BOSTON -- Dentists who routinely examine children's faces and mouths are in an ideal position to spot and report child abuse, but too few do so, a panel of prominent dentists reported last week at a conference of the American Dental Association.

One study has found that dentists report to state authorities only about one third of the cases of suspected abuse and neglect, according to the Dental Coalition to Combat Child Abuse and Neglect. Similar findings were reported in a 1978 study.

While declining to give specific data, one of the authors of the unpublished study, Patricia Macchiarulo, a clinical instructor at the Harvard School of Dental Medicine, said dentists who had been trained to spot signs of abuse and to report it were five times more likely than those without training to notify the Massachusetts Department of Social Services.

Under state law, dentists and many other professionals, including doctors, nurses, psychologists, public or private school teachers and day-care workers, are required to report suspected abuse. Unlike other states, the panel said, dentists in Massachusetts are not required to take a course in child abuse education to renew their licenses.

This year, however, they will be required to notify state officials in writing by Oct. 31 that they know their obligations under the mandatory reporting system.

The number of child abuse and neglect reports has grown steadily since 1980, officials said.

Last year, 76,000 cases of suspected abuse and neglect were reported, more than half of them under the mandatory reporting system.

About 9,000 cases were reported by health professionals.

Howard Needleman, co-chairman of the pediatric dentistry department at the Harvard School of Dental Medicine, said dentists should look for the following indications of abuse: deviations in behavior, such as increased sullenness or aggressiveness; signs of trauma on the face, mouth and elsewhere; and bruises in various stages of healing.