dentine physiology and hypersensitivity Flashcards
describe the innervation to dentine?
what is the sensory supply
- Plexus of Raschkow in cell free area
- Small & large myelinated / unmyelinated fibres
- Pain detection
- Most sensitive near ADJ
- Quite sensitive near pulp
- increased sensitivity when pulp inflamed – toothache!!
sensory supply = Maxillary and mandibular branch of cranial nerve V
- nerve endings are predominantly nociceptive
how are nerves supplying dentine formed?
- Nerve fibres enter through apical foramen during dentinogenesis
- First fibres located close to blood vessels (controlling blood flow)
- Autonomic / sympathetic innervation then follows
- Nerve plexus of Raschkow not established until root formation complete
what are the theories for dentine sensitivity?
- odontoblasts as nerves
- intra-tubular nerve endings
- hydrodynamic mechanism
describe the ‘odontoblast as nerves’ theory of dentine sensitivity
is this the correct theory?
- odontoblasts are of neural crest origin
- can transduce impulses and therefore ‘act as nerves’
- however no real evidence
- membrane potential of cell is too low
- highly unlikely
describe the ‘intra-tubular nerve endings’ theory of dentine sensitivity
is this the correct theory?
- there are nerve endings within some of the dentinal tubules
- can enter tubules but is not extensive
- not theory
- not many nerves in tubules
- nerves develop after eruption - newly erupted teeth are sensitive
- local anaesthetics have little effect on exposed dentine
- would expect a rapid block
describe the ‘hydrodynamic mechanism’ theory of dentine sensitivity
is this the correct theory?
- changes to fluid in dentinal tubules -> hypersensitivity
- movement in fluid registered by nerve endings in the plexus of raschkow
- greater sensitivity at ADJ - more branching of tubules
- believed to be responsible
- explains why local anaesthetics do not block dentine sensitivity
describe the structure and morphology of the dentine tubules
how does sensitivity occur?
- The Tubules are typically filled with fluid and the ends of the tubules are occluded by enamel or cementum
- fluid does not move until there are holes in enamel or gaps in cementum
- = exposure of fluid to external stimuli
- Exposure of the tubules is thought to be the cause of dentine sensitivity
what are nociceptors?
- receptors that respond to noxious stimuli
- Pain can be a result of stimulation of nociceptors
- Nociceptors are free nerve endings & respond specifically to heat, intense pressure, irritants but not innocuous stimuli
what classes of nociceptor are there?
- 3 major classes of nociceptor
- Thermal,
- mechanical,
- polymodal
- Polymodal - response to noxious proteins, cytokines, bacterial proteins etc.
name the nerve fibres which are responsible for pulpal pain and innervation
- A delta fibres
- myelinated
- C fibres
- un-myelinated
what characteristics do A delta fibres have?
what pain are they responsible for?
- Low stimulation threshold
- Fast reaction and conduction
- Communication of short fleeting pain sensation
- Activated by hydrodynamic mechanism
- Fluid movement is mechanical - triggers mechanical nociceptors
- Responsible for sensitivity of dentine
what characteristics do C fibres have?
what pain are they responsible for?
- High stimulation threshold
- Slow reaction and conduction
- Located in the pulp
- Communication of persistent, heavy, dull, intense pain, often throbbing in nature and poorly localised
- Responsible for the pain associated with toothache - inflammatory pain
what are common initiation factors for dentine hypersensitivity?
Cold>brushing>hot>sweet
where is the most common site for dentine hypersensitivity?
why?
- Buccal cervical (premolars)
- thinnest layer of enamel
- predominant gingival recession -
- = increased dentine exposure
Order of Predilection
- Canines and 1st Premolars
- Incisors and 2nd Premolars
- Molars
how do thermal factors trigger dentine hypersensitivity?
- Cold temperatures cause outflow of fluid → sensitivity.
- BUT high temperatures are generally found to have less affect on sensitivity.
- HIGH TEMPERATURES AFFECT LESS AS: it is thought to be because it causes relatively slow inward movement of dentinal fluid.
how do mechanical factors trigger dentine hypersensitivity?
Evaporation from the surface causes outflow of fluid → sensitivity
Brushing causes direct movement of dentinal fluid → sensitivity
how do chemical factors trigger dentine hypersensitivity?
- Such as acidic substances
- fruit juices
- Hyperosmotic solutions will induce an osmotic pressure, which in turn causes flow of dentinal fluid (- the hydrodynamic theory)
- acids removes the smear layer which has formed to protect the exposed dentine, making the tubules patent to the pulp again.
how can sensitivity increase?
what is the cause?
- due to widening of dentinal tubules
- inflammation
how does widening of dentinal tubules increase hypersensitivity?
what is the cause?
- Allows greater outflow of fluid, therefore increasing sensitivity
- cause : consumption of acidic foods
- acid can demineralise peritubular dentine and widen tubules
how does inflammation cause an increased sensitivity?
pulpal inflammation occurs when:
- Plaque builds up on the exposed dentine
- Bacteria may start to penetrate the dentine tubules
- Odontoblasts die causing increased dentine permeability
- Bacterial toxins can then leak into the pulp, resulting in inflammation
- Pulpal inflammation can cause the stimulation of C fibres in the pulp, which produces a duller, more persistent pain.
how can dentifrices be used for dentine hypersensitivity?
- Strontium salts
- occlude dentine tubules
- Strontium Acetate and Strontium Chloride found in Sensodyne
- Potassium Salts
- Occlude dentine tubules
- Potassium Nitrate found in Colgate Sensitive
- Salts dissociates & ions diffuse down the dentine tubule.
- Ions surround nerve fibres preventing depolarisation by maintaining charge. Therefore prevent neural response by chemical intervention
- Or blocking of the tubules
- Prevent fluid flow
- Ions surround nerve fibres preventing depolarisation by maintaining charge. Therefore prevent neural response by chemical intervention
- silica is often added to toothpastes
- occludes dentine tubules
- are resisistant to acidic erosion and mild abrasion
- longer lasting
what clinical treatments can be used for dentine hypersensitivity?
- Sodium Fluoride Varnish - Duraphat (5% NaF)
- Secondary effect → reduces sensitivity
- Applied by dentist as topical application
- Occludes dental tubules
- Semi-permanent, eventually removed by brushing & dietary acids
- Glass ionomer
- Hard restoration used to treat gum recession
- Permanently bonded to tooth
- Dentine tubules occluded
- Much more resistant to wear
- More extreme clinical treatments - root canal therapy, extraction.
how does exposed dentine become sensitive?
- A trigger causes dentinal fluid to flow OUT of the dentinal tubules.
- This results in a pressure change across the dentine.
- This causes activation of intradental nerves
