Tooth Development and Dental Lamina

Tooth Development

• The primitive oral cavity (stomodeum) is lined by stratified squamous epithelium (oral ectoderm).
• The oral ectoderm touches the foregut's endoderm, forming the buccopharyngeal membrane.
• Most connective tissue underlying the oral ectoderm originates from neural crest or ectomesenchyme.
• Tooth development begins in the future maxilla and mandible, progressing posteriorly.
• Primary epithelial band: Areas of basal cells in the oral ectoderm proliferate faster than adjacent cells, creating a band.
• This band invades the underlying ectomesenchyme along the future dental arch's horseshoe shape.

Dental Lamina

• The dental lamina acts as the primordium for the ectodermal portion of the deciduous teeth.
• Later, permanent molars develop from a distal extension of the dental lamina.
• Buds of the permanent teeth form along the dental lamina's leading edges.
• The dental lamina continues to develop the 32 permanent tooth buds.
• The dental lamina is functional from the sixth prenatal week to about four years after birth.
• If remnants remain, they are called epithelial rests of Serres (Serres' pearls).

Physiological Phases of Tooth Development

• Initiation: Tooth germs appear along the dental lamina's invagination.
• Proliferation: Accelerated growth alters the tooth germ's size and shape.
• Histodifferentiation: Formation of specialized dental tissues (enamel, dentin, cementum) and supporting tissues begins.
• Morphodifferentiation: Tooth forms a defined shape.
• Apposition: Deposition of hard dental tissue (enamel and dentin) starts.

Morphological Stages of Tooth Development

• Tooth germs are classified as bud, cap, and bell stages depending on differentiation.
• Bud stage: Round or ovoid swellings emerge from dental lamina. The cells of the tooth bud have higher RNA content and increased oxidative enzyme activity compared to the overlying oral epithelium.
• Cap stage: The enamel organ invaginates into a cap shape, the deeper surface is more defined and surrounded by ectomesenchyme, now called dental papilla.
• Bell stage: The dental organ becomes bell-shaped with distinct cell layers (outer and inner enamel epithelium). Cells in the inner enamel epithelium will differentiate into ameloblasts and the surrounding ectomesenchyme into odontoblasts.

Transitory Structures

• Enamel knot: A localized cluster of cells in the center of the inner enamel epithelium.
• Enamel cord: An extension of the enamel knot.
• Enamel niche: An apparent structure that results from how the dental lamina is arranged in a histological section.

Early Bell Stage

• High degree of histodifferentiation happens in the early bell stage. The enamel organ shows four distinct layers:
  • Inner enamel epithelium: Single-layered cells, differentiating into ameloblasts.
  • Stratum intermedium: Layer of flattened cells between the inner enamel epithelium and stellate reticulum.
  • Stellate reticulum: Intercellular spaces filled with fluid, likely related to osmotic effects.

Dental Papilla

• Encased in the enamel organ. Peripheral cells differentiate into odontoblasts under the epithelium's influence.
• Develops into the dental pulp once dentin formation starts.

Dental Sac

• Fibers arranged in a circular pattern. It becomes the periodontal ligament as the tooth develops its roots.

Advanced Bell Stage

• Hard tissues (enamel and dentin) develop in the advanced bell stage, also called crown stage.
• The inner enamel epithelium changes shape from cuboidal to columnar to form pre-ameloblasts.
• Boundary between the inner enamel epithelium and odontoblasts defines the future dentin-enamel junction.

Dental Lamina Function

• Initiates deciduous tooth development;
• Initiates the development of permanent successors to deciduous teeth.
• Extends distally in some instances to form the developing molar tooth germs.

Fate of Dental Lamina

• Functional in forming 52 teeth from 6 prenatal weeks to 4 years old;
• Degenerates during the late bell stage.
• Remnants called epithelial rests of Serres may remain in the jaw.

Tooth Development Nutrition

• Calcium, phosphorus, and vitamins A, C, and D, are essential nutrients for healthy tooth development.