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Teeth: Anatomy

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.

Last updated: Aug 15, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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 Aggregation The attachment of platelets to one another. This clumping together can be induced by a number of agents (e.g., thrombin; collagen) and is part of the mechanism leading to the formation of a thrombus. Coagulation Studies → each tooth bud is created
    • The tooth bud moves into underlying mesoderm Mesoderm The middle germ layer of an embryo derived from three paired mesenchymal aggregates along the neural tube. Gastrulation and Neurulation 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 Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology
    • 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 Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology.
    • Differentiation of mesenchymal cells in the dental papilla creates odontoblasts.
    • Odontoblasts produce predentin, which will become dentin.
    • Inner enamel epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology 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 Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types)
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

Gross Anatomy

Location

  • Teeth are within the oral cavity, which is an anatomic space that forms the outer limit Limit A value (e.g., pressure or time) that should not be exceeded and which is specified by the operator to protect the lung Invasive Mechanical Ventilation of the alimentary canal.
  • Specifically located in the alveolar processes of the mandible Mandible The largest and strongest bone of the face constituting the lower jaw. It supports the lower teeth. Jaw and Temporomandibular Joint: Anatomy and maxilla Maxilla One of a pair of irregularly shaped bones that form the upper jaw. A maxillary bone provides tooth sockets for the superior teeth, forms part of the orbit, and contains the maxillary sinus. Skull: Anatomy
  • Held in position by the periodontal ligament
Human mandible left

Mandible Mandible The largest and strongest bone of the face constituting the lower jaw. It supports the lower teeth. Jaw and Temporomandibular Joint: Anatomy with teeth in place within the alveolar processes

Image: “Human mandible Mandible The largest and strongest bone of the face constituting the lower jaw. It supports the lower teeth. Jaw and Temporomandibular Joint: Anatomy 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 Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess 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 Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology
    • Posterior superior alveolar arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology
  • Mandibular jawline: inferior alveolar arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology
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.

Microscopic Anatomy

Each tooth comprises 4 components:

  • Enamel (enamelum): 
    • Most superficial layer of the tooth
    • Light yellow to grayish white
    • Composed of calcium Calcium A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes. Electrolytes hydroxyapatite crystals Hydroxyapatite crystals A group of compounds with the general formula m10(PO4)6(OH)2, where m is barium, strontium, or calcium. The compounds are the principal mineral in phosphorite deposits, biological tissue, human bones, and teeth. They are also used as an anticaking agent and polymer catalysts. Calcium Hemostasis and Bone Metabolism (98%)
    • Originates from ameloblastin (secreted by ameloblasts)
  • Dentin (dentinum): 
    • Extension Extension Examination of the Upper Limbs of the enamel within the jaw Jaw The jaw is made up of the mandible, which comprises the lower jaw, and the maxilla, which comprises the upper jaw. The mandible articulates with the temporal bone via the temporomandibular joint (TMJ). The 4 muscles of mastication produce the movements of the TMJ to ensure the efficient chewing of food. Jaw and Temporomandibular Joint: Anatomy 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 Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue: Histology
    • Contains:
      • Blood vessels
      • Nerves
      • Fibroblasts Fibroblasts Connective tissue cells which secrete an extracellular matrix rich in collagen and other macromolecules. Sarcoidosis and pre-odontoblasts
      • Macrophages Macrophages The relatively long-lived phagocytic cell of mammalian tissues that are derived from blood monocytes. Main types are peritoneal macrophages; alveolar macrophages; histiocytes; kupffer cells of the liver; and osteoclasts. They may further differentiate within chronic inflammatory lesions to epithelioid cells or may fuse to form foreign body giant cells or langhans giant cells. Innate Immunity: Phagocytes and Antigen Presentation and T lymphocytes Lymphocytes Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. Lymphocytes: Histology
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 Acids Chemical compounds which yield hydrogen ions or protons when dissolved in water, whose hydrogen can be replaced by metals or basic radicals, or which react with bases to form salts and water (neutralization). An extension of the term includes substances dissolved in media other than water. Acid-Base Balance generated by bacterial plaque Plaque Primary Skin Lesions. These cavities are associated with the intake of excessive sugars and acids Acids Chemical compounds which yield hydrogen ions or protons when dissolved in water, whose hydrogen can be replaced by metals or basic radicals, or which react with bases to form salts and water (neutralization). An extension of the term includes substances dissolved in media other than water. Acid-Base Balance contained in certain beverages and foods. Treatment consists of the elimination Elimination The initial damage and destruction of tumor cells by innate and adaptive immunity. Completion of the phase means no cancer growth. Cancer Immunotherapy of the infectious agent and restoration or rehabilitation of the tooth.
  • Ameloblastoma: benign Benign Fibroadenoma tumor Tumor Inflammation typically arising from the mandible Mandible The largest and strongest bone of the face constituting the lower jaw. It supports the lower teeth. Jaw and Temporomandibular Joint: Anatomy and much less commonly from the maxilla Maxilla One of a pair of irregularly shaped bones that form the upper jaw. A maxillary bone provides tooth sockets for the superior teeth, forms part of the orbit, and contains the maxillary sinus. Skull: Anatomy. Ameloblastomas are slow-growing, painless lesions that normally appear near the angle of the mandible Mandible The largest and strongest bone of the face constituting the lower jaw. It supports the lower teeth. Jaw and Temporomandibular Joint: Anatomy 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 Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types, 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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