SURGICAL ANATOMY

SURGICAL ANATOMY OF THE MANDIBLE AND PRINCIPLES IN TREATMENT OF MANDIBULAR FRACTURES

The mandible is basically a tubular long bone which is bent into a blunt V shape, and is composed of the body and 2 rami, with their junction or angle forming the prominent gonion. The angle formed varies from 110 to 140C with a mean of 125. The angle changes slightly during growth, during the condylar changes, shape and size and the angle becomes more obtuse.

The body is V-shaped has an external and internal cortical surfaces. The external cortical plate is thickest at the mental protuberance and in the 3rd molar region. There is also a thickened triangular mental protuberance bounded laterally by the mental tubercles.

The mental foramen is located on the external surface in relation to root apices of 1st and 2nd premolars, and variations are present. The opening is directed backward and laterally and transmits the mental nerve and vessels. After total extraction due to extreme atrophy, the mental foramen almost comes at the margin of the crest of the ridge.

The external oblique line runs from just inferior to the mental foramen, posteriorly and superiorly to the ascending ramus.

The internal cortical surface is elevated in the midline near the inferior border by the mental spine. 2 pairs of discrete bone prominences are also seen here, called genial tubercles, which represent the origin of the geniohyoid muscle (inferiorly) and genioglossus muscle (superiorly).

Running upwards and backwards is the oblique ridge, i.e. the mylohyoid line, representing the attachment of the mylohyoid muscle. Below this is a shallow depression, the submandibular fossa, and superiorly and anteriorly is the sublingual fossa.

The ramus is quadrilateral structure. The lateral surface in the region of the angle may be rough and thickened by the insertion of the masseter. On the medial surface is the mandibular foramen, which leads downwards and forwards, into the mandibular canal and transmits the inferior alveolar nerve and vessels. The lingula is a medial bony projection to which the sphenomandibular ligament is attached. The mylohyoid groove starts from the lingula, and runs anteriorly and inferiorly to the submandibular fossa. Below this is a roughened area created by insertion of the medial pterygoid muscle.

The mandibular notch is located on the superior edge of the ramus bounded anteriorly by the coronal process and its temporalis attachment, and posteriorly by the neck and head of the condyle.

The condylar head is a semi-cylindrical process 15-20mm long and 8-10mm thick. The long axis of the condyle is related to the position of the ramus, and not to the skeletal or frontal plane. The angle formed by the two condylar axes varies from 145-160. The articulating surface of the condyle faces superiorly and forwards, giving the condylar neck an appearance of being bent forwards. When viewed anteriorly, the condylar head projects significantly medial to the inner surfaces of the ramus but less so laterally.The body of the mandible supports the alveolus and dental structure. The body and alveolus have dense outer and inner cortices with central spongy/cancellous bone.

As with all tubular bones, strength resides in its dense cortical plates. The cortical bone is thicker anteriorly and at the lower border, while posteriorly the lower border is extremely thin. The central cancellous bone of the body forms a lose network with frequent large bone free spaces, so the mandible is strongest anteriorly in the midline, with progressively less strength towards the condyles.

The mandible differs from all other long bones in 2 important respects:A. Any movement inevitably causes both condyles to move with respect to the skull base.

B. Although anatomically condyles are the articular surfaces of the mandible, functionally the occlusal surface of mandibular teeth subserves this role.

The periodontal ligament and bone alveolus also combine with the trabecular pattern in the cancellous bone and are directed in a parallel fashion upto the ramus to transmitpressures upto the condylar region. The thickening of the inner aspect of the condylar neck or crest of the neck apparently acts as a main buttress of the mandible as it transmits pressure to the TMJ and base of the skull.

The temporal crest runs from the coronoid process to the retromolar triangle distal to the terminal molar.

In children, the body of the mandible is weakened by the presence of developing buds of permanent teeth, but naturally protected due to the resiliency of the base.

Dingman and Grabb (1962) investigated the distribution of the mandibular branch of the facial nerve in relationship to the angle of the mandible and the overlying deep cervical fascia.

Following the dissection of the mandibular branch of the facial nerve in 100 cases, the principal conclusions were as follows:

1. In 81% of cases the nerve, posterior or proximal to the point where the facial artery crossed the mandible, passed above the inferior border.

2. In the remaining 19% the nerve described a downward arc, the lowest point of which was 1cm below the inferior border.

3. In 98% of cases the mandibular branch passed over the superficial surface of the posterior facial vein and could readily be identified at this site. 100% of cases showed that the nerve passed superficially to the anterior facial vein. The nerve lay superficial to the facial artery, being situated immediately anterior or posterior to the vessel, and not infrequently upon the artery. The submandibular lymph node lay immediately posterior to the artery, was constant in position and was a useful landmark.

4. The mandibular and buccal branches anastomesed in only 5% of cases.

5. The mandibular ramus consisted of two branches in 67% of specimens; a single branch in 21%; a triple branch in 8% and four or more in 3% of the dissection performed.

The facial artery lies immediately beneath the deep cervical fascia and can be observed pulsating beneath this layer.Strength of mandible:

Bones fracture at sites of tensile strain, since their resistance to compressive forces is greater.

Areas of Weakness (Vulnerable for Fracture):1. The junction of the alveolar bone and basal mandibular bone creates a line of weakness. Dentoalveolar fractures can be seen independently without or with the fracture of basal bone.

2. Symphysis region is formed by the bony union of two halves in the center at first year of life. Symphysis fracture is seen at this line of weakness.

3. Parasymphysis region lateral to the mental prominence is a naturally weak area susceptible for parasymphyseal fracture. This is because of the presence of the incisive fossa and mental foramen.

4. The body of the mandible is considerably thicker than the ramus and the junction of these two portions constitutes a line of structural weakness.

5. Strength of the lower jaw also varies with the presence or absence of teeth. The presence of impacted lower third molars or excessive long roots of canines make the area more vulnerable for fracture. With the age, the loss of the teeth and resorption of alveolar bone leads to a decrease in the vertical height of the mandible, making it prone to fracture.6. The slender neck of the mandibular condyle renders it particularly liable to fracture as a result of direct violence applied to the chin. This anatomical weakness actually acts as a safety mechanism, as a fracture of the neck of the condyle prevents injury to the middle cranial fossa.Blood Supply1. Central blood supply through the inferior alveolar artery.2. Peripheral blood supply through the periosteum. When a fracture of the mandible occurs, blood vessels involved in the line are torn, resulting effusion of blood into surrounding tissues producing ecchymosis and hematoma formation. If the periosteum on the lingual side is torn, it can lead toward sublingual hematoma. The intact periosteum maintains the collateral blood supply.

In the severely atrophic mandible, there is greater dependence on periosteal blood supply than the central supply. Therefore, if open reduction is planned, stripping of the periosteum in such cases should be kept to a minimum.

Nerve Supply

Damage to the inferior alveolar nerve after fracture, results in the paraesthesia or anaesthesia of the lower lip on the affected side.

Muscle Action1. The muscles of facial expression, which are attached on the outer aspect of the anterior part of the mandible and which are inserted into the skin, exert no effect on the displacement of the fragments following mandibular fracture.

2. The muscles originating from the inner aspect of the mandible, the mylohyoid, geniohyoid, genioglossus and anterior belly of digastric exert their effect in centripetal manner. The fractured fragments, therefore, tend to collapse posteriorly or medially.

3. The lateral pterygoid muscle is inserted into the medial fossa on the anterior aspect of the condyle. Therefore, in condylar fractures, the head is displaced anteriorly and medially and may also undergo lateral rotation due to the spasm of the muscle.4. The mandible anterior to a line passing through the anterior margin of the masseter muscle, is influenced by the depressor group of muscles, while the ramus is influenced by the elevator group.Muscles of Mastication:

These are the muscles which:

1. Inserted to the ramus of mandible.

2. Supplied by mandibular nerve.

3. Developed from first pharyngeal arch.

4. Helps in mastication and speech.

It includes:

1. Masseter.

2. Temporalis.

3. Lateral pterygoid.

4. Medial pterygoid.

Masseter: It is a quadrilateral muscle of mastication.

Origin:

1. From lower border and outer surface of zygomatic process of temporal bone.

2. Lower border of temporal process of zygomatic bone.

3. Lower border of body at zygomatic bone.

Insertion: To the lower 2/3rd of lateral surface of ramus of mandible.

Action:

1. Elevates the mandible to close the mouth.

2. Protracts the mandible.

3. Maintains occlusal position of mandible.

4. Helps in mastication and speeh.

Temporalis: It is a fan shaped muscle of mastication.

Origin:

1. Floor of the temporal fossa of skull.

2. Inferior temporal line.

3. From the temporal fascia covering the muscle.

Insertion: To the coronoid process and anterior border of ramus of mandible.

Action:

1. It elevates the mandible to close the mouth.

2. Posterior fibres retract the mandible.

3. It maintains the occlusal position of mandible.

4. Helps in mastication and speech.

Lateral pterygoid: It is present in the infra temporal fossa.

Origin: It has two head:

a. Upper head: arises from infra temporal crest and infra temporal surface of greater wing of sphenoid band.

b. Lower head: arises from lateral surface of lateral pterygoid plate.

Insertion:

To the anterior side of neck of mandible (pterygoid fovea) some of the fibres continue as articular disc of temporo mandibular joint.

Nerve supply: Nerve to lateral pterygoid branch of anterior division of mandibular nerve.

Action:

1. Protracts the mandible.

2. Decreases the mandible to open the mouth.

3. Helps side to side movement of mandible.

4. Helps in mastication and speech.

Medial pterygoid: It is present in the infra temporal fossa.

Origin: It has two heads:

a. Superficial head: arises from the maxillary tuberosity.

b. Deep head : Arises from medial surfaces of lateral pterygoid plate.

Insertion: Inner surface of angle of mandible.

Action:

1. Elevates the mandible to close the mouth.

2. Protracts the mandible.

3. helps side to side movement of mandible.

4. Helps in mastication and speech.

MANDIBULAR FRACTURES

Fractures of the mandible are common in patients, who sustain facial trauma.

Study conducted by Hang et al in 1983, showed the ratio of 6:2:1 of mandibular, zygomatic, maxillary fractures incidence respectively. Approximately two-thirds of all facial fractures are the mandibular fractures (nearly 70%) Tables 1 & 2).

Sex: most mandibular fractures are seen to occur in male patients. Ratio is approximately 3:1.

Age: thirty-five per cent of mandibular fractures occur between the age of 20 to 30 years.

ETIOLOGY AND INCIDENCE OF MANDIBULAR FRACTURES

The causes of fracture mandible are chiefly RTA, interpersonal violence, falls, sporting injuries, and industrial trauma. Rarely it may occur from missile injuries in war situations.

These factors again are influenced by:

Geography.

Social trends.

Road traffic legislation.

Seasons.

a. Injuries caused by fights were more common in rural areas. Whereas in urban areas, RTAs are the most common causes.

b. In urban areas, especially in the recent years, interpersonal violence has accounted for an increased proportion of mandibular fractures.

c. Vehicle design has been influenced both by research and legislation, and in some countries, use of seatbelts is mandatory, which has resulted in a dramatic decrease in injury in general and severe injury in particular. This trend has been reflected in the incidence of facial injury. Enforced low speed limits do not appear to carry the same benefit as far as mandibular fractures are concerned.

d. Seasonal variation is seen in most temperate zones which reflects the increased traffic and increased urban violence in summer months, and adverse road conditions in presence of snow/ice in winter.

Incidence regarding site of mandibular fractures varies a lot, Dingman and Natvigs classification of mandibular fracture by anatomic region.

Body

- 22%

Condyle - 29%

Angle -25%

Symphysis -16%

Ramus -4%

Coronoid -1%

Parasymphysis - 16%

Dentoalveolar - 3%

Generally, incidence of body, condylar and angle fractures do not vary much and fractures of ramus and coronoid process are rare.

Classification

There are several ways to classify the mandibular fractures.

i. General classification.

ii. Anatomical locations.

iii. Relation of the fracture to the site of injury.

iv. Completeness.

v. Depending on the mechanism.

vi. Number of fragments.

vii. Involvement of the integument.

viii. The shape or area of the fracture.

ix. According to the direction of fracture and favourability for the treatment.

x. According to presence or absence of teeth.

xi. AO classification relevant to internal fixation.

1. Krugers General Classification

Simple or closed: The linear fracture which does not have communication with the exterior. Such a fracture does not produce a wound open to the external environment either through the skin, mucosa or periodontal membrane. It may or may not be displaced.

Examples Fractures in the region of the condyle, coronoid process, ascending ramus, etc.

Compound or open This fracture has communication with the external environment through skin, mucosa or periodontal membrane. All the fractures involving the tooth bearing area of the mandible or where an external or intraoral wound is present involving the fracture line.

Comminuted A fracture in which the bone is splintered or crushed into multiple pieces. These types are generally due to a greater degree of violence or high velocity impact. Gunshot wounds, where missiles are traveling at a high velocity can produce these fractures.Complicated or complex Fractures associated with the damage to the important vital structures complicating the treatment as well as prognosis.

Example: Fracture with injury to the inferior alveolar vessels or nerve, facial nerve or its branches, facial vessels, condylar fractures with associated injuries to middle crania fossa, etc.Impacted Rarely seen in mandibular fractures. More commonly seen in maxilla. This is a fracture in which one fragments is firmly driven into the other fragment and clinical movement is not appreciable.

Greenstick A fracture in which one cortex of the bone is broken with the other cortex being bent. It is an incomplete fracture seen in young children because of inherent resiliency of the growing bone.

Pathological Spontaneous fracture of the mandible occurring from mild injury or as a result of a normal degree of muscular contraction. This is because of weakness caused due to the pre-existing bone pathology.

Areas of structural weakness may result from the following:

a. Generalized skeletal disease:

i. Endocrinal disorders Hyperparathyroidism or postmenopausal osteoporosis.

ii. Development disorders Osteopetrosis, osteogenesis imperfecta.

iii. Systemic disorders Reticuloendothelial disease, Pagets disease, osteomalacia and severe anaemia.

b. Localized skeletal disease Various cysts, odontomoes, tumours, osteomyelitis, osteoradionecrosis affect the local region.

2. Anatomical LocationRow and Killeys classification

A. Fractures not involving the basal bone are termed as dentoalveolar fractures.

B. Fractures involving the basal bone of the mandible.

Subdivided into following:

ii. Single unilateral.

iii. Double unilateral.

iv. Bilateral.

v. Multiple.

Dingman and Natvigs classification by anatomic region:

A. symphysis fracture (midline fracture).

B. Canine region fracture.

C. Body of the mandible between canine and angle.

D. Ramus region bounded by the superior aspect of the angle to two lines forming an apex at the sigmoid notch.

E. Coronoid region.F. Condylar fractures.

G. Dentoalveolar region.

3. Relation of the Fracture to the Site of injuryii. Direct fractures.

iii. Indirect (countercoup)fractures.

4. Completeness

Complete and incomplete fractures.

5. Depending on the mechanism

ii. Avulsion fracture.

iii. Bending fracture.

iv. Burst fracture.

v. Countercoup fracture.

vi. Torsional fracture.

6. Number of Fragments:

Single, multiple, comminuted, etc.

7. Involvement of the integument

Closed or open fracture.

Grades of severity I-V

8. Shape or area of the Fracture

Transverse, oblique, butterfly, oblique surfaced.

9. According to the Direction of Fracture and Favourability for treatment b. Horizontally favourable fracture.

c. Horizontally unfavourable fracture.

d. Vertically favourable fracture.

e. Vertically unfavourable fracture.

This classification is aimed toward the angle fractures. Here, the direction of fracture line is important for resisting the muscle pull. When the muscle pull resists the displacement of the fragments then the fracture line is considered as favourable. If the muscle pull distracts the fragments away from each other, resulting in displacement, then the fracture line is considered as unfavourable.

a. When the fracture line passes from the alveolar margin, downward and forward, then upward displacement of the posterior fragment is prevented by physical obstruction caused by the body of the mandible. Hence, such a fracture line is termed horizontally favourable.

b. If, on the other hand, the line of the fracture passes downward and backward, then the upward movement of the posterior fragment is unopposed. This type of fracture is termed horizontally unfavourable.c. The fracture line which passes from the outer or buccal plate obliquely backward and lingually, will tend to resist the muscle pull and is thus termed a vertically favourable type of fracture.d. When the fracture line pass from the inner or lingual plate obliquely backward and buccally, inward movement of the posterior fragment will take place as a result of the medial pterygoid muscle pull. This type of fracture is termed vertically unfavourable.

This classification is of clinical importance for the treatment planning and fixation, the amount of displacement can be judged and the type of fixation device can be chosen.

10. According to Presence or Absence of Teeth in Relation to the Fracture lineIt is very essential to note the presence or absence of teeth in relation to the fracture line, also the periodontal status as well as teeth size also matters for planning fixation method.

Kazanjian and converse classificationClass I when the teeth are present on both sides of the fracture line.

An adequate number of teeth of suitable shape and stability. Wiring direct, continuous or multiple loop or interdental eyelet type, use of prefabricated arch bars.

Class II When the teeth are present only on one side of the fracture line.

b. Short edentulous posterior fragment

ii. If favourable, immobilization of main fragment by interdental wiring or arch bars. Minor displacement can be accepted.

iii. If unfavourable open reduction with direct fixation is a must.

c. Long edentulous posterior fragment:

i. Without displacement conservative treatment.

ii. With vertical and medial displacement requires open surgical reduction and fixation.

Class III When both the fragments on each side of the fracture line are edentulous.

i. Simple or compound fracture without much displacement in the body region. Simple Gunning type splints.

ii. Simple fractures which are unfavourable. Open reduction and fixation.

iii. Compound fractures. Surgical intervention.

11. AO Classification (Relevant to Internal Fixation)1. F: Number of fracture or fragments.

2. L: Location (site) of the fracture.

3. O: Status of occlusion.

4. S: Soft tissue involvement.

5. A: Associated fractures of the facial skeleton

Such a classification is helpful in terms of:

Patient selection and treatment planning.

Evaluation of therapeutic results.

Comparison of different treatment methods.

Information and communication.

These criteria can be objectified clinically and radiographically:1. F: Number of fracture.

F0: Incomplete fracture.

F1: Single fracture.

F2: Multiple fracture.

F3: Comminuted fracture.

F4: Fracture with a bone defect.

2. Categories of localization (site) L1-L8

L1: Precanine.

L2: Canine.

L3: Postcanine.

L4: Angle

L5: Supra-angular

L6: Condyle

L7: Coronoid.

L8: Alveolar process

3. Category of occlusion O0-O2

O0: No malocclusion.

O1: Malocclusion.

O2: Non existent occlusion Edentulous mandible.

4. Categories of soft tissue involvement S0-S4

The risk of infection and healing depends on the condition of the soft tissues surrounding the fracture.

S0: Closed.

S1: Open intraorally.

S2: Open extraorally.

S3: Open intra and extraorally.

S4: Soft tissue defect.

5. Categories of associated fractures A0-A6

A1: Fracture and / or loss of tooth.

A2: Nasal bone.

A3: Zygoma.

A4: LeFort I

A5: LeFort II

A6: LeFort III

Grades of severity I-V

Grade I and II are closed fracture.

Grade III and IV open fractures.

Grade V open fracture with a bony defect (gunshot).

GENERAL PRINCIPLES IN THE TREATMENT OF MANDIBULAR FRACTURESThe patients general physical status should be carefully evaluated and monitored prior to any consideration of treating mandibular fractures.

It is all too easy for the clinician to focus on an obvious isolated mandibular fracture without noting a fractured cervical spine, subdural hematoma, pneumothorax or ruptured spleen.

Diagnosis and treatment of mandibular fractures should be approached methodically, not with an emergency-type mentality.Patients rarely die of mandibular fractures, so the clinician has time to carefully and thoroughly evaluate the nature and extent of mandibular injuries. Diagnosis on the basis of the history and local physical and radiologic examination should be expedited in an orderly, efficient manner, and treatment should be instituted in a controlled environment and fashion.Dental injuries should be evaluated and treated concurrently with treatment of mandibular fractures. Teeth are often injured with mandibular fractures, and although the teeth may not have to be restored immediately, dental knowledge is vitally important in determining which teeth can and should be maintained.

Reestablishment of occlusion is the primary goal in the treatment of mandibular fractures.With multiple facial fractures, mandibular fractures should be treated first. The old adage inside out and from bottom to top applies to the proper sequence to follow when treating facial fractures. To build a foundation on which the facial bones can be laid, it is proper that the mandible be reconstructed first.

Intermaxillary fixation time should vary according to the type, location, number, and severity of the mandibular fractures as well as the patients age and health and the method used for reduction and immobilization.

Historically, a period of 6 weeks of intermaxillary fixation has been used to allow healing to occur. However, this time is only empirical and should vary with the patient and the clinical situation.

Prophylactic antibiotics should be used for compound fractures.

Numerous studies in the literature demonstrate the advantages of antibiotics in the management of compound mandibular fractures and despite the number of new antibiotics, penicillin remains the agent of choice.

Nutritional needs should be closely monitored postoperatively.

Excellent reduction and fixation techniques may fail in a patient who has undergone significant weight loss and a catabolic nutritional status.

Most mandibular fractures can be treated by closed reduction.

With the current enthusiasm for open reduction and rigid fixation in the treatment of mandibular fractures, it is important to remember that closed reduction techniques have a long history of success. Although open techniques have advantages, such as more exacting bone fragment reapproximation and earlier return to function by the patient, significant disadvantages exist as well). Prolonged anesthesia, may increase the risk of infection, metal rejection, damge to adjacent teeth and nerves, intraoral or extra oral scarring and increase hospitalization time and cost.

Basic Principles of Treatment of a Fracture1. Reduction.

2. Fixation.

3. Immobilization.

Aims:

i. Satisfactory facial form.

ii. Satisfactory functional occlusion.

iii. Satisfactory post-treatment range of movement of the jaw.

iv. No second surgery for facial recontouring or malocclusion.

v. No bone grafting.

Reduction: Restoration of the fractured fragments to their original anatomical position. The restoration of the fragments to their correct position may be brought about by:a. Closed reduction (Alignment without visualization of the fracture line).

i. Reduction by manipulation.

ii. Reduction by traction.

No surgical intervention is needed in closed reduction. Fracture fragment alignment can be done without surgery. Occlusion of the teeth is used as a guiding factor.

Advantages and disadvantages of closed reduction:Advantages:

Inexpensive.

Only stainless steel wires needed (usually arch bars also).

Easy availability, convenient.

Short procedure, stable.

Gives occlusion some leeway to adjust itself.

Generally easy, no great operator skill needed.

Conservative, no need for surgical tissue damage.

No foreign object or material left in the body.

No operating room needed in most cases, outpatient treatment. Callus formation (secondary bone healing) allows bridging of small bony gaps.

Disadvantages: Cannot obtain absolute stability (contributing to nonunion and infection).

Non compliance from patient due to long period in IMF. Difficult (liquid) nutrition.

Complete oral hygiene impossible.

Possible temperomandibular joint sequelae.

Muscular atrophy and stiffness.

Denervation of muscles alteration in fibre types.

Myofibrosis.

Changes in temperomandibular joint cartilage.

Weight loss.

Irreversible loss of bite force.

Decrease range of motion of mandible.

Risks of wounds to operators manipulating wires.

The closed reduction can be achieved either by manipulation or by traction method:i. Reduction by manipulation: When the fractured fragments are adequately mobile without much overriding or impaction and the patient comes for treatment immediately after trauma (fresh fractures), then the digital or hand manipulation for reduction can be used. Specially designed instruments for grasping the fragments are available (Disimpaction forceps, bone holding forceps). It can be done under LA with sedation or under GA depending on the need of the patient.ii. Reduction by traction:

a. Intraoral traction method.

b. Extraoral traction method.

In intraoral traction method, prefabricated arch bars are attached to maxillary and mandibular dental arches by means of interdental wiring. Here the fractured fragments are subjected to gradual elastic traction by placing the elastics, from upper to lower arch bars in a definite manner and direction depending on the fracture line. In extraoral traction method, anchorage is taken usually from the intact skull of the patient and different types of head gears are used for various attachments, coming down over the face and connected to the arch bars by elastic and wires. Whenever the traction method is used, patient is encouraged to open and close the mouth slowly, so that the elastic traction starts functioning. Patient should be kept on analgesics for pain control, so that the elastic traction can be smooth. Once the proper occlusion is achieved, then the elastics are replaced by wires to carry out intermaxillary fixation or ligation (IML or IMF). It is also known as MMF (Maxillo-mandibular fixation). After the elastic traction is given, then the patient should be observed for the period of 12 to 24 hours. At the end of 48 hours, if satifactory occlusion is not achieved, then open reduction is opted for. b. Open reduction (surgical reduction allows visual identification of fractured fragments).Advantages and disadvantages of open reduction with rigid internal fixation.

Advantages:

Early return to normal jaw function.

Normal nutrition.

Normal oral hygiene after a few days.

Avoidance of airway problem.

Can get absolute stability, promotes primary bone healing.

Bone fragments re-approximated exactly by visualization.

Avoids IMF for patient with occupational benefits in avoiding mandible fixation e.g. Lawyers, teacher, sale people, seizure disorders.

Helpful in special nutrition requirements (diabetics, alcoholics, psychiatric disorders, pregnancy).

Easy oral access (for example in intensive care unit patients).

Decreased patient discomfort, greater patient satisfaction.

Less myoatrophy.

Decreased hospital time.

Substantial savings in overall cost of treatment.

Lower risk of major complications.

Lower infection rates, improved overall results.

Lower rate of malunion/nonunion?

Disadvantages:

Most obvious; need for an open procedure.

Significant operating room time.

Prolonged anaesthesia.

Expensive hardware.

Some risk to neuromuscular structure and teeth.

Need for secondary procedure to remove hardware.

Unforgiving procedure, the rigidity of the plate means no manipulation is permissible.

Need much operator skill, meticulous technique needed.

Higher frequency malocclusion.

Higher frequency facial nerve palsy.

Scarring (extraoral and intraoral).

No bridging of small bone defect (absence of callus)

Fixation: In this phase the fractured fragments (after reduction) are fixed, in their normal anatomical relationship to prevent displacement and achieve proper approximation. Fixation devices can be placed internally or externally.

a. Direct skeletal fixation Consists of: i) external direct, skeletal fixation, where the device is outside the tissues, but inserted into the bone percutaneously or (ii) internal direct skeletal fixation by devices which are totally enclosed within the tissues and uniting the bone ends by direct approximation. In external direct fixation, bone clamps or pin fixation can be used, while internal direct skeletal fixation is carried out with transosseous or intraosseous wiring or using bone plating system.

b. Indirect skeletal fixation. Here, the control of bone fragments is done via the denture bearing area. By means of arch bars and IML or Gunning splint, if the patient is edentulous. It can be extraoral or intraoral method.

Immobilization:During this phase, the fixation device is retained to stabilize the reduced fragments into their normal anatomical position, until clinical bony union takes place. The fixation device is utilized for a particular period to immobilize the fractured fragments. Immobilization period will depend on the type of fracture and the bone involved. For maxillary fractures 3 to 4 weeks of immobilization period is sufficient, while for mandibular fracture it can vary from 4 to 6 weeks. In condylar fracture the recommended immobilization periods is 2-3 weeks only, for prevention of ankylosis of TMJ.Next steps: Are prevention of infection and gradual rehabilitation of function.

In the teeth bearing region of the jaws, any fracture reduction is guided by checking the occlusion of the teeth.

Different types of dental wiring techniques:

i. Essigs wiring.

ii. Gilmers wiring.

iii. Risdons wiring.

iv. Ivy eyelet wiring.

v. Col. Stouts multiloop wiring.

Armamentarium for wiring:

Presterilized 26 gauge stainless steel wire spool or wires cut into lengths of 20cm each. The wires should be prestretched about 10 per cent to prevent loosening after fixing it to the teeth.

Arch bars

Many types of prefabricated arch bars are available. But the most popular one and commonly used is the

1) Erich arch bar; 2) Jelenko; 3) German silver bars.

Custom made splints

Custom made appliances are fabricated for individual patient. The splints can be constructed using acrylic material or cast metal.

Indications:

1. When the wiring of the teeth will not provide adequate fixation.

2. When both the jaws are edentulous.

3. In case of growing children, where mixed dentition is present and number of firm teeth for anchorage are not adequate.

Acrylic splints:

1. Lateral compression splint.

2. Gunning splint.

Wiring procedure:

1. Prealveolar wiring procedure.

2. Circumferential (circummandibular) wiring procedure.Anatomy of Biomechanics of the Mandible:

Champs ideal osteosynthesis lines:

In every mandibular fracture, the forces of mastication produce tension forces at the upper border and compression forces at the lower border. Therefore, distraction of the fractured fragments will be seen at the alveolar crest region. In the canine region, there are overlapping tensile and compressive loads in both the directions. Besides this torsional forces are also significant.

Internal fixation by means of bone plate osteosynthesis:

The direct internal fixation of the fractured fragments can be carried out by bone plate osteosynthesis method. It either totally eliminates the need of IMF or minimizes the period of IMF.

Indications:

1. Cases where there is absolute contraindications to IMF, i.e. in epileptics, mentally retarded uncooperative patients, asthmatics, alcoholics, drug abusers, pregnant women etc.2. When the patient wants to return back to work early.

3. Edentulous patients with loss of bone segments, which need the maintenance of the gap or grafting, if indicated.4. In subcondylar and angle fractures of the mandible, early mobilization of the joint is required.

Contraindications:

a. In heavily contaminated fractures, where there is active infection and discharge. However, some surgeons advocate the use of compression osteosynthesis in such cases.b. In badly comminuted fracture, where open reduction may pose risk of compromising vascularity.

c. In children having mixed dentition, where there is a danger of injuring the developing teeth buds.

d. Presence of gross pathological abnormalities in the bone.

Bone plate osteosynthesis:1. Compression plate with bicortical screw system.

2. Non compression plate with monocortical screw system. The bony union can be promoted when the fragments are approximated firmly under pressure against each other. This principles is utilized in the development of compression bone plate system (AO system) by European surgeons. This system offers rigid fixation with infrafragmentary compression. There is no need for IMF postoperatively. Here, there is no infrafragmentary gap or it is less than 0.8mm. During healing there is no callus formation. But there is primary healing of the bone, characterized by direct restoration of lamellar bone. In this technique precision is needed, will not allow any occlusal discrepancy correction later on.

AO system:1. Dynamic compression plate (DCP).

2. Eccentric dynamic compression plate (EDCP).

Plates and screws are made up of stainless steel and need removal later on. These plates are very bulky. DCP system makes compression osteosynthesis possible because of the screw holes designed according to the spherical gliding principle for a 2.7mm screw. In EDCP there are eccentric grinding hole principle is used. In eccentric dynamic compression plate, there are two lateral oblique holes in addition to conventional spherical gliding hole. When the screw with the spherical head is driven into the two inner holes, they provide interfragmentary compression. It is possible by means of two outer holes to produce additional compression at the alveolar margin of the fractured fragment. The two lateral oblique holes takeover the function of the tension bend in the alveolar margin.Miniplate osteosynthesis (Noncompression monocortical screw system)

This is complete different concept than compression bone plate system. This is developed in France by Michelet in 1973 and made clinically popular by Champy in 1975.

Therapeutic principle: Fixation by stability: Stability is achieved by a perfect anatomic reduction and intrafragmentary approximation without compression. Champy recognized that in function, it is possible to identify the lines of tension, which when controlled will stabilize the lines of tension, he also noted that the reciprocal compression force at the lower border, controlled by bone to bone contact across the fracture line.

Reconstruction plates:

These are capable of temporary load bearing and therefore useful in comminuted fractures, defect fractures and infected fractures. It is also useful in the case of severely displaced angle fracture. Reconstruction plate absorbs all functional loads and permits early mobilization.Large screw:

Oblique fracture of the mandible can be rigidly immobilized by inserting two or more screws whose threads engages only the inner plate of bone. When tightened head of the screw engages in the outer plates and the oblique fracture is compressed.References:1) Oral and Maxillofacial Trauma Fonseca, Vol. 1, 2nd edition.

2) Rowe and Williams Maxillofacial Injuries Vol. 1

3) Clinically Oriented Anatomy Keith L. Moore.

4) Oral and Maxillofacial Surgery Vol. 3, Peterson.

5) Maxillofacial Surgery Vol. 1, Peter Ward Booth.

6) Oral and Maxillofacial Surgery. Vol. 1, Daniel M. Laskin.

7) Killeys fractures of the mandible 4th edition, Peter Banks.

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