dentine pulp complex Flashcards
notes on odontoblasts
are formative, collagen producing multi functional cells that lay down predentine matrix for mineralisation
- play important roles in innate and adaptive pulp immune defense
- are aligned at the periphery of pulp, adjacent to predentine layer
- in coronal dentine, density and diameter of dentinal tubules increase from peripheral of 1.5 microm to deep dentine close to pulp (2.5-3 microm)
- in root dentine, tubuler densities are less than in crown and diminish apically. tubule diameter close to pulp in root dentine is about 1.5 microm
- larger at young age, become more sclerotic as peritubular dentine becomes thicker
- each odontoblast extends a single cytoplasmic process (Tomes fiber) into a single dentinal tubule
- odontoblast cell bodies are intimately related and communicate among themselves, are connected by gap junctions that allow them to form a semi permeable membranec
classification of dentine
primary: dentine laid down by secretory odontoblasts prior to tooth eruption
secondary: continued, physiologic deposition of tubular dentine by secretory, mature, old odontoblasts after tooth eruption
- rate and thickness not influenced by external injury/ irritants
tertiary:
- dentine laid down in localised regions in response to external stimuli
- split into reactionary & reparative
- reactionary: tubular dentine laid down predominantly by upregulating primary odontoblasts
- reparative: an initial layer of atubular dentine, followed by tubular dentine produced by secondary odontoblast like cells recruited to the site of injury following death of primary odontoblasts
histology of pulp
4 distinct regions
1) odontoblast layer
- at periphery of pulp, adjacent to pre dentine layer
2) cell free zone of Weil
- blood vessels (arterioles and venules) enter via the apical foramen up through the root canals, branching laterally to form a subodontoblastic capillary plexus
- sensory and autonomic nerves enter the apical foramen to form an interlacing network of nerve fibers – the subodontoblastic plexus of Raschkow
- from this plexus, nerve fibers emerge from their myelin sheath to terminate as free nerve endings between odontoblasts
3) cell rich zone
- pulpal fibroblasts and undifferentiated mesenchymal cells
4) pulp core
- composed almost entirely of fibroblasts
cells in the pulp
1) FIBROBLASTS
- bulk of dental pulp
- produce collagen, ground substance (ECM) and eliminate collagen in remodeling
- pulp fibroblasts are heterogenous - some can also produce inflammatory mediators, and express surface receptors in response to insults
2) IMMUNE CELLS
- for surveillance and initial response
- dendritic cells are present beneath the odontoblast layer and increase in number in response to dental injury
- macrophages, neutrophils, APC, t lymphocytes
- B and mast cells are NOT residents of normal dental pulp, only present during inflammation
- these immune cells can be upregulated by immunocompetent odontoblasts following stimulation by bacterial components eg LPS, flagellin
3) DENTAL PULP STEM CELLS
- generally remain quiescent in pulp
- differentiate into fibroblasts or secondary odontoblast like cells depending on stimulus
4) ECM
- 75% water, 25% organic materials
- a complex scaffold to stabilize pulp structure
- influence cell migration, proliferation, adhesion, differentiation and function
- contains collagen, GAGs
what is the role of collagen in pulp
part of the ECM
- predom type I collagen and some type III
- mixture of collagen phenotypes provides optimal conditions for pulp homeostasis and promotes pulp repair after injury
- pulp has potential to upregulate collagen synthesis prior to mineralisation, as evident in the formation of a reparative dentine bridge after pulp exposure and aseptic pulp capping
role of GAGs in pulp
glycosaminoglycans
- are non collagenous organic materials
- accumulate in the subodontoblastic region and interact with other extracelular signaling molecules related to pulp cell differentiation and potential pulp repair
- are hydrophilic, gives pulp its unique gel like properties. allows pulp to swell and fill most of the extracellular space, making movement of cells possible
what are vasoactive neuropeptides
substance P, contained by sensory fibers
- affect pulpal blood flow and vessel permability
- stimulate growth of pulpal cells eg fibroblasts and odontoblasts
- recruit immunocompetent cels
what is blood supply of the pulp regulated by
- autonomic control (sympathetic innervation)
- local control (neuropeptides)
fxn of dentine pulp complex
1) formation
- odontoblasts form and maintain dentine throuhg life
2) defensive/ reparative
- responds to pathology through pulp immune inflammation defense system
(elaborate later)
3) nutritive
4) sensory/protective
- 3 KEY events: reflex withdrawal, pain, local increase in blood flow
5) adaptive
- calcification
- physiologic - aging
- pathologic - trauma, disease
what is the innate immune defense in pulp
- receptors on odontoblasts, dendritic cells, fibroblasts and sensory nerve fibers recognise invading microbes and activate signaling pathways
- the innate defense slows down bacterial invasion by increasing dentinal fluid outflow to dilute toxins and contains Ig to protect pulp
- innate response also reduces dentine permeability thorugh intratubular mineralization/ calcification and tertiary dentine formation, reducing diffusion of endotoxins through tubules into pulp
role of odontoblasts in immune response
- primary odontoblasts are the first to respond via cytokines and chemokines to deeper pulp tissue to initiate innate and adaptive inflammatory responses
- odontoblasts have PRRs (eg TLR) that recognise PAMPs
- PAMP- TLR interaction activates NF-kB intracellular signaling pathway, leads to production of proinflammatory cytokines and chemokines - IL1b, IL8, TNFa which recruits immune cells
- odontoblasts can also release antimicrobial peptides to kill Gram + and - bacteria
- regulate vascular permeability and angiogenesis
difference between reactionary and reparative tertiary dentine
reactionary is in mild injuries, primary odontoblasts increase dentine formation along the internal aspect of the dentine beneath the lesion. this form of dentine is continuous with primary and secondary dentine
reparative is for severe injuries that cause death of primary odontoblasts so replacement cells are odontoblast like cells which differentiate from pulpal mesenchymal cells and form reparative tertiary dentine
- this form of dentine appears as a localised dentine deposit on the wall of pulpal cavity subjacent to the lesion
- it is atubular dentine and hence is structurally different from primary and secondary dentine
