#1 Theories of Growth Flashcards
Growth = ?
Increase in size or number
Develoment = ?
Increase in organization, complexity or specialization.
How are deviations from “normal” growth plotted?
on a Standard growth chart that shows height and weight.
What is anthropometry?
A measurement of head circumference
What is interstitial skeletal growth?
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.
What are some examples of interstitial growth?
- All soft tissues
- Cartilage
- Cranial base formation
What is appositional skeletal growth?
“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.
What are some examples of appositional growth?
- Bony surfaces of cranial vault
- Bony surfaces of maxilla and mandible
Can interstitial growth occur within bone?
No
Once cartilage is transformed into bone it continues to grow only by_______.
Appositon
What is Endochondral skeletal growth?
Bone growth within cartilage
- ossification centers occur within cartilage
- Cartilage is transformed into bone
What are some examples of Endochondral skeletal growth?
- Chondrocranium (skull base) = ethmoid, sphenoid and basioccupital bones.
- Epiphyseal plate cartilage of long bones.
What is Intramembranous skeletal growth?
Secretion of bone matrix within and between connective tissue membranes.
* No intermediate formation of Cartilage, nor does it replace cartilage.
What are some examples of Intramembranous growth?
Desmocranium: cranial vault, maxilla and mandible.
The Mandible forms via ____________.
Intramembranous bone formation just lateral to Meckel’s cartilage.
Where does condylar cartilage of the mandible come from?
It develops from an independent secondary cartilage and fuses with the mandibular ramus.
*Not from meckels cartilage.
What is surface remodeling?
Change in shape of bones.
- The result of bone removal (resorption) in one area and bone addition (apposition) in another.
Where does surface remodeling occur?
Occurs at the SURFACES of growing endochondral and intramembranous bones!
What is Internal Remodeling?
Vascular channels within bones bring osteocytes to the area (allows the bone to adapt to mechanical stress)
Does internal remodeling change shape of bone or induce growth?
No
Describe the growth of the cranial vault….
- 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
Describe growth at the Cranial base….
- 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.
What is a Synchondroses?
Cartilaginous immovable joint
What are the 3 most important synchondrosis?
- Spheno-ethmoidal
- Inter-sphenodial
- Spheno-occiptial
At the cranial base, ______ growth occurs within the synchondroses.
Endochodral
*This lengthens the area of the cranial base.
What are the main differences between synchodroses and sutures?
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.
Describe the growth of the nasomaxillary complex…
- Formed entirely by intramembranous ossification.
- No Cartilaginous precursor
- Growth occurs by apposition and surface remodeling
How does translation of the maxilla occur?
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.
How does surface remodeling occur in the maxilla?
- 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.
How does the mandible grow?
- Endochondral growth occurs at the cartilage that cover the mandibular condyle.
- All other areas grow by surface appositon and remodeling.
What directions is the mandible translated?
Downward and forward
Where are the primary growth sites for mandibular translation?
Posterior surface of the rams and the condylar and coronoid processes.
Ultimately, what effect does surface remodeling have on the mandible?
- Body of mandible grows longer
- Ramus grows taller
= more room in the body of the mandible for molars to erupt.
What is the difference between a growth center and growth site?
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.
Are Sutures growth centers?
No! They are growth sites. They react rather than act independently. *the suture theory of growth control is not true.
What are the conclusions of the Cartilage theory of growth control?
- Cranial base synchondroses and nasal septum act as independent growth centers, pushing the maxilla forward.
- Mandibular condyle is merely a growth sites.
What are the principles of the Functional matrix theory of growth control?
- 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!
What is Mandibular Ankylosis?
Mechanical restriction due to scarring that prevents the growth of the mandible. (supports the functional matrix theory)
