“Charity is not a health care system,” Dr. Dickinson said.

Dentists, of course, are no more obligated to serve the poor than are lawyers or accountants. But the issue from a public health standpoint, the critics say, is that even as so many patients go untreated, business is booming for most dentists. They are making more money while working shorter hours, on average, even as the nation’s number of dentists, per person, has declined.

The lack of dental care is not restricted to the poor and their children, the data shows. Experts on oral health say about 100 million Americans — including many adults who work and have incomes well above the poverty line — are without access to care.

A federal survey shows that 27 percent of adults without insurance saw a dentist in 2004, down from 29 percent in 1996, when dental fees were significantly lower, even after adjusting for inflation. For adults with private insurance, the rate was virtually unchanged, at 57 percent, up from 56 percent. Since 1990, the number of dentists in the United States has been roughly flat, about 150,000 to 160,000, while the population has risen about 22 percent. In addition, more dentists are working part time.

Partly as a result, dental fees have risen much faster than inflation. In real dollars, the cost of the average dental procedure rose 25 percent from 1996 to 2004. The average American adult patient now spends roughly $600 annually on dental care, with insurance picking up about half the tab.

Dentists’ incomes have grown faster than that of the typical American and the incomes of medical doctors. Formerly poor relations to physicians, American dentists in general practice made an average salary of $185,000 in 2004, the most recent data available. That figure is similar to what non-specialist doctors make, but dentists work far fewer hours. Dental surgeons and orthodontists average more than $300,000 annually.

“Dentists make more than doctors,” said Morris M. Kleiner, a University of Minnesota economist. “If I had a kid going into the sciences, I’d tell them to become a dentist.”

But despite the allure of rising salaries, the shortage of dentists will almost certainly worsen, because the nation has fewer dental schools and fewer dentists in training than a generation ago. After peaking at 5,750 in 1982, the number of dental school graduates fell to 4,440 in 2003, as several big dental schools closed their doors. The average dentist is now 49 years old, according to the American Dental Association, and for at least the next decade retiring dentists will probably outnumber new ones.