Gummy Smile: Differential Diagnosis and a Multidisciplinary Orthodontic-Surgical Approach

Gummy smile (GS) — defined as exposing more than 3-4 mm of gum during a spontaneous smile — is a condition with an estimated prevalence of 10-14% in the adult population, more common in women (14% vs. 7% in men) due to differences in upper lip dynamics. Perception as an aesthetic problem varies significantly across individuals and cultures, but in clinical case series, requests for correction are rising alongside growing aesthetic awareness. Treating GS is one of the clinical contexts most requiring multidisciplinary integration — orthodontist, oral surgeon, periodontist and, in some cases, plastic surgeon or neurologist for botulinum toxin — for a precise etiopathogenic diagnosis guiding the correct treatment choice.

The etiopathogenic classification of GS is the essential diagnostic starting point. Chu et al. (2004) identify four categories: GS from excessive eruption of the upper anterior teeth (vertical dentoalveolar component), GS from vertical maxillary excess (VME — skeletal component), GS from upper lip hyperactivity (neuromuscular component — the zygomaticus major, minor, levator labii superioris and their contraction patterns during smiling), and GS from apparent short crowns (altered passive eruption or dental wear — periodontal component). In most patients, several components coexist with different relative weights, and diagnosis requires quantifying each component to calibrate each treatment's contribution to the final outcome.

Clinical GS assessment begins with measuring gingival exposure during spontaneous and forced smiling (the difference reflects the dynamic muscular contribution vs. the static anatomical component), followed by measuring the clinical crown length of the upper incisors (norm: 10-11 mm for central incisors in women, 10-11.5 mm in men) and the crown/root ratio (norm: 1:2 for incisors). Cephalometric assessment provides the parameters for quantifying VME: lower anterior facial height (LAFH) greater than the sex/ethnicity norm, an anteriorly downward-tilted upper palate. Measuring the incisal edge position relative to the lower lip during smiling (norm: 0-2 mm of incisal exposure at rest, 2-4 mm when smiling) points toward the vertical dentoalveolar component.

Orthodontic treatment of GS from a vertical dentoalveolar component (excessive incisor eruption) relies on intruding the upper incisors through specific mechanics. Intrusion with a utility arch (Ricketts' "utility arch") on a fixed appliance produces incisor intrusion of 1.5-3 mm in case series, with the side effect of anchor element (molar) extrusion if not managed with anchorage control. TAD-assisted intrusion (anterior palatal mini-screws directly connected to the incisors via elastics or a segmented wire) allows genuine intrusion without extrusion side effects, with results of 2-4 mm of intrusion documented in case series with 18-month follow-up. For every millimeter of incisor intrusion, gingival exposure decreases by about 0.8-1 mm: a 3 mm intrusion therefore produces a roughly 2.5 mm reduction in gingival exposure.

Surgical treatment of GS from skeletal VME in adults is Le Fort I with superior impaction (repositioning the upper maxilla) — the same procedure used for skeletal anterior open bite. Maxillary impaction of 3-5 mm proportionally reduces gingival exposure, with concurrent effects on overbite (increased), closing any associated open bite, and the profile (counterclockwise mandibular rotation and chin advancement). Preoperative digital planning (Dolphin Surgery® or equivalent) with cephalometric simulation of the impaction allows assessing three-dimensional effects before surgery and communicating expected outcomes to the patient. Post-surgical stability of maxillary impaction is good with rigid titanium osteosynthesis — vertical relapse is <1-1.5 mm at 5-year follow-up in more recent case series.

Type A botulinum toxin (Botox®, Dysport®) has a specific indication in GS from upper lip hyperactivity — the pure or dominant neuromuscular component. Injecting 2.5-5 U per side into the levator labii superioris alaeque nasi muscles (injection site: the junction of the nasal ala and nasolabial fold) temporarily reduces the range of lip elevation during smiling, reducing gingival exposure by 2-4 mm for a period of 3-6 months. The injection is technically simple, performable in the dental practice with appropriate training, but requires precise anatomical knowledge of the target muscle's innervation pattern to avoid diffusion into adjacent muscle units (risk of smile asymmetry, eyelid ptosis with injections placed too high). The effect is temporary — a limitation that for some patients is advantageous (allows testing the result before permanent interventions) and for others is accepted as a six-monthly maintenance treatment.