Cap stage

The first signs of an arrangement of cells in the tooth bud occur in the cap stage. A small group of ectomesenchymal cells stops producing extracellular substances, which results in an aggregation of these cells called the dental papilla. At this point, the tooth bud grows around the ectomesenchymal aggregation, taking on the appearance of a cap, and becomes the enamel (or dental) organ. A condensation of ectomesenchymal cells called the dental follicle surrounds the enamel organ and limits the dental papilla. Eventually, the enamel organ will produce enamel, the dental papilla will produce dentin and pulp, and the dental follicle will produce all the supporting structures of a tooth

AGE CHANGES

Progressive apical migration of the dentogingival junction.
Toothbrush abrasion of the area can expose dentin that can cause root caries and tooth mobility.

Histology of the alveolar bone

Near the end of the 2nd month of fetal life, mandible and maxilla form a groove that is opened toward the surface of the oral cavity.
As tooth germs start to develop, bony septa form gradually. The alveolar process starts developing strictly during tooth eruption.

The alveolar process is the bone that contains the sockets (alveoli) for the teeth and consists of

a) outer cortical plates
b) a central spongiosa and
c) bone lining the alveolus (bundle bone)

The alveolar crest is found 1.5-2.0 mm below the level of the CEJ.
If you draw a line connecting the CE junctions of adjacent teeth, this line should be parallel to the alveolar crest. If the line is not parallel, then there is high probability of periodontal disease.

Bundle Bone

The bundle bone provides attachment to the periodontal ligament fibers. It is perforated by many foramina that transmit nerves and vessels (cribiform plate). Embedded within the bone are the extrinsic fiber bundles of the PDL mineralized only at the periphery. Radiographically, the bundle bone is the lamina dura. The lining of the alveolus is fairly smooth in the young but rougher in the adults.

Clinical considerations

Resorption and regeneration of alveolar bone
This process can occur during orthodontic movement of teeth. Bone is resorbed on the side of pressure and opposed on the site of tension.

Osteoporosis
Osteoporosis of the alveolar process can be caused by inactivity of tooth that does not have an antagonist

Amelogenesis and Enamel

Enamel is highly mineralized: 85% hydroxyapatite crystals
Enamel formation is a two-step process
The first step produces partially mineralized enamel: 30% (secretory)
The second step: Influx of minerals, removal of water and organic matrix (maturative)
Again, dentin is the prerequisite of enamel formation (reciprocal induction)
Stratum intermedium: high alkaline phosphatase activity
Differentiation of ameloblasts: Increase in glycogen contents

Formation of the enamel matrix
Enamel proteins, enzymes, metalloproteinases, phosphatases, etc.
Enamel proteins: amelogenins (90%), enamelin, tuftelin, and amelin
Amelogenins: bulk of organic matrix
Tuftelin: secreted at the early stages of amelogenesis (area of the DE junction)
Enamelin: binds to mineral
Amelin

Mineralization of enamel
 No matrix vesicles
Immediate formation of crystallites
Intermingling of enamel crystallites with dentin
"Soft" enamel is formed

Histologic changes

Differentiation of inner enamel epithelium cells. They become ameloblasts
Tomes' processes: saw-toothed appearance
Collapse of dental organ
Formation of the reduced enamel epithelium

Hard tissue formation (Amelogenesis )

Enamel formation is called amelogenesis and occurs in the crown stage of tooth development. "Reciprocal induction" governs the relationship between the formation of dentin and enamel; dentin formation must always occur before enamel formation. Generally, enamel formation occurs in two stages: the secretory and maturation stages. Proteins and an organic matrix form a partially mineralized enamel in the secretory stage; the maturation stage completes enamel mineralization.

In the secretory stage, ameloblasts release enamel proteins that contribute to the enamel matrix, which is then partially mineralized by the enzyme alkaline phosphatase. The appearance of this mineralized tissue, which occurs usually around the third or fourth month of pregnancy, marks the first appearance of enamel in the body. Ameloblasts deposit enamel at the location of what become cusps of teeth alongside dentin. Enamel formation then continues outward, away from the center of the tooth.

In the maturation stage, the ameloblasts transport some of the substances used in enamel formation out of the enamel. Thus, the function of ameloblasts changes from enamel production, as occurs in the secretory stage, to transportation of substances. Most of the materials transported by ameloblasts in this stage are proteins used to complete mineralization. The important proteins involved are amelogenins, ameloblastins, enamelins, and tuftelins. By the end of this stage, the enamel has completed its mineralization.

Histology of the Periodontal Ligament (PDL)

Embryogenesis of the periodontal ligament
The PDL forms from the dental follicle shortly after root development begins
The periodontal ligament is characterized by connective tissue. The thinnest portion is at the middle third of the root. Its width decreases with age. It is a tissue with a high turnover rate.

FUNCTIONS OF PERIODONTIUM

Tooth support
Shock absorber
Sensory (vibrations appreciated in the middle ear/reflex jaw opening)

The following cells can be identified in the periodontal ligament:
a) Osteoblasts and osteoclasts b) Fibroblasts,  c) Epithelial cells
 

Rests of Malassez
d) Macrophages
e) Undifferentiated cells
f) Cementoblasts and cementoclasts (only in pathologic conditions)
The following types of fibers are found in the PDL
-Collagen fibers: groups of fibers
-Oxytalan fibers: variant of elastic fibers, perpendicular to teeth, adjacent to capillaries
-Eluanin: variant of elastic fibers
Ground substance

PERIODONTAL LIGAMENT FIBERS

Principal fibers
These fibers connect the cementum to the alveolar crest. These are:

a. Alveolar crest group: below CE junction, downward, outward
b. Horizontal group: apical to ACG, right angle
c. Oblique group: numerous, coronally to bone, oblique direction
d. Apical group: around the apex, base of socket
e. Interradicular group: multirooted teeth

Gingival ligament fibers
This group is not strictly related to periodontium. These fibers are:

a. Dentogingival: numerous, cervical cementum to f/a gingiva
b. Alveologingival: bone to f/a gingiva
c. Circular: around neck of teeth, free gingiva
d. Dentoperiosteal: cementum to alv. process or vestibule (muscle)
 e. Transseptal: cementum between adjacent teeth, over the alveolar crest
 

Blood supply of the PDL
The PDL gets its blood supply from perforating arteries (from the cribriform plate of the bundle bone). The small capillaries derive from the superior & inferior alveolar arteries. The blood supply is rich because the PDL has a very high turnover as a tissue. The posterior supply is more prominent than the anterior. The mandibular is more prominent than the maxillary.

Nerve supply
The nerve supply originates from the inferior or the superior alveolar nerves. The fibers enter from the apical region and lateral socket walls. The apical region contains more nerve endings (except Upper Incisors)

Dentogingival junction

This area contains the gingival sulcus. The normal depth of the sulcus is 0.5 to 3.0 mm (mean: 1.8 mm). Depth > 3.0 mm is considered pathologic. The sulcus contains the crevicular fluid
 

 
The dentogingival junction is surfaced by:
1) Gingival epithelium: stratified squamous keratinized epithelium 2) Sulcular epithelium: stratified squamous non-keratinized epithelium The lack of keratinization is probably due to inflammation and due to high turnover of this epithelium.
3) Junctional epithelium: flattened epithelial cells with widened intercellular spaces. In the epithelium one identifies neutrophils and monocytes.
Connective tissue
The connective tissue of the dentogingival junction contains inflammatory cells, especially polymorphonuclear neutrophils. These cells migrate to the sulcular and junctional epithelium.
The connective tissue that supports the sulcular epithelium is also structurally and functionally different than the connective tissue that supports the junctional epithelium.

Histology of the Col (=depression)

The col is found in the interdental gingiva. It is surfaced by epithelium that is identical to junctional epithelium. It is an important area because of the accumulation of bacteria, food debris and plaque that can cause periodontal disease.
Blood supply: periosteal vessels
Nerve supply: periodontal nerve fibers, infraorbital, palatine, lingual, mental, buccal

Introduction. The Jaws and Dental Arches

The teeth are arranged in upper and lower arches. Those of the upper are called maxillary; those of the lower are mandibular.

1. The maxilla is actually two bones forming the upper jaw; they are rigidly attached to the skull..
2. The mandible is a horseshoe shaped bone which articulates with the skull by way of the temporomandibular joint the TMJ.
3. The dental arches, the individual row of teeth forming a tooth row attached to their respective jaw bones have a distinctive shape known as a catenary arch.

Maxillary First Deciduous Molar.

-The notation is B or I.

-It looks a bit like an upper 1st premolar.

-There are three roots.

-It has a strong bulbous enamel bulge that protrudes buccally at the mesial.

-It is the smallest of the deciduous molars in crown height and in the mesiodistal dimension.