The mandible or lower jaw is a common site for injury in the horse. The mandible has symmetrical right and left sides with long horizontal parts joining at the symphysis, which is the mid-point of the lower incisors, containing the incisors, canines, wolf teeth and cheek teeth. At the level of the last cheek tooth on each side, the mandible extends vertically, articulating with the skull at the temporomandibular joint.
How Do Mandible Fractures Occur?
Mandibular fractures may follow kicks to the head or significant fall whilst wearing a bitted bridle and usually involve the vertical or horizontal part of one side of the jaw. Fractures are often comminuted – where the bone is in multiple pieces. A common site for injury is the bar of the mouth (interdental space) and first cheek tooth, like the one marked by the circle in the radiograph. These fractures may not have obvious signs of trauma and horses may present with difficulty eating (quidding) and objecting to the bit ridden work. A careful clinical examination should identify the presence of a fracture and the extent and involvement of dental structures assessed using radiography and ultrasound imaging.
How Are They Managed?
These fractures are often managed without surgery, as the other side of the mandible acts as a splint for the injured side. Horses cope well when provided with pain relief, soft slurry diet and rest whilst the fracture heals.
Damage to the teeth is reassessed after the fracture has healed, as extracting damaged teeth at the time of the fracture is likely to destabilise it and cause more damage to the tissues. When horses find a fracture too painful to continue eating, an external fixation device can be used to prevent movement across the fracture site, reducing pain and enhancing healing. Pins are inserted into the bone on either side of the fracture, joined by an acrylic bar to provide external support.
The drawbacks of external fixation are that protruding parts are susceptible to damage and careful pin placement is required to avoid damage to tooth roots.
Fractures of the front of the mandible can occur when horses bite or catch their teeth on fixed objects such as door tops and frames, hanging treat containers or metal bars surrounding stables or over windows. Fractures involving the incisor teeth, whilst dramatic in appearance, can be repaired by wiring the teeth and jaw back together, usually saving the affected teeth and allowing the horse to make a full recovery.
Mandible Fracture Case: Meet Acer
Acer fractured his mandible between incisor 403 and 404 and significantly displacing 404 to the right side. The injury was sustained in the stable, probably occurring when he was rubbing his face on the metal safety bars on the stable window.
He was sedated and the area carefully cleaned and lavaged to remove food material and bacteria. The fracture was replaced into the normal alignment and local anaesthetic used to place wires between his incisors on the left side and the right canine, fixing the fractured tooth and mandible back into its normal position. Purple dental putty was used to cover the sharp ends of the wire to prevent damage to the soft tissue of the mouth when eating.
Acer was able to go home the same day with antibiotics and pain relief for one week. He can graze but is avoiding haynets or anything else he could catch his teeth on and can go back into work when he is comfortable. The wires will stay in place for 6-8 weeks and are then removed under sedation.