Tooth Development Odontogenesis

Stages of tooth development initiation stage – 6th to 7th week bud stage – 8th week cap stage – 9th to 10th weeks bell stage – 11th to 12th weeks apposition stage – vaires per tooth maturation stage – varies per tooth

Tooth formation First signs of formation – day 11 Thickening of the epithelium where tooth formation will occur on the 1st branchial arch Earlier signals – earliest mesenchymal markers for tooth formation are the Lim-homeobox genes (Lhx-6 and Lhx-7) – expressed as early as day 9 in the neural crest cells of the tooth region

Tooth formation more than 90 genes have been identified in the oral epithelium, dental epithelium and dental mesenchyme!! so exact signaling mechanisms remain unclear

Tooth formation -initial stage- involves the physiologic process of induction induction of ectodermal tissues by the developing mesenchyme mechanisms remain unknown at the 6th week the stomatodeum is lined with ectoderm – outer portion is the oral epithelium this gives rise to the primary epithelial bands

Tooth formation -initial stage- also is a developing mesenchyme which contains neural crest cells that have migrated to the area a basement membrane separates the developing oral epithelium and mesenchyme

Cross section (A) Neural crest cells

Basement membrane ECTODERM MESODERM ectomesenchymal cells

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

Tooth formation -initial stage- The dental lamina develops a series of epithelial outgrowths - grow deep into the mesenchyme develops in the future spot for the dental arches will form the midline for these arches arches then form posteriorly from this point the ingrowths represent the future sites for each deciduous tooth

Tooth formation -initial stage- the vestibular lamina cells rapidly enlarge and then degenerate – forms a cleft that becomes the vestibule of the oral cavity The initiation of tooth formation starts around the 37th day of gestation.

Early Dental Lamina Tongue Dental lamina Vestibular lamina ©Copyright 2007, Thomas G. Hollinger, Gainesville, Fl

Late Dental Lamina

Tooth type determination Patterning means the determination of specific tooth type at the correct position. Homodont are animals with same shaped teeth Heterodont are the most mammals with different tooth types Two theories for the determination of tooth type

Tooth type determination The field model theory proposes that factors responsible for the determination reside within the ectomesenchyme, but graded fields for each tooth The clone model theory proposes that each tooth is derived from a clone of ectomesenchymal cells programmed by the epithelium to produce a given pattern.

Bud stage marked by the incursion of epithelium into the mesenchyme period of extensive proliferation and growth of the dental lamina forms into buds or oral masses that penetrate into the mesenchyme each tooth bud is surrounded by the mesenchyme

Bud stage buds + mesenchyme develop into the tooth germ and the associated tissues of the tooth this developing tooth forms from both the ectoderm and mesenchyme and from neural crest cells that have migrated into the mesenchyme

Tongue Bud stage Future dental papilla

Cap stage characterized by continuation of the ingrowth 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 attached to the remaining dental lamina looks like a cap sitting on a ball of condensing mesenchyme

Cap stage occurs for the primary dentition (during the fetal period) this stage marks the beginning of histodifferentiation (differentiation of similar epithelial cells into functionally and morphogically distinct components) the tooth germ also begins to take on form – start of morphodifferentiation

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)

Cap stage below this cap is a condensing mass of mesenchyme – dental papilla – produces the future dentin and pulp tissue (mesenchymal origin)

Cap stage the basement membrane separating the dental organ and the dental papilla becomes the future site for the dentinoenamel 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 ©Copyright 2007, Thomas G. Hollinger, Gainesville, Fl

Cap stage together the enamel organ + dental papilla + dental follicle is considered the developing tooth germ or tooth primordium these primordium will be housed in the developing dental arches and will develop into the primary dentition

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.

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

Bell stage the dental papilla undergoes differentiation and produces two types of cells outer cells of the DP – forms the dentin-secreting cells (odontoblasts) central cells of the DP – forms the primordium of the pulp

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 cervical loop: the IEE and OEE are continuous region where they connect – curved rim of the EO = cervical loop

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

Bell stage – other events Two important events occur at the bell stage: the dental lamina begins to break up into discrete islands of epithelial cells (epithelial pearls) – separates the oral epithelium from the developing tooth these pearls may form cysts and delay eruption or they may develop into supernumerary teeth

Bell stage – other events the IEE completes its folding and you can begin to identify the shape of the future crown pattern.

Bell stage – crown formation the dental papilla is separated from the enamel organ by a basement membrane immediately below this BM is a region called the acellular zone this is where the first enamel proteins will be laid down

Tooth Development Odontogenesis