Mercado Flashcards
what is growth?
an anatomical phenomenon which involves an increase in size or number
what is development?
a physiological phenomenon which involves an increase in organization, complexity or specialization, at the expense of a loss in potential
what happens to the mandible through out life?
mandible does not merely grow
develops by changing positions and shape via translation and remodling
what is the result of how the mandible is developed?
higher specialization for the functions of mastication and speech
according to scammon’s growth curve, what is the maxillary growth similar to? mandibular?
neural for maxillary
general for mandibular
what is the normal percentile of growth?
5-95
what is the timing of growth?
same events may happen at different times
variations in growth due to timing are more evident during adolescence
what is craniometry?
take dry skulls and fixate them and get precise measurement of dimensions
what is anthropometry?
measuring over soft tissues ex head circumference
what is intersitial growth?
growth that occurs by a combination of hyperplasia, hypertrophy and secretion of extracellular matrix
occurs at all points within the tissue
what structures do intersitital growth?
all soft tissues
cartilage
cranial base
what is hyperplasia?
proliferating cells (cell division)
what is hypertrophy?
increase in cell size
what are the steps of interstitial growth?
resting cells in cartilage -> hyperplasia -> hypertrophy -> extracellular matrix
what happens if extracellular matrix is not mineralized?
interstitial growth may continue in soft tissues and cartilages
what is appositional growth?
growth that occurs by a combo of hyperplasia, hypertrophy and secretion of extracellular matrix but ONLY OCCUR AT SURFACE OF BONES
addition of new bone to the surface of existing bone
occurs through the activity of cells in the periosteum
what structures go through appositional growth?
bony surfaces of cranial vault
bony surfaces of maxilla and mandible
what are the steps of appositional growth?
resting cells in periosteum->hyperplasia->hypertrophy->extracellular matrix->bone
what happens when extracellular matrix is mineralized?
bone is formed
interstitial growth cannot occur within bone
what is the connection between interstitial growth and appositional?
cartilage can grow interstitially but bone can;t
once cartilage is transformed into bone, it continues to grow only by apposition
what are the types of skeletal growth?
interstitial vs. appositional
endochondral vs. intramembranous
remodeling
what is endochondral bone formation?
bone growth within cartilage
ossification centers occcur within cartilage
cartilage is transformed into bone
what are examples of endochondral growth?
chondrocranium: ethmoid, sphenoid and basiocciptalbones
epiphyseal plate cartilage of long bones
what is intramembranous bone formation?
secretion of bone matrix within and between connective tissue membranes
no intermediate formation of cartilage*
it does NOT replace cartilage
what are the examples of intramembranous growth?
desmocranium:cranial vault, maxilla and mandible
how is the mandible formed?
through intramembranous bone formation just lateral to meckel’s cartilage
how does the condylar cartilage of mandible form?
does not arise from meckel’s cartilage
develops from an independent secondary cartilage
fuses with mandibular ramus
what is surface remodeling?
change in shape of bones
result of bone removal (Resorption) in one area and bone addition (apposition) in another
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
allows for exchange of calcium and phosphate
internal remodeling does not make bone grow or change its shape
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 (primary) and at inner and outer surfaces
what are cranial sutures and fontanelles lined by?
periosteum
growth of the cranial base
bones of the base of skull formed by endochondral ossification
formed initially in cartilage then transformed to bone
ossification centers result in ETHMOID SPHENOID BASIOCCIPITAL bones
what are the synchondroses of cranial base?
cartilaginous joints between bones of cranial base
immovable joints
what are the most important synchondrosis?
spheno-ethmoidal
inter-sphenoidal
spheno-occipital
what kind of growth occur at synchondroses?
endochondral growth occur within synchondroses to lengthen the area of cranial base
bone surface remodeling also occurs in the cranial base (sphenoid sinus)
what are the features of synchondrosis vs suture?
both junction between adjacent bones
cartilage vs. connective tissue
endochondral ossification vs direct ossification (apposition of bone)
active growth (primary) vs. reactive growth (secondary)
growth of the nasomaxillary complex
formed entirely by intramembranous ossification
no cartilaginous precursor
growth occurs by apposition and surface remodeling
translation of maxilla
maxilla is translated downward and forward- away from cranial base
apposition of bone occurs at circum maxillary sutures which elongates the maxilla
surface remodeling of maxilla
bone in anterior surface of maxilla is resorbed
apposition of bone occurs at maxillary tuberosity(permanent molars later)
bone is resorbed in the floor of the nose
apposition of bone occurs at palate and alveolar process
as a result palate moves mostly downward and widens transversely
growth of the mandible
first formed via intramembranous growth
endochondral growth occurs at the cartilage that covers the mandibular condyle
all other areas grow by surface apposition and remodeling
alveolar bone area- apposition (teeth erupt)
anterior ramus and anterior surface of condyle- removal of bone
posterior surface of ramus and coronoid process- bone apposition
translation of mandible
mandible is translated downward and forward- away from cranial base
principal sites of growth:posterior surface of ramus and condylar and coronoid processes
surface remodling of mandible
body of mandible grows longer
ramus of mandible grows higher
more room in the body of mandible for molars to erupt
Theories of growth control
suture theory
cartilage theory
functional matrix theory
combo
what is site of growth vs center of growth
site of growth- location at which growth occurs
center of growth- location at which independent growth occurs
principles of suture theory
all tissues that form bone have intrinsic potential to do so
growth centers are locations of genetically controlled growth- independent from the environement
includes sutures ,periosteum ,synchondroses ,and mandibular condyle as growth centers
does experimental evidence support suture theory
no
transplantation studies- for growth centers- doesn’t matter where you transplant it- should get bone growth- NOT TRUE
mechanical pull at sutures-child hydrocephaly- suture adjust to the increased cranial pressure (aka not independent from environment)
what is the conclusion of suture theory
sutures and periosteum are growth sites- merely a location of growth
sutures react rather than act independently
principles of cartilage theory
all cartilage are growth centers
cartilage in mandibular condyle controls growth of mandible
cartilage in nasal septum controls growth of maxilla
cartilage in the synchondroses controls growth of cranial base
does experimental evidence support cartilage theory?
partially
transplanted cartilage from synchondroses and nasal septum is capable of growth
transplanted cartilage from mandibular condyle shows significantly less growth
synchondroses and nasal septum act as growth centers, but mandibular condyles does not
after fracture of mandibular condyle, there is some reduction in mandibular growth- however the original condyle is displaced and resorbed- new condyle generated at fracture site
conclusions of cartilage theory
cranial base synchondroses and nasal septum act as independent growth centers- pushing maxilla forward
mandibular condyle is merely a growth site
functional matrix theory principles
heredity and genes play no role in growth of craniofacial skeleton
growth of the face occurs in response to functional needs, mediated by soft tissues in which the bones are embedded
all tissues that form bone are merely growth sites
ex. microcephaly and hydrocephaly
does experimental evidence support fucntional matrix?
partial
not clear how functional needs are transmitted to the tissues around mouth and nose
recent advances in molecular biology and genetics show that genes are involved in the hereditary and mechanical modulation of craniofacial growth and development
combination of theory for cranium?
response to growth of brain (sutures and periosteum =growth sites)
combination of theory for cranial base?
result of endochondral growth at synchondroses (growth centers)
combination of theory for maxilla?
primarily result of apposition and remodeling as the bone is translated by soft tissues (sutures+periosteum=growth sites)
may result from endochondral growth at nasal septum cartilage (growth center)
combination of theory for mandible?
endochondral growth at condyle and surface remodeling as bone is translated by soft tissues (condyle +periosteum=growth sites)
