Dixie Nielsen has a tooth that's a candidate for a crown. It has long had a large "silver" filling, which has expanded and contracted enough times over the years to change, and not for the better. At the least, it needs to be replaced.

Garon Larsen, a dentist at the Alpine Dental Clinic in Alpine, explains that teeth with large metal fillings often at some point must be crowned. Expansion and contraction has cracked the tooth or there's decay under the filling. But if too much of the tooth is gone, replacing the filling simply isn't going to work. Besides, that filling material contains mercury, which he figures may not be really healthy.

Repairing such a tooth has, most of the time, meant the need for at least two dental-office appointments, usually two or more weeks apart. One to have the tooth prepared for a crown and an impression taken so it can be sent to a lab to have the crown manufactured. The tooth is ground down to a peg so the crown can be bonded over it, like a stocking cap on a head, then a temporary cap placed on it to prevent pain until the permanent crown comes back from the lab.

Nielsen, however, is going to get all the work done in a single visit that takes close to an hour, thanks to an increasingly popular dental repair called CEREC, which can be used on a crown, a veneer or a filling.

CEREC is shorthand for "Chairside Economical Restoration of Esthetic Ceramics."

With CEREC, the tooth is not ground to a nub for a crown to cover. Instead, as much of the tooth as possible is left intact. The filling is drilled out and a reflective powder is placed in the opening that's created so that it will reflect light. Then a tiny camera is placed in the mouth to take a three-dimensional photograph of the tooth, which is transmitted to a computer-aided design program on a computer. That picture is the process's equivalent of a dental impression.

It's not all automated. The dentist does some of the work of creating the design that will become an inlay or overlay.

"There are always a few adjustments, but not too much," Larsen notes as he moves the mouse to outline the section of tooth that's being replaced. The goal is to get it close enough to the neighboring tooth that floss will go through, but not food.

When the dentist is happy with the image, it's sent to a special machine where a small piece of tooth-colored (there are different shades to match teeth) and very strong ceramic is shaped precisely using a high-speed diamond burr and a disk mill. After a few minutes, the piece is complete.