displaced upwards. It must be remembered that vertically and horizontally unfavourable fractures may be undisplaced if the periosteum is undisturbed. The concept is only important when the periosteum has been ruptured or stripped from the bone. A favourable facture line will, however, make the reduced fragments easier to stabilize. The presence of an erupted tooth on the posterior fragment will sometimes prevent gross displacement of this fragment in an upward direction if its crown impacts on the opposing upper tooth.
Fractures at the symphysis and parasymphysis : In the symphysis region muscle attachments are also important. The mylohyoid muscle constitutes a diaphragm between the hyoid bone and the
mylohyoid ridge on the inner aspect of the mandible. In transverse midline