Growth & development

The nature of skeletal growth

Hyperplasia

Hypertrophy

Secretion of extra-cellular matrix

Growth of the soft tissues occurs by a combination of hyperplasia and hypertrophy. These processes go on

everywhere within the tissues and the result is what is called interstitial growth which simply means that it

occurs at all points within the tissue.

When mineralization takes places, hard tissue is formed and interstitial growth becomes

impossible

direct or surface apposition

Variability of the growth pattern

In fetal life, at about the third month of intrauterine development, the head takes up

almost 50% of the total body length.

Schematic representation of the changes in overall body proportions during normal growth and development

Concepts of the craniofacial growth

Concept 1: Bones grow by adding new bone tissue on one side of the cortex (deposition, +ve) and the other side undergoes resorption (-ve). This process is termed drift.

Bone apposition & bone resorption

Drift

Concept 2: -The outside and inside of bone surfaces are blanketed by growth fields. -The external surface (periosteum) is not all depository. - If a given periosteal area has a resorptive type, the opposite inside (endosteum) of that same area has a depository field and vice versa.

Concept 3: Periosteal bone comprises about half of all cortical bone. Bone laid down by the lining membrane (endosteum) making up the other half.

Concept 4: Bone does not grow itself; growth is produced by the soft tissue matrix. The operation of the growth fields is carried out by the membranes and other surrounding tissues rather than by the hard part of bone.

Concept 5: Growth fields do not have the same rate of growth activity. Fields having significance in growth are termed growth sites e. g.

condyle.

Concept 6: Remodeling & relocation

Concept 7: Primary displacement

As a bone enlarges, it is carried away from other bones in direct contact with it.

This creates the space within which bony enlargement will take place.

It is a physical movement of the whole bone and occurs by deposition and resorption.

The condyle and ramus grow upward and backward the, ramus becomes longer and wider to accommodate: 1- The increasing mass of the masticatory muscles inserted into it. 2- The enlarged breadth of the pharyngeal space. 3- The vertical length of the naso-maxillary complex.

Concept 8: Secondary displacement: It is the separate movement of bone caused by the enlargement of other bones. Example: Increase in the size of the bone that composes the middle cranial fossa results in a downward and forward movement of separate the naso-maxillary complex.

Concept 9: Posterior growth anterior displacement: The whole maxillary region is displaced downward and forward away from the cranium by the expansive growth of the soft tissues in the mid-facial region and bone deposites in the sutural surfaces between them.

Drift versus displacement: Drift is the deposition process while

displacement is the push contribution. Drift occurs by deposition on one side and

resorption on the other side.

Concept 10: The V principle: Enlow had observed that many surfaces are better expressed as Vs. The inside of the V is where the new tissue is formed; it also represents the surface facing the direction of growth. Growth of the head of a long bone can be

expressed as a series of ever-increasing Vs.

The mandible expressed with the V principle

Concept 11: The law of electrogenesis: -Bone is moldable under certain external forces. -It reaches a normal configuration on the physiologic loads and muscle pulls. -When sufficient load is applied to a bone, bending occurs. -A differential pattern of electrical activity elicites osteoblastic activity on the surface.