SURGICAL ANATOMY OF MANDIBLE.pptx

SURGICAL ANATOMY OF
MANDIBLE
By: Dr. A. Shalini Sampreethi
Sr. Lecturer
Oral and Maxillofacial Surgery
MNR Dental College and Hospital

CONTENTS
• INTRODUCTION
• DEVELOPMENT AND GROWTH OF MANDIBLE
• ANATOMY OF MANDIBLE
• ATTACHMENTS AND RELATIONS OF MANDIBLE
• VASCULAR SUPPLY AND NERVE SUPPLY
• AGE CHANGES OF MANDIBLE
• APPLIED ASPECTS
• CONCLUSION
• REFERENCES

INTRODUCTION
• The mandible or lower jaw, is the largest &
strongest bone of the face.
• The word “Mandible” is derived from Greek word
“mandere” – to masticate or chew.
• The Latin word “ mandibula” – lower jaw.
• It is horse-shoe shaped & the only movable
bone of skull.

GROWTH AND DEVELOPMENT OF MANDIBLE
Growth and development of an individual is divided
into two periods.
Prenatal period
Post natal period

PRENATAL GROWTH PHASE
About the fourth week of intrauterine life,the
pharyngeal arches are laid down.
The first arch is called the mandibular arch and
the second arch the hyoid arch.

• About the 4th week of IU life, the developing brain
& pericardium form two prominent bulges which are
separated by the primitive oral cavity or
stomodeum.
• The floor of stomodeum is formed by the bucco-
pharyngeal membrane, which separates it from
forgut.
• Pharyngeal arches are laid in approximation with
stomodeum.

• Each arch has
1. Outer covering of ectoderm.
2. An inner covering of endoderm.
3. Core of mesoderm.
• Arches are separated from each other by
1.Pharyngeal cleft or groove externally.
2.Pharyngeal pouches internally.

Each of these five arches contain
 A central cartilage rod that form the skeleton of
the arch.
 A muscular component termed as bronchomere.
 A vascular component.
 A neural element.

• The development of face
begins in the 4th to 8th week
of intra-uterine life.
The face is derived from
An unpaired frontonasal
process.
A pair of Maxillary process.
A pair of Mandibular process.

• Mandibular arch gives of a
bud from dorsal end called
maxillary process.
It grows ventro-medially
called mandibular process.
• Mandibular processes of both
sides grow towards each other
& fuse in midline.

INTRAMEMBRANOUS BONE FORMATION
The first structure to develop in the primodium of
the lower jaw is the mandibular division of
trigeminal nerve that precedes the mesenchymal
condensation forming the first [mandibular] arch.

At around 36 -38 days of intrauterine life there is
ectomesenchymal condensation.
Some mesenchymal cells enlarges , acquire a
basophilic cytoplasm and form osteoblasts.
These osteoblasts secrete a gelatinous matrix
called osteoid and result in ossification of an
osteogenic membrane.

The resulting intramembranous bone lies lateral to
meckel’s cartilage of first [mandibular] arch.
In the sixth week of the intrauterine life a single
ossification centre for each half of the mandible
arises in the bifurcation of inferior alveolar
nerve into mental and incisive branches.

During seventh week of intrauterine life bone begin
to develop lateral to meckel’s cartilage &
continues until the posterior aspect is covered
with bone.
Between eigth & tewelth week of intrauterine life
mandibular growth accelerate , as a result
mandibular length increses.

Ossification stops at a piont , which later become
mandibular lingula, the remaining part of meckels
cartilage continues to form sphenomandibular
ligament & spinous process of sphenoid.
Secondary accessory cartilage appear between tenth
& fourteenth week of intrauterine life to form head
of condyle , part of coronoid process & mental
protuberance.

ENDROCHONDRAL BONE FORMATION
Endrocondral bone formation is seen in 3 areas of
mandible.
 The condylar process
 The coronoid process
 The mental process

THE CONDYLAR PROCESS:
At fifth week of intruterine life , an area of
mesenchymal condensation is seen above the ventral
part of developing mandible.
At about tenth week it develops in cone shaped
cartilage.
It migrate inferior & fuses with mandibular ramus
at about 4 month.

• This cone shaped cartilage is replaced by bone but
its upper end persists acting as growth cartilage &
articular cartilage.

THE CORONOID PROCESS-
Secondary accessory cartilage appear in region of
coronoid process at about 10- 14 week of
intrauterine life.
This cartilage become incorporated into
expanding intramembranous bone of ramus &
dissapear before birth.

THE MENTAL REGION:
In mental region , on either side of symphysis ,
one or two small cartilage appear and ossify in
seventh week of intrauterine life to become mental
ossicles.
These ossicles become incorporated into
intramembranous bone when symphysis ossify
completely.

POST NATAL GROWTH PHASE
At birth the two rami of the mandible are short ,
condylar development is minimum and there is no
articular eminence in glenoid fossa. A thin layer
of fibrocartilage & connective tissue exists at the
midline of symphysis to separate right & left
mandibular bodies.
At fourth month of age and end of first year
symphysial cartilage is replaced by bone.

• During first year of life appositional growth is
active at alveolar border, at distal & superior
surfaces of the ramus, at the condyle, along the
lower border of mandible and on its lateral
surface.

After first year of life these changes occurs :
 Mandibular growth become more selective ,condyle shows
considerable activities , mandible moves and grows downward
& forward.
 Appositional growth occurs on posterior border of the ramus
and on the alveolar process.
 Resorption occurs along the anterior border of ramus
lenthening the alveolar border & maintaining the anterior-
posterior dimension of ramus.

 Gonial angle changes after little muscle activity.
 Transverse dimension is mainly due to growth at posterior
border in an expanding V pattern.

The two rami also diverge
outward from below to above
so that additive growth at
coronoid notch , coronoid
process &condyle also
increses the superior inter-
ramus dimension.
Alveolar process of mandible
grows upward & outward on an
expanding arc. This permit
dental arc to accommodate the
larger permanent teeth.

Scott divides the mandible into three basic types
of bone:
1) Basal
2) Muscular
3) Alveolar
 Basal portion is tube like central foundation
running from condyle to the symphysis.
 Muscular portion [gonial angle &coronoid process]
is under influence of masseter, internal pterygoid
& temporal muscle. They determine the ultimate form
of the mandible in these areas.

Alveolar portion exists to hold the teeth &
gradually resorbed in the event of tooth loss.
Reduced muscular activity would account for
flattening of gonial angle and reduction of the
coronoid process.

MOSS say that the mandible as a group of
microskeleton unit:
Coronoid process as one skeleton unit under
influence of temporalis.
Gonial angle is another skeleton unit under
influence of massetor & internal pterygoid
muscles.
Alveolar process is under the influence of the
dentition.
Basal tubular portion of mandible serves as
protection for the mandibular canal and follows
a logarithim spiral in its downward & forward
movement from beneath the cranium.

THE CHIN:
Enlow & harris feel that chin is “associated with a
generalised cortical recession in the flattened
regions positioned between the canine teeth. The
process involves a mechanism of endosteal cortical
growth.”
On lingual surface, behind the chin heavy
periosteal growth occurs , with the dense lamellar
bone merging and overlaping on the labial side of
the chin.

• In male , the apposition of the bone at symphysis
seems to be about the last change in shape during
the growing period. This change is much less
apparent in the females.

BODY OF MANDIBLE
• It is U or Horse shoe shaped and consists of 2 surfaces and 2 borders
A. OUTER SURFACE :
1. Symphysis Menti : The line at which the right and left halves of the
bone meet each other. It is marked by a faint ridge
2. Mental Protuberance : median triangular projecting area in the lower
part of the midline
3. Mental Foramen : It lies below the interval between the premolar
teeth.
4. External oblique Line : Continuation of the sharp anterior border of
the ramus of mandible.
5. Incisive Fossa / Mental Fossa : Depression that lies just below the
incisor teeth

B. INNER SURFACE:
1. Mylohyoid line : Prominent ridge that runs
obliquely downwards and forwards from below the third
molar tooth to the median area below genial tubercle.
2. Submandibular fossa : It lies below the mylohyoid
line, which lodges the submandibular gland.
3. Sublingual fossa : It lies above the mylohyoid
line, which lodges the sublingual gland.
4. Genial tubercles : Posterior surface of the
symphysis menti is marked by four small elevations
called the superior and inferior tubercle.
5. Mylohyoid groove : Extends from ramus to the body
below the posterior end of the mylohyoid line.
6. Digastric fossa : Near the midline the base shows
an oval depression.

Superior Border :
 It is hollowed into Sockets for the reception of
the teeth.
 They vary in depth and size according to the
containing teeth.
Inferior Border :
 Also called Base of the mandible.
 It is rounded, longer than the superior , and
thicker in front than behind.

RAMUS OF MANDIBLE
 It is quadrilateral in shape and it has
A. 2 surfaces
1.Lateral
2.Medial
B. 4 borders
1.Superior
2.Inferior
3.Anterior
4.Posterior
C. 2 processes
1. Coronoid
2. Condylar

 Lateral surface :
flat and bears number of oblique ridges
 Medial surface :
1. MANDIBULAR FORAMEN : It lies little above the
centre of ramus at the level of occlusal plane.
It leads into mandibular canal which opens at
mental foramen.
2. LINGULA : Anterior margin of foramen marked by
tongue shaped projection.
3. MYLOHYOID GROOVE : Begins just below mandibular
foramen, runs forwards and downwards to be
gradually lost over the submandibular fossa.

 Anterior Border :It is thin above
and continuous with coronoid
process , and thick below and is in
continuation with oblique line.
 Posterior Border : It is thick,
rounded & extends from condyle to
angle and is in contact with
Parotid gland.
 Upper Border : It is thin and
Curved downwards forming Mandibular
notch and is surmounted by coronoid
process in front and condylar
process behind.
.

 Lower Border : It is thick,
straight and is backward
continuation of base of
mandible.
 Posteriorly it ends by
becoming continuous with
posterior border of angle of the
mandible.
 Typically everted but inverted
in females.

Coronoid process
 It is flattened triangular
upward projection from the
antero-superior part of ramus.
 Anterior border is continuous
with anterior border of ramus ,
and is palpable below zygoma
while while opening mouth.
 Posterior border bounds the
mandibular notch.

Condylar process:
 It is strong upward
projection from the postero-
superior part of ramus.
 Upper end is expanded side
to side to form head.
 Head is covered with
fibro cartilage and
articulate temporal bone to
form TMJ .
 Constriction is seen below
head is neck.(its anterior
surface has depression
called pterygoid fovea)
 It is convex in all
directions.
 Medial part articulates with
Mandibular fossa of temporal
bone.

 Lateral aspect is blunt
and palpable in front of
tragus.
 Lateral part is separated
from cartilagenous external
accoustic meatus by Parotid
gland.
 Lateral surface of neck
provides attachment to
lateral ligament of TMJ.

ATTACHMENTS AND RELATIONS OF MANDIBLE
1. OUTER SURFACE OF MANDIBLE
• External oblique line - origin to buccinator,
depressor inferioris, depressor anguli oris.
• Incisive fossa - origin of mentalis, mental slips of
orbicularis oris.
• Lateral surface of ramus - insertion for masseter.
• Lower border - deep cervical fascia and platysma.
• Postero-superior lateral surface of ramus - parotid gland.
• Lateral surface of neck - attachment to lateral ligament of
temperomandibular joint , parotid gland.

2. INNER SURFACE OF MANDIBLE
• Mylohyoid line - origin to mylohyoid muscle , attachment to superior
constrictor of pharynx, pterygomandibular raphae.
• Medial surface of ramus - medial pterygoid muscle attachment.
• Superior genial tubercles – genioglossus.
• Inferior genial tubercles – origin to geniohyoid.
• Lingula - sphenomandibular ligament.
• Apex of coronoid process - temporalis attachment.
•
• Pterygoid fovea - lateral pterygoid muscle.
• Diagastric fossa - anterior belly of diagastric.

FORAMINA & OTHER RELATIONS
• Mental foramina - mental nerve and vessels.
• Mandibular notch - massetric nerve and vessels.
• Medial side of neck - auriculo temporal nerve.
• Mylohyoid groove - mylohyoid nerve and vessels.
• Mylohyoid groove in front of ramus - lingual nerve.
• Mandibular canal and foramina - inferior alveolar nerve and
vessels.
• Area above and behind mandibular foramen – Maxillary artery.

AGE CHANGES OF MANDIBLE
At Birth In Childhood

ARTERIAL SUPPLY OF MANDIBLE
• It is mainly divided into 2 categories :
1. Endosteal/ Central blood supply
2. Periosteal/ Peripheral blood supply
• Central blood supply is via Inferior Alveolar Artery except the
coronoid process which is supplied by Temporalis muscle vessels.
• Inferior alveolar artery arises from maxillary artery which in turn
is a branch of External carotid artery.
• Inferior alveolar artery branches :
a) Lingual branch
b) Mylohyoid branch
c) Incisive branch
d) Mental branch
• Peripheral blood supply is mainly via Periosteum via the nutrient
vessels those penetrate the cortical bone and anastamose with the
branches of Inferior alveolar artery.

VENOUS SUPPLY OF MANDIBLE
 Drains into Internal Jugular vein and
External Jugular vein through Maxillary vein,
Facial vein and pterygoid plexus.

LYMPHATIC DRAINAGE OF MANDIBLE
• Most of the mandible and lower teeth drain into Sub
mandibular group of lymphnodes.
• A small wedge in the symphysis region and lower
incisors drain into Sub mental lymph nodes.
Sub Mental group
Sub mandibular
group
Jugulo-omohyoid
group of deep
cervical nodes
Posterior
group of sub
mandibular
nodes
Jugulo
digastric
group of
deep
cervical
nodes

NERVE SUPPLY OF MANDIBLE
• Mainly supplied by Mandibular division of Trigeminal nerve
MANDIBULAR DIVISION (sensory root)
• UNDIVIDED NERVE DIVIDED NERVE
- Nervous spinosus (meningeal)
- Nerve to medial pterygoid
Anterior Division Posterior division
- Nerve to Lat. Ptgd - Auriculotemporal
-Nerve to masseter - Lingual
-Nerve to Temporal - Mylohyoid
-Buccal nerve - IAN : 1.Mental
2.Incisive

• Motor root of Trigeminal nerve passes along with V3
and supplies :
1. Muscles of mastication
2. Mylohyoid
3. Anteror belly of digastric
4. Tensor tympani
5. Tensor veli palatini
• Marginal mandibular branch of facial nerve runs below
the angle of mandible deep to platysma and supplies to
muscles of lower lip and chin.

MUSCLES RELATED TO MANDIBLE
• Muscles of facial expression: 1.Buccinator
2.Mentalis
3.Depressor anguli oris
4.Depressor labii inferioris
5. Platysma
• Muscles of mastication : 1.Temporalis
2.Masseter
3.Lateral pterygoid
4.Medial pterygoid
• Geniohyoid
• Genioglossus
• Anterior belly of digastric
• Superior constrictor of pharynx

MUSCLES PRODUCING MOVEMENTS
• DEPRESSION : 1. Lateral pterygoid - main
2. Digastric
3. Geniohyoid
(Helps when mouth opened wide)
4. Mylohyoid
(against resistance)
• ELEVATORS : 1. Masseter
2. Temporalis
( Ant. Vertical & Middle oblique fibres)
3. Medial pterygoid (both sides)
• PROTRUSION : 1.Lateral pterygoid
2. Medial pterygoid
3. Superficial oblique fibres of Masseter

• RETRACTION : 1. Temporalis
(Posterior horizontal fibres)
2. Masset er
(Deep vertical fibres)
• LATERAL SIDE TO SIDE :
1. Left side : Right lateral and medial pterygoid;
Left Masseter and temporalis
2. Right side : Left lateral and medial pterygoid;
Right Masseter and Temporalis

NERVE BLOCKS OF MANDIBLE
• INFERIOR ALVEOLAR NERVE BLOCK
• MENTAL NERVE BLOCK
• BUCCAL NERVE BLOCK
• INCISIVE NERVE BLOCK
• GOW-GATES TECHNIQUE (OPEN MOUTH TECHNIQUE)
• VAZIRANI-AKINOSI TECHNIQUE (CLOSED MOUTH
TECHNIQUE)

APPROACHES TO MANDIBLE
• In mandibular pathologies and fractures there is
need for exposure to treat the site at the same
time maintaining its harmony and aesthetics.
• The various approaches include :
1. SUBMANDIBULAR APPROACH
2. SUBMENTAL APPROACH
3. VESTIBULAR APPROACH
4. PREAURICULAR APPROACH
5. ALKAYAT BRAMLEY INCISION
6. POST AURICULAR APPROACH

1. MUSCLE INJURIES
2. NERVE INJURIES
3. VASCULAR INJURY
4. TMJ DISLOCATION
5. FRACTURES
6. SPACE INFECTIONS

MUSCLE INJURIES
1. MYLOHYOID MUSCLE :
• Surgical manipulation of the floor of the mouth may
result in edematous swelling of sublingual space
(above mylohyoid muscle) and submandibular space
(below mylohyoid muscle)
• Cellulitis of sublingual space is quite common.
• Excessive bilateral cellulitis of sublingual space may
push the tongue backwards and compress the pharynx –
thus Airway obstruction.

2. GENIOGLOSSUS MUSCLE
 During the elevation of the lingual mucosa before
making an impression for a subperiosteal implant a
portion of the muscle may be reflected from genial
tubercle.
 If the muscle is completely detached from the
tubercle it may lead to retrusion of the tongue and
airway obstruction.
3. MEDIAL PTERYGOID MUSCLE
 The medial pterigoid muscle binds the
pterigomandibular space medially ,during surgical
procedures involving the area of pterigomandibular
space infection may occur and may be dangerous due to
its closed proximity to the pharyngeal space.

Surgical exposure of the tissue posterior to the
maxillary tuberosity may also involve the medial
pterygoid muscle as a part of the muscle
originates from the maxillary tuberosity
3. LATERAL PTERYGOID MUSCLE
The lateral pterygoid muscle fibres are placed in
an angulated manner and because of this there may
be pain in patients with a full arched sub
periosteal implant or prosthetic splint.

4. MENTALIS
Complete reflection of the mentalis muscle for the
purpose of extension of a subperiosteal implant may
result in a condition known as witch’s chin
If there is failure of the mentalis muscle reattachment
following the implantation drooping of lower lip occurs.
An external bandage is applied for four days to help in
the reattachment of the muscle.

5. BUCCINATOR MUSCLE
• Myositis of the detached buccinator muscle in
patients with subperiosteal implants may cause
swelling and pain at the site of origin of the
muscle.

6. TEMPORALIS MUSCLE
• Surgical exposure medially
may injure tendon of
Temporalis while harvesting
bone from external oblique
ridge or placing incisions
for sub periosteal Implants.
7. MASSETER MUSCLE
• Masseteric space infections
may result during surgery to
expose bone for ramus
extension needed Implant.

NERVE INJURIES
1. INFERIOR ALVEOLAR NERVE
 The nerve may be damaged
easily when making an
incision or reflection
of the mucosa in its
area therefore position
of the inferior dental
canal in vertical and
buccolingual dimension
is of great importance
during site preparations
for implants.

2. LINGUAL NERVE
 The position of the nerve
is medial to the retromolar
pad.
 The incision should remain
lateral to the pad and the
mucosal reflection should
be done with a periosteal
elevator in constant
contact with the bone to
prevent injury to the
nerve.
 Injury of nerve causes
causes ipsilateral
paraesthesia , loss of
taste and reduction of
salivary secretion.

3. MYLOHYOID NERVE
 The nerve lies in
closed relation to
the ramus of
mandible hence it
is prone to get
damaged during
surgical
intervention.

4. LONG BUCCAL
NERVE
 When the ramus
is accessed
for the
purpose of a
block graft
excision great
care must be
take to
protect this
nerve from
injury.

5. MENTAL NERVE
Tremendous variation in
the position of mental
nerve seen.
In preprosthetic surgery
nerve repositioning is
done as nerve is present
more towards alveolar
border in old age.
Injury to nerve causes
paresthesia of skin of
chin, lower lip and
labial mucosa.

VASCULAR INJURIES
1. INFERIOR ALVEOLAR
VESSELS
During surgical
orthognathic surgery
procedures, the major
nutrient vessels of
mandible can sometimes get
damaged.
2. FACIAL ARTERY
Facial artery preservation
is important while giving
sub mandibular incisions.

MANUAL REDUCTION :
• Downward pressure followed by posterior and
upward movement.

FRACTURES OF MANDIBLE
• Most weakest point of mandible is canine socket area (
due to long canines) and next common site is Angle.
(due to presence of impacted molars)
• Bilateral parasymphysis fracture can cause airway
obstruction if associated with loss of consciousness.
• With advancing age resorption of alveolar process and
decrease in vertical height thereby making it prone to
fracture.
• Slender neck of condyle makes it liable to fracture as
a result of direct violence to chin- this acts as
safety mechanism to prevent injury to mid cranial
fossa.
• Sideway blow causes fracture of opposite condyle along
with same side parasymphysis fracture.

Sagittal split osteotomy – splitting the ramus of
mandible bilaterally in sagittal plane for
correcting micrognathia
osteomyelitis is more common in mandible than
maxilla as it has rich blood supply

# OF ANGLE OF MANDIBLE
• It is second common site of fracture after condyle
• It is impotant to distingiush i) Clinical angle
ii) Surgical angle
iii) Anatomical angle
• CLINICAL ANGLE : It is the junction between alveolar bone and
ramus at the orijin of internal oblique line.
• SURGICAL ANGLE : Junction between body of the mandible and
ramus at the external oblique ridge.
• ANATOMICAL OR GONIAL ANGLE : Here the lower border meets the
posterior border of ramus.

SPACE INFECTIONS RELATED TO MANDIBLE
• Submandibular space infection
• Sub mental space infection
• Pterygomandibular space infection
• Sublingual space infection
• Buccal space infection
• Masseteric space infection
• LUDWIGS ANGINA – bilateral cellulitis involving sub
mandibular, submental and sublingual space.

SYNDROMES ASSOCIATED WITH MANDIBLE
• Mandibulofacial Dysostosis or Treachers collin
syndrome – Bird like face (Hypoplasia of mandible)
• Crouzons syndrome – Psedoprognathism (maxillar
retrusion)
• Apert syndrome – Psedoprognathism with open bite
(mid face hypoplastic)
• Hemicraniofacial microsomia – Short mandibular
ramus (chin deviation , micrognathia)
• Pierre robin syndrome – Retrognathic mandible

SURGICAL CONSIDERATION
Mandibular canal Partially or completely
edentulous cases→ placement of implants difficult.
Injury to the mental nerve  paraesthesia to the
skin of the chin, the lower lip and the labial
mucosa.
Injury to the lingual nerve during flap reflection,
releasing incisions, anesthestic injections.

External oblique ridge:
Resective surgery difficult because of the amount
of bone to be removed.
Apical positioning of the flap is difficult in
these areas.
 A high buccinator attachment results in a shallow
vestibule, making grafting procedures difficult.

Mandibular tori:
The mucosa over the tori region is usually thin and
hence is subject to tearing.
Source of autogenous bone for grafting procedures.

Mylohyoid ridge:
A prominent ridge may →broad bony ledge resulting
in limited surgical access and also makes flap
reflection difficult.

Coronoid process:
• A prominent coronoid process may be in close
proximity to the maxillary tuberosity
resulting in limited surgical access
Genial tubercle:
• In cases of severe horizontal bone loss they
may pose a problem during implant placement
and flap reflection
Alveolar process:
• Prominent teeth results in marginal tissue
recession, bony dehiscence or fenestration

CONCLUSION:
• The selection of an appropriate surgical technique
that can best satisfy the treatment goals &
objectives is directly influenced by through
knowledge of anatomic relations between bone, soft
tissues & teeth. The study of anatomy of mandible &
surrounding structures is essential.

REFERENCES:
• Gray’s anatomy, 38th edition.
• Human anatomy, B.D Chaurasia, 7th edition.
• Essentials of human anatomy, A.K Datta, 2nd edition
• Human Embryology , I B Singh
• Contemporary orthodontics ,Proffit ,4th edition.
• Text book of orthodontics ,S.I Bhalaji ,3rd edition.
• Text book of Oral and Maxillofacial Surgery , Laskins.
• Text book of Oral and Maxillofacial Infections
,Topazain.

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