General Overview:

Anatomy

Options  General considerations   Nerves: Motor nerve/cranial nerve VII/facial nerve   Nerves: Facial vessels   Nerves: Sensory nerves - branches of the mandibular nerve (CN V3)   Muscles: Mentalis muscle   Muscles: Buccinator muscle   Muscles: Buccal fat pad   Bones: Bony cross sections and intraosseous structures

General considerations

Transoral or transfacial surgical approaches, pin placement for external fixators, reduction and fixation using an internal system can interfere with the following anatomic structures.

Nerves: Motor nerve/cranial nerve VII/facial nerve

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Main trunk of facial nerveThe main trunk of the facial nerve and its two major divisions (temporofacial and cervicofacial) cross the posterior border of the mandible ramus in the subcondylar neck region.

Marginal mandibular branch of the facial nerveThe nerve is at risk for injury in transfacial approaches to expose the posterior and lateral surfaces of the mandible (submandibular, retromandibular, facelift approaches).

Frontotemporal branches of the facial nerveThe frontotemporal branches of the facial nerve ascend from the main trunk in a diagonal course to the forehead and they are at risk of injury in preauricular or extended coronal approaches.

Nerves: Facial vessels

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The facial vessels cross the inferior border of the mandible at the level corresponding to the anterior border of the masseter muscle. The vessels are embedded in the lower extensions of the buccal fat pad.

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The artery is always located anterior to the vein. A periosteal layer separates the vascular bundle from the lateral bony surface of the mandible.

Nerves: Sensory nerves - branches of the mandibular nerve (CN V3)

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Clinically important ramifications of the 3rd division of trigeminal nerve (CN V3):The third or mandibular division of the trigeminal nerve passes the skull base through the foramen ovale into the infratemporal fossa and divides into a smaller mainly motor portion that gives off branches to the muscles of mastication. There is a larger branch that is predominantly sensory in nature. The sensory buccal nerve arises from the smaller portion.

The larger sensory trunk divides into the auriculotemporal, lingual, and inferior alveolar nerves. They provide sensation to:

Parts of the external auditory canal The parotid The temporal region The inner cheek The anterior two-thirds of the hemitongue The floor of the mouth The mandibular teeth The lower lip/chin area

Auriculotemporal nerve:The auriculotemporal nerve (mainly sensory) loops around the middle meningeal artery by two roots and reunites laterally. Then it curves posteriorly in a plane on the inner aspect of the medial pterygoid muscle and continues superiorly between the temporomandibular joint and the external

acoustic meatus before it enters the upper part of the parotid gland and accompanies the superficial temporal vessels. It has a number of small branches to the temporomandibular joint, to the skin of the external auditory canal and the lateral surface of the tympanic membrane, to the tragus and lower auricular concha and to supply the facial nerve with sensory and parasympathetic fibers for the innervation of the skin over the parotid region and cheek. The upper terminal branch supplies sensation to the lateral side of the head in a zone similar to the vascularization by the superficial temporal artery.

The auriculotemporal nerve and its branches are at risk for injury in external preauricular approaches to the temporomandibular joint and in rhytidectomy incisions.

Lingual nerve:The lingual nerve lies anterior to the inferior alveolar nerve and first descends deep to the lateral pterygoid muscle and superficial to the medial pterygoid muscle. From the lower border of the lateral pterygoid muscle the nerve passes obliquely forward between the medial pterygoid muscle and the inner aspect of the ascending ramus until it reaches the bottom fold of the pterygomandibular space. At the height of the posterior mylohyoid line it exits the space and curves anteriorly to take a longitudinal direction. For a short distance it lies close to the lingual cortex of the inner mandibular angle (temporal crest), the retromolar trigone and third molar region. Towards the oral cavity it is covered by the mucous membrane and the posterior tail of the submandibular gland, so that it can often be visualized as a pale shade by tautening the soft tissues of the posterior glossoalveolar sulcus. On its course to the dorsum and the tip of the tongue it then turns medially and crosses the lateral side of the superior pharyngeal constrictor, styloglossus and hyoglossus muscles to split into its terminal branches.

Exiting from the petrotympanic fissure the chorda tympani joins the back of the lingual nerve in an acute angle already at the level of the lateral pterygoid muscle.

The lingual nerve provides pain, temperature and touch sensation to the anterior two-thirds of the hemitongue, the glossoalveolar sulcus and the lingual gingiva of the entire lower quadrant. Taste mediating fibers from the anterior two-thirds of the hemitongue are conveyed centrally via the chorda tympani. The chorda tympani also contains visceral efferent fibers travelling to the sublingual and submandibular gland.

The lingual nerve is prone to injury during intraoral approaches exposing the medial side of the retromolar trigone and the inner aspect of the ascending ramus. Sometimes the nerve is hit while drilling or with transverse screw insertion along the upper border (oblique line) of the inner bony angle. The chorda tympani itself is out of reach during fracture repair procedures but its fascicles inside the lingual nerve can be affected.

Inferior Alveolar Nerve:The inferior alveolar nerve (IAN) is the largest branch of the mandibular nerve and carries sensory and motor fibers. On its way from the infratemporal fossa and mandibular foramen at the medial surface of the ascending ramus it descends in a parallel route (posterior and lateral) to the lingual nerve. The mylohyoid nerve branches off posteriorly just before the main nerve enters the mandibular foramen. The mylohyoid nerve runs inferiorly and anteriorly in the mylohyoid

groove and further forward into the digastric triangle. It provides motor innervation to the mylohyoid muscle and the anterior belly of the digastric muscle. It provides sensory fibers that supply a small circular zone of skin above the mental protuberance.Furthermore the IAN can separate collateral branches in its precanalicular segment, which independently run downward on the bony surface and pierce into the bone through accessory foramina and small vents in the retromolar area. If encountered during exposure at the inner angle it is hard to decide whether they can be transected, because their contribution to the sensory innervation is not to be determined.

The IAN is accompanied by the inferior alveolar vessels in its course through the mandibular canal.

The mandibular canal can be positioned at a variable vertical height that has to be assessed in the preoperative imaging. Within the canal or in their intraosseous course the fascicles of the IAN can either unite into single or double stranded bundles as well as ramify into an ample plexus formation. These neural structures give rise to the inferior dental branches and the inferior gingival branches providing sensation to the teeth and gums. The latter branches often do not directly stem from the inferior alveolar nerve bundle or plexus but arise as a second series from the dental branches.The IAN bifurcates at the mental foramen with a major portion exiting as the mental nerve to the lateral side. The minor quantity of fibers continues anteriorly inside a canalicular structure as an incisal bundle.

As a matter of principle the intraosseous IAN structures are at potential risk for lesions through insertion of osteosynthesis screws and must be examined on the basis of the preoperative radiographic findings.

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Mental nerve (mental neurovascular bundle)The mental neurovascular bundle exits the mental foramen, which is the anterior opening of the mandibular canal. The bony foramen is usually positioned at a vertical height midway between the alveolar and basal border of the mandibular body just below the apices of the premolars. In the sagittal plane the mental foramen is located at a level projecting between the tips of the first and the second premolar.

The mental nerve is the major terminal branch of the inferior alveolar nerve. The branches enter the skin of the chin, the vestibular gingiva in the symphyseal region, and the mucosa of the labial sulcus and the lower lip vermillion.

Photographs show the branches of the mental nerve.

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Buccal nerveThe buccal nerve (sensory branch of mandibular nerve) passes medial to the ascending ramus and divides into a multitude of small branches overlying the lateral surface of the buccinator muscle. The terminal branches pierce the muscle for innervation of the buccal gingiva and the buccal mucosa between the pterygomandibular raphe and the corner of the mouth.

Muscles: Mentalis muscle

The mentalis muscles are paired and function as elevators of the lip and chin. They arise directly from the bony surface of the anterior symphysis in a zone between the labial sulcus and the apices of the lower incisors, located in front of the mental foramina. If the mentalis muscle is cut during an anterior vestibular approach it must be carefully reattached to avoid a sagging or drooping chin.

Muscles: Buccinator muscle

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The bony attachments of the buccinator muscle run a course below the mucogingival junction opposite to the molars and along the oblique line ascending as the anterolateral rim of the ascending ramus. The attachments extend back into the pterygomandibular raphe. The buccinator is innervated by the buccal branch of the facial nerve. The muscle belongs to the mimetic muscle system and has a unique functional structure allowing for movement comparable to peristaltic motion. Its detachment can result in an impaired bolus transport.Reminder: The buccinator muscle belongs to the mimic muscle system and has a unique functional structure allowing for a movement comparable to a peristaltic motion. The deep fibers run in parallel bundles from the modiolus to the pterygomandibular raphe at the level of the occlusal plane (intercalar region) and account for the buccinator mechanism building up a ridge towards the occlusal plane. Its detachment can result in an impaired bolus transport out of the buccal space which can be annoying for the patient. The buccinator is innervated by the motor buccal branch of the facial nerve.

Muscles: Buccal fat pad

The buccal fat pad first described by Marie Bichat in 1801 is located in an extended three-dimensional compartment with its main mass or cheek portion overlying the posterolateral aspect of the buccinator muscle and the maxillary tuberosity, which is partly covered by the anterior border of the masseter muscle. The major processes of the fat pad stretch into deep temporal, pterygomaxillary and pterygoid region. The fat is distinct from facial fat and similar to orbital fat in consistency and its globule-like structure, to which it connects through the infraorbital fissure. The facial vessels run along the anterior border of the cheek portion. The fascial layers (capsule)

enveloping the buccal fat pad on the medial surface next to the buccinator muscle are rarely ruptured in a subperiosteal dissection along the mandibular body and angle. However, when going up the ramus subsequent to a vertical division of the buccinator muscle anterior to the pterygomandibular raphe in order to reach beyond the coronoid notch the inner capsule of the fat pad can be breached leading to a herniation that will obstruct the vision in the surgical field.

Bones: Bony cross sections and intraosseous structures

Tooth roots Mandibular canal/inferior alveolar nerve/no man’s land

See also:Heibel H, Alt KW, Wächter R, Bähr W. (2001)Cortical thickness of the mandible with special reference to miniplate osteosynthesis. Morphometric analysis of autopsy materialMund Kiefer Gesichtschir; 5(3):180-5.

Biomechanics of the mandible

Options

  Introduction   Muscle forces   Tension and compression zones   Hunting bow concept   Clinical findings

Introduction

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Biomechanics of the mandible is a complex topic. Forces applied to the mandible cause varying zones of tension and compression, depending on where the bite force is located. The superior portion of the mandible is designated as the tension zone and the inferior portion is designated as the compression zone.

Muscle forces

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The mandible is a hoop of bone that deforms with movement based on the origin and insertion of the muscles of mastication.

Tension and compression zones

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The superior border of the mandible is the tension zone and the inferior border is the compression zone.

Hunting bow concept

The mandible is similar to a hunting bow in shape, strongest in the midline (symphysis) and weakest at both ends (condyles). The most common area of fracture in the mandible is therefore the condylar region.

A blow to the anterior mandibular body is the most common reason for condylar fracture. The force is transmitted from the body of the mandible to the condyle. The condyle is trapped in the glenoid fossa. Commonly, a blow to the ipsilateral mandible causes a contralateral fracture in the condylar region. If the impact is in the midline of the mandible, fractures of the bilateral condylar region are very common.

Clinical findings

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Direct trauma to the TMJ area is unusual but may be associated with fractures of the zygomatic complex.

With a condylar fracture, there is very often shortening of the ramus on the affected side. This will result in an ipsilateral premature contact of the teeth. In case of bilateral fractures, the patient may present an anterior open bite. The condylar fragment may be displaced (most often laterally) based on the angulation of the fracture and predominant muscle pull.

Mandibulomaxillary fixation (MMF)

Options  Principles: general considerations   Arch bars: indications   Arch bars: general considerations   Arch bars: preparation   Arch bar: bar position   Arch bars: bar fixation   Arch bars: mandibulomaxillary fixation (MMF)   Other methods: Ernst ligatures   Other methods: bone supported devices

Principles: general considerations

Rigid fixation techniques in the dentate patient begin with fixation of the occlusion. This ensures that the patients maintain their preoperative occlusal status. There are several techniques to providing mandibulomaxillary fixation (MMF). Many surgeons agree that the gold standard in MMF is the use of arch bars. However, there are various methods of MMF to be used in specific clinical situations.

Common MMF methods are:

Arch bars (described in this document) Ernst ligatures (click here for a detailed description) Bone supported devices including intermaxillary fixation (IMF) screws, hanger plates

and interarch miniplates (click here to learn more about bone supported devices)

There other methods of wire fixation such as Ivy loops, Gilmer wiring, Stout wiring and Kazanjian buttons to name but a few.

Click here for the AO Teaching video on mandibulomaxillary fixation (MMF).

Arch bars: indications

Arch bars are preferred:

For temporary fragment stabilization in emergency cases before definitive treatment As a tension band in combination with rigid internal fixation For long-term fixation in conservative treatment For fixation of avulsed teeth and alveolar crest fractures

Arch bars: general considerations

There are important points to consider before starting.The occlusion must be checked. In the case of jaw malformations, such as a deep bite deformity, it may be impossible to use arch bars.There should be calculable tension forces on both bars, so the hooks should be symmetrically positioned in the upper and lower jaw. This symmetry is essential for functional training with elastics.

One pitfall when using arch bars is the risk of contamination of bloodborne infection from patients. Passing the wires to secure the arch bar can result in a puncture or tear in the surgeon’s glove and the possibility of disease transmission to the surgeon.

Arch bars: preparation

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Check occlusionBefore inserting the arch bars, check the occlusion. There should be full interdigitation of the teeth with regular contacts.

Determine if the patient has a normal occlusion or a preexisting malocclusion before taking the patient to the operating room.

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Adjusting the shapeThe prefabricated arch bar must be adjusted in shape and length according to the individual situation. The arch bar should not damage the gingiva.

Firstly, the bar is adapted closely to the dental arch. The bar should be placed between the dental equator and the gingiva.

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Trimming the barThe bar should be trimmed to allow ligation to as many teeth as possible. The bar should not extend past the most distal tooth or protrude into the gingiva as this will be an irritation to the patient.

Arch bar: bar position

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Symmetric bar positionTo achieve calculable tension forces on both bars, the hooks must be positioned symmetrically in the upper and lower jaw. This symmetry is essential for functional training with elastics.

Arch bars: bar fixation

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Ligature preparationTo fix the arch bar in place, prepare a ligature in the premolar region of each side. The wire ends should not damage the surrounding soft tissues.

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Attaching the barPosition the arch bar and fix it using the wire twister.

In the premolar and molar regions one end of the wire is above the arch bar and the other end below it.

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Wire endCut the wire with the cutter and turn the ends away from the gingiva to prevent damage.

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Make sure the wire rosettes do not protrude away from the arch bar as this will be an irritation to the patient.

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Photographs show arch bars applied to mandible and maxilla.

enlargeMandibulomaxillary fixation (MMF)

Arch bars: mandibulomaxillary fixation (MMF)

General considerationsMandibulomaxillary fixation (MMF) can be used either intraoperatively to establish the correct occlusion or as part of postoperative management of the patient’s injury. MMF may be accomplished with wires or training elastics depending on the overall treatment plan for this patient.

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With wiresThe wire loop is placed over the maxillary and mandibular lugs of the arch bar and the wire loop is tightened.

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MMF completed with wire fixation. At least three wires, a posterior wire loop in each side, and an anterior wire loop will provide stable fixation.

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ElasticsSome surgeons prefer MMF with elastics for intraoperative management of the occlusion. Additionally, postoperative training elastics can be used to manage condylar fractures in a closed manner.

Mandibulomaxillary fixation (MMF) - Ernst ligatures

 

TechniquePrinciplesLigature applicationFixation of occlusionFlexible occlusion

Other methodsArch barsBone supported devices

 

Click here for the AO Teaching video on mandibulomaxillary fixation (MMF).

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Principles

IndicationThe major indication for Ernst ligatures are temporary fixation prior to definitive operative treatment, and intraoperative MMF during surgery for simple fractures.

ContraindicationComminuted and displaced fractures and unstable, segmented fractures.Ernst ligatures do not provide adequate stability when dealing with complex fractures.

General considerations

There are important points to consider before starting: The occlusion must be checked. In patients with jaw malformations (dysgnathias) it may be impossible to use Ernst

ligatures. Mobile teeth should not be included in the ligatures. The ligatures of the upper and lower jaw must be in opposite, symmetric positions for

correct immobilization. There is a risk of contamination via wire puncture injuries from infected patients.

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Ligature application

General considerationAn Ernst ligature is based on two neighboring teeth in the same segment of one dental arch.

If possible, the premolars are used in the maxilla and mandible.

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Passing the wire through the interdental spaceUse a 0.4 mm wire of approximately 15 cm length.Pass one end of the wire through the interdental space between molar no. 6 and premolar no. 5.

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Thread it back from the lingual to the buccal side via the interdental space of premolars 4 and 5.

Other methods: bone supported devicesMandibulomaxillary fixation (MMF) - Bone supported devices

 

Technique

PrinciplesScrew designScrew placementMandibulomaxillary fixationAlternative: screws and plateAlternative: interarch miniplates

Other techniquesArch barsErnst ligatures 

Click here for the AO Teaching video on mandibulomaxillary fixation (MMF).

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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

enlargeBefore 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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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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Correct screw locationsVarious 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.

enlargeFor 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.

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

 

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

enlargeMandibulomaxillary 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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established.

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

enlarge… around the lower screw.

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

enlargeThe 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.

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

enlargeAlternative: 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.

enlargeAfter 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.

enlargeAlternative: interarch miniplates

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

Plate types

Options  General considerations   Mandible plates 2.0   Miniplates   Locking plates 2.0   Dynamic compression plates 2.4   Universal fracture plate 2.4   Locking reconstruction plates 2.4

General considerations

A large variety of plates are available for application to the mandible. Types of plates include:

Mandible plates 2.0 Locking plates 2.0 (Locking) reconstruction plates Dynamic compression plates Universal fracture plates

Plate names are commonly given together with a number (eg, locking plate 2.0) which indicates the diameter of screws to be used with the plate.

Note that there are different names internationally in use for the same plate. For example, with regard to the screw diameter, the number representing the screw diameter can either follow the plate name, eg, locking plate 2.0 or precede it, eg,2.0 locking plate. The latter is used throughout AO Surgery Reference.

Mandible plates 2.0

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Mandible plates 2.0 are available in various shapes and lengths but can only be used with nonlocking screws.

Miniplates

The term “miniplate” is a generic term and refers to all plates used in CMF surgery with a plate thickness of 1.3 mm or less. Therefore, small and medium profile locking plates 2.0 and mandible plates 2.0 are considered miniplates. Mandibular miniplates are designed to be used with monocortical screws. Bicortical screws maybe used for additional stability in some cases (with plate thickness being the limiting factor).

Locking plates 2.0

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Locking plates 2.0 are available in a variety of plate thicknesses (referred to as profile). All locking plates 2.0 can hold either locking head screws or standard (nonlocking) screws.

Locking plates 2.0 available are:

Small profile locking plate 2.0 Medium profile locking plate 2.0

Large profile locking plate 2.0 Extra-large profile locking plate 2.0

Click here  for further details on the locking plate principle.

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These illustrations show typical medium profile locking plates 2.0.

Dynamic compression plates 2.4

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This illustration shows dynamic compression plates 2.4. Screws inserted bicortically are needed when using 2.4 plates

Click here  for further details on the compression principle.

Universal fracture plate 2.4

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This illustration shows a universal fracture plate 2.4. They are designed to be used with bicortical screws. Universal fracture plates offer more biomechanical stability than DCP 2.4 plates

Locking reconstruction plates 2.4

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This illustration shows locking reconstruction plates 2.4 in various shapes. Reconstruction plates are used for load bearing osteosynthesis of mandibular fractures

Load bearing versus load sharing

Options  Introduction   Load-bearing osteosynthesis   Load-sharing osteosynthesis   Different levels of force distribution

Introduction

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There are two basic types of fracture fixation, load-bearing osteosynthesis (A) and load-sharing osteosynthesis (B).

Load-bearing osteosynthesis

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(stabilization by splinting)The plate bears the forces of function at the fracture site. This is accomplished with a locking reconstruction plate. Clinical uses are the management of atrophic edentulous fractures, comminuted fractures, defect fractures, and other complex mandibular fractures.

Load-sharing osteosynthesis

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General considerationStability at the fracture site is created by the frictional resistance between the bone ends and the hardware used for fixation. This requires adequate bony buttressing at the fracture site. Examples of load-sharing osteosynthesis include lag screw fixation technique and compression plating . Load-sharing osteosynthesis cannot be used with defect fractures or comminuted fractures, due to the lack of bony buttressing at the fracture site.

enlargeAnother form of load-sharing osteosynthesis is the miniplate fixation technique popularized by Champy. This is also known as functionally adequate fixation or semi-rigid fixation.

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Ideal lines of osteosynthesisChampy popularized the treatment of mandible fractures with miniplate fixation along the ideal lines of osteosynthesis. This is a form of load-sharing osteosynthesis to be applied in simple fracture patterns having an acceptable amount of bone stock.

Click here for a description of the biomechanics of the mandible.

Different levels of force distribution

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OverviewIn the load-bearing situation the plate assumes all the forces, in the load-sharing situation there are different levels of force distribution between the plate(s) and the bone.

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Load bearingIn load-bearing fixation the plate assumes 100% of the functional loads.

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This is an example of load-bearing osteosynthesis for the treatment of a defect fracture in the angular region. The osteosynthesis assumes all the masticatory loads while the bone graft matures and consolidates in a protected environment.

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Intermediate load-sharing situationIntermediate load-sharing situation where the osteosynthesis and the bone share the functional loads almost equally.

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This is an example of load-sharing osteosynthesis for the treatment of a simple angular fracture. The two miniplates share the loads with the bone in an anatomical region where the bone stock and force distribution are not ideal.

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Ideal load-sharing situationIdeal load-sharing situation where the bone assumes most of the functional loads.

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In this example a simple mandibular body fracture was considered suitable for a single miniplate osteosynthesis in the neutral zone because of the good bone stock and optimal force distribution.

Terminology

Options  Introduction   Fracture location   Complete versus incomplete   Fracture morphology   Other terms

Introduction

Six descriptors are commonly used to describe and categorize them:1. Location2. Complete versus incomplete3. Fracture morphology4. Open/compound versus closed/noncompound5. Displaced versus nondisplaced6. Mobile versus nonmobile

Fracture location

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Most clinicians generally subdivide the mandible into the following anatomic locations:

Symphysis and parasymphysis Body Angle and ramus Condylar process and head Coronoid process Alveolar process

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Multiple fractures

Multiple fractures are those involving more than one anatomical location of the mandible.

Complete versus incomplete

Complete fracturesFractures of the mandible in adults are usually complete so that they interrupt entirely the continuity of the mandibular arch. Such fractures are usually mobile and have various degree of displacement.

Incomplete fractures

On the other hand, incomplete fractures do not extend through both the buccal and the lingual cortices as well as the alveolar and basal borders. This occasionally occurs in adults but more often in children. In such cases, the fracture will be nondisplaced and nonmobile. The incomplete fracture might not therefore require surgical treatment and may be managed only by soft diet.

Fracture morphology

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The fracture morphology refers to the type of fragmentation (number of fragments and fracture lines) and the displacement.

Fractures fall into one of two categories:

Simple Complex

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Simple

Simple fractures are linear (one fracture line) resulting in two fragments.

Complex

Complex fractures involve at least two fracture lines and three or more fragments. Complex fractures include:

Basal triangle (wedge) fractures Segmental fractures Comminuted fractures Defect fractures

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Basal triangle (wedge) fracture

A basal wedge fracture involves a triangle of bone at the inferior border.

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Segmental fractures

Segmental fractures present two fracture lines, both being complete, within the same anatomic location.

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Comminuted fractures

Comminuted fractures involve multiple fracture lines in the same anatomic location resulting in multiple fragments of bone. The bone is often shattered in the area of fracture, with fracture lines running in three dimensions.

Many clinicians consider comminuted fractures as synonymous with multifragmentary fractures.

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Defect fractures

Defect fractures are characterized by a loss of bony structure at the fracture site.

Other terms

Open or closed

Intraoral and facial soft tissues adjacent to a fracture can be involved in the injury.

When the fracture site communicates either intraorally through the mucosa or periodontal ligament, or extraorally through a laceration or avulsive injury of the overlying skin, the fracture is considered as open. Therefore all fractures involving the tooth-bearing areas of the jaws are considered as open fractures.

The terms open fractures and compound fractures are synonymous.

The soft tissues (intra and extraoral) adjacent to a closed fracture are intact.

Displacement

Fractures can be considered displaced or nondisplaced depending on the relationship of the fracture ends. A fracture is displaced if the fragments are not perfectly anatomically aligned.

Displacement is grossly graded as minimal, moderate and severe. Nevertheless, there is no universally accepted definition for these terms.

The importance of “displacement” is that the more displaced the fracture, the more likely it is to be mobile and contaminated when open.

The terms dislocated, subluxated, and luxated are used to describe the abnormal relationship of the articular surfaces of the condyle and glenoid fossa to one another. These terms are synonymous. Some surgeons consider them a subcategory of displacement.

Mobile versus nonmobile

The first five fracture characteristics can all be gleaned from the x-rays. The sixth characteristic, fracture mobility, can be inferred in many cases from the x-rays when there is displacement, but is really a clinical descriptor that requires the clinician to use both hands, one on either side of the fracture, to feel for mobility.

Mobile fractures are more painful to the patient because any movement of the mandible such as in speaking, eating or swallowing creates discomfort.

Specific Surgical treatment of Mandible fracture:

1. Symphysis and parasymphysis, simple Closed treatment

Closed treatment of simple fractures is still well accepted as an alternative to open treatment.

Indications for closed treatment may include:

Nondisplaced or minimally displaced fractures in a patient who accepts MMF Patient refusal of operative treatment (eg, for religious/cultural or financial reasons) Conditions making open reduction and internal fixation difficult:

■ Massive edema/hematoma■ Medically unstable patient who can not be treated under local anesthetic or a very short general anesthesia, etc.■ Underlying bleeding disorder■ Anticoagulation treatment that cannot be reversed■ Premorbid or instable medical condition preventing general anesthetic■ Associated mandibular injuries (such as alveolar fractures) limiting open treatment and plate fixation

Unavailability of plates and screws

Closed treatment

1Treatment

2Case example

1 Treatment

Arch bars are applied to the teeth and MMF is secured. The patient is monitored using x-rays for positional changes of the mandibular ramus. At 6 weeks MMF is released and fracture stability determined by manipulation. The patient is placed on a soft diet and if the occlusion maintains for a two-week period, the arch bars may be removed.

2 Case example

Diagnosis

Panoramic and PA view of a minimally displaced comminuted symphyseal/body fracture in an adolescent patient.

Note: treatment of a simple or a basal triangle fracture would be no different.

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Pretreatment occlusal relationshipA malocclusion is the result of this minimally displaced comminuted symphysis/body fracture.

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Treatment

Closed treatment was selected for this patient mandibulomaxillary fixation (MMF) because the extended area of comminution would have required a large reconstruction plate being placed.

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The patient did not object to a course of MMF and did not want a larger operation.

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Postoperative x-rays

"Postoperative" x-rays following closed treatment and MMF show good alignment of bone fragments and reestablishment of occlusion.

Aftercare following closed treatment of mandibular fractures

The patient should be instructed how to release the MMF in case of emergency. Some surgeons prefer to provide wire cutters to the patient for the period of MMF. During this period, wire fatigue and loosening can occur. The patient should report any loosening of the MMF to the surgeon immediately.

As an alternative, the MMF may be achieved by using elastics instead of wires. With an adequate number of elastics, the same level of reliability can be reached minimizing the risk of accidents during an emergency situation.

Postoperative x-rays are taken within the first days after surgery. In an uneventful course, follow-up x-rays are taken prior to releasing the MMF.

It will be necessary to see the patient approximately 1 week postoperatively to assess the stability of the occlusion and to check for infection of the surgical wound. The intermaxillary fixation wires or elastics must be assessed and proven to hold the patient tightly in occlusion. Patients also have to be periodically re-examined to rule out signs of infection. At each visit, the surgeon must evaluate patientability to perform adequate oral cleaning. It may be necessary to provide additional instruction to assure appropriate hygiene and wound care.

Adequate dental care is required in most patients having suffered a mandibular fracture.

There should be no malocclusion detected as occlusion is determined and secured in the operating room.

On releasing the MMF, physiotherapy can be prescribed. The mandible will be hypomobile after the period of MMF, and the muscles will be atrophic and “tight.” Opening and excursive exercises should be demonstrated and implemented. Goals should be set, and typically, 40 mm of maximum interincisal mouth opening should be attained by 4 weeks postoperatively. If the patient cannot fully open his mouth, additional passive physical therapy may be required such as Therabite or tongue-blade training.

MMF renders eating, speaking and oral hygiene more difficult. Patients will therefore have to follow three basic instructions:

1. DietThe diet has to be in a liquid or semi-liquid form. For patients with a full complement of teeth, the diet must be more liquefied than when there are gaps with teeth missing. Because the diet will be no-chew, more fluids are required to assist in swallowing the food. A blender, or preferably, a juicer is useful. Anything can be made into a liquid or semi-liquid form with these tools. Liquid dietary supplements from the grocery store help maintain caloric intake. The patient should monitor their body weight on a weekly basis during the period of MMF to evaluate any dramatic changes.

2. Oral hygienePatients must be instructed in oral hygiene procedures. The presence of the arch-bars and MMF wires makes this a much more difficult procedure, and the inside of the teeth cannot be reached with a toothbrush. A soft toothbrush (dipping in warm water makes softer) should be used to clean the buccal/labial surfaces of the teeth, arch-bars and wires. Chlorhexidine oral rinses should be prescribed and used at least 3 times each day to help sanitize the mouth. The tongue can be used to swipe the lingual surfaces of the teeth. With larger debris, a 1:1 mixture of

hydrogen peroxide/chlorhexidine can be used. The bubbling action of the hydrogen peroxide helps remove debris. A Waterpik® is a very useful tool to help remove debris from the wires.

3. SpeechPatients are told to speak as freely as possible. Over the course of 1–2 weeks, patients can usually speak quite intelligibly, although voice projection remains difficult during the period of MMF.

2. Symphysis and parasymphysis, simple ORIF

Open reduction internal fixation (ORIF) is usually the method of choice for simple symphyseal fractures in order to avoid the drawbacks and inconveniences of MMF in the majority of patients.

It is recommended in all displaced fractures and noncompliant patients.

3. Symphysis and parasymphysis, simple Two lag screw fixation

The anterior mandible, from mental foramen to mental foramen, is uniquely suited to the application of lag screw fixation for three reasons:

The most important reason is the curvature of the anterior mandible. This allows placement of lag screws across the symphysis, from one side to the other for sagittal fractures, and from anterior to posterior for oblique fractures.

The mandible is well suited to lag screw fixation due to the thickness of the bony cortices which provides extremely secure fixation when the screws are properly inserted, providing interfragmentary compression.

There are no anatomical hazards below the apices of the teeth until the mental foramina are encountered.

Sagittal fractures where a minimum of two lag screws can be placed from one side of the symphysis to the other, extending from one buccal plate to the buccal plate on the opposite side of the fracture.

Oblique fractures where a minimum of two lag screws can be placed from the buccal to the lingual cortices.

The advantages of the lag screws over plate fixations are:

1. Rapid application with a high level of stability.2. Perfect bony reduction after interfragmentary compression.3. Lower cost compared to plate and screw fixation.4. Intraosseous location avoiding palpability.

Disadvantages are:

Technically demanding

Difficult implant removal (if needed)