An endosteal implant is placed directly into the alveolar bone to provide stable support for prosthetic teeth. The implant achieves osseointegration, a crucial process where the bone grows around and bonds with the implant surface, ensuring long-term stability. Insertion into soft tissues like gingiva, mucosa, or sinus lacks this bony support and fails to provide adequate anchorage, leading to implant failure. Therefore, precise surgical preparation of the bone site is essential to accommodate the implant and promote healing.

Reference: Contemporary Implant Dentistry, Carl E. Misch, 4th Edition.