ANATOMY AND ANATOMY AND FRACTURES OF THE FRACTURES OF THE

MANDIBLEMANDIBLE

ANATOMY

Mandible interfaces with skull base via the TMJ and is held in position by the muscles of mastication

Anatomic units of the mandible

Muscles of the mandible – Posterior group

OriginOrigin InsertionInsertion InnervationInnervation ActionAction

MasseterMasseter Inferior 2/3 zygomatic Inferior 2/3 zygomatic bone & medial bone & medial surface of zygomatic surface of zygomatic archarch

Lateral ramus and Lateral ramus and angle of mandibleangle of mandible

Masseteric branch of Masseteric branch of anterior division of anterior division of mandibular nerve (V)mandibular nerve (V)

Elevate and protrude Elevate and protrude mandiblemandible

TemporalisTemporalis Limits of temporal Limits of temporal fossafossa

Medial surface Medial surface coronoid process, coronoid process, anterior surface of anterior surface of ramus down to ramus down to occlusal planeocclusal plane

Two deep temporal Two deep temporal branches of branches of mandibular nerve mandibular nerve (V), sometimes (V), sometimes reinforced by middle reinforced by middle temporal nervetemporal nerve

Elevates mandible, Elevates mandible, posterior fibres are posterior fibres are the only muscle the only muscle fibres to retract the fibres to retract the mandiblemandible

Medial Medial pterygoidpterygoid

Pterygoid fossa, Pterygoid fossa, mainly medial mainly medial surface of lateral surface of lateral pterygoid processpterygoid process

Medial surface of Medial surface of ramus and angle of ramus and angle of mandiblemandible

Branch from main Branch from main trunk of mandibular trunk of mandibular nervenerve

Pulls angle of Pulls angle of mandible superiorly, mandible superiorly, anteriorly and anteriorly and mediallymedially

Lateral Lateral pterygoidpterygoid

Upper head from Upper head from infratemporal surface infratemporal surface of skull, lower head of skull, lower head from lateral pterygoid from lateral pterygoid plateplate

Upper head inserts Upper head inserts into TMJ capsule, into TMJ capsule, lower head into lower head into anterior surface of anterior surface of condylar neckcondylar neck

Branch of anterior Branch of anterior division of division of mandibular nervemandibular nerve

Lateral movement, Lateral movement, protrusion, important protrusion, important in active opening of in active opening of the mouththe mouth

Muscles of the mandible – Anterior group

OriginOrigin InsertionInsertion InnervationInnervation ActionAction

GenioglossusGenioglossus Superior part of Superior part of mental spine of mental spine of mandiblemandible

Hypoglossal nerve Hypoglossal nerve (XII)(XII)

Depresses tongue, Depresses tongue, posterior part posterior part protrudes tongueprotrudes tongue

GeniohyoidGeniohyoid Inferior part of mental Inferior part of mental spine of mandiblespine of mandible

Body of hyoid boneBody of hyoid bone C1 through C1 through hypoglossal nerve hypoglossal nerve (XII)(XII)

Pulls hyoid bone Pulls hyoid bone anterosuperiorly, anterosuperiorly, shortens floor of shortens floor of mouth and widens mouth and widens pharynxpharynx

MylohyoidMylohyoid Mylohyoid line of Mylohyoid line of mandiblemandible

Raphe and body of Raphe and body of hyoid bonehyoid bone

Mylohyoid nerve, a Mylohyoid nerve, a branch of inferior branch of inferior alveolar nerve (V3)alveolar nerve (V3)

Elevates hyoid bone, Elevates hyoid bone, floor of mouth and floor of mouth and tongue during tongue during swallowing and swallowing and speakingspeaking

DigastricDigastric Anterior: Digastric Anterior: Digastric fossa of mandiblefossa of mandible

Posterior: Mastoid Posterior: Mastoid notch of temporal notch of temporal bonebone

Intermediate tendon Intermediate tendon to body and superior to body and superior (greater) horn of (greater) horn of hyoid bonehyoid bone

Anterior: Mylohyoid Anterior: Mylohyoid nerve (V3)nerve (V3)

Posterior: Facial Posterior: Facial nerve (VII)nerve (VII)

Depresses mandible, Depresses mandible, raises hyoid bone raises hyoid bone and steadies it during and steadies it during swallowing and swallowing and speakingspeaking

Muscles of Mastication

OUTER SURFACE

Muscles of Mastication

INNER SURFACE

Muscles of Mastication

4 muscles of mastication Masseter

Temporalis

Medial pterygoid

Lateral pterygoid

Supplied by V3, testament to same embryologic origin as the mandible from the 1st branchial arch

Masseter Divided into 3 heads

Superficial: largest head Arises anterior 2/3rds of the lower border of the

zygomatic arch Wide insertion to angle, forwards along lower

border and upwards to lower part of ramus

Intermediate: Middle 1/3 of the arch

Deep: Deep surface of the arch

Action: elevator and drawing forward the angle

Masseter Intermediate and deep fuse and pass

vertically downwards to fuse with ramus

Nerve and artery divide muscle incompletely into 3 parts

Masseteric nerve (Br of anterior division of V3) runs between deep and intermediate

Br of superficial temporal and transverse facial runs between superficial and intermediate

Temporalis Arises temporal fossa between inferior

temporal line and infratemporal crest

Inserts at posterior border of the coronoid process and ascending ramus

Upper and anterior fibres elevate the mandible

Posterior fibres (horizontal) retract the mandible (only muscles that do so)

Medial pterygoid 2 heads:

Deep: Larger

Medial surface of the lateral pterygoid plate and the fossa between 2 plates

Superficial : Tuberosity of the maxilla and pyramidal process

of palatine bones

Insert lower and posterior part of angle (with masseter)

Action: upwards and forwards and medially

Lateral pterygoid 2 heads:

Superior: Infratemporal fossa

Inferior: Lateral surface of the lateral pterygoid

Fuse into a short thick tendon that inserts into pterygoid fovea

the upper fibres passing into articular disc and anterior part of the capsule

Action: side-to-side plus only muscle to open jaw

Temporomandibular Joint

Articulation Synovial joint between the condyle of the

mandible and the mandibular fossa in the squamous part of the temporal bone

Both bone surfaces covered with layer of fibrocartilage identical to the disc

No hyaline cartilage, therefore an atypical joint

Temporomandibular Joint

Unique feature of the TMJs is the articular disc.

Composed of fibrocartilaganeous tissue

Divides each joint into 2: Inferior compartment

Superior compartment

Temporomandibular Joint

Inferior compartment Allows for pure rotation of the condylar head,

corresponds to the first 20 mm or so of the opening of the mouth. (opening and closing movements)

Superior compartment involved in translational movements

sliding the lower jaw forward or side to side

Temporomandibular Joint

Temporomandibular Joint Atypical synovial joint separated into upper and lower cavities by a

fibrocartilaginous disc

No hyaline cartilage

Capsule attached high on neck of mandible around articular margin, then to transverse prominence or articular tubercle and as far posteriorly as squamotympanic fissure

Fibrocartilage attached around periphery to capsule

Anteriorly near head of mandible, so mobile

Posteriorly near temporal bone, so more fixed

Thinner in middle than periphery, crinkled fibres to allow movement and contouring

Lateral TM ligament is a stout fibrous band passing from zygomatic arch to posterior border of neck and ramus, blending with capsule

Tightens with movements away from rest

Sphenomandibular ligament runs between sphenoid spine and lingula of mandible

Remains constant tension through range of motion as the lingula is the axis of rotation of the mandible

Sensation supplied by auriculotemporal nerve with some supply from nerve to masseter (Hiltons law)

TMJ Ligaments 3 ligaments associated with the TMJ:

1) Temporomandibular ligament (Major)

is really the thickened lateral portion of the capsule, and it has two parts: an outer oblique portion (OOP)

and an inner horizontal portion (IHP)

Lower border of zygomatic arch to posterior border of the neck and ramus

TMJ Ligaments 2) stylomandibular ligament (minor)

separates the infratemporal region from the parotid region

runs from the styloid process to the angle of the mandible

3) Sphenomandibular ligament (minor) runs from the spine of sphenoid to the lingula

of the mandible

TMJ Ligaments The minor ligaments are important in that

they define the limits of movements, ie the farthest extent of movements of the

mandible.

Not connected to joint

However, movements of the mandible made past these extents functionally allowed by the muscular attachments BUT will result in painful stimuli

TMJ Ligaments

TMJ Ligaments

Mandibular Forces

Nerve Supply Inferior alveolar nerve branch of the

mandibular division of Trigeminal (V) nerve, enters the mandibular foramen and runs forward in the mandibular canal, supplying sensation to the teeth.

At the mental foramen the nerve divides into two terminal branches: Incisive nerve: supplies the anterior teeth

mental nerve: sensation to the lower lip

Evaluation - History Always remember ABCs of life along with

secondary and tertiary survey

Mechanism of injury MVA associated with multiple comminuted #

Fist often results in single, non - displaced #

Anterior blow to chin - bilateral condylar #

Angled blow to parasymphysis can lead to contralateral condylar or angle #

Clenched teeth can lead to alveolar process #

Physical Exam - Occlusion

Change in occlusion - determine preinjury occlusion

Posterior premature dental contact or an anterior open bite is suggestive of bilateral condylar or angle fractures

Posterior open bite is common with anterior alveolar process or parasymphyseal fractures

Unilateral open bite is suggestive of an ipsilateral angle and parasymphyseal fracture

Retrognathic occlusion is seen with condylar or angle fractures

Condylar neck # are assoc with open bite on opposite side and deviation of chin towards the side of the fx.

Angle’s classification Class I:

Normal Mesial buccal cusp of the upper 1st molar

occludes with mesial buccal groove of the mandibular molar

Class II: Retrocclusion, mandibular deficiency

Class III: Prognathic occlusion, maxillary deficiency,

mandibular excess

Dental classification of occlusion Angle’s classification (1887)

Based on relationship of permanent 1st molars and to a lesser degree the permanent canines to each other

ClassClass Molar Molar relationrelation

Canine relationCanine relation

II Mesiobuccal cusp of Mesiobuccal cusp of maxillary 1maxillary 1stst molar is in molar is in line with buccal groove line with buccal groove of mandibular 1of mandibular 1stst molar molar

Maxillary permanent canine Maxillary permanent canine occludes with distal ½ of occludes with distal ½ of mandibular canine and mesial mandibular canine and mesial half of mandibular 1half of mandibular 1stst premolar premolar

IIIIDiv1 – OverjetDiv1 – Overjet

Div2 – Lingual Div2 – Lingual inclinationinclination

Buccal groove of Buccal groove of mandibular 1mandibular 1stst molar is molar is distal to mesiobuccal distal to mesiobuccal cusp of maxillary 1cusp of maxillary 1stst molarmolar

Distal surface of mandibular Distal surface of mandibular canine is distal to mesial surface canine is distal to mesial surface of maxillary canine by at least of maxillary canine by at least width of a premolarwidth of a premolar

IIIIII Buccal groove of Buccal groove of mandibular 1mandibular 1stst molar is molar is mesial to mesiobuccal mesial to mesiobuccal cusp of maxillary 1cusp of maxillary 1stst molarmolar

Distal surface of mandibular Distal surface of mandibular canine is mesial to mesial canine is mesial to mesial surface of the maxillary canine surface of the maxillary canine by at least the width of a by at least the width of a premolar premolar

Malocclusion

Physical Exam Anaesthesia of the lower lip

Abnormal mandibular movement unable to open - coronoid fx

unable to close - # of alveolus, angle or ramus

trismus

Lacerations, Haematomas, Ecchymosis

Loose teeth

swelling

Physical Exam Multiple fractures sites are common:

1 fracture: 50%

2 fractures: 40%

>2 fractures: 10%

Dual patterns: Angle contralateral body

Symphysis and bilateral condyles

15% another facial fracture

General Principles of treatment

ABCs

Tetanus

Nutrition

Almost all can be considered open fractures as they communicate with skin or oral cavity

Reduction and fixation

Post-op monitoring for N/V, use of wire cutters

Oral care - H2O2 , irrigations, soft toothbrush

Aims of Management

1) Achieve anatomical reduction and stabilisation

2) Re-establish pre-traumatic functional occlusion

3) Restore facial contour and symmetry

4) Balance facial height and projection

Fracture Frequency

Classification of Fractures

Open vs Closed

Displaced vs non-displaced

Complete vs greenstick

Linear Vs comminuted

Relationship to the teeth Class I: teeth both sides of fracture Class II: teeth one side of fracture Class III: edentulous

Favourable vs unfavourable

Treatment options No treatment

Soft diet

Maxillomandibular fixation

Open reduction - non-rigid fixation

Open reduction - rigid fixation

External pin fixation

IMF

IMF

Islet IMF

Open reduction - nonrigid fixation

External Fixation

Principles of fixation Usually one plate with 4

cortices of fixation are required for adequate immobilisation

Anterior to mental foramen, 2 levels of fixation are required to overcome torsional forces

Unfavourable fractures usually require 2 levels of fixation for stability

Fixation along Champy’s line allows better fixation due to the strong buttress structure

Condylar fractures Classification

Condylar Intra- or extra-capsular

subcondylar

Watch for intracranial condylar head

Condylar heads tend to dislocate anteromedially towards pterygoid plates due to pull from medial pterygoid

Indications for open reduction are angulation > 30°, fracture gap > 5mm, lateral override, bilateral fractures of head/neck Risks avascular necrosis of

condylar head, facial nerve injury, hypertrophic scarring (10%)

Alveolar fractures 3% total fractures, often in combination with other fractures

Can often be reduced and fixed with arch bars (can be acrylated) or Essig splints

May require monocortical plate fixation

Teeth are often insensate and require orthodontic evaluation

Gross comminution or loss of blood supply increases the risk of infection and primary debridement of the devitalised segment with soft tissue coverage may be a better long term option

Can have compression fractures of alveolus resulting in loosened teeth Miller Grade 1 - < 1mm looseness Miller Grade 2 – 1-3mm looseness Miller Grade 3 - > 3mm looseness and loose superoinferiorly in

socket

Teeth in fracture line Important in fracture stability when using IMF

Less important in fracture stability when plates used to fix fractures

Reasons to extract the tooth Severe tooth loosening with chronic periodontal disease Fracture of the root of the tooth Extensive periodontal injury and broken alveolar walls Displacement of teeth from their alveolar socket Interference with bony reduction and reestablishing occlusion

Third molars tend to cause the most controversy Third molars that are erupting normally need not be removed

unless they are interfering with fracture reduction Impacted third molars can be removed as they are rarely a

functional part of the occlusion Removal of third molars unnecessarily leads to increased

conversion from closed reduction to open reduction

Edentulous mandible No occlusal plane

Lack of mandibular height due to atrophy

Changed pattern of fracture – body is more common as atrophy is greatest

Changed position of inferior alveolar nerve and artery

Changed pattern of blood supply – more circumferential than radial

Role of recon plates and bone grafting

Role of dentures

Paediatric mandible Often greenstick fractures that heal within 2-3

weeks

65% mandibular fractures in children < 10yo are in condylar region, 40% in 11-15yo

Arch bars are common use to avoid damage to secondary teeth, but primary teeth are conically shaped

Acrylic splint secured by circumferential wiring is safe and effective

Condyle is the major growth centre of the mandible and has some ability to remodel, and poorly tolerates periosteal stripping

Crush of condylar head (esp. < 3y) can lead to altered mandibular growth and TMJ ankylosis secondary to haemorrhage

Complications Airway esp with IMF (wire cutters and pre-op

education)

Infection

Delayed and non-union Inadequate immobilisation, fracture alignment Inteposition of soft tissue or foreign body Incorrect technique

Inferoir alveolar nerve damage 56%pre-treatment 19% post-treatment

Malocclusion

TMJ ankylosis esp intracapsular condyle #