Which one of the following terms describes an appliance used to close an anatomical defect of the oral cavity that has been left following surgery?

An obturator is specifically designed to close an anatomical defect in the oral cavity, such as those left after surgical procedures like maxillectomy or for patients with congenital conditions. The primary function of an obturator is to restore the continuity of the oral cavity, enabling the patient to improve speaking, swallowing, and aesthetic appearance by covering the defect. It may also assist with nasal airflow and improve the overall oral function.

Other options present different dental appliances for various functions. A functional appliance is typically used to facilitate dental growth and development or correct dental alignment rather than to close a defect. An immediate denture is a full or partial denture placed immediately following tooth extraction to provide aesthetics and function during healing, but it does not serve to close surgical defects. An overdenture is a removable prosthesis that fits over remaining teeth or implants, providing support but not addressing the closure of anatomical defects in the oral cavity. Thus, the obturator is the appropriate choice for the situation described.