Serial extraction is the carefully planned and selective removal of baby (primary) teeth to create room for incoming permanent (secondary) teeth. Dentists or orthodontists consider removing teeth because after age 8, the space for a child's teeth (arch length) doesn't increase. Severe crowding of teeth at this age means that permanent teeth are likely to come in out of place. This can result in a bad bite or crooked teeth (malocclusion).
Often an orthodontist will remove the primary canine teeth after the two front secondary incisors on top and bottom have erupted. This makes room for the permanent incisors. After 2 years, when the first premolars and permanent canines are ready to erupt, the orthodontist again checks for crowding. More teeth are removed if needed. Often the orthodontist chooses to remove the first premolars.