CHICAGO (Reuters) - Treating infant ear infections with the common antibiotic amoxicillin doubles children's risk they will suffer a problem later on with their permanent teeth, a study said on Monday.

The condition, dental fluorosis, results from exposure to excessive fluoride during teeth enamel formation. The effect on incisors and molars can range from barely noticeable white flecks to pits and brown stains -- and may spell dental trouble later on in life.

Overall, 24 percent of study participants developed dental fluorosis, and use of the antibiotic between the age of three and six months doubled the risk of the condition.

"Duration of amoxicillin use was related to the number of early-erupting permanent teeth with fluorosis," study author Liang Hong wrote in the current issue of the Archives of Pediatrics and Adolescent Medicine.

Hong, now at the University of Missouri, completed the study while at the University of Iowa in Iowa City.

In the study, 579 children were followed from birth to 32 months, and 91 percent used amoxicillin at least once -- a sign of the antibiotic's popularity and its potential impact on dental health.

"The findings suggest that amoxicillin use in infancy could carry some heretofore undocumented risk to the developing teeth," the study said. "While the results of this one study do not warrant recommendations to cease use of amoxicillin early in life, they do further highlight the need to use antibiotics judiciously, particularly during infancy."