Tooth Development: Odontogenesis

• Tooth development (odontogenesis) involves tooth formation, eruption, and integration with surrounding tissues.

Human Dentition Development

• Primary dentition develops prenatally and consists of 20 teeth.
• Permanent teeth gradually erupt, replacing primary teeth (exfoliation), totaling 32 teeth.
• Mixed dentition is the overlapping of primary and permanent teeth, typically starting around ages 6-7.

Calcification

• Calcification is the accumulation of calcium salts in body tissue.

Eruption

• Eruption involves teeth entering the mouth and becoming visible.

Attrition

• Attrition is the loss of tooth structure from tooth-to-tooth contact.

Odontogenesis Parallels

• The odontogenesis process is similar to the formation of other embryonic structures.

Physiological Processes Include

• Induction starts the process of formation.
• Proliferation involves the multiplication of numerous cells.
• Differentiation is when cells grow distinct characteristics.
• Morphogenesis determines the shape of the tooth.
• Maturation involves the attainment of adult form.

Timing

• First mandibular anteriors are first develop

• Second maxillary anteriors are second to develop

• Third Posterios develop thereafter

• Mandibular anteriors erupt first in infants.

• Primary dentition develops during the prenatal period, in both embryonic and fetal stages.

• Most permanents are developed during the fetal period.

• Teeth have the longest developmental period of any organ.

• Permanent posterial are the last to develop

Stages in the life cycle of a Tooth

• They include: Initiation, Proliferation, Histodifferentiation, Morphodifferentiation, Apposition, Calcification, Eruption, Attrition

Embryonic Period: Physiological Processes

• Embryological cell interaction is induction.
• Controlled cellular growth and accumulation of by-products is proliferation.
• Change in identical embryonic cells to become structurally and functionally distinct is differentiation.
• Morphogenesis is the development of specific tissue morphology through embryonic cell migration and interactions.
• Attainment of adult form and size is maturation.

Initiation Stage

• This occurs during the sixth to seventh week of prenatal development.
• The stomodeum is the primitive mouth, its outer ectoderm gives rise to the oral epithelium.
• Oral epithelium is the primary epithelial band.

Oral Epithelium Development

• Begins as two horseshoe-shaped bands of tissue on the surface of the stomodeum, known as the primary epithelial band/odontogenic epithelium.
• One for each future arch (maxillary or mandibular).
• During the 7th week, the oral epithelium grows into the ectomesenchyme.
• It induces the production of the dental lamina and vestibular lamina in developing jaw areas, starting in the midline and progressing posteriorly.

Vestibular Lamina Development

• Develops independently, labial and buccal to the dental lamina.
• The lip furrow band hollows and forms the oral vestibule between the alveolar portion of the jaws and the lips/cheeks.

The Bud Stage

• This starts at the beginning of the 8th week of development
• An extensive proliferation of dental lamina into buds or oval masses penetrates the ectomesenchyme.
• By the end of proliferation, there are 10 buds in each arch (maxillary and mandibular).
• The basement membrane separates each bud from growing ectomesenchyme.

Tooth Germ Development

• This is where a tooth bud develops with surrounding ectomesenchyme.
• Both ectoderm and ectomesenchyme, influenced by neural crest cells, develop all teeth and associated tissues.

Cap Stage

• Between the eighth and tenth week of development is the prenatal cap stage.
• Different portions of the tooth bud exhibit unequal growth, leading to a cap shape attached to the dental lamina.
• Proliferation, differentiation, and morphogenesis occur.

Enamel Organ

• The deepest part of each tooth bud forms a cap - enamel organ, derived from ectoderm.
• It produces enamel on the outer surface of the tooth, and its innermost margin shapes the future crown (cusps).

Dental Sac Development

• Remaining ectomesenchyme condenses around the enamel organ to form dental sac/follicle.
• Originates from ectomesenchyme, it produces the periodontium (cementum, periodontal ligaments, alveolar bone).
• The initiation occurs in the 10th week for the anterior teeth of the permanent dentition.
• An extension of the dental lamina forms, into the ectomesenchyme lingual to developing primary tooth germs (successional dental lamina).
• Permanent molars are nonsuccedaneous (no primary predecessor), developing from a posterior extension of the dental lamina, distal to primary 2nd molar.

Bell Stage

• The 11th to 12th week, has 4 different cells: Inner enamel epithelium (IEE), Outer enamel epithelium (OEE), Stellate reticulum (SR), Stratum intermedium (SI).
• Includes 2 stages: Early and late

Early Bell Stage

• During the 14th week, the dental lamina breaks down, disconnecting the enamel organ from the oral epithelium and shows distinct cell layers with OEE, SR, SI, & IEE.

Late Bell Stage

• During the 18th week, the IEE becomes taller to become pre-ameloblasts.
• Peripheral cells of the dental papilla are odontoblasts.
• They secrete ground substance and the dentin matrix.
• The cap of enamel organ becomes bell-shaped.
• The external cuboidal cells are the outer enamel epithelium.
• The inner structures are barriers for the rest of the enamel organs during enamel production.
• Inner tall columnar cells are inner enamel epithelium.
• The star-shaped cells are the Stellate reticulum.
• Flat to cuboidal cells are the Stratum intermedium that support enamel production.

Dental Papilla Differentiation

• Undergoes extensive differentiation, now consist of two cell types.
• Its periphery is the outer cells
• Its center is the inner cells
• The outer/peripheral cells differentiate into odontoblasts, which secrete dentin.
• Inner/central become the primordium of the pulp.

Enamel Composition

• Composed of Rods or Prisms that:
• Are the fundamental morphologic unit of enamel
• Are bound by interprismatic substance
• Which, are formed in increments by single enamel-forming cells (ameloblasts).

Lines of Retzius

• AKA striae of Retzius that:Are concentric lines in a cross-section of the crown, brown in transmitted light, and colorless in reflected light
• Run obliquely inward from the surface and toward the root on the longitudinal section
• Are artifacts left when ameloblasts retreat in incremental steps

Perikymata

• AKA imbrication lines of Pickerill that:
• Are transverse, wavelike grooves or tiny valleys that travel around the crown
• Mark the termination of Retzius lines on the tooth surface.
• Are external manifestations of Retzius lines.
• Continuous around the tooth, lying parallel to each other and the CEJ.

Hunter-Schreger Bands

• Alternating light and dark lines in dental enamel beginning at the DEJ, is the border between the dentin and enamel and ending before the enamel surface.
• Seen in longitudinal ground sections, found in the inner two thirds of the enamel.

Gnarled enamel

• Enamel rods appear twisted together over the cusps of teeth in complex arrangements.

Tomes Processes

• Cytoplasmic extensions on ameloblasts jut into and interdigitate with newly forming enamel.
• This gives the enamel and ameloblast junction a picket-fence appearance.
• Secretory surface secretes the enamel matrix, facing the dentinoenamel junction (DEJ).

Enamel Lamellae

• Partially calcified vertical defects in enamel resembling cracks or fractures, that traverse the crown from the surface to the DEJ.
• They are narrower and longer than enamel tufts.

Enamel Tufts

• Fan-shaped, hypocalcified enamel rods and interprismatic substance projecting from DEJ into proper enamel, extending 1/5 to 1/3 of thickness.
• Optical illusion from fibers in different planes.

Enamel Spindles

• Dentinal tubules that penetrate a short distance into the enamel and end blindly that:
• Originate from odontoblasts crossing the basement membrane before it mineralized the DEJ, becoming trapped during the apposition of enamel matrix to the mineralized.
• May serve as pain receptors

Apposition Stage Events

• The stages and final end result of development and consist of enamel, dentin and cementum which are:
• Secreted as a partially mineralized matrix.

Processes within

IEE (inner cells) grows, becomes more columnar and elongates Preameloblast forms first Then, preameloblast differentiates into Ameloblast.

Odontoblast and Dentin Matrix Formation

• Outer cells of the dental papilla are induced by preameloblasts to become odontoblasts.
• Dentinogenesis is the apposition of dentin matrix/predentin.

Ameloblast and DEJ Enamel Matrix Formation

• After odontoblast differentiation from dental papilla and predentin formation, the basement membrane disintegrates.
• Preameloblast touches predentin, inducing its differentiation into Ameloblast.
• Dental sac (Increasing amount of collagen fibers forming around enamel organ.) can be found
• differentiating into cementum, periodontal ligament, and alveolar bone
• Outer Enamel Epithelium (Outer cuboidal.) serves as a protective barrier for enamel.
• Stellate Reticulum supports enamel matrix creation
• Inner Enamel Epithilium differentiates into ameloblast and makes that matrix
• Stratium Intermedium also aids with the matrix.
• OOuter cells of dental papilla form odontoblast with will create dentin
• Inner cells for the pulp

HERS Function

• HERS, Hertwig's Epithelial Root Sheath, inducing dentin formation in roots.
• Shapes the roots
• Determines the number of roots.
• Epithelial diaphragm is the apical segment, ensuring the tapered shape of the root that eventually forms the apical foramen.

Root Sheath

• Has a proliferating zone (cervical loop) and is architected around HERS

Radicular Dentin

• As radicular dentin forms from disintegrating HERS.
• This leaves epithelial cells known as epithelial rests of Malassez.

HERS Collapse

This enables the dental follicle's ectomesenchymal to contact dentin and differentiate into periodontal formative cells, such as:

• Cementoblasts
• Osteoblasts
• Fibroblasts

Developmental Distrubances

• May result in Concrescence or Enamel pearls that are a type of enamel dysplasia, in cases like:
• Hutchinsons incisors
• Mulberry molars
• Turners spot / turners tooth
• Amelogenesis imperfecta

Enamel Makeup

• Is: Crystalline, hardest in body, pressure resitant, avascular, without nerves, that undergoes mineralization with with:
• 96% inorganic, 1%organic, 3% water
• Calcium hydroxyapatite
• RadioPaque

Amelogenesis

• The Proccess: Process of enamel matrix formation occurring during the apposition stage.

The cells of IEE become 40 microns in height with the migration of nuclei to the proximal end. The dentinal ends of ameloblasts are united with each other by means of terminal bars which present a honeycomb network enclosing the ameloblast (seen on surface) X-section – terminal bars appear as DOTS

Changes

• The reticulum reduces, loses fluid The OEE loops with the capillaries Dentin is now first laid

Amelogenesis Phases

• Phases can undergo a formative stage of matrix creation, or the transforming crysal form phase. That formative proccess consists of:
• Forming Denten, the Tomes process and material fill in before segmentation and rod forming
• Unique because the enamel matrix has less matrix

Ameloblasts Fate

• Enamel becomes a epithelium that then becomes 2 protective coverings of enamel and forms

Fate of the the organ includes

• morphogenic interactions, organized interactions with the cells, formative structure, and material structure that then desolyes and reduces
• Nasmyth membranes that protect the enamel

More facts

• prismatic rods run cylinderical perpendicularly with varying height, with crystaline structures
• Striae are extending lines of the the surface
• Hyperkymata are lines on the surface

Dentin

There has to be reciprocal induction between Enamel and Dentin

• Innermost later is the hardest layer and has a cellular surface
• Has a zone for forming cementum, bones, and periodonal attachments Consists of a papilae and is related to tubules

Formation

• Collagen is formed along with an organic matrix
• Fiber growth helps it, then ground substance
• It synthesizes protein on the end and it mineralizes to form denten
• Incremintation happens slowly

Key properties

• It is a hard type that forms bone and is subject to deformation, especially as it ages.
• Tubules: run from the the pulpa to surface with a widening section