Oral Biology Overview and Dental Anomalies

Oral Biology

• Oral biology provides a basis for dental subjects and practice.
• Oral biology is the study of the structure, function, and diseases that relate to the mouth and its surrounding structures.

Topics Studied

• Tooth development
• Enamel structure and amelogenesis
• Dentin structure and Dentinogensis
• Cementum structure and cementogenesis
• Pulp structure
• PDL structure
• Alveolar bone and osteointegration
• Radiographic interpretation to the maxillary and mandibular landmarks

Dental Congenital Anomalies

• Supernumerary teeth: Extra teeth
• Teeth fusion: Two teeth are joined together
• Macrodontia: Abnormally large teeth
• Microdontia: Abnormally small teeth

Tooth Development Stages

• Morphological Stages: Dental lamina formation, bud, cap, and bell
• Physiological Stages: Induction, proliferation, morpho-differentiation, histo-differentiation, apposition, and maturation.
• Sonic hedgehog (Shh) and different types of growth factors are responsible for the development of teeth, their numbers, and their specific morphology.

Shh Signaling

• Shh is secreted by the odontogenic epithelium.
• Shh diffuses to the dental ectomesenchyme.

Morphological Stages of Tooth Development

• Dental lamina initiation: Starts at 5 weeks in utero.
  • The odontogenic epithelium covers mesenchymal tissues rich in Shh.
  • Neural crest cells differentiate into odontogenic cells.
  • The primary epithelial band forms.
  • The band bifurcates into the general (main) dental and vestibular laminae.
  • Main dental lamina gives rise to deciduous dentition.
  • Posterior proliferation of the main dental lamina gives rise to permanent molars.
  • Lingual proliferation gives rise to successional dental laminae.
  • Vestibular lamina forms the vestibular mucosa.
  • Induction and proliferation are the key physiological processes.
• Bud stage: Begins at 6 weeks in utero.
  • The dental lamina induces dental placodes to form buds.
  • Induction and Proliferation are the key physiological processes.
• Cap stage:
  • The bud shows unequal growth, forming a cap shape called the enamel organ.
  • The ectomesenchyme divides into the dental papilla and dental sac.
  • The basement membrane separates the epithelium from the connective tissue.
  • Enamel organ, dental papilla, and dental sac form the tooth germ.
  • Proliferation is the key physiological process.
  • Cells within the enamel organ are organized into the outer and inner enamel epithelium and stellate reticulum.
  • The stellate reticulum cells are polygonal and synthesize glycosaminoglycans, pulling water into the enamel organ.
• Bell stage:
  • The enamel organ develops into a bell shape.
  • This stage is subdivided into early bell and late bell.
  • The enamel knot is a signaling center for cuspal morphogenesis.
  • The enamel cord is a strand of cells extending from the stratum intermedium to the outer enamel epithelium.

Transitory Structures

• Enamel knot: A cluster of non-dividing epithelial cells that appear in the cap stage and bulge into the dental papilla.
• Enamel cord: A strand of cells seen at the early bell stage, extending from the stratum intermedium to the outer enamel epithelium.