Classification of Cementum

1. Embryologically

Primary and secondary

2. According to cellular component

Acellular: Thin, Amorphous, First layer to seal the dentin tubules

Cellular: Thick, Better structure, Apical surface

Layers of cellular and acellular cementum alternate (randomly)

3. Based on the origin of the collagenous matrix
Extrinsic
Intrinsic
Mixed

4. Combined classification
a. Primary acellular intinsic fiber cementum
b. Primary acellualar extrinsic fiber cementum
c. Secondary cellular intrinsic fiber cementum
d. Secondary cellular mixed fiber cementum
e. Acellular afibrillar cementum

5. Depending on the location and patterning
Intermediate and mixed stratified cementum

Participating Cells

Cementoblasts

Active
Cells are round, plump with basophilic cytoplasm (rough endoplasmic reticulum)
Inactive
Cells have little cytoplasm
Cementocytes

1. Cementocyte lacuna
2. cementocyte canaliculus

Cells have fewer organelles compared to cementoblasts. They are found in lacunae and have numerous processes toward the periodontal ligament. Eventually they die due to avascularity

Cementicles

a) free
b) attached
c) embedded

Gingiva

The connection between the gingiva and the tooth is called the dentogingival junction. This junction has three epithelial types: gingival, sulcular, and junctional epithelium. These three types form from a mass of epithelial cells known as the epithelial cuff between the tooth and the mouth.

Much about gingival formation is not fully understood, but it is known that hemidesmosomes form between the gingival epithelium and the tooth and are responsible for the primary epithelial attachment. Hemidesmosomes provide anchorage between cells through small filament-like structures provided by the remnants of ameloblasts. Once this occurs, junctional epithelium forms from reduced enamel epithelium, one of the products of the enamel organ, and divides rapidly. This results in the perpetually increasing size of the junctional epithelial layer and the isolation of the remenants of ameloblasts from any source of nutrition. As the ameloblasts degenerate, a gingival sulcus is created.

PULP

Coronal

Occupies and resembles the crown,

Contains the pulp horns

It decreases in size with age

Radicular

Occupies roots

Contains the apical foramen

It decreases in size with age

Accessory apical canals

PULP FUNCTIONS

Inductive: The pulp anlage initiates tooth formation and probably induces the dental organ to become a particular type of tooth.

Formative: Pulp odontoblasts develop the organic matrix and function in its calcification.

Nutritive: Nourishment of dentin through the odontoblasts.

Protective: Sensory nerves in the tooth respond almost always with PAIN to all stimuli (heat, cold, pressure, operative procedures, chamical agents).

Defensive or reparative: It responds to irritation by producing reparative dentin. The response to stimuli is inflammation.

 Histologically the pulp consists of delicate collagen fibers, blood vessels, lymphatics, nerves and cells. A histologic section of the pulp reveals four cellular zones:

Odontoblastic

Cell-free (Weil)

Cell-rich

Pulp core

HISTOLOGY OF THE ODONTOBLAST

Formation of Dentin

Mantle dentin: First formed dentin
Type I collagen with ground substance
Formation of the odontoblast process

Matrix vesicles
Appearance of hydroxyapatite crystals
 

Predentin
Primary physiologic (circumpulpal) dentin
All organic matrix is formed from odontoblasts
Smaller collagen fibers
Presence of phosphophoryn

Mineralization
Globular calcification
Interglobular dentin: Areas of incomplete calcification
Incremental lines of von Ebner: Daily, 4mm of organic matrix is deposited. Also every 5 days the arrangement of collagen fibers changes. This creates the incremental lines of von Ebner.
Intratubular dentin

Dentin tubules
S-shaped in the coronal aspect, straight in root dentin

Von Korff fibers
They are an artifact

The very first histological evidence of tooth development appear during the second month of intrauterine life. Calcification of deciduous incisors begins at 3-4 months in utero.

MANDIBULAR FIRST MOLAR

It is the first permanent tooth to erupt.

Facial Surface:- The lower first permanent molar has the widest mesiodistal diameter of all of the molar teeth. Three cusps cusps separated by developmental grooves make on the occlusal outline The mesiobuccal cusp is usually the widest of the cusps. The mesiobuccal cusp is generally considered the largest of the five cusps. The distal root is usually less curved than the mesial root.

Lingual: Three cusps make up the occlusal profile in this view: the mesiolingual, the distolingual, and the distal cusp which is somewhat lower in profile. The mesiobuccal cusp is usually the widest and highest of the three. A short lingual developmental groove separates the two lingual cusps

Proximal: The distinctive height of curvature seen in the cervical third of the buccal surface is called the cervical ridge. The mesial surface may be flat or concave in its cervical third . It is highly convex in its middle and occlusal thirds. The occlusal profile is marked by the mesiobuccal cusp, mesiolingual cusp, and the mesial marginal ridge that connects them. The mesial root is the broadest buccolingually of any of the lower molar roots. The distal surface of the crown is narrower buccolingually than the mesial surface. Three cusps are seen from the distal aspect: the distobuccal cusp, the distal cusp, and the distolingual cusp.

Occlusal There are five cusps. Of them, the mesiobuccal cusp is the largest, the distal cusp is the smallest. The two buccal grooves and the single lingual groove form the "Y" patern distinctive for this tooth

Roots :-The tooth has two roots, a mesial and a distal.

Contact Points; The mesial contact is centered buccolingually just below the marginal ridge. The distal contact is centered over the distal root, but is buccal to the center point of the distal marginal ridge.

Roots: Lower molars have mesial and distal roots. In the first, molar, the mesial root is the largest. It has a distal curvature. The distal root has little curvature and projects distally.