What structure protects the underlying bone and seals the teeth?

The attached gingiva is the correct choice as it plays a crucial role in oral health by protecting the underlying bone and helping to securely attach the teeth to the gums. This structure is a part of the gingiva that is firmly bound to the underlying alveolar bone and provides a barrier against infection and mechanical forces that could damage the tooth-supporting structures.

Additionally, the attached gingiva contributes to the overall stability of the gums, helping to prevent periodontal diseases and maintaining the integrity of the dental arch. It helps to seal the teeth by forming a tight connection with the teeth and surrounding tissues, which is integral to oral health and function.

Understanding the function of the attached gingiva is important for recognizing the importance of soft tissue health in overall dental care and addressing issues like gum recession and tooth mobility.