Extraoral anchorage systems, such as headgear, are designed to apply significant and controlled force to restrict maxillary growth or move teeth effectively. The optimal force range for extraoral anchorage is 500-900 grams because forces below this range are often insufficient to achieve the desired orthodontic effects, while forces above may cause discomfort or damage to tissues. This force intensity ensures effective skeletal or dental movement without compromising patient safety or compliance. Maintaining this force range is crucial for stable and predictable orthopedic correction.

Reference: Proffit, Contemporary Orthodontics, 6th Edition.