Lecture 3 Flashcards
why is the study of growth of the craniofacial complex so important in orthodontics?
conditions related to malocclusion will typically have a skeletal component, which will contribute to the malocclusion, and must therefore be incorporated into the patients treatment plan
many theories of growth examine one or more of what 3 structures?
bone, cartilage, and the soft tissue matrix
what is the major difference in the theories of growth?
the location at which the genetic control is expressed (ie. through the periosteum of the bone, inside the cartilage, or throughout the soft tissues)
growth is strongly influenced by what two main factors?
genetics and environment (nutrition, health, illness, physical activity, etc.)
___ = the role of genetic preprogramming is presumed to have establishing basic facial pattern
the genetic blueprint model
what is the theory of growth that states that cartilage controls growth?
-for many bones, cartilage does the growing, while bone merely replaces it
what is the theory of growth that states that bioelectric signals control growth?
- bioelectric signals occur from distortions of the crystals in bone, causing a minute deformation of the bone matrix due to mechanical strain
- this generates bioelectric charges which trigger osteoblastic and osteoclastic responses
what is wollf’s law (theory of growth)?
- bone in a healthy person or animal will adapt to the loads under which it is placed
- if loading on a particular bone increases, the bone will remodel itself over time to become stronger to resist that sort of loading
what is the mechanostat model (theory of growth)?
- refinement of wollf’s law that states that bone growth and bone loss is stimulated by the local mechanical elastic deformation of bone
- bone adapts its mechanical properties according to the needed mechanical function
the mechanostat model describes the linear relationship in the healthy body between muscle cross sectional area and the bone cross sectional area. why are these relationships important for bone loss situations like osteoporosis?
an adapted training utilizing the needed maximum forces on the bone can be used to stimulate bone growth and hence prevent or help to minimize bone loss
what is the theory that sutures control growth?
- master growth centers in the body control growth
- it was once thought that the mechanism for translation of the maxilla was the result of pressure created by growth at the sutures, so that the maxilla was literally pushed downward and forward
- THIS THEORY IS FALSE
a ___ is a location at which growth occurs
growth site
a ___ is a location at which independent (genetically controlled) growth occurs regardless of the growth and development of adjacent structures
growth center
what is the nasal cartilage theory of growth?
- the cartilaginous nasal septum causes the midface to displace anteriorly and inferiorly as it grows in size
- sutures of the maxilla serve as reactive areas by forming new bone when the sutures are pulled apart
- the nasal septum is considered an important growth center
are sutures considered growth sites or growth centers?
- growth sites
- if the area of a suture between two facial bones is transplanted to another location, the tissue does not continue to grow
do sutures have intrinsic growth potential?
no
-they produce new bone at the sutural edges of the bone fronts in response to external stimuli
growth at the sutures allows growth of the cranial vault to be coordinated with growth of the ___
neurocranium
too little or delayed bone growth at the sutures will result in ___, whereas too much or accelerated bone growth at the sutures will result in ___
- wide-open fontanelles
- osseous obliteration of the sutures (craniosyostosis)
experiments indicate that cranial base synchondroses are endowed with an ___ growth potential and are comparable to ___ with regards to their tissue-separating capacity
- independent
- epiphyseal plates
the independent growth potential of synchondroses are also evident from the observation that their growth continues for a longer duration than that of the brain, which means ___
the growth of the cranial base and the brain is not closely interdependent
the theories of synchondroses growth suggest what?
- synchondroses are genetically coded in craniofacial growth and will develop even in the absence of functional activity
- this would make synchondroses growth centers similar to epiphyseal plates
what is the functional matrix theory of growth?
- there is an innate growth potential in the long bones, but neither the cartilage of the mandibular condyle nor the nasal septum is a determinant of jaw growth
- growth of the face occurs as a response to functional needs and neurotrophic influences, and is mediated by soft tissue
- as the soft tissues grow, both bone and cartilage react
in terms of this class, do we agree with moss’s functional matrix theory of growth?
-this theory contradicts the textbook which considers the nasal septum as a primary growth center (we are going to consider this to be true for this class; in other words, we don’t really agree with moss’s functional matrix theory)
Moss’s functional matrix theory of growth theorized that the major determinant of growth of the maxilla and mandible is the enlargement of the ___ and ___, which grow in response to functional needs
nasal and oral cavities
___ typically refers to an increase in size, but it can tend to be more linked to change than anything else
growth
___ is a more descriptive term, meaning an increased degree of organization, complexity, or specialization
development
the concept of pattern in growth refers to what two things?
- a set of proportional relationships at a point in time
- the change of these proportional relationships over time
T or F:
not all of the tissue systems of the body grow at the same rate
true
the cephalocaudal growth gradient is strongly influential in the growth and proportions of the ___ and ___
head and face
using growth charts, if a child is measured above ___ or below ___, they should be evaluated for an abnormal growth pattern
above 95% or below 5%
the average peak growth for girls is around age ___, and for boys is around age ___
12, 14
girls will generally start growth sooner/later than boys, will grow for a longer/shorter amount of time, and will grow more/less than boys
sooner, shorter, less
generally speaking, the earlier the growth spurt, the shorter/longer duration of the growth spurt, and the more/less overall growth
shorter, less
is chronological age a good indicator of an individuals growth status?
not usually; it is best to use physical signs that indicate the patient has started puberty rather than using age
at the cellular level, what are the 3 possibilities for growth?
- hypertrophy - increase in cell size
- hyperplasia - increase in cell number
- cells secrete extracellular material causing an increase in size
all 3 of these processes occur in skeletal growth
growth of soft tissues occurs by a combination of ___ and ___
hyperplasia and hypertrophy
___ means that growth can occur at all points within a tissue
interstitial growth
___ growth of cartilage occurs by the recruitment of fresh cells (chondroblasts) which adds new matrix to the surface
appositional
cartilage is pressure tolerant and is able to provide flexible support due to what two things?
- it is avascular
- it contains an intracellular matrix of proteoglycans
when mineralization takes place and hard tissue is formed, what type of growth becomes impossible?
interstitial
in mineralized tissues, hyperplasia, hypertrophy, and secretion of extracellular material can only occur ___
- on the surface
- this process is called direct or surface apposition and involves the addition of new bone to the bones surface through activity of cells in the periosteum
the periosteum consists of a ___ outer layer, and a ___ inner layer which contains ___
- fibrous
- cellular
- osteoblasts
T or F:
bone is often formed as primary tissue
false
it always replaces a preexisting support tissue
what are the two types of bone formation?
- intramembranous - bone replaces collagen membrane frameworks
- endochondral - ossification (bone replaces cartilage)
changes to bone shape can only occur through what two processes?
resorption and apposition
the greatest period of cranial growth occurs between what years of age?
birth - five years of age
what four areas is the craniofacial complex divided into?
- cranial vault
- cranial base
- nasomaxillary complex
- mandible
the bones that cover the upper and outer surface of the brain comprise the ___
cranial vault
the bony floor under the brain, which also is the dividing line between the cranium and the face, comprises the ___
cranial base