Skull Overview and Applied Anatomy of Face and Jaws

Question 1

What plane is used to compare skulls?

Answer 1

Frankfurt horizontal (FH) plane

Question 2

What 3 points define the Frankfurt horizontal plane?

Answer 2

• Right and left porion points (located at top of each external acoustic meatus)
• Left orbitale (located at bottom of left orbit)

Question 3

Using FH, skulls are viewed from 5 standard perspectives. What are these perspectives?

Answer 3

1. Norma verticalis (from above)
2. Norma lateralis (from side)
3. Norma occipitalis (from behind)
4. Norma frontalis (from front)
5. Norma basilaris (from below)

Question 4

What gives the skull its strength despite being lightweight?

Answer 4

It’s large number of bones.

Question 5

how many bones does the skull have at least?

Answer 5

23 (including the hyoid)

Question 6

What does the large number of bones in the skull also contribute to?

Answer 6

It’s versatility.

Question 7

What are the 3 benefits of having more joints between bones in the skull?

Answer 7

1. More joints between bones enables babies with bigger heads to be born.
2. More joints facilitate complex growth patterns.
3. More joints increase the resilience of the structure and so reduces the danger of fractures assuming catastrophic proportions.

Question 8

What is the role of the skull?

Answer 8

To support and protect the brain and organs of special sense as well as housing the first part of the respiratory and alimentary tracts.

Question 9

The skull can be divided into 2 parts, what are these 2 parts?

Answer 9

1. The neurocranium (braincase)

2. The viscerocranium

Question 10

What does the neurocranium consist of?

Answer 10

• A base

- A vault whose side walls and roof (calvaria) complete the bony covering

Question 11

What is the role of the neurocranium

Answer 11

To support & protect the brain

Question 12

What does the viscerocranium consist of?

Answer 12

• Consists of most of face, hyoid and larynx
• The upper part forms the orbits and nose
• The lower part, together with the mandible, constitutes the jaws

Question 13

What is the role of the viscerocranium?

Answer 13

Aids breathing and eating

Question 14

What are the 2 types of Neurocranium?

Answer 14

1. Membranous neurocranium

2. Cartilaginous neurocranium

Question 15

What is the membranous neurocranium also known as?

Answer 15

Dermatocranium

Question 16

What is the cartilaginous neurocranium also known as?

Answer 16

Chondrocranium

Question 17

What makes up the membranous neurocranium?

Answer 17

The flat bones of skull cap

eg frontal, parietal

Question 18

What makes up the cartilaginous neurocranium?

Answer 18

The bones of base of skull

eg ethmoid, sphenoid

Question 19

What is the membranous neurocranium formed by?

Answer 19

Formed by intramembranous ossification

Question 20

What is the cartilaginous neurocranium formed by?

Answer 20

Formed by endochondral ossification

Question 21

Is the membrane bone more protective or more supportive?

Answer 21

Membrane bone is more protective

Question 22

Is the endochondral bone more protective or more supportive?

Answer 22

Endochondral bone is more supportive

Question 23

Name 5 design features of the adult skull that combine to increase chances of survival to reproductive age.

Answer 23

1. Lightness
2. Strength
3. Keeping airway open
4. Warming & humidifying air breathed in through nose
5. Supporting muscles involved in chewing & swallowing

Question 24

Name a design feature of the neonatal skull that increases chance of survival?

How is there conflict for the mother in this design feature?

Answer 24

Bigger head: this means bigger brain and therefore better survival chances for baby (better developed protective reflexes).

Foetal size too big for mothers pelvis- pelvic disproportion- mother and child can die

Question 25

Name 2 design features of the neonatal skull that facilitate birth?

Answer 25

1. the babies head is DEFORMABLE (“moulding” within the birth canal) 2. Minimal development of inessential parts (eg. small jaws - liquid diet - no chewing, small nose - no sense of smell)

Question 26

What anatomical features give the neonatal skull its deformability?

Answer 26

- wide sutures - fontanelles - thin, deformable bones of the neurocranium

Question 27

What happens to the sutures in the skull as you become older?

Answer 27

They become interdigitated.

Question 28

What is the Fontanelle?

Answer 28

An area of membrane that has not yet turned bone- known as a soft spot- facilitates moulding to reduce size of head during child birth.

Question 29

What are the flat bones of the dermatocranium made from?

Answer 29

The flat bones of the dermatocranium are made from an outer and an inner plate of thin compact bone

Question 30

How many layers of compact bone are there? Name these layers.

Answer 30

3 layers 1. Outer cortex or outer compact bone 2. Diploe 3. Inner cortex or inner compact bone

Question 31

What is found interspersed between these layers of compact bone ?

Answer 31

Diploe

Question 32

What process do all three layers form by?

Answer 32

Intramembranous ossification

Question 33

What are 3 characteristics of diploe?

Answer 33

1. Light 2. Strong 3. Flexible

Question 34

How does the Dermatocranium restrict crack propagation?

Answer 34

By consisting of multiple smaller bones as to one big bone. This stops the crack from spreading further from the point of injury.

Question 35

What do the joints in the skull act as?

Answer 35

"crack stoppers" preventing fracture propagation- wont travel through diploe or inner cortex- will just remain on outer cortex.

Question 36

When looking at traumatic forces to the facial skeleton, | what happens as a result of a blow to the mid-face (maxillary region)?

Answer 36

- The bones crumple rather than remaining intact to be driven towards and through the base of the skull. - Le Fort pattern fractures separate face from the base of skull rather than damaging base of skull.

Question 37

When looking at traumatic forces to the facial skeleton, | what happens as a result of a blow to the lower face (mandible)?

Answer 37

- Dense bone so can absorb forces to a certain extent. | - Will fracture itself rather than be driven via its condyle through the base of the skull.

Question 38

The face doesn’t crumple everytime we chew. What stops this from happening?

Answer 38

Due to buttresses (thicken area of bone in the facial skeleton)

Question 39

The maxilla is made of thin bone and is hollow; due to this what must it do when masticatory forces are applied to prevent it from fracturing?

Answer 39

it has to dissipate biting (occlusal) forces away from itself and onto the neurocranium via three pathways (the “buttress system”) or it might fracture

Question 40

The maxilla is a light bone with THREE strengthened areas through which the forces are channelled to the whole skull. The strengthened parts are called CRANIO-FACIAL BUTTRESSES. Name these cranio-facial buttresses.

Answer 40

1. Frontonasal 2. Zygomatic 3. Pterygoid

Question 41

How many Le Fort Fractures of the Facial Skeleton are there? What is each fracture? Rank them in order of severity.

Answer 41

Le Fort I - when the alveolar maxilla separates from rest of face. This is the least serious fracture. Le Fort II - entirety of midface separates. Le Fort III - complete separation of viscerocranium to neurocranium. This is the most serious fracture.

Question 42

What are the two points that define the Le Fort III fracture and what does this fracture divided?

Answer 42

1. Above the orbits 2. Below the ears This fracture divides the bones of the cranial vault from the bones of the face.

Question 43

What is the most common mandibular fracture?

Answer 43

The most common mandibular fracture is separation of the condyle.

Question 44

What is the second most common fracture?

Answer 44

Separation from the body.

Question 45

What is the least common fracture?

Answer 45

Fracture of the ramus