prenatal & postnatal growth of mandible

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DEPARTMENT OF PEDODONTICS AND PREVENTIVE DENTISTRY

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DEPARTMENT OF PEDODONTICS AND

PREVENTIVE DENTISTRY

MAXILLA MANDIBLE

SOMU MAJUMDAR FINAL YEAR BDS

2010 - 2011

INTRODUCTION 1 - 7 PRENATAL EMBRYOLOGY

OF MAXILLA 8 - 13 PRENATAL EMBRYOLOGY

OF MANDIBLE 14 - 18 DEVELOPMENT OF PALATE 19 - 23 POSTNATAL GROWTH OF

MAXILLA 24 - 28

POSTNATAL GROWTH OF

MANDIBLE 29 - 35 AGE CHANGES IN MAXILLA 36 -37 AGE CHANGES IN MANDIBLE 38 - 41

INDEX PAGE NO.

MAXILLA

1

It is the second largest bone of face. The two maxillae form the whole of upper jaw, and each maxilla enters into the formation of face, nose, mouth, orbit, the infratemporal fossa and ptyerygopalatine fossae.

It has a body and four process, the frontal, zygomatic, alveolar and palatine.

BODY OF MAXILLA

It is pyramidal in shape, with its base directed medially at the nasal surface, apex directed laterally at the zygomatic process.

The surfaces are:

Anterior or facial Posterior or infratemporal Superior or orbital Medial or nasal

2

ANTERIOR SURFACE OF MAXILLA 3

POSTERIOR SURFACE OF MAXILLA

ORBITAL SURFACE OF MAXILLA4

MEDIAL SURFACE OF MAXILLA

MANDIBLE

It is the largest and strongest bone of the face.

It develops from the first pharyngeal arch.

It has a horse - shoe body which lodges the teeth, and a pair of rami which projects upwards from the posterior ends of the body and provide attachments to muscles.

5

BODY OF THE MANDIBLE

Each half of body has outer and inner surfaces, upper and lower surfaces.

6

7

OUTER AND INNER SURFACE OF MANDIBLE

8

9

Comparision of prenatal embryology of Amphibian, Reptile and Mammal

10

Around the 4th week of intra-uterine life, a prominent bulge appears on the ventral aspect of embryo corresponding to the developing brain.

Below the bulge a shallow depression which corresponds to the primitive mouth appears called STOMADEUM.

The floor of stomodeum is formed by the buccopharyngeal membrane which seperates it from the foregut.

11 By around the 4th week of intra-uterine life, 5 branchial

arches form in the region of the future head and neck.

Each of these arches give rise to muscles, connective tissue, vasculature, skeletal components and neural components of the future face.

The first branchial arch is called the mandibular arch and plays important role in the development of naso-maxillary region.

The mesoderm covering the developing forebrain proliferates and forms a downward projection that overlaps the upper part of stomadeum. This is called FRONTO-NASAL PROCESS.

12

The stomadeum is thus overlapped superiorly by the fronto-nasal process. The mandibular arches of both

sides form the lateral walls of the stomadeum. The mandibular arch gives off a bud from its dorsal end called THE MAXILLARY PROCESS.The maxillary process grows ventro-medial-cranial to the main part of the mandibular arch which is now called THE MANDIBULAR PROCESS. Thus., at this stage the primitive mouth or stomadeum is overlapped from above by frontal process, below by the mandibular process and on either side by maxillary process.The ectoderm overlying the fronto-nasal process shows bilateral localized thickenings above the stomodeum. These are called the NASAL PLACODES. These soon sink and form the NASAL PITS.The formation of these nasal pits divides the frontonasall process into 2 parts:

a. Medial nasal processb. Lateral nasal process.

13

The two mandibular processes grow medially and fuse to form the lower lip and lower jaw.

As the maxillary process undergoes growth, the fronto-nasal process becomes narrow so that the 2 nasal pits come closer.

The line of fusion of maxillary process and the medial nasal process corresponds to the naso-lacrimal duct.

14

Around the 4th week of intra-uterine life, the developing brain and the pericardium form two prominent bulges on the ventral aspect of the embryo. These bulges are seperated by the primitive oral cavity or stomodeum.

The floor of stomodeum is formed by the buccopharyngeal membrane which seperates it from the foregut.

The pharyngeal arches are laid down on lateral and ventral aspects of the cranialmost part of the foregut which lies in close approximation with the stomodeum.

15 Initially, there are 6 pharyngeal arches, but the 5th one

usually disappears as soon as it is formed leaving only five.

They are seperated by 4 branchial grooves.

The first arch is called MANDIBULAR ARCH and second arch is called HYOID ARCH.

Each of these arches contain: A central cartilage rod that forms the skeleton of the

arch. A muscular component called branchiomere. A vascular component. A neural element.

Microscopic picture

16MECKEL’S CARTILAGE

It is derived from the first branchial arch around the 41st – 45th day of intra-uterine life. It extends from the cartilaginous otic capsule to the midline or symphysis and provides a template for guiding the growth of the mandible.

A major portion of this cartilage disappears during growth and the remaining part develops into following structures:

The mental ossicles Incus and malleus Spine of sphenoid bone. Anterior ligament of malleus Spheno - mandibular ligament

17

The first one to develop in the primordium of the lower jaw is the mandibular division of trigeminal nerve. This is followed by the mesenchymal condensation forming the 1st branchial arch.

The ossifying membrane is located lateral to the meckle’s cartilage and its accompanying neuro - vascular bundle.

As ossification continues, the meckle’s cartilage becomes surrounded and invaded by bone. Ossification stops at the site that will later become the mandibular lingula from where the meckle’s cartilage continues into the middle ear and develops into the auditory ossicles i.e. incus and malleus.

18

A = mental foramen, B = external wall, C = internal wall, D = coronoid process, E = sensory canal, F = meckelian fossa, G = ventral process.

19

20

The fronto – nasal The palate is formed by the contribution of:

• Maxillary process• Palatal shelves given off by the maxillary process.• Fronto – nasal process

The fronto – nasal process gives rise to the premaxillary region while the palatal shelves form the rest of the palate. As the palatal shelves grow medially, their union is prevented by the presence of the tongue.

Thus, initially the developing palatal shelves grow vertically downwards the floor of mouth.

They change from vertical to a horizontal position. Various reasons are:

Alteration in biochemical and physical consistency of the connective tissue of the palatal shelves. Alteration in vasculature and blood supply to the palatal shelves. Appearance of an intrinsic shelf force. Rapid differential mitotic activity. Muscular movements.

21Stage 1

Stage 2

22

Face and the palate

Stage 3

Stage 4

Primitive palate of a human embryo of thirty-seven to thirty-eight days.

23Stage 5

The mouth cavity. The cheeks have been slit transversely and the tongue pulled forward.

24

Maxilla is attached to the cranial base by means of a number of sutures.Thus, the growth of the cranial base has a direct bearing on the naso - maxillary growth.

The naso – maxillary complex is simply moved anteriorly as the middle cranial fossa grows in that direction. The passive displacement of the maxilla is an important growth mechanism during primary dentition years but becomes less important as growth of cranial base slows.

It takes place by:

Displacement Growth of sutures Surface remodeling

DISPLACEMENT

GROWTH OF SUTURESThe maxilla is connected to the cranium and cranial base bya number of sutures:

Fronto – nasal Fronto – maxillaryZygomatico – temporalZygomatico – maxillaryPterygo - palatine

25

26

2. Inferior orbital fissure3. Optic canal4. Infraorbital foramen5. Lacrimal crests6. Lacrimal groove7. Zygomaticomaxillary suture8. Zygomatico frontal suture9. Orbital plate of the ethmoid bone

1. Superior orbital fissure

27

sutures seen on the lateral aspect of the skull.       

28SURFACE REMODELING

In addition to the growth occurring at the sutures, there is massive remodeling by: 1) Increase in size2) Change in shape of bone3) Change in functional relationship

29

RAMUS

a. The ramus moves progressively posterior by a combination of deposition and resorption.

b. Resorption occurs in the anterior part of ramus while bone deposition occurs on the posterior region.

30

BODY OF THE MANDIBLE As observed, the anterior border of adult ramus exhibits

bone resorption while posterior border shows bone deposition.

Additional space is available by means of resorption of the anterior border of ramus is made use of to accommodate the erupting permanent molars.

31ANGLE OF THE MANDIBLE

resorption

deposition

On the lingual side of the angle of mandible, resorption occurs on the postero – inferior aspect and deposition occurs on the anterio – superior aspect.

This results in flaring of the angle of the mandible as age advances.

32

THE LINGUAL TUBEROSITY

Major site of growth for the lower bony arch.It forms the boundary between the ramus and the body.It moves posteriorly by deposition on its posteriorly facing

surface.The prominence of the tuberosity is increased by the

presence of large resorption field just below it. Thus, it produces a lingual fossa.

THE ALVEOLAR PROCESSIt develops in response to the presence of tooth buds.As the teeth develops and increases in height by bone deposition at the margins.It adds to the height and thickness of the body of the

mandible and is particularly manifested as a ledge extending lingual to the ramus to accommodate the 3rd molars.

33CONDYLAR PROCESS

1. It has been recognized as the important site of growth.2. The head of the condyle is covered by a thin layer of

cartilage called the condylar cartilage.3. The presence of this is an adaptation to withstand the

compression that occurs at the joint.4. There are 2 school of thoughts regarding its growth. They

are: It was earlier believed that growth occurs at the surface of the condylar cartilage by means of bone deposition and the condyle grows towards the cranial base. As the cranial base pushed against the cranial base, the entire mandible gets displaced forwards and downwards.

34

It is now believed that the growth of soft tissues including the muscles and connective tissues carries the mandible forwards away from the cranial base (CARRY AWAY PHENOMENON.) Bone growth follows secondarily at the condyle to maintain constant with the cranial base.

The condylar growth rate increases at puberty reaching a peak between 12 ½ - 14 years. The growth ceases around 20 years of age.

35

CORONAL PROCESS

The growth of coronal process follows the enlarging “ v “ principle. Viewing, the longitudinal section coronoid process from

the posterior aspect, it can be seen that deposition occurs on lingual { medial } surfaces of the left and right coronoid process.

Viewing it from the occlusal aspect, the deposition on the lingual of the coronoid process brings about a posterior growth movement in the “ v ” pattern.

Briefly it has a propeller- like twist, so that its lingual side faces 3 general directions all at once, i.e. posteriorly , superiorly and medially.

36

AT BIRTH :The transverse and anteroposterior diameters are more than the vertical diameter.Frontal process is well marked.Body consists of a little more than the alveolar process, the tooth sockets reaching to the floor of orbit.Maxillary sinus is a mere furrow on the lateral wall of the nose.

Inferior surface of maxilla at birth.

Anterior surface of maxilla at birth.

37

IN ADULT : Vertical diameter is greatest due to the development of the alveolar process and increase in the size of the sinus.

IN THE OLD :

The bone reverts to infantile condition.Its height is a result of absorption of the alveolar process.

38

IN INFANTS AND CHILDREN:

39

The two halves of mandible fuse during the first year of life.

At birth the mental foramen, opens below the sockets for the two deciduous molar teeth near the lower border. This is because the bone is made up of only of the alveolar part with teeth sockets.

The mandibular canal runs near the lower border.

The foramen and canal gradually shift upwards.

Lower jaw of child and adult, showing the mental foramen.

40IN ADULTS:

The mental foramen opens midway between the upper and lower borders because the alveolar and subalveloar parts of the bone equally developed.

The mandibular canal runs parallel with the mylohyoid line.

The angle reduces to about 110 or 120 degrees because the ramus becomes almost vertical

41IN THE OLD AGE:

Teeth fall out and alveolar border is absorbed, so that the height of the body is markedly reduced.

The mental foramen and the mandibular canal are close to the alveolar bone.

The angle again becomes obtuse about 140 degrees because the ramus is oblique.