Facial Growth Flashcards
How does the mandible develop
Intra-membranous ossification
What are the two phases and durations of life in utero?
Embryonic = 1-8 weeks
Foetal = 8 weeks to term
When are deformities most likely to happen?
In the embryonic period.
External environmental influences can cause craniofacial abnormalities in this period as facial structure has typically already formed in the first 8 weeks
How does the neural tube form? What does failure to fuse cause?
Forms by neural folds migrating together to form the tube. These migrating Neural crest cells eventually come together until the groove forms a tube.
Failure leads to spina bifida
What does the neural tube develop into in a human? What does incorrect neural tube development cause?
Forms brain and spinal cord
Failure to develop will lead to anencephaly (absence of cerebral hemispheres and cranial vault)
What forms the pharyngeal arches?
Ectomesenchyme
Cranial neural crest cells that are migrating
What cells form the majority of the face?
Migrating Neural crest cells
Why can cleft lip and alveolus form independently of cleft palate and vice versa?
Upper lip and anterior palate have different embryological origin to the posterior palate
What are the 5 protruberances in the development of the face, caused by cranial neural crest cells? What happens to them?
Frontonasal prominence
2 x maxillary prominence
2 x mandibular prominence
As development carries on, they move forward and towards the midline, and form the upper and lower jaws
What is intramembranous ossification? Where does this occur?
Bone is directly deposited from centres of ossification
These bone spicules radiate from ossification centres to the periphery
This fuses adjacent ossification centres
Neurocranium, maxilla and most of mandible
What is endochindrial ossification? Where does this occur?
Hyaline cartilage framework is systematically replaced by bone.
Long bones and base of skull where there are foramina
What is unique about the intramembranous ossification of the maxilla and mandible?
Although they form via intramembranous ossification, they form adjacent to a cartilaginous framework typical of endochondrial ossification
Maxilla = nasal capsule
Mandible = meckels cartilage
What would occur if one is born with no masseter or medial pterygoid?
The angle of the mandible will not form on that side as there is no reason to be there.
Same apples for the coronoid area if one is born without temporalis
The body of the mandible forms due to the interdental nerve
What are the secondary cartilages that form? Implications for one?
Condylar cartilage
Coronoid cartilage
Symphyseal cartilage
Condylar cartilage grows until around 20 yrs old, abnormal growth on one side can cause asymmetry
When does ossification of the face and skull begin?
7-8 weeks
What is a primary abnormality?
Defect in structure of an organ that can be traced back to an anomaly in development
E.g. spina bifida
What is a secondary abnormality?
Interruption in development of an organ that can be traced back to influences other than developmental issues
E.g. viruses, chemicals or trauma
What facial syndromes can arise due to very early problems with facial development? (1-8wks )
Foetal alcohol syndrome
Hemi facial microsomia
Treacher Collins syndrome
Cleft lip and palate
What is foetal alcohol syndrome? Causes? Complications?
High maternal intake of alcohol
Character theorised by small head (microcephaly),
Short palpebral fissures - small eyes,
Indistinct philthrum,
Small mandible,
Midface deficiency,
Can cause intellectual impairment
This occurs at 17 days in utero
What is hemifacial microsomia? Causes? Complications?
Multi-factorial, so idiopathic cause
Spectrum disorder
3D progressive facial asymmetry
Unilateral mandibular, zygomatic arch, ear hypoplasia
No intellectual impairment, but cardiac and renal problems along with deafness
What is treacher collins syndrome? When occur?
A deformity of the 1st and 2nd branchial arches
Leads to hypoplastic or absent zygomatic arches
Hypoplastic mandible
Deformed pinna of ear and conductive deafness
19-28 day incidence
What is cleft lip and palate? How does it occur?
Multi factorial development depending on sex, genetics, social deprivation can increase incidence, smoking, alcohol, anti-epileptics
Cleft lip results from a failed merging of the maxillary and medial nasal elevations on one or both sides due to the inadequate migration of neural crest cells
Cleft palate results from the failure of the lateral palatine processes to meet and fuse with each other.
What are some dental features of cleft lip crossing the alveolus?
Impacted teeth
Crowding
Hypodontia or supernumerary teeth
Hypoplastic teeth
Caries
What is achrondoplasia?
Issue with endochindrial ossification leading to defects in short bones - dwarfism
Hence issue with base of the skull
What is crouzons? Craniofacial dysostosis
Premature closure of cranial sutures - especially coronal and lamboid
Leads to shallow orbits so the eyes look bulging
Retrusion and vertical shortening of the mid face
Class 3 occlusion
What is apert’s syndrome?
Premature closure of almost all sutures
Leads to maxillary hypoplasia,
class 3 occlusion,
Byzantine arch - narrow palate with high arch
Tall skull - acrocephalic
syndactyly of fingers and toes- fusion
What are sites of facial growth?
Sutures
Synchondroses
Surface deposition
What are cranial sutures? How do they facilitate growth?
Fibrous joints situated between intramembranous bone, they have osteopenia cells in the centre that promote growth when the suture is widened.
Sutures are widened in growth, by growth of the structure within the sututre e.g. the brain
What are synchondroses? Where found?
Cartilaginous based growth centre found along midlines, bones either side are moved apart as growth occurs
New cartilage is formed in the middle
Found between the sphenoid, ethmoid and occipital bones
How is growth achieved via bone deposition?
Basically bone remodelling
Deposition and resorption
Change in position of bone due to remodelling = cortical drift
How does the cranial vault grow up to age 7?
Bone growth at sutures
Bone deposition and resorption on the inner and outer surfaces displaced bones radially
Continues until sutures and fontanelles closed
How does the maxilla grow up to age 7?
It is displaced downwards and forwards through sutural growth and bone remodelling
This forward movement allows formation of maxillary tuberosities and allows for eruption of molar teeth
How does the mandible grow?
Grows downwards and outwards
Growth occurs at the condylar cartilage via bone remodelling with deposition mainly posteriorly and laterally
Endochondrial ossification at condylar cartilage
Intra membranous ossification to remodel ramus, coronoid and alveolar ridges
Differences in maxilla and mandible growth?
Maxilla grows by 8mm in males and 5.5mm in females
Mandible grows 26mm in males and 20mm females
Mandible growth accelerates significantly in puberty but maxilla finishes around 7 years old
How might someone have a long face or a short face
Due to an imbalance in the growth of anterior and posterior face heights
What is the SNB angle? What’s its normal value?
Sella - naison - point B (greatest concavity of mandibular symphysis)
79 degrees +- 3 degrees
What is the SNA angle? Whats its normal value?
Sella - naison - point A angle (deepest concavity on anterior maxilla alveolus)
81 degrees +- 3 degrees
What is the ANB angle? Whats its normal value?
A point - naison - B point
3 degrees +- 2 degrees
What is the Ui-Mx angle? Whats its normal value?
Upper incisor - maxillary plane angle
109 degrees
Plus minus 6 degrees
What is the Li-Md angle? Whats its normal value?
Lower incisor - mandibular plane angle
93 degrees
Plus minus 6 degrees
What is the MMPA angle? Whats its normal value?
Maxillary mandibular plane angle
27 degrees
Plus minus 4 degrees
What is LAFHt/TAFHt? Whats its normal value?
Facial height proportions
55%
What are the ANB Eastman values that determine skeletal base?
ANB….
> 8 = severe class 2
6-8 = moderate class 2
4-6 = class 2
2-4 = class 1
0-2 = mild class 3
-3-0 = moderate class 3
<-3 = severe class 3
