2. CONTENTS
• Introduction
• Pre- natal growth of mandible
• Post- natal growth of mandible
• Fate of Meckel’s cartilage
• Secondary cartilages
• Age changes in mandible
• Clinical considerations
• Conclusion
• References
3. INTRODUCTION
Mandible is the largest and
strongest bone of the face, serves
for the reception of lower teeth.
It consists of curved, horizontal
portion, the body; and two
perpendicular portions the rami,
which unite with the ends of the
body nearly at right angles.
4. About the fourth week of
intrauterine life, the
pharyngeal arches are laid
down.
The first arch is called the
mandibular arch.
Courtesy:Human Embryology,I.B.Singh
5.
The first branchial arch, also called the first pharyngeal arch
and mandibular arch, is the first of six pharyngeal arches.
This arch divides into a maxillary and a mandibular process,
giving rise to structures including the bones of the lower
two-thirds of the face and the jaw.
The maxillary process becomes the maxilla (or upper jaw),
and palate while the mandibular process becomes the lower
jaw. This arch also gives rise to the muscles of mastication.
6. The first structure to
develop in the primodium
of the lower jaw is the
mandibular division of
trigeminal nerve.
7. Meckel’s cartilage has a close
relationship to the mandibular nerve,
beginning two thirds of the way along the
length of the cartilage.
At this point the mandibular nerve divides into lingual and
inferior alveolar branches, which run along the medial and lateral
aspects of the cartilage, respectively.
The inferior alveolar nerve further divides into incisive and
mental branches more anteriorly.
8. Development of:
Body or Corpus of
mandible
Rami of mandible
Condylar process
Coronoid process
Alveolar process
DEVELOPMENT OF
MANDIBLE
9.
The cartilage of the first arch, Meckel’s cartilage, has a close
relationship to the developing mandible.
At 6 weeks of development, this cartilage extends as a solid
hyaline cartilagenous rod surrounded by a fibrocellular capsule.
Body of mandible
10. Its proximal or cranial ends are connected with the ear capsules, and
their distal extremities are joined to one another at the symphysis by
mesodermal tissue.
The two cartilages of each side do not meet at the midline but are
separated by a thin band of mesenchyme.
11. During the 6th week of embryonic development, on the lateral aspect of
Meckel’s cartilage, a condensation of mesenchyme occurs in the angle
formed by the division of inferior alveolar nerve and its incisive and
mental branches.
At, 7th week intramembranous ossification begins in this condensation,
forming the first bone of the mandible.
12. From this centre of ossification, bone formation spreads rapidly
anteriorly to the midline and posteriorly to the point where the
mandibular nerve divides into lingual and inferior alveolar
branch.
Courtesy: Ten Cate
13.
The new bone forms a trough that consist of medial and
lateral plates that unite beneath the nerve.
The trough is soon converted into a canal as bone forms
over the nerve, joining the lateral and medial plates.
15. The ramus of the mandible develops by a rapid spread of ossification
backwards into the mesenchyme of the first branchial arch diverging
away from Meckel’s cartilage.
This point of divergence is marked by the lingula in adult mandible,
where the inferior alveolar nerve enters mandibular foramen.
16.
Thus by 10 weeks of development, the rudimentary
mandible is formed almost entirely by intramembranous
ossification.
17. Meckel’s cartilage has the following fate:
H & E stained section-Meckel’s cartilage
Prenatal Development of the Human Mandible. THE ANATOMICAL RECORD 263:314–325(2001)
Its posterior end forms the malleus and incus of the
inner ear and the sphenomandibular ligament; but its
fibrocellular capsule persists to form the
sphenomandibular ligament .
From the lingula forward to the division of the
alveolar nerve into its incisive and mental branches,
Meckel’s cartilage degenerates.
18.
The further growth of mandible is influenced by the
appearance of 3 secondary cartilages:
1) Condylar cartilage
2) Coronoid cartilage
3) Symphyseal cartilage
19. Carrot shaped cartilage appears (at 12 weeks of development) in the
region of the condyle and occupies most of the developing ramus.
It is rapidly converted to bone by endochondral ossification.
It gives rise to:
• Condyle head and neck of the mandible.
• The posterior half of the ramus to the level of inferior dental
foramen.
At 20 weeks a thin layer of cartilage remains in the condylar head.
Remnants of cartilage persists until the end of 2nd decade of life.
The condylar cartilage
20. The coronoid cartilage:
It is relatively transient growth cartilage center ( 4th MIU).
It gives riseto:
• Coronoid process.
• The anterior half of the ramus to the level of inferior dental foramen.
Disappears long before birth.
21. They are two in number.
Appear in the connective tissue between the two ends of
Meckel’s cartilage.
They are obliterated within the 1st year afterbirth.
Symphyseal cartilage:
23. It starts when the deciduous tooth germs reaches the early bell
stage.
The bone of the mandible begins to grow on each side of the tooth
germ.
By this growth the tooth germs come to be in a trough or groove
of bone, which also includes the alveolar nerves and blood vessels.
Later on, septa of bone between the adjacent tooth germs develop,
keeping each tooth separate in its bony crept.
The mandibular canal is separated from the bony crypts by a
horizontal plate of bone.
The alveolar processes grow at a rapid rate during the periods of
tooth eruption.
26. Growth by secondary cartilage
Increase in height of the
mandibular ramus
Increase in the overall length of
the mandible
Increase in the inter-condylar
distance
I. Growth of secondary cartilage
27. II. Development of the alveolar process:
The alveolar process develops in response to the presence of
tooth buds.
As the teeth erupt the alveolar process develops and increases in
height by bone deposition at the margins.
The alveolar bone adds to the height and thickness of the body of
the mandible.
In case of absence of teeth, the alveolar bone fails to develop and
it resorbs in the event of tooth extraction.
28. III. Sub-periosteal bone apposition:
Bone deposition Bone resorption Result in
External surface of
the mandible
Inner surface of the
mandible
Increase the
transeverse
dimension
Posterior border of
the ramus
Anterior border of
the ramus
Adjust the thickness
of the ramus
Anterior border of
the coronoid
process
Posterior border of
the coronoid
process
Displacement of the
coronoid process
Chin region ــــــــــــــــــــــــ
Modeling of the
lower face
30. At birth
The body of the bone is a mere shell, containing the sockets of the
two incisor, the canine, and the two deciduous molar teeth,
imperfectly partitioned off from one another.
The mandibular canal is of large size, and runs near the lower border
of the bone.
The mental foramen opens beneath the socket of the first deciduous
molar tooth.
The angle is obtuse (175°), and the condyloid portion is nearly in
line with the body. The coronoid process is of comparatively large
size, and projects above the level of the condyle.
31.
Childhood
The two segments of the bone become joined at the symphysis,
from below upward, in the first year; but a trace of separation may
be visible in the beginning of the second year, near the alveolar
margin.
The body becomes elongated in its whole length, but more
especially behind the mental foramen, to provide space for the
three additional teeth developed in this part.
The depth of the body increases owing to increased growth of the
alveolar part, to afford room for the roots of the teeth, and by
thickening of the subdental portion which enables the jaw to
withstand the powerful action of the masticatory muscles.
32.
The mandibular canal, after the second dentition, is
situated just above the level of the mylohyoid line; and
the mental foramen occupies the position usual to it in
the adult. The angle becomes less obtuse, owing to the
separation of the jaws by the teeth; about the fourth year
it is 140°.
33.
Adulhood
The alveolar and subdental portions of the body are
usually of equal depth. The mental foramen opens
midway between the upper and lower borders of the
bone, and the mandibular canal runs nearly parallel with
the mylohyoid line.
The ramus is almost vertical in direction, the angle
measuring from 110° to 120°.
34.
Old age
The bone becomes greatly reduced in size, for with the
loss of the teeth the alveolar process is resorbed.
The mandibular canal, with the mental foramen opening
from it, is close to the alveolar border.
The ramus is oblique in direction, the angle measures
about 140°, and the neck of the condyle is more or less
bent backward.
37.
Agnathia
• Hypoplasia or absence of mandible.
• The entire mandible or one side
may be missing or only the
condyle or the entire ramus.
38. Micrognathia
• Means small jaw.
• Maxilla or mandible
may be affected.
• Can be due to small jaw
or to an abnormal
positioning or abnormal
relation of one jaw to
another.
40.
Exhibit an enlargement which is confined to one side of the
body, unilateral macroglossia, and premature development,
and eruption as well as increased size of dentition.
Facial hemihypertrophy
41.
Progressive wasting of subcutaneous fat accompanied by
atrophy of skin, cartilage, bone and muscle.
Facial hemiatrophy
42.
Class II
Class III
Abnormalities of dental arch relations
43. Median mandibular cyst
- Originate from proliferation of epithelial remnants
entrapped in the median mandibular fissure during
fusion of the bilateral mandibular arches.
- Primodial cyst originating from a supernumerary
enamel organ in the anterior mandibular segment.
Developmental Cysts
44.
Alveolar cyst of newborn
- Arise from epithelial remnants of deeply budding
dental lamina during tooth development.
45. All the events taking place during development of mandible
play an important role in determining the final structure of
mandible, any deviation of which can give rise to various
abnormalities in the oro-facial region.
CONCLUSION
46. 1) Ten Cate’s Oral Histology, Development, Structure And Function, 7th
Edition.
2) Orban's Oral Histology And Embryology, 12th Edition.
3) Histology and Embryology, James Avery, 3rd Edition.
4) Human Embryology, Inderbeer Singh, 10th Edition.
5) Shafer’s Textbook of Oral pathology, 7th Edition.
6) Orthodontics- The Art and Science, S.I. Bhalajhi, 6th Edition.
7) Textbook of Oral Madicine, Anil Govindrao Ghom, 3rd Edition.
8) Vishwanathan R. Alveolar cyst of the newborn: a case report. Arch Orofac
Sci 2012;7: 85-7.
REFERENCES
Total 6 arches
5th disappears as soon as it is formed
1st arch mandibular arch
2nd arch hyoid arch
Each arch contains
Central cartilage rod that forms the skeleton of the arch
A muscular component called branchiomere
A vascular component
A neural element
