Histology of the Pulp

Histology of the Pulp

• Embryonic origin is the ectomesenchyme of the dental papilla

Anatomy of the Pulp

• Encased in the pulp cavity and surrounded by mineralized tissues
• Coronal pulp is located in the pulp chamber
• Root pulp is located in the root canal(s)
• The number of cusps a tooth has corresponds to the number of pulp horns

Composition

• Highly vascular, soft connective tissue made up of 75-80% water and 20-25% organic material
• Contains cells like odontoblasts, fibroblasts, undifferentiated cells, and defense cells
• Contains an extracellular matrix, fibers, ground substance, blood vessels, lymph vessels, and nerves

Structural Composition

• Has 4 zones:
  • Odontoblast zone lines the periphery of pulp
  • Cell-free zone is the space between zones with only few fibers
  • Cell-rich zone contains all cells except odontoblasts
  • Pulp core contains blood vessels, nerves & some cells

Odontoblasts

• Processes extend into dentine
• Functions include dentinogenesis and sensory transduction

Fibroblasts

• Prevalent in cell-rich zone
• Functions include maintaining the extracellular matrix and ground substance
• Very active in young pulp, then reduces

Undifferentiated Cells

• Located in cell-rich zone and pulp core
• Includes ectomesenchyme cells, odontoblasts, and fibroblasts
• Includes mesenchymal stem cells

Defense Cells

• Located in pulp core
• Consists of macrophages, T-lymphocytes, B-lymphocytes, some leukocytes, and dendritic cells

Extracellular Matrix

• Fibers and Collagen increase in content with age; the apical pulp contains the greatest concentration
• Ground substance is loose connective tissue that supports the cells
• Consists of glycosaminoglycans, glycoproteins, and water

Nerve Supply

• Richly supplied with nerves that enter through the apical foramen to the pulp core, like vascular and lymph
• It enables pulp to recognize stimuli, perceived as pain, and trigger defense responses
• In the coronal portion, the Nerve Plexus of Raschkow can be found just beneath the cell-free zone
• Most nerve bundles end as free nerve endings in the plexus
• Some continue to end between the odontoblasts and into the dentinal tubules
• Has sensory afferent nerves of the trigeminal nerve (pain)
• Sympathetic nerve branches from the superior cervical ganglion help regulate blood flow in the smooth muscles of the vascular vessels
• The nerve bundles are both myelinated and unmyelinated

Vascular & Lymph Supply

• Circulation to the pulp is found in the pulp core
• Vessels enter and exit through the apical foramen along with the nerve supply, and some through accessory foramina
• The largest vessels are arterioles and venules that branch into an extensive capillary network in the coronal portion

Function of the Pulp

• Over time, the deposition of secondary dentine reduces the size of the pulp tissue and diameter of the apical foramen
• This has several impacts, reduced circulation, reduced innervation, fewer odontoblasts, and increased fibers & collagen
• Formative ability to continue forming dentinogenesis (pre & post eruptive); primary & tertiary dentine

Circulation

• Nutrients & Oxygen removes waste products Undergo inflammatory response reaction
• Linked to blood & vascular supply

Protective

• Innervation enables response to stimuli & perceive as pain & defense cells

Clinical Significance

• In response to stimuli or injury, the pulp experiences inflammation, either reversible pulpitis or irreversible pulpitis (painful)
• While the pulp has some ability to repair itself, the response is limited to the size of the apical foramen and can lead to necrosis of the pulp

Structural Anomalies

• Pulp stones are small calcified areas of tissue similar to dentine found in pulp tissue
• Can be either free or attached to the dentine
• Reduces cell content in pulp and poses a challenge for endodontic treatment

Accessory Canals

• Disruptions during the development of the root leads to a break in the continuity of Hertwig's epithelial root sheath
• Is a disruption in odontogenesis of the root
• Implications for the ingress of bacteria to the pulp if it becomes exposed, leading to periodontal and endodontic problems

Histology of Dentine

Composition and Structure

• 70% inorganic minerals, Calcium hydroxyapatite
• 20% organic materials
  • 18% collagenous rich matrix
  • <2% non-collagenous matrix proteins & lipids
• 10% water
• Flexible, Avascular, Mineralized, Connective Tissue

Dentine Tubules

• The main structure permeates the dentine structure, extending from the DEJ to the border of the pulp chamber
• Traverse in an S shape which withstands forces
• Underneath cusps, incisal edges & root tips are almost straight tubules
• More widely separated near DEJ Compared to near the pulp is tapered outline
• The pattern reflects the path of odontoblasts during dentinogenesis that becomes crowded and some may die off to make space
• Walls of tubules are peritubular/intratubular dentine, highly calcified with minimal collagen
• Dentine in between the tubules is less calcified and is called intertubular dentine, bulk of dentine
• Extends inwards to the pulp chamber

Dentine Tubule Contents

• Odontoblastic process extends cytoplasmically, a surrounding periodontoblastic space (filled with fluid)
• Communication from dentine to protection which is key for understanding dentine hypersensitivity

Structural Features

Interglobular Dentine

• Areas of unmineralised dentine (hypomineralised)
• Fails to fuse together at the zone of mineralisation during dentinogenesis
• Often found in the circumpulpal dentine, below mantle dentine
• Prevalent in teeth where vitamin D deficiency or high fluoride exposure has occurred during the maturation stage of dentinogenesis
• Matrix structure is normal, but mineralisation maturation wasn't fully completed, and doesn't include peritubular dentine

Sclerotic Dentine

• Dentine tubules can calcify via a physiological process of mineral deposition
• Most common in the apical third of the root & midway in the crown between the DEJ & pulp
• The amount of sclerotic dentine increases with age, reducing permeability of dentine

Dead Tracts

• Empty dentine tubules where the odontoblastic process has died or retracted and sealed off
• May result from physiological or pathological processes
• Thought to be the first part of sclerotic dentine increasing with age and reduces permeability of dentine

Incremental Lines

• Reflects the pattern of dentinogenesis laid in increments called Lines of Von Ebner
• Dentinogenesis secretes matrix and then mineralises, etc
• More distinct incremental line is present at the interface between primary and secondary dentine
• Called Contour lines of Owen and change in the direction of the dentine tubules

Granular Layer of Tomes

• Narrow layer of dentine with granular appearance
• Found only in root dentine below CDJ
• More numerous towards apex
• Thought to result from interference with the mineralisation of dentine by the inner layer of the dental sac

Types of Dentine

• Heterogenous different types of dentine according to the location and timing of formation (dentinogenesis)
• Mantle dentine initial formed dentine that outlines the periphery of the dentine adjacent to the enamel and cementum,
• Circumpulpal dentine is the bulk of the dentine, Contains the dentine tubules that lie between the mantle & pre-dentine
• Pre-dentine is a dentine matrix that surrounds the pulp chamber to enable dentinogenesis to continue throughout the tooth's life

Primary Dentine

• The bulk of dentine within the tooth which forms prior to the completion of root formation
• Made up of both dentine and circumpulpal dentine

Secondary Dentine

• Begins after root formation is complete
• Forms slowly throughout life
• Does not form evenly concentrated over the roof floor of the pulp
• Over time, reduces the size of the pulp chamber pulp recession
• Similar in structure to primary dentine with tubules, however, is less regular and a distinction is visible histologically

Clinical Significance

• As people age, the pulp essentially shrinks, protecting itself
• In restorative dentistry a carious or incidental pulp exposure is more likely in younger teeth due to the prominent pulp horns

Tertiary Dentine

• Response to various stimuli in reactionary or reparative forms
• It is usually localised to the area of stimulus
• The structure varies according to the intensity and duration of stimulus which may affect the odontoblasts if strong enough
• May have tubules Continuous with Secondary dentine or may not appear Irregular in arrangement

Clinical Significance

• With various stimuli initiating tertiary dentine are caries, attrition, and Abrasion (from tothbrush)

Reactionary vs Reparative Tertiary Dentine

• Reactionary dentine is deposited by preexisting odontoblasts
• Reparative dentine is deposited by newly differentiated odontoblast-like cells from the ectomesenchyme of the pulp
• Forms osteodentine

Functions of Dentine

• Rigid which is 70% mineralised
• Elastic as 20% of it is collagen and able to absorb some degree of shock.
• Supports enamel
• Protects the pulp
• Communicates with the pulp via the odontoblastic process
• Repairs or triggers repair

Clinical Significance

• Detects for a disease like caries, tooth surface loss and pulpal involvement
• Reassuring for health by yellowing of teeth with age and new adult teeth and canines

Colour of Dentine

• Is more yellow when healthy because it has less mineralised and absorbs more light than the enamel
• In a diseased state, its color changes to brown which changes the appearance of the crown to a grey shadowing appearance

Permeability

• Dentine tubules and the organic content make dentine permeable and this varies with structure
• Tubules that end at CDJ are the least permeable due to their narrow diameter while tubules that extend sbove the pulp are more permeable
• Progression of Caries quicker and is more extensive than enamel
• Innervation of dentine due to porous tubules allow for communication with pulp

Communication

• Dentine tubules and the odontoblastic process facilitate communication with the pulp, triggering sensation (feel).
• Clinical relevance is that communication facilitates restorative procedures for both aesthetic and dentine hypersensitivity

Fluid Content in Dentine

• Dentine hypersensitivity: when dentine is exposed, movement of fluid occurs due to pressure changes (triggering sensitivity or pain).
• Restorative procedures, for example, etching and bonding plastic materials to dentine.

Histology of the Periodontal Ligament

• Connective tissue that surrounds the root & connects it with the bone
• It's continuous with the connective tissue of the gingiva & communicates with the marrow spaces through vascular channels in the bone
• At the root apex, the PDL merges with the dental pulp.

Functions of the PDL

• Physical Support is a Shock absorber
• Formative helps remodeling and is a cell builder while resorptive degrades old cells and width has to be maintained.
• Nutritive has a rich blood supply
• Sensory has nerve fibers that picks up messages
• The average width of PDL is 0.2mm (range 0.15mm to 0.38mm)

PDL on Radiographs

• A radiolucent ared between the lamina dura bone proper and radiopaque cementum
• Is narrower in permanent teeth than deciduous teeth

PDL Forms the Dental Follicle

• Forms shortly after root development begins

Development of PDL

• As a crown comes to oral mucosa, fibroblasts in a follicle become active & produce collagen
• Initially fibers lack organization but then become oblique to tooth
• 1st fibers are apical to CEJ
• As eruption progresses more fibers develop & become attached to new cementum & bone
• In eruption cemental Sharpey's fibers appear first followed by Sharpey's fibers in bone

Structural elements of PDL

• Cells have extra cellular substances or fibers with synthetic cementoblasts
• Also help resportion with cementoclasts and osteoclasts

PDL Defense

• Made up of Stem cells, undifferentiated mesenchymal cells
• Has high cell turnover - mitotic division that replace dying cells
• Helps defense with mast cells or macrophages Epithelial Rest -found mostly near cemental side of PDL or Hertwig's epithelial root Sheath

Blood Supply to PDL

• Principal blood supply is superior & inferior alveolar arteries
• Has Apical vessels
• Penetrating vessels from the alveolar bone
• Anastomosing vessels from the gingiva
• There are 2 types of nerves sensory and autonomic

Nerge Supply to PDL

• Branches of 2nd & 3rd division of 5th Cranial nerve - Trigeminal nerve
• Fibres made of collagen
• PDL wider near apex & cervical margin of tooth
• Most are principal fibres-organised into groups according to orientation and function (resemble spliced ropes)
• Embedded ento cementum & bone - Sharpey's fibers
• Distribute forces of mastication & speech

Principal Fiber Group - Overall functions to resist rotational forces

• ① Has Alveolar Crest Group
• ② The group is a Horizontal Group
• ③ Oblique Group
• ④ Apical Group
• ⑤ Interradicular Group

Alveolar Crest Group Fibres

• Location is just beneath the joining epithelium
• Originates in Cementum below CDJ
• Insertion runs downwards and upwards and inserts into alveolar crest.
• Significance prevents the extrusion of teeth and resists tilting

Horizontal Group of Fibres

• Limited to coronas/4 of POL
• Origin the Cementum apical to the alveolar crest group. Insertion runs right angles and inserts bone

Significance resists the tipping of tooth

Oblique Group Fibres

• Located 2/3 POL.
• Origin runs downwards and and inserts into outer space
• The largest group assists chewing

Apical Group fibres

• Is rooted at the tip
• Cement around the apex is the origin
• It extends the socket

Significance resists vertical and twisiting forces, protects nerve vessels also

Inter-radicular Group Fibres

• Found multirooted teeth
• origin is in cementum
• insertion in the Interradicular septum
• SIGNIFICANCE - resists vertical and has lateral Movement, tipping

Interdental ligament/transseptal fibres

• Are important to fibres
• They are embedded on neighbouring tooth and inserted interdentally
• The rotation resistance is made up of the ligaments that connect the alignent

Ground Substance

• has support
• Exchange of metabolites
• 70% water and has tissue support
• Has strong binding

Age Changes

• There is a decrease in fibrous tissues
• There is a decrease of mitosis
• Narrowing the PDL at scalloping
• PDL decreases

Clinical Considerations

• Has pressure, trauma, infection,ortho or restored
• Helps natural implant of the tooth

Composition of cementum

• Inorganic & is 45-50% of hydroxyapatite crystall
• Critical pH=6.7
• Organic content is 50-55% with collagen and type 1 fibers
• Also contains water
• Has acellular and cellular types with Sharpey's fibers or lack of

Acellular Cementum Primary

• Covers the cervical & middle third of the root and 40-70% of root surface.
• The first formed cementim adjacent cementum function
• Forms Sharpey's fibers slow with dental origin.

Acellular Fibriller Cementum

• Is located in the same area covering dentin
• Has good support
• Supports support and attachment

Functions

Is connected and is part of the periodonticum cementum Supports to the tooth position with the alveolar socket with periodontal fibers

Extrinsic fiber are attached

Supports Sharpy's fibers Alveolar bone support

Cellular Cementum Secondary

• Cementiod is located around the cementum. They are parallel fibers
• Overtime or celluar

Cellular Cementum Cell

Helps form via cementogenesis

• It makes speed and composition
• This originatates from the dental sac.

Cementoblast Characteristics

• Is located tip of gums
• Interradicular tooth. With roots that are located on the side.

Adaptive Functions

• Helps adapt and movement the tooth from reshaping the tooth
• Deposition maintain occlusion
• Thickness compensate and allows for strongness

Dentine or Cementum Clinical

• cellular cementum help repaier of soft tissue
• It has the ability to help with this tissues and PDL

The Cementin Over Time

• Cementogenesis happens at different part in life.
• Increases mineral in

Clinical Significance

Functions Overlap 65 % to gap 10% with high senditivity

Hypercementosis

• Excess cementum due to inflammation
• May effective a simple tooth
• Also is known as asypmtomatic
• Creates extractions

Histology of Enamel

Composition

• Inorganic = 96% minerals
• calcium hydroxyapatite (Ca3(PO4)3OH)
• Has Carbonate & fluoride
• Contains organic at a rate of 4% with fibrous martial collagen and some protein

Enael Structure

• There are many roods structures also known as prisms
• They packed organize and help shape section
• Each rod contains many Also keyhole like and heads

Enamel Crystallities

• There are tons of crystals that pack with many crystallies tighted together
• Is hard
• The shapes is what gives the strength

Enamel Rod Characteristics

• Account for shapes
• The rodes
• Tips where horizontal

Incremental Lines

• Enmelosgeness what occurs waves to rest teeth with Retizaus

Perikyma

• Has shadow that will show the surfac Will only show on teeth surface.

Prismelss Characteristics

• With some prism.
• Show usual prism that is 39.35 microns and opaque
• It may interact eith ethiching

Detine Anamel

• The two started together
• The materials locked and scalled so it strengthen and locked.