Phase I, or early interceptive treatment, is limited orthodontic treatment (e.g., expander or partial braces) initiated before all of the permanent teeth have erupted. Such treatment typically is started between the ages of six and ten and usually lasts for one year or less. Interceptive treatment is often indicated to make more space for developing teeth, break harmful oral habits, and correct crossbites, deep overbites, or underbites.
Phase II treatment, or comprehensive orthodontic treatment, is started after most or all of the permanent teeth have erupted, usually between the ages of eleven and thirteen.