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
the ___ is made up of the nose, maxilla, and associated small bones
nasomaxillary complex
sutures are formed during embryonic development at the sites of approximation of the membranous bones of the ___; they serve as major sites of ___ during postnatal craniofacial growth
- craniofacial skeleton
- bone expansion
what is required for sutures to function as growth sites?
they need to remain in an unossified state, yet allow new bone to be formed at the edges of the approximating bone fronts
the cranial vault is made up of a number of ___ bones that are formed embryonically, by what type of bone formation?
- flat
- intramembranous bone formation
once embryonic development is complete, bones that are formed by intramembranous bone growth grow by ___ on the bones surfaces, and by ___ at sutures
- apposition and resorption by the periosteum on the bones surfaces
- periosteal bone formation at sutures
cranial vault growth is entirely the result of ___ activity at the bony surfaces and at the periosteum-lined contact areas between adjacent skull bones called the ___
- periosteal
- cranial sutures
what is the major mechanism for growth of the cranial vault?
- apposition of new bone at the cranial sutures
- old bone is removed from the inner surface, while new bone is added on the exterior surface (bone remodeling)
the ___ is the most complex structure of the human skeleton, and its main function is to ___
- cranial base
- protect and support the brain
what is the first region of the skull to reach adult size?
- the cranial base
- it is also the structural foundation of many aspects of the craniofacial architecture
in orthodontics, what is used as a reference point during cephalometric analysis to evaluate and compare a patients overall growth and development?
the anterior cranial base
how are the bones of the cranial base formed?
they are initially formed in cartilage and are later transformed into bone by endochondral ossification
ossification centers appear early in embryonic life in the ___
chondrocranium (cranial base)
ossification centers in the chondrocranium (cranial base) indicate the eventual location of what 3 structures?
- basioccipital
- sphenoid
- ethmoid bones that form the cranial base
the chondrocranium (cranial base) develops from 3 pairs of cartilagenous precursors. what are they?
- the ethmoid prechordal cartilages
- the sphenoid hypophyseal cartilages
- the occipital parachordal cartilages
in the development of the chondrocranium (cranial base), ossification progresses in an orderly pattern from the ___ to the ___, and finally fuses into a single irregular and much-perforated base plate (cranial base)
posterior to anterior
the bones of the chondrocranium (cranial base) are preformed in cartilage and ossify by the process of ___; the chondrocranium forms the skull/cranial base and supports what 4 structures?
- endochondral ossification
- supports the brain, olfactory organs, eyes, and inner ears
relative to the chondrocraium, what happens in the 4th month in utero?
- the growing size of the chondrocranium requires an internal blood supply, so during the 4th month in utero, there is an in-growth of blood vascular elements into various points of the chondrocranium
- these areas become ossification centers
during ossification of the chondrocranium, bands of cartilage called ___ remain between the centers of ossification
synchondroses
what are the names of the synchondroses formed during ossification of the chondrocranium?
- spheno-occipital synchondroses
- inter-sphenoid synchondroses
- spheno-ethmoid synchondroses
cranial base synchondroses are regarded as important ___ of the craniofacial skeleton
growth centers
which of the cranial base synchondroses is a particularly important growth center and why?
the spheno-occipital synchondrosis because of its late ossification and because of its important contribution to post-natal cranial base growth
the spheno-occipital synchondrosis is situated ideally to influence both ___ growth and ___ growth
maxillary midface and mandibular growth
the inter-sphenoid and spheno-ethmoid synchondroses form the ___, and are typically fused and stable after age ___
- anterior cranial base
- 7 years old
histologically, synchondroses look like a two-sided epiphyseal plate with an area of ___ in the center and bands of ___ extending in both directions; near the outer end of each synchondrosis is a zone of ___
- cellular hyperplasia
- maturing cartilage cells
- actively dividing cartilage cells
some of the actively dividing cartilage cells at the outer end of each synchondrosis are pushed more toward the outer layers by what process?
cell proliferation
what happens to the cells that are pushed toward the outer layers of the synchondrosis?
- they undergo hypertrophy
- they secrete an extracellular matrix
- they eventually degenerate as the matrix begins to mineralize, which is then rapidly replaced by bone
in what situation does growth of the synchondroses continue? what situation is synchondrosal bone growth considered complete?
- as long as the rate at which cartilage cells proliferate is equal to or greater than the rate at which they mature, then growth will continue
- eventually the rate of maturation exceeds the rate of proliferation, and the last of the cartilage is replaced by bone, the synchondrosis disappears, and synchondrosal bone growth is complete
does growth in the zones on either side of the synchondroses growth centers have to be the same? why or why not?
- no
- typically, more bone deposition occurs on the ethmoid bone at the spheno-ethmoidal synchondrosis and on the occipital bone at the spheno-occipital synchondrosis
the growth pattern of the face requires that the maxilla move a considerable distance ___ and ___ relative to the cranium and cranial base
downward and forward
in what two ways does the maxilla move downward and forward relative to the cranium and cranial base?
- a push from behind is created by cranial base growth
- compensatory growth at the sutures in response to the displacement of the maxilla through soft tissue growth
the maxilla is attached to the ___ end of the cranial base, and so lengthening of the cranial base pushes the maxilla forward up until about what age?
- anterior
- 7 years
what is the major mechanism for growth of the maxilla before age 7?
structures of the nasomaxillary complex are displaced forward as the anterior cranial base lengthens and the anterior lobes of the brain grow in size
what is the mechanism of growth for the maxilla after age 7?
- cranial base growth stops after age 7, so sutural growth is the only mechanism for bringing the maxilla forward, which is accomplished through growth of the soft tissue
- as soft tissue growth continues, a space opens up at the maxillary posterior and superior sutural attachments, which is then filled in with a proliferation of bone from the periosteum, on both the maxillary and cranial aspects of bone
what are the two processes that are occurring as the maxilla grows downward and forward?
as the maxilla grows downward and forward, its front surfaces are remodeled, and bone is removed from the most anterior surface while simultaneously added to the most posterior surface
T or F:
remodeling of the palatal vault is different than remodeling of the maxilla
- true
- the palatal vault is carried downward and forward along with the rest of the maxilla, but at the same time, bone is removed on the nasal side and added on the oral side, thus creating an additional downward and forward movement of the palate
during remodeling of the palatal vault, some bone is removed from the ___ surface, which cancels out some ___ translation
- anterior
- forward
the two hemimaxillas are connected by the ___ suture
intermaxillary
when an individual is growing, the intermaxillary sutures contain ___
cartilage
what does the presence of cartilage in the intermaxillary suture allow during growth?
it allows the maxilla to expand, separating the two hemimaxillas along the intermaxillary suture
in orthodontics, an expander device is used to separate the intermaxillary suture, typically to correct ___ and alleviate ___
- crossbites
- crowding
at the end of the intermaxillary suture expansion process, a space is usually seen where?
between the maxillary central incisors (this shows that the two hemimaxillas were separated at the intermaxillary suture
almost any expansion device will tend to separate the midpalatal suture and move teeth in a child up to what age? what is needed to separate the midpalatal suture after this age is reached?
- 9-10
- by adolescence, a heavier force from a rigid jackscrew device is needed to separate the partially interlocked suture, which must be microfractured to separate the intermaxillary suture
when separating the intermaxillary suture, what does it look like from an anterior view? what about from an occlusal view?
- from an anterior view, the maxilla opens as if on a hinge superiorly at the base of the nose
- from an occlusal view, it opens more anteriorly than posteriorly causing a larger separation between the anterior region near the maxillary central incisors
the mandible, in embryonic life, develops in the same area as ___
meckel’s cartilage
T or F:
the mandible is a bony replacement of meckel’s cartilage in the same way that the sphenoid bone beneath the brain replaces the cartilage in that area
- false
- the development of the mandible begins as a condensation of mesenchyme just lateral to meckel’s cartilage, at the angle formed by the division of the incisive and mental nerves and proceeds entirely as intramembranous bone formation
during development of the mandible, where does bone formation spread from the ossification center?
- anteriorly to the midline
- posteriorly towards the point where the mandibular nerve divides into the lingual and inferior alveolar nerves
during development of the mandible, bone formation spreads rapidly and surrounds the ___ to form the ___
- inferior alveolar nerve
- mandibular canal
during development of the mandible, as developing bone is further spread in anterior and posterior directions, it produces a plate of bone on the lateral aspect of ___, which extends toward the midline where it comes into approximation with a similar bone forming on the opposite side
meckel’s cartilage
during development of the mandible, the two plates of bone remain separated by a fibrous tissue called the ___
mandibular symphysis
in mandibular development, the symphyseal cartilage appears between what weeks of embryonic development?
10-14
T or F:
in mandibular development, the two symphyseal cartilages develop in the connective tissue between the two ends of meckel’s cartilage, and throughout intrauterine life, the left and right mandibular processes are not fused at the midline
true
in mandibular development, the symphyseal cartilages are replaced by bone during what time period?
the first year of life after birth
if the mandibular plates of bone forming lateral to meckel’s cartilage are deficient in growth, what might happen?
a mandibular cleft could occur
during mandibular development, continued bone formation markedly increases the size of the mandible with development of the ___, which surrounds the developing tooth germs forming the body of the mandible
alveolar process
the ramus of the mandible develops by a rapid spread of ossification __anteriorly/posteriorly__ into the mesenchyme turning __toward/away__ from meckel’s cartilage; this point of divergence is marked by the ___ in the adult mandible
- posteriorly
- away
- lingula
as the mandible develops by ___ bone formation, meckel’s cartilage disintegrates and largely disappears; remnants of meckel’s cartilage are transformed into a portion of the ___ but not into a significant part of the mandible
- intramembranous
- middle ear
what 3 secondary cartilages develop between the 10-14th weeks?
- condylar cartilage
- coronoid cartilage
- symphyseal cartilage
which secondary cartilage is the largest?
condylar
condylar cartilage is the largest of the secondary cartilages and appears as a carrot shaped cartilage beneath the ___ layer of the future condyle and occupies most of the developing ___
- fibrous articular layer
- ramus
condylar cartilage is converted to bone by ___ ossification and fuses with the mandibular ramus during the ___ month of embryonic life
- endochondral
- 4th
condylar cartilage gives rise to the ___ and ___
condylar head and neck of the condyle
the condylar cartilage is replaced by bone, but the upper end persists through adolescence and adulthood as a ___ cartilage and then continues on as an ___ cartilage during adulthood
- growth
- articular
the condylar growth rate increases at puberty and peaks between what ages?
12-14 years
the growth phase of the condylar cartilage is typically complete by what age?
20 years old
the coronoid cartilage is associated with the ___ and develops in that region and gives rise to the ___
- coronoid process
- coronoid process
the coronoid cartilage becomes incorporated into the expanding intramembranous bone of the ramus through ___ ossification and disappears before ___
- endochondral
- birth
growth of the mandible occurs by both ___ at the condyle and by ___ at the bony surfaces
- endochondral proliferation
- apposition and resorption of bone
it has been shown that the mandible is translated in space by growth of the ___ and that addition of new bone at the condyle is in response to ___
- muscles and other adjacent soft tissues
- these soft tissue changes (functional matrix theory)
describe the surface remodeling of the mandible
- the mandibular ramus grows and develops by having bone removed from its anterior surface and by having bone added to the posterior surface
- bone is also added to the chin area, inferior border of the mandible, and alveolar process
it appears that growth of the cranium occurs by ___, and growth at the cranial sutures, and occurs almost entirely in response to ___
- surface apposition
- growth of the brain
growth of the cranial base is primarily the result of ___ growth with bony replacement at the ___, which have independent growth potential but are perhaps slightly influenced by growth of the ___
- endochondral
- synchondroses
- brain
growth of the maxilla and its associated structures occurs from a combination of what two things?
- growth at sutures
- direct remodeling of the surfaces of the bone
for the sake of this class, what 3 things contribute to the forward repositioning of the maxilla?
- surrounding soft tissue growth/functional matrix
- cranial base growth
- nasal septum
mandibular growth occurs through ___ and ___ in response to soft tissue/functional matrix growth
surface remodeling and growth at the mandibular condyle
