Bone supported devices

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Principles

The use of IMF screws and plates with screws for mandibulomaxillary immobilization are considered to be a reserve method.

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Indications:

• Emergency cases
• In contagious patients
• As an alternative if arch bars can not be applied
• Selected patients with simple fracture patterns or undergoing orthognathic and reconstructive surgery

Contraindications:

• Severely comminuted and displaced fractures
• Unstable, segmented fractures
• Children, if tooth buds are still in place
• Fracture patients with multiple mobile teeth

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Before starting, check the position of the teeth roots and the infraorbital and inferior alveolar nerves.

The position of the screws should be symmetrical from jaw to jaw and should not interfere with the operative approach or internal fixation devices.

Long-term immobilization is not recommended, because of the injuries to the mucosa.

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Screw design

IMF screws are made of stainless steel. They are self-drilling and self-tapping.

The screw head is elongated and contains two holes in a cruciform configuration for wire placement.

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Screw placement

Correct screw locations
Various IMF screw placement patterns exist and are dictated by fracture location.

The field of application is limited by the position of the inferior alveolar nerve, the position of the infraorbital nerve and the teeth roots.

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For correct placement, IMF screws must be located superior to the maxillary teeth roots and inferior to the mandibular ones and are either lateral or medial to the long axis of the canine roots. A more lateral approach gives increased lateral stability and greater control over the posterior occlusion, but implyies an increased risk of complications, specifically to the neurovascular bundle.

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Screw insertion
Introduce self-drilling and self-tapping screws directly through the mucosa. Take care that the screw head does not compress the gingiva when fully seated.

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Insert two more IMF screws on the opposite side in the same manner.

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Mandibulomaxillary fixation (MMF)

Mandibulomaxillary fixation is performed with 0.4 mm wires.
The wire ligature is wrapped around the screw head grooves.

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Before tightening the wires, the correct occlusion has to be established.

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Place another wire on the other side, this time through the hole in the upper screw and …

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… around the lower screw.

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“X” pattern
For more stability, wiring in an “X” pattern can be added.

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The results reveal some problems. Tightening the wires may create a posterior open bite. But additional IMF screws or Ernst ligatures placed on the posterior dentition may prevent or correct this condition.

Overtightening the wires can also lead to a lateral rotation of the fragment.

There may be a lack of stability due to the elasticity of the long wires.

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Alternatively, plates and screws can be used as a bone supported device.

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Alternative: screws and plate

Cut from a mandible plate 2.0 pieces of 2-hole length for the maxilla and usually pieces of 3-hole length for the mandible.

Bend these pieces away from the bone and fix them monocortically with 6 mm long 2 mm screws.

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After establishing the occlusion mandibulomaxillary fixation is done with 0.4 mm wires.
There may be a lack of stability because of the elasticity of the long wires.

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Alternative: interarch miniplates

Edentulous fragments can be secured by use of interarch miniplates which are applied transmucosally.