QUIZ 1 Development of the Craniofacial Skeleton

Question 1

describe the general composition of bone

Answer 1

• hydroxyapatite formed on a collagenous matrix
• non-collagenous proteins

Question 2

name and describe the two types of bone growth processes

Answer 2

• endochondral ossification
  
  • bone that is formed on a cartilage template
    
    • long bones
• intramembranous ossification
  
  • bone that is formed from a condensation of mesenchyme
    
    • most of the mandible, skull plates

Question 3

what is initiation?

Answer 3

start of ossification, whether conversion of cartilage to bone, or condensation and ossification of mesenchyme/neural crest

Question 4

what is growth?

Answer 4

addition of more bony matrix to a pre-existing bone; thickening, elongation, etc.

Question 5

what is primary displacement?

Answer 5

• movement of a bone due to its own growth
• can occur in either direction, depending on the ratio of resorption to deposition and other structures
• bones often move in the opposite direction from which they are depositing matrix, as is often the case in articular surfaces and joints

Question 6

what is secondary displacement?

Answer 6

• movement of a bone due to the growth of other bones

Question 7

what is remodeling?

Answer 7

• growth involving simultaneous deposition and resorption on all peri- and endosteal surfaces
• changes size, shape, proportion, relationship with adjacent structures

Question 8

what is drift?

Answer 8

remodeling that results in movement of a bone towards the deposition surface

Question 9

what is functional matrix?

Answer 9

a tissue that guides a bone’s growth by exerting a force upon the bone

Question 10

describe directional bone growth

Answer 10

• can occur by the deposition of bone on a surface, with concomitant resorption on another
  
  • typically asymmetric growth so as to maintain some proportion
  • some surfaces grow more than others, and some undergo resorption more than others
  • deposition and resorption rates at a surface can change over time and even switch
• can occur at the endosteal or periosteal surfaces

Question 11

describe an example of bone growth as a result of a combination of primary and secondary displacement

Answer 11

distal phalanges grow directionally (primary displacement), but most of the movement is due to growth of long bones of the arm (secondary displacement)

Question 12

directional bone growth

what is a growth field?

Answer 12

where matrix can be laid down or resorbed

Question 13

directional bone growth

what are growth sites?

Answer 13

fields of significance to growth of a bone (ex. mandibular condyle, maxillary tuberosity)

Question 14

directional bone growth

what are growth centers?

Answer 14

special growth sites, control overall growth of bone (epiphyseal plates of long bones)

Question 15

what is the neurocranium?

Answer 15

• the bones encasing the brain
• consists of the calvaira and cranial base

Question 16

describe the calvaria

Answer 16

• “skull cap”
• intramembranous bone
• both paraxial mesoderm and neural crest in origin
• also called the desmocranium

Question 17

describe the cranial base

Answer 17

• base of the skull
• derived from special sense organ capsular tissues
• endochondral bone, primarily neural crest
• early form called chondrocranium

Question 18

what is the viscerocranium?

Answer 18

• derived from pharyngeal arches
• consists of what is considered the face (anterior, lower skull)

Question 19

how many bones make up the facial skeleton? what are they?

Answer 19

• 14
• 2 nasal bones
• 2 lacrimal bones
• 2 inferior nasal conchae
• 2 maxillae
• 2 palatine bones
• 2 zygomatic bones
• 1 vomer
• 1 mandible

Question 20

describe postnatal growth of the skull

Answer 20

• the skull does not grow equally in all directions or regions
• this is of interest to the dentist
  
  • the viscerocranium grows much more postnatally than the desmocramium

Question 21

what bones make up the calvaria/desmocranium?

Answer 21

frontal, parietal, parts of the occipital, temporal, and sphenoid bones

Question 22

what type of ossification is the desmocranium/calvaria formed?

Answer 22

intramembranous ossification

Question 23

the calvaria/desmocranium

condensed ___ forms a bilayer membrane that encapsulates the developing ___

Answer 23

• mesenchyme
• brain

Question 24

describe the bilayer membrane formed by condensed mesenchyme

Answer 24

• inner layer (endomeninx)
  
  • neural crest, gives rise to the pia mater and arachnoid mater
• outer layer (ectomeninx)
  
  • neural crest and paraxial mesoderm, gives rise to dura mater and calvaria/bone

Question 25

what ossifies to form the frontal bones and parietal bones?

Answer 25

superficial ectomeninx in the cranial vault

Question 26

which layer remains unossified and forms the dura mater?

Answer 26

ectomeninx

Question 27

the various bones of the skull are initially held together by \_\_\_

Answer 27

sutures

Question 28

what are sutures?

Answer 28

mesenchymal gaps between bones of the calvaria

Question 29

what are fontanelles?

Answer 29

unossified sutures between 2 or more skull bones

Question 30

\_\_\_ and ___ allow for growth of the skull to make room for more brain

Answer 30

sutures and fontanelles

Question 31

what event marks the end of bone growth?

Answer 31

eventuall ossification of sutures

Question 32

what is anencephaly?

Answer 32

* a calvaria/desmocranium defect * failure of rostral neural tube to close around week 4 * results in loss of telencephalon * illustrates requirement of brain for calvaria ossification

Question 33

what is craniosynostosis?

Answer 33

* a calvaria/desmocranium defect * premature fusion of the cranial vault sutures * variable defects include deformities of calvaria and neurologic deficits

Question 34

what bones make up the cranial base/ chondrocranium?

Answer 34

frontal, parietal, parts of the occipital, temporal, and sphenoid bones

Question 35

describe formation of the cranial base/ chondrocranium

Answer 35

* ectomeninx in the floor of the brain forms cartilage in response to notochord and other epithelial signals * becomes chondrocranium * later undergoes endochondral ossification

Question 36

what is the nasal capsule?

Answer 36

the embryological tissue that is going to form the nasal cavity

Question 37

growth of nasal septal cartilage plays a role in \_\_\_/\_\_\_ growth of the midface

Answer 37

downard/forward

Question 38

does all of the nasal capsule ossify?

Answer 38

no ex. septal cartilage

Question 39

what happens as the chondrocranium grows?

Answer 39

it pushes the maxilla and the rest of the facial skeleton down and forward

Question 40

describe development of the maxilla proper

Answer 40

* intramembranous ossification of mesenchyme * forms from the maxillary prominence/process

Question 41

describe development of the premaxilla

Answer 41

* intramembranous ossification of mesenchyme * forms from frontonasal process * forms primary palate * fuses early with maxilla proper

Question 42

where are secondary cartilages found within the facial skeleton?

Answer 42

* zygomatic process * alveolar plate * hard palate between palatine processes * mostly fetal growth roles

Question 43

the maxilla forms and grows down and forward via both ___ and ___ from growth of the ___ and ___ cartilages

Answer 43

* primary and secondary displacement * zygomatic and nasal septum

Question 44

\_\_\_ at sutures pushes the maxilla down, forward, and out

Answer 44

secondary displacement

Question 45

what is closely associated with the cartilage of the nasal capsule and zygomatic or malar cartilage?

Answer 45

ossification center

Question 46

what do the alveolar plates form from?

Answer 46

they form from the forming maxilla and the junction of the palatal process

Question 47

the alveolar plates house the \_\_\_

Answer 47

tooth germs

Question 48

ossification from the developing maxilla spreads to the palatine process to form most of the \_\_\_

Answer 48

hard palate

Question 49

describe the primary and secondary displacement involved in growth of the facial skeleton

Answer 49

Question 50

what type of ossification forms the mandible?

Answer 50

intramembranous ossification

Question 51

bone of the mandible forms lateral to what?

Answer 51

Meckel's cartilage (hyaline)

Question 52

ossification of the mandible spreads in what direction, and to form what features?

Answer 52

posteriorly to form the body and ramus of the mandible

Question 53

does Meckel's cartilage become part of the mandible proper?

Answer 53

no it largely disappears anteriorly

Question 54

describe secondary/accessory cartilages of the mandible

Answer 54

* condylar, coronoid, and symphyseal * form from meckel's cartilage at 10-14 weeks of development * condylar cartilage expands into a cone running along the ramus and ossifies through endochondral ossificaiton * remains at the articular ends on the head of the condyle

Question 55

the mandible is both ___ and ___ in nature, but the cartilage is ___ instead of \_\_\_

Answer 55

* membranous and endochondral * secondary instead of primary (meckel's)

Question 56

in the mandible, the ___ cartilage disappears before birth, and the ___ cartilages disappear the first year of birth

Answer 56

* coronoid * symphyseal

Question 57

coronoid and symphyseal cartilages of the mandible contribute transiently to what?

Answer 57

growth and development of the surrounding tissues

Question 58

what type of cartilage is an important growth center for the ramus? why?

Answer 58

* condylar cartilage * it drives intramembranous ossification, and then ossifies itself through endochondral ossification

Question 59

condyle cartilage functions in both ___ and \_\_\_

Answer 59

articulation at the TMJ and in growth