5. Muscles of the mandible –
Posterior group
Origin Insertion Innervation Action
Masseter Inferior 2/3 zygomatic
bone & medial
Lateral ramus and
angle of mandible
Masseteric branch of
anterior division of
Elevate and protrude
mandible
surface of zygomatic mandibular nerve (V)
arch
Temporalis Limits of temporal
fossa
Medial surface
coronoid process,
Two deep temporal
branches of
Elevates mandible,
posterior fibres are
anterior surface of mandibular nerve the only muscle
ramus down to (V), sometimes fibres to retract the
occlusal plane reinforced by middle mandible
temporal nerve
Medial Pterygoid fossa,
mainly medial
Medial surface of
ramus and angle of
Branch from main
trunk of mandibular
Pulls angle of
mandible superiorly,
pterygoid surface of lateral mandible nerve anteriorly and
pterygoid process medially
Lateral Upper head from
infratemporal surface
Upper head inserts
into TMJ capsule,
Branch of anterior
division of
Lateral movement,
protrusion, important
pterygoid of skull, lower head lower head into mandibular nerve in active opening of
from lateral pterygoid anterior surface of the mouth
plate condylar neck
6. Muscles of the mandible – Anterior
group
Origin Insertion Innervation Action
Genioglossus Superior part of
mental spine of
Hypoglossal nerve
(XII)
Depresses tongue,
posterior part
mandible protrudes tongue
Geniohyoid Inferior part of mental
spine of mandible
Body of hyoid bone C1 through
hypoglossal nerve
Pulls hyoid bone
anterosuperiorly,
(XII) shortens floor of
mouth and widens
pharynx
Mylohyoid Mylohyoid line of
mandible
Raphe and body of
hyoid bone
Mylohyoid nerve, a
branch of inferior
Elevates hyoid bone,
floor of mouth and
alveolar nerve (V3) tongue during
swallowing and
speaking
Digastric Anterior: Digastric
fossa of mandible
Intermediate tendon
to body and superior
Anterior: Mylohyoid
nerve (V3)
Depresses mandible,
raises hyoid bone
Posterior: Mastoid (greater) horn of Posterior: Facial and steadies it during
notch of temporal hyoid bone nerve (VII) swallowing and
bone speaking
9. 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
10. 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
11. 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
12.
13. 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)
14.
15. 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
16.
17. 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
18.
19. 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
20. Temporomandibular
Joint
Unique feature of the TMJs is the articular
disc.
Composed of fibrocartilaganeous tissue
Divides each joint into 2:
Inferior compartment
Superior compartment
21. 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
23.
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)
24. 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
25. 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
26. 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
30. 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
31.
32.
33. 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 #
34. Physical Exam -
Occlusion occlusion
Change in occlusion - determine preinjury
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.
35. 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
36. 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 Canine relation
relation
I Mesiobuccal cusp of
maxillary 1st molar is in
Maxillary permanent canine
occludes with distal ½ of
line with buccal groove mandibular canine and mesial
of mandibular 1st molar half of mandibular 1st premolar
II Buccal groove of
mandibular 1st molar is
Distal surface of mandibular
canine is distal to mesial surface
Div1 – Overjet distal to mesiobuccal of maxillary canine by at least
Div2 – Lingual cusp of maxillary 1st width of a premolar
inclination molar
III Buccal groove of
mandibular 1st molar is
Distal surface of mandibular
canine is mesial to mesial
mesial to mesiobuccal surface of the maxillary canine
cusp of maxillary 1st by at least the width of a
molar premolar
39. 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
40. 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
41. General Principles of
ABCs
treatment
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
42. 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
44. 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
45.
46.
47. Treatment options
No treatment
Soft diet
Maxillomandibular fixation
Open reduction - non-rigid fixation
Open reduction - rigid fixation
External pin fixation
53. 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
54. 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%)
55. 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
56. 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
57. 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
58. 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
59. 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 #
Editor's Notes
CLASSICAL INDICATIONS FOR CLOSED REDUCTION: GROSSLY COMMINUTED FX - HEAL BETTER IF PERIOSTEUM INTACT BUT MAY NEED EXT. FIX OR RECON. BAR FX WITH SIGNIFICANT LOSS OF SOFT TISSUE EDENTULOUS MANDIBLES - CLOSED REDUCTION WITH A GUNNING SPLINT FX IN KIDS- OPEN REDUCTION CAN DAMAGE DEVELOPING TEETH CONDYLAR FX - EARLY JAW MOBILIZATION IS REQUIRED TO AVOID ANKYLOSIS OF THE TMJ. KIDS - WEEKLY, ADULTS BIWEEKLY
CANDY CANE WIRES WEAR FACETS REMEMBER, MMF CONTRAINDICATED IN EPILEPTICS, ALCHOLICS, PSHYCHIATRIC ANDFRAIL PTS WHO CANNOT TOLERATED. ALSO DIABETICS
IVY LOOPS - NOT AS STRONG AS THE ARCH BAR, USEFUL IN SELECTIVELY BRINGIN OCCLUSAL PAIRS OF TEETH TOGHETHER. APPLICATION IN KIDS WITH M IXED DENTITION, IN PARTIALLY EDENTULOUS PTS WHO WILL HAVE ADDITIONAL FORMS OF FIXATION, AND PTS WHO NEED TEMPORARY OCCLUSION WHILE OTHER METHODS ARE BEING APPLIED (PLATES OR EXT-FIX) TO MAKE; 26 GUAGE WIRE IS CUT TO 16 CM. SMALL LOOP IS FORMED HEMOSTAT. THE ENDS ARE INSERTED BETWEEN TWO SUITABLE TEETH. THE MESIAL END IS PASSE D THROUGH THE LOOP AND THEN TIGHTENED 28 GUAGE WIRES GO THROUGH THE EYE LITS FOR FIXATION
CLASSICAL INDICATION FOR OPEN REDUCTION MALOCCLUSION DESPITE MMF DISPLACED UNFAVORABLE FX THROUGH THE ANGLE DISPLACED, UNFAVORABLE FX OF THE BODY OR THE PARASYMPHYSIS MULTIPLE FX OF THE FACIAL BONES - MANDIBLE IS FIXED FIRST PROVIDING A STABLE BASE FOR RESTORATION - BOTTOM UP MALUNION - OSTEOTOMIES AND ORIF ----- NON RIGID FIXATION MORE FORGIVING, EASIER TO PLACE. STILL REQUIRES MMT, USEFUL IN ANGLE AND PARASYMPHYSEAL FX. CAN GO EXTRAORAL OR TRANSORAL(FOR A HIGH WIRE)
USUALLY NECESSARY IN COMMUNUTED FX. THOSE WHO CANNOT TOLERATE MMF OR GSW