Tooth shape and perceived age are linked mostly through two things: the biting edges flatten, and less upper tooth shows when the face is relaxed. Neither is about colour, and one of them is not about the teeth at all. Most of the change people describe as "my teeth look older" is a millimetre or so of edge wear, a gum margin that has moved, and an upper lip that has gradually lengthened over decades.
Key takeaways
- Colour is a separate subject and is covered in our article on why teeth look yellower with age, so this page is about shape and display only.
- Magne, Gallucci and Belser measured average incisal loss between unworn and worn teeth of 1.02 mm on central incisors, 0.93 mm on canines and only 0.41 mm on lateral incisors.
- The same study found width is unaffected by wear while length is reduced, so a central incisor outline squares up from about 78 per cent to about 87 per cent width-to-length.
- Awad and colleagues found upper incisor display at rest falls from 2.93 mm in the youngest group to 0 mm over 60, while clinical crown length did not change significantly.
- Albandar and Kingman found in NHANES III that 22.5 per cent of US adults aged 30 and over had at least one site with 3 mm or more of recession, mostly on the outer surfaces.
- Panel studies consistently rate rounded and semi-rounded incisal corners above square or rectangular ones, for both male and female smiles.
What this article covers, and what it does not
Colour is out of scope. If you are here because your teeth look more yellow than they used to, read our article on why teeth look yellower with age, which deals with enamel thinning, dentine and staining properly, and our guide to tooth shade matching covers how shade is assessed. Everything below is about shape, proportion and how much tooth is visible. Most of it is normal anatomy over time rather than disease, and it is described here so you can understand what you are looking at.
Incisal embrasures: the change nobody names
Look at a young smile straight on and you will see small triangular gaps between the biting edges of the front teeth. They are smallest between the two central incisors and get progressively larger toward the canines. Those are the incisal embrasures, and they are the most visually distinctive shape feature of an unworn smile.
Stappert, Tarnow, Tan and Chu measured what creates them. In the International Journal of Periodontics and Restorative Dentistry in 2010, they examined 20 healthy patients and 140 proximal contact sites and found that the apico-incisal length of the contact area between the upper front teeth falls steadily going back from the midline: 4.2 mm between the two centrals, 2.9 mm between central and lateral, 2.0 mm between lateral and canine and 1.5 mm between canine and premolar. As a proportion of clinical crown length that is 41, 32, 20 and 18 per cent. The authors note these contact proportions determine the papillary and incisal embrasures. Shorter contacts leave more room below them, which is why the gaps grow toward the back.
As the biting edges wear flat, those gaps close and the incisal outline becomes a straighter line. Morley and Eubank described the embrasure progression as a design principle in the Journal of the American Dental Association in 2001. No study has directly measured embrasure dimensions in young versus older groups, so the closing of the embrasures is an explanation drawn from the contact and wear data rather than a measured finding.
Edge wear, and why the laterals escape it
Magne, Gallucci and Belser published the most on-topic study for this subject in the Journal of Prosthetic Dentistry in 2003. They measured 146 extracted anterior teeth and split them into worn and unworn groups according to whether there was a wear facet with dentine exposure. Average incisal loss between the two groups was 1.02 mm on central incisors, 0.93 mm on canines and only 0.41 mm on lateral incisors.
That asymmetry is not random. The centrals and canines take the brunt of edge-to-edge and protrusive contact, while the laterals sit slightly shorter and are largely protected. It explains why your two front teeth and your canines often look flatter than the teeth in between.
On how common wear is, Van't Spijker and colleagues, in a systematic review in the International Journal of Prosthodontics in 2009, predicted that the percentage of adults with severe tooth wear rises from 3 per cent at age 20 to 17 per cent at age 70. Entezami and colleagues, in a Griffith University-led review in the Journal of Dentistry in 2021 covering 65 studies and 63,893 participants, found higher-educated adults had a lower risk. That is international data; no verifiable Australian figure for anterior tooth wear could be found.
One caution about numbers you may have seen. There is no published per-year or per-decade rate of enamel loss in millimetres. Magne's figures are a difference between two groups of teeth, not a rate. Our article on attrition, erosion and abrasion separates the mechanisms.
Incisal translucency as a structural change
The edge of a young incisor is a thin shell of enamel with no dentine behind it. That is how Magne and colleagues selected their unworn group: the unworn incisor has a thin rounded incisal edge, while the worn incisor shows a marked wear facet with well-defined dentine exposure. Wear removes that enamel-only edge and brings dentine up to the biting surface, and the optical behaviour of the region changes because you are no longer looking through a thin translucent layer with nothing behind it. Wee and colleagues, in the Journal of Prosthetic Dentistry in 2023, measured spectral reflectance of the mid-incisal region in 120 people across four racial groups and five age ranges, and found a mean translucency parameter for central incisor enamel of 10.1, differing significantly among age groups. Their abstract does not state the direction of that age effect, so it would be wrong to tell you translucency simply decreases with age.
Width-to-length ratio, and the number everyone repeats
You will read almost everywhere that the ideal width-to-length ratio of a central incisor is 75 to 80 per cent. That figure traces back to Chiche and Pinault's 1994 textbook on the aesthetics of anterior fixed prosthodontics. It is a textbook guideline, not a measurement study, and it does not match what has been measured.
Sterrett and colleagues, in the Journal of Clinical Periodontology in 1999, measured clinical crowns on casts from adults with no recession, no attachment loss and no wear into dentine. They found a central incisor ratio of 0.85 in males and 0.86 in females, a lateral incisor ratio of 0.76 and 0.79 and a canine ratio of 0.77 and 0.81, with an overall anterior mean of 0.81.
Magne and colleagues, measuring anatomic crowns on extracted teeth, found unworn central incisors at 78 per cent and worn central incisors at 87 per cent, with worn canines at 81 per cent and worn laterals at 79 per cent. Their teeth measure roughly a millimetre wider and longer than Sterrett's because they measured to the cementoenamel junction rather than to the gingival margin.
Put those together and nothing measured lands at 75 to 80 per cent for a clinical central incisor. Magne's own words are that increased width-to-length ratios would appear to have an ageing effect, and that low-ratio crowns are dominated by length while high-ratio crowns fit into a rather square shape. Their central incisor lost 1.02 mm of length while its width was unaffected, moving the ratio from 78 to 87 per cent. That is the arithmetic of a smile squaring up.
The gum line, and the crown that gets longer
The other way a tooth changes shape visually is that more of it becomes visible. Albandar and Kingman analysed NHANES III data for the Journal of Periodontology in 1999, covering 9,689 US adults aged 30 to 90. They found 22.5 per cent of adults had one or more sites with 3 mm or more of gingival recession, that prevalence, extent and severity all increased with age, that males had significantly more recession than females, and that recession was much more prevalent and severe on the outer surfaces than between the teeth. The outer surface is exactly the one on display when you smile. That data is US and now dated, and no comparable verifiable Australian figure could be located.
Recession does not lengthen the tooth. It moves the visible boundary, so the clinical crown gets longer while the anatomic tooth stays the same. Our article on receding gums, causes and treatment covers why it happens.
Display at rest: the change that is not about your teeth
Here is the finding missing from almost every consumer article on this subject. Vig and Brundo, in the Journal of Prosthetic Dentistry in 1978, described a gradual reduction in the amount of maxillary central incisor exposure with an increase in age, accompanied by a gradual increase in the mandibular tooth exposure. The upper teeth show less. The lower teeth show more. Their reported sex means were 3.4 mm for women and 1.9 mm for men on the upper incisors at rest, and 0.5 mm for women and 1.2 mm for men on the lower.
The 1978 paper is hard to obtain and its age-band figures circulate through secondary reproductions, so the better citation is a modern replication. Awad, Alghamdi and Alghamdi published one in the International Journal of Dentistry in 2020, measuring 157 people aged 19 to 69 with a digital caliper. Upper central incisor display at rest fell from 2.93 mm in the 19 to 24 group to 2.57, 2.32, 1.47 and finally 0 mm in the over-60 group. Lower central incisor display rose across the same bands from 0.89 mm to 1.12, 1.54, 2.09 and 2.14 mm. Both trends were highly significant.
Here is the important part. Clinical crown length in that study did not change significantly with age, going from 10.57 mm to 10.24 mm with a p value of 0.36. The teeth were not shorter. Less of them was showing.
Van der Geld, Oosterveld and Kuijpers-Jagtman explain the mechanism. In the European Journal of Orthodontics in 2008 they followed 122 males across cohorts aged 20 to 25, 35 to 40 and 50 to 55 and found upper lip length increased significantly by almost 4 mm while upper lip elevation did not change. The lip lengthens and covers more tooth. Drummond and Capelli, in the Angle Orthodontist in 2016, reached the same conclusion with 265 participants aged 19 to 60 using videography.
Does reduced display make someone look older to an observer? Pausch and Katsoulis tested it in the Journal of Cranio-Maxillofacial Surgery in 2017, with 42 evaluators rating two models across eight graded levels of tooth and gum exposure. The level at which no tooth was visible produced the highest estimated age.
Square or round corners: what the evidence says
There is a long-standing idea in dentistry that square, prominent teeth read as masculine and small, rounded teeth read as feminine. It comes from Frush and Fisher's dentogenic series published in the Journal of Prosthetic Dentistry between 1955 and 1959, built around what they called the SPA factor of sex, personality and age. It was an aesthetic philosophy for arranging complete dentures so they did not look like dentures. There was no sample, no statistics and no observer panel.
The related idea that tooth form matches face form has been tested and does not hold. Varjao and colleagues, in Quintessence International in 2006, compared photographic outlines for 160 people and found tooth form matched face form in only 23.75 per cent of cases, with three prosthodontists agreeing with each other only 30.62 per cent and then 24.37 per cent of the time. Sellen, Jagger and Harrison, in Primary Dental Care in 1998, found insufficient correlation in 50 adults.
What observer panels actually prefer is more consistent. Anderson, Behrents, McKinney and Buschang, in the American Journal of Orthodontics and Dentofacial Orthopedics in 2005, showed three incisor and canine shapes to 120 restorative dentists, 113 orthodontists and 102 laypeople. For women's smiles, orthodontists preferred round and square-round while laypeople did not discriminate between incisor shapes at all. For men's smiles, all three groups preferred square-round. Heravi, Rashed and Abachizadeh, in the same journal in 2011, found judge sex and age had no effect and that square incisors scored significantly lower than square-round and round in both male and female smile sets, recommending mildly rounding the corners of square incisors.
Duarte and colleagues, in the Journal of Esthetic and Restorative Dentistry in 2017, asked 240 evaluators to rate 12 manipulated photographs, and semi-rounded embrasures were preferred overall. Schwefer and colleagues, in Clinical Oral Investigations in 2022, found the best-rated canines had a right-angled to rounded incisal edge, with tapered edges rated least aesthetic. Fermeiro and colleagues, in the Journal of Clinical and Experimental Dentistry in 2025, surveyed 1,226 participants and reported the most attractive embrasure was round and the least attractive rectangular.
The net reading is that modern panel data supports rounded and semi-rounded corners over squared or rectangular ones for both male and female smiles, and does not support the old idea that observers read square as masculine and round as feminine.
| Shape feature | In a young smile | What tends to change over time | What the research measured | Source |
|---|---|---|---|---|
| Incisal embrasures | Small at the midline, larger toward the canines | Wear flattens the outline and closes the gaps | Proximal contact length falls from 4.2 mm central to central, to 2.9, 2.0 and 1.5 mm going back | Stappert and colleagues 2010, n=20 |
| Incisal edge and enamel at the edge | Thin, rounded enamel edge with no dentine at the tip | A flat wear facet develops and dentine reaches the edge | Average incisal loss: centrals 1.02 mm, canines 0.93 mm, laterals 0.41 mm | Magne, Gallucci and Belser 2003, 146 teeth |
| Width-to-length proportion of the central incisor | Longer than it is wide | Wear shortens without narrowing, so the outline squares up | Anatomic ratio 78 per cent unworn versus 87 per cent worn; width unchanged | Magne, Gallucci and Belser 2003 |
| Clinical crown proportion | Gum margin sits at the cervical bulge | Recession moves the margin, lengthening the visible crown | 22.5 per cent of US adults aged 30 and over had a site with 3 mm or more of recession, mostly on outer surfaces | Albandar and Kingman 1999, NHANES III, n=9,689 |
| Upper tooth display at rest | More upper incisor visible | Progressively less upper incisor visible | Falls from 2.93 mm at 19 to 24 years to 0 mm over 60; crown length did not change significantly | Awad and colleagues 2020, n=157 |
| Lower tooth display at rest | Little or no lower incisor visible | More lower incisor visible | Rises from 0.89 mm at 19 to 24 years to 2.14 mm over 60 | Awad and colleagues 2020 |
| Upper lip length | Shorter lip, more tooth shows | Lip lengthens and covers more tooth | Increased by almost 4 mm across cohorts aged 20 to 25 and 50 to 55; elevation did not change | Van der Geld and colleagues 2008, n=122 |
| Incisal corners | Softly rounded mesial and distal corners | Wear squares the corners off | Rounded and semi-rounded corners rated most attractive; square or rectangular lowest | Heravi 2011; Duarte 2017, n=240; Fermeiro 2025, n=1,226 |
Frequently asked questions
Do teeth change shape as you get older?
Yes, mostly at the biting edge. Magne and colleagues measured average incisal loss of about 1.02 mm on central incisors and 0.93 mm on canines between unworn and worn teeth, with width unaffected. Recession can also move the gum margin, which lengthens the visible crown without changing the tooth itself.
Why are my front teeth flat on the bottom?
Because the incisal edges have worn. Centrals and canines take most of the edge-to-edge contact and lose the most, while laterals sit slightly shorter and lost only 0.41 mm on average in Magne's sample. As the edges flatten, the small triangular gaps between them close and the outline becomes a straighter line.
Why do my teeth look shorter than they used to?
Often they are not shorter. Awad and colleagues found clinical crown length did not change significantly with age, while the amount of upper incisor visible at rest fell steadily. Van der Geld and colleagues measured an increase of almost 4 mm in upper lip length across cohorts, which covers more of the tooth without changing it.
Why can I not see my top teeth when my mouth is relaxed?
Upper incisor display at rest declines with age in every study that has measured it, reaching an average of 0 mm in the over-60 group in Awad and colleagues' data. The mechanism is a lengthening upper lip rather than teeth moving or sinking, and it is a normal change.
Why do my bottom teeth show more than they used to?
The same lip change works in the opposite direction below. Vig and Brundo described increasing mandibular tooth exposure with age, and Awad and colleagues measured it rising from 0.89 mm in the youngest group to 2.14 mm in the over-60 group. Drummond and Capelli found the same pattern in both sexes.
Do square teeth or round teeth look better?
Panel studies lean toward rounded and semi-rounded. Heravi and colleagues found square incisors scored lowest in both male and female smile sets, Duarte and colleagues found semi-rounded embrasures preferred by 240 evaluators, and Fermeiro and colleagues found round most attractive and rectangular least across 1,226 participants. The old idea that square reads masculine and round reads feminine is not supported.
Do receding gums make your teeth look longer?
They make the visible part of the tooth longer, yes. The anatomic tooth is unchanged; the gum margin has moved, so more of the crown is exposed. Albandar and Kingman found recession was much more prevalent and severe on the outer surfaces, which are the ones on display when you smile.
If you would like to talk it through
None of these changes has to be treated, and most of them are simply what teeth do over time. If you would like an assessment and an explanation of what you are seeing in your own mouth, the team at Lumi Dental in Melrose Park can go through it with you. Where people do want to discuss options, our comparisons of edge bonding and crowns versus veneers set out what each involves, including the trade-offs, and suitability always depends on an individual examination. You can book a complimentary cosmetic consultation, and our current offers page lists what else is available. 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. The measurements described are population averages from published research rather than targets, and suitability for any treatment varies from person to person.
