What Is an Orthodontic Expander? – Types & Clinical Indications An orthodontic expander is used to widen a narrow upper jaw, correct posterior crossbites, create space for crowded or impacted teeth, and support more stable orthodontic treatment. This guide explains the main types of orthodontic expanders, including rapid palatal expanders, slow expanders, removable appliances, MARPE, and SARPE. It also compares appliance selection by age, skeletal maturity, anchorage, activation method, and patient compliance, while covering treatment expectations, retention, oral hygiene, discomfort, and common appliance problems to help patients and clinicians better understand the expansion process.