L9

Question 1

Eruption

Answer 1

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

Question 2

Physiologically, a tooth will move in all directions except

Answer 2

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

Question 3

The movements of eruption are a cellular activity involving

Answer 3

different cell types of

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

Question 4

The fibroblast, most numerous

Answer 4

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

Question 5

Stages of Eruption:

Answer 5

1 Preemergence 2 Prefunctional 3 Functional

Question 6

Prefunctional stage:

Answer 6

main direction

of movement is occlusially

Question 7

Functional stage: main direction

of movement is

Answer 7

mesially

Question 8

Histologic Views of Preemergence Stages

Answer 8

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

Question 9

Preemergence

Answer 9

The primary tooth germ and secondary dental lamina stages

The main direction of movement is facially

Question 10

Fate of enamel organ cell layers:

Answer 10

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

Question 11

1 Preemergence

Answer 11

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

Question 12

Preemergence stage: before start of

Answer 12

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

Question 13

Review of physiologic events occurring during the Preemergence Stage

Answer 13

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

Question 14

2 Prefunctional stage of eruption:

Answer 14

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

Question 15

Prefuctional begins with start of

Answer 15

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

Question 16

Events occurring during prefunctional stage:

Answer 16

*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

Question 17

Functional stage

Functional stage starts at

Answer 17

occlusial plane and continues throughout life

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

Question 18

Functional stage: Events at this stage:

Answer 18

• Continued dentin and cementum formation

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

Question 19

Hertwig’s epithelial sheath (HERS):

Answer 19

covers root dentin – determines root dentin outline

apical end continues as diaphragm:determines number of root canals

Question 20

Reduced enamel epithelium (REE)

Answer 20

is attached to surface

by a basal lamina

Question 21

Prefunctional stage

Answer 21

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

Question 22

Fate: Hertwig’s Epithelial Root Sheath Cells

Answer 22

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

Question 23

Epithelial rest of Malassez

Answer 23

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

Question 24

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

Answer 24

cell death

B = The coronal most part emerges into oral cavity

Question 25

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

Answer 25

prefunctional stage of eruption

Question 26

Emergence into oral cavity: reduced enamel epithelium

becomes the

Answer 26

junctional epithelium (JE)

Question 27

Certain Events occurring during Prefunctional Stage:

Answer 27

• 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

Question 28

Functional Stage of Eruption

Answer 28

Starts at the occlusial plan and physiologically continues throughout life

Main movement mesially: ‘physiologic mesial drift’

Question 29

Junctional epithelium attachement position changes during functional eruption

Answer 29

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

Question 30

Functional arrangement of principal fiber bundles of PDL

Answer 30

occurs

during functional stage of eruption

Question 31

Changes during functional eruption:

Answer 31

attrition, dead tracts, reparative (teritary) dentin

Question 32

Changes during Functional stage of eruption:

Answer 32

Continued dentin formation, reduced pulp tissue volume, ectopic mineralization

Question 33

Physiological Events Occurring During Functional Stage:

Answer 33

• 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.

Question 34

The primary teeth are in the

Answer 34

functional stage of eruption.

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

Question 35

S h e d d i n g:‘

Answer 35

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

Question 36

Shedding is caused by

Answer 36

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)

Question 37

Shedding primary central incisor and eruption of

Answer 37

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

Question 38

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

Answer 38

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……. (?)