Line Angles and Point Angles

CEMENTUM

(Morphology, Cytologic, and Histologic structures)

Morphology

 • There are 2 types of cementum:

 1. Acellular Cementum (Non-cellular or primary cementum)

 2. Cellular Cementum (Secondary Cementum)

Acellular Cementum

 (Non-cellular or primary cementum) 

• Clear layer of cementum without cells; lying on top on top of granular layers of tomes.
•  Thinnest at neck of the root (20-50 microns).
•  Thickest at the apex (150-200 microns).
•  Sometimes ay extend into the inner wall of dentin.
•  2 kinds of structural composition:

 1. Fibers (collagen and sharpey's fibers).

 2. Calcified ground substance.

 Cellular Cementum

 (Secondary Cementum) 

* Layer of cementum with cells.

* Always thickest at the apex.

* Structural components:

1.Cementocytes (contained in lacuna and canaliculi).

2.Intercellular ground substance (made of collagen fibrils and calcified ground substance).

3. Lacuna and canaliculi (dark because of the air).

Histological Elements of Cementum:

 1. Cementum Matrix - Consists of collagen fibrils from the dental sac used in the formation of the matrix, and cernenting ground substance.

** Lines of Salter - are incremental lines to mark the layers.

2. Sharpey's fibers - are fibers of periodontal ligament embedded in the matrix of cementum.

3. Cernentocytes (cementum corpuscles) - are cementoblasts embedded in the cementum matrix. 

4. Lacunae - the spaces within the matrix which house the cell bodies of the cementocytes. 

5. Canaliculi - elongated tiny spaces housing the processes.

Comparison of Cementum and Bone

Histologically:

* Both consist of fibrous intercellular substance from matrix with lacunae and canaliculi.

* Lacunae in bone contains osteocytes and have uniform shapes and sizes.

* The canaliculi radiate equally from the cell body.

* In cementum, the lacunae contain cementocytes and have variable form arnd size. 

* The canaliculi containing the processes of the cementocytes are sometimes directed mostly towards the periodontal ligament.

Physiologically:

* There is continuous deposition of cementum but little resorption and usually if resorption occurs, it is usually pathological and shallow. 

* If resorption takes place in cementum the method of cementoclasia is the same as that of osteoclasia. 

* In bone, continuous deposition and resorption are normal or physiological activities. 

* The difference in the resistance of bone and cementum to pressure could be due to the fact that the bone is richly vascularized tissue and cementum is avascular tissue.