5.1 Periodontal Surgical Planning

Nowadays, the concept of smile and dental esthetics is no longer limited to the teeth. The essentials of a smile involve the relationship between the three primary components: the teeth, lip framework, and the gingival scaffold [1]. In spite of common notions about facial esthetics being usually based on subjective opinions rather than proven scientific data, and being influenced by cultural variants, emerging research shows how the amount of gingival display significantly influences the perception of smile attractiveness, independent of age and sex [2]. Excessive gingival display while smiling, also usually known as a “gummy smile,” is a common esthetic concern among dental patients and, being largely viewed as unesthetic, leads many patients to seek some form of treatment to address the issue [3].

The gummy smile has been broadly defined as a nonpathological condition causing esthetic disharmony, in which more than 3–4 mm of gingival tissue is exposed when smiling. The anatomical landmarks that factor into the gummy smile are the maxilla, lips, gingival architecture, and teeth. All these structures must lie in harmony with one another to achieve an esthetic smile. When diagnosing and treating patients with a gummy smile, the clinician must accurately understand and identify the etiology of the condition. Potential causes of excessive gingival display involve short lip length, hypermobile/hyperactive lip activity, short clinical crown, dentoalveolar extrusion, altered passive eruption, vertical maxillary excess, and gingival hyperplasia [3].

When the gummy smile brings the patient to seek esthetic dental treatment, after thorough consideration of its etiology, some conservative surgical approaches can be of interest to solve the condition and improve the smile harmony (Figure 5.1). When the incisal edge position is correct, crown lengthening surgery can be used to increase the clinical crown length as a stand‐alone esthetic procedure. However, when the incisal edge position is inadequate and there is excessive gingival display, crown lengthening in conjunction with restorative treatment is indicated. This surgical technique involves apically positioning the gingival margin and may require the removal of supporting bone. The periodontal surgical procedure must also result in a proper biological width and adequate keratinized tissue [4].

A previous study has stated that when attempting to enhance esthetic outcomes, the influence of two biological concerns must be fully understood [5].

• Location of the base of the sulcus, which influences the cervical termination of tooth preparation and allows for intracrevicular location of the restoration margin.
• Knowledge of location of the osseous crest is required before altering gingival levels.

Particularly in periodontal‐prosthodontic interdisciplinary therapy, where subgingival restorative margins are desired, it is prudent to discuss the concept of the so‐called biological width, which is characterized by the tissues concerning the dentogingival junction –the supraalveolar connective tissue attachment and the junctional epithelium – along with the alveolar crest and the base of the gingival sulcus [6, 7]. The total volume of the biological width varies among individuals, but remains constant within each individual, and i’s average dimension varies in the range of 1.8 and 2.4 mm [7]. In contemporary practice, it is generally accepted that a 3 mm distance between the osseous crest and the clinical crown margins is the safest alternative to prevent chronic inflammation [6].

Consideration of this width is fundamental while planning crown lengthening procedures, whether there will or will not be future esthetic restorations with subgingival margins. That essentially means that bone resection can be necessary along with the gingivectomy procedure in various types of conditions.

Through performing digital exams and obtaining three‐dimensional data corresponding to the oral tissues of the patient (from Standard Tesselation Language (STL) files acquired by an intraoral scan (IOS) of the patient’s mouth) and the radiographic osseous information from the Digital Imaging and Communications in Medicine (DICOM^®) files acquired by cone beam computed tomography (CBCT), it is possible to form a virtual patient, superimposing these puzzle pieces and allowing for complete diagnosis and treatment planning [8].

5.2 CAD‐CAM Surgical Guides for Clinical Crown Lengthening

The most important concepts concerning dentogingival esthetics are the positioning and contour (regular, concave arch) of the gingival margin, which directly affect dental shape and proportion [1]. These factors are related not only to clinical crown length delimitation but also the dental cervical profile, strongly influencing anatomical crown shape and the visual proportion of the tooth (i.e., square, oval, or triangular).

The positioning and contour of the gingival margin depend on the entire dentogingival unit, which is composed of the alveolar bone, periodontal ligament, dental enamel and cementum, connective tissue, and keratinized epithelial tissue. This unit reflects the periodontal health, the stage of eruptive development, and the phenotypic characteristics of the individual.

The positioning reference of the gingival margin, as well as its esthetic and integrity characteristics, rely on both their relationship with the cementoenamel junction (CEJ) and the association between clinical and anatomical dental crowns. The clinical crown is generally smaller than the anatomical, i.e., the gingival margin positioning is coronally located to the CEJ. In cases of short clinical crowns related to parafunctions and presenting worn incisal edges and/or compensatory extrusion, clinicians expect to identify larger anatomical crowns beneath the gingival margin. However, sometimes, the gingival margin is very close to the CEJ or there may even be cemental exposure with normal eruptive development, resulting in a smaller clinical crown than the real anatomical one.

In most cases of short clinical crowns or disproportion between width and height, clinical crown lengthening provides an increase in crown height, an improvement in visual proportion, and a better contour of the regular concave arch and the interdental papillae, which usually lead to a need to reestablish a novel contour of the gingival margins prior to esthetic rehabilitation [1].

The final positioning of the gingival margins is traditionally determined taking into consideration the avoidance of exposing dental cement, i.e., the novel gingival margin should be positioned as close as possible to the CEJ or exactly over it. Considering the need for a new creation of the biological space to maintain gingival margin stability, plus better esthetic contour and alveolar ridge volume, osteotomy and osteoplasty are suggested in most cases of crown lengthening. The extension of both surgical procedures is determined by the patient’s periodontal phenotype and the new proportional relationship between the clinical crown and root attachment. Often, according to these concepts, there will be discrepancies between surgical and esthetic periodontal planning for a novel rehabilitation or even treatment relapse.

Another important factor is reference loss during the periodontal surgical procedure concerning the expected gingival margin contour planned in the final esthetic rehabilitation. This occurs mainly when there is a need to establish a new relationship between visual esthetic proportion and emergence profile in cases where the new margin does not coincide exactly with the CEJ contour. Therefore, it is essential to manufacture periodontal surgical guides based on the final prediction of the esthetic rehabilitation to orientate the surgical contour of the gingival margins, joining the surgical periodontal and esthetic rehabilitation plans together.

5.2.1 Planning for Periodontal Surgical Guide Manufacturing

With reverse planning, it is possible to analyze the need for gingival plastic surgery to reestablish esthetic patterns of soft tissues of the smile. This surgery can be performed with the aid of a periodontal guide, created either from tomographic analysis or facial study once the references of digital wax‐up contour or even the new contour of the gingival margins in the digital surgical simulation have been established (Figure 5.4).

Computed tomography is an important tool in this process, allowing periodontal analysis of each tooth. From it, clinicians can evaluate the size of anatomical crowns, the quantity of enamel covered by gingiva (total anatomical crown), distance to the CEJ, and the need for osteotomy to reestablish biological distances. Moreover, further esthetic rehabilitation can be evaluated if necessary according to the expectations of the professional and patient (Figures 5.5 and 5.6).

The guide presents two segments: a window for cutting which will support the scalpel blade (allowing internal bevel incision) (Figure 5.7), laser tip, or electrocautery (gingivectomy only), and a 3 mm structure for bone wear reference. The cut line design is defined according to the patient’s anatomical characteristics and the wax‐up obtained for cases of rehabilitation, respecting the esthetic patterns and dental proportions and placing the gingival zeniths slightly distalized.

The surgical guide is then impressed by a 3D device using polymerizable resin (thickness of 1.5 mm) (Figure 5.8). Following this, the printed guide is washed in isopropyl alcohol for 15 minutes to remove unpolymerized resin residues on the surface, and then it is placed in an oven for postcuring polymerization for 30–60 minutes. Finally, the support structures are removed and the guide is polished.

As described above on the integration of prerehabilitation periodontal planning, a digital workflow involving orthodontic treatment, more complex preprosthetic surgeries, and dental implants can also be developed before the final rehabilitation. In both provisional and definitive rehabilitation phases, laboratory planning is necessary, which includes the prosthetic design (CAD) based on references determined by digital planning guided by facial analysis. Therefore, the final rehabilitation follows references of smile proportions according to the characteristics of the patient’s face and natural textures (natural algorithms) from the donor library used in the planning phase [9].

5.3 Image‐Guided Periodontal Surgery

The entire planning process for guided periodontal surgery begins with a thorough initial assessment of the patient, involving not only the anamnesis but also facial visualization and information records before periodontal examination. Facial image registration can be performed using either photography, to record the exposition of gingivae (gingival smile) on smiling, or videos, in which the dynamics of lip movements during speech and faint and forced smiles are depicted. It is important to highlight that many patients who are dissatisfied with their smile tend to hide or limit it by controlling contraction of the labial levator muscles in a spontaneous smile. On the one hand, photographs and facial scanning require more complex equipment and recording techniques while on the other, smartphones provide video recordings easily and with very high quality.

The initial clinical evaluation depends mainly on evaluating periodontal health and establishing a diagnosis on probing depth, gingival level, and clinical attachment level. Thus, it is possible to establish a correct relationship between the clinical and anatomical crown by the determination of hidden enamel under the gingiva (i.e., the position of both the CEJ and gingival margin).

After parameterization and spreadsheet compilation of periodontal measurements, it is possible to obtain an overview of the possibilities of esthetic clinical crown lengthening with dental enamel exposure only or perspective of cementum exposure prior to esthetic rehabilitation and subsequent coverage. Later, these periodontal parameters are confirmed from tomographic exams [10], which provide greater precision, since standard periodontal probes present 1.0 mm markings, and tomographic exams avoid injury to the periodontal tissues and anesthesia to evaluate the bone crest parameters.

For a complete visualization of the soft tissues in tomographic exams, it is extremely important to acquire the scans with the patient’s head stabilized on the tomography device and using lip retractors (Expandex™ or those for dental whitening) so there will be no overlap of lip structures on the vestibular dental mucosa and of the tongue on lingual or palate dental mucosae [10]. These tomographic exams should be performed on each arch separately and with caution in relation to the device’s parameters for better visualization of soft tissues. Moreover, the files should be in DICOM format which allows complete visualization of tomographic sections and the possibility of 3D reconstruction of dental and bone structures. Virtual periodontal measurements present greater accuracy on sagittal slices, although they can also be performed on well‐fitted 3D reconstructions. These reconstructions are essential for periodontal guide design, even with some distortion of the original anatomical structure due to radiological artifacts, which are more evident on the surface of these reconstructions.

For a more detailed and reliable reproduction of the dental anatomy, intraoral scanning files are necessary. The STL files from the IOS should be fully aligned with 3D bone reconstruction and consequently with the tomographic slices. Later, they will also be aligned with the photographs or facial scans for correct spatial positioning in relation to the patient’s face. These aligned models are thus superimposed by the facial image, which is cut, allowing visualization of the structures in planes. On the external plane is the facial integument contour; on the intermediate, the IOS shows the clinical crowns and external gingival contour; on the innermost one are the anatomical crowns, roots, and bone structures, obtained from 3D tomographic reconstruction of DICOM files.

The guide designing and printing processes described above result in the possibility of starting esthetic clinical crown lengthening surgery with clinical guidance from the entire process that has been planned from the virtual environment. This results in precise reproduction of the planned gingival design and a reliable orientation regarding area and extension of osteotomy and osteoplasty to be performed, leading to better tissue stability and cosmetic contour.

The internal window in the guide reproduces the desired shape of the gingival margin contour and its occlusal adaptation is achieved directly on the patient’s incisal edges and natural cusps (references obtained in the IOS). On the other hand, the upper edge of the periodontal guide guides the osteotomy which was planned according to tomographic reconstruction of the DICOM files.

After anesthesia, the guide is positioned through the occlusal insertion axis and should have small openings to verify adaptation on the supporting teeth. Similarly, the upper edge, which orientates the osteotomy, should also be perfectly adapted to the gingiva, facilitating gingival cut and providing increased stability of the gingival margin, especially in thin gingival phenotypes showing margins that will be removed by less than 1.0 mm.