Teeth and supporting tissues. Teeth and supporting tissues. Development and structure of the Development and structure of the

teeth.teeth.

CATEDRA HISTOLOGIE, CITOLOGIE ŞI EMBRIOLOGIETATIANA GLOBA

UNIVERSITATEA DE STAT DE MEDICINĂ ŞI FARMACIE “NICOLAE TESTEMIŢANU”

CROWN CROWN ((enamel layer over dentin))

(anatomical & (anatomical & clinical)clinical)

NECK NECK ((acellular cementum +

dentin ))

ROOT (ROOT (cellular and acellular calcified cementum over

dentin))

TOOTH STRUCTURETOOTH STRUCTURE

Clinical CrownAnatomical Crown

Tissues of the teeth can be divided into 2 groups:

hard and soft tissues.

Hard tissues of the tooth:

• ENAMELENAMEL

• DENTINDENTIN

• CEMENTUMCEMENTUM

Soft tissue of the tooth:

• DENTAL PULP DENTAL PULP (crown pulp & root (crown pulp & root canal)canal)

EnamelEnamel

• is a cell free extracellular tissue.• is the translucent

outer layer of the tooth.• is the hardest

substance in the human body.

Consists of: - 96% inorganic salts- 4% organic

substances-glycoproteins enamelin.

EnamelEnamel

• Is an extracellular product of enamel organ cells.

• Is produced by the AMELOBLASTS.

• Consists of RODS or PRISMS (the morpho-functional unit of enamel).

DentinDentin

• forms the bulk of the tooth.• It supports enamel and

acts as the skeleton of the tooth.• It is the second hardest

tissue in the human body.

Consists of:- 72% inorganic salts (Ca

phosphate, Mg phosphate)- 28% organic substances

(collagen type I, proteoglycans and glycoproteins).

DentinDentin

• Is produced by the ODONTOBLASTS (these cells have cylindrical cell body and a long cytoplasmatic extension, the odontoblastic process).

• Dentin is a living tissue, it has the ability for constant growth and repair that reacts to physiologic (functional) and pathologic (disease) stimuli.

• The dentin is perforated by dentinal tubules. Each tubule is filled with an elongated cellular process of an odontoblast, and nerve endings.

CementumCementum

• is the third mineralized tissue of the tooth and is as hard as bone is, but has no Haversian systems.

• Covers the root of the tooth in a thin layer.

• Is avascular tissue.

Consists of:- 50% inorganic salts- 50 % organic substances

(collagen, proteoglycans).

CementumCementum

• Cells of the cementum are:– Cementocytes that are located in lacunae

– Cementoblasts that are located on the outer surface of the cementum, adjacent to the periodontal ligament

• Cementum is capable of formation, destruction and repair and remodels continually throughout life. It is nourished from vessels within the periodontal ligament.

• Functions:– It protects the dentin (occludes the dentinal tubules)

– It provides attachment of the periodontal fibers

– It reverses tooth resorption

• There are 2 types of cementum:I. Cellular – contains cementocytes and cementoblasts

II. Acelular – has no cells.

PulpPulp - consists of loose connective tissue, contains blood vessels & nerve fibers, cellular content: odontoblasts, fibroblasts, fibrocytes, macrophages, lymphocytes, mast cells, plasma cells & other.

Root canalRoot canal - canal in the root of the tooth where the nerves and blood vessels travel through.

Soft tissue of the tooth:

Nerves - relay signals such as pain to and from brain

Blood vessels - carry nutrients to the tooth.

Periodontal Ligament

• Provides for attachment, support, bone remodeling (during movement of a tooth), nutrition of adjacent structures, proprioreception and tooth eruption.

Bone - alveolar bone forms the tooth socket and provides it with support.

Tooth development begins from the 6th week of the intrauterine development

2 embryonic origins:

I. Ectoderm - oral epithelium - enamel

II. Ectomesenchyme (neural crests)– dentin, cement, dental pulp, periodontal ligament

FUNCTIONAL STAGES OF TOOTH DEVELOPMENT

• Initiation

• Proliferation

• Morpho-differentiation and Histo-differentiation

• Apposition

• Root development

MORPHOLOGICAL STAGES OF TOOTH DEVELOPMENT

• Bud stage

• Cap stage

• Bell stage (early & late)

• Early & late crown

• Early root formation

Correlation of morphological stages of

tooth development and functional features Morphological stage Main functional activity

Dental lamina Initiation of tooth germ

Bud stage Proliferation (cell division)

Cap stage Proliferation Beginning of histo-differentiation

Bell stage Prominent histo-differentiationMorpho-differentiation

Early crown stage Apposition (formation of dentin & enamel)

Late crown stage Continued apposition of dentin & enamel including enamel maturation

Early root stage Formation of radicular dentin & cementum

BUD stageBUD stage CAP stageCAP stage

BELL stageBELL stage LATE CROWN stageLATE CROWN stage

PRIMITIVE EPITHELIAL BANDPRIMITIVE EPITHELIAL BAND

Is subdivided into: 1. VESTIBULAR LAMINA

2. DENTAL LAMINA

1

2

Teeth are organs which develop primarily through inductive interactions between dental epithelium and surrounding ectomesenchyme.

Bud stage - oral epithelium proliferates and a plate of epithelium grows into the underlying ectomesenchyme and form the dental lamina. Shortly after appearance dental lamina increases its mitotic activity and form epithelial structures,called tooth buds.

DENTAL BUDDENTAL BUD

Dental budDental bud - is the future enamel

organ

Ectomesenchyme of this Ectomesenchyme of this region region – is the future

dental papilla

Ectomesenchyme of this regionEctomesenchyme of this region – is the future dental sac

Cap stageCap stage • During the cap stage, an unequal growth (mitotic

activity) of epithelial cells grows down to form a concavity around the mesenchyme. The tooth bud differentiates into a cap-shaped enamel organ extending from the dental lamina.

• Enamel organ is composed of 3 layers:– The convex OUTER ENAMEL EPITHELIUM– The concave INNER ENAMEL EPITHELIUM– STELLATE RETICULUM

• During the cap stage are formed the dental papilla & dental sac

ENAMEL ORGANENAMEL ORGAN

1

2

3Enamel organ consists of:1. Outer enamel epithelium2. Stellate reticulum3. Inner enamel epithelium

• DENTAL PAPILLA: is a concentration of ectomesenchyme, which is in part enveloped by the invaginated inner enamel epithelium. Mesenchymal cells within the dental papilla are responsible for formation of tooth pulp. The dental papilla contains cells that develop into ODONTOBLASTS, which are dentin-forming cells.

• DENTAL SACK: is a concentration of ectomesenchyme that encircles the enamel organ and the dental papilla. The dental sack gives rise to three important entities: cementoblasts, osteoblasts, and fibroblasts. Cementoblasts form the cementum of a tooth. Osteoblasts give rise to the alveolar bone around the roots of teeth. Fibroblasts develop the periodontal ligaments which connect teeth to the alveolar bone through cementum.

CAP stageCAP stage

7 – dental papilla

8 – dental sac

HISTO-DIFFERENTIATION & MORPHO-HISTO-DIFFERENTIATION & MORPHO-DIFFERNTIATIONDIFFERNTIATION. . BELL stageBELL stage

Bell stage • is known for the histodifferentiation and morphodifferentiation

that takes place.• The caracteristics of the stage:

– Cellular differentiation– Morphological specialization, both with alternative,

inductive and receptive role.• We recognized two different processes during this stage:

– Dentinogenesis (cells at the periphery of the dental papilla differentiate into odontoblasts and begin to elaborate predentin and dentin) – which precedes and follows what comes next, that is

– Amelogenesis (cells of the inner enamel epithelium differentiate into ameloblasts which begin to elaborate enamel)

• The dentin and enamel adjoin each other and the junction between them is called the dentino-enamel junction.

INNER ENAMEL EPITHELIUMINNER ENAMEL EPITHELIUM

ODONTOBLASTSPREAMELOBLASTSInitiate the differentiation

of

ENAMEL ORGAN (bell ENAMEL ORGAN (bell stage) stage)

Consists of 4 epithelia:

1. Outer enamel epithelium

2. Stellate epithelium

3. Stratum intermedium

4. Inner enamel epithelium

1.1.

2.2.

3.3.

4.4.

1.1. 3.3.

2.2.

4.4.

ENAMEL ORGAN ENAMEL ORGAN

LATE BELL stageLATE BELL stage

Is characterized of:

-Appearance of dentin

-Appearance of enamel

-Transformation of the dental papilla into DENTAL PULP

-Morphological changes appear in the dental sac

• Deposition of the dentin & enamel occurs by apposition with alternation of active & resting states

APPOSITION. LATE CROWN stageAPPOSITION. LATE CROWN stage

ENAMELENAMEL

DENTINDENTIN

PREDENTINPREDENTIN

Histogenesis of tooth tissues

ROOT FORMATION

• Begins after complete formation of the tooth crown & continues after the eruption.

• Key elements, that take part in the root formation, are:

1.1. Cervical loopCervical loop – that is transformed into EPITHELIAL ROOT SHEATH OFEPITHELIAL ROOT SHEATH OF HERTWIGHERTWIG , that differentiates into EPITHELIAL EPITHELIAL DIAPHRAGMDIAPHRAGM

2.2. Dental sacDental sac

CERVICAL LOOPCERVICAL LOOP

The layer of low columnar cells The layer of low columnar cells of the inner enamel epithelium of the inner enamel epithelium is continuous with the layer of is continuous with the layer of cuboidal cells that form the cuboidal cells that form the outer enamel epithelium at the outer enamel epithelium at the structure termed the structure termed the cervical cervical loop.loop.

Tooth eruption is defined as:

“ The movement of a tooth from its site of development within the alveolar process to its functional position in oral cavity,”

Stage of tooth eruption• Pre-eruptive

• Eruptive (intraosseous & extraosseous)

• Post-eruptive