Dentine and pulp Flashcards
What are the functions of dentinal fluid?
Outwards flow protects against bacterial/ bacterial product ingress towards pulp
Rapid fluid movement of fluid in tubule can transmit shear forces to nerves
Calcification of peritubular dentine
Hydrates dentine, dehydrated dentine is harder and les elastic, fractures easier
What are the essential differences between the subtypes of tertiary dentine?
Reactionary dentine: Upregulated odontoblasts lay reactionary dentine down in response to mild to moderate stimuli (slow progressing lesions), and it has tubular continuity with physiologic secondary dentine
Reparative dentine: Strong stimulus (deep caries or pulp exposure) kills the original odontoblasts so replacement odontoblast-like cells lay down irregular, tubular or atubular (depending on circumstances)
What is mantel dentine?
First formed dentine
How is mantel dentine thought to contribute to the strong bond between enamel and dentine so that the two structures do not delaminate in function?
Collagen fibres protrude from mantle dentine layer into enamel,
scalloping of enamel and mantel dentine layers for greater surface area for bonding as well as discontinuous stress concentration,
less hard than ordinary dentine, allows for gradual transition from dentine to enamel
What changes occur in the dental pulp as the tooth ages
Pulp volume decreases: secondary dentine formation,
reduced cellularity: inherent healing ability of aged pulps is reduced,
odontoblasts downregulate
Pulpal calcifications: Pulp can mineralise in the form of pulp stones, more often found in coronal region, impede root canal treatment
Fibres increase, increased number and thickness of collagen, forming bundles
What is an advantage of the pulp being surrounded by dentine
There is a hard protective covering to the soft tissue of pulp
What is a disadvantage of the pulp being surrounded by dentine?
It forms a low compliant environment/system with limited capability to respond to severe inflammatory reactions.
What is sclerotic dentine?
Dentine filled with whitlockite crystals
What causes sclerotic dentine?
Initiated by external stimulus (caries, attrition, abrasion)
Defence mechanism to reduce permeability to the pulp against caries, attrition, erosion and aging
Where are dentine tubules wider?
Wider near the pulp and narrower near the enamel-dentine junction
Why are dentine tubules narrower near the EDJ and wider near the pulp
Peritubular dentine is laid down as dentine is formed so the earliest formed dentine at the EDJ will have the thickest deposition of peritubular dentine than the newest formed dentine near the pulp
How does the tertiary dentine produced under a carious lesion in response to caries aid in the defence of the pulp
Decreases permeability of dentine tubule to reduce diffusion towards pulp
Maintain buffer zone
What is primary dentine?
It is the most prominent dentine in the tooth and is the dentine produced before the root of the tooth is completely formed. It consists of mantle and circumpulpal dentine
What is secondary dentine?
I tis laid down by down-regulated odontoblasts after eruption of the tooth. it grows much more slowly than primary dentine, and has a similar structure to primary dentine. Its deposition around the pulp chamber is not always even. It is this frowth of secondary dentine that leads to the shrinking of pulp chamber with age.
What is tertiary dentine?
Reactionary and reparative, formed by odontoblast in direct reaction to external stimuli, such as caries
What is peritubular dentine?
Peritubular dentine forms a ring inside the dentinal tubule and is extremely high in mineral content. (more highly calcified) and is consequently harder than intertubular dentine. Responsible for anisotropy of dentine
What is intertubular dentine?
Comprises hydroxyapatite crystals embedded in a network of collagen fibres providing hardness and elasticity. It is the dentine between dentinal tubules
What are the differences between mantle and circumpulpal dentine.
Mantle dentine is first-formed dentine adjacent to enamel and circumpulpal dentine forms the bulk of dentine
Collagen fibres of mantle dentine are arranged in the same direction as the dentinal tubules. Collagen fibres of circumpulpal dentine are arranged perpendicular to the dentinal tubules.
Mantle dentine contains lower density of tubules and is less mineralised, circumpulpal dentine is harder and less elastic
Mantle dentine mineralised by vesicle mineralisation, circumpulpal by crystal growth
What are the main functions of odontoblasts?
Form dentine throughout life of tooth, act as a mechano-thermoreceptor (sensory organ) and acts as an antigen-presenting cell (APC) in defence of the dentine-pulp complex
What is thought to be the reason for von Ebner’s lines seen on a ground section of dentine?
The cicadian rhythm (~24hour cycle) of the laying down of collagen.
Name the 2 main types of sensory nerves found in the pulp.
Myelinated A fibres @pulp dentine border (responsible for sharp pain), one of the last major structures to appear in the developing tooth, can drill into newly erupted teeth without causing pain
Unmyelinated C fibres @pulp core and extends to cell-free zone (responsible for dull pain)
What is the purpose of microcirculation in the dental pulp?
Limited compliance of the surrounding dentine reduces the threshold of pain, swelling of pulp due to inflammation must be restricted. Microcirculation plays a critical role in maintaining pulp health when it is inflamed
What junctional complexes are found between odontoblast cells?
tight junction: acts as a barrier between pulp and dentinal fluid
Intermediate junction: acts as a belt to maintain cell to cell positioning
Gap junction: allows movement of signalling molecules and ions between cells
Why does the pulp volume reduce as the tooth ages?
Secondary dentine is laid down continuously after the tooth erupts
How much of dentine’s organic matrix is collagen?
90%, mainly type 1, provides elasticity, felt-like framework or scaffold for mineralisation
What is the similarity and difference in the mineralisation in bone and dentine?
Similarity: extrafibrillar mineralisation (interfibrillar)
Difference:
Intrafibrillar mineralisation
in gap zones between microfibrils unique to dentine, higher mechanical properties compared with bone
What is the direction or pathway of dentine formation
Formed by odontoblasts starting from EDJ and moving centripetally (towards the pulp)
What is the difference between coronal and root dentine
Coronal: mantle dentine, root: hyaline and granular layer
Coronal: higher tubular density than root
Coronal has more peritubular dentine than root
What is the chemical composition of dentine?
70% inorganic, 20% organic, 10% water by weight
50% inorganic, 30% organic and 20% water by volume
How does dentine compare to bone and enamel in terms of hardness
bone
What is the difference between peritubular dentine and intertubular dentine?
Peritubular more mineralised than ITD by 40%
Carbonated apatite crystals smaller than ITD but 5x harder
PTD lacks collagenous fibre matrix
Where is there more ITD?
More at EDJ, reduces pulpally
When there are more tubules at the pulpal area (less ITD) less tubules at EDJ (more ITD)
How does ITD abundance affect susceptibility to cyclic stress
Cyclic stress cracks form at 40% lower stress in deep vs superficial dentine (deep dentine less ITD)
How is mantle dentine mineralised?
By matrix vesicles, not by nucleation
Which teeth have more pronounced scalloping at the DEJ?
Teeth with higher masticatory loads (molars)
Does mantle dentine have low or high tubule density?
Low tubule density (site of terminal branching of tubules) some tubules extend into the enamel as enamel spindles
How thick is mantle dentine?
20-150 nanometer
What is unique about mantle dentine’s collagen arrangement?
Its collagen fibrils run perpendicular to DEJ
Where is hyaline layer located?
In the root, between cementum and granular layer
What is the structure of the hyaline layer?
Non-tubular layer which is relatively structureless
Where is the granular layer located?
In the root, between circumpulal dentine and hyaline layer
What are the GAGs present in dentinal pulp
Hyaluronan
Heparin sulfate
Dermatan sulfate
Chondroitin sulfate
What is the function of GAGs in ECM of dentinal pulp?
Reservoir for bioactive molecules
Forms gels as they are hydrophilic molecules, provide anchorage and support to cells
Mechanical barrier against bacteria
What is the purpose of fibronectin?
Connects cell to cell, cell to ECM componentws like collagen, binds membrane receptor proteins like integrins
Where is elastin found in the pulp?
Arterioles
What collagen is found in dentinal pulp?
Collagen 1 (56%) Consistency and strength Synthesised by both fibroblasts and odontoblasts
Collagen 3 (41%)
More elastic, synthesised by fibroblasts
Absent in cell free zone
What cells are present in the dentinal pulp?
Odontoblasts: dentine formation
Fibroblasts: Cell rich zone, ECM formation, can differentiate into odontoblasts
Immunocompetent cells
Dendritic cells: immunosurveillance, antigen presenting, triggers T-cell dependent immunity
Macrophages: Antigen presenting, phagocytosis of dead cells and foreign bodies, destroy with lysosomal enzymes
Lymphocytes: Memory T lymphocytes recognise antigen presented by above two cells, T cell activation, initiation of T-cell dependent immunity
Undifferentiated mesenchymal cells: can differentiate into odontoblasts/fibroblasts
Which supporting systems absorb low molecular weight solutes and high molecular weight solutes
Blood vessels: low m.w.
Lymphatic system: high m.w.
Which nerves modulate blood flow in the pulp?
Sympathetic efferent (motor) fibres from trigeminal nerve modulate blood flow through the vasoconstriction of the arterioles
What are myelinated A fibres sensitive to
Sharp pain (hot and cold sensitivity)
What are unmyelinated C fibres sensitive to
Dull pain (toothache sensation)
Where are myelinated A fibres found?
Dentinal-pulp border
Where are unmyelinated C fibres found
mainly found in pulp core, extends to cell free zone
What are the functions of dentine-pulp complex?
Inductive Nutritive Formative Preventive Defensive
Describe inductive function
Dental papilla cells interact with inner enamel epithelium of enamel organ to determine crown form
Participates in initiation and development of dentine
Describe Nutritive function
Blood vascular system of pulp provides nutrients essential for dentine formation and maintaining pulp integrity
Describe formative function
Ameleoblast: enamel
Odontoblast: dentine
Describe protective function
Highly innervated, perceive pain
Odontoblasts act as mechanosensory cells
Describe defensive function
against caries, attrition, erosion and abfraction or iatrogenic or the leakage of restorations
Dentinal fluid flows outwards, flushes bacteria out, contains immunoglobulins
Intratubular fibres in dentinal tubules can help trap bacteria
How does dentine pulp complex cause inflammatory response?
Immunocompetent cells mount inflammatory attack to bacteria in response to lipotheichoic acid of gram positive bacteria and lipopolysachharides of gram negative bacteria
Odontoblasts secrete tertiary dentine to reduce dentine permeability
Normally, blood capacity in the pulp is not at maximum, blood vessels are not constantly perfused, allows for increase in volume due to inflammation
What are the age changes in pulp?
Pulp volume decreases: increase in secondary dentine formation, reduces the size of the pulp
Cells decrease: gradual reduction of all pulp cells, nerves and blood vessels, inherent healing ability of aged pulps reduced
Fibres increased: increase in number and thickness of collagen fibres, forming bundles
Pulpal calcification, pulp stones increase: free, attached or embedded, found more in coronal reasons, may impede root canal treatment
