Practice Test for Ortho

Question 1

What is growth?

Answer 1

Increase in anatomical size and/or shape

Question 2

What is a distance curve?

Answer 2

It is a cumulative curve showing accumulation of size increases.

Question 3

What is a velocity curve?

Answer 3

It is an incremental curve that shows amount of size increase over time makign it easy to view the stages of growth and growth spurts.

Question 4

What does the typical velocity of growth curve look like?

Answer 4

Velocity of growth is greatest at birth and decreases through infancy until 3 or 4 years of age.

Then it continues at a constant velocity with a few ups and downs until adolescence.

Velocity then increases at the adolescent growth spurt at around 12 years old

Growth spurt peaks at 14 years of age before decreasing gradually.

Growth velocity is 0 when growth stops around 20 years old.

*Timing varies among genders, races, and individuals.

Question 5

How does bone grow at the cellular level?

Answer 5

Hypertrophy - increase in size of cells

Hyperplasia - increase in the number of cells

Secretion of ECM - (this later calcifies into bone) most active cellular activity during bone growth

Question 6

What are the hard tissues of the body?

Answer 6

Bone, teeth, and SOMETIMES cartilages

Question 7

How do soft tissues of the body grow?

Answer 7

Growth by hyperplasia and hypertrophy within the tissues (interstitial growth) Secretion of ECM can occur but isn’t important.

Question 8

How does endochondral ossification take place?

Answer 8

Interstitial growth of cartilage takes place

hypertrophy takes place

ECM secretion follows

ECM degenerates forming mineralized tissue

Bone formation occurs

Question 9

How do bones grow following mineralization into hard tissue?

Answer 9

Hyperplasia, hypertrophy, and secretion of ECM can only occur on the surface of the mineralised mass not within it.

Question 10

What is intramembranous ossification?

Answer 10

Direct secretion of bone matrix into CTs without any intermediate cartilage.

Question 11

Which parts of the skull undergo endochondral ossification?

Answer 11

Mandibular condyle

Basal part of the skull

Question 12

Which part of the skull undergoes intramembranous ossification?

Answer 12

Cranial vault

Jaws

Mandible

Maxilla

Question 13

What is modelling and remodelling?

Answer 13

Modelling is formation of new bone from cartilage or directly within mesenchyme

Remodelling is the resorption of bone in one area and apposition in another to reshape the bone.

Question 14

What is craniofacial microsomia?

Answer 14

Previously called hemifacial microsomia but both cranial and facial structures are affected so it was renamed.

Question 15

When does craniofacial microsomia occur?

Answer 15

During the 3rd stage of embryonic craniofacial development. Origin, migration and interaction of cell populations.

Days 19 - 28 meaning it occurs before the mother even knows she’s pregnant.

Question 16

What percentage of live births have craniofacial microsomia?

Answer 16

1 in 5000 live births

Question 17

What happens during craniofacial microsomia? (signs and symptoms)

Answer 17

Lack of development in lateral facial areas on the affected side. (90% unilateral and 10% bilateral)

Ear abnormalities - small or ear tags (deformed)

Underdeveloped external acoustic part of the ear. Including ossicles - malleus stapes and incus.

Deficient or missing ramus of the mandible and associated soft tissues (muscles of mastication and fascia)

Small or absent parotid gland

Can also affect condylar cartilage

Maxilla can also be deficient on the affected size, since deficient mandible reduces maxillary growth

Facial asymmetry of mandible and chin

CVS and vertebral abnormalities on affected side.

Question 18

How does craniofacial microsomia occur?

Answer 18

Loss of neural crest cells during migration usually affecting those with long migration path so midline defects are rare in this syndrome.

Question 19

What causes craniofacial microsomia?

Answer 19

Haemorrhage of ECA (3rd arch) or stapedial artery (2nd arch) due to ruptured artery

Teratogens such as 13-cis retinoic acid

Ischaemia (eg due to maternal smoking)

Question 20

What is the nasomaxillary complex?

Answer 20

Nose, maxilla, and associated smaller nasal and palatine bones

Question 21

How is the maxilla moved during its development?

Answer 21

Postnatally the maxilla is moved forward and downward relative to the cranium by endochondral growth of the cranial base behind it.

Forward movement only occurs if the cranial base is growing which is usually until the age of about 6.

Question 22

How do we know translation occurs?

Answer 22

Superimposed tracings of cephalometric x-rays.

Failure of cranial base to lengthen normally means maxilla doesn’t move forward and this leads to a midface deficiency.

Question 23

How does the nasomaxillary complex grow?

Answer 23

Intramembranous ossification by apposition and surface remodelling

Surface remodelling

Question 24

Which sutures are involved in bringing the maxilla forward?

Answer 24

Fronto-maxillary = superiorly at the end of the frontal process

Zygomatico-maxillary = superiorly-laterally along the zygomatic process

Mid-palatal = midline of the palate (mechanism for widening the midface and upper dental arch - transverse growth)

Posterior and superior sutures allow downward and forward repositioning

Question 25

How does surface remodelling take place in the maxilla?

Answer 25

It is dramatic and important; bone is removed from the anterior surface of the maxilla except a small area around the anterior nasal spine.

Resorption opposes the forward translation due to growth but adds to downward translation.

Sometimes remodelling has an additive effect on forward translation such as that seen in downward and forward translation of the palate.

Question 26

How does apposition at sutures take place in nasomaxillary growth?

Answer 26

By apposition at sutures that connects maxilla to cranium and cranial base. At 7 years of age the cranial base stops growing and sutural growth becomes more important for bringing the maxilla forward

Also by surface remodelling.

As the maxilla translates, new bone is added on both sides of the sutures so that they remain the same width and so that connection is maintained with the cranium.

Also apposition takes place at the tuberosity area on the posterior border of the maxilla which is a free surface. Bone is added to create space for primary and permanent molars.

Question 27

What are the overall mechanisms of nasomaxillary growth?

Answer 27

Cartilage push (cranial base)

Soft tissue pull (Cartilage pull? nasal septum?)

Evidence indicates a role of nasal septum as a possible growth center.

Question 28

What is the determinant of nasomaxillary growth?

Answer 28

Pull from facial soft tissues (epigenetic/potentially neurotrophic)

Question 29

What is considered normal birth weight?

Answer 29

2000 - 4000 grams

Question 30

What weight is considered a risk factor for problems in immediate postnatal period?

Answer 30

<2500g

Question 31

What causes lower birth weight?

Answer 31

Twins are usually lower birth weight as they compete in utero

Premature birth

Question 32

What generally happens to people with low birth weight later on?

Answer 32

They are small into the 2nd year of life but then they usually overcome the initial handicap. Growth will follow initial pattern of potential and associated percentile.

By 3rd year of life they usually cannot be distinguished from normal-term infants in attainment of developmental milestones. (o Most catch up in terms of growth & development. But in some cases there may be a lasting effect)

Question 33

What does chronic disease do to growth?

Answer 33

Other requirements of the body must be met before skeletal growth can occur. Body suppresses functions that are least important first.

Acute illness leads to temporary cessation of growth, no long-term effect.

If the illness persists persists, growth deficit is cumulative and the individual continues to deviate while affected by the disease. (If treated they move back towards their initial growth percentile but usually below it)

Growth usually continues at a percentile lower than initial.

Question 34

What is the hierarchy of shutdown?

Answer 34

Body suppresses functions that are least important first. Growth first, then activity, then excretion, then basal activity)

Question 35

What kind of chronic illnesses can lead to growth impairment which returns to normal?

Answer 35

Congenital hormone deficiencies (Hormone replacement fixes everything)

In extreme cases, psychological and emotional stress affect physical growth in a similar way as chronic illness.

Question 36

What does malnutrition do in chronic illness?

Answer 36

Chronic malnutrition leads to similar affects on growth as chronic illness.

Malnutrition in infancy and adolescence has the greatest effect on growth.

Once nutritional adequacy is achieved, additional intake isn’t a stimulus to more rapid growth.

Question 37

What secular trend affects people in the last 300 - 400 years regarding size of people and age of sexual maturation?

Answer 37

Somewhat related to better nutrition; faster growth and weight gain.

Limited protein, trace minerals and vitamins may have limited rate of growth in the past.

Trend also in populations whose nutritional status doesn’t seem to have improved significantly.

Exposure to environmental chemicals with oestrogenic effects seem to be contributing to earlier sexual maturation.

Question 38

How does early mesial shift of teeth occur?

Answer 38

At 6 years of age; mandibular 6s erupt and shift mesially to close the primate spaces.

Losing these developmental spaces lead to early shift from flush terminal plane to class 1.

Question 39

Where are primate spaces located?

Answer 39

Maxillary primate spaces are located mesially to the canine.

Mandibular distally to the canine.

Early mesial shift occurs in arches with a mandibular primate space (2/3 of cases)

Question 40

How does late mesial shift take place?

Answer 40

At 12 years of age when 2nd primary molars are lost the 1st permanent molars move mesially relatively rapidly into the leeway space.

Leeway space difference betwen mandibular 6 and maxillary 6 leads to mesial shift of ~1mm.

Question 41

What is the leeway space?

Answer 41

Diffference between D and E and the 4 and 5. Premolars are smaller than the primary molars that they replace.

Question 42

How big is the mandibular leeway space?

Answer 42

2.5mm on each side

Question 43

How big is the maxillary leeway space?

Answer 43

1.5mm on each side of the arch.

Question 44

Does incisor crowding affect the late mesial shift? What is the clinical signficance of this?

Answer 44

No, the leeway space still ends up being taken by mesial shift.

This provides an opportunity for orthodontic treatment since crowding could be relieved by using the leeway space.

Question 45

What is the overall outcome of the mesial shift?

Answer 45

This mesial movement of molars leads to dec. arch length & circumference

Question 46

What other factors lead to the mesial shift from flush terminal plane to class 1 occlusion?

Answer 46

Differential growth of maxilla and mandible due to cephalocaudal gradient.