In the first reported case of its kind, a New York City dentist apparently has become infected with the AIDS virus as a result of treating patients. But experts emphasized that the risk to dental professionals is extremely low.

The unidentified Manhattan dentist is the only one of 1,231 dental professionals who tested positive for human immunodeficiency virus (HIV) in a study reported yesterday.

"The risk is low," said Dr. Robert S. Klein, of Montefiore Medical Center in New York, who reported the results. "But we have to realize the risk is not zero."

The HIV-infected dentist "frequently practiced without gloves, even though he often had obvious breaks in his skin," Klein said. He had never treated a patient known to have AIDS, but had treated numerous patients thought to be at risk for the disease.

The dentist told researchers that he had not used intravenous drugs or received blood transfusions and that his only sexual contacts in the past 12 years had been with his wife, Klein said. The man's wife also denied using intravenous drugs or having sexual contacts with anyone but her husband.

Previous cases of HIV infection in dental professionals have involved people identified as members of groups at high risk for AIDS, such as sexually active homosexual or bisexual men or intravenous drug users, a spokesman for the American Dental Association in Chicago said. The 1,231 dental professionals in the study included 1,104 dentists and 127 dental hygienists. About 15 percent reported having treated known AIDS patients. But 31 percent of the dentists and 73 percent of the hygienists said they always use gloves.