Facial Growth 2 Flashcards
what is the majority fo the face derived from
The majority of the face is derived from neural crest cells
where do neural crest cells come from
Neural crest cells come from the edge of the neural groove as the neural plate folds
why are the neural crest cells known as ectomesenchyme
These cells are known as ectomesenchyme because they come from the ectodermal layer in the embryo
what processes develop into the skeleton of the face
The frontonasal process and the maxillary and mandibular processes of the first brachial arch make up the regions of the embryo within which the skeleton of the face will develop
how do the bones of the face and skull form
Bones of the face and skull form either by intramembranous or endochondral ossification
Majority of facial bones are derived intramembranously
how do the maxilla and mandible develop
Both the maxilla and the mandible develop intramembranously
what is the pre-existing cartilaginous skeleton for the maxilla
Nasal capsule for the maxilla
what is the pre-existing cartilaginous skeleton for the mandible
Meckel’s cartilage for the mandible
what happens to these cartilages as the embryo develops
As the individual embryo develops, these cartilages change
There are very few remnants of Meckel’s cartilage left by the time the child is born
is the neonatal face a miniature of the adult
The neonatal face is not merely a miniature of the adult
In the infant the face is small compared to the cranium, the eyes are large and the ears are low set
what are the differences between the floor of the nasal cavity and the floor of the orbit in the neonatal skull
The floor of the nasal cavity and the floor of the orbit are very closely related to each other in the neonatal skull
Whereas there is a must bigger difference between the floors of these cavities in the adult
what is the neonatal forehead look like
The forehead is upright and bulbous and the face appears broad
Adult forehead tends to slope backwards more
what is the nasal region like in the neonatal skull
The nasal region is vertically shallow, with the nasal floor close to the inferior orbital rim
In the adult the midface expands and the nasal floor has descends
what are the sites of facial growth
- Sutures
- Synchondroses
- Surface Deposition
what are sutures
• Specialised fibrous joints situated between intramembranous bone
○ Centre is made of connective tissue
○ Periphery has osteogenic cells turning into bone
• Each suture is a band of connective tissue which has osteogenic cells in the centre and the most peripheral of these cells provide new bone growth
○ Bone deposition at the periphery
how does growth occur at the sutures
• Growth at the sutures occurs in response to growing structures separating the bone
e.g. growth of the calvarium in response to development of the brain
Where the bones are pushed apart new bone forms in the suture. In the suture growth occurs in areas of tension.
Suture responds to the growth of internal organs so the developing brain pushes the sutures apart, causes tension within the sutures and in these areas of tension, bone gets deposited
what happens when facial growth is complete
When facial growth is complete the sutures fuse and become inactive.
where are synchondroses found
These are found in the midline
where are synchondroses in the cranial base
They exist between the ethmoid, sphenoid and occipital bones
what are synchondroses
• A cartilage – based growth centre with growth occurring in both directions.
○ A cartilaginous growth plate and growth occurs at either end of the plate
○ The plates push the bone on either side apart
how does growth occur at synchondroses
The bones on either side of the synchondrosis are moved apart as growth takes place.
We think the bones move apart with a bit of intrinsic ability and it is not just in response to things going on around them
New cartilage is formed in the centre of a synchondrosis as cartilage at the periphery is transformed into bone
○ New cartilage is formed constantly in the centre of the synchondroses but is ossified at the edges
○ But it is ossified at the edges of the synchondroses
what is another term for surface deposition
remodelling
what is surface deposition
New bone is deposited beneath the periosteum over the surfaces of both the cranial and facial bones
In order for bones to maintain their shape as they grow resorption is also taking place
what is the process of deposition and resorption known as
remodelling
what is a ‘drift’
The change in position of a bone due to remodelling is known as “drift”
what is the cranial vault comprised of
comprised of:
- Frontal,
- Temporal,
- Occipital and
- Parietal Bones
these are all meeting at sutures and growth occurs both by sutural growth and remodelling)
what does the cranial vault expand in response to
Expands in response to the growing brain until age 7 years when the brain is fully grown
when is the rate of growth for the cranial vault the greater
The rate of growth is greatest in the first 3 years of life
This is when the majority of change takes place
This is when the head is getting much bigger
what are the 2 ways growth of the cranial vault occurs
Growth occurs in 2 ways
○ Bone growth at the sutures
○ External and internal surfaces are remodelled through surface deposition and resorption to displace the bones radially
where does resorption and deposition occur in the cranial vault
We see resorption of the bone on the internal surface of the calvarium and deposition of the bone at the outer surface
after neural growth how does the forehead continue to enlarge
After neural growth the forehead continues to enlarge in response to accommodate expanding air sinuses (pneumatisation)
Generally more pronounced in males
What is pneumatisation
= expansion in response to the growth of the air sinuses
where does fontanelles exist
Fontanelles exist where more than 2 bones meet
how many fontanelles are present at birth
6 fontanelles are present at birth (in the neonatal skull)
what are the purpose of fontanelles
The purpose of these is to allow the skull bones to move slightly relative to each other during child birth
when do fontanelles close
close by age 18 months
when do all sutures fuse
When facial growth is complete all of the sutures fuse
what comprises the cranial base
- Frontal,
- Ethmoid,
- Sphenoid,
- Temporal and
- Occipital Bones
growth in the cranial base is due to what
Growth here is due to synchondroses
There are 3 synchondroses
what synchondroses is most effective and influential on the post-natal facial growth
The one which has the most effect and influence on our post-natal facial growth is the spheno-occipital synchondroses which remains patent for the longest time
growth in the cranial base occurs in what ways
Growth occurs in 2 ways:
○ Endochondral ossification
§ Cartilage plate changing to bone
○ Surface remodelling
half the growth in the cranial base is completed when
Half the growth in this area is completed by age 3 years
when does the sphenoid-ethmoidal synchondrosis fuse
The spheno-ethmoidal synchondrosis fuses at around 7 years
when does the sphene-occipital synchondrosis close
The spheno-occipital synchondrosis closes at around 13 -15 years in females and 15-17 years in males
The one which has most influence on facial growth post-natally
when does the sphenoid-occipital synchondroses fuse
The spheno-occipital synchondroses fuses at around 20 years
The bone itself doesn’t fuse until this age
what does growth between the ages of 4 to 20 cause
Growth between the ages of 4 to 20 years causes an overall increase in length of the cranial base.
what can be said about the anterior cranial base after the age of 4
the anterior cranial base is relatively stable after the age of 4 years and so has been used for superimposition in cephalometric analysis.
ie The anterior part of the cranial base does not change a lot during this time
§ Talking about the area from the sella turcica (midpoint of this is called sella on a lateral cephalogram) to the junction between the frontal and nasal bone called the nasion = anterior cranial base
The angle between the anterior cranial base and the posterior cranial base is relevant to growth of the face
This allows the orthodontist to assess skeletal changes due to growth and /or treatment.
what is the cranial base important in determining
The cranial base plays an important role in determining how the maxilla and mandible relate to each other.
The shape or angle of the cranial base affects the jaw relationship: ○ A small angle is more likely to be associated with a class III skeletal relationship ○ A large angle more likely to be associated with a class II skeletal pattern because the mandible ends up located more posteriorly
what bones comprise the maxilla or naso-maxillary complex
- Orbits,
- Nasal Cavity,
- Upper Jaw and
- Zygomatic Processes
where is the maxilla in relation to the anterior cranial base
The maxilla is displaced downwards and forwards relative to the anterior cranial base
what is displacement
When a mass of bone is moved relative to its neighbours it is termed displacement
Displacement is brought about by forces exerted by the soft tissues and by intrinsic growth of the bone itself
what can be said about growth of the maxilla / nasomaxillayr complex
Growth tends to follow neural growth of the brain early on and so slows down towards age 7 years
what does forward displacement of the maxillary complex do
Forwards displacement of the maxillary complex creates space posteriorly for development of the maxillary tuberosities and space for eruption of molar teeth
As this area moves downwards and forwards that leaves space posteriorly for the length of the maxilla to grow by bony deposition at the posterior part of the maxilla and this creates more space to allow for the development of the permanent molar teeth
what way does the maxilla grow
The way the maxilla grows is a combination of sutural growth and surface deposition and remodelling
in the maxilla where does sutural growth take place
• Sutural growth takes place at the zygomatic and frontal bones and mid palatine suture
[Between maxilla and zygomatic and frontal]
○ Suture between 2 halves of the palate
The mid-palatine suture is very relevant to orthodontics because if we are looking to try to widen the upper jaw then we want to make use of a patent mid-palatine suture
where does surface deposition and resorption occur in the maxilla / nasomaxilary complex
deposition on the lower border (inferior surface) of the hard palate and the alveolar process
and resorption on the floor of the nasal cavity and the floor of the orbits
Where this takes place is to encourage downward and forward growth of the maxilla
what direction does the mandible grow
Grows downwards and forwards
how does the mandible grow
Grows by a combination of remodelling (surface deposition and resorption) and through cartilage
what are the sutures of the mandible
There isn’t a suture in the mandible which is active into early childhood and adulthood but there is a cartilage (secondary cartilage called the condylar cartilage)
where does growth occur in the mandible
• Growth occurs at the condylar cartilage ( maybe adaptive growth rather than intrinsic)
○ ie we don’t know whether the condylar cartilage is driving the growth or whether it is adapting to the tissues around it but it does have a large role to play in growth of the mandible
where does growth in the mandible occur by remodelling
• Growth occurs by surface remodelling (resorption and deposition of bone)
resorption mainly anteriorly and lingually
and deposition posteriorly and laterally
what does remodelling result in
Results in increase in height of the ramus and increase in length of the dental arch to accommodate the permanent teeth
○ Increase in length of dental alveolar process and dental base to allow for the eruption of teeth
○ Increase in height of ramus also helps to accommodate the developing dentition
what is the difference in the increase in length between the mandible and the maxilla
mandible: Increases in length by 26mm in males and 20mm in females between ages 4-20 years
maxilla: Increases in length by 8mm in males and 5.5mm in females between ages 4-20 years
what is the difference in the growth of the mandible and the maxilla
mandible:
- Growth accelerates significantly during the pubertal growth = time of greatest growth rate
Want to make use of this during ortho treatment
- Growth slows to adult level around age 17 years in females and 19 years in males
ie growth goes on for longer in the mandible
maxilla:
- After age 7 years growth of the maxilla proceeds very slowly (very small increments, very slowly)
- Growth slows to adult levels at around 12 years
Tends to be before puberty
what are similarities in the growth of the maxilla and mandible
For both the maxilla and the mandible:
• growth in width slows first,
○ Usually around the time the permanent canines have appeared the arches have achieved the width it is going to be with the permanent dentition in place
- then growth in length
- and finally growth in height
what ages does the pubertal growth spurt occur in boys and girls
For girls: around 12-14 years of age
For boys: a little later on, around 14/15 years of a
treatment which utilises growth of the mandible will work best when
Treatment which utilises growth of the mandible will work best if carried out during the pubertal growth spurt
ie treatment is best if we time it correctly
So around 12/13 years for girls and 14/15 years for boys
treatment which utilises the growth of the maxilla will work best when
Treatment which utilises growth of the maxilla will work best before the circumaxillary sutures and palate have fused i.e. early teenage years
Ie when it comes to making a change to the maxilla in either pulling the maxilla forwards using head gear or expand the mid-palatine suture then these treatments would work better if done a little bit earlier
Looking then at the pre-pubertal growth spurt because you want to treat the patient before the circumaxillary sutures and the palatine sutures close
Definitely want to do this treatment before age 16 years but possibly quite a bit younger
can we predict facial growth
• Not really with any degree of precision!
• Hand-wrist radiographs have been investigated but ossification events in this location did not correlate well with predicting the pubertal growth spurt
[There was thought to be an association with the growth of the wrist bone and the growth of the skeleton but didn’t correlate to the growth spurt so it isn’t of any relevance to us now so no longer done]
• Cervical vertebrae – there is some evidence of correlation between ossification stages of cervical vertebrae and timing of growth of the mandible
○ Looking at maturation of cervical vertebrae but this is weak evidence - not something that would be routine practice
• Most clinicians will consider patient height in relation to chronological age and presence of secondary sex characteristics to help determine whether or not a patient has entered the pubertal growth spurt
○ This helps us decide whether the patient has any growth potential left
○ Patient’s shoe size (feet) tend to stop growing before the patient stops growing in height ~ so can ask if their feet are still growing to get an indication of whether there is growth potential there
○ Not exact science but children do tend to grow to be around the height of their parents so can ask the child if they are as tall as mum or dad yet
○ Few questions to try and get a handle on the child’s growth potential
what are the 4 theories of craniofacial growth
ie what is the driving force for facial growth? what determines how the shape of the face ends up?
- The Remodelling Theory
- The Sutural Theory
- The Cartilaginous Theory
- The Functional Matrix Theory
what is the remodelling theory
○ Everything just grows by a process of deposition and resorption
○ The sutures and cartilages do not exert an intrinsic force
what is the sutural theory
○ Growth occurs at the sutures and cartilages but the growth at the sutures is the prime factor
what are the cartilaginous theory
○ The cartilages ie nasal septal cartilage and synchondrosis generate the force to develop the bones in a specific direction
what is the functional matrix theory
○ Growth occurs in response to individual units which are developing to provide a function
○ Each unit (functional matrix) is composed of tissues / organs and spaces
§ Little areas of the face = functional matrix
○ Thus it is the force exerted by the growing soft tissues that determines the direction and extent of growth
○ Growth of the face occurs in response to try to allow the functions of why we have the face to take place
§ Ie this was more based around the face growing in response to the soft tissues
what are recent views on the control of growth
- A combination of genetic and environmental influences are involved
- Growth in one part of the skull influences another.
- The primary cartilages of the cranial base and nasal septum have intrinsic growth potential and exert a genetic influence over growth .
• The condylar cartilage (secondary cartilage) of the mandible seems to act differently. Controversy exists as to whether it is a primary growth force or purely adaptive.
○ Not sure about this
○ Does it have intrinsic growth potential or is it just responding?
• It is possible that the mandible responds to changes in maxillary position with adaptive growth to maintain the position of the condyle within the glenoid fossa and maintain occlusal relationships.
what is the impact of facial growth on orthodontic treatment
• Growth can affect the severity of a malocclusion - either improving it or making it worse
○ Irrespective of orthodontic treatment
• Growth can be utilised by the orthodontist to facilitate treatment outcome
○ Use of functional appliances
○ Use of rapid maxillary expansion
○ Use of protraction headgear
• Continued “unfavourable” growth patterns following orthodontic treatment can lead to relapse of the orthodontic treatment result
what is facial growth like in adults
• Very variable
• Continues slowly throughout life
○ Tiny increments very slowly
- Growth in length of face continues into early 20s in males, late teens in females
- Tendency to increase overall length and prominence of nose and chin (and forehead in men)
• Lips become thinner and more retrusive (soft tissue changes)
○ Changes in soft tissue tone
what is a growth rotation
A growth rotation is due to the difference in the relative growths of the posterior facial height and the anterior facial height
what happens when there is more growth in the posterior part of the mandible than in the anterior part
When there is more growth in the posterior part of the mandible than the anterior part of the mandible then the mandible tends to rotate anti-clockwise and this is called a forwards growth rotation
what happens when there is more growth in the anterior part of the mandible than in the posterior part
there is greater growth in the anterior part of the face than the posterior part of the face then the mandible rotates clockwise and this is called a backwards growth rotation
what is a growth rotation due to
A growth rotation is due to an imbalance in the growth of the anterior and posterior face heights
what does forward rotations lead to
Forward rotations lead to a short face = decrease in the overall face height
what does backwards rotations lead to
Backwards rotations lead to a long face = increase in the overall face height
what happens when growth rotations occur to an extreme
When growth rotations occurs to an extreme = adverse growth
when there is continued growth with a significant growth rotation what can happen
Continued growth when there is a significant growth rotation can make a malocclusion worse
what is the result of a forwards growth rotation
patient with a forwards growth rotation ends up with:
○ a very short face (A decreased lower face height), ○ a reduced Frankfurt’s Mandibular Plane Angle
○ and there is a deepening of the bite (increase in vertical overlap of the incisors)
can lead to a the development of a deep bite
what is the result of a backwards growth rotation
patient with a backwards growth rotation
○ Tends to develop an anterior open bite
○With excessive lower face height (a really long face)
can lead to the development of an anterior open bite
what way does facial growth occur
In general, facial growth is downward and forward, but there is considerable individual variation with growth rotations
when does growth slow
Growth slows after 16-17 years in girls and 18-20 years in boys but continues throughout adulthood in very small amounts with the face getting ‘flatter’ and longer
what cartilage has the greatest contribution to the post-natal development of the mandible
condylar cartilage
describe the growth mechanism by which the cranial vault increases in size
- deposition of bone at the periphery of the sutures
- resorption of bone on the inner surface of the calvarium
- deposition of bone on the outer surface of the calvarium
to utilise growth potential when expanding the maxilla with an orthodontic appliance treatment should be carried out at what age
before the age of 16 years
what synchondrosis remains active for the longest period of time during facial growth
sphene-occipital synchondrosis
describe a forward growth rotation of the mandible
the increase in posterior face height is greater than the anterior face height
a short face type is produced
what are the 3 types / sites of bone growth which influence the shape of the face
• Sutures
○ Fibrous connective tissues joints with bone being deposited at the periphery
• Synchondroses
○ Cartilage based growth centre
○ Found in the cranial base
• Surface deposition and resorption
○ Remodelling
what role does the cranial base play
The cranial base plays an important role in determining how the maxilla and mandible relate to each other
how can the cranial base affect the jaw relationship
The shape or angle of the cranial base affects the jaw relationship
- Smaller angle = more likely class III
- Larger angle = more likely class II
how long does the sphene-occipital synchondrosis continue growing for
The spheno-occipital synchondrosis continues growing into the teenage years
○ In the base of the skull
○ Remains active for the longest period of time
○ Has the biggest influence when it comes to growth of the face
what is relatively stable after the age of 4 and what is it’s use
The anterior cranial base is relatively stable after the age of 4 years and so has been used for superimposition in cephalometric analysis
Useful in analysis and determining growth patterns in a patient or any changes in the face which would be useful for orthodontic treatment
what direction does the maxilla grow
The maxilla is displaced downwards and forwards relative to the anterior cranial base
where does sutural growth occur in the naso-maxillary complex
Sutural growth takes place at the zygomatic and frontal bones and mid palatine suture
where does surface deposition and resorption occur in the naso-maxillary complex
Surface deposition and resorption eg deposition on the lower border of the hard palate and the alveolar process and resorption on the floor of the nasal cavity and the floor of the orbits
○ Deposition on the roof of the palate, the anterior maxilla, the posterior alveolus to create more space for the teeth and expanding the air sinuses and the orbit
○ Corresponding areas of resorption as well
how direction does the mandible grow
Grows downwards and forwards
where does growth occur in the mandible
Growth occurs at the condylar cartilage
Primary driving force or adaptive to changes in surrounding musculature and soft tissue
how does growth occur in the mandible
Growth occurs by surface remodelling (resorption and deposition of bone)
Resorption mainly anteriorly and lingually and deposition posteriorly and laterally
when should Treatment which utilises growth of the mandible be carried out
Treatment which utilises growth of the mandible will work best if carried out during the pubertal growth spurt
Growth of mandible is fastest during this time
when should Treatment which utilises growth of the maxilla be carried out
Treatment which utilises growth of the maxilla will work best before the circumaxillary sutures and palate have fused ie before 12 years
