Keynote Address: Do Craniofacial Bones Require Loading?

The skull does not bear body weight, causing speculation that craniofacial bones are not dependent on loading for their maintenance, unlike limb bones.  The relative ease of changing alveolar bone using orthodontic forces seems to belie this notion, as do experiments modifying sutural and condylar growth using applied loads.  Nevertheless, these may be special cases involving periosteum/periodontium surfaces and may not apply to bone density.  During normal function, loading of craniofacial bones can only come from contraction of jaw muscles.  The force of contraction can be manipulated by changing the consistency of the diet or by selectively paralyzing muscles.  These indicate a substantial effect.  For example, 1 month after a single dose of botulinum toxin to one masseter of adult rabbits, trabecular bone in the ipsilateral condylar head was reduced by 40%.  Craniofacial bones are just as sensitive to loading as are limb bones.