissue after gingival resection, the surgical guide outer edge contour only is necessary.¹⁰

The surgical procedure can be finished in the normal fashion ready for the prosthetic stages to correct the incisal cant. The results can be seen in Figure 8 at suture removal.

It is worth mentioning that this analogue work flow could also be streamlined digitally.