#1 Theories of Growth

Question 1

Growth = ?

Answer 1

Increase in size or number

Question 2

Develoment = ?

Answer 2

Increase in organization, complexity or specialization.

Question 3

How are deviations from “normal” growth plotted?

Answer 3

on a Standard growth chart that shows height and weight.

Question 4

What is anthropometry?

Answer 4

A measurement of head circumference

Question 5

What is interstitial skeletal growth?

Answer 5

Interstitial = “inside the tissues”, growth that occurs by a combination of hyperplasia, hypertrophy, and secretion of extracellular matrix.
*Occurs at all points within the tissue.

Question 6

What are some examples of interstitial growth?

Answer 6

• All soft tissues
• Cartilage
• Cranial base formation

Question 7

What is appositional skeletal growth?

Answer 7

“Addition to surfaces” Growth that occurs by a combination hyperplasia, hypertrophy, and secretion of extracellular matrix.

• Occurs through the activity of cells in the periosteum.
• Occurs only at SURFACE of bones.

Question 8

What are some examples of appositional growth?

Answer 8

• Bony surfaces of cranial vault

- Bony surfaces of maxilla and mandible

Question 9

Can interstitial growth occur within bone?

Answer 9

No

Question 10

Once cartilage is transformed into bone it continues to grow only by_______.

Answer 10

Appositon

Question 11

What is Endochondral skeletal growth?

Answer 11

Bone growth within cartilage

• ossification centers occur within cartilage
• Cartilage is transformed into bone

Question 12

What are some examples of Endochondral skeletal growth?

Answer 12

• Chondrocranium (skull base) = ethmoid, sphenoid and basioccupital bones.
• Epiphyseal plate cartilage of long bones.

Question 13

What is Intramembranous skeletal growth?

Answer 13

Secretion of bone matrix within and between connective tissue membranes.
* No intermediate formation of Cartilage, nor does it replace cartilage.

Question 14

What are some examples of Intramembranous growth?

Answer 14

Desmocranium: cranial vault, maxilla and mandible.

Question 15

The Mandible forms via ____________.

Answer 15

Intramembranous bone formation just lateral to Meckel’s cartilage.

Question 16

Where does condylar cartilage of the mandible come from?

Answer 16

It develops from an independent secondary cartilage and fuses with the mandibular ramus.
*Not from meckels cartilage.

Question 17

What is surface remodeling?

Answer 17

Change in shape of bones.

- The result of bone removal (resorption) in one area and bone addition (apposition) in another.

Question 18

Where does surface remodeling occur?

Answer 18

Occurs at the SURFACES of growing endochondral and intramembranous bones!

Question 19

What is Internal Remodeling?

Answer 19

Vascular channels within bones bring osteocytes to the area (allows the bone to adapt to mechanical stress)

Question 20

Does internal remodeling change shape of bone or induce growth?

Answer 20

No

Question 21

Describe the growth of the cranial vault….

Answer 21

• Flat bones formed by intramembranous formation from ossification centers.
• No Cartilaginous precursors
• Periosteal activity results in bone remodeling both at sutures and at inner and outer surfaces

Question 22

Describe growth at the Cranial base….

Answer 22

• Bones of the base of the skull formed by endochondral ossification
• Formed initially in cartilage then transformed to bone.
• Ossification centers result in ethmoid, sphenoid and basioccipital bones.

Question 23

What is a Synchondroses?

Answer 23

Cartilaginous immovable joint

Question 24

What are the 3 most important synchondrosis?

Answer 24

1. Spheno-ethmoidal
2. Inter-sphenodial
3. Spheno-occiptial

Question 25

At the cranial base, ______ growth occurs within the synchondroses.

Answer 25

Endochodral | *This lengthens the area of the cranial base.

Question 26

What are the main differences between synchodroses and sutures?

Answer 26

While both are junctions between adjacent bones: - Syn. are cartilage and sutures are CT. - Syn. have endochodral ossification while sutures have direct ossification - Syn. = active growth, while sutures = reactive growth.

Question 27

Describe the growth of the nasomaxillary complex...

Answer 27

- Formed entirely by intramembranous ossification. - No Cartilaginous precursor * Growth occurs by apposition and surface remodeling

Question 28

How does translation of the maxilla occur?

Answer 28

The Maxilla is translated downward and forward (away from the cranial base) by the apposition of bone that occurs at circus-maxillary sutures which elongates the maxilla.

Question 29

How does surface remodeling occur in the maxilla?

Answer 29

- Bone in Ant. surface of the maxilla is resorbed and Apposition of bone occurs at the maxillary tuberosity - Bone also resorbed in the floor of the nose and apposition of bone occurs at the palate and alveolar process. (this makes palate move downward and widen transversely.

Question 30

How does the mandible grow?

Answer 30

1. Endochondral growth occurs at the cartilage that cover the mandibular condyle. 2. All other areas grow by surface appositon and remodeling.

Question 31

What directions is the mandible translated?

Answer 31

Downward and forward

Question 32

Where are the primary growth sites for mandibular translation?

Answer 32

Posterior surface of the rams and the condylar and coronoid processes.

Question 33

Ultimately, what effect does surface remodeling have on the mandible?

Answer 33

1. Body of mandible grows longer 2. Ramus grows taller = more room in the body of the mandible for molars to erupt.

Question 34

What is the difference between a growth center and growth site?

Answer 34

Site of growth = location at which growth occurs. Growth center = location at which independent growth occurs. *All growth centers are growth sites, but the reverse is not true.

Question 35

Are Sutures growth centers?

Answer 35

No! They are growth sites. They react rather than act independently. *the suture theory of growth control is not true.

Question 36

What are the conclusions of the Cartilage theory of growth control?

Answer 36

- Cranial base synchondroses and nasal septum act as independent growth centers, pushing the maxilla forward. - Mandibular condyle is merely a growth sites.

Question 37

What are the principles of the Functional matrix theory of growth control?

Answer 37

- Heredity and genes play NO role int he growth of craniofacial skeleton. - Growth of the face occurs in response to functional needs mediated by the soft tissue in which bone are embedded. - ALL tissues that form bone are nearly growth sites!

Question 38

What is Mandibular Ankylosis?

Answer 38

Mechanical restriction due to scarring that prevents the growth of the mandible. (supports the functional matrix theory)