Teeth

Normally, an adult has 32 teeth: 16 maxillary and 16 mandibular. These teeth are divided into 4 quadrants with 8 teeth each. Each quadrant consists of 2 incisors (dentes incisivi), 1 canine (dens caninus), 2 premolars (dentes premolares), and 3 molars (dentes molares). Teeth are located within the alveolar processes and are held in position by the periodontal ligament. Teeth are composed of enamel, dentin, and dental cement.

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Development

Embryologic development

The teeth are derived from the 1st pharyngeal arch.

Stages:

  • Dental lamina: C-shaped; site where the teeth form
  • Bud: 
    • Dental lamina thickens by cell aggregation → each tooth bud is created
    • The tooth bud moves into underlying mesoderm while keeping contact with the surface via the dental lamina.
  • Cap: 
    • Formation of enamel organ (ectodermal layer), which then divides into the outer and inner enamel epithelium
    • Dental papilla is formed (will produce dentin and pulp).
    • Surrounding mesenchyme starts to form condensation, eventually making the dental sac → forms cementum and periodontal ligament
  • Bell: 
    • The dental organ is bell-shaped.
    • Stellate reticulum presents between the outer and inner enamel epithelium.
    • Differentiation of mesenchymal cells in the dental papilla creates odontoblasts.
    • Odontoblasts produce predentin, which will become dentin.
    • Inner enamel epithelium forms ameloblasts, which produce enamel.
    • Dental sac forms cementoblasts, which produce cementum.
    • Development of the root of the tooth begins after the enamel and dentin formation is advanced.
    • Inner and outer enamel epithelia come together to form the epithelial root sheath, which starts forming the root of the tooth.
    • Pulp cavity reduces to a root canal, which will serve as a passageway for vessels and nerves.
    • Periodontal ligament: derivative of the dental sac that connects the tooth to the jawbone
  • Maturation: development of hard tissue (bone)
Formation of dental lamina

Formation of the dental lamina arch (A) and tooth bud (B)

Image by Lecturio.
Formation of dental papilla and dental sac

A and B: Formation of the dental lamina and tooth bud
C and D: Formation of the enamel organ
E: Formation of the dental papilla and dental sac
F: Formation and development of the enamel and dentine layers
G: Early stage of tooth eruption
H: Fully erupted deciduous tooth
I: Cross-section of a developing tooth showing its composition

Image by Lecturio.

Childhood development

Teeth begin to erupt within 6 months to 1 year of life, usually beginning with the lower incisors.

Table: Upper teeth
Teeth Expected age at eruption Expected age at shedding
Central incisor 8–12 months 6–7 years
Lateral incisor 9–13 months 7–8 years
Canine 16–22 months 10–12 years
1st molar 12–19 months 9–11 years
2nd molar 25–33 months 10–12 years
Table: Lower teeth
Teeth Expected age at eruption Expected age at shedding
2nd molar 23–31 months 10–12 years
1st molar 14–18 months 9–11 years
Canine 12–23 months 9–12 years
Lateral incisor 10–16 months 7–8 years
Central incisor 6–10 months 6–7 years

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Gross Anatomy

Location

  • Teeth are within the oral cavity, which is an anatomic space that forms the outer limit of the alimentary canal.
  • Specifically located in the alveolar processes of the mandible and maxilla
  • Held in position by the periodontal ligament
Human mandible left

Mandible with teeth in place within the alveolar processes

Image: “Human mandible left” by Djexplo. License: CC0 1.0

Classification

  • Each jawline (mandibular and maxillary) has 4 incisors, 2 canines, 4 premolars, and 6 molars.
  • Incisors: central and lateral
  • Canines
  • Premolars: 1st and 2nd
  • Molars: 1st, 2nd, and 3rd
Classification of teeth

Location of the incisors, canines, premolars, and molars within the jawline

Image by Lecturio.

Parts

  • Crown
  • Pulp cavity
  • Neck of tooth
  • Dental root
  • Root canal
Structure of a tooth

The tooth and its parts

Image: “Structure of a tooth” by Phil Schatz. License: CC BY 4.0

Neurovasculature

Blood supply:

  • Maxillary jawline:
    • Anterior superior alveolar arteries
    • Posterior superior alveolar arteries
  • Mandibular jawline: inferior alveolar arteries
Blood supply of the teeth

Blood supply of the teeth

Image by Lecturio.

Innervation:

  • Maxillary jawline: superior alveolar nerves
  • Mandibular jawline: inferior alveolar nerves
Innervation of the teeth

Innervation of the teeth

Image by Lecturio.

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Microscopic Anatomy

Each tooth comprises 4 components:

  • Enamel (enamelum): 
    • Most superficial layer of the tooth
    • Light yellow to grayish white
    • Composed of calcium hydroxyapatite crystals (98%)
    • Originates from ameloblastin (secreted by ameloblasts)
  • Dentin (dentinum): 
    • Extension of the enamel within the jaw bones
    • Secreted by the odontoblasts
    • Softer than enamel
  • Dental cement (cementum)
    • Secreted by cementoblasts
    • Yellowish coloration 
    • Softer than dentin and enamel
    • Periodontal ligaments attach here.
  • Dental pulp:
    • Central part of the tooth
    • Soft connective tissue
    • Contains:
      • Blood vessels
      • Nerves
      • Fibroblasts and pre-odontoblasts
      • Macrophages and T lymphocytes
Micro parts of a tooth

The tooth and its parts

Image: “Diagram of a healthy human molar” by KDS4444. License: CC BY-SA 4.0

Clinical Relevance

  • Dental cavities: also known as tooth decay. Dental cavities are a multifactorial disease characterized by the destruction of the tissues of the teeth as a consequence of the demineralization caused by acids generated by bacterial plaque. These cavities are associated with the intake of excessive sugars and acids contained in certain beverages and foods. Treatment consists of the elimination of the infectious agent and restoration or rehabilitation of the tooth.
  • Ameloblastoma: benign tumor typically arising from the mandible and much less commonly from the maxilla. Ameloblastomas are slow-growing, painless lesions that normally appear near the angle of the mandible and arise in the 3rd–5th decades of life. If left untreated for long periods, ameloblastomas can become quite disfiguring. Treatment is surgical, but there is a high rate of recurrence (50%–90%).
  • Cementoblastoma: rare neoplasm of the alveolar ridge (cementoblasts) with very few confirmed cases in the literature. The median age at diagnosis of cementoblastoma is 20 years. Cementoblastomas demonstrate increased density as compared with the adjacent bone, which is represented by a lucid halo with imaging. Treatment is surgical, and recurrence is common if not completely excised.

References

  1. Paintal, A. (2021). Pathology of head and neck neoplasms. UpToDate. Retrieved August 20, 2021, from https://www.uptodate.com/contents/pathology-of-head-and-neck-neoplasms
  2. Chow, A.W. (2020). Complications, diagnosis, and treatment of odontogenic infections. UpToDate. Retrieved August 20, 2021, from https://www.uptodate.com/contents/complications-diagnosis-and-treatment-of-odontogenic-infections
  3. Lodi, G. (2020). Oral lesions. UpToDate. Retrieved August 20, 2021, from https://www.uptodate.com/contents/oral-lesions

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