It's still not really clear how thumb-sucking and other sucking affect a child's teeth, although it seems possible they would affect the way the face develops. Researchers in Italy looked at young children's teeth to learn more.

What the researchers wanted to know: How do the type of feeding as an infant and other sucking affect preschoolers' teeth?

What they did: In 1998, pediatricians, dentists, and nurses in the town of Cava de' Tirreni in southern Italy examined 1,130 children born between 1993 and 1995. They also asked parents whether children were breast-fed or bottle-fed and whether they sucked on a thumb or pacifier.

What they found: Children who'd sucked on a thumb or pacifier for more than a year were twice as likely to have misaligned teeth. They were four times as likely to have an open bite, in which the front teeth don't meet right. Children who were bottle-fed were more likely to have a posterior cross-bite, in which molars don't line up, but otherwise bottle-feeding or breast-feeding didn't seem to make a difference.

What the study means to you: Babies who are fed with bottles have to suck harder to get their food than breast-fed babies. That may affect the way their faces develop; posterior cross-bite may be less likely to clear up on its own, the researchers say.

Caveats: The researchers don't know what those early behaviors and early malocclusions mean for the children's later facial development—if the teeth realign spontaneously, it may not matter how they line up when a child is young.

Find out more: Information on malocclusion from Lucile Packard Children's Hospital

Read the article: Viggiano, D., et al. "Breast Feeding, Bottle Feeding, and Non-Nutritive Sucking; Effects on Occlusion in Deciduous Dentition." Archives of Disease in Childhood. December 2004, Vol. 89, No. 12, pp. 1121-1123.

Abstract online: http://adc.bmjjournals.com