Which of the following is a known risk factor for external root resorption during orthodontic treatment?

• A. Heavy continuous forces
• B. Short treatment duration
• C. Normal tooth color
• D. Short arch length differences

Answer: (B)

External root resorption is driven by how much and how long the teeth are moved. When forces are heavy and applied continuously, the periodontal ligament becomes stressed and areas of hyalinization can form, triggering clastic cells to resorb cementum and dentin at the root apex. The longer teeth are under such moving forces, the higher the chance for resorption to develop. Among the options, heavy continuous forces are the recognized risk factor. A shorter treatment duration would actually lessen risk, while normal tooth color and short arch length differences don’t in themselves predict external root resorption.