1. INTRODUCTION

Conceiving new smiles demands knowledge of biology and the proper use of periodontal or peri-implant plastic surgery to combine esthetics and function. It is necessary to evaluate the contour of the soft tissue to establish harmony between the whole set to perform rehabilitation in the anterior region. Tissue recontouring can be used to correct long or short clinical crowns¹.

Achieving an adequate gingival architecture is necessary, especially in patients with high and intermediate smile lines. However, it can also be an aim of patients with a low smile line with high esthetic demand. Thus, the treatment plan should be guided by the future position of the gingival zeniths².

When the treatment plan involves implants, surgical and prosthetic planning should initially determine the final gingival contour³. Based on this treatment plan, it is possible to determine the position of the implant. It also allows verifying the need for orthodontic corrections to modify the gingival zenith in the horizontal and vertical directions. Alternatively, surgical procedures may be necessary to modify the position of the gingival zenith vertically.

Both periodontal recession, with root surface exposure, and short clinical crowns, due to excess periodontal tissue, can cause changes in the appearance of the length of the teeth⁴. To correct the position of the gingival margin, periodontal plastic procedures can be performed to recontour the tissue and provide a suitable contour for rehabilitation. This chapter addresses the treatment of patients with short clinical crowns and gummy smile.

OBJECTIVES

At the end of the chapter, the reader should be able to:

• Understand the clinical and biological concepts in the treatment of short clinical crowns.

• Choose the appropriate treatment for patients with a gummy smile.

• Perform appropriate surgical treatment of teeth with short clinical crowns.

2. SCIENTIFIC BACKGROUND

2.1 GINGIVAL EXPOSURE

The harmonious relationship between face, lips, teeth, and periodontium is a common desire among patients who have a high degree of gingival exposure when smiling. The tooth should ideally have a height/width ratio of around 75–85% (Figs 01A–D). A reduced clinical crown results in an anti-esthetic condition known as short tooth syndrome⁵. It can be caused by tooth wear on the incisal edges, gingival hyperplasia, or altered passive eruption (Figs 02A–C).

Together with a reduced clinical crown, the patient may also have a high smile line, making short crowns more noticeable. In a spontaneous smile, if exposure of gingival tissue is greater than or equal to 3 mm, the smile is classified as a gummy smile⁶. Studies assessing the perception of dentists and patients about the amount of gingival exposure and contouring have shown that exposure of more than 2 mm of gingival tissue when smiling or the presence of gingival asymmetries will impair facial esthetics^7,8.

A gummy smile may be caused by dental, gingival, lip, or jaw changes⁶. Both a gummy smile and the presence of short teeth may be associated and intensify the existing discrepancy. Diagnosis of the etiology of a gummy smile is necessary to determine the best treatment plan. Several factors may act alone or in combination to cause excessive gingival exposure when smiling (Table 01).

Table 01 Factors that may influence gingival exposure in the smile

2.2. TEETH AND CHANGES IN SKELETAL POSITIONING

Orthodontics can treat bone alterations or dental mispositioning. Orthognathic surgery may be necessary for three-dimensional repositioning of the maxilla and correction of the gingival smile. The presence of vertical maxillary excess is determined by augmentation of the middle third of the face. The diagnosis is made by clinical and radiographic methods (Figs 03A–G). This change is one of the frequent causes of a gummy smile, and its treatment needs to take into consideration surgical and orthodontic planning and treatment⁹.

Alteration of teeth positioning by extrusion or protrusion can be treated exclusively using orthodontic procedures, depending on severity. In these situations, it is necessary to understand the dental changes that may occur during tooth movement. Tooth intrusion should be performed extremely slowly to avoid damage to the periodontium and root surface. In these situations, approximately 30% of the periodontal volume is expected to accumulate in the cervical region of the tooth, increasing gingival thickness. Periodontal or restorative procedures to correct the dental proportion may be required^10,11 (Figs 04A–F).

Lingual tooth movement usually reduces the length of the clinical crown and also increases the gingival volume and may promote spontaneous resolution of gingival recessions¹⁰.The opposite may occur if the tooth is inclined or moved buccally. Care must be taken.

Tooth extrusion aims to increase the amount of bone and gingival height but should be associated with surgical or restorative procedures to rehabilitate the case (Figs 05A–C and 06A–F).

2.3. CHANGES IN MUSCULATURE

The lip musculature is activated in the act of smiling and can express an authentic or social smile¹². In an authentic smile, there is an involuntary contraction of the muscles lifting the upper lip and orbicularis oculi muscle(where it is possible to verify the formation of slight wrinkles laterally to the eye). Unlike a social smile, it is not possible to control the amount of gingival exposure. It is the smile used for diagnosis and planning in dentistry (Figs 07A, B). The upper lip rises between 6 mm and 8 mm from the resting to the smiling position. When muscle hyperactivity is present, this distance may even double¹³.

To treat lip hyperactivity, we do not recommend invasive procedures on the lip or upper lip elevator muscles because there is no scientific evidence on the stability of long-term outcomes¹⁴. Few scientific studies are available on these techniques and only provide 6 months of results. Due concerns with the recurrence of a gummy smile, these techniques have been questioned¹⁵. Given the long-term outcome of these techniques and their invasiveness, semiannual botulinum toxin therapy (Figs 08A, B) has proven more effective, with the advantage of being less invasive¹⁶.

Short or thin lips may increase the amount of gingival exposure when smiling; treatment can be performed by injecting temporary filling material¹⁷. The commonly used material is hyaluronic acid, which has the potential to increase lip volume and improve its contour. A randomized clinical trial on the use of hyaluronic acid showed significant improvement in upper and lower lip esthetic evaluations; reported adverse effects such as bruising, edema, and pain were mild and reversible¹⁸. Although it is a minimally invasive procedure, it should only be performed by trained and experienced professionals since major complications like thromboembolism and bruising may occur¹⁷.

Exposure of gingival tissue while smiling is typical of young patients; over the years, there is accommodation of the musculature and a tendency to reduced teeth and gingival exposure¹⁹. Many patients with adequately proportioned teeth and a gummy smile show self-correction of this change over the years, requiring no intervention (Figs 09A–D). If there is any degree of asymmetry between the gingival margins or a change in the high/width ratio, it can be resolved by surgical and/or restorative procedures.

2.4. PERIODONTAL CHANGES

The patient may have a thin, intermediate, or thick gingival biotype. The biotype influences the thickness of the gingival and bone tissue and the shape of the tooth (Figs 10A–L). In addition, periodontal changes may partially cover the clinical crown so that it appears shorter. This condition impairs esthetics due to changes in the height/width ratio of the tooth and by altering the gingival contour and papillae.

2.4.1. GINGIVAL HYPERPLASIA

Gingival hyperplasia is a change in the periodontium that can occur from periodontal inflammation due to biofilm accumulation, drugs, or genetic alterations. The edema that occurs in gingivitis may be potentiated with biofilm accumulation and excess gingival tissue reduces the length of the visible clinical crown²⁰. Treatment of this alteration involves adequate oral hygiene and basic periodontal therapy. The tissue becomes healthy and returns to its prior dimensions with the reduction of inflammation and maintenance of low biofilm levels. If it remains altered, surgical removal of excess tissue may be indicated²⁰.

Gingival hyperplasia can also be caused by medications that act at the systemic level and are potentiated when biofilm is present (Figs 11A, B). Anticonvulsive drugs, immunosuppressants, and calcium channel blockers are among the drugs that can affect gingival tissue. Any area of the arch may be affected, but it most frequently affects the facial surface of the anterior teeth, beginning in the interdental papillae²¹. Prevention of this alteration focuses on biofilm control before beginning drug therapy and maintenance of low biofilm levels during the medication use. Treatment of drug-induced gingival hyperplasia involves control of biofilm and basic periodontal therapy. After restoring gingival health, the need for a surgical intervention is verified.

Hereditary gingival fibromatosis (Figs 12A, B) is a condition caused by a rare genetic disorder (1:750,000), with family aggregation, which is clinically characterized by slow, continuous, and progressive growth of gingival tissue in the maxilla and mandible²². Clinically, the gingiva has normal coloration and firm consistency; it is asymptomatic and nonhemorrhagic²³. Severe gingival growth causes esthetic and functional impairment to the point of causing diastema, interfering with speech, chewing, occlusion, dental positioning, and facial appearance²⁴. Treatment involves excision of all hyperplasia tissue to restore the proper shape of the gingiva; further interventions may be necessary due to slow and continuous gingival growth.

2.4.2. ALTERED PASSIVE ERUPTION

Tooth eruption can be described in distinct stages: active eruption and passive eruption. Active eruption is the displacement of the tooth from its developmental position in the bone, through the oral epithelium, erupting into the oral cavity. Active eruption happens until the tooth contacts the opposing tooth, thus starting to function. This movement brings with it the periodontal tissues; at the end of this process, the gingival margin and part of the junctional epithelium still significantly cover the anatomical crown. Then, the passive eruption stage begins, where there is apical migration of these tissues in relation to the cementoenamel junction (CEJ)²⁵. There is an impression of “eruption” with increased exposure of the crown, giving this stage its name (passive eruption) the passive eruption name. In certain situations, most commonly in sites with thick tissue biotype, this migration is incomplete (Figs 13A–F and 14A–E). Thus, the tooth, despite having a satisfactory anatomical crown, shows a short clinical crown, compromising the esthetics of the tooth^5,26.

The definition of altered passive eruption (APE) should take into account the age of the patient and should not be diagnosed until the passive eruption process has been completed. This process occurs during adolescence and is usually completed around the age of 27²⁷. Coslet et al²⁸ classified APE into two types (Figs 15A, B) according to the amount of gingival tissue measured from the free gingival margin to the mucogingival line:

• Type I: Short clinical crowns associated with an excessive amount of keratinized tissue (measurement of mucogingival junction to free gingival margin). This type is usually present in patients with athick biotype;

• Type II: Short clinical crowns associated with keratinized tissue dimensions of less than or equal to 2 mm.

In patients with type I APE, it is possible to excise the excessive gingival tissue without removing keratinized tissuecompletely. On the other hand, patients with type II APE, because of the small band of keratinized tissue, this tissue cannot be removed. Techniques for apical tissue repositioning are recommended²⁹.

In addition, a change in biologic width may occur, and the alveolar bone crest (ABC) may be located closer to the CEJ. Classical studies show that, on average, the connective tissue attachment and junctional epithelium have a vertical dimension of 1 mm each, while the histologic gingival sulcus is approximately 0.7 mm³⁰. In patients with a healthy periodontium, both connective tissue attachment and junctional epithelium have stable dimensions; the sulcus may present different measurements and lead to morphologic changes in the appearance of the clinical crown. There are two subcategories of APE regarding the position of the bone crest in relation to the CEJ:

• Subcategory A: The distance from the ABC to the CEJ is greater than 2 mm, with adequate space for the insertion of the connective tissue attachment fibers. Thus, osteoplasty during the surgical procedure is not necessary (Figs 16A, B).

• Subcategory B: The distance from the ABC to the CEJ is less than 2 mm and there is not enough space for the insertion of the connective tissue fibers apical to the CEJ. Thus, osteotomy is required to re-establish the biologic width (Figs 17A, B).

Bone probing and periapical radiographs can be used to determine the size of the clinical crown (Figs 18A, B and 19A, B)^6,31. It is also possible to estimate the position of the CEJ but with limited accuracy. To verify the real relationship between the CEJ and buccal bone, it is necessary to perform a coe beam computed tomography scan, which also enables measuring the gingival thickness when using a lip retractor³². By establishing the relationship between the ABC and CEJ, it is possible to classify the APE and define the surgical treatment plan (Figs 20A–C and Table 02).

Table 02 APE types and subcategories followed by the procedure required for the treatment of each condition

2.5. SURGICAL TECHNIQUES FOR PERIODONTAL RECONTOURING

2.5.1. GINGIVECTOMY

Each surgical technique should be defined according to the type of periodontal alteration present. Gingivectomy alone is indicated when:

• Excessive gingival tissue is present without bone involvement.

• The patient has suprabony (false) pockets.

• It is necessary to treat irregular gingival contours.

The choice between making an internal or external bevel should take into account the need for bone tissue removal and gingival thickness reduction (Figs 21A–G). The external bevel should be performed when there is considerable gingival hyperplasia to recreate the facial gingival anatomy and also in the papillae region. This technique has the disadvantage of creating a wide bloody area with second-intention healing but allows for a significant reduction in gingival volume.

Conventional gingivectomy in several teeth with gingival hyperplasia, involving the gingival margin and papillae, is invasive. The hyperplasic regions are probed and the measurement is transferred to the facial through bleeding points. These points should be connected to create a drawing of the parabolic gingival contour. An external bevel with the blade positioned from apical to coronalis made. The incision is made by following the drawing with the blade touching the dental surface. Next, the tissue is incised mesiodistally with an Orban periodontal scalpel. The gingival band is then removed with curettes and the dental surface is cleaned to remove the biofilm. Refinement can be done with microscissors, conventional or ceramic burs, and with the scalpel blade itself to allow proper contouring of the gingival tissue. If an extensive bloody area is created, it may be possible to use materials to protect the region and prevent postoperative pain (Figs 22A–I). Modification of this technique aims to reduce the amount of bloody tissue and use of surgical cement, which may hinder the healing process and presents an antiseptic aspect when used in the anterior region.

The choice of an internal bevel incision (Figs 23A–F)

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