Overview of Dentitions

Dentitions

• The term "dentition" describes the natural teeth in the jaws.

• Humans have two dentitions in a lifetime:

  • Primary dentition

  • Permanent dentition

Tooth Types

• Primary Dentition:

  • Includes 8 incisors, 4 canines, and 8 molars.

  • Total of 20 teeth.

• Permanent Dentition:

  • Includes 8 incisors, 4 canines, 8 premolars, and 12 molars.

  • Total of 32 teeth.

Tooth Designation

• Universal Numbering System (UNS):

  • Most widely used in the United States.

  • Adaptable to electronic data.

  • Primary teeth are designated A through T (clockwise, starting with the maxillary right second molar).

  • Permanent teeth are designated 1 through 32 (clockwise, starting with the maxillary right third molar).

  • Example: Permanent maxillary right central incisor is "number eight."

• International Numbering System (INS) / International Designation System:

  • Accepted by the International Standards Organization (ISO) and the World Health Organization (WHO).

  • Based on the system of the Fédération Dentaire Internationale (FDI).

  • Uses a two-digit code.

    • First digit indicates the quadrant.

    • Second digit indicates the tooth’s position in the quadrant.

    • Permanent dentition quadrants: 1-4 (clockwise).

    • Primary dentition quadrants: 5-8 (clockwise).

    • Tooth positions: 1-8 for permanent teeth, 1-5 for primary teeth (starting at the midline).

  • Example: Permanent maxillary right central incisor is "number one-one."

• Palmer Notation Method / Military Tooth Numbering System:

  • Commonly used in orthodontics.

  • Uses a right-angle symbol to indicate the quadrant and arch, with the tooth number inside.

Dentition Periods

• Three periods due to overlap:

  • Primary

  • Mixed

  • Permanent

• Each patient should be assigned a dentition period for effective treatment.

Primary Dentition Period

• Begins with the eruption of the primary mandibular central incisors.

• Occurs approximately between 6 months and 6 years of age.

• Only primary teeth are present.

• Full eruption completed at 30 months, usually when the primary second molars are in occlusion.

Mixed Dentition Period

• Follows the primary dentition period.

• Occurs approximately between 6 and 12 years of age.

• Both primary and permanent teeth are present.

• Shedding of primary teeth and eruption of permanent teeth begin after crowns are completed.

Clinical Considerations

• Considered an "ugly duckling stage" due to:

  • Different tooth colors

  • Disproportionately sized teeth

  • Various clinical crown heights

• Temporary edentulous areas and crowding are present.

• Gingiva may become inflamed due to changes and hormonal fluctuations.

• Early aggressive periodontitis (previously juvenile periodontitis) may be suspected if:

  • Slight gingival inflammation with little dental biofilm.

  • Severe bone loss around newly erupted permanent first molars and mandibular anteriors.

Permanent Dentition Period

• Final dentition period.

• Begins with the shedding of the last primary tooth.

• Usually begins just after 12 years of age.

• Includes eruption of all permanent teeth, except congenitally missing or impacted teeth (usually third molars).

General Dental Terms

• Alveolus: Tooth socket.

• Alveolar Process: Tooth-bearing part of each jaw.

• Dental Arch: Alveolar process of the jaws (maxillary or mandibular).

• Maxillary Teeth: Teeth in the maxilla.

• Mandibular Teeth: Teeth in the mandible.

• Occlusion: Contact between teeth of the mandibular arch and maxillary arch.

• Midline: Imaginary vertical plane dividing each dental arch into two equal halves.

• Anterior Teeth: Incisors and canines (closer to the midline).

• Posterior Teeth: Molars (and premolars) (farther from the midline).

• Quadrant: Division of each dental arch into two quadrants, resulting in four quadrants in the entire oral cavity.

• D-A-Q-T System: Method for describing an individual tooth.

  • D: Dentition

  • A: Arch

  • Q: Quadrant

  • T: Tooth Type

  • Example: permanent (D) mandibular (A) left (Q) first premolar (T).

• Sextants: Further division of each dental arch into three parts:

  • Right posterior sextant

  • Anterior sextant

  • Left posterior sextant

Tooth Designation (ISO)

• To prevent miscommunication globally, the ISO (International Organization for Standardization) also includes designation of areas in the oral cavity, with each area designated by a two-digit number, where at least one of the digits is zero.

Tooth Anatomy Terms

• Crown: Covered by enamel.

• Root: Covered by cementum.

• Dentin: Inner part of both crown & root; covers the pulp cavity.

• Pulp Cavity: Contains:

  • Pulp chamber

  • Pulp canal(s) with apical foramen(ina)

  • Pulp horn(s)

• Anatomic Crown: Part covered by enamel; remains constant, except for attrition.

• Clinical Crown: Part of the anatomic crown that is visible and not covered by the gingiva; its height is determined by the location of the marginal gingiva.

• Anatomic Root: Part of the root covered by cementum.

• Clinical Root: Part of the anatomic root that is visible, subject to variability over time related to gingival recession.

• Root Axis Line (RAL): Imaginary line representing the long axis of a tooth, bisecting the root and crown in the cervical area.

Root Traits

• Widest at the CEJ and tapers toward the apex.

• More bulk on the facial surface than on the lingual surface.

• Tapers more dramatically on the lingual surface.

• Root Concavities: Depressions on the root surfaces, commonly on the proximal surfaces of anteriors and posteriors, and buccal/lingual surfaces of molars.

• Furcation: Area between two or more roots.

Root Concavities Example

• In maxillary first molars sectioned $2 ewline mm$ apical to the furca:

  • Concavities present in:

    • $94\%$ of MB (mesiobuccal) roots

    • $31\%$ of DB (distobuccal) roots

    • $17\%$ of P (palatal) roots

  • Deepest concavity is in the furcal aspects of the MB root (mean $0.3 \newline mm$).

  • Furcal aspect of the buccal roots diverges toward the palate in $97\%$ of teeth (mean $22$ degrees).

Clinical Considerations with Tooth Anatomy: Restorations

• Full Artificial Crowns (Caps): Cover the entire anatomic crown area.

• Post and Core: May be placed within the crown and root to help with the buildup of restorative materials.

• Crown Lengthening: Surgical periodontal procedure to increase the amount of the clinical crown and reduce surrounding gingival tissue by removal.

Biologic Width

• Distance established by the junctional epithelium and connective tissue attachment to the root surface.

• Important for dental restorations to respect the natural architecture of gingival attachment.

Assessment

• Measure the distance between the bone and the restoration margin using a periodontal probe after pushing it through the anesthetized attached gingiva into underlying bone.

• If the distance is less than $2 \newline mm$ at one or more locations, a diagnosis of biologic width violation can be confirmed.

Crown-to-Root Ratio

• Disproportionate crown-to-root ratio and reduced root surface can make the periodontium more susceptible to injury by occlusal forces.

Root Anatomy

• Increased emphasis on detailed knowledge of root anatomy due to:

  • Importance of precise periodontal root instrumentation.

  • Preserving the crown of the teeth by restorations.

Root Concavities

• Should be carefully explored during instrumentation appointments and charted.

• Can be exposed by periodontal disease but hidden under a periodontal pocket.

• Complicates periodontal or endodontic instrumentation and homecare.

• Daily homecare of concave/irregular proximal surfaces is important.

• Interdental brush may be more effective than dental floss on long root surfaces with concavities.

Orientational Tooth Terms

• Five surfaces: facial, lingual, masticatory, mesial, and distal.

• Facial: Surface closest to the face.

  • Labial: Facial surface closest to the lips.

  • Buccal: Facial surface closest to the inner cheek.

• Lingual: Surface closest to the tongue; palatal on the maxillary arch.

• Masticatory: Chewing surface.

  • Incisal: For anterior teeth.

  • Occlusal: For posterior teeth.

• Mesial: Surface closest to the midline.

• Distal: Surface farthest away from the midline.

• Proximal: Mesial and distal surfaces between adjacent teeth.

• Interproximal Space: Area between adjacent tooth surfaces.

CEJ Curvature

• Greatest on anterior teeth and least on posterior teeth.

• Approximately similar on mesial and distal surfaces of adjacent teeth.

• Greater on the mesial aspect of a tooth than on the distal aspect.

Contact Area/Contact

• Area where crowns of adjacent teeth physically touch on each proximal surface.

• Usually the location of the height of contour on the proximal surfaces.

Height of Contour / Crest of Curvature

• Greatest elevation of the tooth incisocervically or occlusocervically on a specific surface.

• Facial and lingual surfaces also have a height of contour.

Embrasures

• Triangular-shaped spaces between two teeth, created by sloping away of mesial and distal surfaces.

• Diverge facially, lingually, occlusally, or apically.

Line Angle

• Formed by the junction of two crown surfaces.

• Name is derived by combining the names of those two surfaces.

Point Angle

• Junction of three surfaces of the crown, taking its name from those three surfaces.

Thirds

• Crown surface can be divided horizontally and vertically into three parts or thirds.

Clinical Considerations for Tooth Surfaces

• Tooth's angles, height of contour, and spaces define the aesthetics of a smile.

• Altering placement and shape of these features changes the tooth's appearance.

• Ideally, the mesial part of the face and silhouette of a tooth is more angled vertically than the distal part.

Tooth Form

• Each tooth type has specific form related to its function during mastication, speech, and esthetics.

• Form and function are similar for both primary and permanent dentitions.

• Tooth forms of the crown roughly follow specific geometric shapes.

Incisors and Canine

• Incisors function in biting and cutting (triangular proximal form).

• Canines function to pierce or tear food (tapered shape and prominent cusp).

Premolars

• Only in permanent dentition.

• Assist canines in piercing and tearing (prominent cusps).

• Assist molars in grinding (wide occlusal surface).

Molars

• Largest and strongest crowns.

• Function in grinding food (wide occlusal surface and prominent cusps).

Clinical Considerations for Tooth Form: Variation

• Variation of teeth within a particular tooth type is common.

• Individual tooth form and function can be lost due to attrition, caries, trauma, extraction, or shedding.

• Lost functional tooth form can be approximated by restorative treatment:

  • Artificial crowns

  • Replacement bridges

  • Partial or complete dentures

  • Implants

• Extracoronal restorations are used for teeth with extensive damage that cannot be managed with intracoronal restorations.

Considerations for Dental Anatomy Study

• Values are mean values of ideal teeth; real teeth vary in size, and do not always reflect proportionate jaw size.

• Descriptions are of ideal teeth.