How Your Dentist Sets the Length of Your Front Teeth: Rest, Smile, and Speech

By Dr. Boris Zusin · Published October 9, 2026

When we plan veneers, crowns, or a full rebuild of a worn bite, the first decision isn't tooth color or shape — it's where the edges of your upper front teeth should sit. That single position dictates the angle of your biting plane, how far your jaws are apart when you bite, how long your teeth look, and how clearly you speak. Get it wrong and everything built after it is compromised, which is why it's set before any other cosmetic or bite decision.

It's determined in a set order: first how much tooth shows at rest, then refining the length against your full smile, then double-checking with speech, and finally trying it out in your mouth.

The Four Steps at a Glance

The diagram below is an original illustration built for this post, not a reproduction of any published figure.

Step 1: How Much Tooth Shows at Rest

With you sitting upright, head in a natural position, and lips relaxed, we measure how much of the upper front teeth peeks out below your resting upper lip. A simple way to get a true relaxed position is to have you say “Emma” and then let your lips part slightly on their own.

The typical range is roughly 1 to 4 millimeters of the upper central incisors, adjusted for your age, sex, lip length, and lip tone. The classic age pattern is about 3 mm at age 30, about 1 mm at 50, and under 1 mm by 60, because the upper lip gradually lengthens over time. That's why a smile that looked right at 30 can look “flat” or toothless at rest decades later.

The ideal isn't a single number, either. It depends on lip form: a straight lip looks best with only around 2 mm of show, while moderate or high lip forms look best with roughly 4 to 5 mm. In people whose teeth have worn down, there's often no tooth showing at rest at all. If the edges sit, for example, 3 mm short of the lower border of the upper lip, lengthening by roughly 3.5 to 4 mm is a reasonable starting estimate for bringing the edges back into view. The canine is often the steadiest reference point for judging this, since how much of the central incisors shows varies so widely from person to person.

Step 2: Refine It Against Your Full Smile

Next we watch how far your lip travels from rest to your biggest, natural smile. That tells us whether you have a low, medium, or high smile line, and how much extra length is esthetically safe before too much gum starts to show. We also look at your smile arc — how the curve of your upper edges lines up with the curve of your lower lip — and note how much gum you show at full smile. Women, on average, show a little more gum in a social smile than men do.

To keep these measurements reliable rather than eyeballed, we use standardized photographs, facial reference tools, and digital rulers laid over overlapping photos, so the rest and smile positions can be compared side by side.

Step 3: Check It With Speech

Your speech is a surprisingly precise test of whether the edges are in the right place:

• “F” and “V” sounds. When you say these, the upper front edges should lightly touch the boundary between the wet and dry parts of your lower lip. If the teeth are too long or too far forward, they'll hit the dry part of the lip or its inner side; if they're too short or set too far back, they won't touch at all.
• “S” sounds. The upper and lower front teeth should come close during an “S” but not touch, leaving a very small gap (the “closest speaking space”). Edges that are too long can cause a lisp or an audible clicking. We test a range of sounds — S, Z, Sh, and Ch — rather than relying on just one, since a single sound isn't reliable on its own.

The sibilant sounds also mark the most forward, highest position your lower jaw reaches while speaking, which makes them a practical functional check on how long the upper edges should be.

Step 4: Test-Drive It Before It's Permanent

The appearance-based and speech-based findings complement each other, and the speaking-space and display measurements vary widely between people, so no single method should decide on its own. Once we've combined them, we transfer the planned edge position into a diagnostic wax-up or a mock-up you can wear. That lets you and us check, in your own mouth, how much shows at rest, how it sounds, and how the smile looks — and adjust — before any permanent restoration is made.

After the Edge Is Set: Orienting the Biting Plane

Once the front edge position is chosen, it becomes the anchor for everything behind it. The occlusal plane — the imaginary flat surface where your upper and lower teeth meet — is then oriented to that front edge and to reference lines on your face, not the other way around. In other words, the front edge comes first; the plane, the height of your bite, the length of your teeth, and how you speak all follow from it. An error at the front edge carries through the entire bite, which is why it's settled before anything else.

From the Front: Lines Across Your Face

Looking straight on, the line between your pupils is the main horizontal reference — one study found it usable in roughly 88% of faces — with the line between the corners of your mouth as the second reference and your facial midline as the vertical one. The catch is that about 64% of faces in that same study were asymmetric, and the human eye can pick up a tilt of as little as about 1 degree. So these lines can't be assumed; each is checked on your face individually. It also matters which horizontal we trust: a “true horizontal” taken with your head in its natural position can differ from your pupil line, and building a bite to a pupil line that is itself tilted can exaggerate a cant rather than correct it, leaving tilted tooth axes and uneven lengths in the planned smile.

From the Side: Camper’s Plane

From the profile, the biting plane is classically set roughly parallel to Camper’s plane (a line from the base of the nose to the ear), or to a plane running from the hamular notch behind the upper teeth to the incisive papilla behind the front ones. Where on the ear the line ends matters: in one 3D study, the line through the top of the tragus matched the natural upper plane most closely. Even so, individual variation is wide. In one study of people with their natural teeth, the biting plane differed from the true horizontal by an average of about 3 degrees, but individuals ranged from roughly 9 degrees below to 18 degrees above. Another reported that a commonly used guide for denture rims works well when teeth are missing but is less reliable when natural teeth are present, since they introduce their own variability. The takeaway is that these lines are a starting point, not a rule.

Putting It Together Before Anything Is Permanent

No single landmark is valid for everyone, so we combine the front edge position, the facial reference lines, and your bite height in a diagnostic wax-up, setting the plane and any change in bite height together before any irreversible preparation. That plan is then transferred to your mouth as a mock-up you can wear, so we can confirm how it looks, how it sounds, and how the plane sits on your face first.

Why Your Face Matters More Than a Formula

Lip length and thickness change the ideal quite a bit. Thinner lips may look better with slightly more forward front teeth, and the rule-of-thumb display numbers don't hold up for very high or very low lip forms. We also check your horizontal reference lines — the line between your pupils, the corners of your mouth, and your facial midline — individually, because most faces aren't perfectly symmetrical. The goal is for your front teeth to look natural with your face as it actually is, not to match an idealized symmetry.

What This Means for You

If you're considering veneers, a smile makeover, or rebuilding teeth that have worn down from grinding, this sequence is what happens behind the scenes before anything is made. If your teeth look short, flat, or barely visible when you're relaxed, or you notice a lisp or whistle when you speak, mention it at your consultation — those are exactly the clues this process is designed to catch. For more on the proportions we design around once the edge position is set, see Anatomy of a Perfect Smile.