What Makes a Smile Look Natural: Proportion, Symmetry and the Smile Line
For anyone curious about smile aesthetics: proportion, the smile arc, midline and symmetry, buccal corridors, the gum line, texture and translucency. Most of these principles rest on expert opinion and perception studies. Reviews have found no formula that works as a standard guide, and small, deliberate differences between teeth are the principle behind a natural look, on indirect, mixed evidence.
5.0 from 550+ Google reviews
Open 8am to 8pm, seven days
Free parking at the door
CQC & GDC registered
No referral needed
Clinically reviewed by Dr Ibraheem Ijaz, dentist · GDC 301711
Medical disclaimer: This page is for general information only. It does not replace an examination or treatment by a dentist.
This page is reviewed by Dr Ibraheem Ijaz, the practice's principal dentist and a General Dental Practitioner (GDC 301711). His qualifications are BDS, BSc (Hons), MSc (Leeds), PG Dip Implant Dentistry and PG Cert Restorative and Aesthetic Dentistry.
What is smile aesthetics?
Smile aesthetics is the study of how the teeth, gums and lips look together in a smile, described through dental aesthetic principles. Research on what makes a smile attractive ranges from systematic reviews to expert views.
Is there an ideal tooth proportion?
No single ideal tooth proportion has been found. A 2022 systematic review reported substantial variation in tooth proportions in natural teeth, and none of its studies supported a single mathematical formula for predicting aesthetic success.
The golden proportion sets each lateral incisor's visible width at 62% of the central incisor's, and the canine's at 62% of the lateral's. The 2022 review found it between central and lateral incisors in some cases, rarely between lateral incisor and canine. A 2023 meta-analysis of six studies found evidence for it in natural smiles lacking and called it a myth rather than a fact.
Reviews disagree on the golden percentage. The 2022 review found it a better starting point than the other proportions, but only when adjusted for factors such as ethnicity or facial proportions, and the 2023 review said modified percentages can be applied. Another 2022 review, of 16 studies, 12 from Asia, did not find its values in natural teeth and concluded it could not be used to formulate a smile design.
What are the smile arc and smile line?
The smile arc compares the curve of the upper front teeth's biting edges with the curve of the lower lip in a smile. The incisal edge position, where those edges sit, shapes the upper curve.
A 2011 systematic review of nine studies found they typically link the smile line, a related aesthetic principle, to the upper lip's position, with three quarters or more of the upper front teeth showing on average. Average smile lines were rated most attractive, and a line joining the biting edges commonly followed the lower lip's upper border.
A second 2011 systematic review, of 20 studies, concluded that, in studies of real smiles, the smile arc alone does not seem to affect attractiveness. A 2021 narrative review says the literature favours an arc that follows the lower lip.
How much do the dental midline and symmetry matter?
A small shift in the dental midline is often rated acceptable, though accepted sizes differ between studies.
A 2016 systematic review of 66 studies of laypeople's perceptions identified a lay acceptance threshold for a midline discrepancy of 0 to 3 mm. Its data were too varied for a meta-analysis and lacked detail on how samples were chosen and on selective outcome reporting.
A 2011 review of 20 studies reported that, in its selected articles, a 2.2 mm midline shift can be considered acceptable to both professional and lay raters, while a 10° tilt of the midline is already very apparent.
A 2014 expert article weights the symmetry principle by position, describing a clinical assumption that the nearer a tooth is to the midline, the more symmetry matters, and slight asymmetries further out are more acceptable.
To ask about cosmetic dentistry, book online or call 0114 288 2121.
What are buccal corridors?
Buccal corridors are the spaces at the sides of a smile, between the visible upper back teeth and the corners of the mouth.
Evidence on this aesthetic principle is mixed. A 2014 expert article reports no consensus; in its author's study, medium corridors were judged more attractive than wide or narrow ones, yet it calls them not critical to smile aesthetics. A 2011 review of 20 studies concluded that, in studies of real smiles, buccal corridor size alone does not seem to affect attractiveness.
How does the gum line affect a smile?
A 2014 expert article calls some gum showing not a negative feature, citing a 3.0 mm upper limit from its author's earlier study. A 2016 systematic review put lay acceptance thresholds for gum showing at 1.5 to 4 mm.
In a 2018 study, 100 laypeople sorted 67 altered versions of one smile photograph. Changes to the gum between teeth (black triangles) were ranked most negatively. Changes to gum contour and the gingival zenith, the gum line's highest point above a tooth, had the least impact, and for features such as the gum margin level without recession, a one-sided change was rated less attractive than the same change on both sides.
What are surface texture and translucency?
Surface texture is a tooth's fine surface detail, and translucency is how much light passes through the tooth.
In a 2025 laboratory study of slices from extracted teeth, enamel was more translucent than dentine, and 1 mm slices more than 2 mm slices. The White Esthetic Score, which rates a restored front tooth against a natural one, includes surface texture and translucency or characterisation among its five domains; a 2026 narrative review reported that agreement between assessors varies by domain.
Tooth colour is explained under dental shade matching, and the surface shine of bonded composite under composite polishing and gloss retention.
Why can teeth that are too uniform look artificial?
Deliberate imperfection, meaning small, planned differences between teeth rather than identical copies, is the principle behind a natural-looking result. The evidence for it is indirect and mixed, from expert opinion and perception studies.
In a 2010 UK study, 105 dentists, dental technicians and patients ranked altered photographs of one smile. Incisal embrasures, the V-shaped spaces between neighbouring biting edges, widening steadily away from the centre were judged most attractive and none at all least attractive, but equal contact areas between teeth ranked most attractive and ones lengthening away from the centre least. The authors noted their findings did not wholly match ideals suggested in earlier dental literature.
In a 2006 survey, 147 people without natural teeth compared photographs of three denture tooth arrangements. The natural one, closest to the anatomical average, was preferred by 55%, a 'denture look' by 26% and a 'supernormal' one by 19%; preferences changed between test subjects.
What are the limits of smile aesthetics research?
Smile aesthetics research describes how groups rate smiles, often in photographs, so its thresholds are not standards for one person's smile.
A 2014 expert article calls its own principles a starting point, not universal rules, because ideas of beauty vary.
Where are treatments and smile planning explained?
Treatment pages include the porcelain veneer page, and the cosmetic dentistry page introduces the practice's cosmetic treatments.
Cosmetic planning steps at Deepcar Dental Care, set out on the smile design page, include a second consultation before committing and a written plan before anything starts.
Other science pages are among the options in this section.
Frequently asked questions
Do dental professionals and the public judge smiles the same way?
Not always. A 2010 UK study of incisal embrasures and a 2011 systematic review of the smile line found professional and lay raters broadly agreed. In a 2022 study of gum changes in one smile, ratings differed significantly between groups, and some groups of dentists tended to score altered smiles lower than laypeople.
Do age and sex change how a smile looks?
They can. A 2011 systematic review found smile lines influenced by age and gender, and a 2021 narrative review describes women's upper biting edges as more curved than men's, with both curves tending to flatten, and the lips sitting lower, with age.
Are smile proportions the same in every population?
Not necessarily. A 2024 meta-analysis of 26 studies covering 3,786 people in 12 countries found formulas such as the golden proportion and golden percentage did not give consistent results for use as a standard guide, and concluded that dental aesthetic ratios should be set by a population's racial and ethnic character.
Can a photograph change how a smile looks?
Yes. A 2021 narrative review describes how head tilt and camera angle change the smile arc's apparent curve: photographed from above, the curves look more marked, and from below they may look flatter. A 2026 review of an aesthetic scoring index reported better agreement with standardised photographs and calibrated assessors.
Does a small gap between front teeth affect attractiveness?
It depends on its size and position. A 2016 systematic review, from data too varied to pool, identified a lay acceptance threshold of 0 to 2 mm for a diastema, while a 2014 expert article suggested findings like this may be too optimistic; in its author's study, larger gaps nearer the centre looked less attractive.
Book a consultation.
Online in under a minute, or call and speak to a real person.
We look after patients from Deepcar, Stocksbridge and Oughtibridge, and from across north Sheffield, including Wadsley, Hillsborough and Fulwood. Many travel further, from Penistone, Barnsley and Rotherham. The practice is on the A6102 at 334 Manchester Road, and no referral is needed.
334 Manchester Road
Deepcar, Sheffield S36 2RH
0114 288 2121
Contact us
Opening hours
Open 8am to 8pm, seven days
Free parking at the door