DR Go DR Gopin Gopinath pinath ath tthi thila hillak akk . p.s p.s 1st year postgraduate Dept. of Oral & Maxillofacial surgery
Contents
Development Prenatal Post natal Anomalies
A Anatomy of mandible
Muscle attachments muscles of mastication
ter y, y, vein ,ner ve ve supply and lymphatic d r ainage ainage Ar Ar te
gical anatomy A Applied sur gical
ounding soft tissue A Applied anatomy of surr ounding
Development
Prenatal Postnatal
Pr enatal
Development
The car tilages and the bones of the mandibula r skeleton for m f ro m embr yonic neur al cr est cells that or iginate f ro mid- and the hindbr ain r egions of the neur al m the midfolds. These cells migr ate ventr ally to for m the mandibular facial pr ominences, wher e they differ entiate into bones and connective tissue
The fir st str uctur e to develop in the r egion of the lower jaw is the mandibula r division of the tr igeminal ner ve that pr ecedes the ectomesenchymal condensation fo r ming the fir st phar yngeal ar ch .
The mandible is de r ived f r om ossification of an osteogenic membr ane at 36 to 38 days of development.
Mandibular ectomesenchyme must inter act initially with the epithelium of of mandibula r ar ch befor e pr imar y ossification can occu r; the r esulting intr amembr anous bone lies later al to Meckel,s car tilage of the fi r st phar yngeal ar ch.
conception - a single ossification 6th week post conceptioncentr e for each half of mandible a r ises in the r egion of the bifu r cation of the infe r ior alveolar ner ve and ar ter y into mental and incisive br anches.
Fr om the pr imar y centr e ossification spr eads upwar ds to for m a tr ough for the developing teeth
.
The spr ead of the intr a membr anous ossification dor sally and ventr ally for ms the body and r amus of the mandible
Meckel,s car tilage becomes surr ounded and invaded by bone
Ossification stops dor sally at the site that will become the mandibula r lingula , wher e meckel,s car tilage continues into the middle ear .
10th and 14th weeks post conceptionconception- secondar y accessor y car tilage appear to for m the head of the condyle , par t of of cor onoid pr ocess , and mental pr otuber ance .
10th week post conception ± the condylar secondar y car tilage appear s as a cone shaped str uctur e in the r amal bone .
14th week ± the fir st evidence of of endochondr al bone appear s in the condyle r egion
In
the mental r egion , on the eithe r side of symphysis , one or two small car tilages appear and ossify which late r for ms the symphysis menti menti..
The condylar gr owth r ate incr eases at puber ty , peaks between 121/2 and 14 year s of age , and nor mally ceases at 20 year s of age .
Post
natal development
Fetal mandible
The ascending r amus of the neonatal mandible is low and wide The cor onoid pr ocess is r elatively lar ge and pr ojects well above the condyle The body is mer ely an open shell containing the buds and par tial cr own of the deciduous teeth
The mandibular canal r uns low in the body
4th and 12th months after bir th ± ± initial seper ation of the r ight and the left bodies of the mandible at the midline symphysis menti is gr adually eliminated . A As ossification conve r ts
the syndesmosis into synostosis , uniting the two halves.
Developmentally and functionally mandible is divided into seve r al skeletal subunits .
The gr owth patter n of each of these skeletal subunits is influenced by a functional mat r ix that acts upon the bone
The main sites of postnatal mandibular gr owth ar e at the condylar car tilages , the poster ior bor der s of the mi, and the alveolar r ami, r idges .
A Any damage to the condylar car tilages r estr icts the gr owth
potential .
In
infant, condyles of the mandible ar e inclined almost hor izontally, , so that the condylar gr owth leads to an incr ease in the length of the mandible r ather than to incr ease in height. Gr owth follows a v shape patter n
The attachment of the elevating muscles of mastication to the buccal and the lingual aspects of the r amus and to the mandibula r angle and cor onoid pr ocess influences the ultimate size and pr opor tions of these mandibular elements.
The for war d shift of the gr owing mandibular body changes the dir ection of the mental for amen dur ing infancy and childhood
Clinical implication :
In
infants and childr en - the syr inge needle may be applied at r ight angles to the body of the mandible to enter the mental for amen .
In
adults: needle must be applied obliquely f ro m behind to achieve ent r y.
The location of the mental for amen also alter s its ver tical r elationship within the body of the mandible f r om infancy to old age .
Age changes mandibular vs maxilla
Fetal life : ± mandible is consider ably lar ger than maxilla . Initially ± Later gr eater development of maxilla takes place . 8 weeks of post conception ±maxilla ± maxilla over laps the mandible 11 weekweek- r elatively gr eater gr owth of mandible r esults in the appr ox equal size of the upper and the lower jaws. 13th and 20th weeks weeks-- mand gr owth lags behind max m Meckel,s car tilage to gr owth due to change over f ro condylar secondar y car tilage .
Bir th:
The mandible tend to be r etr ognatic to the maxilla although the two may be equal size. Ear ly post natal life ± ±r apid mand gr owth and for war d displacement to establish an Angles class I maxillomandibularr r elationship.
Anomalies of Development
A Agnathia
Micr ognathia: gnathia: Pierre robin syndrome cri du chat Treacher collins syndrome Treacher Progeria downs syndrome Hallermann--streiff Hallermann streiff syndrome Turner syndrome Goldenhar syndrome Goldenhar
Macr ognathia C ongenital ngenital hemifacial hemifacial hypertrophy
Unilateral condylar Unilateral condylar hyperplasia
Pierr e
Robin syndr ome
Tr eacher collins syndr ome
Parr y
Romber g syndr ome
Goldenhar Syndr ome
Agnathia
Anatomy
cor onoid
Condylar head
neck Pter ygoid
fovea Anter ior r amus and cor onoid
Uner upted 3r d molar
notch
Alveolar par t
Oblique line
body
Base
Mental for amen
of mandible Mental tuber cle Mental
Cor onoid pr ocess
Mandibular notch
r amus
angle
r amus
lingula Sublingual fossa
Pulaoster ior bor der
of r amus Mandibular for amen
Super ior and infer ior mental spines
Mylohyoid gr oove
Mylohyoid line Digastr ic fossa
Angle
Submandibular fossa
Mandibular notch
angle
Cor onoid pr ocess
Muscle Attachment
Capsule of the tmj
Later al pter ygoid
tempor alis
buccinator
platysma masseter Depr essor anguli or is mentalis
Depr essor labii infer ior is
Pmr and
Scmp
Buccinator
mylohyoid
Medial pter ygoid
buccinator
Sphenomandibular ligament
mylohyoid
Stylomanbula ligament
genioglossus
geniohyoid
Medial pter ygoid
Anter ior belly of digastr ic
Muscle of Mastication
Masseter Muscle
Quadr angular in shape
or igin: z ygomatic gomatic arch and maxillary process of z ygomatic bone
: lateral surface of
Inser tion
ramus of mandible
ner vesupply: anterior division of mandibular of mandibular nerve
Tempor alis muscle
Lar ge
fan shaped muscle
Or igin : Bone of the temporal fossa and temporal fascia. Inser tion
ronoid process process of :C oronoid
the mandible and anterior margin of the ramus of the mandible almost to the last molar tooth. Ner ve
supply:
anterior division of of mandibular nerve
Medial
Quadr angular in shape
Or igin
Pter ygoid
Deep
Head: Superficial head:
Inser tion:
medial surface of mandible near angle supply: main trunk of mandibular nerve mandibular Ner ve
Super ficial head
Deep head
Later al Pter ygoid .
Thick Tr iangular muscle
Or igin: upper head :
Upper head
lower head:
Inser tion :C apsule of the TMJ
joint in the region of attachment to articular disc and articular and pterygoid pterygoid fovea on the neck of the mandible .
Lower head
gical Applied Sur gical anatomy
The mandible is basically tubula r long bone which is bent into a blunt ³v´ ±shape ±shape
The cor tical tical bone is thicker anter io ior lly ya and nd at at the lower bor de der of mandible , while poster io ior lly y tthe he lowe lower bor de der is r elatively elatively thin.
Thus the mandible is str ongest ongest anter io ior lly y iin n tthe he midline with pr og ogr essively essively less str ength ength towar ds ds the condyle.. condyle
The teeth
Restor ation of occlusion is the pr ime aim in the tr eatment of f ra ctur es of the mandible . The pr esence of the teeth is extr emely helpful in the of mandibula r f ra r eduction and fixation of ctur es Complete f ra ctur e of the body of the dentate mandible will lead to the soft tissue tear over the f ra ctur e both bucally and lingually and thus ar e open into or al cavity and exposed to possible infection .
The mandible is commonly f ra ctur ed because of their pr ominent position. For war d falls will r esult in point of chin str iking the gr ound Chin and body of mandible for m an inviting landmar k in fights.
Str ength of the mandible
Huelke (1961) and Hodgson(1967) Hodgson(1967) investigated into the r esistance of the mandible to applied fo r ces.
Bones f r actur e
at sites of tensile str ain, since their r esistance to compr essive for ces is gr eater
Huelke (1961) shown that isolated mandible is liable to par ticular patter ns of distr ibution of tensile str ain when for ces ar e applied to it
The mandible is a st r ong bone , the ener gy r equir ed to f r actur e it being of the or der of 44.6 of 44.6--74.4 kg/m, kg/m, which is about the same as the zygoma and about half that for the f r ontal bone .(Hodgson 1967)
The infer ior dental neur ovascular bundle
The fibr ous sheath pr ovides consider able suppor t for the contained vessels and ner ve ,which accounts for the low incidence of per manent ner ve damage after f ra ctur e.
The disposition of mandibula r f r actur e line
Hagan and Huelke ,1961 has detailed site of injur ing for ce
1.
The condylarr r egiongion- most common
2.
The angle ± ± 2nd most
3.
Multiple f r actur e mor e common
20
21
Condylarr r egion Localisation The zygomatic ar ch gives some pr otection to the condyle f ro m dir ect tr auma
Condylar injuries are Condylar usually caused by an indirect impact through the body of the mandible
Impact tr ansmitted
thr ough the Condylar neck
ctur e Fail to cause f ra
Contuse the capsular ligament Capsulitis Effusion of Inflammator y exudate or Bleeding into joint
Haemar thr osis
The ar ticular eminence limits the extent of for war d tr anslator y movement of of condyle
Due to lax capsule hyper mobility, obility, subluxation , or dislocation over the eminentia occur s.
f ra ctur e
E xtra
capsular or subsubcondylar fracture.
Intracapsular ±Head Intracapsular ±Head fractured within joint cavity often comminuted
Sub condylar f ra : ctur e:Result of voilence to the mental pr ominence or contr alater al body of the mandible.
The line of f ra ctur e, ver y significantly ,lies just above the poster ioosuper ior inser tion of the masseter muscle.
Condylar neck is the site of maximum tensile st r ain with anter ior and anter olater al applied for ces.
Impor tance
of Meniscus in TMJ Injur y
Meniscus:- inter vening Meniscus:disc divides ar ticular space into Tempor odiscal or super ior compar tment Condylodiscal or infer ior compar tment
Impor tance
Loss of Meniscus leads to eventual degenerative changes in condylar ar ticulation. Spr intz (1966) Tear ing or displacement of the meniscus may be an imp r equir ement for ankylosis after condylar f ra ctur e . Laskin (1977) Tr auma may initiate clicking or locking in the TMJ due TMJ due to inco--or dination of inco of tr anslator y movement of of condyle and meniscus under influence of later al pter ygoid muscle , par ticular ly if a tear is cr eated in the meniscal attachments to capsule .Toller (1974)
Ramus and the Co r onoid pr ocess
Fr actur e causes minimal displacement
Ramus of mandible - splinted by by masseter muscle on lateral aspect and medial medial pterygoid pterygoid on deep aspect.
Cor onoid pr ocesscess- splinted by tendinous inser tion of of tempor alis muscle.
The angle of Mandible
2nd common site of f r actur e
Clinical angle Sur gical angle Anatomical angle
Factor s r esponsible
1.
Shape of the bone W eakness
of the angle produced by abrupt change in direction between body and ascending ramus
2. A par tly er upted or uner upted wisdom teeth
A
3.
The insertions of the masseter and medial masseter pterygoid muscles and pterygoid the anterior limit of their insertion which just lie behind 3rd molar
C
B
Favour able able and unfavour able able Fr actu actur es es
Ver tically tically favour able able f r a ractu ctur e Lingual plate
Buccal
plate
Ver tically tically unfavour able able f r a ractu ctur e
Hori z zontally o ntally Favourable fracture
Hori z zontally o ntally unfavourabl unfavourable e fractures
Displacement
of the posterior fragment is only marked if the fracture line is unfavourable in both the planes .
Hor izontally izontally and ver tically tically favour
Hor izontally izontally and Ver tically tically unfavour able able
Fr actur e of the body of the mandible
Result f r om dir ect violence . concentr ated in the 1st molar or the canine r egions.
For war d the site of f ra ctur e , the mor e is the upwar d displacement of the elevator s counter acted by the downwar d pull of of mylohyoid muscle attached to mylohyoid r idge on the lingual aspect of mandible.
Multiple f ra ctur es of the mandible
Fr actur e of the Body and opposite angle or condyle
Bilater al
subsub-condylar f ra ctur es Anter o-medial deviation or dislocation
of condyle. Gr oss anter ior open bite.
Bilater al
angle f ra s- Two poster ior ctur esf ra gments ar e dr awn upwar ds and for war ds and anter ior tooth bear ing f ra gment is r otated downwar ds by inf ra mandibular musculatur e.
Bilater al
body f ra ctur es
Applied anatomy of the surr ounding
soft tissue
The condylar r egion
Condyle and its capsule ar e cover ed by the gland------Par otid gland glenoid lobe
Gland Enclosed in a capsule der ived f ro m the investing layer of the deep cer vical fascia
The fasia fuses with the per icondr ium and per iosteum of the exter nal auditor y meatus,, and also the tempor al meatus fascia behind the joint capsule at the r oot of the zygomatic ar ch .
Dissection to expose the joint carr ied out in close contact and dir ection with per icondr ium and per iosteum cover ing the anter ior wall of exter nal auditor y meatus
A sur gical cleft is thus cr eated along an almost avascular plane which leads natur ally to the poster ior aspect of the joint
capsule behind and beneath the glenoid lobe and its contained ar ter ies , veins and ner ves
Incision
should follow gene r al dir ection of the meatus downwar d , for war d and inwar ds and not in r ight angle to the su r face
Failur e to appr eciate this fact Result in tr ansection of the car tilaginous anter ior wall of the meatus and might injur e tympanum .(Rowe 1982)
The tempor al fascia blends with the per iosteum over lying the upper bor der of of zygomatic ar ch The zygomatic br anches of the facial ner ve cr ossing the ar ch lie immediately supe r ficial to the per iosteum. osteum. Super ficial tempor al ar ter y and vein
Temp and zyg br anch of facial ner ve
hence dissection must pr oceed super ficial to the bone and deep to the per iosteum if injur y to ner ves to is to be avoided .
The maxillar y ar ter y will be in close medial pr oximity to the condylar neck Impor tant
in case of ankylosis char acter ised by massive bone for mation in r elation to medial poles of the condyle.. condyle
Maxillar y ar ter y
the
Infer ior alveolar
ar ter y
Lingual ner ve Infer ior alveolar
ner ve
The angle and body
Natur al skin cr eases of neck r un in a corr ect dir ection for avoiding the impor tant under lying anatomical str uctur e Subcutaneous fat and super ficial fascia Platysma
muscle(car e taken to avoid exter nal jugular vein)
Super ficial layer of deep cer vical fascia
Mar ginal mandibular br anch of facial ner ve( ner ve stimulator used)
Facial ar ter y lies immediately beneath the deep cer vical fascia and can be obse r ved pulsating beneath this layer
20% cases mandibular br anch of facial ner ve tur ns upwar ds and accompanies the vessel, anter ior br anch of the poster ior facial vein may also be seen tr ansver sing this ar ea Disected away and r etr acted if not possible divided and ligated
Dissection contiued beneath the fascia fascia to the infe infer ior bor der of mandible
Submandibular gland and its capsule becomes evident
Lower pole of the par otid may be encounter ed
Dissection carr ied out taking car e to r etr act ner ve fibr es super ior ly to r each the masseter muscle
Masseter muscle shar ply divided at the infer ior bor der to expose the bone
Books
of Refer ence
Cr aniofacial development, Sper ber
Rowe and Williams, maxillofacial inju r ies second edition.
Mc Minns colour atlas of head and neck anatomy, Logan Bar i M Or al and Maxillofacial Tr auma, Raymond j. Fonseca
Gr ay,s Anatomy for students, Richar d L.Dr ake
Inter net
sour ce
