Summary of Oral Anatomy, Tooth Tissues, and Tooth Numbering Systems

Tooth Numbering Systems

  • Palmer Notation System (AKA: 8 Tooth Quadrant or Symbolic System)

    • 1861 — Developed by Adolph Zsigmondy.
    • Born in Hungary, practiced in Austria; 1870 — Corydon Palmer from Ohio, USA.
    • Palmer presented the Palmer Notation at an ADA meeting.
    • Zsigmondy’s name faded from the system; Grid sign named and added by Palmer.
    • 1947 — Roman numerals were replaced by an alphabetic/symbolic system by the ADA, which recommended the symbolic system especially for orthodontists, pedodontists, and dental schools.
    • Advantages:
    • System is easy to use; easier for beginners since permanent and deciduous teeth are indicated differently.
    • Disadvantages:
    • Does not show maxillary vs mandibular arch clearly; hard to input into computers because there is no grid; no provisions to identify supernumerary teeth; each segment has only one number for a specific tooth; difficult for verbal transmission.

  • Universal Notation System

    • Developed by Julius Parreidt (1882) and Cunningham (1883).
    • 1968 — Adopted by the ADA for USA and Canadian dentists.
    • Primarily used by orthodontists and pedodontists in the USA and Canada.
    • Advantages:
    • Separate number/alphabet for an individual tooth; easy to visualize and easy to communicate.
    • Disadvantages:
    • Can be confusing when comparing with Palmer Notation System; confusing with FDI and difficult to memorize; does not clearly indicate jaw quadrant, so similar teeth may have different numbers in different quadrants.

  • Fédération Dentaire Internationale (FDI) System — Also called Two-digit system, ISO-3950 notation

    • 1966 — Developed by the Berlin dentist Dr. Jochen Viohl.
    • First digit indicates the quadrant and whether the tooth is permanent or primary: 1–4 for permanent dentition, 5–8 for primary dentition.
    • Second digit indicates the tooth within the quadrant: 1–8 for permanent teeth, 1–5 for primary teeth.
    • 1970 — Accepted by FDI and adopted by WHO and IADR.
    • Advantages:
    • Very simple, accurate, and easy to memorize; user-friendly; prevents errors in differentiating left/right, upper/lower arches, and tooth type; easy to translate into computer input; simple in conversation and print.
    • Disadvantages:
    • In deciduous teeth, some confusion and memorization can be challenging; for specialists other than pedodontists it can be difficult to understand; somewhat long to enter multiple teeth in different arches for routine use.
    • Note: Also referred to as ISO-3950 notation.

  • Victor Haderup System

    • European (Denmark) system.
    • Identifies teeth by using a number for each permanent tooth and a + or - sign to indicate the position of each tooth.
    • Advantages:
    • Computer-friendly; easy to understand.
    • Disadvantages:
    • Can be very confusing for recording mixed dentitions; difficult to dictate, making routine use impractical.

The Crown and Root

  • Clinical Crown
    • Portion of the tooth visible in the mouth.
    • May or may not correspond to the anatomical crown depending on the level of soft tissue; may include part of the anatomical root.
  • Anatomical Crown
    • Portion of the tooth covered by enamel.
  • Clinical Root
    • Portion of the tooth not visible in the mouth.
    • A clinical root is an ever-changing entity and may or may not correspond to the anatomical root.
    • If a root becomes visible, that portion becomes part of the clinical crown (since there is no cementum in that exposed area).
  • Anatomical Root
    • Portion of the tooth covered by cementum.
    • Anything covered by the gum is still considered part of the clinical root.

Other Terminologies

  • Cervical line (Neck)
    • Thin line that separates the anatomical crown and root, aka the cemento-enamel junction (CEJ).
    • Divides the crown and root; a constant anatomical boundary.
  • Root trunk
    • Part of the root from the cervical line to the furcation area of multirooted teeth (posterior teeth only).
  • Furcation
    • Junction of roots in multirooted teeth (posterior).
    • Plural: Furca.
    • Root type distinctions:
    • Monorooted: Incisors, Canines, premolars (except maxillary first premolar).
    • Bifurcation: Mandibular molars & maxillary first premolar.
    • Trifurcation: Maxillary molars.
  • Apex
    • Tapered end of the root tip.
  • Apical Foramen
    • Opening between the periodontal membrane and the pulp; usually present at the root apex.
    • Nerves and nutrients exit/enter here.

Pulp and Pulp Anatomy

  • Pulp

    • Living soft tissue occupying the pulp cavity of a vital tooth; contains nerves, blood vessels, lymphatics.
    • Located in the pulp cavity, which occupies the central portion of the tooth.
    • Divided into two parts:
    • Coronal pulp: in the crown portion.
    • Radicular (root) pulp: canals extending from the cervical region of the crown to the root apex.

  • Pulp Cavity components

    • Pulp canal/root canal: located in the root.
    • Pulp chamber: enlarged portion of the pulp cavity in the crown.
    • Pulp horns/cornu: pointed extensions usually corresponding to cusps; often open to cusps.
    • Accessory nerves/canals: additional nerve canals that may exist within the roots.

  • Dentin (Substantia Eburnuea)

    • Forms the major portion of the tooth; provides shape and support after enamel.
    • Lies beneath enamel in the crown and cementum in the root; surrounds the pulp.
    • Reacts to physiological and pathological changes and stimuli.
    • Dentin physiology: when enamel is intact, dentin is not easily felt; dentin sensation occurs when stimuli reach odontoblastic processes to the pulp.

  • Characteristics of Dentin

    • Main functions: covers the pulp; helps shape the tooth; contains dentinal tubules.
    • Location: beneath enamel (crown) and cementum (root).
    • Hardness: less hard than enamel; harder than bone and cementum.
    • Color: permanent dentin is yellow; deciduous dentin is light-yellow.
    • Transparency: semi-transparent.
    • Permeability: permeable due to dentinal tubules.
    • Elasticity: very high but less radiopaque than enamel due to lower mineralization.
    • Consistency: higher organic content than enamel (roughly 65% inorganic, 35% organic).
    • Dentinal tubules: provide high permeability; contain odontoblastic processes.
    • Enamel has no cells; dentin has odontoblastic cells.
    • Odontoblastic activity allows transmission of stimuli to the pulp when dentin is affected.

  • Peritubular dentin

    • Dentin that immediately surrounds the dentinal tubules.

Cementum

  • Cementum (Substantia Ossea)
    • Covers the root of the tooth; extends from the CEJ to the apical foramen.
    • CEJ provides attachment to the periodontal ligament, connecting the tooth to the alveolar bone.
    • Alveolar proper: periodontal ligament anchors the tooth to bone.
  • Characteristics of Cementum
    • Thickness: thickest at the apical foramen and near furcation areas.
    • Permeability: permeable to various substances.
    • Calcification: calcified but less hard and less calcified than dentin.
    • Weight: lighter than dentin.
    • Color: light yellow.
    • Development origin: derives from the dental sac; embryologic layers include Endoderm, Mesoderm, and Ectoderm (the dental sac belongs to these layers).
    • Composition: approximately 45–50% inorganic (hydroxyapatite) and 50–55% organic (type I collagen, proteins, polysaccharides).
  • Types of cementum
    • Acellular cementum: thinner; covers cervical (coronal) root.
    • Cellular cementum: thicker; covers the apical root and contains cells.
  • Locations
    • Radicular cementum: cementum on the root surface up to the apex.
    • Coronal cementum: near the cervical line (in the coronal region).

DEJ, CEJ, and Pulp Relationships

  • Dentinoenamel Junction (DEJ)
    • Internal line where dentin meets enamel in the anatomical crown of a tooth.
    • The boundary between enamel and dentin; crucial for cavity progression risk near this junction.
  • Cementoenamel Junction (CEJ)
    • A junction where cementum meets enamel; several possible relationships:
    • Cementum overlapping enamel.
    • End-to-end approximation of enamel and cementum.
    • Gap between enamel and cementum (absence of connection).
    • Enamel overlapping the cementum.
    • The CEJ is the anatomical boundary for attachment to the periodontal apparatus.
  • Alveolar process (alveolar bone) and supporting structures
    • Alveolar process: the bony structure surrounding and supporting all teeth in each jaw.
    • Alveolus: the bony socket that houses an individual tooth.
    • Periodontal ligament: fibrous connective tissue that attaches cementum to the alveolar bone.
    • Gingiva (gums): fibrous tissue covered by mucous membrane that surrounds the necks of the teeth and covers the alveolar processes.

Summary of Key Points and Concepts

  • Multiple tooth numbering systems exist to record data and communicate, each with distinct advantages and trade-offs.
  • The crown/root terminology differentiates visible vs. hidden tooth portions and their coverings (enamel for crown, cementum for root).
  • The CEJ and DEJ define critical junctions between tooth tissues relevant to caries risk and periodontal attachment.
  • The dental tissues—enamel, dentin, cementum, and pulp—have distinct compositions, properties, and roles in tooth vitality and response to stimuli.
  • The alveolar process, periodontal ligament, and gingiva constitute the supporting apparatus that anchors teeth in the jaw and protect surrounding structures.

Notable numerical references and formulas

  • Enamel hardness: 5 ext{ to } 8 ext{ Mohs}

  • Enamel thickness examples: 2 ext{–}3 ext{ mm} (incisors incisal edges); 3 ext{–}4 ext{ mm} (cusps)

  • Enamel composition: 96 ext{ ext{% inorganic}} ext{, } 4 ext{ ext{% organic and water}}

  • Dentin composition: 65 ext{ ext{% inorganic}} ext{, } 35 ext{ ext{% organic}}

  • Cementum composition: 45 ext{ ext% to } 50 ext{ ext{% inorganic}} ext{, } 50 ext{ ext{% to } 55 ext{ ext{% organic}}}

  • Embryology (dental sac derivatives): three germ layers: ext{Endoderm}, ext{Mesoderm}, ext{Ectoderm}

  • Abbreviations to remember:

    • CEJ = Cementoenamel Junction
    • DEJ = Dentinoenamel Junction
    • Pulp canal/root canal, Pulp chamber, Pulp horns/cornu
    • Alveolus = bony socket
    • Furcation = junction of roots in multirooted teeth
    • Monorooted, Bifurcation, Trifurcation

Connections to broader concepts

  • Clinical relevance: proximity of cavity preparation to the DEJ and CEJ influences caries risk, sensitivity, and periodontal health.
  • Diagnostic and treatment planning implications: the numbering system used affects record-keeping, communication with specialists, and charting efficiency; the FDI system is often favored for its clarity across arches and dentitions.
  • Biological relevance: dentin's tubules and odontoblastic cells explain dentinal sensitivity and reparative dentin formation in response to caries or trauma.
  • Embryology linkage: cementum and periodontal ligament development ties to the dental sac and three germ layers, underscoring the tissue origins of supporting structures.

Ethical and practical implications

  • Accurate tooth numbering and anatomy knowledge are essential for patient safety, treatment planning, informed consent, and interprofessional communication.
  • Choosing a numbering system may depend on clinical setting, interprofessional collaboration, and technology compatibility (e.g., electronic records and software).