It's best for the orthodontist to see children by age 7 to advise if orthodontic treatment is required and the best time for that patient to be treated. The first permanent molars and incisors have usually come in by that time and crossbites, crowding and other problems can be evaluated.
When treatment is begun early, the orthodontist can guide the growth of the jaw and guide incoming permanent teeth. Early treatment can also regulate the width of the upper and lower dental arches, gain space for permanent teeth, possibly avoid the need for permanent tooth extractions, reduce likelihood of impacted permanent teeth, correct thumb-sucking, and eliminate abnormal swallowing or speech problems. In other words, early treatment can simplify later treatment.