During bone regeneration, the surrounding bone undergoes remodeling to support the healing process. New bone tissue is formed, integrating with the existing bone to restore structure and function.

it begins with chondrogenesis as a repair process them to osteogenesis and simultaneously integration to existing bone

Bone regeneration is a dynamic process that balances the breaking down of old bone, the generation of new bone, and the infiltration of these areas with blood vessels. (Cell Biology!)

Two broad categories of cell populations available as sources of bone regeneration include osteoblasts and multipotent cells.

Check this source for further Insight>

Article Stem Cells in Bone Regeneration

What happens to the surrounding bone depends on the type of injury and how repair is stimulated. Standard fracture healing involves making a callus that is larger than the original footprint of the bone but less dense, and has to go through a lot of remodeling to get back to the original shape and density (if at all). If a defect is big enough to require a scaffold, you typically need to add growth factors to stimulate the healing, and potentially have fixation devices which will cause some degree of injury response in the bone ends. The bone will remodel and all going well integrate with the new tissue formed, but there is no standard change in density (usually people don't quantify the original bone though). Muscle damage and unloading can also independently cause bone loss, so in a serious defect this may also be a factor.