Final answer:
The implant that is not placed into the bone is a subperiosteal implant
Step-by-step explanation:
The correct answer is C. subperiosteal. A subperiosteal implant is a type of dental implant that is placed on top of the jawbone, but under the gums. It is used when there is not enough bone to support an endosteal implant, which is inserted directly into the bone.
For example, if a patient has experienced bone loss due to periodontal disease, a subperiosteal implant may be recommended as an alternative to an endosteal implant.
Other options mentioned in the question, such as endosteal, titanium, and transosteal implants, all involve the placement of the implant directly into the bone.