Tooth shape and facial harmony: what to look at

The eye reads the whole, not one tooth

When you look at a smile, the eye does not separate the teeth one by one. The line traced by the edges of the upper teeth, how much gum shows when you smile, and how the teeth sit against the lower lip are all read together. A tooth that looks out of proportion on its own therefore goes unnoticed within the whole more often than not. The reverse holds too: teeth whose individual measurements are fine still look unnatural if the edge line runs unevenly. Facial harmony rests largely on how that whole is read.

The width-to-length ratio of the front tooth

The two teeth at the centre of the upper jaw are the most visible part of a smile, and proportion is discussed on them more than anywhere else. What is measured is the visible width of the tooth against its length. In most people that ratio falls between 75% and 85%, so the tooth is a little narrower than it is long. The smaller the figure, the longer and finer the tooth reads; the larger it is, the shorter and wider. This is an observation and not a target: the same ratio looks different on different faces and varies from person to person.

• The ratio compares the width of the tooth with its own length, not with the neighbouring tooth or the width of the face.
• If the gum line sits lower, the visible length shortens, the ratio rises and the tooth reads wider.
• Wear shortens the biting edge and has the same effect: the tooth moves towards a square.
• When the two front teeth differ noticeably in ratio, the eye picks that up before it notices the shape of either one.

Square, rounded, triangular: the difference in form

The corners and side outlines of a tooth define its form. In a square form the biting edge runs flat and the corners are defined; the flat area on the front surface stays wide, so the tooth looks larger. In a rounded form the corners soften and the tooth looks slightly smaller and gentler. A triangular form is narrow at the gum and wide at the edge, and small triangular gaps can be left between the teeth near the gum. All three occur naturally and none of them is more correct on its own.

Where the midline runs

The midline is the vertical line between the two upper front teeth, and it is compared with the centre of the face. A sideways shift of 1–2 mm is common, and most people do not notice it even in their own photographs. What catches the eye is something else: a tilted line. A midline that has shifted sideways but stays vertical usually goes unnoticed, while a line tipped by the same amount is spotted at once. The upper and lower midlines matching exactly is not the expected finding either; in most people the two do not line up.

Matching teeth to face type is not a rule

The idea that a square face takes square teeth and an oval face rounded ones has been discussed in dentistry for a long time and gives planning a starting point. It is not a correspondence that holds for everyone: two people with the same face type can have completely different natural tooth forms. Applied as a rule, the match ends in a template rather than in that particular face. Your own older photographs are a firmer place to begin; the shape of a tooth before it wore down says more than any table of face types.

A detail that jumps out in a photograph is usually invisible in conversation; a smile is read in movement, not in a frozen frame.

Wear changes the form over the years

The edge of a tooth shortens over the years and the form changes with it. As the length drops, the width-to-length ratio rises, the corners flatten and the tooth moves towards a square. Over the same period less of the upper teeth shows at rest and more of the lower teeth comes into view. Grinding, acidic drinks and stomach acid reaching the mouth all speed this up. If an edge is shortening quickly, turning translucent or chipping, see a dentist; rebuilding the form early means removing less tooth tissue. For people who grind at night, a night guard is one of the options that may come up.

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