Facial Growth Flashcards
What are the 2 stages of in utero development?
Embryonic - 1-8 weeks
Foetal - 8 weeks to full term
Why do we treat GROWING children?
We can predict changes
We can utilise growth to correct malocclusion
We can time orthodontics and surgery
What condition occurs if the neural tube does not fuse?
Spina bifida
What nerve and muscles are derived from the 2nd pharyngeal arch?
The facial nerve and the muscles of facial expression
Associated with Reichert’s cartilage
What nerve and muscles are derived from the 1st pharyngeal arch?
The trigeminal nerve and the muscles of mastication
Associated with Meckel’s cartilage - which goes on to form the lower jaw
How is it that cleft lip and palate can happen independently of one another?
They upper lip and anterior part of the palate have different embryological origins from the posterior palate and they fuse at different times.
Why is facial growth important?
The size, shape and position of the underlying jaws determines the position of the teeth and therefore malocclusion.
What weeks in utero is most of face development done?
Mainly in the first 8 weeks
What are the 2 parts of the skull?
Neurocranium - brain
Viscerocranium - skeleton of the facew
What type of bone formation forms the neurocranium and viscerocranium?
Neurocranium - intramembranous ossification
Viscerocranium - endochondral ossification
Briefly describe intramembranous bone formation
Bone is deposited as a direct conversion of mesenchyme into bone.
Osteoblasts group into clusters and form an ossification centre.
Typically for flat bones.
Briefly describe endochondral bone formation.
Where hyaline cartilage model is then replaced by bone.
Occurs at epiphyseal plates in long bones - bones that need to grow - limbs, spine, ribs and VISCEROCRANIUM.
What bone is not ossified at birth?
The nasal septum - not ossified as this is important for forwards and downward growth of the maxilla
What type of bone formation are the maxilla and mandible formed by?
Intramembranous bone formation but are preceded by a CARTILAGENOUS facial skeleton
What is hemifacial microsomia and how does it occur?
It is a 3D progressive facial asymmetry
Occurs due to lack of neural crest cells migrating to the front on one side during fusion of the 2 neural folds.
How does Treacher Collin’s syndrome occur?
The neural crest cells do not migrate at all on either side of the neural tube.
Deficiency of 1st and 2nd branchial arches
Roughly what days in utero do the lips fuse?
28-38 days
Roughly what days in utero do palatal shelves elevate?
42-55 days
What is the demarcation between lip and palate?
The incisive foramen.
What are the dental features of a cleft palate?
Impacted teeth
Crowding
Hypodontia
Supernumeraries
Hypoplastic teeth
Caries
When does ossification of the face and skull commence?
7-8 weeks
What is the definition of a primary abnormality?
Defect in the structure of an organ or part of an organ that can be traced back to an anomaly in its development (e.g. spina bifida)
What is the definition of a secondary abnormality?
Interruption of the normal development of an organ that can be traced back to other influences
e.g. trauma, infection, chemicals (thalidomide)
What are some symptoms of Foetal Alcohol Syndrome?
Microcephaly (small head)
Small mid-face and mandible
Short palpebral fissures
Long and thin upper lip with deficient philtrum.
Mild mental difficulties
Where are the sites of facial growth?
Sutures
Synchondroses
Surface deposition
What does surface deposition ensure is done?
Surface deposition of bone allows bone to increase in size but maintain their shape as they grow.
How does bone formation around synchondroses work?
It is a cartilage-based growth centre with growth occurring in both directions - bone is “pushed apart”
NOTE - synchondrosis is a primary cartilaginous joint where 2 bones are completely joined by hyaline cartilage.
What is a suture?
Specialised joints that are situated between intramembranous bone.
A band of connective tissue which has osteogenic cells and the ones on the periphery can provide new bone growth
How does growth at sutures occur?
Occurs in response to growing structures separating the bone e.g. growth of the calvarium in response to development of the brain.
Where bones are pushed apart new bone forms in the suture - growth occurs in areas of tension.
What is the cranial vault comprised of?
Frontal
Temporal
Occipital
Parietal bones
When does cranial vault stop growing/ expanding?
Until age 7 (in response to growing brain)
What 2 ways does bone growth occur in cranial vault?
Bone growth at sutures
External and internal surfaces are remodelled through surface deposition and resorption to displace bones easily.
What makes up the cranial base?
Frontal
Ethmoid
Sphenoid
Temporal
Occipital
Bones
What 2 types of growth occur in cranial base?
Endochondral ossification
Surface remodelling.
What determines the relationship between the maxilla and mandible - how close or far apart they are?
Difference in growth between anterior and posterior cranial base
What skeletal class is a small angle in the cranial base more likely to be associated with?
Class III Skeletal relationship
What skeletal class is a large angle more likely to be associated with?
Class II skeletal relationship
Where does resorption and deposition of bone occur in the mandible?
Resorption - anteriorly and lingually
Deposition - posteriorly and laterally
When is treatment of the mandible most effective?
Treatment that utilises the pubertal growth spurt.
What ages does facial growth slow in males and females?
Females - growth slows after 16-17 years
Males - 18-20
What are some indications for taking a lateral cephalogram in ortho?
To aid diagnosis - skeletal class (marked AP discrepancy)
Aid location and assessment of unerupted, malformed or misplaced teeth
Gives indication for upper incisor root length
What is a lateral cephalogram?
A standardised, reproducible lateral radiograph of the face and base of skull.
What do forward and backward growth rotations lead to?
Forward - short face
Backward - long face
