POST NATAL DEVLOPMENT OF MAXILLA AND MANDIBLE

Presented by: MUDIT KUMAR (29)

Some definitions related to Growth

- The self multiplication of living substance – JX Huxely.

- Increase in size, change in proportion & progressive complexity.- Krogman

-Entire series of sequential anatomic & physiological changes taking place from the beginning of prenatal life to senility –Meredith.

Terminology Related To Growth:

Growth Sites :

Growth sites are growth fields that have a special significance in the growth of a particular bone.

Eg. Mandibular condyle in the mandible,

Maxillary tuberosity in the maxilla.

The growth sites may process some intrinsic potential to growth.

Growth Centers:Growth centers are special growth sites , which control

the overall growth of the bone.

Eg. Epiphyseal plates of long bone.

It is the differential growth activity involving simultaneous deposition & resorption on all the inner & outer surfaces of the bone.

Eg. Ramus moves posteriorly by a combination of resorption & deposition.

Remodelling

Mechanism Of Bone Growth

-BONE DEPOSITION & RESORPTION

-CORTICAL DRIFT

-DISPLACEMENT

Bone deposition & resorption:Bone changes in shape & size by two basic

mechanisms.

The bone deposition & resorption together is called “ BONE REMODELING”.

The changes that bone deposition & resorption can produce are:

A) Change in size

B) Change in shape

C) Change in proportion

D) Change in relationship of the bone with adjacent structures.

Cortical Drift:

- A combination of bone deposition & resorption resulting in a growth movement towards the deposition surface is called “Cortical Drift”.

- If bone deposition & resorption on either side of a bone are equal - the thickness of the bone remains constant.

- If in case more bone is deposited on one side & less bone resorbed on the opposite side –The thickness of the bone increases.

Displacement: It is the movement of the whole bone as a unit.

Displacement can be of two types.

Primary displacement: If a bone gets displaced as a result of its own growth,it is called “Primary displacement”.eg. Growth of the maxilla at the tuberosity region results in pushing of the maxilla against the cranial base which results in the displacement of the maxilla in a forward & downward direction.

Secondary displacement: If the bone gets displaced as a result of growth & enlargement of

an adjacent bone, it is called Secondary displacement.eg. The growth of the cranial base causes the forward & downward displacement of the maxilla.

Characteristics of Bone Growth

Bone formation occurs by 2 methods of differentiation of mesenchymal tissues that may be of mesodermal or ectomesenchymal origin.

Accordingly 2 types of bone growth is normally seen.

1) Intramembranous ossification : The transformation of mesenchymal

connective tissue usually in membranous sheets,into osseous tissues.

2) Endochondral ossification:

The conversion of hyaline cartilage prototype models into bone.

The cartilage ‘template ‘ is then replaced by endochondral bone accounting for indirect bone growth.

POST-NATAL GROWTH Of MAXILLA

Since, the maxillary complex is attached to the cranial base, there is a strong influence of the latter on the former. Although there is no sharp line of demarcation between the cranium & maxillary growth gradients,yet the position of the maxilla is dependent upon the growth at spheno-occipital & spheno-occipital synchondroses.Hence, while discussing the growth of nasomaxillary complex, we have to look into three aspects.

1)The displacement in the position of the maxillary complex,-Primary displacement- occurs in a forward direction.This occurs by growth of the maxillary tuberosity in a posterior direction .This results in the whole maxilla being carried anteriorly. -Secondary displacement- Occurs in a downward & forward direction as the cranial base grows.

2) Growth at sutures:.- Sutural connective tissue, - Proliferation - Ossification - Surface apposition - Resorption - Translation are the mechanisms for

maxillary growth.- Maxilla is related to cranium at least partially by the, - Frontomaxillary suture - Zygomaticotemporal suture - Pterygogopalatine sutureThe growth in these areas would serve to move the maxilla

downward & forward.

3)Surface Remodelling:

Remodeling occurs by bone deposition & resorption to bring about:

a) Increase in size

b) Change in shape

c) Change functional relationship

Bone remodeling seen in the midfacial region

Bone remodeling of the palate resulting in its downward displacement

Growth of the palate exhibiting V pattern of growth

The naso-maxillary complex as it emerges from beneath the cranium

POST NATAL GROWTH PHASE OF MANDIBLE

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

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.

During first year of life

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 lengthening the alveolar border & maintaining the anterior- posterior dimension of ramus.

After first year of life these changes occurs

Growth in mandible

1. ENDOCHONDRAL 2. INTRAMEMBRANOUS

Mandibular ossification Patterns

1. PERIOSTEAL APPOSITION

2. SURFACE REMODELLING.

Patterns of growth in mandible

Patterns of growth in mandible

The body of the mandible grows longer by periosteal apposition of bone on posterior surface of mandible.

The ramus grows higher by endochondral replacement at condyles accompanied by surface remodelling.

1. The ramus 2. The condylar 3. The coronoid process.

Principle sites of growth in mandible

Thus the mandible is now being translated downwards and forwards and at the same time its growing in size upwards and backwards.

The surface remodelling suggests that mandible grows longer by apposition of new bone on the posterior surface of the ramus and at the same time large quantities of bone are removed from the anterior surface of ramus.

This in turn suggests that ramus moves away from the chin.

As the growth proceeds, the

posterior surface may become the anterior as the remodelling

continues.

In infancy the ramus is located at a spot where the primary

first molar will erupt.

Progressive posterior remodelling thus creates space for the second

primary molar and the sequentially for the permanent

first molar.More often than not this growth ceases before enough space has been created

for the eruption of third permanent molar which becomes impacted.

Prominence of chin

The change in the contour of chin occurs because the area just above the chin and the base of the alveolar process is a resorptive area.

With maturity the prominence increases due to overall growth pattern of the mandible and with the resorption of the area above the chin.

Mandibular growth in accordance to TMJ

When the TMJ remains in the same antero- posterior position relative to the cranial base the growth expressed is entirely as the forward movement of the chin.

On the other hand when the TMJ moves downwards and backwards in relation to the cranial base not much growth of chin is expressed.

Enlow’s v principle

According to Enlow, many facial bones show a 'V' typegrowth pattern.

The growth movements and enlargement occur towards thewide 'V' ends of the bone.

This type of growth occurs at the base of themandible, ends of long bone, palate, body of mandible

Drift and displacement Growth movement of enlarging portion of bone by

remodelling :DRIFT. The combinations of deposition and resorption

result in growth movement toward the depository surface.

The growth movement of the whole bone as a unit :DISPLACEMENT.

The bone is carried away from its articulation in relation to other bones.

THE NET GROWTH OCCURS IN THE DIRECTION OF DRIFT PLUS DISPLACEMENT.

Rotations of jaws during growth

Types of rotations: Internal rotation: rotation occurring in core

of each jaw and tends to be masked by the surface changes and alterations in the rate of tooth eruption.

External rotations : includes surface changes.

The overall change in the orientation of each jaw results from combination of these two.

Components of internal rotation

Matrix rotation: the rotation around the condyles ;

Intramatrix rotation: centered within the body of the mandible.

Conventionally, the range of internal rotation is about 10-15 degrees.

Implant studies of jaw rotation Carried out by Bjork.

The mandible consists of three functional processes:

Alveolar process Muscular process Condylar process

In these studies, implants are placed in stable areas away from functional processes and significant jaw rotation in the core can be observed.