A gummy smile — more than a few millimetres of gum on full smile — is often misunderstood. Most people assume it is a problem of teeth or jaw that only surgery can touch. Often it is simpler: the muscles that lift the upper lip pull harder than average, hoisting the lip higher than the design intended. Muscles that overpull can be relaxed, precisely and reversibly.
The smile is analysed in motion — which elevators overpull, by how much, and from where.
A gummy smile is more than about three to four millimetres of gum showing on full smile, most often caused by overactive upper-lip elevator muscles rather than the teeth or jaw. Smile analysis separates this hypermobile lip from vertical maxillary excess or altered tooth eruption, which need dental or surgical input, before botulinum toxin is considered.
Key facts
Gingival display
The amount of gum visible on full smile; more than 3–4 mm reads as 'gummy' in most smile analyses
Lip elevators
A group of paired muscles — chiefly levator labii superioris alaeque nasi (LLSAN) and neighbours — that lift the upper lip
Hypermobile lip
The commonest gummy-smile mechanism: normal anatomy, overactive elevation
Other mechanisms
Vertical maxillary excess, altered tooth eruption and a short upper lip — the cases that need dental or surgical input
BTX rebalancing
Micro-doses into the overactive elevators reduce excess lift while preserving a natural smile
Onset & duration
Effect builds gradually and wears off over time, in line with BTX behaviour elsewhere in the face
Reversibility
Muscle-relaxant effects wear off fully — the treatment is inherently trial-able
A gummy smile shows more than about three millimetres of gum above the upper teeth when smiling. If the cause is a hyperactive lip-elevator muscle, a small dose of botulinum toxin into the levator labii superioris relaxes the lift for a period that varies between people; if the cause is a short lip, a long gum or a vertically long upper jaw, toxin helps less and dental or surgical options are discussed. Dr Sin Yong assesses the cause before offering toxin.
What makes a smile 'gummy'
Smile analysis measures gingival display: how much gum shows between the upper lip and the teeth at full smile. Up to about three millimetres reads as youthful and normal; beyond that, the gum line starts to compete with the teeth for attention, and owners of such smiles often train themselves to smile guardedly — a genuine cost, paid daily, for a few millimetres of anatomy.
The mechanisms matter more than the label. A minority of gummy smiles are skeletal (the upper jaw is vertically long) or dental (teeth erupted with too much gum coverage) — those belong with orthodontists, periodontists and maxillofacial specialists. The majority are muscular: everything is built normally, but the lip elevators contract too enthusiastically, lifting the lip several millimetres higher than average on smiling. That subset — the hypermobile lip — is where injectable treatment shines. A 2022 systematic review of nine prospective studies, in the British Dental Journal, supported botulinum toxin for gum display caused by overactive smile muscles, and noted its use as a diagnostic aid as well as a treatment.
Gummy smile causes compared: muscle, teeth, jaw or lip
Gummy smile treatment depends on why the gum shows. Most gummy smiles come from lip-lifting muscles that pull too far, but some come from the teeth, the jaw or a short upper lip, and those are treated by other specialists. This table sets out how each is recognised and who treats it.
Cause
How it is recognised
Who treats it
Do injections help?
Overactive lip elevators
Teeth and jaw normal; the lip lifts higher than average on smiling
A doctor, with micro-doses of botulinum toxin
Yes: this is where injections fit
Excess gum over the teeth
Teeth look short and square; gum covers more of each tooth
A periodontist or dentist
No
Long upper jaw
Gum shows even at rest; the lower face looks long
An orthodontist or maxillofacial specialist
No, or little
Short upper lip
The lip at rest covers little of the teeth
Assessed case by case
Sometimes partly, if the muscle also overacts
Mixed causes are common: a slightly long jaw with an overactive lip, for example. Injections can soften the muscular part even then, but they do not change teeth or bone, which is why the examination looks at the smile at rest, at full smile and in profile. For how the medicine is used elsewhere on the face, see botulinum toxin in Singapore; for lip shape and proportion, see lip fillers.
Dr Sin Yong measures how much gum shows and checks the teeth and jaw before suggesting treatment, and refers to a dentist where the cause is dental or skeletal.
The muscles doing the overwork
Several paired muscles raise the upper lip, and one — the levator labii superioris alaeque nasi, running beside the nose — contributes most to the central gum flash. Polo's work established the injection approach: micro-doses of muscle relaxant placed precisely into the overactive elevators reduce the excess lift while leaving normal smile mechanics intact. The word that matters is excess. The goal is not a weakened smile but a rebalanced one — the lip still rises, the teeth still show, the extra centimetre of gum stays covered.
“The goal is not a weaker smile. It is the same smile, minus the centimetre it never needed.”
Dr Sin YongOn rebalancing rather than freezing
What treatment involves
After smile analysis — in motion, not from a photograph alone — treatment is a handful of tiny injections at mapped points; recovery varies, and there may be pinpoint marks. The effect assembles over days, is reviewed once settled, and lasts months before gradually wearing off. Because the pull is symmetrical by design, dosing respects symmetry too; an asymmetric smile is analysed for which side overpulls and dosed accordingly, which is where experience earns its keep.
How Dr Sin Yong treats a gummy smile, step by step
Dr Sin Yong assesses and treats every gummy smile himself, at the clinic on Orchard Road, Singapore.
He analyses the smile in motion, not from a photograph alone, and notes how much gum shows at full smile.
He separates a hypermobile lip from a vertically long upper jaw, gum-heavy tooth eruption or a short lip; those causes are pointed to a dental or surgical opinion.
Where the cause is muscular, he maps which lip elevators overpull, by how much and from where.
Botulinum toxin is placed as tiny injections at the mapped points, and an asymmetric smile is dosed for the side that overpulls.
The smile is reviewed once the effect has settled.
Honest limits, and who should look elsewhere
BTX cannot shorten a vertically long maxilla, re-cover teeth that erupted gum-heavy, or lengthen a genuinely short lip — and a doctor should say so at assessment rather than treat everyone who walks in. Marked skeletal cases deserve a dental-surgical opinion; some patients combine approaches. And because muscle-relaxant effects are fully temporary, the muscular version of this treatment carries a built-in safety: if the rebalanced smile is not to your taste, the previous one returns on its own within months.
Related on this site
A lip flip targets a different muscle, and the two are sometimes planned together.
Gummy Smile — Frequently Asked Questions
A gummy smile caused by overactive upper-lip elevator muscles can be treated without surgery, using small doses of botulinum toxin placed in those muscles to reduce how far the lip lifts. The effect is temporary and wears off fully. A gummy smile caused by a long upper jaw, excess gum over the teeth or altered tooth eruption needs a dentist, orthodontist or maxillofacial specialist, so smile analysis comes first.
A gummy smile is usually described as more than about 3 to 4 mm of gum showing above the upper teeth on a full smile. Less than that is generally within the usual range, and how much shows also depends on lip length, tooth size and how far the lip rises. The amount is measured during smile analysis, in motion, before any treatment is discussed.
Most commonly, hyperactive lip-elevator muscles lifting the upper lip higher than average on smiling. Less commonly, a vertically long upper jaw, gum-heavy tooth eruption, or a short upper lip — those variants need dental or surgical input rather than injections. Assessment distinguishes them.
Micro-doses of muscle relaxant are injected into the specific elevator muscles that overpull, reducing the excess lift. The smile still rises naturally; the extra gum display is simply reduced. Effect builds gradually and wears off over time.
Dosed correctly, no — the treatment targets excess pull, not the smile itself. The commonest report is that nobody notices anything except that photographs look better. Overdosing can flatten a smile, which is why conservative dosing with review beats a heavy first session.
Months, in line with muscle-relaxant treatments elsewhere — with gradual, complete wear-off. Many patients settle into two to three sessions a year once their dose is dialled in.
It is a handful of very fine injections taking a few minutes; most patients rate it easier than they expected. Recovery is discussed at consultation.
Injectable treatment is temporary by nature. Permanent correction exists for the skeletal and dental variants — orthognathic surgery, crown lengthening — but those are bigger undertakings for bigger anatomical causes. For muscular gummy smiles, most people prefer a reversible treatment they control.
Asymmetric gum show usually means one side's elevators pull harder. The analysis maps which muscles on which side, and dosing is tailored — asymmetry is an indication for precision, not a reason to avoid treatment.
Anyone whose gum display comes primarily from jaw or tooth anatomy — injections cannot move bone — and anyone unwilling to accept a temporary result. A proper assessment will tell you honestly which group you are in before anything is injected.
At the small doses used it rarely does; over-dosing can flatten the smile or make the upper lip feel heavy for a few weeks, which is why Dr Sin Yong starts low and reviews at two weeks.
Polo M. A simplified method for smile enhancement: botulinum toxin injection for gummy smile. Plast Reconstr Surg 2013;131(5):934e–935e. source
Polo M. Botulinum toxin for gummy smile correction. Am J Orthod Dentofacial Orthop 2020. source
The Role of Toxins and Fillers in Optimizing Perioral Rejuvenation. PubMed. pubmed.ncbi.nlm.nih.gov
The role of botulinum toxin A in the management of different types of excessive gingival display: a systematic review. British Dental Journal, 2022. pubmed.ncbi.nlm.nih.gov
