anatomy and fractures of the mandible
DESCRIPTION
semoga bermanfaatTRANSCRIPT
ANATOMY
Mandible interfaces with skull base via the TMJ and is held in position by the muscles of mastication
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
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 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
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
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
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
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 #