Many people get porcelain veneers on their teeth to improve their smile and appearance because their natural teeth became worn, shortened and chipped over the years. So, how does a cosmetic dentist know how long to make the new teeth?
Cosmetic dentistry is an art and there is no absolute rule, but there are many guidelines and generalities that I use in determining the length of the teeth.
One thing is how much of the teeth show when smiling? When the upper lip is at rest and the mouth is slightly opened so that the back teeth are not hitting, we usually like 1-2 millimeters of the upper front teeth to be showing (around 1/8"). That would be consistent with unworn teeth on a person in their 20s or 30s. Even patients in their 40s or 50s usually want to look a little younger, so that is a good guideline.
Another thing is if a person smiles, do they show the gum line of the upper teeth and the entire length of the four front teeth? If so, then another thing comes into play – the length to width ratio of the front teeth. Studies have shown that both dentists and patients like the appearance of the upper front teeth most often if their length is 1.29 times longer than the tooth width. Or, said another way, if the width of the front teeth is 75-80% of the length of the front teeth.
The lower lip gives us another guide, as when the patient smiles the teeth generally look very good if they follow the curve of the lower lip, which dentists call “the smile line”. Here is a photo of my patient Jill Frick (who was previously Mrs. U.S.Globe). Note how her teeth beautifully follow her lower lip. 
Most cosmetic dentists find that the actual length of the front two teeth will look best if they are between 10mm and 12mm long, and the average length of an unworn upper front tooth is 11.5mm.
The above are just some guides, but the ultimate guide is “does the patient like it” and “do they look good with that length of teeth?” And this decision should be made prior to fabricating the final veneers.
How can this be done? A good cosmetic dentist should always verify that the patient likes and approves of the length of the front teeth BEFORE we tell our ceramist how long to make them. This is done by having the patient wear temporary veneers, called “the trial smile”, for several days and then comes back to the cosmetic dentist for verification. This gives the patients an opportunity to actually function with the length of the new teeth before making them. It’s important that they like the length, and also have no speech challenges with the new length. If they are too long, sometimes patients will have challenges with the “f” sounds (like “fire truck” or “fifty-five”) or "v" sounds ("victory", "victor"). Or, if the upper veneers or crowns are too thick on the back or lower veneers or crowns are too thick on the front, challenges with the “s” sounds (like “sixty-six”) can happen.
The “trial smile” is a beautiful way for cosmetic dental patients to preview and sample the length of the new veneers and solves many of the challenges. If the patient says that they are too long, then the trial smile teeth can be shortened to the patient’s liking and then measured for the lab. If they are too short, the trial smile teeth can be lengthened as well.
You can see that cosmetic dentistry really is more of an art than a science. Good cosmetic dentists have many cosmetic concepts and principals to go by, but it is extremely important is that the length of the front teeth be a decision made by both the patient and the cosmetic dentist together, and not made solely by the ceramist (who probably has never seen the patient in the flesh).
Dr. Norman Huefner, General and Cosmetic Dentistry, Laguna Niguel, CA
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