2.3- growth and development- sites and types

What is primary growth?

Is produced by bone formation on the surface of the bone

What are the 3 main types of growth at the sutures of the cranial vault?

Primary

Secondary growth

Remodelling

Which mechanisms occur on the surface and sutures of bones?

Primary growth, primary displacement, active displacement

What is primary displacement?

Bone moves to another position due to deposition, resorption and when space is created by enlarging bones

What is secondary growth/passive displacement?

Bone appears to grow due to growth of adjacent bones, which transports the bone into a new position

What are the types of growth of adjacent bones?

Secondary growth, secondary displacement, passive displacement

What is secondary displacement?

Bone moves to another position, due to surrounding physical forces not deposition or resorption

What is surface remodeling?

Changes in the shape and size of the bone due to apposition and resorption

What are examples of remodelling mechanisms that occur on outer and inner surfaces of the cranial vault?

Remodelling

Cortical drift

Active displacement

What is the cranial vault made up of?

Flat bones formed by intramembranous bone formation

Where does the growth of the bone of the cranial vault occur?

At the cranial sutures- periosteum

At birth what happens to the skull bones/cranial vault?

separated by fontanelles- loose connective tissue, allows deformation during childbirth

What happens to the skull bones after birth (post natal growth)?

Apposition along the edges of fontanelles- closes soft spots

Bones remain separated by thin sutures, fuse in adult life

What are the mechanisms of growth in the cranial vault?

Apposition of new bone at sutures

Remodelling- allows for changes in contour during growth, bone removed from inner surface and new bone added to exterior

How does growth at the sutures of cranial vault occur?

Primary growth at coronal, sagittal, parietal, temporal, occipital sutures- to accommodate rapid brain expansion

As brain expands, bones are displaced outwardly

Intramembranous sutural growth replaces fontanelles

What kind of growth occurs at the outer and inner surfaces of the cranial vault?

Periosteal and endosteal remodelling

Resorption at endosteal lining and apposition at periosteum causes overall thickness of medullary space

What is the structure within a synchondrosis?

2 sided epiphsyeal plate

Cellular hyperplasia in centre

Bands of maturing cartilage cells extends in both direction

Mature cartilage eventually replaced by bone

Where is the intersphenoidal synchondrosis located?

Between anterior and posterior portion of sphenoid

Doesn’t contribute to growth after birth

Where is the sphenoethmoidal synchondrosis?

Between sphenoid and ethmoid bone

Max activity from birth to 7 yrs- passive displacement

Where is sphenoccipital synchondrosis?

Between sphenoid and occipital bone

Doesn’t ossify till 13-15 yrs so major determining factor of vertical development of upper half of face and position of superior dentoalveolar complex in sagital plane

What is a synchondrosis and where is it found causing growth in?

Cartilaginous joint where hyaline cartilage divides and becomes bone

Found between and within the ethmoid, sphenoid, and occipital bones- causes growth of cranial base

Why does what happens to cranial base affect the structure, dimension and placement of various facial parts?

Acts as a template from which the face develops and other bones grow

In the embryo stage how is the maxillary bone formed and give a type of the cartilage?

Apposition- growth cartilages help make the head longer and help move maxilla forward but don’t actually become the maxilla

Malar cartilage completely disappears and replaced by bone before birth

What happens to the maxilla in postnatal development?

connects to the rest of the skull at sutures

Surface remodelling

Is pushed forward by growth of cranial base

In the maxilla, what occurs after the cranial push at the sutures?

The posterior and superior sutures allow it to grow down and forwards

Apposition occurs during the movement

Sutures remain same width but increase in length

What occurs as the maxilla grows downward and forward?

Front surfaces are remodelled

Bone removed from anterior surface which moves forwards

What is the additive effect of the palate bone?

Nasal side bone removed, added to oral side- thickens palate

Anterior part of alveolar process is a resorptive area so it cancels out some forward growth

How does the growth of the nasomaxillary complex occur, how does nose grow?

Passive displacement

Nose grows more rapidly than rest of face

Proliferation of lateral cartilages alters shape of nose

Where does the mandible develop?

In same area as cartilage of 1st pharyngeal arch-Meckels, which disintegrates as mandible develops

What are the points about post natal growth of mandible?

Endochondral and periosteal activity

Displacement of TMJ is a minimal role

Cartilage covers surface of Condyle at TMJ - hyperplasia, hypertrophy, endochondral replacement

What are the growth sites of the mandible?

Chin - inactive, translated forward and downward

Mandible body- grows by periosteal apposition

Ramus- endochondral replacement

What is an area of resorption in the mandible?

Anterior border of the chin

What is the order in which growth is completed in the different planes of space and which age is each completed?

Width, length, height

W 10-12

L 14-16

H 18-20