HE L6

Tooth Development

Chapter 6 Overview

Development of the Dentitions

• Dentition Definition: Refers to the natural teeth in the jaws.

• Types of Dentition:

  • Primary Dentition: Also known as baby teeth; consists of 20 teeth developed during the prenatal period.

  • Permanent Dentition: Develops as primary teeth are lost; consists of 32 teeth.

Stages of Tooth Development

• Odontogenesis: The process of tooth development occurring in multiple stages.

• Primary Dentition Initiation: Begins between the 6th-7th week of prenatal development during the embryonic stage.

Initiation Stage

• Overview: First stage involving embryological tissues' interactions (induction).

• Ectoderm: The embryo's primitive mouth (stomodeum) lined with ectoderm forms the oral epithelium.

• Dental Lamina Formation: Oral epithelium grows into the ectomesenchyme, leading to the creation of dental lamina in the late seventh week.

• Basement Membrane: Exists between the oral epithelium and ectomesenchyme to separate the two during development.

Developmental Disturbances in the Initiation Stage

• Anodontia: Absence of teeth due to initiation failures.

  • Partial Anodontia (Hypodontia): Missing a few teeth, commonly affects maxillary lateral incisors, third molars, and mandibular second premolars.

• Supernumerary Teeth (Hyperdontia): Development of extra teeth due to anomalous initiation from the dental lamina.

  • Commonly occurs as mesiodens (between central incisors), distomolars (near third molars), or perimolars (in premolar region).

Bud Stage

• Overview: Occurs beginning of the 8th week of prenatal development.

• Dental Lamina: Proliferates into buds, each eventually developing into tooth germs.

• Ectomesenchyme: Also proliferates beneath each bud while a basement membrane separates the dental bud and ectomesenchyme.

Developmental Disturbances during Bud Stage

• Microdontia/Macrodontia: Abnormally sized teeth (larger or smaller than normal) due to faulty proliferation.

Cap Stage

• Overview: Occurs between the 9th-10th week. Characterized by tooth bud differentiation and morphological changes leading to cap shape.

• Enamel Organ Formation: Inner structure where tooth germ begins to develop structure for the future crown.

• Existing Structures:

  • Dental Papilla: Forms from the condensed ectomesenchyme within the enamel organ.

  • Dental Sac: Surrounding tissue that condenses into structure supporting the tooth.

Developmental Disturbances during Cap Stage

• Dens in Dente: Abnormal invagination of the enamel organ into the dental papilla, commonly affects maxillary lateral incisors.

• Gemination: An attempt by a single tooth germ to divide, leading to a large, malformed tooth.

• Fusion: The union of two tooth germs, affecting appearance and possibly reducing the overall tooth count in the dentition.

Bell Stage

• Overview: Occurs between the 11th-12th week, marked by extensive differentiation and cell types within the enamel organ.

• Enamel Organ Structure:

  • Outer Enamel Epithelium (OEE): Protects inner components.

  • Inner Enamel Epithelium (IEE): Differentiates into enamel-secreting cells (ameloblasts).

  • Stratum Intermedium and Stellate Reticulum: Support enamel production.

Apposition and Maturation Stages

• Apposition Stage: Involves secretion of enamel, dentin, and cementum in layers, beginning with the crown formation.

• Maturation Stage: Final phase where matrix becomes fully mineralized.

Developmental Disturbances During Stages of Apposition and Maturation

• Enamel Dysplasia: Faulty enamel development affected by local or systemic conditions affecting ameloblasts.

  • Hutchinson Incisors and Mulberry Molars: Evidence of enamel hypoplasia from syphilis exposure impacting enamel matrix quality.

• Amelogenesis Imperfecta: Genetic condition leading to defective enamel formation impacting both dentitions.

• Dentin Dysplasia: Interference during dentinogenesis affecting the structural integrity of dentin.

Root Development

• Cervical Loop: Area responsible for root growth, extending into ectomesenchyme and forming Hertwig's epithelial root sheath for shaping and forming dentin in roots.

• Dentin Formation: Begins after crown completion, initiated by differentiation of odontoblasts from the dental papilla.