Tooth Development (Odontogenesis) PDF

Tooth Development (Odontogenesis) Prepared by: Dr.Abdelatif Galal Introduction The development of the tooth and it’s supporting structures is involves many complex biological processes: 1-Epithelial mesenchymal interaction. 2-Morphogenesis. 3-calcification (mineralization). D...

Tooth Development (Odontogenesis) Prepared by: Dr.Abdelatif Galal Introduction The development of the tooth and it’s supporting structures is involves many complex biological processes: 1-Epithelial mesenchymal interaction. 2-Morphogenesis. 3-calcification (mineralization). Dentition: is a process of teeth eruption occurs in different stages of human’s life : Primary dentition – develops during embryonic and fatal periods of prenatal developments – 20 teeth ( lateral dental lamina). Permanent dentition – develops as the jaw grows and matures – 32 teeth (successor D.L). Mixed dentition period - between the primary and permanent periods during which an individual has some teeth from both – during the preteen years (Distal extension of D.L). Teeth are derived:  Ectoderm (Dental or enamel organ)  Mesoderm (Dental papilla)  Mesoderm (Dental Sac) Dental organ Enamel Dental papilla Pulp Dentin Dental sac Cementum Periodontal membrane  Basement membrane ECTODERM MESODERM ectomesenchymal cells Tooth development can be divided into three phases, which are : 1- Initiation : during this phase , the sites of the future teeth are established with the appearance of tooth germs called dental lamina. 2- Morphogenesis : During this phase , the shape of the teeth are determined by a combination of cell proliferation and cell movement. 3- Histogenesis : During this phase , differentiation of the cell (began during morphogenesis) proceed to give rise to the fully formed dental tissues, both mineralized (such as enamel , dentin , and cementum ) and unmeneralized ( such as pulp and periodontal ligaments). STAGES of TOOTH DEVELOPMENT – initiation stage – 6 th to 7 th week bud stage – 8 th week cap stage – 9 th to 10th weeks bell stage – 11th to 12th weeks apposition stage – varies per tooth maturation stage – varies per tooth Tooth formation:. Initial stages – The interaction between the oral epithelium and the underlying mesenchymal cells results in tooth development. The first sign of tooth development begins when the embryo is about 6 th weeks; a continuous band of thickened epithelium forms around the stomodeum( primitive oral cavity) this gives rise to the primary epithelial band Tooth formation -initial stage-  Primary epithelial bands: Horseshoe-shaped bands that appear approximately around the 37th day of development, one for each jaw.  There are two subdivisions: vestibular lamina and dental lamina By 7th week the primary band divides into two processes a buccally located vestibular lamina and a lingual one the dental lamina.  Primary epithelium band: will gives rise to:- 1-Vestibular lamina :(an outer or buccal band of epithelial thickening). Also termed the lip furrow band. it subsequently hollows and forms the oral vestibule between the lips and cheeks from one side and the dental arch from other side. 2-Dental lamina: It is an inner band of epithelium , the dental lamina develops in the future spot for the dental arches  Dental lamina appears as a thickening of the oral epithelium adjacent to condensation of ectomesenchyme. 20 areas of enlargement or knobs appear, which will form tooth buds for the 20 primary teeth. by the eighth week the dental lamina appears as an arch shaped band of epithelial tissue carrying a series of swellings. Not all will appear at the same time. The first to develop are those of the anterior mandibular region The dental lamina begins to function at 6 th prenatal week and continues to 15th year of birth (3 rd molar) Function of dental lamina 1.Forming buds of the 20 primary teeth 2.Form the buds of permanent dentition lingual to the buds of the primary teeth Vestibular lamina  the vestibular lamina cells rapidly enlarge and then degenerate – forms a cleft that becomes the vestibule of the oral cavity. STAGES of TOOTH DEVELOPMENT  initiation stage – 6 th to 7 th week  bud stage – 8 th week  cap stage – 9 th to 10th weeks  bell stage – 11th to 12th weeks  apposition stage – varies per tooth  maturation stage – varies per tooth Morphogenesis:  bud stage  cap stage  bell stage Bud stage  Marked by the incursion of epithelium into the mesenchyme  The enamel organ in the bud stage appears as a simple, spherical to ovoid. Tongue Bud stage Future dental papilla Bud stage  This developing tooth forms from both the ectoderm and mesenchyme and from neural crest cells that have migrated into the mesenchyme. The epithelial component is separated from the adjacent mesenchyme by a basement membrane. STAGES of TOOTH DEVELOPMENT  initiation stage – 6 th to 7 th week  bud stage – 8 th week  cap stage – 9 th to 10th weeks  bell stage – 11th to 12th weeks  apposition stage – varies per tooth  maturation stage – varies per tooth  Cap stage  characterized by continuation of the in growth of the oral epithelium into the mesenchyme.  tooth bud of the dental lamina proliferates unequally in different parts of the bud ◼ forms a cap shaped tissue ◼ looks like a cap sitting on a ball of condensing mesenchyme  Cap stage  By the 11th week, morphogenesis has progressed, the deeper surface of the enamel organ invaginating to form a cap-shaped structure. Enamel organ are arranged to form the:  Outer enamel epithelia (cuboidal cell)  inner enamel epithelia(columnar cell).  Stellate reticulum(cell contain glycosaminoglycans). Cap stage  a depression forms in the deepest part of each tooth bud and forms the cap or enamel organ (or dental organ) – produces the future enamel (ectodermal origin) the adjacent mesenchymal cells continue to proliferate and surround the enamel organ. The part of the mesenchyme lying beneath the internal enamel epithelium is termed the dental papilla. while that surrounding the tooth germ forms the dental follicle(dental sac). Cap stage  below this cap is a condensing mass of mesenchyme – dental papilla (mesenchymal origin ) produces the future dentin and pulp tissue Cap stage  the basement membrane separating the dental organ and the dental papilla becomes the future site for the dentino-enamel junction (DEJ) Cap stage  Remaining mesenchyme surrounds the dental/enamel organ and condenses to form the dental sac or the dental follicle  Cap Stage of Tooth Development Dental (enamel) organ Dental papilla dental follicle ©Copyright 2007, Thomas G. Hollinger, Gainesville, Fl Oral Histology, 5th edition, A R Ten Cate Cap stage  Enamel knots are clusters of nondividing epithelial cells visible in sections of molar cap stage tooth germs.  They play an important role by the cuspal morphogenesis. STAGES of TOOTH DEVELOPMENT  initiation stage – 6 th to 7 th week  bud stage – 8 th week  cap stage – 9 th to 10th weeks  bell stage – 11th to 12th weeks  apposition stage – varies per tooth  maturation stage – varies per tooth Bell stage  Continuation of histodifferentiation and morphodifferentiation  cap shape then assumes a more bell-like shape  differentiation produces four types of cells within the enamel/dental organ 1. inner enamel epithelium 2. outer enamel epithelium 3. stellate reticulum 4. stratum intermedium Oral cavity Outer dental epithelium Dental lamina Enamel knot Stellate reticulum Stratum intermedium Inner dental Epithelium Dental papilla Differentiation of the Enamel organ  outer enamel (dental) epithelium (OEE):  cuboidal shape  protective barrier during enamel production  very little cytoplasm  cells are separated from the dental follicle by a basement membrane Differentiation of the Enamel organ  inner enamel (dental) epithelium (IEE)  short, columnar cells  differentiates into the enamel secreting cells = ameloblasts  separated from the dental papilla below it by a basement membrane also  cells accumulate large amounts of glycogen Differentiation of the Enamel organ  stellate reticulum  star-shaped cells in many layers  center of the enamel organ  forms a network = reticulum  supports production of enamel Differentiation of the Enamel organ  stratum intermedium  inner layer of compressed flat to cuboidal cells  very high levels of the enzyme alkaline phosphatase  supports production of enamel Dental Papilla in early bell stage : before the IEE completes its folding to differentiate into ameloblast to produce enamel.  the dental papilla undergoes differentiation and produces two types of cells 1. outer cells of the DP – forms the dentin-secreting cells (odontoblasts) 2. central cells of the DP – forms the primordium of the pulp Dental sac in early bell stage: Before formation of the dental hard tissue begins , the dental sac shows a circular arrangement of its fibers and it resemble a capsular structure. With the development of the root , the fibers of D. S. differentiate into periodontal fibers that become embedded in the cementum and alveolar bone. STAGES of TOOTH DEVELOPMENT  initiation stage – 6 th to 7 th week  bud stage – 8 th week  cap stage – 9 th to 10th weeks  bell stage – 11th to 12th weeks  apposition stage – varies per tooth  maturation stage – varies per tooth B -Late or advanced bell stage(apposition and maturation stage) The late bell stage represents the final stage of odontogenesis, and it is characterized by apposition and maturation of dental tissues. Apposition means formation and secretion of the dental tissues; enamel, dentin, and cementum in successive layers. The basal margin of the E. organ (cervical loop ) gives rise to the epithelial root sheath which Initiate formation of dentin in root. Dental sac cells will differentiate into cementoblast to form cementum. Maturation stage is reached when the dental tissues are fully mineralized. Fate of dental lamina 1- dental lamina is functional in developing 52 teeth from 6 prenatal weeks until 4 years after birth (development of third permanent tooth). 2- The dental lamina degenerates by mesenchymal invasions in late bell stage. 3- Developing tooth lose its connection with dental lamina 4- some times remnants of dental lamina remains in the jaws as epithelial rests of serres ( serres’ pearls). Nutrition and tooth development Nutrition has an effect on the developing tooth. Essential nutrients for a healthy tooth include calcium, phosphorus, and vitamins A, C, and D. Calcium and 6 phosphorus are needed to properly form the hydroxyapatite crystals(minerals), and their levels in the blood are maintained by Vitamin D. Vitamin A is necessary for the formation of keratin, and Vitamin C is for collagen. Fluoride is incorporated into the hydroxyapatite crystal of a developing tooth and makes it more resistant to demineralization and subsequent decay. Deficiencies of these nutrients In situations where calcium, phosphorus, and vitamin D are deficient, the hard structures of a tooth may be less mineralized. A lack of vitamin A can cause a reduction in the amount of enamel formation. Fluoride deficiency causes increased demineralization when the tooth is exposed to an acidic environment, and also delays remineralization. Furthermore, an excess of fluoride while a tooth is in development can lead to a condition known as fluorosis Developmental disturbances of teeth: 1-Anodontia: is a complete lack of tooth development. Anodontia is very rare, most often occurring in a hereditary condition called ectodermal dysplasia. 2-Hypodontia (congenital missing tooth or teeth): It is one of the most common developmental abnormalities. The absence of third molars is very common, followed in prevalence by the second premolar and lateral incisor. 3-Hyperdontia(supernumerary teeth): It is believed to be associated with the remanent of dental lamina or epithelial rest of Serres. 4-Dilaceration: is an abnormal bend found on a tooth, and is nearly always associated with trauma that moves the developing tooth bud. 5-Regional odontodysplasia is rare, but is most likely to occur in the maxillary anterior teeth. The enamel, dentin, and pulp of teeth are affected, so the teeth are very brittle. On radiographs the teeth appear more radiolucent than normal, so they are often described as "ghost teeth". 6-Amelogenesis imperfect: is hereditary condition characterized by a defect in dental enamel formation. Teeth are often free of enamel, small, misshapen, and tinted brown. 7- Dentinogenesis imperfecta: is hereditary condition characterized by a defect in either dentin matrix formation or mineralization of dentin. 8-Natal and neonatal teeth : Natal teeth are present at the time of birth. Neonatal teeth will erupt during the first 30 days after birth. Natal teeth are three times more common than neonatal teeth. 9- Gemination: arises when 2 teeth developed from one tooth bud, as a result patient have extra tooth Reference  Graff, V.D. 2001. Human Anatomy. 6th Ed. The McGraw Hill.  Langman. Medical Embryology. 11th ed.  Sperber. 2001. Craniofacial Development. London. B.C Dekker Inc