01: Craniofacial Growth Flashcards
In early 20th century, what was believed about Craniofacial Growth?
That genetics controlled all aspects of craniofacial growth (Bone, Cartilage, Soft Tissue, Muscle)
Who was the forefather of the genetic growth model
Sicher
In the 50’s research noticed that environment had an effect on CF growth…what was this theory called?
Epigenetics
Under epigenetic theory, it was believed that genetics had the heaviest direct effect on which tissue?
Cartilage
Who proposed the Cartilaginous growth theory?
Scott, 1953
What happened when Scott removed the cartilage from the face of rabbits?
It severely stunted the growth of the rabbits facial bones
What particular piece of human cartilage was Scott focused on?
Cartilage of the Nasal Septum
According to epigenetics how does the cartilage of the nasal septum influence the direction the facial bones grow in?
Down and forward
After genetics and epigenetics, what is the 3rd theory of CF growth?
Environmental
Who promoted the environmental theory
Moss (Functional Matrix Theory)
What was the basic tenet of the Func. Matrix Theory
The environment provides the stimulation, and the bones respond in form so that their shape meets the functional requirements demanded by the environment
Which theory is correct?
None and All. Individually none of the theories explain it all, but they all have described a portion of the process
Which bones are influenced primarily through genetics?
Endochondral bones of the skull
Are the cranial bones intramembranous
Yes
How do the skull bones respond to the growth of the brain?
As the brain volume increases, the bones are pushed apart at the sutures and then they respond by getting bigger to fill the gaps
What force at the suture causes the cranial bones to grow
Tension
Where are the endochondral bones of the head located
The base of the brain
What are the endochondral bones of the head
Sphenoid
Ethmoid
Occipital
What are the “epiphyseal plates” of endochondral bones
Synchondroses
How does the growth of the synchondroses differ from the epiphyseal plate?
A synchondroses will grow in both directions
What are the three synchondroses of the cranial base
Sphenoethmoid
Spheno-occipital
Intersphenoid (between greater and lesser wings)
At what age does the sphenoethmoid sychondroses ossify
7
At what age does the intersphenoid sychondroses ossify
3
When does the spheno-occiptal synchondroses ossify
~18 (16-25 range)
What kind of bone is the maxilla
Intramembranous
If the maxilla is intramembranous how might a dentist be able to affect its growth?
Intramembranous = Environmentally Influenced
Dentist can affect the bone’s environment by altering the maxillary teeth
What does the maxilla migrate away from
The Cranial Base by appositional growth at the sutures
What two types of remodeling are happening during the maxilla’s “migration”
Resorption on the anterior side
Deposition on the posterior side
(Resulting from a tension force maybe supplied by the cartilage of the nasal septum)
Who studied the bone remodeling process
Enlow
How is remodeling performed on the palatal vault?
Resorption on the Nasal side
Deposition on the palatal side
What is the name of the principle that describes the remodeling of the maxilla
the V principle
The mandible also migrates away from the cranial base, but where does the appositional growth occur?
At the Condyle
What part of the mandible is subject to extensive apposition and resorption?
Ramus
How does apposition effect the ramus of the mandible
Resorption on Anterior of Ramus
Deposition on Posterior of Ramus
Why can’t you look at a 10 year old and know if he will have room for his third molars
because you cannot tell how much of the ramus will be resorbed
How does the growth pattern negatively affect kids that don’t have enough room in their jaw for their teeth?
The way the mandible grows, there will never be spontaneous growth in the middle of the mandible, where the teeth would benefit from the extra space
What is the name of Bjork’s Theory?
Bjork’s Mandibular Growth Rotation Theory
How did Bjork’s work suprise researchers?
His research revealed that rotational growth occurs as the mandible grows
What is the most common growth/rotational patter in people
Moderate Growth
Moderate Eruption
w/Small Closing Rotation
What part of the the mandibular growth pattern contributes to an “adult looking” face
The mandibular rotational growth creates a thicker jawline and a more prominent chin region
Besides the common model, what model is still seen often
???
Extreme growth model
Moderate Growth
Little Eruption
Lots of Closed Rotation
(Small crowded mouths with anterior overbites)
Extreme growth model 2
Little growth
Lots of Eruption
Backwards rotation
(Longer lower face with an open anterior bite)
What are Scammon’s Growth
Curves that track growth rates where 100 on the scale = 100% of normal adult size
According to the Scammon’s Curve how does the brain grow
Brain size grows rapidly from birth and crests in the teenage years. Brains start “shrinking” in the early 20s
According to Scammons what tissue grows to 2x normal size by the age of 12 before shrinking during puberty and reaching “normal” size by 20
Lymphoid (Adenoids, Tonsils)
If you believe that the bones closer to the brain, grow like the brain. which bone grows more like the brain (Maxilla/Mandible)
Maxilla
If we need to impact the growth of the maxilla, at what age must it be done?
Around 7-8 because the maxilla grows like the brain, ie early and reaching full size by 10-12
Which bone is “easier” to influence the growth of? Maxilla or Mandible
Maxilla
Why is the mandible harder to control the growth of?
Because the condyle is cartilagenous
But, why is there hope that the mandible might be able to be manipulated more than other bone growing appositionally from cartilage?
Because the condyle is fibrous cartilage, not hyaline
How does head gear help fix a class 2 malocclusion
It retards the growth of the maxilla and allows the mandible to “catch up”
If nothing is done to retard the maxilla, why will the mandible never fix itself?
Because the maxillary teeth will respond via feedback mechanism and migrate forward along with the mandibular growth
Could you treat Class II by forcing disclusion during the growth period?
Yes, because the feedback mechanism is based on the intercuspal relationship between the maxillary and mandibular teeth
Rank Stature, Mandible, Maxilla in Growth in Size
Stature>Mandible>Maxilla
What is the Cranial-Caudal Gradient of Growth
Structures further from the brain grow later and greater
Structure close to the brain grow early and less overall
Out of Height, Length, and Width which stops growing first
Width
Length and Height are 2nd and 3rd
To take advantage of the mandibular growth curve, when is the optimal time for ortho treatment
Girls = 12 Boys = 14
Girls = 2 years earlier on average with lots of individual variation for both boys and girls
How can Cephalometric Radiographs help predict peak growth windows
Superimpose sequential films and create a growth curve
Start looking for curvature in the cervical vertebrae
How can hand-wrist x-rays predict growth windows
By looking at the epiphyseal plates in the fingers, you can predict peak growth to an accuracy of 6 months
What are the three ways to measure age
Chronological
Skeletal
Dental Age
What are accuracy rates of the different ways to measure age
Asking age and comparing to averages (70%)
Skeletal = Direct (100%)
Dental = Looking at teeth to see which is erupted (60%)
Best indicator for maturation for girls
Onset of menstruation is past peak of growth by 12 months
What is the best maturation indicator for boys
Less clear then girls
Mustache hair is pre-peak
Chin hear is post-peak
