Expansion is a valuable treatment form, and is often a better alternative to extracting teeth. As the maxillary canines are erupting is usually the ideal time for expansion. If expansion is performed too early it will need to be repeated later when these teeth erupt.
Remember, the last teeth to come into the mouth are often the canines in the upper jaw, also known as the eye teeth. Each canine tooth on average is 3 mm wider than the baby tooth it replaces. Because of this many early treatments fail at this stage. Any alignment of the teeth by expansion must allow for 6 mm of space that will be needed for the canine teeth.