In true micrognathia, the jaw is small enough to interfere with the infant's feeding. Infants with micrognathia may need special nipples in order to feed properly.
Micrognathia often corrects itself during growth, especially at puberty when the jaw grows quite a bit. It can be caused by certain inherited disorders and syndromes.
Micrognathia is one cause of abnormal alignment of the teeth. You can see this in the way the teeth close. Often there will not be enough room for the teeth to grow. Talk to an orthodontist when the child's adult teeth come in. At times, children can outgrow micrognathia. It makes sense to wait to treat the condition until they are older.