Osseointegration is the process where there is a direct structural and functional connection between living bone and the surface of a load-bearing implant. This intimate contact occurs at the light microscopic level, allowing the implant to become stable and firmly anchored in the bone without any intervening fibrous tissue. The absence of a soft tissue interface is critical for implant success, ensuring long-term implant stability and load transfer. Any fibrous tissue or bone resorption around the implant indicates a failure of osseointegration and jeopardizes implant function.

Reference: Dental Implant Prosthetics, Carl E. Misch, 2nd Edition.