Wisdom teeth -- the much maligned giant molars that appear when children reach the late teens -- should not be removed, even if they are "impacted" unless they are also diseased, according to a new recommendation of the National Institute of Dental Research.

More than 2 million impacted wisdom teeth are plucked out each year by oral surgeons, according to one estimate, because of the fear they may crowd other teeth or cause problems later in life.

But the newly released consensus of a conference of surgeons, dentists and researchers at the National Institutes of Health is that there is no evidence that extracting wisdow teeth prevents crowding other teeth. Even impacted teeth, those still partly embedded in bone, can be left in place and watched with periodic x-rays, the experts decided.

There are good reasons for removing some impacted teeth -- most often either infection, which is common in a wisdom tooth that has only partly broken through the gum, or cysts, which can form over the years in wisdom teeth that never erupt, said Dr. Walter C. Guralnick, professor or oral surgery at Harvard Dental School and chairman of the NIH conference.

But these complications do not happen routinely, and they can be seen on dental x-rays. "The idea of removing teeth just because they are impacted is not really fully established," he said.

The experts also agreed that the practice of removing wisdom tooth buds in children, based on x-rays done from age 7 to 9, is "not currently acceptable" because future problems usually cannot be predicted so early. Guralnick said healthy wisdom tooth buds need be removed in a child only if it were obvious that they would obstruct needed correction of the alignment of the other teeth. t

Guralnick said many oral surgeons disagree with the NIH recommendation, and adhere to the practice of removing all impacted wisdom teeth because surgery causes fewer problems in a young person than it may later in life. He said they view impacted wisdom teeth much as some surgeons do the appendix -- as useless structures with a risk of disease.

But he said most dentists now have access to new panoramic x-ray machines, with which they can easily monitor the health of impacted wisdom teeth. He recommended that patients be x-rayed every three or four years.