L14

Question 1

Ossification Centers:

Answer 1

initial appearance/s of bone tissue in the area where each of the 206 Bone Organs of the body form:
(1 mandible and 2 maxillae of the 22 adult skull bone organs)

Question 2

The ossification centers appear in different environments Within mesenchyme:
called

Answer 2

intramembranous bone organ development On or within a cartilage model:
called endochondral bone organ development

Question 3

Intramembranous bone (organ) ossification center:

Answer 3

Examples: the 1 mandible: 2 ossification centers (1 for each halve)
the 2 maxillary bones: 2 ossification centers for each bone

Question 4

Endochondral bone (organ) ossification center

Answer 4

Examples: ulna 3 ossification centers: femur..5 ossification centers

Question 5

Note: some bones, such as the temporal bones, have both intramembraneous and endochondrial ossification centers and are referred to as having

Answer 5

‘mixed ossification centers’

Question 6

*2 Growth Sites: addition of bone tissue to a

Answer 6

bone organ
Growth sites of bone tissue formation: the periosteum, endosteium, haversian and volkman canals and of special interest the periodontal ligament (PDL)
(For this lecture, areas of cartilage tissue will be discussed as growth sites of the forming mandible)

Question 7

Note: No matter what environment bone tissue forms in or on, it always forms within a

Answer 7

highly vascular connective tissue that is referred to, by some, as ‘intramembranous’ bone tissue formation not to be confused with ‘intramembrane ossification centers’ of some bone organs

Question 8

Paired Meckel’s Cartilages:

One in each mandibular process of branchial arch I

Answer 8

Role:
1. Temporary skeleton of mandibular processes of branchial arch I
2. Serve as temporary attachment for muscles
that eventually attach to the mandible
3. Each cartilage serves as models for 2 ear ossicles:
malleus and incus
4. Each serve as site for the appearance of 2 ligaments:
anterior mallelar and sphenomandibular
5. Serve as temporary anterior lingual plate of forming mandible halves
6 Serve as enclosed growth sites at the chin end of the mandible halves

Question 9

Mecke’s Cartilages fate:

Answer 9

Fate:
From the proximal part (inner ear cavity) to the distal part (chin), each cartilage
1 2
3
serves as sites for:
Endochondral ossification centers for 2 ear ossicles: incus and malleus Undergo retrogressive changes becoming 2 ligaments:
anterior mallelar and sphenomandibular
Undergo growth, mineralization and resorption while serving as anterior
growth sites and replaced as temporary anterior lingual plates by
the encroaching bone tissue of the growing mandible halves

Question 10

Note: Meckel’s cartilages serve as both

Answer 10

ossification centers of ear ossicles

and as a growth site of each mandible halve

Question 11

The enclosed anterior parts of Meckel’s cartilages serve as:

Answer 11

• temporary lingual plate of the mandible halves

* growth site of the developing mandible halves

Question 12

The mandible develops as

Answer 12

2 bilateral halves that exist throughout the interuterine period.
It becomes 1 of the 22 skull bones when osseous union occurs between the halves at the end of the first postnatal year

Question 13

Mandible:

1. begins development in the

Answer 13

sixth (6th) embryonic week

Question 14

Mandible 2. arises from

Answer 14

2 bilateral ossification centers within mesenchymal tissue,

lateral to Meckel’s cartilages

Question 15

Mandible 3. the ossification centers appear in the area where the

Answer 15

inferior alveolar nerve

branches into the mental and incisive nerves or site of future mental foramina

Question 16

Mandible 4. bone grows anterior and posterior from the

Answer 16

centers:
anterior: the bone incorporates the distal parts of Meckel’s cartilages:
this incorporated part of each cartilage becomes the temporary lingual plate and a growth site of each mandible halve
posterior: the bone is in the form of a ‘U’ featuring facial and lingual plates; the posterior end of the facial plate incorporates an independent piece of hyaline cartilage that becomes ‘condylar cartilage’ another
growth site of each mandible half

Question 17

Note: condylar cartilage does NOT arise from

Answer 17

Meckel’s cartilage: it’s independent

Question 18

Bilateral ossification centers (O)

They appear in the

Answer 18

6th embryonic week within the mesenchyme lateral to Meckel’s cartilages in the area of the branching of the mandibular nerve into mental and incisive nerves: site of future mental foramen

Question 19

At the end of the first postnatal year, an osseous union occurs between

Answer 19

2 mandibular halves at distal or chin site: mandible becomes 1of the 22 skull bones

Question 20

Condylar cartilage:

Answer 20

enclosed growth site of mandible

Question 21

The incorporated distal ends

of Meckel’s cartilages serve as the

Answer 21

temporary anterior lingual plates and growth sites of the

forming mandible halves

Question 22

Proximal end of each cartilage serves as the model for

Answer 22

2 ear ossicles and 1 ligament * malleus and incus ossicles (bones)
* anterior mallelar ligament

Question 23

Meckel’s Cartilage Middle area:

Answer 23

• sphenomandibular ligament

Question 24

Meckel’s Cart. Distal end:

Answer 24

temporary anterior lingual plate and * growth sites of the mandible halves

Question 25

Fate of distal end of Meckel’s cartilages (MC)

Answer 25

1 start MC enclosure
2 MC enclosed
3 MC mineralizing,
resorbing, replaced by bone tissue:
anterior lingual plate of mandible

Question 26

Osseous union between mand. processes occurs at the end of

Answer 26

first year,

suture disappears – remodeled: mandible becomes one bone

Question 27

Frontal view of Meckel’s cartilages and mandible halves: area of

Answer 27

primary canine epithelial buds

Question 28

Area of the developing primary second molar bud (red arrows) Meckel’s cartilages (M) serve as

Answer 28

temporary skeleton of the lower jaw, and as a strut or attachment for the muscles of mastication.
Here, the mylohyoid muscle (black arrows) is attached to the medial sides of Meckel’s cartilages

Question 29

Definition of Joints or Articulations:

Answer 29

‘The place of union or junction between two or more bones of the skeleton

Question 30

Synarthrosis- permits

Answer 30

little or no mobility (fibrous and suture joints)

Ex. = between maxillary bones: between temporal and paretal bones

Question 31

Amphiarthrosis- permits

Answer 31

slight mobility (cartilaginous joints) Ex. = pubis symphysis

Question 32

Diarthrosis -

Answer 32

permits a variety of movements (synovial joints) Ex. = temporomandibular joint (TMJ)

Question 33

Ginglymoarthrodial joint,

Answer 33

referring to its dual compartment structure and function:ginglymo and arthrodial.

Question 34

Two bones form the TMJ joint:

Answer 34

temporal = squamous portion
mandible = condyloid process (condyle

Question 35

Unique features of Temporomandibular Joint
Temporal bone Zygomatic arch
A C

Answer 35

Complete articular disc.. (C) Two joint cavities…….. (B) Soft connective tissue
articlating surfaces……(A)

Question 36

Blastema or rudiments of TMJ and site of condylar cartilage appearance

Answer 36

No cavitation in 8 week embryo

Question 37

Articular disc (A) is present but

Answer 37

cavitation is not evident; it occurs during the third month in utero .

Question 38

Appositional growth occurs between the

Answer 38

articular connective tissue surface
and the condylar cartilage
At the lower end, the cartilage is mineralized, resorbed and replaced by
bone tissue
The condylar cartilage remains until about the age of 25 when it is replaced
by compact bone tissue (Which see)

Question 39

Appearance of 2 ossification centers of mandible……

Answer 39

Sixth week IU

Question 40

Osseous union of mandibular halves………………….

Answer 40

End of 1st year

Question 41

Appearance of blastema (rudiments) of TMJ………

Answer 41

Eighth week IU

Question 42

Cavitation within blastema of TMJ………………..

Answer 42

Third month IU

Question 43

Replacement of condylar cartilage by compact bone…

Answer 43

Twenty- fifth year +/_

Question 44

the blastema is a

Answer 44

rudimentary (embryonic) substance from which cells, tissues, or organs are formed

Question 45

The TMJ blastema is where the following form:

Answer 45

Condylar cartilage
Articular disc
Two joint cavities
Soft tissue articular surfaces