L8 Flashcards
The Dental Pulp
Soft connective tissue that supports dentin
Unique as tooth tissue
vascular
not calcified
The Dental Pulp: Embryonic origin
ectoderm- neural crest ectomesenchyme-dental papilla
The Dental Pulp: Constituents:
cells & cellular elements
blood and lymphatic vessels
extracellular matrix
Like dentin, pulp has an
extracellular matrix and contains parts of cells (nerve fibers). Unlike dentin, pulp has blood vessels & whole cells.
Functions in Development: 2. “formative” function:
DENTINOGENESIS
ODONTOBLASTS:
secrete
organic matrix of dentin
collagen is major component; provides scaffold for mineralization
Odontoblasts: participate in
mineralization
transport Ca++ ions that comprise the HAP crystal
secrete proteins important in controlling mineralization
dentin phosphoprotein (from DSPP gene)
Dentin Phosphoprotein
Relatively Specific to dentin (< amts., transient in bone, cementum, or enamel) Prominent dentinal protein (> 50% NCP’s) Binding sites for collagen Highly phosphorylated High in serine/aspartic acid Acidic/anionic
DPP: Binds to
collagen in forming dentin matrix
Attracts Ca++ ions to INITIATE MINERALIZATION
Dentinogenesis (crown) begins during the
“BELL STAGE”
Just prior to dentinogenesis
Tissue layers of dental organ present
Crown outline present
No odontoblasts or ameloblasts
Late Bell Stage
Inner enamel epithelial cells… Ameloblasts
Undifferentiated mesenchymal cells (dental papilla)… Odontoblasts
Dentin secreted
Enamel secreted
Dentinogenesis:
cusp tips to cervix
Dentinogenesis:
periphery to pulp center
Odontoblast differentiation begins when cells in the
outer layer of the papilla stop dividing. Following the last mitosis, cells closest to the future DEJ proceed through dramatic changes that modify their shape and transform their function. First, the undifferentiated papilla cells began to elongate into a columnar shape & nuclei migrate to basal part of the cell. They subsequently grow processes that extend toward the future DEJ and begin to secrete dentin. The organic matrix of dentin is secreted 1st & subsequently the matrix is mineralized. When dentin secretion begins, the cells are considered ODBs and the dental papilla becomes the dental pulp. Dentin is laid down over a period of time. During this time, ODBs migrate toward the pulp center and one major ODB process becomes dominant and elongates.
WHAT KICKS OFF (INDUCES) odontoblast differentiation?
Inductive signal for odontoblast differentiation: secreted molecules from enamel organ- most likely the enamel knot (epithelial-mesenchymal interaction)
multiple molecules:
several families of signaling/growth factors implicated
2 prominent & best documented:
BMP’s (bone morphogenetic protein)
Wnt’s *(pronounced “went”)
Evidence for a role of Wnt10a in odontoblast differentiation
Technique:
At multiple time points:
Stained for Wnt10a using “in situ hybridization” (detects mRNA for Wnt10a)
Stained for dentin sialophosphoprotein (DSPP, a sign of odontoblast differentiation)
Wnt10a
1st expressed in enamel knot(s)
Then pre-odontoblasts at the cusp tip
Then successively more cervical parts of teeth
In other words, Wnt10a expression immediately precedes the “wave” of odontoblast differentiation
Wnt Signaling is Also Important in the Adult Pulp
In adult, Wnt is released by pulp cells after injury
Modifying the Wnt receptor complex to amplify effects of Wnt binding increases production of reparative dentin & dentin proteins in animal models
Pulp in the crown is the
“pulp chamber” or “coronal pulp”. Coronal pulp includes extensions into each cusp called ‘pulp horns’. Pulp in the roots constitutes the “root canal”/“radicular pulp”. The root canal is continuous with periodontium at the apical foramen, a very small opening (.3-.4mm) normally at the base of the tooth.
Pulp is not “normally” calcified, but ectopic* calcifications are common… 2 types:
Pulp stones
Diffuse calcifications
The cause of pulp stones and diffuse calcifications is
unknown and the degree to which they indicate pathology is not clear. However, they can be found in teeth which appear perfectly healthy. A relationship with age is often claimed, but the empirical evidence is variable. It has been difficult to assess whether these ectopic calcifications harm pulp. However, they can complicate endodontic therapy.
Pulp core=
is located central to the odontogenic zone & contains fibroblasts & trunks of larger branches of both nerves & blood vessels.
Odontoblasts –
bodies in pulp, process in dentin.
Fibroblasts –
pulp only, secrete ECM for pulp only.
Dendritic cells usually in
periphery in cell – usually around cell free/cell rich area.
Odontoblasts
Fibroblasts
confined to pulp
secrete ECM
Resident immune cells
macrophage
lymphocytes
eosinophils
dendritic cells
inflammation
plasma cells
mast cells
pmn’s
PG’s & Associates (the GAGs)
smaller: decorin, byglycan (most prevalent)
larger: versican, syndecan
GAGs: dermatan, chondroitin, heparin sulfate
Functions:
matrix for diffusion
collagen fibrillogenesis
water retention ( pressurizes pulp resist compressive forces)
Glycoproteins
e.g., fibronectin
Function: role in cell adhesion to ECM
Collagen (I & III)
both fibrillar collagens
Function: tensile strength
Similarities & differences compared to dentin:
Dentin has type I collagen but little or no Type III (consistent with the fact it’s a hard connective tissue)
(Mature) pulp does not contain DSPP!
STEM CELLS
high capacity for self-renewal
“plastic”: can generate multiple cell types*
PLENTIFUL DURING DEVELOMPENT BUT ALSO PRESENT IN ADULTS
Dental pulp stem cells can be
induced to form a number of cell types, not only odontoblasts & also adipocyte- and glial-like cells in vitro…
Stem Cell Niches Probably Present
in
Multiple Locations of Mature Pulp
Precise roles of different stem cell populations in the pulp are just being
worked out, but they probably play a role in response to injury
A role for pericytes (perivascular cells) in the response to pulp injury was recently studied….
Transgenic mice can be
used to track the role of different stem cell populations after injury
Pericytes (and ONLY pericytes) are
marked in this transgenic mouse
The staining can be controlled so that it
“turns on” at a defined point in time
This experiment tracked
pericytes after injuring the original odontoblasts
The results demonstrated that pericytes transform into new odontoblasts
However, not all new odontoblasts came from pericytes suggesting that other types of stem cells also contribute
Successes with dental stem cells
Creating tooth buds or repairing tooth structure in animal models
Treating other conditions like multiple sclerosis (MS) or spinal cord injury
Limitations with dental stem cells
Size and shape of engineered teeth poorly controlled
How to integrate an engineered tooth into the jaw?
Human teeth take months-years to form
Due to limitations, a more practical use for DPSC’s is likely to be
repair
E.g., regenerating pulp tissue lost to caries
Much research is currently focusing on the optimizing such procedures in preclinical models
Canine Model of Total Pulp Regeneration
Isolated stem cells from maxillary canines for autologous implants
Removed pulp tissue from incisors
Implanted stem cells, G-CSF (granulocyte colony stimulating factor) in combination or separately using a biocompatible, degradable collagen matrix
Performed functional tests (e.g. blood flow), removed repaired teeth, analyzed histology.
Good repair took place
Combination of stem cells and G-CSF was important
G-CSF*: named for its function in transforming leukocyte precursors into granulocytes (neutrophils)
Produced by many tissues
Variety of functions
Chemotactic for many types of stem cells, including DPSCs
Promotes neurogenesis & angiogenesis
Anti-apoptotic
Hypothesized Mechanisms: DPSCs are
multipotent, providing raw material for new pulp tissues
BUT, they have other important functions:
Anti-inflammatory
Secrete trophic factors promoting angiogenesis & neurogenesis
G-CSF promotes these processes :
Keeps DPSC’s in the area, because DPSC’s have G-CSF receptors
Attracts other stem cells from surrounding tissues
Anti-apoptotic & proliferative effects
Odontoblasts
unique to pulp2nd most numerous cell type in pulp
Odontoblasts: Functions:
Dentinogenesis Nutrients to dentin (provides water) Immune support potentially. Cell bodies & processes (extent- still an open?) Cell body dimensions: Crown: 25-50uX5-7u Root: more cuboid Processes thinner
Junctions Between Odontoblasts
Desmosomes & Adherens junctions: “sticky”, maintain position and polarity
Gap Junctions: channels between cells; coordinate dentiogenesis
Tight: apical“weld” membranes
Depending on the exact form of the proteins & their extent , tight junctions can form an inter-cellular barrier
Functional assays suggest that although some smaller molecular weight substances can pass between adjacent odontoblasts,
TIGHT JUNCTIONS inhibit the passage of larger molecules and probably bacteria
Pulp is:
highly vascularized
also has a lymphatic system
presence of blood & lymphatic vessels distinguish it from other tooth tissues
Blood flow in pulp under neural control…
Sympathetic: CONSTRICTS!
Alpha-adrenergic receptors
Parasympathetic (? But doubtful)
Sensory!
The nervous system controls
pulpal blood flow. The autonomic component of this control is mainly sympathetic, via norepinephrine and alpha adrenergic receptors. Parasympathetic control is doubtful. However, importantly, sensory nerves also affect pulp blood flow (see below).
Don’t’ get confused! It’s true that sympathetic activation usually causes
skeletal vasculature to dilate. However, it causes vasculature to the GI tract and skin, as well as the dental pulp to constrict.
Lymphatic Vessels in Pulp
Note similarity to vascular pattern
Importance in Healing:
Drain proteins accumulated during inflammation
The tooth interior (pulp & dentin) is
highly innervated
Small Adelta & C fibers
A delta– sensory pain fibers
C- some are sensory pain fibers, others are sympathetic
Also Abeta
Sensory pain fibers
Previously thought that innervation was nearly exclusively by small diameter nerve fibers but a contribution of Abeta fibers is now recognized
!! Main sensation arising from activating nerve fibers innervating the pulp (& surrounding dentin) is PAIN
Pulp innervation begins at
Bell stage
density of innervation increases until
eruption & more slowly until a few years afterward
innervation probably
decreases with aging
both primary & secondary dentition is
innervated
nerves enter through the
apical foramen & terminate in pulp-dentin border zone and dentin
mature teeth, odontoblasts do not
extend all the way to the DEJ.
However, remember: early in dentinogenesis, odontoblasts processes reach
outer dentin
Later, they seem to retract*
*However, note that the issue of the extent of the odontoblast process is still controversial
Nerve Fibers Also
Profusely Innervate the Pulp-Dentin Border Zone
Hydrodynamic
Theory
of Dentinal Pain
If nerve fibers do not extend all the way to the DEJ, what accounts for the fact that a patient will feel pain as soon as a drill passes from the enamel into the dentin; in other words, what accounts for the high pain sensitivity @ the DEJ? Also, once the dentin is exposed, it is clear that MANY stimuli can give rise to pain, including air drying, osmotic stimuli such as foods that contain a high concentration of sugar or cold stimulation.
Current thinking is that the most likely explanation for dentinal sensitivity is the HYDRODYNAMIC THEORY. Hydrodynamic theory proposes that all dentinal stimuli that cause pain–, have something in common: each of these stimuli cause fluid movement in dentinal tubules. This fluid movement in turn causes deformation of mechanically-sensitive nerve endings, close to and in the dentin.
Original evidence for the hydrodynamic mechanism came from experiments done on extracted human teeth. An investigator named Branstromm measured fluid flow thru dentin that resulted from various stimuli and was able to show a rough correlation with the ability of these stimuli to cause pain when applied to superficial dentin in a person.
Mechanically-activated ion channels (“mechanoreceptors”) are
embedded in the membranes of nerve fiber endings of AΔ & Aβ fibers in the pulp/dentin border region
When the nerve fiber endings are deformed:
Ion channels open
Na+ sodium flows into the nerve endings,
Depolarizing them & giving rise to action potentials
However, the odontoblast most likely has some function in
dentinal sensitivity, at the very least, due to crowding & proximity in tubule, the odontoblast process affects fluid dynamics around nerve process.
BOTTOM LINE: HYDRODYNAMIC MECHANISM CONSIDERED MOST IMPORTANT FOR DENTIN SENSITIVITY BUT ROLE OF ODONTOBLAST STILL
UNDER INVESTIGATION
PAIN ALSO ARISES DIRECTLY FROM
STIMULI IN THE PULP
hydrodynamic fluid flow not required
Other pulp nerve fiber endings, especially C fibers, have receptors for
inflammatory & thermal stimuli
Members of the TRP receptor family
TRP receptors are a family of transmembrane receptors for thermal & inflammatory pain in many regions of the body
Multiple types of nerve fibers & receptors underlie pain from the
tooth interior (pulp & dentin)
Pulpal (inflammatory) stimuli activate more C fibers, probably those that terminate
deeper, in subodontoblastic layer. This activation of different types of nerve fibers by different types of stimuli may account for why the quality of pain experienced is different for dentinal versus pulpal stimuli. Stimuli applied to dentin (A fibers) cause sharp, piercing pain; pulp inflammation (C fibers) is associated with pain described as dull & aching. The quality of pain can therefore be useful on a diagnostic basis. Of course, in many clinical situations, these types of pain are intermingled because integrity of dentin is disturbed, in conjunction w/pulpal inflammation.
It is interesting and significant that pain nerve fibers in the tooth have functions that extend beyond the
sensory. Certainly, one role of these fibers is sensory: to inform the organism that the tooth is injured, and this in turn serves a protective role by limiting use. However, it is now appreciated that these fibers also have an important regulatory influence on the pulp itself. This is mediated largely by the release of a class of neuromodulators called neuropeptides. Tooth nerves contain a variety of neuropeptides: two prominent ones are substance P AND CGRP (calcitonin-gene related peptide).
Peptides sythesized in cell body in trigeminal ganglion:
@ central endings: transmitter function
Peptides bind w/receptors on brain neurons pain
@ peripheral endings: local regulatory function
Peptides bind w/receptors on vasculature/local cells pro-inflammatory
These substances are synthesized in the
cell bodies of these neurons (in the trigeminal ganglion). From there, they are transported to the central endings of the fibers in the central nervous system (the trigeminal nucleus of the brainstem) also to the peripheral endings in the tooth. When these fibers are activated by a painful stimulus, e.g., injury or inflammation, neuropeptides are released at both the central and peripheral ends. In the brain, they serve a neurotransmitter role. However in the pulp, they have effects on local cells with appropriate receptors.
Vasodilation
(opposes sympathetic control)
Interactions with immune cells
Stimulation of cytokine production by macrophages
Chemotactic effects on immune cell migration
