Hard tissues of the tooth:• ENAMEL• DENTIN• CEMENTUMSoft tissue of the tooth:•DENTAL PULP(crown pulp & rootcanal)
Tooth development begins from the 6th week of the intrauterine development2 embryonic origins:I. Ectoderm - oral epithelium - enamelII. Ectomesenchyme (neural crests)– dentin, cement, dental pulp, periodontal ligament
2 main processes in the tooth development• Crown formation• Root formation (is usually completed approximately 2 -3 years after the tooth erupts)
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 activityDental lamina Initiation of tooth germBud stage Proliferation (cell division)Cap stage Proliferation Beginning of histo-differentiationBell stage Prominent histo-differentiation Morpho-differentiationEarly crown stage Apposition (formation of dentin & enamel)Late crown stage Continued apposition of dentin & enamel including enamel maturationEarly root stage Formation of radicular dentin & cementum
Tooth development• The first recognizable sign of tooth development in humans occurs during the 5-6th week of intrauterine life.• At this time is characteristic the appearance of vestibular & dental laminae as a result of proliferation of oral epithelium.
VESTIBULAR LAMINA• It is an ectodermal epithelial extension from the lining of the oral cavity that proliferates into the underlying ectomesenchyme of the maxilla and the mandible lateral to the dental lamina. The central cells of this lamina disintegrate to form the sulcus which is the space between the maxilla and the mandible on one side and the lips and the cheeks on the other side.
DENTAL LAMINA• it is derived from the ectodermal epithelial lining of the oral cavity. These epithelial cells form a sheet-like structure that extends into specific areas of the ectomesenchymal tissues within the alveolar processes of the maxilla and mandible. These areas are parts of the developing dental arch regions where teeth form and eventually erupt.
THE INITIATION. BUD STAGE•Epithelial cells are inductors in the tooth development•Epithelial cells produce growth factors (TGFß1, BMP2, IGF),that transmit the role of inductor through the basementmembrane to ectomesenchyme
•The progressive proliferation of the dental lamina into theectomesenchyme results in the formation of a DENTAL BUDat the distal end of the dental lamina.
DENTAL BUD Dental bud - is the future enamel organ Ectomesenchyme of this region – is the future dental papillaEctomesenchyme of this region – is the future dental sac
Cap stage• The dental bud differentiates into a cap-shaped enamel organ.• The epithelial dental organ looks like a head cap with a round convex side and a straight or slightly concave one.• During the cap stage are formed the dental papilla & dental sac.
PROLIFERATION. CAP stage - enamel organ - dental papilla - dental sacare differentiated at this stage
ENAMEL ORGAN 1 2Enamel organ consists of: 31. Outer enamel epithelium2. Stellate reticulum3. Inner enamel epithelium
ENAMEL KNOT• appears as a densely packed accumulation of cells projecting from the inner enamel epithelium into the dental papilla.
Dental papilla & dental sac• The concentration of ectomesenchyme, which is in part enveloped by the invaginated inner enamel epithelium, is named the dental papilla.• The dental sac is a concentration of ectomesenchyme that encircles the enamel organ and the dental papilla.
Outer enamel epithelium, intermedium epithelium & stellateepithelium become thinner and together form STRATIFIEDEPITHELIUM
REDUCED ENAMEL EPITHELIUM• Takes part in the crown modeling• Induces the dentinogenesis of the crown & root• Assists in enamel formation & in the formation of dentin-gum connection• Isolates the enamel from the connective tissue of the dental sac• Takes part in the tooth eruption
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. Cervical loop – that is transformed into EPITHELIAL ROOT SHEATH OF HERTWIG , that differentiates into EPITHELIAL DIAPHRAGM2. Dental sac
CERVICAL LOOPThe layer of low columnarcells of the inner enamelepithelium is continuous withthe layer of cuboidal cells thatform the outer enamelepithelium at the structuretermed the cervical loop.
ROOT FORMATION• After complete formation of the crown of the tooth, the root begins to form. An extension of the enamel organ, called the epithelial root sheath of Hertwig, continues to grow apically. The epithelial root sheath induces the differentiation of odontoblasts which form root dentin. The apical most portion of the root sheath turns inward toward the radicular pulp cavity (that portion of the pulp cavity inside the root) and is called the epithelial diaphragm.
EPITHELIAL ROOT SHEATH OF HERTWIG & EPITHELIAL DIAPHRAGM EPITHELIAL ROOT SHEATH OF HERTWIG EPITHELIAL DIAPHRAGM
• Hertwigs root sheath determines the number, size and shape of roots and is presumably the inductor of dentin formation in the developing root.
THE EPITHELIAL ROOT SHEATH OF HERTWIG• The epithelial root sheath is made up of inner and outer enamel epithelial layers without the other two interposing layers. Following the induction of odontoblast and dentin formation, the epithelial root sheath disintegrates forming epithelial rests, small groups of epithelial cells that can remain around the root.
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,”