Ortho module 1 part C Flashcards
What is a growth site and a growth center?
An area where growth is occurring is a growth site
An growth site that has the ability to grow on its own independently of its surroundings is a growth center.
What is mode and mechanism of growth?
Mode of growth: The way it occurs. In the case of skeletal growth there are 2 possible modes: replacement of cartilage or direct apposition of bone.
Mechanism of growth: How growth changes occur at a higher level such as downward and forward movement of the jaws or expansion of the cranial vault.
What is determinant of growth?
The cause of the observed growth changes and what controls them.
What is suture theory?
A theory developed by Harry Sicher to describe the growth of bone at synchondroses of the cranial base, at the mandibular condyle, and at the sutures of the cranial and facial bones. He theorized that pressures created by formation of new bone at these sites literally pushed the bones apart.
What are sutures in Sicher’s theory?
They are both sites and centers of skeletal growth.
In his view this was also the case for synchondroses, condylar cartilage, and at least to some extent periosteal surfaces
He did not think of mode of growth much because he assumed that the mechanism of growth was bones being pushed away from the site of bone formation.
How accurate was Sicher’s theory?
Sutures and periosteal surfaces are not primary determinants of craniofacial growth and must be considered sites, but not centers, of growth. Growth at sutures does not push bones apart, instead, when sutures are pulled apart growth occurs to fill in the gaps.
What evidence indicates that bone growth does not push the bones apart and instead the gaps are made prior to bone being formed?
2 lines of evidence:
First, when sutures are transplanted at different locations they fail to grow as centers would.
In both animal experiment and humans with growth problems, it can be shown that sutures respond to outside influences. If the cranial or facial bones are pulled apart at the sutures, new bone will fill in and the bones end up bigger than they would have been otherwise and the opposite occurs if the bones are pushed closed to each other.
What was James Scott’s theory?
That main determinant of craniofacial growth is the growth of cartilages. Cartilage growth would push the bones to new positions; in response bone would fill in at sutures and surface remodeling would occur.
What did Scott believe about mandibular growth?
Scott accepted evidence that sutures reacted rather than acted on their own, and so did not push bones apart by growing independently.
He agreed with Sicher about cartilage push by the cartilages of the cranial base and the mandible as a major mechanism for cranial and facial growth
Good way to visualize the mandible:
Considering it as analagous to the diaphysis of a long bone bent into a horseshoe and with the epiphyses removed.
The condylar cartilage represents half an epiphyseal plate on each end of the bone. This representation means the condyle is seen as the growth center.
How is the pace of growth of the maxilla controlled according to Scott?
In the 1950s Scott hypothesized that the cartilaginous nasal septum serves as a “pacemaker” for other aspects of maxillary growth.
What are the potential outcome of growth center experiments?
If growth center:
Transplanting cartilage leads to growth of surrounding tissue
If cartilage removed the growth of surrounding tissues is inhibited.
If it has innate growth potential:
It can grow when transplanted elsewhere
What experimental support is there for epiphyseal plate growth?
When cartilage from an epiphyseal plate is transplanted, it grows very nicely.
What evidence is there of the cranial base synchondroses being centers of growth?
Experimental evidence is hard to get. However, this cartilage is a remnant of original skeelatl cartilages like the epiphyseal plates which indicates its likely.
Mutations prevent growth from taking place in these areas.
What does experimental evidence indicate about nasal septum cartilage and condylar cartilage?
Transplanting cartilage from the nasal septum gives equivocal results. Sometimes it grows reasonably well, sometimes it doesn’t.
When mandibular condyles are transplanted, they hardly grow at all.
Based on this evidence, we have to doubt that the mandibular condylar cartilage could possibly act as a growth center, and we would have some doubts about the nasal septum.
