A gummy smile — defined by the display of 3 mm or more of maxillary gingiva during a full, natural smile — is a common cosmetic concern with a well-characterised muscular aetiology that responds predictably to botulinum toxin injection when patients are appropriately selected.
Aetiology & Definition
Gingival display during smiling is influenced by a complex interplay of skeletal, dental, and soft tissue factors. The most clinically relevant and correctable contributor is hyperactivity of the upper lip elevator muscles.1 When the levator labii superioris (LLS), levator labii superioris alaeque nasi (LLSAN), and zygomaticus minor contract excessively during smiling, the upper lip rises beyond its resting position, exposing an aesthetically disproportionate band of gingiva.2 Prevalence estimates suggest gummy smile affects approximately 10% of young adults, with a higher incidence in females.3
It is important to distinguish muscular hyperfunctional gummy smile — the primary indication for botulinum toxin — from gummy smile arising from vertical maxillary excess, altered passive eruption, or short clinical crown height, which require orthodontic or surgical management.1
Mechanism of Action
Botulinum toxin type A (BTX-A) inhibits acetylcholine release at the neuromuscular junction by cleaving SNAP-25, producing a reversible, dose-dependent reduction in muscle contractility.4 Applied to the lip elevator complex, this attenuates upward lip displacement during smiling without abolishing natural lip movement, provided dosing remains conservative. Onset is typically observed within three to five days, with maximal effect at two weeks.5
Injection Approaches
Two principal techniques are described in the literature, each targeting a different point along the elevator muscle complex:
Yonsei Point
Targets the confluence of the LLS, LLSAN, and zygomaticus minor approximately 10 mm lateral to the alar base. Produces a stronger reduction in lip elevation but demands precise placement to avoid inadvertent weakening of adjacent musculature.6
Nasolabial Point
Placed 5–6 mm lateral to the alar base, bypassing the zygomaticus minor. A more conservative approach offering a subtler effect with a lower risk of smile distortion — preferred for first-time treatments.6,7
Injections are administered superficially at a depth of 2–3 mm into the superficial muscular layer, avoiding deeper penetration that risks orbicularis oris involvement.7 Bilateral technique is standard, with careful attention to symmetry at each session.
Dosing Protocol
| Parameter | Recommendation |
|---|---|
| Starting dose | 2 units BTX-A per side |
| Injection depth | 2–3 mm (superficial muscular plane) |
| Maximum dose | 5 units per side |
| Titration | Reassess at 2 weeks; adjust at follow-up |
| Duration of effect | Approximately 3–6 months5 |
| Retreatment interval | Every 4–6 months as needed |
Conservative initial dosing is paramount — under-correction is easily addressed at follow-up, while over-correction producing a flattened or 'joker' smile distortion cannot be reversed except by waiting.
Adverse Effects & Limitations
BTX-A for gummy smile is generally well tolerated, with a favourable safety profile in published series.8 However, clinicians and patients should be counselled regarding several potential adverse outcomes. Asymmetry is the most common complication, arising from unequal dosing or anatomical variation in muscle insertion points.7 Excessive weakening of the elevator complex may produce an unnatural flattening of the smile arc — colloquially termed the "joker smile" — or transient difficulty with pronunciation of labial consonants and eating.6 All effects are fully reversible with time, typically resolving within three to four months, though this reversibility also constitutes a practical limitation requiring regular maintenance.
Patient Selection
Optimal candidates for BTX-A gummy smile treatment share several characteristics: a gingival display of 3–6 mm on full smile, demonstrable hyperactivity of the upper lip elevator muscles on clinical examination, realistic expectations regarding the modest and temporary nature of the result, and a preference for a non-surgical, reversible intervention.2,8 The treatment also serves as a valuable diagnostic and reversible trial for patients contemplating surgical lip repositioning or orthognathic correction, allowing them to preview the aesthetic outcome before committing to a permanent procedure.1
Relative contraindications include severe skeletal gummy smile, prior lip surgery, neuromuscular disorders, pregnancy, and allergy to BTX-A formulation components. Patients with very thin upper lips warrant caution, as further reduction in lip elevation may accentuate lip thinning on animation.7
Conclusion
Botulinum toxin offers a simple, predictable, and well-tolerated approach to the dynamic aetiology of gummy smile. High patient satisfaction is consistently reported in the literature when selection criteria are respected and dosing is titrated conservatively.8 As with all neuromodulator treatments, outcomes are optimised by a thorough pre-treatment assessment, anatomical precision at the point of injection, and structured follow-up to refine dose across successive sessions.
References
- Garber DA, Salama MA. The aesthetic smile: diagnosis and treatment. Periodontol 2000. 1996;11:18–28.
- Polo M. Botulinum toxin type A in the treatment of excessive gingival display. Am J Orthod Dentofacial Orthop. 2005;127(2):214–218.
- Tjan AHL, Miller GD, The JGP. Some esthetic factors in a smile. J Prosthet Dent. 1984;51(1):24–28.
- Pirazzini M, Rossetto O, Eleopra R, Montecucco C. Botulinum neurotoxins: biology, pharmacology and toxicology. Pharmacol Rev. 2017;69(2):200–235.
- Suber JS, Dinh TP, Prince MD, Smith PD. OnabotulinumtoxinA for the treatment of a "gummy smile." Aesthet Surg J. 2014;34(3):432–437.
- Hwang WS, Hur MS, Hu KS, et al. Surface anatomy of the lip elevator muscles for the treatment of gummy smile using botulinum toxin. Angle Orthod. 2009;79(1):70–77.
- Mazzuco R, Hexsel D. Gummy smile and botulinum toxin: a new approach based on the gingival exposure area. J Am Acad Dermatol. 2010;63(6):1042–1051.
- Nasr MW, Jabbour SF, Sidaoui JA, Haber RN, Kechichian EG. Botulinum toxin for the treatment of excessive gingival display: a systematic review. Aesthet Surg J. 2016;36(1):82–88.