Development of Teeth and Oral Mucosa

• The session aims to describe the stages of tooth and oral mucosa development, link oral structures to embryonic origins, relate developmental stages to the embryonic timeline, and recognize the clinical significance of oral embryology
• Understanding the formation of oral tissues like teeth, gingiva, and supporting structures allows effective support, maintenance, and restoration of oral health

Recap of Oral Tissues

• Enamel surrounds the crown of the tooth
• Dentine forms the bulk of the crown and root
• Cementum surrounds the root
• The periodontal ligament connects the root to the alveolar bone
• Pulp resides inside the tooth
• The alveolar bone holds the teeth in place
• Oral mucosa is the soft tissue lining of the oral cavity, including the lamina propria and gingiva

Embryonic Origins

• Oral structures originate from the ectoderm and neural crest cells
• The ectoderm gives rise to oral epithelial cells, which form ameloblasts and the oral mucosa
• Neural crest cells form ectomesenchyme, which gives rise to pulp, cementum, periodontal ligament, alveolar bone, and odontoblasts
• Oral epithelial cells are highly organized, forming a compact tissue layer
• Ectomesenchymal cells are soft, jelly-like, and loosely arranged

Complexity of Oral Tissue Embryology

• Oral tissues develop in the stomadeumof the embryo through interactions between epithelial cells and ectomesenchyme, with over 300 genes involved
• Signals exchanged by cells and genes regulate development
• Understanding is based on studies of animal and human embryos, fetuses, and infants, with morphological aspects studied for 150 years and development mechanisms for 50 years
• Research continues today with stem cells in tooth regeneration

Stages and Functions of Tooth Development

• Stages include dental lamina, bud, cap, and bell stages
• Functions include initiation, morphogenesis, cell differentiation, and matrix secretion

Stages of Tooth Development

• The dental lamina appears first in the process
• Then the Bud Stage
• Then the Cap Stage
• Followed by the Bell Stage
• Finally Eruption

Initiation of the Dental Lamina

• Occurs at weeks 6-7
• Oral epithelial cells in the mandibular and maxilla prominences form the primary epithelial band
• In week 7, this band divides into the dental lamina and the vestibular lamina
• The dental lamina extends to follow the developing dental arches

Initiation of the Vestibular Lamina

• Occurs at week 7
• Vestibular lamina forms adjacent to the dental lamina and gives rise to the vestibule
• The basement membrane separates the two cell layers and facilitates communication during tooth development

The Dental Lamina

• Occurs at week 8
• Forms epithelial swellings called dental placodes, which give rise to teeth
• Placodes are surrounded by ectomesenchyme cells
• Interactions between oral epithelial cells and ectomesenchyme cells initiate the next stage of tooth development

The Bud Stage

• Occurs at weeks 9-10
• Oral epithelial cells of the dental placode proliferate to form a bud
• The bud presses into the underlying ectomesenchyme, forming the enamel organ
• The enamel organ will produce one tooth

The Cap Stage

• Occurs at week 11
• Enamel organ changes shape by hollowing out to resemble a cap
• Ectomesenchymal cells proliferate rapidly inside the hollow, forming the dental papilla (DP)
• Surrounding the dental papilla and enamel organ, ectomesenchymal cells proliferate to form the dental follicle (DF)

Morphogenesis

• The transition from the bud to cap stage signifies morphogenesis, where the tooth's crown morphology begins to form
• The enamel knot drives morphogenesis of the cusp shape and outline, continuing up to the bell stage

The Bell Stage

• The enamel organ changes shape further by hollowing out and extending to map the tooth crown's size and shape
• The enamel organ separates from the dental lamina
• The bell stage is split into the early and late stages

Histo-differentiation

• Histo-differentiation (cell differentiation) occurs in the bell stage
• Cells within the enamel organ and dental papilla differentiate into specialized cell types to form the tooth's tissue structures

The Early Bell Stage

• The early bell stage is characterised by cell differentiation pathways
• These forms dental papilla and enamel organs

Enamel Organ in the Early Bell Stage

• Oral epithelial cells differentiate into outer enamel epithelium (OEE), stellate reticulum (SR), stratum intermedium (SI), and inner enamel epithelium (IEE)
• OEE cells, cuboidal in shape, lie along the periphery play a key role in the eruption process
• SR cells, star-shaped, lie on the inside of the outer enamel epithelium and play a key role in facilitating amelogenesis
• SI cells are flattened, and lie the inside of the inner enamel epithelium with a key role in facilitating amelogenesis
• IEE cells are tall and columnar, lining the inside and eventually differentiating into ameloblasts

Dental Papilla in the Early Bell Stage

• Ectomesenchyme cells in the dental papilla differentiate into odontoblasts or pulpal cells
• Odontoblasts, derived from pre-odontoblasts, lie along the periphery of the dental papilla and carry out dentinogenesis
• Pulpal cells lie in the centre and become the pulp of the tooth

Late Bell Stage

• After cellular differentiation, the enamel organ undergoes crown formation
• Crown formation includes amelogenesis to form enamel and dentinogenesis to form dentine

Development of the Oral Mucosa

• Oral mucosa lines the oral cavity
• Oral epithelial cells in the vestibular lamina and lingual regions undergo proliferation, migration, and differentiation
• This leads to masticatory, lining, and specialized mucosa like gingiva
• Underlying ectomesenchymal cells give rise to lamina propria(connective tissue) and submucosa

Timeline of Primary Dentition Development

• Occurs from 30 weeks in utero to approximately 4.5 months
• Tooth buds and bell stage present
• The eruption stage forms the permeant teeth

Developmental Anomalies

• Can result from environmental or genetic interruptions during tooth development
• Supernumerary or extra buds can occur
• Missing teeth or no initiation
• Impacts on shape during the cap and early bell stage
• Impacts the quality during the bell stage
• Can range from none to significant levels

Future Learning

• Includes histology of oral tissues and histopathology of oral diseases
• Clinical practice of enamel hypoplasia is also important to consider
• As well as considering developmental anomalies

This session describes tooth and oral mucosa development stages, linking oral structures to their embryonic origins and relating developmental stages to the embryonic timeline. Understanding the formation of oral tissues enables effective support, maintenance, and restoration of oral health. Key oral tissues include enamel, dentine, cementum, periodontal ligament, pulp, and alveolar bone.