Smile Proportions

Smile Proportions analysis evaluates how the upper teeth and gums relate to the lips and to each other in a frontal, smiling photograph. It brings together several classic esthetic parameters — the smile arc, incisor display, gingival display, and the relative widths and dimensions of the anterior teeth — into a single diagnostic picture of "how the smile looks" rather than just "how the teeth are aligned."

This matters in orthodontic diagnosis because a technically well-aligned arch can still produce an unesthetic smile if the incisal edges do not follow the lower lip, too much or too little tooth (or gum) shows, or the visible teeth are disproportionate to one another. Smile Proportions findings help the clinician set esthetic goals for treatment — not just occlusal ones — and explain them to the patient in terms they can see in their own photo.

What It Evaluates

On a frontal smiling photograph, this analysis looks at:

Smile arc — whether the curve formed by the edges of the upper front teeth follows the curve of the lower lip (consonant) or is flatter/reversed relative to it.
Incisor display — how many millimeters of the upper central incisors are visible with the lips relaxed (at rest) and how much show on a full smile.
Gingival display ("gummy smile") — how much gum tissue shows above the upper front teeth on a full smile.
Golden proportion of anterior teeth — the relative visible widths of the central incisor, lateral incisor, and canine as seen from the front.
Tooth width-to-length ratio — the proportion between how wide and how tall the central incisors appear, which affects whether they read as square, ideal, or elongated.

Learn more: Conservative Treatment of a Non-Consonant Smile Arc - Dentistry Today

Key References / Landmarks

Smile arc (consonant vs. flat/reverse) — Ideally, the curve of the upper incisal edges runs parallel to the curve of the lower lip on smiling (a "consonant" smile arc). A flatter or reversed curve relative to the lip is generally judged less esthetic and often looks aged or "worn."
Maxillary incisor display at rest — With lips relaxed, roughly 2–4 mm of the upper central incisor is considered pleasing (averaging lower in men, higher in women). Display at rest decreases with age as the lip lengthens and tooth wear reduces crown height, which is why reduced display reads as an older smile and greater display reads as more youthful.
Incisor display on full smile — On a full smile, the ideal is close to full display of the crown height of the upper central incisors, with minimal to no gingival show, forming the basis of the gingival-display assessment below.
Gingival display / "gummy smile" threshold — Roughly 1–2 mm of gum show on smiling is considered normal; display beyond about 3 mm is widely regarded as a "gummy smile" and less attractive, though exact cutoffs vary by observer (orthodontists tend to flag it around 2 mm, the general public around 3 mm, and general dentists closer to 4 mm).
Golden proportion (Levin's concept) — A classic guideline states that, viewed from the front, the visible width of the lateral incisor should be about 62% (the golden ratio, 0.618) of the visible width of the central incisor, and the visible width of the canine about 62% of the lateral incisor. In practice this ratio is rarely found exactly in natural, attractive dentitions — studies report it in well under a majority of cases — so it is used today as a rough design reference rather than a strict rule, and rigid application can create an unnaturally narrow arch with an overly dominant central incisor.
Central incisor width-to-length ratio — A width equal to roughly 75–80% of the tooth's length is the traditionally cited esthetic ideal (some sources center on ~78%), producing a pleasing rectangular crown shape; ratios that are too high look square, and ratios that are too low look narrow/elongated. Some more recent preference studies find patients and clinicians rating slightly wider ratios (into the low-80s%) as most attractive, so this is treated as a target range rather than a fixed number.

Learn more: Proportions of Maxillary Anterior Teeth Relative to Each Other and to Golden Standard in Tabriz Dental Faculty Students

Clinical Interpretation

These measures let the orthodontist translate a patient's smile photo into concrete, treatable goals. A flat or reverse smile arc may point toward leveling the incisal plane differently during aligner staging so the upper arch curve better follows the lower lip. Reduced incisor display at rest or on smile can prompt discussion of incisal edge position, extrusion, or restorative lengthening, while excessive display — especially with several millimeters of visible gum — raises the question of a gummy smile, which may need vertical control of the maxillary anteriors, gingival contouring, or, in skeletal cases, a combined orthodontic-surgical plan. The golden proportion and width/length ratio are used less as hard rules and more as a sanity check: if the visible teeth are markedly out of these ranges, it flags a case where tooth-size discrepancies, interproximal reduction, or restorative build-up/reduction may need to be factored into the treatment plan so the finished smile reads as proportionate, not just aligned.

Learn more: Effectiveness and Personalized Approaches in the Correction of Gummy Smile: A Systematic Review of Orthodontic and Surgical Treatments