Transcript ANATOMY AND FRACTURES OF THE MANDIBLE

ANATOMY AND
FRACTURES OF THE
MANDIBLE
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
Origin
Insertion
Innervation
Action
Masseter
Inferior 2/3 zygomatic
bone & medial
surface of zygomatic
arch
Lateral ramus and
angle of mandible
Masseteric branch of
anterior division of
mandibular nerve (V)
Elevate and protrude
mandible
Temporalis
Limits of temporal
fossa
Medial surface
coronoid process,
anterior surface of
ramus down to
occlusal plane
Two deep temporal
branches of
mandibular nerve (V),
sometimes reinforced
by middle temporal
nerve
Elevates mandible,
posterior fibres are
the only muscle
fibres to retract the
mandible
Medial
pterygoid
Pterygoid fossa,
mainly medial
surface of lateral
pterygoid process
Medial surface of
ramus and angle of
mandible
Branch from main
trunk of mandibular
nerve
Pulls angle of
mandible superiorly,
anteriorly and
medially
Lateral
pterygoid
Upper head from
infratemporal surface
of skull, lower head
from lateral pterygoid
plate
Upper head inserts
into TMJ capsule,
lower head into
anterior surface of
condylar neck
Branch of anterior
division of
mandibular nerve
Lateral movement,
protrusion, important
in active opening of
the mouth
Muscles of the mandible – Anterior
group
Origin
Insertion
Innervation
Action
Hypoglossal nerve
(XII)
Depresses tongue,
posterior part
protrudes tongue
Genioglossus
Superior part of
mental spine of
mandible
Geniohyoid
Inferior part of mental
spine of mandible
Body of hyoid bone
C1 through
hypoglossal nerve
(XII)
Pulls hyoid bone
anterosuperiorly,
shortens floor of
mouth and widens
pharynx
Mylohyoid
Mylohyoid line of
mandible
Raphe and body of
hyoid bone
Mylohyoid nerve, a
branch of inferior
alveolar nerve (V3)
Elevates hyoid bone,
floor of mouth and
tongue during
swallowing and
speaking
Digastric
Anterior: Digastric
fossa of mandible
Posterior: Mastoid
notch of temporal
bone
Intermediate tendon
to body and superior
(greater) horn of
hyoid bone
Anterior: Mylohyoid
nerve (V3)
Posterior: Facial
nerve (VII)
Depresses mandible,
raises hyoid bone
and steadies it during
swallowing and
speaking
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


Sphenomandibular ligament runs between sphenoid spine and lingula of
mandible


Tightens with movements away from rest
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
Class
Molar
relation
Canine relation
I
Mesiobuccal cusp of
maxillary 1st molar is in
line with buccal groove
of mandibular 1st molar
Maxillary permanent canine
occludes with distal ½ of
mandibular canine and mesial
half of mandibular 1st premolar
II
Buccal groove of
mandibular 1st molar is
distal to mesiobuccal
cusp of maxillary 1st
molar
Distal surface of mandibular
canine is distal to mesial surface
of maxillary canine by at least
width of a premolar
Buccal groove of
mandibular 1st molar is
mesial to mesiobuccal
cusp of maxillary 1st
Distal surface of mandibular
canine is mesial to mesial
surface of the maxillary canine
by at least the width of a
Div1 – Overjet
Div2 – Lingual
inclination
III
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 #