Tissue of the teeth
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Tissue of the teeth. Dr Jamal Naim PhD in Orthodontics. Enamel. Introduction.

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Tissue of the teeth

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Tissue of the teeth

Tissue of the teeth

Dr Jamal Naim

PhD in Orthodontics

Enamel


Introduction

Introduction

The current-day clinical practice of the dentistry involves the prevention of enamel demineralization, the promotion of enamel remineralization, the restoration of cavitated enamel where demineralization has become irreversible, and the diagnosis and treatment of developmental enamel malformations, which can be caused by environmental or genetic factors.


Introduction1

Introduction

On a daily basis, dental health providers make diagnostic and treatment decisions that are influenced by their understanding of tooth formation.

A systemic condition during tooth development, such as high fever, can produce a pattern of enamel defects in the dentition.

Knowing the timing of tooth development permits estimates about the timing of the disturbance.


Introduction2

Introduction

The process of enamel maturation continues following tooth eruption, so that erupted teeth can become less susceptible to decay over time.

Mutations in the genes encoding enamel proteins lead to amelogenesis imperfecta, a collection of inherited diseases having enamel malformations as the predominant phenotype.


Enamel compositions

Enamel compositions

Tooth enamel is unique among mineralized tissues because of its high mineral content.

Enamel is made up of highly organized, tightly packed crystallites that comprise 87% percent of its volume and 95-96% of its weight.


Enamel compositions1

Enamel compositions

The inorganic Material (mineral structure):

  • is calcium hydroxyapatite [Ca10(PO4)6(OH)2]

  • contains impurities, such as carbonate substituting for phosphate in the crystals.

    Calcium hydroxyapatite can be synthesized from chemicals in the lab, but the shape, size, and organization of the crystals are always radically different from those of dental enamel.


Enamel compositions2

Enamel compositions

The organic materials are enamel proteins such as amelogenin (90%), ameloblastin and enamelin, (both 10%).

The organic materials forms an organic network that transport minerals during the Enamel formation (amelogenesis) and determine the nature and direction of crystal growth.


Review of tooth development

Review of tooth development


Tissue of the teeth

Cross section (A)

Neural crest cells


Tissue of the teeth

Ectoderm

Mesoderm

Basement membrane

Basal cell layer


Tissue of the teeth

Primary epithelial Band


Tissue of the teeth

Basement membrane

ECTODERM

MESODERM

ectomesenchymal cells


Tissue of the teeth

Bud stage


Tissue of the teeth

Bud stage

Future dental papilla


Tissue of the teeth

cap stage

Future dental papilla


Tissue of the teeth

Late Bell stage


Life history of ameloblasts

Life History of ameloblasts

It begins at the early Bell stage with:

  • Morphogenic Stage

  • Organizing stage

  • Formation stage (crystal lengthening)

  • Maturation stage (crystal thickening)

  • Protective stage

  • Desmolytic stage

  • Degenerative Stage


Life history of ameloblasts1

Life History of ameloblasts

P

Bud stage

Cup stage

Bell stage

P

P

Bell stage

Bell stage

Root formation


Life history of ameloblasts2

Life History of ameloblasts

  • Morphogenic Stage:

    During embryonic development, cells covering the cranial neural crest (CNC) invade the underlying connective tissue and migrate into the maxillary and mandibular prominences.

    These migratory cells share characteristics of epithelial and connective tissues and are commonly referred to as “ectomesenchyme” .


Life history of ameloblasts3

Life History of ameloblasts

Interactions between ectomesenchyme and the cells of the inner dental epithelium ultimately lead to the formation of two opposing sheets of columnar cells: ameloblasts and odontoblasts.

Dentin forms on the side of the odontoblasts, and enamel forms on the side of the ameloblasts.

The histology of tooth formation is classically divided into bud, cap, and bell stages.


Life history of ameloblasts4

Life History of ameloblasts


Tissue of the teeth

Morphogenic stage

Preameloblast

Basement membrane

Basement membrane


Life history of ameloblasts5

Life History of ameloblasts

2. Organizing stage:

  • Organizing of the preameloblasts in one cell layer

  • Changing of the cytomorphology

    • Migration of nucleus, centrions and Golgi regions from distal to proximal ends.

      This Stage begins directly after the initiation of dentin formation.


Tissue of the teeth

Morphogenic stage & Organizing stage

Basement membrane


Life history of ameloblasts6

Life History of ameloblasts

Secretory ameloblasts are tall, columnar cells with a proximally polarized nucleus and proximal and distal cell-cell junctions.

Their length is about 40-50 micrometer and their thickness is about 5 micrometer.


Life history of ameloblasts7

Life History of ameloblasts

3. Formation (secretory) stage:

prior to the onset of biomineralization, preameloblasts secrete enamel proteins on top of the predentin matrix.

Some of the enamel proteins penetrate the predentin and are absorbed by odontoblasts.


Life history of ameloblasts8

Life History of ameloblasts

Immediately following the initial secretion of enamel proteins, the basement membrane disappears, and ameloblast cell processes extend into irregularities on the predentin surface.


Tissue of the teeth

Formation stage

reciprocal induction


Life history of ameloblasts9

Life History of ameloblasts

Enamel crystallites are initiated within these irregularities, in close proximity to both the ameloblast cell membrane and collagen fibers protruding from the predentin.

The ameloblastic processes appear to retreat back to the cell body, extending the incipient enamel crystallites as they go.


Life history of ameloblasts10

Life History of ameloblasts

This fills in the irregular (villus) surface of dentin with enamel crystallites and converts it into the smooth, undulating surface of aprismatic enamel, which is perforated by odontoblastic processes.


Life history of ameloblasts11

Life History of ameloblasts


Life history of ameloblasts12

Life History of ameloblasts

Dentin and enamel are intimately linked at the dentino-enamel junction.

The collagen-based organic matrix gives dentin its tensile strength and flexibility, and allows it to cushion the more brittle enamel covering.


Life history of ameloblasts13

Life History of ameloblasts

After depositing the aprismatic enamel layer, secretory ameloblasts develop a specialized, cone-shaped Tomes’ process at their secretory (distal) ends.

TP


Life history of ameloblasts14

Life History of ameloblasts

Enamel Formation During the Secretory Stage:

  • Crystal Elongation

    Mineral deposition occurs primarily at a mineralization front very near to the ameloblast cell membrane.

    Enamel crystallites extend in length at extracellular growth sites a short distance away from the secretory faces of the ameloblast cell membrane.


Life history of ameloblasts15

Life History of ameloblasts

During the secretory stage, enamel crystals do not grow continuously, but rather extend in increments (4 micron).

Each increment represents the amount of crystal elongation that occurs in a single day, and is manifested structurally as prism cross-striations.


Life history of ameloblasts16

Life History of ameloblasts

4. Maturation stage:

The ameloblasts become attached to the enamel matrix and exhibit microvilli at their distal ends.

This alterations indicates the absorptive function of ameloblasts.

In this stage the organic materials of enamel are being removed.


Life history of ameloblasts17

Life History of ameloblasts

Ameloblast in the maturative stage


Life history of ameloblasts18

Life History of ameloblasts

A significant feature of the maturation stage is that the pH of the fluid surrounding enamel crystals oscillates from less than 6 to 7.2. These pH fluctuations are similar to those the tooth will experience naturally, following its eruption into the oral cavity.


Life history of ameloblasts19

Life History of ameloblasts

The developing enamel crystals are not structurally homogeneous. Crystals that are more susceptible to acid dissolution (i.e., those with high carbonate content) are selectively removed during the low pH part of the cycle.

Therefore, during the maturation stage, an evolutionary process occurs in which relatively acid labile mineral is replaced by more acid- resistant apatite.


Life history of ameloblasts20

Life History of ameloblasts

If the crown of a tooth become exposed to the oral cavity prematurely, such a tooth would be expected to decay rapidly due to the incomplete state of enamel maturation.

This happens, when an unerupted third molar is transplanted into the socket of an extracted second molar. It should be treated with fluoride and sealant as soon as possible after the transplantation procedure.


Life history of ameloblasts21

Life History of ameloblasts

At the end of the maturation stage, about 90 percent of the enamel volume is mineral, which contains less than 1 percent residual protein.


Life history of ameloblasts22

Life History of ameloblasts

5. Protective stage:

After accomplishing of amelogenesis, the ameloblasts secrete or leave structure less material on enamel surface, known as primary enamel cuticle.

The dental organ epithelium becomes reduced in thickness (reduced enamel epithelium) and functions as a protection against contact with connective tissue to inhibit cementum deposition or enamel resorption.


Life history of ameloblasts23

Life History of ameloblasts

In this stage the composition of Enamel can be modified.


Life history of ameloblasts24

Life History of ameloblasts

6. Desmolytic stage:

The reduced enamel epithelium seems to induce atrophy of the mesoderm which separate it from the oral epithelium. It leads to eruption.


Life history of ameloblasts25

Life History of ameloblasts

7. Degenerative Stage:

As the tooth erupts in the mouth cavity, reduced enamel epithelium and oral epithelium fuse together.

The new epithelium is called primary attachment epithelium. This degenerates and becomes replaced by oral epithelial cells forming the secondary attachment epithelium.


Life history of ameloblasts26

Life History of ameloblasts


Life history of ameloblasts27

Life History of ameloblasts


Life history of ameloblasts28

Life History of ameloblasts

  • Morphogenic

  • Organizing

  • Formative

  • maturative

  • Protective

  • desmolytic

Dealing with the dental epithelium

Functions of differentiated ameloblasts

Functions of reduced enamel epithelium


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