Oral  histology    

Lab  5    

Cementum  and  periodontal  ligament    

Slide  1                                          A – dentin B - epithelial rests C – cementoblasts D - cementum

E - resting lines F - periodontal region

Formation of Cementum

Dentin (A) lies along the right margin of the field, the periodontal region

occupies the left side. Note the islands of epithelial cells (B) near the

center of the field. These islands are called epithelial rests (of Malassez).

As the epithelial root sheath breaks up, connective tissue of the dental

follicle (sac) comes into contact with the dentin. In these regions multi

potential cells of the dental follicle differentiate into cementoblasts (C)

adjacent to the dentin. They deposit a ground substance around collagen

fibers of fibroblast origin. The osteoid-like mixture of ground substance

with collagen fibers is called cementoid. Mineralization converts

cementoid to cementum.

Cementum (D) in this image contains several basophilic "resting" lines

(E) that reflect periods when formation slows down or stops and then

starts again. Resting lines are incremental lines formed by fiber-free

ground substance. No cells are trapped in this cementum so it is classified

as acellular cementum - the first type to be formed. It is also referred to as

primary cementum.

                                                     

Slide  2                                            A  -­  epithelial  rests          B  –  cementoblasts      C  –  cementum      

D  -­  cementoid  E  -­  periodontal  region      F  –  dentin      G  –  osteocytes        

H  –  osteoblasts      J  -­  alveolar  bone        K  -­  primary  cementum      

L  -­  it  is  acellular  

   

   Epithelial   rests   (A)   appear   as   a   broken   string   of   small   dense  

basophilic   structures.   Identify   cementoblasts   (B)  whose  dark  nuclei  

stand  out  along  the  thin   line  of   light  pink  staining  material  between  

the   cementum   (C)   and   the   cementoblasts.   This   lighter   layer   is  

cementoid  (D)  indicating  active  formation  of  cementum.    

 

 

 

 

Slide  3  

                                     A  -­  periodontal  region  B  -­  epithelial  rests  C  -­  primary  cementum    D  -­  dentin  E  -­  Sharpey's  fibers  F  -­  principal  fibers                                      

   

Slide  4    

                                     Primary Cementum

This is a ground section of a tooth. From the bottom of the field up

identify the following layers: dentin with dentinal tubules (A), Tomes'

granular layer (B), primary (acellular) cementum (C). Note that primary

cementum is a relatively clear layer, containing no cells (cementocytes).

 

                     

   

Slide  5    Cementocyte                                                    A  -­  resting  lines  

B  –  canalculi.  

C-­cementocyte  lacuna    

 

                             

Slide  6  

Overlapping  at  C-­E  Junction  

                                   A  -­  cementum  

B  -­  enamel  margin  

C  –  dentin  

Enamel  Pearl  in  Section  

 

 

Slide  7  Enamel  pearl  

Enamel pearls are localized masses of enamel that develop ectopically, typically over the root surface (A) in close proximity to the cemento-enamel junction (B)                          

       

     

Slide  8  

 

Principal  fibers                                                  

A  -­  labial  mucosa      B  -­  labial  gingival      C  -­  gingival  fibers    D  -­  alveolar  crest  

fibers    E  -­  oblique  fibers    F  -­  alveolar  bone    G  -­  enamel  space  

                               

     

Slide  9  

Horizontal Fibers of the PDL

Horizontal principal fibers (A) are seen in this field. Note they pass

horizontally from cementum (B) to the alveolar bone (C) just below its

crest. This initial group of horizontal fibers was once referred to as

"cervical fibers". Note that Sharpey's fibers (D) can be seen inserting into

the cemntum on the right, and the alveolar bone on the left.