orrection Appended

HAWORTH, N.J.

YOU sit down, you open your mouth, you say "ahhh." The dentist leans down and peers in, metal probe in one hand, angled mirror in the other, and starts poking.

That scene plays out in dentists' offices every day. But when Kevin McMahon sank into the chair in Examination Room 4 at Dr. Andrew Spector's office here for a routine checkup, the process was a bit different.

Ilene Levine, the hygienist, reviewed Mr. McMahon's chart and images on her flat-panel display, then reached for a wandlike device called a Difoti. She positioned it above each tooth in turn. As she did, light passed through the enamel in a process called transillumination. Any cavities or other irregularities altered the light pattern, and the information was captured by the wand's sensor - a charge-coupled device, the kind used in many digital cameras - and transmitted to a display that she and Mr. McMahon were watching.

"This is one we need to monitor," Mrs. Levine said, pointing to what looked like a black-and-white photograph of a molar with an old silver amalgam filling. Shielded by the metal, the new decay would have gone undetected by X-rays.

The Difoti (the name is an acronym for digital imaging fiber optic transillumination) is one of a range of new digital technologies that are helping to close what Dr. Spector calls the diagnostic void. "Now we're catching problems sooner," he said - for example, when a cavity is too small to be seen by the naked eye or even picked up by a traditional X-ray. "These days kids have fewer cavities, and adults aren't ending up with major crowns."

Lasers, sonar, digital radiography and rapid manufacturing are making dental work more efficient, less painful, and of better quality. Even offices that have not made the switch to digital radiography are starting to scan their X-rays; the digitized images can be stored electronically and sent easily to specialists or insurance companies.

Moreover, companies like Logicon, a division of Lockheed Martin, and Trophy, now owned by Kodak, have introduced software that can enlarge and enhance images for specific detection tasks. "It's the difference between radio and television," Dr. John Flucke, a dentist in Lee's Summit, Mo., said of the collection of new tools. "The technology allows practitioners to see what we used to ascertain by experience and feel."

Some dentists also say that imaging technologies play an important role in their relationship with patients. The buzzword is "co-diagnosis," and the idea is that patients will gain a better understanding of their periodontitis if they can see it on a wide-screen monitor. (Hence Mrs. Levine's narrated walk-through of Mr. McMahon's mouth.) Though many patients would rather forgo the viewing pleasure, the premise is that they will be more willing to go ahead with a root canal if they have witnessed the sorry state of the root.

Another advantage of these powerful detection and imaging techniques is that they can sometimes help to reduce the discomfort of examinations and treatments. The drill, the workhorse of dentistry for more than a century, may not disappear, but several companies are hoping to sideline it.

One alternative is the soft-tissue laser, which Dr. Paul Feuerstein, a dentist in the Boston area and the technology editor of Dental Economics, calls "the big boy of minimally invasive tools." First used for whitening, diode lasers are increasingly being used to shape the gum line and treat gum disease because they are much kinder to the tissue than a scalpel, and patients require no anesthetic when they are used.

Dr. Larry Emmott, a dentist and technology consultant in Phoenix, had a patient with chronic gum disease who was not responding to traditional treatments. "The periodontist we'd been collaborating with on the case said she'd just have to get dentures," he recalled. Instead, Dr. Emmott successfully treated the problem by cutting away the infected layer with a soft-tissue laser.

Then there is the Cerec 3, a two-foot tower with a swiveling monitor and a small keypad, which aims to make getting a crown a less daunting prospect.