Facial Growth 1 Flashcards
what is malocclusion determined by
The malocclusion is determined by the size, shape and position of the underlying jaws
Why is the Study of Facial Growth Important to Orthodontists?
- We treat growing children so it gives an insight into growth of the face
- Understand development of facial anomalies
• To measure changes in growth and treatment using cephalometry
○ Look at treatment before and after to see what has been achieved
○ Need favourable growth to have a good success along with the treatment provided by the orthodontist
why is an insight into the growth of the face important
○ Predict changes
§ Ie will it get better on its own or do we have to intervene
○ Utilise growth to correct malocclusion
§ Can we grow the mandible?
§ Can make significant changes vertically, maybe not the AP, which can correct the malocclusion
○ Time our orthodontics and surgery
§ Ie time treatment with growth
§ For the patients above they need more than orthodontic treatment, they need surgery as well but you need to time the surgery for whenever they have finished growing otherwise if you do the surgery too soon and then the patient continues to grow you will just have to re-do the surgery another time
§ Orthognathic surgery is usually done in the late teens, early 20s
what are the 2 phases of life in utero
○ Embryonic: 1-8 weeks
§ This is when everything happens
○ Foetal: 8 weeks to term
The foetus is just growing in size
what forms within the first 2 months
All of the limbs and organs including the face have formed within the first 2 months and the embryo has a characteristic human form
what can cause cranio-facial abnormalities very early on in pregnancy
External environmental influences can cause cranio-facial abnormalities very early on in the pregnancy
why do 10% of all embryos miscarry
10% or more of all embryos miscarry because the bits don’t get in the right place at exactly the right time therefore you have a miscarriage
when do the chances of miscarriage becomes low
Once you get beyond the 8 weeks the chances of miscarriage is very low
what size is the fertilised egg on day 1
0.1mm
what is the egg called on day 2/3
morula
what is a blastocyst
16 to 32 cells
approx day 4-5
what happens at implantation
- At implantation the egg remains the same size
- Placenta begins to develop
- Then you get the germ layers forming
what are the 3 germ layers
- endoderm
- mesoderm
- ectoderm
what does the neural groove develop into
neural tube
what is important for the development of the face
Neural crest cell migration is very important in the development of the face
The cranial neural crest cells are very important for facial development
○ These are sometimes called ectomesenchyme because they originate from the ectoderm
○ But then they migrate in and come forwards to help with the formation of the pharyngeal arches (which are really important for facial development)
when does the neural tube form
The neural folds fuse to form the neural tube, towards the end of week 3
what does the neural tube develop into
The neural tube develops into the brain and spinal cord
what happens if the neural tube fails to develop
Failure to develop will lead to anencephaly (in which the cranial hemispheres and the cranial vault are absent)
what happens during the folding of the neural plate
During the folding of the neural plate, cells develop from the ectoderm along the edge of the groove, termed neural crest cells
These undergo extensive migration within the developing embryo and ultimately differentiate into many cell types
Eg spinal and autonomic ganglia, Schwann cells, adrenal medulla, meninges of the brain
what does the ectomesenchyme contribute to
This neural crest derived ectomesenchyme contributes to branchial arch cartilage, bone and connective tissue proper, as well as dental tissues - pulp, dentine, cementum and periodontal ligament
Vitally important for tooth development
what size is the embryo on day 30
3-5mm
what does the pharyngeal arches form from
neural crest cells
there are lots of specific slides on the day to day growth of the embryo but like could be too much detail / I don’t understand it
therefore I direct your attention to the notes x
when does formation of the face occurs
Formation of the face occurs during the first 8 weeks after fertilisation
what does most of the face form from
Most of the face forms from migrating neural crest cells, either in the fronto-nasal process or the branchial arches (pharyngeal arches)
Interference with this migration can lead to severe facial deformities
what happens if there is failure of fusion between the facial processs
Failure of fusion between the various facial processes or between the palatine processes may lead to cleft formation
There are certain parts we want to fuse and they must fuse at certain times and if they don’t fuse at these certain times then you are left with a cleft
Origin of cleft lip / cleft palate (but these are 2 separate events)
can cleft lip occur independent to cleft palate
cleft lip and alveolus can occur independently of cleft palate and vice versa
The upper lip and anterior part of the palate have different embryological origins from the posterior palate and they fuse at different times
where can a cleft lip affect
A cleft lip doesn’t only involve the lip, it can only involve the lip, but it is anything from the lip (alveolus) to the incisive foramen
Because this crosses over the alveolus it can cause problems with the teeth (supernumerary teeth, missing teeth, all sorts of problems)
where can a cleft palate affect
A cleft palate is from the incisive foramen back
If you have a cleft palate, because it doesn’t cross over the alveolus the baby will have normal teeth
what happens in week 4 of development
migrating neural crest cells form the frontonasal process and laterally the branchial arches
what happens in weeks 5-7
○ See the extension and fusion of the facial processes
○ Early phase
○ Lateral and medial nasal processes
○ Maxillary process comes round to fuse in the middle
At the beginning of the 5th week the 3rd and 4th pharyngeal arches develop
what is another name for the 2nd pharyngeal arch
hyoid arch
where does the 2nd pharyngeal arch grow
The 2nd pharyngeal arch (hyoid arch) begins to grow over the 3rd and 4th pharyngeal arches and forms the operculum and, behind it, a lateral, ectodermal pit: the sinus cervicalis (visible from stage 12)
the trigeminal nerve is associated with what pharyngeal arch
first pharyngeal arch
the facial nerve is associated with what pharyngeal arch
second pharyngeal arch
what happens during week 6 of development
In the course of the 6th week the lower edge of the 2nd pharyngeal arch covers the 3rd and 4th arches, which shift towards the rear and now form the base of the sinus cervicalis that is closing itself
The arches fuse together to form various structures
what is the foetal stage
8 weeks to term
what 2 parts can the skull be divided into
○ The neurocranium
○ The Viscerocranium
what is the neurocranium
§ Which forms a protective case around the brain
§ The neurocranium can be divided into the flat bones of the vault which develop intramembranously and the endochondral elements of the base of the skull
§ Ie the large flat bones which make up most of the head
what is the viscerocranium
§ forms the skeleton of the face and the base of the skull
what is intramembranous bone formation / ossification
• Bone is deposited directly into primitive mesenchymal tissue
• Needle-like bone spicules form, which progressively radiate from the primary ossification centres to the periphery
○ Progressive bone formations results in the fusion of adjacent bony centres
• Arrives from spicules at primary ossification centres which then all fuse together
○ Get bone within mesenchyme
what bones are formed by intramembranous ossification
• Intramembranous bones include the vault of the skull, the maxilla and most of the mandible