Many people notice in their forties or fifties that their top teeth seem to have shrunk, or that the bottom teeth now show when they talk. The teeth have usually not changed at all. The upper lip has slowly lengthened and covers more of the upper teeth, while the lower lip shows more of the lower ones. That shift is one reason dentists record your face with the lips relaxed, not only when you smile.
Two records, two questions
A dentist planning cosmetic work, dentures, implants or orthodontic treatment usually looks at two positions. The first is repose: the face relaxed, the lips resting and the teeth slightly apart. The second is a full smile. Repose shows where the biting edges of the upper front teeth sit relative to a relaxed lip. The full smile shows how far the lip travels when the smiling muscles pull it up. One cannot be worked out from the other, because people's lips move very different distances.
This article is about the resting position and what changes it. Gum showing when you smile is a separate topic covered in our article on gummy smile causes and treatment.
Repose has to be coached
Most people tense their lips the moment they know they are being photographed, and pressing the lips together is not the same as resting. Clinicians often use speech to find the relaxed position, for example asking you to say a word ending in an "m" sound, then let the face and jaw go loose. Repeating the position until it looks the same twice in a row, or recording a short video, gives a more reliable picture than one posed photograph. Lighting and camera angle can also change how a smile appears from one image to the next.
How much tooth shows varies widely
A 1978 survey in the Journal of Prosthetic Dentistry (Vig and Brundo) is still the study most often quoted on this. With the lips gently parted at rest, it found that the amount of upper central incisor showing fell gradually with age, while the amount of lower front tooth showing rose. Its specific averages are widely reproduced, but the original paper gave little detail about its methods, so they are best treated as historical figures.
A 2008 pilot study in the Journal of Prosthodontics (Misch) measured 104 adults aged 30 to 59 with a ruler. Women showed an average of 3.8 mm of upper central incisor at rest, ranging from 1 mm hidden under the lip to 8 mm visible. Men averaged 2.5 mm, ranging from 3 mm hidden to 7 mm visible. In both groups the average fell with each decade. The average figure fitted fewer than 30% of the people measured, so the author concluded it could not be used to predict where an individual's teeth should sit.
The same study found that the tip of the upper canine was far more consistent. Average canine exposure was within about 1 mm of the resting lip in both men and women across every age group, which led the author to suggest the canine as a more useful guide when setting tooth position for people who have lost their teeth. As a pilot in one population, it needs confirming in larger studies.
The lip changes, not the teeth
Two later studies used video to measure people of different ages. A 2008 study of 122 men in the European Journal of Orthodontics (Van der Geld and colleagues) compared men aged 20 to 25, 35 to 40 and 50 to 55. In the older men the upper lip was almost 4 mm longer, while the distance it lifted when smiling did not change. Less upper tooth showed at rest and when smiling, and more lower tooth showed at rest.
A 2016 study of 265 adults aged 19 to 60 in the Angle Orthodontist (Drummond and Capelli) found the same pattern in both sexes. Upper lip length increased with age, more so in men; upper incisor display decreased, especially in men; and lower incisor display increased in both men and women.
These are soft tissue changes. The skin and muscle of the lip lose firmness and lengthen over time, so the lip drapes lower over the same teeth. Gum recession is a separate change that can make teeth look longer when they do show; our guide to receding gums covers it.
A high lip line is not automatically a gummy smile
"Lip line" or "smile line" describes where the upper lip sits at full smile relative to the front teeth, usually labelled high, average or low. A 1984 study of 454 smiling photographs of dental and dental hygiene students (Tjan and colleagues, Journal of Prosthetic Dentistry) found that an average smile shows roughly the full length of the upper front teeth, with the edges of those teeth following the curve of the lower lip.
Gum display is a measured amount of visible gum, and there is no single agreed cut-off for "too much". The two usually travel together but not always. A lip that sits high at rest can move very little, so no gum shows when smiling. A lip that rests normally can lift a long way, so a lot of gum appears in a broad smile. That is why the resting record and the smiling record are both needed.
What the two records tell the dentist
| Lips at rest | Full smile | |
|---|---|---|
| What it shows | Where the upper lip sits when relaxed | How far the upper lip lifts |
| Upper front teeth | Often a few millimetres in younger adults, usually less with age | Usually most or all of the tooth length |
| Lower front teeth | Tends to show more with age | Mostly hidden by the lower lip |
| Gum | Not normally visible | May or may not show, depending on lip movement |
| Used for | Setting the edge position of front teeth, dentures and implant teeth | Planning gum display and how the smile is framed |
Normal covers a wide range
Every study above found large differences between individuals, and most were small, from one population, or decades old. None of the averages is a target for your own smile. Two people with identical teeth can show very different amounts because of lip length, lip thickness and how far the lip moves, and both can look entirely natural. The midline and the width of the smile are separate features again; see our articles on why a smile can look off centre, buccal corridors and facial asymmetry.
Questions patients ask about tooth display
How much should my front teeth show at rest?
There is no single right amount. Studies report wide ranges, with a few millimetres common in younger adults and less with age. What suits you depends on your lip length, lip shape and age.
Why do my top teeth show less than they used to?
Most often because the upper lip has lengthened with age and covers more of the teeth. The lower lip also tends to reveal more of the lower teeth over time.
Why did my dentist photograph me with my lips relaxed?
Because the resting position shows where the edges of your front teeth sit relative to a relaxed lip, which matters when planning veneers, crowns, dentures, implants or orthodontic treatment. A smiling photo alone cannot show this.
Having your smile assessed
At Lumi Dental we take clinical photographs in a dedicated photography room as part of a cosmetic assessment, and can talk through what is normal variation and what, if anything, may be worth discussing. You can book a free cosmetic consultation at Melrose Central, Melrose Park, or see our current offers page. We are open Monday to Saturday.
This article is general information only and is not a substitute for an examination and individual advice from a registered dental practitioner. Individual results and suitability vary, and the measurements described here are population averages rather than targets for any one person.
