Treatments to Replace Facial Muscle Loss or Bone Loss?

Ideally the best treatment for a condition is the underlying cause.  

Bone loss can be corrected with facial implants such as malar, chin or prejowl sulcus implants.  Radiesse, which is injectable bone, can be used for this purpose as well when placed directly ontop of the bone.  

Muscle loss is not as commonly discussed.  One reason is that the muscles of the face are typically thin and sheet like and different than those found on the limbs of the human body.  Another is the lack of studies looking at this.  The masseter muscle has been studied to some extent and is found to get smaller to some extent.   In relationship to facial fat, theoretic atrophy of the muscles of the face will play a smaller role.  In addition, correction of this atrophy would be difficult with and possibly counterproductive with facial exercises.

In summary, bone loss of the face is a well studied and understood phenomenon of aging.  Its management is more straightforward.  Muscle loss of the face is less well studied, and most likely less impactful in facial aging, and its treatment is of the use of well placed fillers.

You insight is very keen. Yes the radiesse or other fillers are generally used to compensate for soft tissue loss and occasionally bony loss.
Use of facial implants is another method to compensate for bony loss.
Muscle atrophy and bulk are difficult to restore. Many claims for electrical stimulation or facial exercises have been made but never truly proven to be practical. In many ways repetitive muscle contraction may result in increased wrinkles. Therefore, we often use Botox to cease the action of muscles rather than build them up.