Dental Anatomy and Physiology

DENTAL ANATOMY & PHYSIOLOGY

•      Primary (deciduous)

•      Secondary (permanent)

A tooth is made up of three elements:

•      Water

•      Organic materials

•      Inorganic materials

•      Elements

Primary (deciduous)

•      Consist of 20 teeth

•      Begin to form during the first trimester of pregnancy

•  
    Typically begin erupting around 6 months

•      Most children have a complete primary dentition by 3 years
of age

Secondary (permanent)

•      Consist of 32 teeth in most cases

•      Begin to erupt around 6 years
of age

•      Most permanent teeth have erupted by age 12

•      Third molars (wisdom teeth) are the exception; often do not appear until late teens or
early 20s

•      Dentition (teeth): There are two dentitions

Classification of Teeth:

•      Incisors (central and lateral)

•      Canines (cuspids)

•      Premolars (bicuspids)

•      Molars

•      Incisors function as cutting or shearing instruments for food.

•      Canines possess the longest roots of all teeth and are located at the corners of the dental arch.

•      Premolars act like the canines in the tearing of food and are similar to molars in the grinding of food.

•      Molars are located nearest the temporomandibular joint (TMJ), which serves as the fulcrum during function.

•      Apical

•      Labial

•      Lingual

•      Distal

•      Mesial

•      Incisal

•      Apical: Pertaining to the apex or root of the tooth

•      Labial: Pertaining to the lip; describes the front surface of anterior teeth

•      Lingual: Pertaining to the tongue; describes the back (interior) surface of all teeth

•      Distal: The surface of the tooth that is away from the median line

•      Mesial: The surface of the tooth that is toward the median line

Dental Tissue

•      Enamel (hard tissue)

•      Dentin (hard tissue)

•      Odontoblast Layer

•      Pulp Chamber (soft tissue)

•      Gingiva (soft tissue)

•      Periodontal Ligament (soft tissue)

•      Cementum (hard tissue)

•      Alveolar Bone (hard tissue)

•      Pulp Canals

•      Apical Foramen

•      The Dental Tissues:

•      Anatomic Crown

•      Anatomic Root

•      Pulp Chamber

The 3 parts of a tooth:

•      The anatomic crown is the portion of the tooth covered by enamel.

•      The anatomic root is the lower two thirds of a tooth.

•      The pulp chamber houses the dental pulp, an organ of myelinated and unmyelinated nerves, arteries, veins, lymph channels, connective tissue cells, and various other cells.

•      The 4 main dental tissues:

•      Enamel

•      Dentin

•      Cementum

•      Dental Pulp

Structure

•      Highly calcified and hardest tissue in the body

•      Crystalline in nature

•      Enamel rods

•      Insensitive—no nerves

•      Acid-soluble—will demineralize at a pH of 5.5 and lower

•      Cannot be renewed

•      Darkens with age as enamel is lost

•      Fluoride and saliva can help with remineralization

•        Enamel can be lost by:^3,4

–      Physical mechanism

–     Abrasion (mechanical wear)

–     Attrition (tooth-to-tooth contact)

•        Abfraction (lesions)

–     Chemical dissolution

•       Erosion by extrinsic acids (from diet)

•       Erosion by intrinsic acids (from the oral          cavity/digestive tract)

•        Multifactorial etiology

–    Combination of physical and chemical      factors

Dentine

•      Softer than enamel

•      Susceptible to tooth wear (physical or chemical)

•      Does not have a nerve supply but can be sensitive

•      Is produced throughout life

•      Three classifications

•      Primary

•      Secondary

•      Tertiary

•      Will demineralize at a pH of 6.5 and lower

Three classifications:

•      Primary dentin forms the initial shape of the tooth.

•      Secondary dentin is deposited after the formation of the primary dentin on all internal aspects of the pulp cavity.

•      Tertiary dentin, or “reparative dentin” is formed by replacement odontoblasts in response to moderate-level irritants such as attrition, abrasion, erosion, trauma, moderate-rate dental caries, and some operative procedures.

•      Dentinal tubules connect the dentin and the pulp (innermost part of the tooth, circumscribed by the dentin and lined with a layer of odontoblast cells)

•      The tubules run parallel to each other in an S-shape course

•      Tubules contain fluid and nerve fibers

•      External stimuli cause movement of the dentinal fluid, a hydrodynamic movement, which can result in short, sharp pain episodes

•      Presence of tubules renders dentin permeable to fluoride

•      Number of tubules per unit area varies depending on the location because of the decreasing area of the dentin surfaces in the pulpal direction

Association between erosion and dentin hypersensitivity³

•         Open/patent tubules

          – Greater in number

          – Larger in diameter

•         Removal of smear layer

•         Erosion/tooth wear

•      Thin layer of mineralized tissue covering the dentin

Dental Tissue—Cementum

•      Softer than enamel and dentin

•      Anchors the tooth to the alveolar bone along with the periodontal ligament

•      Not sensitive

•      Innermost part of the tooth

•      A soft tissue rich with blood vessels and nerves

•      Responsible for nourishing the tooth

•      The pulp in the crown of the tooth is known as the coronal pulp

•      Pulp canals traverse the root of the tooth

•      Typically sensitive to extreme thermal stimulation (hot or cold)

 Dental Pulp

•        Pulpitis is inflammation or infection of the dental pulp, causing extreme sensitivity    and/or pain.

•        Pain is derived as a result of the hydrodynamic stimuli activating mechanoreceptors in the nerve fibers of the superficial pulp (A-beta, A-delta, C-fibers).

•        Hydrodynamic stimuli include: thermal (hot and cold); tactile; evaporative; and osmotic

•        These stimuli generate inward or outward movement of the fluid in the tubules and activate the nerve fibers.

•        A-beta and A-delta fibers are responsible for sharp pain of short duration

•        C-fibers are responsible for dull, throbbing pain of long duration

•        Pulpitis may be reversible (treated with restorative procedures) or irreversible (necessitating root canal).

•        Untreated pulpitis can lead to pulpal necrosis necessitating root canal or extraction.

Periodontal Tissues

•      Gingiva

•      Alveolar Bone

•      Periodontal Ligament

•      Cementum

•      Periodontal Tissues⁶

•      Gingiva: The part of the oral mucosa overlying the crowns of unerupted teeth
and encircling the necks of erupted teeth, serving as support structure for
subadjacent tissues.

•      Dental Tissue—Dental Tissue⁶

•      Alveolar Bone: Also called the “alveolar process”; the thickened ridge of bone
containing the tooth sockets in the mandible and maxilla.

•      Periodontal Ligament: Connects the cementum of the tooth root to the alveolar
bone of the socket.

•      Cementum: Bonelike, rigid connective tissue covering the root of a tooth from the cementoenamel junction to the apex and lining the apex of the root canal. It also serves as an attachment structure for the periodontal ligament, thus assisting in tooth support.

Oral Cavity and Enviroment

•      Plaque

•      Saliva

•      pH Values

•      Demineralization

•      Remineralization

Plaque:

•      is a biofilm

•      contains more than 600 different identified species of bacteria

•      there is harmless and harmful plaque

•      salivary pellicle allows the bacteria to adhere to the tooth surface, which begins the formation of plaque

Saliva:

•      complex mixture of fluids

•      performs protective functions:

–    lubrication—aids swallowing

–    mastication

–    key role in remineralization of enamel and dentin

–    buffering 

•      Oral Cavity

•      Dental Anatomy and Physiology

pH values:^7,8

•      measure of acidity or alkalinity of a solution                       

•      measured on a scale of 1-14   

•      pH of 7 indicated that the solution is neutral

•      pH of the mouth is close to neutral until other factors are introduced

•      pH is a factor in demineralization and remineralization

Demineralization:

•      mineral salts dissolve into the surrounding salivary fluid:    

–    enamel at approximate pH of 5.5 or lower

–    dentin at approximate pH of 6.5 or lower

•      erosion or caries can occur

Remineralization:

•      pH comes back to neutral (7)

•      saliva-rich calcium and phosphates

•      minerals penetrate the damaged enamel surface and repair it:

–    enamel pH is above 5.5

–    dentin pH is above 6.5