Review of Dentinogenesis

• Outer cells of the dental papilla are induced by preameloblasts to differentiate into odontoblasts
• Odontoblasts lay down predentin, which becomes the dentin matrix
• Odontoblasts move away from the DEJ, depositing dentin and becoming trapped in dentinal tubules
• Dentinogenesis occurs throughout the life of the tooth

Dentin Properties

• Dentin is avascular
• Dentin consists of fluid-filled tubules
• Tubules contain odontoblastic processes and myelinated afferent axons
• Enamel covers the crown and cementum covers root surfaces
• Mature dentin is composed mainly of calcium hydroxyapatite

Enamel vs. Dentin Composition

• Enamel consists of 96% inorganic material, 1% organic material, and 3% water
• Dentin consists of 70% inorganic material, 20% organic material, and 10% water

Dentin Matrix Formation

• A long cytoplasmic process of the odontoblast stays behind in each dentinal tubule as dentin forms
• Maturation of dentin, also known as mineralization of predentin, happens shortly after appositional growth

Dentin Maturation

• This process has two phases: primary and secondary mineralization
• Primary mineralization becomes interglobular dentin, which is less mineralized
  • This is commonly found in coronal dentin, near the DEJ, and in anomalies like dentin dysplasia
• Secondary mineralization creates globular dentin, which is more mineralized
• Calcium hydroxyapatite crystals initially form as globules, also called calcospherules in collagen fibers of predentin
• Expansion and fusion of globules occurs
• The process is similar to watercolor paint blobs running together
• Secondary mineralization occurs in new areas as globules form
• New areas of crystal formation layer on initial crystals and fuse
• Analogous to additional blobs of paint over a fuzzy painted background

Dentinal Tubules

• The basic structure of dentin is made up of dentinal tubules containing odontoblastic processes and fluid
• Primary curvature reflects the overall tubule path over time, resembling a large S-shape
• Secondary curvature consists of small, delicate curves showing daily odontoblast direction changes during apposition

Dentin Types

• Dentin is not uniform, instead varying from region to region
• Dentin types can be designated based on relationships to dentinal tubules, the DEJ and pulp, or time of formation

Dentin Types: Relationship to Dentinal Tubules

• Peritubular
  • Dentin that creates the wall of a dentinal tubule
  • Highly mineralized following dentin maturation
• Intertubular
  • Dentin that is found between the tubules
  • Highly mineralized, but not to the extent of peritubular dentin

Dentin Types: Relationship to the DEJ and Pulp

• Mantle
  • The first predentin forms and matures near the DEJ under the enamel
  • Contains collagen fibers, which are perpendicular to the DEJ
• Circumpulpal
  • Located around the pulp
  • Makes up the bulk of dentin
  • Contains collagen fibers, which run parallel to the DEJ

Dentin Types: Relationship to Time of Formation

• Primary
• Secondary
• Tertiary
  • Reparative
  • Reactive
  • Sclerotic

Primary Dentin

• Primary dentin develops in a tooth before the apical foramen of the root completes formation
• It features a regular tubule pattern
• Most of the dentin in a tooth is primary

Secondary Dentin

• Secondary dentin forms after the apical foramen of the root completes formation
• Formation continues throughout life
• Forms more slowly than primary dentin
• Tubule pattern is slightly irregular
• Maintains same mineral content as primary dentin, but is less mineralized
• Results in pulp recession by filling in the pulp chamber along the outer wall

Tertiary Dentin

• This dentin type has an irregular tubule pattern
• Reactive
  • Created quickly in response to a localized injury that exposes dentin
  • Injury sourced from caries, cavity preparation, attrition, or gingival recession
  • Occurs underneath exposed dentinal tubules along the outer pulpal wall to seal the injured area
  • Existing odontoblasts form it in response to injury
• Reparative
  • New odontoblasts from neighboring undifferentiated mesenchymal cells in the pulp form it
  • This is only when existing odontoblasts have been injured
  • It is also called dental pulp stem cells

Sclerotic Dentin

• This is a type of dentin resulting from chronic injuries from caries, attrition, abrasion, gingival recession, and aging
• Also known as transparent dentin
• This is due to odontoblastic processes dying off and leaving tubules vacant
• Hollow tubules (dead tracts) become retrofilled and mineralized, occluding the space
• Occlusion helps lower permeability to prevent caries and prolong pulp vitality.
• It looks dark and smooth where there are caries arresting

Dentin Histology

• Imbrication Lines of Von Ebner
  • Transverse lines across dentinal tubules
  • They have a regular pattern in dentin matrix
  • Analogous to the lines of Retzius
  • 4 μm of dentin are deposited each day
  • Every 5th day, collagen fiber orientation slightly differs and leads to imbrication lines
• Contour Lines of Owen
  • Several parallel imbrication lines
  • Similar to growth rings of a tree, like the lines of Retzius
  • Illustrate a disturbance in body metabolism, like illness, affecting odontoblasts
  • Appear as a series of dark bands
  • The most pronounced line is the neonatal line, and can sometimes occur with tetracycline staining

Tomes Granular Layer

• Found beneath the cementum layer on the root, near the DCJ
• Appears dark and granular
• The cause is unknown, but it could be decreased mineralization of dentin in this area or from branching/crisscrossing of the dentinal tubules

Clinical Considerations for Dentin Pathology

• Resorption
  • Natural dentin resorption occurs during primary tooth shedding
  • Dentin maintains stability during the tooth’s lifespan, normally
  • Sometimes, permanent teeth experience dentin resorption, the cause is unknown, but can be linked to trauma
  • Resorption may be external or internal
  • Radiographs are needed for diagnosis
  • Granulation tissue lies beneath translucent enamel, causing the "pink tooth" appearance during assessment
  • Teeth can be treated via endodontics if caught early, or extraction

Dentinal Caries

• Demineralization of dentin originates from acids produced by cariogenic bacteria
• Dentin demineralizes when pH drops below 6.8
• Cariogenic bacteria then use the dentinal tubules as chutes to push further into the pulp center
• Caries moves more quickly through dentin than enamel as dentin has higher organic material

Dentinal Hypersensitivity

• Occurs from dentin exposure, often caused by cavity preparation, caries, gingival recession, attrition, tooth anatomy, or vigorous scaling
• Exposed dentin becomes sensitive to various stimuli and causes a painful response for the patient
• Can be caused by tooth anatomy, enamel and cementum failing to meet which leaves gaps, and vigorous scaling or instrumentation leading to temporary sensitivity
• Stimuli for dentinal hypersensitivity include thermal changes, mechanical irritation, dehydration from air, and chemical exposure from certain foods or tooth-colored restorations
• It is normally a short, sharp pain, but may be a diffuse causing it to be hard to localize
• This pain may be wrongly interpreted as caries, soft tissue inflammation, or pulpal/gingival infections
• Hydrodynamic Theory is the newest theory on the action mechanism
  • The sensitivity is caused by changes in the dentinal fluid associated with odontoblastic processes in the tubules
  • It may be due to evaporation/loss of dentinal fluid, movement of fluid, or ionic changes
• Stimulation of the exposed dentinal tubules cause changes which transmit to nerves that connect with odontoblast cell bodies in the pulp
• Treatments include desensitizing agents like professional products at dental offices, or OTC products, or restorations

Aging Dentin

• Aging dentin experiences a diameter decrease in the dentinal tubules due to increased peritubular dentin
• Causes less stimuli to transmit to the pulp
• There is less content in organelles of odontoblasts
• There is an increase in secondary dentin levels
• Increased dentin becomes exposed in the oral cavity
• Dentinal translucency helps with dental age estimation

Dentin-Pulp Complex

• Dentin and pulp are closely linked and reliant on each other for survival/development
• Odontoblastic processes are within dentinal tubules where fluid provides odontoblasts with nutrition from pulp's blood vessels
• Afferent myelinated axons are within some of the tubules
• Neuron cell bodies sit within adjacent pulp

Pulp

• Innermost tissue of the tooth
• Less dense than other dental tissues leading to a dark appearance on xrays
• Connective tissue in pulp contains cells, intercellular substance, tissue fluid, lymphatics, vascular system, nerves, and fibers that are mainly collagen
• There are 2 main types of cells within the pulp: fibroblasts and odontoblasts
  • Fibroblasts
    • The most predominant cell type, spindle shaped, makes CT fibers and intercellular substance for tissue components
  • Odontoblasts
    • Second largest group of cells, the cell bodies are located in the outer pulpal wall
    • Contain undifferentiated mesenchymal cells, dental pulp stem cells (DPSCs) which can differentiate into newly formed odontoblasts or reparative dentin
• Myelinated Nerves
  • Make up about 20-30% of nerves in the pulp
  • This is the type of nerves in the dentinal tubules with odontoblastic processes
  • Their cell bodies are located between odontoblast cell bodies in odontoblastic layer of pulp
• Unmyelinated Nerves
  • Make up about 70-80% of nerves in pulp
  • Associated with blood vessels
  • Nerve fibers originate from mandibular and maxillary branches from the trigeminal nerve(Cranial Nerve V)
  • Cell bodies are in trigeminal ganglion
• Functions of pulp include;
  • Support, maintenance, and continued formation of dentin from cell bodies of odontoblasts sitting remaining in outer wall of pulp
    • Sensory - to detect extremes in pressure, temperature, or trauma that cause pain
    • Nutritive- keeps the organic molecules of the mineralized tissue supplied with moisture and nutrients
    • Protective - to trigger the formation of secondary and tertiary dentin from odontoblasts
    • Immune-White blood cells in the blood supply can trigger inflammation and immune response

Anatomy of Pulp

• Pulp chamber houses a large mass of pulp in the tooth
• Shape of pulp chamber aligns with the overall shape of the tooth
• It has two main divisions: coronal and radicular
  • Coronal pulp sits in the crown of the tooth
    • Pulp horns extend into posterior tooth cusps, but recede with aging
  • Radicular pulp also named “root” pulp sits more apically in the tooth
• Apical Foramen/ Foramina
  • Allows entry/ exit of arteries, veins, nerves and lymphatics from the PDL
  • The opening of the pulp leading into the surrounding PDL, near the apex(bottom) of the tooth, which sits right inside cementum
  • If there is more than 1 foramen, the primary one is called the apical foramen, the secondary foramina are named accessory foramina
• Accessory Canal Formation
  • Forms when Hertwig epithelial root sheath(HERS) meets a blood vessel when roots are forming
  • Root structure then develops around the blood vessel and forms the connecting accessory canal
  • It can be found at apical foramina, or accessory canals, in surrounding PDL
  • Not all teeth have them but is imperative to find all canals during endodontic therapy
• After endodontic therapy, (Root canal Treatment), the tooth;
  • Loses vitality, may darken, and becomes brittle as a result
    • As it no longer is a functioning tissue it is advised to protect the tooth in place with a restorative crown post therapy
• Pulp Zones
  • There are 4 zones, only seen under a microscope:
    • 1. Odontoblastic layer
    • 2. Cell-free zone
    • 3. Cell-rich zone
    • 4. Pulpal core
  • Odontoblastic layer is the first innermost, closest to dentin
    • Lines outer pulp wall, consisting of layer of odontoblast cell bodies whose cytoplasmic processes are in dentinal tubules and forms secondary or tertiary dentin along outer pulpal wall
  • Cell-free zone is the next inward from odontoblastic layer, with relatively few cells
    • It contains a nerve and capillary plexus
  • Cell-rich zone is the zone the furthest inward from the cell-free zone providing an extensive vascular supply
    • It also contains many cells mainly; macrophages, fibroblasts and dental pulp stem cells DPSCs
  • Pulpal Core- sits in the center of pulp chamber providing a similar content as the cell-rich zone but contains a highly extensive network for delivery and vascular supply

Aging Pulp

• From an aging perspective, pulp horns recede in posterior coronal pulp
• With this, we often see an addition of secondary and tertiary dentin limiting pulp size and chamber volume
• Lower sensitivity will be present due to dying odontoblasts, leading to decrease in intercellular substance, water, and cells when filling in with increased amount of collagen fibers

• of undifferentiated mesenchymal cells ,DPSCs will be reduced

• Becomes more fibrotic as a result of being age filled and leads to a reduction in the regenerative ability of pulp, ultimately resulting in regenerative capacity with loss of DPSCs-a known Pulp Recession
• Pulp Cavity commonly recedes in size from secondary and/or tertiary dentin formed that adds to within the pulp chamber, limiting volume overtime
• Lack of sensitivity is normal in older teeth because pulp horns recede back, leading to pulp fibrosis and added dentin- ultimately no local anesthesia is commonly used on older patients

Clinical Pathology of Pulp

• Pulp Stones, also called denticles, fill the pulp chambers and show up as radiopaque masses on radiographs, but is usually an issue unless that tooth requires endodontic therapy
• When pulp is injured inflammation may undergo causing Pulpitis
  • Initially confined within tooth causing extreme pain when edema presses against afferent nerves
  • Nicotine can reduce blood flow causing higher endodontic therapy risk > 70%
    • This may look “reversible”
    • Or look like an”irreversible” issue
    • Often left “necrotic”
• Reversible Pulpitis often only exists in the coronal pulp
  • This may be a result of trauma, infection or/after a restorative procedure
  • Exhibiting quick, distinct response to any thermal testing but it subsides following removal of same stimulus
    • However, if it shows these traits-the Pulp may stay treated and remain vital with proper therapy
    • It may be covered correctly with a pulp cap or, may indicate the need for a pulpotomy
• Irreversible Pulpitis occurs when the pulp is dead
  • This is often a lingering sharp response following the first sign of thermal testing
    • This often, too comes with spontaneous pain, even without stimulus testing
  • This can show infection in the form of periapical abscess or cyst which resides surrounding the periodontium
    • If not addressed properly- this infection can travel through apical foramina, too, through accessory canals as result

Necrotic Pulp

• With this we note: no stimuli, no signs, an asymptomatic
• often the tooth loses vitality and becomes non-vital with its tissue- which more times than not exhibits a tooth often becomes discolored(often turns darker than normal) due to left over biodegradative products from necrosis that is traveled passed through dentinal tubules
  • There is no reperation and is often “Non-reparable, BUT removed surgically through RCT or Extraction-Treatment for Irreversible Pulpitis or Pulp Necrosis”

Root Canal Therapy

• A procedure where all infected pulp tissues are surgically removed
• An inert, radiopaque rubbery product Guttta Percha is surgically placed to fill the pulp region and through radicular portions
• The Tooth then loses all Vitality(becomes no longer alive) and then needs a surgical placement of a Restorative crown placed around remaining tooth portion after Rct placement, protecting it from possible breaks