The smile is a focal feature of the face. Studies across the world repeatedly demonstrate that smiling is the most common means of communication and, hence, all elements of a smile are crucially important (Thomas et al, 2014).
Definition of a gummy smile
A gummy smile (GS) is defined as excessive maxillary gingival display (the amount of gingivae showing from the zenith of the crown to the lower curtain of the upper lip) during smiling or laughing, which can be considered aesthetically undesirable (Chang et al, 2011; Springer et al, 2011). This can be a significant aesthetic concern for some patients, as it may interfere with their self-confidence and psychological status. As a result, they often camouflage or restrict their smiles (Brizuela and Ines, 2022). It can also be referred to as a high gingival smile line, lip line or short upper lip (Peck et al, 1992). A gingival display of 1–2mm is considered normal (Brizuela and Ines, 2022). Some authors state a GS is 3–4mm of exposed gingival tissues, whereas others consider over 2mm to be a GS; however, there is no unanimous agreement regarding classification (Suber et al, 2014; Rao et al, 2015; Mostafa, 2017; Mercado-Garcia et al, 2021; Brizuela and Ines, 2022). It is subjective to both cultural and ethnic preferences, between males and females, and between professionals and laypeople. In some European countries, gingival display of up to 4mm or more is considered acceptable, whereas, in the US, gingival exposure greater than 2–3mm is considered unsightly (Mercado-Garcia et al, 2021).
The golden proportion establishes that the upper third of the incisor teeth should be covered by the upper lip (de Maio and Rzany, 2007). Of the three smile patterns (‘Mona Lisa’, ‘canine’ or ‘full denture’ smile), the second most common (35%) is that producing a GS (de Maio and Rzany, 2007). A GS can be classified as anterior, posterior, mixed or asymmetric, depending on the area of gingival tissue exposed and the identification of the muscles involved (Mazzuco and Hexsel, 2010; Suber et al, 2014).
Approximately 10–29% of patients aged between 20 and 30 years of age present with a GS, and the occurrence is particularly more prevalent in women (Mostafa, 2017; Haddadi et al, 2021; Brizuela and Ines, 2022). Due to the ageing process, the prevalence of GS decreases as the upper lip becomes flaccid and lengthens with age, which can make a temporary and less invasive treatment option more appealing (Suber et al, 2014; Brizuela and Ines, 2022).
The degree of GS can be classified to improve communication regarding diagnosis and treatment. A simple classification that establishes the degree of severity depending on the amount of gingival display on smiling was proposed (Chu et al, 2004). Level I corresponds to display between 2–4mm, Level II corresponds to display between 4–8mm and Level III corresponds to display greater than 8mm (Chu et al, 2004).
The Mercado-Rosso GS classification incorporates aesthetic, functional and etiopathogenic considerations of the smile, assisting with treatment planning, and is discussed in Table 1 (Mercado-Garcia et al, 2021).
Table 1. Classification of gummy smile types and corresponding treatment option using hyaluronic acid dermal filler using the Mercado-Rosso Gummy Smile Classification
| Type of gummy smile | Cause | Treatment area | Muscle affected | Needle/cannula | Depth | Technique | Filler |
|---|---|---|---|---|---|---|---|
| Type 1 | Lack of support due to bone deficiency or a lack of projection of the maxilla | Whole white lip from entrance at piriformis fossa to the midline | Orbicularis oris | Blunt microcannula (25 G, 50 mm) | Deep supramuscular layer | Retrograde fanning technique, acts to support the white lip and increases its resistance to be folded | 0.6 ml of 23 mg/mL |
| Type 2 | Imbalance between the strength (excess) and the resistance (defect) of the levator muscles | Piriformis fossa, levator labii superioris alequae nasi and anterior nasal spine | Levator labii superioris and levator labii superioris alequae nasi | Blunt microcannula (25 G, 50 mm) | Deep supramuscular and intramuscular layer | Combination of multiple boluses and retrograde fanning of hyaluronic acid (HA) filler | 0.2 ml–0.4 ml of 23 mg/ml HA |
| Type 3 | Overactive zygomatic muscles causing a wide smile | Malar region | Zygomaticus major and zygomaticus minor | Needle (27 G, 30 mm) | Periosteum | Two boluses per side | 0.2–0.4 ml of 25 mg/ml HA |
Anatomy in this region
A full smile is produced by the levator labii superioris (LLS), the zygomaticus minor (ZMi) and superior fibres of the buccinator muscle under the nasolabial fold (Rubin et al, 1989). It was thought that the LLS contributed the least to the elevation of the upper lip, and the zygomaticus muscle was considered to contribute the most (Pessa, 1992). However, recent evidence indicates that, of the upper lip muscles (LLS, levator labii superioris alequae nasi (LLSAN), levator anguli oris (LAO) and zygomaticus muscles), it is the LLS that elevates the lip that is primarily responsible for producing a GS (de Maio &Rzany, 2007; Mostafa, 2017).
Different aetiology of gummy smiles
Crucially, determining the individual or multiple causes of excessive maxillary gingival display allows appropriate successful treatment plan selection, as it will differ depending on the aetiology (Brizuela and Ines, 2022). A GS can result from a short or hypermobile upper lip; altered passive dental eruption; vertical maxillary excess; and/or dentoalveolar extrusion (Gibson and Tatakis, 2017; Mostafa, 2017; Dym and Pierre, 2020; Haddadi et al, 2021; Brizuela and Ines, 2022).
A full facial analysis, including lip analysis in static and dynamic movement, must be carried out to distinguish the aetiology of a GS (Brizuela and Ines, 2022). When the underlying cause of a GS is due to the lips, as opposed to the teeth or underlying maxillary bone, it is caused by a short and/or hypermobile lip (Brizuela and Ines, 2022). Both a short lip and hypermobile upper lip (HUL) GS aetiology can be treated with botulinum toxin A (BoTNA) injections (Mostafa, 2017).
Short lip
The upper lip length corresponds to the distance between the subnasale to the upper lip stomion (lower border of the upper lip), and the average length in adults is 20–24mm (Brizuela and Ines, 2022). Less than 20mm is considered a short lip, which may also present with GS incompetence (Brizuela and Ines, 2022).
Hypermobile (hyperactive) upper lip
A HUL results from increased activity of the upper lip elevator muscles when smiling. Hyperactive LLS muscles increase the exposure of the teeth and gingival tissues when smiling due to a higher lip position, resulting in a GS (Brizuela and Ines, 2022). HUL can be treated surgically or non-surgically (BoTNA injections) (Gibson and Tatakis, 2017). A HUL is usually the most common aetiology of a GS, often presented in combination with APE (Andijani and Tatakis, 2019).
Altered passive dental eruption
An altered passive dental eruption (APE) arises when the gingival tissue is unable to migrate apically during the eruption of the teeth. Teeth will appear short and square because gingival tissues are coronal to the cemento-enamel junction (CEJ) (Brizuela and Ines, 2022). APE can be treated with a gingivectomy, crown lengthening and surgical lip repositioning.
» Differentiation of other causes of excessive gingival display must be made prior to treatment to ensure correct diagnosis, appropriate treatment planning and, thus, effective results for patients «
Vertical maxillary excess
Vertical maxillary excess (VME) is an overgrown maxillary bone in the vertical plane that gives an elongated appearance to the lower half of the face (Brizuela and Ines, 2022). It is one of the most common causes of excessive gingival display, and so, it must be ruled out before proceeding to treatment, which can be determined by cephalometric analysis (Aly and Hammouda, 2016). Treatment can involve orthognathic surgery, which requires hospitalisation, and is associated with high morbidity (Mostafa, 2017; Haddadi et al, 2021).
Anterior dentoalveolar extrusion
Anterior dentoalveolar extrusion (ADE) is the over-eruption of the maxillary incisors, resulting in excessive gingival display (Brizuela and Ines, 2022). It can be treated successfully with orthodontic therapy (Mostafa, 2017).
Considerations for treatment and patient selection
Differentiation of other causes of excessive gingival display must be made prior to treatment to ensure correct diagnosis, appropriate treatment planning and, thus, effective results for patients. For example, gingival hyperplasia (overgrowth) can be a secondary effect of certain medications (such as calcium channel blockers, anticonvulsants or immunosuppressants) and can result in gingival overexposure (Dym and Pierre, 2020; Brizuela and Ines, 2022). The aforementioned treatments would not be considered appropriate for a patient presenting with gingival hyperplasia.
Treating a gummy smile
Historically, a surgical approach was needed to treat a gummy smile; however, treatment alternatives have allowed clinicians to offer a broader range of choices. Treatment choice should be assessed on a case-by-case basis, and patient preference and budget should be considered (Gibson and Tatakis, 2017). The treatment options will be discussed starting from the least invasive.
Neuromodulators
BoTNA injection is used to temporarily paralyse the muscles responsible for a hyperactive lip, thus treating a GS. Muscle paralysis is induced by BoTNA inhibiting the presynaptic release of acetylcholine at the neuromuscular junction, producing partial chemical denervation of the muscle that results in localised reduction in elevator muscle activities (Mostafa, 2017; Haddadi et al, 2021; Brizuela and Ines, 2022; Polo, 2022). Treatment of a GS with BoTNA is considered to be quick, minimally invasive, predictable and affordable, despite its short-term effect compared to surgical means (Polo, 2005; Gracco and Tracey, 2010; Mostafa, 2017).
Contraindications
As with all BoTNA treatments, they are contraindicated in pregnant or lactating women, those with neuromuscular disorders and those with a history of hypersensitivity reactions to BoTNA or saline solution (Mostafa, 2017). It is recommended to treat with caution in patients under treatment with calcium channel blockers, cyclosporine and aminoglycosides (Mostafa, 2017). It is advised that treatment is not repeated before the effect has completely faded to avoid the formation of antibodies against the toxins (Mostafa, 2017).
Technique and anatomy
BoTNA is injected into the LLSAN and LLS on both sides of the face (Brizuela and Ines, 2022). Multiple sources of literature describe the Yonsei point as the most effective point of intramuscular BoTNA injection, where the elevator muscles pass by (Mostafa, 2017). The Yonsei point is a safe and reproducible injection site used by the author for treatment, and it corresponds to the point located at the centre of a triangle formed by LLSAN, LLS and ZMi (Mostafa, 2017). Extraorally, this injection site is located on each side of the nasolabial fold, 1cm lateral and below the nasal ala (Mostafa, 2017). The depth of injection is intramuscular with the needle perpendicular to the skin surface and the bevel facing upwards (Mostafa, 2017).
The resulting effect usually becomes apparent within the first 3–7 days, reaching the peak result at 14 days and lasting an average of 3–6 months. Studies have demonstrated that there is an average 75.09% decrease in the degree of gum display (Mazzuco and Hexsel, 2010). The longevity of BoTNA effectiveness is not related to dose but depends on the frequency of the muscles' mobility and the length of gingival exposure during smiling.
If an insufficient result is seen at 2 weeks, additional BoTNA can be administered to the Yonsei point on either side of the nose. Supplementary anatomical points can be considered, which include injecting each side of the nasolabial fold, at the point of greatest lateral contraction during a maximum smile and into the orbicularis oris muscle below the nose (Mostafa, 2017). It has also been discussed that three injections can be made bilaterally into both the LLSAN and LLS in an inverted triangle pattern (Suber et al, 2014).
Dose
A standard dosing regime is 2U of onabotulinumtoxin A per side of the nasolabial fold at the Yonsei Point. The dose should be given in two visits, as recommended for safer technique by many authors—this involves administering a low dose of BoTNA initially and retouching at 2 weeks to avoid overdosing complications (Mostafa, 2017).
Generically, the recommended dose of BoTNA varies between men and women, depending on the lip muscle volume. Men usually have larger muscle volume and, therefore, may require more units of BoTNA to achieve the same results compared to women (Mostafa, 2017).
Studies have shown that, despite gingival display increasing from 2 weeks post-injection through to 24 weeks, there had not been a return to baseline gingival display at 24 weeks (Polo, 2008). Based on predictions following this study, the baseline average excessive gingival display would likely not return until 30–32 weeks post-injection (Polo, 2008).
It has been indicated that multiple injections may result in prolonged muscle paralysis, so that reduced gingival exposure would remain, even following metabolism of the BoTNA (Haddadi et al, 2021).
Complications
BoTNA treatment is considered safe and effective with an appropriate technique and dose. Localised side effects can include pain, bruising, inflammation, infection, insufficient loss of muscle strength, nerve palsy and haematoma (Mostafa, 2017). Improper injection technique can result in an asymmetrical appearance of a smile and difficulties in speech, eating and/or drinking (Mostafa, 2017; Haddadi et al, 2021). Overdosing the area can result in drooping or lip ptosis below the gingival margin, resulting in an obstruction of the visible teeth on a full smile (Mostafa, 2017). Additionally, collapsing of the oral commissure can result in a sad appearance, and lengthening of the upper lip can occur.
Patient case
The patient was shown videos and photographs of previous cases to explain the treatment plan and give an understanding of the expected results. There was no previous history of aesthetic treatments and, after a detailed discussion of the procedure, including complications, written informed consent was obtained. The patient also elected to share non-identifiable clinical photos.
Before injection, BoTNA was diluted to produce a resulting dose of four units per 0.1ml by adding 2.5ml 0.9% bacteriostatic saline solution to 100u of vacuum-dried Clostridium BoTNA. Insulin syringes of 0.3ml with a 29g needle were used. Using an assessment of the dynamic movement and the concept of the Yonsei point, 2U of BoTNA (Botox®) was administered per side for a total dose of 4u. The patient reported very minimal discomfort, no adverse events and a very satisfactory result at the 2-week review. Figure 1 shows pre- and post-treatment with BoTNA taken at full smile, respectively.
Dermal fillers
There are multiple approaches discussed in the literature for the correction of GS using dermal filler.
Hyaluronic acid (HA) dermal filler can be used as a corrective technique to reduce excessive gingival display by injecting a small bolus into the paranasal region, compressing the lateral fibres of the LLSAN and inhibiting its ability to elevate the upper lip (Brizuela and Ines, 2022). The site to be injected will depend on each individual's anatomical landmarks; however, a helpful reference point is the most cranial part of the nasolabial fold, around 3mm lateral to the wing of the alar cartilage (Brizuela and Ines, 2022). This corresponds closely to the same anatomical site where BoTNA is injected, known as the Yonsei point.
The technique to reduce the appearance of GS using HA dermal filler can also include injecting to stretch ligaments, modulate muscle activity or increasing the resistance of soft tissues to be folded (known as the RD Dynamic Restructuring® concept), and is outlined in Table 1 using the Mercado-Rosso GS classification (Mercado-Garcia et al, 2021).
Technique and anatomy
This area is rich in vasculature and, hence, it requires an experienced injector with vast knowledge of anatomy and a safe injection technique, which would include aspiration prior to injecting (Brizuela and Ines, 2022). There is likely to be improved longevity of result with HA dermal filler in comparison to BoTNA injections to treat a GS.
Polymethylmethracylate-based cement
Labial repositioning can be caried out to reduce a GS using polymethylmethracylate (PMMA)-based cement following crown-lengthening (Arcuri et al, 2018). The prosthesis is placed in the subnasal pit, allowed to polymerise, refined and fixed onto the bone with two titanium-based bone graft fixation screws. This acts as a filling material for subnasal depression, providing new lip support (Arcuri et al, 2018) (Freitas de Andrade et al, 2021).
Surgical treatments
Gingivectomy
Gingivectomy can be used to correct GS by restoring the normal dentogingival relationship, also resulting in a functional improvement (Haddadi et al, 2021). This can be supplemented by bony surgical methods, depending on the available biological width in the surgical site (Haddadi et al, 2021).
Crown lengthening
Crown lengthening involves recontouring the crestal bone levels and moving the gingival margin apically to reduce excessive gingival display (Mahn, 2016). This can be combined with lip repositioning surgery to achieve a more successful result.
Lip repositioning surgery (conventional and modified techniques)
The first discussion of lip repositioning surgery to treat a GS was by Rubinstein and Kostianovsky and then advocated by Litton and Fournier in 1979 (Pandurić et al, 2014; Bouguezzi et al, 2020). The technique was modified in 2006 and presented to dentists. Surgical lip repositioning is accomplished by removing a strip of mucosa from the maxillary buccal vestibule, and then suturing the lip mucosa to the mucogingival line (Simon and Rosenblatt, 2006). The modified lip repositioning technique (MLRT) involves removing two strips of mucosa from the maxillary buccal vestibule on both sides, without affecting the frenum as it would in the conventional technique (Rao et al, 2015). This technique has also been performed successfully using laser to reduce a GS (Oztura et al, 2014).
It is also known as a mucosal repositioned flap and is effective in the treatment of GS caused by VME (Aly and Hammouda, 2016). This precise resection of the maxillary mucosal tissues with reattachment of the lip in a more coronal position reduces the size of the GS (Jacobs & Jacobs, 2013). The procedure is considered safe, with fewer side effects, and provides faster recovery and a less-invasive alternative to orthognathic surgery to correct a GS (Gaddale, 2014; Pandurić et al, 2014; Deepthi et al, 2018; Haddadi et al, 2021; Hakobyan, et al, 2022).
Patients presenting with both VME and HUL can have a multifaceted treatment, starting with lip repositioning surgery, then BoTNA injections 2 weeks post-operatively when surgery alone may prove inadequate (Aly and Hammouda, 2016).
When VME is the cause of a GS, treatment can be selected based on a simple classification (Garber and Salama, 1996), as seen in Table 2.
Table 2. Summary of gummy smile treatment when vertical maxillary excess is the causative factor, based on the class of severity
| Vertical maxillary excess class | Amount of gingival display | Management |
|---|---|---|
| Class I | 2–4 mm |
|
| Class II | 4–8 mm |
|
| Class III | Over 8 mm |
|
Lip repositioning can also be carried out with myotomy (of the LLS) and by inserting polyester threads as a physical barrier acting to prevent relapse (Ishida et al, 2010; Horn and Joly, 2022). Studies have also shown that an alternative surgical approach exists, involving treatment during surgical rhinoplasty by incising at the gingiva-labial sulcus, to expose the orbicularis oris and depressor nasi muscle (Barbosa et al, 2013).
Orthognathic surgery
For patients with severe VME, orthognathic surgery is the optimal long-term treatment option for GS (Khojasteh and Mohaghegh, 2022). Le Fort I can be performed in conjunction with horseshoe osteotomy or partial turbinectomy (Khojasteh and Mohaghegh, 2022).
Complications
The downsides of performing surgical lip repositioning include the chance of recurrence and a decrease in the vestibular depth following surgery, as well as the increased downtime, pain and post-operative healing associated with surgical treatments (Rao et al, 2015). Stable results were achieved in a study after a 3-year follow-up, with no recurrence of a GS (Chacon, 2020). However, two studies showed a single partial relapse at 3 months and one at 1 year (Adbullah et al, 2014; Bouguezzi et al, 2020).
Conclusion
An attractive smile is a fusion of a harmonious relationship between the teeth, the extent of gingival display and how the lip frames the smile (Brizuela and Ines, 2022).
Excessive gingival display is a key factor in smile attractiveness and can be of huge psychological impact to patients and cause them to limit or hide their smile in social situations. Consequently, treatment can be life-changing for patients. Therefore, it is vitally important to correctly diagnose and treat appropriately to ensure a successful aesthetic outcome.
Key points
- The definition of a gummy smile can vary but it is generally agreed that it corresponds to excessive gingival display of 2 mm or more
- The cause of a gummy smile can be multifactorial, and it is vital to determine the cause, as the treatment options will differ
- Historically, gummy smiles were mainly treated with surgery but advancements in knowledge and techniques in non-surgical treatments have meant that these can also be offered to patients
- Classification of the severity of gummy smiles assists in treatment selection, improving aesthetic outcomes and success.
CPD reflective questions
- Define a gummy smile
- Describe two classifications of gummy smile severity
- What are the five aetiologies of a gummy smile?
- What reference point has been described in the literature for treating a gummy smile with botulinum toxin type A? What does the reference point correspond to?
- How does the treatment of a gummy smile with dermal filler differ depending on severity? Which classification is used to describe this?