While parents and infants give a thumbs up to this usually harmless habit, dentists vote thumbs down because pressure from the thumb against the inside of the upper front teeth can cause an overbite and other dental malocclusions. Yet seldom does thumb sucking become a dental problem in children under the age of 2, and certainly at 11 months it is unlikely to affect your daughter's teeth. At this age, I would recommend that you let her enjoy her thumb; chances are she will wean herself before it causes a problem.
Telltale signs that your infant is sucking hard enough to bother the formation of her new teeth are sores on the skin of her thumb, such as a callous, or cracking or bleeding. If she sucks hard enough to damage the skin, she could be putting harmful pressure on her teeth. If that's the case with your daughter, try these time-tested tips to satisfy her need to suck in other ways:
Keep little thumbs busy. Toddlers tend to suck their thumbs when they're bored, so as soon as you see your child's thumb making its way to her mouth, distract your daughter and involve her in another kind of hands-on activity.
Let her suck on your clean finger. New insight into the physiological benefits of sucking reveal that non-nutritive sucking (sucking without feeding) not only calms babies, but stimulates the flow of saliva, which can in turn act as a lubricant to settle an upset stomach.
The most severe thumb sucking malocclusions were in children who sucked their thumbs intensively all night. If a toddler always goes to sleep sucking her thumb, she will tend to revert back to this comforting habit throughout the night, especially when she wakes up. Put her to bed with sleep-inducing alternatives, such as rocking together, listening to soft music, and singing.
If during your daughter's second year neither your pediatrician nor your child's dentist is worried about the effect of thumb sucking on her teeth, let her enjoy her oral prop. Parents of an older child may want to be sure the family pediatrician and dentist are aware of any late thumb sucking, so they can be on the look-out for potential dental problems