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Oral Histology > L9 > Flashcards

Flashcards in L9 Deck (38)
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1
Q

Eruption

A

‘The movements a tooth makes to attain and maintain its position in the jaw’

2
Q

Physiologically, a tooth will move in all directions except

A

apically
to attain and maintain its position in the jaw: also, normally, tooth movement
occurs throughout life.

3
Q

The movements of eruption are a cellular activity involving

A

different cell types of

the periodontal ligament (PDL): cementoblasts, osteoblast, osteoclasts and fibroblasts

4
Q

The fibroblast, most numerous

A

cell type of the PDL, is thought to play a key role
in tooth movement. It serves several functions within the PDL:
* secretes extracellular substance (fibroblast),
* lysis the extracellular substance (‘fibroclast’),
* may beome a contracting cell called a ‘fibromyocyte’ myofibroblast:
this cell is connected (by integrins: receptors) to principal collagen fiber bundles
that connect the tooth to alveolar bone, when it contracts the collagen fibers
contract moving the tooth:

     Note: Fibronectin is a glycoprotein that exhibits elastic properties and
               serves as an integrin (similar to cell integrins) that binds to 
               extracellular components such as collagen
5
Q

Stages of Eruption:

A

1 Preemergence 2 Prefunctional 3 Functional

6
Q

Prefunctional stage:

A

main direction

of movement is occlusially

7
Q

Functional stage: main direction

of movement is

A

mesially

8
Q

Histologic Views of Preemergence Stages

A

Starts with appearance of dental lamina and continues to the appearance of reduced enamel epithelium and Hertwig’s root sheath, just prior to start of root dentin formation. During this stage the teeth move in different directions, but their main direction of movement is facially

9
Q

Preemergence

A

The primary tooth germ and secondary dental lamina stages

The main direction of movement is facially

10
Q

Fate of enamel organ cell layers:

A

Reduced enamel epithelium: attached to completed enamel surface by a
basal lamina, last secretion of ameloblasts
2. Hertwig’s epithelial root sheath: inner and outer layers of enamel organ

11
Q

1 Preemergence

A

Outer and inner layers coming together forming Hertwig’s epithelial root sheath
The sheath serves 2 main functions:
1. Determines number of root canals of tooth
2. Determines root dentin outline

12
Q

Preemergence stage: before start of

A

root formation
Diaphragm of Hertwig’s epithelial root sheath (arrows)
Number of root canals are determined at this stage

13
Q

Review of physiologic events occurring during the Preemergence Stage

A

Start of odontogenesis: epithelial stages and tooth germ appearances

  • Differentiation of ameloblasts, odontoblasts and fibroblasts
  • Appearance of crown dentin
  • Enamel formation begins and is maturing
  • Appearance of pulp chamber
  • Establishment of dentinoenamel junction
  • Enamel organ over the enamel becomes the
    reduced enamel epithelium that is attached to the enamel by a
    basal lamina
  • The outer and inner layers of the enamel organ
    come together at the cevical loop to form: Hertwig’s epithelial root sheath (diaphragm)
  • Number of root canals a tooth will have is determined at this stage
  • Bone crypt: undergoing remodeling
14
Q

2 Prefunctional stage of eruption:

A

Starts with root dentin formation and ends when tooth reaches occlusial plane:
Main direction of movement is occlusially

End of prefunctional stage:
Beginning of functional stage

15
Q

Prefuctional begins with start of

A

root dentin formation
Ends at the occlusial plane
Main movement is occlusially or vertically

16
Q

Events occurring during prefunctional stage:

A

*Start of root dentin formation
* Break=up Hertwig’s sheath
*Cementum formation (cementogenesis)
*Formation of periodontal ligament
*Rreduced enamel epithelium becomes the junctional epithelium:
Note: as was true for the reduced enamel epithelium , the junctional epithelium is
attached to the tooth surface by a basal lamina
*Enterance into oral cavity

17
Q

Functional stage

Functional stage starts at

A

occlusial plane and continues throughout life

Main movement is mesially: Referred to as ‘physialogic mesial drift’

18
Q

Functional stage: Events at this stage:

A
  • Continued dentin and cementum formation

* Age changes: decreased pulp volume, attrition, and etc.

19
Q

Hertwig’s epithelial sheath (HERS):

A

covers root dentin – determines root dentin outline

apical end continues as diaphragm:determines number of root canals

20
Q

Reduced enamel epithelium (REE)

A

is attached to surface

by a basal lamina

21
Q

Prefunctional stage

A

Hertwig’s root sheath along root dentin
Left: Hertwig’s sheath in tact along forming root dentin:
Here the sheath is preforming one of its functions: determining root dentin outline
Right: cementogenesis at cervical most part of root dentin

22
Q

Fate: Hertwig’s Epithelial Root Sheath Cells

A
  1. Sheath: diagragm stage – number of root canals determined: tooth erupts
    occlusially from this level
  2. Sheath elongates: determines root dentin outline.
    diaphragm remains at relatively same level
  3. Root dentin forms: Sheath breaks - up: Cementum forms on exposed dentin:
    this sequence continues apically until root dentin is completed
23
Q

Epithelial rest of Malassez

A

Remanents of epithelial cells from Hertwig’s root sheath in the periodontal ligament
Appear during prefuctional stage of eruption

24
Q

A = During the prefunctional stage of eruption, the merged oral epithelium and
reduced enamel epithelium undergo

A

cell death

B = The coronal most part emerges into oral cavity

25
Q
Merger of reduced enamel epithelium (REE) and 
       oral epithelium (OE) during
A

prefunctional stage of eruption

26
Q

Emergence into oral cavity: reduced enamel epithelium

becomes the

A

junctional epithelium (JE)

27
Q

Certain Events occurring during Prefunctional Stage:

A
  • Starts with the begining of root dentin formation
    * Break-up Hertwig’s epithelial root sheath
    * Appearance of Epithelial rest of Malassez
    * Differentiation of cementoblasts
    * Cementogenesis
      * Formation of periodontal ligament site 
             - Maturing dental follicle part of the tooth germ
    
      * Collagen fiber bundles of PDL are not functionally arranged in groups: arranged obliquely
      * Merging of reduced enamel epithelium with oral epithelium
      * Emergence into oral cavity
    
      *Reduced enamel epithelium becomes the junctional epithelium of free gingiva
         -Note: as was true for the reduced enamel epithelium, the junctional epithelium
           is attached to the tooth surface by a basal lamina
    
      *Ends when tooth reaches the occlusial plane
28
Q

Functional Stage of Eruption

A

Starts at the occlusial plan and physiologically continues throughout life

Main movement mesially: ‘physiologic mesial drift’

29
Q

Junctional epithelium attachement position changes during functional eruption

A
A = attached to enamel
B = attaced to enamel and cementum
C = attached to cementum
30
Q

Functional arrangement of principal fiber bundles of PDL

A

occurs

during functional stage of eruption

31
Q

Changes during functional eruption:

A

attrition, dead tracts, reparative (teritary) dentin

32
Q

Changes during Functional stage of eruption:

A

Continued dentin formation, reduced pulp tissue volume, ectopic mineralization

33
Q

Physiological Events Occurring During Functional Stage:

A
  • Starts at occlusial plane and physiologically continues throughout life
    • Functional arrangement of the principal fiber bundles of PDL
    • Maintenance (preservation) of alveolar process (remodeled bone crypt)
    • Continued dentin (secondary and teritary) and cementum formation:
    • Main direction of eruptive movement is mesial: Physiological mesial drift
    • Junctional epithelium moves from its attachment to just enamel,
      to enamel and cementum, then to just cementum (physiologic passive eruption)
   *  Reciprocal induction occurs between the junctional epithelium and adjacent 
           connective tissue (lamina propria)
  • Age changes: unique changes of each tooth tissue.
34
Q

The primary teeth are in the

A

functional stage of eruption.

Permanent teeth seen are in either preemergence or prefunctional stages of eruption

35
Q

S h e d d i n g:‘

A

The physiologic elimination of primary teeth caused by the resorptive action of odontoclasts’

36
Q

Shedding is caused by

A

physiologic odontoclastic activity:
The odontoclast like the osteoclast originates in the bone marrow
and conveyed to the site of activity by blood vessels.
(Odontoclasts resorb the 3 mineralized tissues of teeth)

37
Q

Shedding primary central incisor and eruption of

A

permanent central incisor
Note the resorbed area of the primary root
(lingual surface - black arrrow)

38
Q

The openings in the bone located lingual to the primary anterior teeth are called

A

gubernaculum canals: a gubernaculum ligament passes through the canal
to the dental follicle of a succeedaneous tooth (seen in the canal) and are
thought to help guide the tooth into the oral cavity……. (?)