Which one of the following is not an endosseous implant?

The correct choice is that a subperiosteal implant is not classified as an endosseous implant. Endosseous implants are designed to be placed within the bone, typically within the jaw, allowing for direct integration with the bone through a process called osseointegration.

In contrast, a subperiosteal implant is positioned under the periosteum but above the bone surface. This type of implant is typically used in cases where there is insufficient bone height or volume, making it a suitable alternative when endosseous implants cannot be used effectively.

The other options, such as basket root form implants, zygomatic implants, and taper screw type implants, are all considered endosseous implants, as they are specifically designed to be inserted into the jawbone, providing a stable foundation for prosthetic replacement of missing teeth. Each of these designs offers different benefits and indications, but they all share the common characteristic of being located within the bone itself.