Infants who sleep on their stomachs may well develop receding chins, crooked teeth, narrow faces curved spines and nasal septum deviations, according to a dentist who has made a study of the subject.

But if you turn them over, he says they eventually may straighten themselves out. "When you put a kid to sleep on his stomach, you mash his face," says Dr. Hal A. Huggins, of Colorado Springs, Colo. "I used to look at kids and say, 'Your teeth are too big for your mouth.' But, in fact, it was not their inheritance that made their teeth too crowded in their jaws . . . it was the fact that they had been sleeping on their stomachs." Huggins explained that at birth the skull is primarily composed of cartilage that eventually calcifies or hardens. The first part to calcify is the area on the back of the head, while the last part is the frontal area, site of over 40 little membrane bones that will eventually determine facial features. "The calcification of the bones around the face begins at about two years," he said. "And by then in many cases the damage is done because of pressure exerted during sleep." He said there are areas of the world where people are almost free from malocclusions -- abnormalties in the coming together of teeth. And in those areas, children and adults sleep on their backs, he said. After studying New Mexico and Arizona Indians who were raised on cradleboards, Huggins said, "They have outstanding postures and a lack of crowding of teeth in their jaws." When his orthodontic patients first came to him, "their postures were slouched forward and their shoulder blades stuck out like wings," he said. "They had receding chins, severe anterior crowding and narrow faces." Side sleepers, he said, had one shoulder blade that stuck out and were more prone toward unilateral crossbite. People who slept on their stomachs or sides with their hands under their heads sometimes developed; one nostril that was smaller than the other because of pressure against the nose, he said. Asked how a pillow or a hand could exert enough pressure to alter bone structure, Higgins said that most orthodontic tools used to correct such things as malocclusions exert only 30 or 40 grams of force, while "a human head weighs 16 pounds."