Oral Anatomy and Physiology I - Week 1: Terminology and the Dentitions

Anatomic Position

  • The nomenclature (terminology) of anatomy is based on the body being in anatomic position.

    • Anatomic Position Description:

    • The body is standing erect.

    • Arms are positioned at the sides.

    • Palms are directed forward.

    • Toes are pointed forward.

    • Eyes are looking forward.

  • This position is assumed even when the body may be supine (on the back) or upright when sitting in a dental chair.

Terminology

  • Anterior/Ventral: Towards the front.

  • Posterior/Dorsal: Towards the back.

  • Superior: Towards the head.

  • Inferior: Towards the feet.

  • Apex (plural, apices): Pointed end of a conical structure such as the apex or tip of the tongue.

Anatomic Planes

  • Midsagittal Plane (Median Plane): Divides the body into equal right and left halves.

  • Sagittal Plane: Divides the body parallel to the midsagittal plane.

  • Coronal Plane (Frontal Plane): Divides the body into anterior and posterior parts.

  • Transverse Plane (Axial Plane): Divides the body at any level horizontally into superior and inferior parts.

    • Always perpendicular to the midsagittal plane.

Additional Terminology

  • Median: At the midsagittal plane.

  • Medial: Closer to the midsagittal plane; also referred to as mesial within the dentition.

  • Lateral: Farther from the midsagittal plane; also referred to as distal within the dentition.

Ipsilateral and Contralateral Terminology

  • Ipsilateral: Structures on the same side of the body.

  • Contralateral: Structures on the opposite side of the body.

  • Superficial: Structures located toward the surface of the body.

  • Deep: Structures located inward toward the center of the body.

Overview of Dentitions

  • The dentition refers to the natural teeth in the jaws.

  • A person has two dentitions during a lifetime: primary and permanent.

    • Primary Dentition:

    • First dentition present.

    • Composed of primary teeth/baby teeth/deciduous teeth.

    • Primary teeth are completely replaced by the permanent dentition.

    • Permanent Dentition:

    • The second dentition composed of adult teeth.

Tooth Types in Dentition

  • Primary Dentition Tooth Types (both maxillary: top and mandibular: bottom):

    • 8 incisors

    • 4 canines

    • 8 molars

    • Total: 20 teeth

    • Note: No premolars in the primary dentition.

  • Permanent Dentition Tooth Types (both arches):

    • 8 incisors

    • 4 canines

    • 8 premolars

    • 12 molars

    • Total: 32 teeth

Universal Numbering System (UNS)

  • Most commonly used in the United States for tooth designation because it is adaptable to electronic data.

  • Primary Teeth:

    • Designated using consecutive arrangement of capital letters (A through T).

    • Starts with the maxillary right second molar, moving clockwise, ending with the mandibular right second molar.

  • Permanent Teeth:

    • Designated using consecutive arrangement of digits (1 through 32).

    • Starts with the maxillary right third molar, moving clockwise, and ending with the mandibular right third molar.

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

International Numbering System (INS)

  • Also known as the International Designation System.

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

  • Recognized internationally and by electronic data transfer.

  • Two-digit code:

    • The first digit indicates the quadrant:

    • Permanent dentition: Digits 1 through 4 are used in clockwise manner.

    • Primary dentition: Digits 5 through 8 are used in clockwise.

    • The second digit indicates the tooth’s position in the quadrant:

    • Permanent teeth: Digits 1 through 8 starting at the midline and numbering distally.

    • Primary dentition: Digits 1 through 5 starting at the midline and numbering distally.

  • Example: Permanent maxillary right central incisor referred to as "number one–one."

Palmer Notation Method

  • Commonly used in orthodontics, also known as the Military Numbering System.

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

    • Primary Dentition: Uses capital letters A through E, starting at midline and moving distally.

    • Permanent Dentition: Uses digits 1 through 8, starting at midline and moving distally.

Dentition Periods

  • There are three dentition periods throughout a person's life:

    • Primary Dentition Period:

    • Approximate time span: ~6 months to ~6 years.

    • Teeth marking start of period: Eruption of primary mandibular central incisor.

    • Dentition Present: Primary.

    • Mixed Dentition Period:

    • Approximate time span: ~6 years to 12 years.

    • Teeth marking start of period: Eruption of permanent mandibular first molar.

    • Permanent Dentition Period:

    • After 12 years.

    • Shedding of the last primary tooth typically indicates the beginning.

Primary Dentition Details

  • Begins with eruption of primary mandibular central incisors (approx. 6 months to 6 years).

  • Only primary teeth present, with full eruption completed by 30 months.

  • Jaw growth begins to accommodate larger permanent teeth.

  • Ends with the eruption of permanent mandibular first molar.

Mixed Dentition Details

  • Begins with eruption of the first permanent tooth (usually permanent mandibular first molar).

  • Occurs approximately between 6 and 12 years of age.

  • Exfoliation of primary teeth coincides with the eruption of permanent teeth.

  • Primary teeth are typically whiter, while permanent teeth are more yellow, with smaller crowns and shorter roots for primary teeth.

  • Fastest growth of the jaws occurs during this period and ends with the exfoliation of the last primary tooth.

Permanent Dentition Details

  • Final dentition period begins with shedding of last primary tooth.

  • Occurs after 12 years of age, with eruption of remaining permanent teeth.

General Dental Terms

  • Alveolus (plural, alveoli): The bone of the tooth socket surrounding and supporting each tooth.

  • Alveolar Process: The tooth-bearing part of each jaw, also considered as the dental arch.

    • Maxillary teeth are those in the maxilla, and mandibular teeth are those in the mandible.

  • Occlusion: The method by which the teeth of the mandibular arch contact those of the maxillary arch; also describes the anatomic alignment of teeth.

  • Midline: An imaginary vertical plane dividing each dental arch into equal halves (right and left).

    • Similar to the midsagittal or median plane of the body, significant in evaluating a patient’s smile.

Quadrants in Dentition

  • The dental arch can be divided into four quadrants in total:

    • Maxillary Right (Quadrant 1)

    • Maxillary Left (Quadrant 2)

    • Mandibular Left (Quadrant 3)

    • Mandibular Right (Quadrant 4)

Describing Tooth Location

  • The D-A-Q-T System is used to describe an individual tooth based on quadrants:

    • D for dentition, A for arch, Q for quadrant, T for tooth type.

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

Sextants in Dentition

  • Each dental arch can be divided into three parts based on midline relationship:

    • Right Posterior Sextant

    • Anterior Sextant

    • Left Posterior Sextant

  • Total of six sextants:

    • Maxillary Right Posterior (Sextant 1)

    • Maxillary Anterior (Sextant 2)

    • Maxillary Left Posterior (Sextant 3)

    • Mandibular Left Posterior (Sextant 4)

    • Mandibular Anterior (Sextant 5)

    • Mandibular Right Posterior (Sextant 6)

Tooth Anatomy Terms

  • Each tooth consists of a crown and one or more roots:

    • The crown has dentin covered by enamel.

    • Each root has dentin covered by cementum.

    • Pulp Cavity: Located in the center of the tooth; contains:

    • Pulp Chamber: Area containing nerves and blood vessels.

    • Pulp Canal: Connects to the apical foramen.

    • Possible Pulp Horns: Extensions of pulp found within the crown.

  • The enamel and cementum meet at the Cementoenamel Junction (CEJ).

Anatomic and Clinical Crown

  • Anatomic Crown: The part of the crown covered by enamel; remains mostly constant throughout the tooth's life except due to attrition.

  • Clinical Crown: The part of the anatomic crown visible and not covered by the gingiva; height determined by the location of marginal gingiva and can change over time with gingival recession.

  • Anatomic Root: The part of the root covered by cementum;

  • Clinical Root: The visible portion of the anatomic root, which can change overtime, related to gingival recession.

Root Anatomy

  • All roots are widest at the CEJ and taper toward the apex.

  • Three basic shapes of roots on cervical cross section: triangular, oval, or elliptical.

  • Roots may have depressions, or root concavities, commonly occurring on:

    • Proximal root surfaces of anterior and posterior teeth.

    • Buccal and lingual surfaces of molars.

  • The area between two or more roots is known as a furcation.

Orientational Tooth Terms

  • Each tooth has five surfaces:

    • Facial: Closest to the surface of the face.

    • Labial: Facial surface closest to the lips.

    • Buccal: Facial surface closest to the inner cheek.

    • Lingual: Closest to the tongue.

    • Palatal: Lingual surface closest to the palate on maxillary arch.

    • Masticatory Surface: Chewing surface on the most superior surface of the crown; specific to:

    • Incisal surface for anterior teeth.

    • Occlusal surface for posterior teeth.

    • Mesial: Surface closest to the midline.

    • Distal: Surface farthest from the midline.

Additional Orientational Tooth Terms

  • Proximal: Mesial and distal surfaces between adjacent teeth.

  • Interproximal Space: Area between adjacent tooth surfaces.

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

    • Checked when dental floss is passed between two teeth with resistance felt.

    • Proper contact relation prevents food impaction and stabilizes dental arches.

Height of Contour

  • Refers to the greatest elevation of the tooth either incisocervically or occlusocervically on a specific surface of the crown when viewed from the labial or buccal and the lingual.

  • Typically, the contact area on mesial and distal surfaces also serves as the height of contour when viewed from the proximal aspects.

Embrasure

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

    • Directs food away from gingiva.

    • Provides mechanism for teeth to be more self-cleansing.

    • Protects gingiva from frictional trauma.

Line Angle

  • Formed by the lines created at the junction of two crown surfaces; the name is derived by combining the names of the two surfaces.

    • Example: Combining mesial and labial = mesiolabial.

Point Angle

  • Junction of three surfaces of the crown, named from those three surfaces.

    • Example: Combining mesial, labial, and incisal = mesiolabioincisal.

Tooth Divided into Thirds

  • A crown surface can be divided both horizontally and vertically into three parts, or thirds.

Tooth Form and Function

  • Each tooth type has a specific form that relates to its function during mastication as well as its role in speech and aesthetics.

  • Tooth Functions:

    • Incisors: Biting and cutting.

    • Canines: Piercing or tearing.

    • Premolars: Assist canines with piercing and tearing and molars with grinding.

    • Molars: Grinding.

  • Tooth forms follow a rough outline of specific geometric shapes depending on type.