Tissues of the teeth canbe divided into 2 groups: hard and soft tissues.Hard tissues of the tooth:• ENAMEL• DENTIN• CEMENTUMSoft tissue of the tooth:• DENTAL PULP(crown pulp & rootcanal)
Enamel• 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.
Enamel• Is an extracellular product of enamel organ cells.• Is produced by the AMELOBLASTS.• Consists of RODS or PRISMS (the morpho- functional unit of enamel).
Dentin• 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).
Dentin• 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.
Cementum• 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).
Cementum• 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.
Soft tissue of the tooth:Pulp - consists of looseconnective tissue,contains blood vessels &nerve fibers, cellularcontent: odontoblasts,fibroblasts, fibrocytes,macrophages,lymphocytes, mast cells,plasma cells & other.Root canal - canal inthe root of the toothwhere the nerves andblood vessels travelthrough.
Blood vessels -carry nutrients tothe tooth.Nerves - relaysignals such aspain to andfrom brain
Periodontal Ligament• Provides for attachment, support, bone remodeling (during movement of a tooth), nutrition of adjacent structures, proprioreception and tooth eruption.
Bone - alveolarbone forms thetooth socket andprovides it withsupport.
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
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
BUD stage CAP stage LATE CROWN stageBELL stage
Teeth are organs which develop primarily through inductiveinteractions between dental epithelium and surroundingectomesenchyme.Bud stage - oral epithelium proliferates and a plate of epitheliumgrows into the underlying ectomesenchyme and form the dentallamina. Shortly after appearance dental lamina increases itsmitotic activity and form epithelial structures,called tooth buds.
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• 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 ORGAN 1 2Enamel organ consists of: 31. 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.
HISTO-DIFFERENTIATION & MORPHO- DIFFERNTIATION. BELL 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 EPITHELIUMPREAMELOBLASTS ODONTOBLASTS Initiate the differentiation of
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 columnar cellsof the inner enamel epitheliumis continuous with the layer ofcuboidal cells that form theouter enamel epithelium at thestructure termed the cervicalloop.
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
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