Ch19 Dental Lamina and Enamel Organ

Dental Lamina

Overview of Tooth Development

  • First signs of tooth development seen during the sixth embryonic week.

  • Oral epithelium (stratified squamous) begins to thicken.

  • Thickening of epithelium results in downward growth into the connective tissue without an initially visible ridge.

  • This thickened epithelium is known as the dental lamina.

  • Shape: U-shaped thickening in the primitive oral cavity, corresponds to the future arrangement of teeth (dental arch).

  • Progression: Thickening starts at the anterior midline and spreads posteriorly toward the molar region, taking several weeks to reach the position of future primary molars.

    • By eighth embryonic week, there are 10 areas of thickening in both the upper and lower arches (total: 20 areas), relating to future primary dentition.

    • Formation of enamel is associated with these thickened areas.

  • Ectodermal Dysplasia: Affects enamel development along with other structures from ectoderm (e.g., sweat, salivary glands, skin, hair).

    • Can also affect sclera coloring of the eye.

Enamel Organ Stages

Bud Stage

  • Initial development from the dental lamina leads to bud stage.

  • Appearance: Blob-like projections of cells from dental lamina into connective tissue.

  • Cells in buds:

    • Middle of the buds: Derived from outer/superficial layers of the oral epithelium.

    • Periphery of the buds: Derived from deep/basal layers of the oral epithelium.

  • Buds elongate as they develop. The deepest parts begin to concave as they prepare to transition to the cap stage.

Cap Stage

  • As the enamel organ progresses to cap stage, it develops three components:

    • Outer Enamel Epithelium (OEE):

    • Outermost layer composed of low columnar or cuboidal cells, continuous with basal oral epithelium.

    • Inner Enamel Epithelium (IEE):

    • Forms the concave outline, continuous with OEE; composed of cells from the basal layer.

    • Stellate Reticulum:

    • Composed of cells between IEE and OEE, originating from the superficial layers of oral epithelium; may mimic embryonic mesenchymal cells but are ectodermal cells.

  • As cap deepens, it transitions into the bell stage.

Bell Stage

  • Transition to bell stage is marked by the formation of a fourth layer of epithelium:

    • Stratum Intermedium:

    • Composed of flattened squamous cells lying between IEE and stellate reticulum.

  • Changes occurring:

    • Definition of the future tooth crown outline.

    • Cells, particularly IEE, prepare for enamel production.

Functions of Layers in the Enamel Organ

  1. Outer Enamel Epithelium (OEE):

    • Protective layer; plays a role in attaching gingiva to the tooth.

  2. Inner Enamel Epithelium (IEE):

    • Elongates and transforms into ameloblasts responsible for enamel formation.

  3. Stellate Reticulum:

    • Provides cushioning and possible nourishment to IEE; allows vascular fluid exchange.

  4. Stratum Intermedium:

    • Nourishes IEE, contributes proteins, interacts with ameloblasts.

Successional Lamina

  • Extension of the dental lamina to the lingual side of each developing tooth; referred to as successional lamina.

  • Follows similar stages (bud, cap, bell) and develops into permanent incisors, canines, and premolars.

  • Permanent molars develop from posterior growth of the general lamina and are classified as non-successional.

  • Formation rates vary with permanent teeth developing slower than primary teeth; laminar attachment degrades as the tooth enters the bell stage, first in the anterior region.

Vestibular Lamina

  • Development of the vestibular lamina begins as a thickening of oral epithelium moving facially from the dental lamina.

  • Cleft forms in thickened area, eventually developing into the mucobuccal or mucolabial fold in the future vestibule.

  • Absence of vestibular lamina results in difficulties in denture construction.

Dental Papilla and Dental Sac

  • Dental Papilla:

    • Small area of condensed cells from mesoderm located adjacent to IEE; forms dentin and pulp of the tooth.

    • Observed first during late bud stage, enlarges significantly through development.

  • Dental Sac:

    • Comprised of flattened cells surrounding the dental papilla that is not in contact with the IEE.

    • Also arises from mesoderm; forms cementum, periodontal ligament, and parts of alveolar bone.

Review Questions

  1. First sign of tooth development: Thickening of oral epithelium seen during the sixth embryonic week.

  2. Oral epithelium arrangement: Stratified squamous epithelium.

  3. Origin of enamel organ: Ectoderm.

  4. Stages of enamel organ: Bud, cap, bell; involves changes in structure and cell differentiation.

  5. Ectodermal dysplasia significance: Poor development of ectodermal derivatives, including enamel; affects teeth and other structures.

  6. Four layers in the bell stage: OEE, IEE, stellate reticulum, stratum intermedium; respective functions range from protection to nourishment and enamel production.

  7. Definitions and roles:

    • Successional lamina: Develops permanent teeth from extensions of dental lamina.

    • Vestibular lamina: Forms mucobuccal folds, critical for oral cavity structure.

    • Dental papilla: Forms dentin and pulp from mesoderm, involved in tooth structure development.

    • Dental sac: Forms cementum and supporting structures surrounding the tooth.