iDENTical The Development of Upper & Lower Jaw Models

iDENTical The Development of Upper & Lower Jaw Models

GROWTH OF MAXILLA:

• Maxilla is a membranous bone and development/growth of maxilla is completed early & when compared to mandible.
• Maxilla (width) follows closely neural growth curve more than the general growth curve in scammon's curve
• Maxilla cannot be considered as separate bone it has to be nasomaxillary complex because of close association or attachment of maxilla to cranial base.

GROWTH OF MAXILLA ALONG WITH NASOMAXILLARY COMPLEX:

Growth of nasomaxillary complex occurs in following ways:

• Displacement
• Growth at sutures
• Surface remodelling

2 Basic growth movements:

Drift (Cortical remodelling)

Combination of simulatneous deposition and resorption resulting in a growth movements towards the depositing surface which has been described as cortical drift Enlow

Displacement:

Maxilla is attached to the cranial base with the means of number of sutures, thus the growth of cranial bae has a strong influence on the nasomaxillary growth

Primary displacement (translation):

is the movement of bone due to its bone growth.

This results in the whole maxilla being carried anteriorly as the bone is displaced by its own enlargement

Passive or Secondary displacement occurs in a downward or forward direction as the cranial base grows

GROWTH SITE OF MANDIBLE:

• The mandible,at Birth is small, with short ramus,large gonial angle, and flat
• mandibular fossa with no articular eminence.The condyles are at the level of the occlusal plane.
• It appears as if mandibular growth is forward and downwards, and as such one could suppose that the mandible enlarges by growth at the anterior end.

Growth of the mandible was thought to occur principally by growth at condyle. Superior and posterior growth of condyle presses against the glenoid fossa/ Cranial base providing an anterior thrust to displace the lower jaw forward (similar to growth of maxilla).

• Limited growth takes place at the symphysis menti until fusion occurs.
• At the condylar cartilages
• Posterior border of ramus
• Alveolar Ridges

These areas of bone, deposition largely account for increase in the height, length and width of the mandible

Superimposed upon this basic incremental growth are numerous regional remodeling changes that are subjected to functional changes that are subjected to the local functional changes that are subjected to local functional influences involving selective resorption and displacement of individual mandibular elements.

The concept of posterior growth and anterior Displacement leads to primary displacement.

The CONDYLAR HEAD

The cartilaginous covering on the condyle serves a dual function:

1. It Represents An Articular Cartilage(although covered by a fibrous membrane),and

2. It functions as a growth cartilage.

The condyle is a major site of growth involved in the upward and backward elongation thermus,in combination with coordinated growth activity by the periosteum and endosteum in cortical parts of the condyle,neck,and ramus.

The Condylar growth centre is however, not the primary centre for the growth of the entire mandible and is not responsible for governing overall mandibular growth.

Formation of bone within the condylar heads causes the mandibular rami to grow upward & backward displacing the entire mandible in an opposite forward & downward direction

As It Grows,the deeper portion of the proliferating cartilage becomes continuously replaced by endochondral bone,thereby producing medullary bone additions in the condyle and its neck.This process is continuous,and as the condyle moves by growth,former levels of the condyle become simultaneously converted into the elongating neck

Bone resorption subjacent to the condylar head accounts for the narrowed condylar head

The outer cortical plate is produced by the activity of the periosteum and endosteum independent of the growth cartilage but inconjunction with it.

RESORPTION AT RAMUS OF THE MANDIBLE:

Resorption occurs along the anterior border of the ramus lengthening the alveolar border & maintaing the antero posterior dimension of the ramus.

The CONDYLAR NECK

• Growth Progresses,bone from one leve lin the condyle‐upper ramus region, getsincorporatedintothenextlevellowerdown.
• Insequence:Condylar head parts incorporated into new upper Condylar neck
• Upper parts of the neck undergo remodelling conversion into the new lower parts The lower portions receive direct remodelling changes into the ramus proper.