Lec3&4

Question 1

difference btwn growth and development?

Answer 1

growth– increase in size, shape, position– “autonomic” process

development– increase in organization and complexity– “physiological” process

Question 2

what are the concepts of growth and what defines them?

Answer 2

1. pattern– proportions– eg. cephalo-caudal gradient of growth
2. predictability– time dimension of proportional relationship – patterns repeat
3. variability– everyone is different (although stand growth charts exists– 90% in shaded areas)
4. timing– different timing in sex, environment

Question 3

cephalo-caudal gradient of growth?

Answer 3

• pattern of changing spatial proportions over time during growth
• different tissue system grows at different rates and times

* growth proportions
head-body vs. legs-body
3 months IU: 50, rudimentary
birth: 30, 30
adult: 12, 50

Question 4

head vs. face growth?

Answer 4

1. cephalo-caudal gradient of growth with head and face
2. infanct has smaller face compared to its head
3. face grows more than head as you get old
4. *mandible grows more and later than maxilla
5. at birth, face and jaws are relatively underdeveloped compared to in adult

Question 5

what does the growth velocity curve tells?

Answer 5

1. shows patterns and predictability

2. but we can’t make a cookie cutter estimation because everyone is different

Question 6

what is the main function of the standard growth chart and how is it used?

Answer 6

• main function: to tell whether growth in normal or not
  1) children outside the 97% range should receive special study
  2) to evaluate whether there is an unexpected change in growth pattern, the growth should plot the same percentile line at all ages, but marked changes indicate an abnormality that needs a further investigation by physician

Question 7

timing of growth btw females vs. males and early vs. late?

Answer 7

1. girls typically enter puberty 2 years earlier than boys
2. late growers have more robust (faster and more at a given time)
3. menarche (menstrual cycle) is a good indicator of sexual maturity in females and accompanied by a growth spurt

Question 8

what are the methods for studying physical growth?

Answer 8

1. craniometry– on a dry skull, cross-sectional in design, the same individual only at one point but different age groups as samples
2. anthropometry– longitudinaal data, one individual over periods of time
3. cephalometric radiology– direct measure of skeletal landmarks over a period of time

Question 9

two ways of craniofacial skeleton grow?

Answer 9

1. intramembranous– direct bone formation from neural crest cells (with membranes), calvarial and facial regions of the skull
2. endochondral– neural crest ells form cartilage which them forms bone, cranial base and some calvarium portions

Question 10

cartilage growth in face: when and how?

Answer 10

1. chondrocranium at 8 & 12 weeks
2. peak development of cartilage– during 3rd month
3. cranial base– a cartilage plate that extends from nasal capsule to foramen magnum
4. in-growth of vascular elements– during 4th month
5. these areas become centers of ossification

Question 11

chondrocranium development in face development?

Answer 11

• 8 weeks: a cartilage bar forms from nose to back of the head
• 12 weeks: an endochondral ossification centers appear within the cartilage bar and intramembranous bone formation of jaws and brain is beginning
• after 12 week: bone replaces cartilage so that only small synchondroses of cartilage remain connecting cartilage and cranial base bone

Question 12

how does cranial base grow?

Answer 12

via endochondral ossification

1. cartilage plate becomes bone
2. small bone first surround by cartilage
3. cartilage grows but replaced by bone
4. eventually all cartilage replaced, except for small areas btwn bone becoming ethmoid, sphenoid, basioccipial bones
5. any residual cartilage are potential pacemakers for growth and this is called synchondroses

Question 13

what is synchondroses?

Answer 13

• cartilage site of continued growth
• named after the bones they connect
  1) spheno-occipital
  2) intersphenoid
  3) spheno-ethnoidal
• transformed into bone by endochondral ossification
• area of cell hyperplasia in the middle with increasingly mature cartilage push outward on either side and this is eventually replaced by bone
• no cartilage remains, so immovable joints

Question 14

achondroplasia?

Answer 14

• growth plate malfunction– no growth there

* deficient middle face– maxillary and mandibular not push forward

Question 15

timelines of facial skeleton growth?

Answer 15

1. maxilla– intramembranous week 7
2. mandible– intramembranous week 6
3. cranial base– endochondral week 6 (including condylar)
4. upper cranial vault– intramembranous week 7

Question 16

how does nasomaxillary complex grow?

Answer 16

downward and forward

1) push from behind due to growth of cranial base (endochondral)
2) apposition of bone at the sutures connecting maxilla and cranium (intramembranous)

Question 17

why does front face not keep growing while maxilla is carried downward and forward?

Answer 17

• although maxilla is growing forward, bone is removed/resorbed from the anterior surface (but to lesser extent)
• except for anterior nasal spine (this continues forward, no resorption)*

Question 18

how does mandible grow?

Answer 18

• as the maxilla is growing forward and downward, it translates its growth to the mandible through “teeth” which connects jaws from one to the another
• mandible responses to this translation by increasing in size “upward and backward”
• principal sites of growth:
  1) posterior ramus
  2) condylar and coronoid process

Question 19

how do you get long face?

Answer 19

• maxilla usually rotates forward (and downward) and this make it move up anteriorly
• when maxilla rotates backward, this causes moving down anteriorly
• now this causes mandible down and back (mandible usually grows up/back)*
• anterior face gets longer
• anterior open bite
• lower incisors flare forward to contact an upper tooth
• steep mandibular plane
• “dolicofacial”

Question 20

how do you get short face?

Answer 20

• when mandible grows up/forward (mandible usually grows up/back)
• flattens the mandibular plane
• anterior over bite (deep bite)
• short, sqaure-ish face
• upper central incisors are retroclined and upper lateral are flared
• crowding in both jaws

Question 21

how does excessive mandibular growth cause underbite?

Answer 21

• mandible grows later than the rest of the face
• late mandibular growth means differential growth of mandible vs maxilla during late teens
• lower incisors tip lingually
• mandi teeth banging into upper teeth, underbite

Question 22

why thumb sucking is bad?

Answer 22

• thumb sucking> lower tongue> cheeks closer> upper molars lingually> lower molars at pressure from both cheek and tongue

Question 23

3 classes of skeletal relationships?

Answer 23

class i-- straight
class ii-- convex (bottom retreating back) 
class iii-- concave (bottom coming out)

Question 24

what happens when incisors flare forward or backward?

Answer 24

forward: align on a larger arch and it alleviates crowding
backward: less space and crowding becomes worse

Question 25

primary cartilage theory?

Answer 25

1) when the nasal septum is expanding, it pulls the maxillary complex to move down/forward
2) spheno-occipital synchondrosis (after other primary cartilages are ossified by age 6) is responsible for cranial base growth
3) first appears 5th week prenatal
4) condrocranium formed at 8th week as precursor of adult crania base, nasal, otic structures)
5) important in early life (by mid-childhood, most primary cartilage becomes bone)

Question 26

functional matrix theory?

Answer 26

1) metabolic demands like eating and breathing dictate growth of organs and muscles and this causes bone growth
2) craniofacial structure develops accordingly (to the functions)
3) functions in head (eg. CNS, PNS, respiration, deglutition) need space (eg. nasal, pharyngeal, oral)
4) brain gets big fast during prenatal and early postnatal life, and this causes the calvarial bony plates outward/mid-face forward
5) you didn’t need to breath during prenatal, but since birth you need it– tongue and mandible forward makes that airway

Question 27

palatal vault/nasal floor movement during development?

Answer 27

• nasal floor(=palatal vault) moves down (translatory)
• bone is removed from the nasal floor and added to the root of the mouth
• anterior surface of mouth is removed by canceling the forward translation partially
• • nasal floor moves downward, the same process of bone remodeling also widens it

Question 28

mandible growth?

Answer 28

the mandible is “translated” downward and forward as it grows upward and backward in response to this translation and maintaining its contact with the skull

Question 29

growth center vs. growth site

Answer 29

1. growth center: where tissues pushes to grow (eg. hyaline cartilage, nasal septum/ ant nasal spine, epiphyseal/growth plates, synchondroses of the cranial base)
2. growth site: where bone is deposited to grow, but secondarily (eg. sutures of maxilla, condyle
3. growth site is not always growth center; growth center is always growth site

Question 30

primary cartilage vs. secondary cartilage

Answer 30

1. primary– growth center and site (it’s the one telling things to grow)
2. secondary– growth site (not center) (it’s not the one telling things to grow)

Question 31

what is symphysis?

Answer 31

the center where two halves of the mandible joins

Question 32

what kind of cartilage is condyle formed?

Answer 32

• secondary cartilage that is added to the bone lateral to Meckles cartilage
• secondary cartilage is not a growth center but reactive

Question 33

how does mandible grow in terms of deposition and resorption?

Answer 33

• deposition posteriorly, resorption anteriorly
• deposition: @ head of condyle, posterior ramus, posterior coronoid process
• resorption: @ anterior ramus
• deposition posteriorly makes the mandible body longer

Question 34

how do permanent molars have room to erupt into the mouth?

Answer 34

because mandible get resorbed at the anterior part of the ramus, leaving some space for the teeth to erupt

Question 35

what was the initial theory on the mandibular growth that came as false?

Answer 35

it was assumed that the mandible was like a long bone bent into a “U” shape with primary cartilage directing the growth and its shape modified by the soft tissue (and muscle attached and teeth anchored that caused the U shape)

But this was wrong, because it’s the secondary cartilage in the condylar (not primary) that dictate the mandibular growth.

Question 36

what does it mean that the condylar has “secondary” cartilage?

Answer 36

• not growth center, but growth site
• no growth plate
• the condyle grows both on the surface and interstitially (growing inside) due to its fibrous covering
• there is always cartilage, meaning source of bone via endochondral ossification (ossification without a growth plate that would stop growing at some point)
• needs outside influence (eg. movement/function like chewing) to grow/translate downward and forward
• doesn’t grow well in culture media

Question 37

Acromegaly?

Answer 37

• excess growth hormone, pituitary tumor
• all the epiphyseal plates in an adult cannot grow because they are replaced by bone (so already closed)
• only bone that can grow is the mandible (since there is no epiphyseal/growth plate)

Question 38

Condylar ankylosis?

Answer 38

• when the motion of the condyle is limited due to injury or bony fusion of TMJ, the mandible does not translate downward and forward

Question 39

When do you use functional appliances?

Answer 39

• as a treatment for mandibular retrognathia Class II (mandible too far backward)
• it posture the mandible downward and forward
• however, the condyle is unloaded 80% of the time, so this appliance is not so useful

Question 40

What happens to the width of the mandible during its development?

Answer 40

• as the condyle grows backward, it grows out so that it contributes to the width of the mandible
• posterior growth in an expanding V
• increasing the size of the dental arch is from the back addition (posterior growth)

Question 41

What is the facial growth pattern?

Answer 41

• when child, face is convex due to the underdeveloped mandible
• midface is used to be down/forward motored by nasal septum, but by age of 6~7, replaced by bone (so stop moving)
• mandible grows as condylar continues to grow (later development than maxi/midface)
• the mandible translates forward and teeth left behind, this creates chin button (male>female)

Question 42

How is the chin button made?

Answer 42

• as the mandible comes forward in a rotational fashion due to the condyles grown upwards (which rotates the mandible down), it tends to thrust the chin forward (esp. when teeth erupted)
• males have more prominent chin button because they grow more and longer than females

Question 43

why is perichondrium important?

Answer 43

it ensures the cartilage in TMJ is never completely transformed into bone. Bone is made, but periochondirum always make some cartilage at the head of condyle.

Question 44

other notes on facial growth?

Answer 44

• soft tissues changes can hide some of the underlying skeletal changes
• upper lip thickens more than lower lip during growth
• males grow later, longer, and stronger
• anterior part of your nasal cartilage remain and continue to grow (nose and ears keep growing!)
• face keeps getting longer as you get older
• women undergo a growth spurt during their first pregnancy
• face grows forever