Transcript The mandible osteology

THE
MANDIBLE
OSTEOLOGY
DR. MUHAMMAD MUSTAFA
DPT,KMU
MANDIBLE
The mandible or lower jaw is the largest and strongest bone of the
face.
it articulates with the skull at the temporo- mandibular joint.
Horse shoe shaped body which lodges the teeth .
A pair of rami which projects upward from the posterior ends .
The body of the mandible meets the ramus on each side at the angle
of the mandible
THE BODY
Each half of the body has outer and inner surfaces and upper and
lower borders
Outer surface:
1) the symphysis menti is the line at which the right and left halves
meet each other. It is marked by a faint ridge.
2) the mental protuberance (chin) is a median triangular projection
area in the lower part of the midline.
The inferiolateral angles of the protrubrence form the mental
tubercles.
3The mental foramen can be seen below the second premolar tooth; it transmits the terminal branches of the inferior
alveolar nerve and vessels.
4) the oblique line is the continuation of the sharp anterior
border of the ramus of the mandible
It runs downward and forward towards the mental tubercle
5) incissive fossa is a depression that lies just below the
incisor teeth.
SYMPHISIS MENTI
The upper border of the body of the mandible is called the
alveolar part; in the adult, it contains 16 sockets for the roots
of the teeth.
The lower border of the body of the mandible is called the
base.
INCISSIVE FOSSA
MENTAL TUBERCLE
The inner surface:
The mylohyoid line can be seen as an oblique ridge that runs backward
and laterally from the area of the mental spines to an area below and
behind the third molar tooth .
2) below the mylohyoid line the surface is slightly hollowed out to form
the submandibular fossa,which lodges the superficial part of the
submandibular gland.
3) above the anterior part of mylohyoid line there is the sublingual fossa
in which the sublingual glands lie .
4) the posterior surface of the symphysis menti is marked by 4 small
elevations called the superior and inferior genial tubercles
5) the mylohyoid groove(present on the ramus) extends onto the body
below the posterior end of the mylohyoid line.
The upper or alveolar border bears sockets for the teeth.
The lower border is called the base. near the midline the base shows an
oval depression called the diagastric fossa.
THE RAMUS
Its quadrilateral in shape and has two surfaces
Lateral
Medial
It has four borders
Upper and lower
Anterior and posterior.
Coronoid and condyloid process
The lateral surface is flat and bears a number of oblique ridges.
Medial surface
1)Mandibular foramen lies a little above the centre of the ramus .it
leads into the madibular canal which descends into the body of the
mandible and opens at the mental foramen
2)The anterior margin of the mandibular
foramen is marked by a sharp tongue
shaped projection called the lingula. The
lingula is directed towards the head of the
mandible.
3) the mylohyoid groove begins just below
the mandibular foramen,and runs
downwards and forwards to be gradually
lost over the submandibular fossa
The upper border of the ramus is thin and
is curved downwards forming the
mandibular notch
.
The lower border is the backward continuation of the base of
the mandible. Posteriorly it ends by becoming continous with
the posterior border at angle of the mandible
The anterior border is thin while the posterior border is thick
The condyloid process is flattened triangular upwarsd
projection from the posterosuperior part of the ramus . Its
upper end is expanded from side to side to form the head.
The head is covered with fibrocartilage and articulates with
the temopral bone to form the temporomandibular joint .
below the head is the neck.its anterior surface presents a
depression called the pterygoid fovea.
FORAMINA AND
RELATIONS TO NERVES
AND VESSELS
1) the mental foramen transmits mental nerve and vessels.
2) inferior alveolar nerve and vessels enter the mandibular canal
through the mandibular foramen ,and runs forwards within the
canal.
3) the mylohyoid nerves and vessels lie in the mylohyoid groove.
4) the lingual nerve is related to the medial surface of the ramus in
front of the mylohyoid groove.
5) the area above and behind the mandibular foramen is related to
the inferior alveolar nerve and vessels and to the maxillary artery
6) the masseteric nerve and vessels pass through the mandibular
notch
7) the auriculotemporal nerve is related to the medial side of the
neck of the mandible .
TEMPORO MENDIBULAR JOINT
TEMPOROMANDIBULA
R JOINT
Articulation
Articulation occurs between the articular tubercle and the
anterior portion of the mandibular fossa of the temporal bone
above and the head (condyloid process) of the man- dible
below. The articular surfaces are covered with fibrocartilage.
TYPE OF JOINT
The temporomandibular joint is synovial. The articular disc
divides the joint into upper and lower cavities
Capsule
The capsule surrounds the joint and is attached above to the
articular tubercle and the margins of the mandibular fossa
and below to the neck of the mandible.
LIGAMENTS
The lateral temporomandibular ligament
Its fibers run downward and backward from the tubercle on
the root of the zygoma to the lateral surface of the neck of
the mandible .
This ligament limits the movement of the mandible in a
posterior direction and thus protects the external auditory
meatus.
SPHENOMANDIBULAR LIGAMENT
lies on the medial side of the joint
It is a thin band that is attached above to the spine of the
sphenoid bone and below to the lingula of the mandibular
foramen .
STYLOMANDIBULAR
LIGAMENT
It lies behind and medial to the joint and some distance from
it. It is merely a band of thickened deep cervical fascia that
extends from the apex of the styloid process to the angle of
the mandible .
The articular disc divides the joint into upper and lower
cavities. It is an oval plate of fibrocarti- lage that is attached
circumferentially to the capsule.
It is also attached in front to the tendon of the lateral
pterygoid muscle and by fibrous bands to the head of the
mandi- ble.
These bands ensure that the disc moves forward and
backward with the head of the mandible during protrac- tion
and retraction of the mandible .
The upper surface of the disc is concavoconvex from before
backward to fit the shape of the articular tubercle and the
mandibular fossa; the lower surface is concave to fit the
head of the mandible.
Synovial Membrane
This lines the capsule in the upper and lower cavities of the
joint.
Nerve Supply
Auriculotemporal and masseteric branches of the mandibular nerve
MOVEMENTS
The mandible can be depressed or elevated, protruded or
retracted. Rotation can also occur, as in chewing.
In the position of rest, the teeth of the upper and lower jaws
are slightly apart. On closure of the jaws, the teeth come into
contact
CLINICAL SIGNIFICANCE OF THE
TEMPOROMANDIBULAR JOINT
The temporomandibular joint lies immediately in front of the
external auditory meatus. The great strength of the lateral
temporomandibular ligament prevents the head of the mandible from passing backward and fracturing the tympanic plate
when a severe blow falls on the chin.
The articular disc of the temporomandibular joint may
become partially detached from the capsule, and this results
in its movement becoming noisy and producing an audible
click during movements at the joint.
DISLOCATION OF THE
TEMPOROMANDIBULAR JOINT
Dislocation sometimes occurs when the mandible is
depressed. In this movement, the head of the mandible and
the articular disc both move forward until they reach the
sum- mit of the articular tubercle. In this position, the joint is
unsta- ble, and a minor blow on the chin or a sudden
contraction of the lateral pterygoid muscles, as in yawning,
may be sufficient to pull the disc forward beyond the summit.
In bilateral cases, the mouth is fixed in an open position, and
both heads of the mandible lie in front of the articular
tubercles
Reduction of the dislocation is easily achieved by pressing
the gloved thumbs downward on the lower molar teeth and
pushing the jaw back- ward. The downward pressure
overcomes the tension of the temporalis and masseter
muscles, and the backward pressure overcomes the spasm
of the lateral pterygoid muscles.