OE L7 Dentine Physiology and Sensitivity Flashcards
What causes dentine senitivity?
Movement of fluid in the dentinal tubules.
Fluid moves when there are holes in enamel or cementum which expose to the tubules external stimuli.
Is tissue fluid in the pulp in equilibrium with tissue fluid in tubules?
Yes
What is the main nerve plexus of the pulp?
The plexus of Raschkow
Describe the plexus of Raschkow.
Only established once root formation is complete.
Mixture of small and large myelinated/unmyelinated fibres.
When do nerves fully form for primary teeth?
At 12-18 months post eruption.
When do nerves fully form for permanent teeth?
Up to 3 years post eruption.
What are the 3 proposed theories for the cause of dentine sensitivity?
- Odontoblasts as nerves
- Intra-tubular nerve endings
- Hydrodynamic theory
Describe the theory for sensitivity of odontoblasts as nerves.
- Odontoblasts are ectomesenchymal in origin
- Neural crest cells infiltrate the mesenchyme and therefore odontblasts have this neural crest element
- No real evidence to support
- Membrane potential too low to permit transduction
Describe the theory for sensitivity of intra-tubular nerve endings.
- Presence of nerve endings within tubules
- Poor evidence
- Some nerves enter tubules but to a very small degree
- Local anaestethics have little effect on exposed dentine, disproves theroy
Describe the hydrodynamic theory.
- Any alteration to hydrodynamics of the fluid in the tubules gives rise to hypersensitivity
- Movement in fluid registered by nerve endings
- Explains why local anaesthetics do not block dentine sensitivity
- Cold air blown on to cavity prep causes pain due to movement of fluid which triggers nerves, patients register this as pain.
- Greater sensitivity at ADJ: due to profuse branching of tubules in this area
What causes fluid to move in the tubules?
Exposure of the tubules through enamel loss or cementum loss.
Dentine exposure then allows direct contact of pulp with external stimuli, and tubular fluid shifts stimulate mechanoreceptors in the pulp.
Which nerves are involved in dentine sensitivity?
- Maxillary and mandibular branches of the trigeminal nerve
What type of nerve fibres are involved in dentine sensitivity?
- Mostly nociceptive fibres (communicating discomfort and pain through A delta and C fibres)
- Proprioceptive fibres
- Autonomic fibres controlling blood vessel tone
Describe nociceptors and their 3 types.
Nociceptors are receptors at the end of nerve fibres which respond to noxious stimuli, stimulation of them will cause the psychological response of pain.
- Thermal (temperature change)
- Mechanical (pressure and strecth)
- Polymodal (noxious proteins, cytokines, bacteria)
What is the difference between A delta and C nerve fibres?
2 fibre groups which when activated cause tooth pain.
Quality of pain (severity) depends on stimulus and type of fibre activated.
Describe A delta fibres.
- Dentine sensitivity
- Low stimulation threshold
- Fast reaction and conduction
- Short fleeting pain
Describe C fibres.
- Inflammatory, prolonged, dull toothache
- High stimulation threshold
- Slow reaction and conduction
- Communication of persistent, heavy, dull, intense pain
- Poorly localised, usually throbbing
Describe the prevalence of dentine hypersensitivity.
- 15% of population, increasing in prevalence
- Peak incedence age 20-40
- Affects more women
- Less likely in children
Which teeth are most commonly affected by sensitivity?
- Canines and first premolars
- Incisors and second premolars
- Molars
Where enamel is thinnest and gingival recession is predominant.
Which area of the tooth is most commonly affected by sensitivity?
- Buccal cervical region where enamel is thinnest
What is the relationship between dentine sensitivity and plaque?
- Negative correlation with plaque scores- plaque serves to cover and occlude the dentine
Explain gingival recession and dentine sensitivity.
- Shifting of gingival margin apically exposes part of root
- Cementum exposed, loss of cementum then exposes dentine
- Causes: periodontal diseases, inappropriate tooth brushing (too hard or hard bristles)
Explain enamel loss and dentine sensitvity.
- Attrition (mechanical) e.g. bruxism
- Abrasion (mechanical)
- Erosion (chemical)
Most susceptible at cementoenamel junction as there may be only a thin layer of enamel.
Name 3 types of triggers of sensitivity.
Thermal triggers:
- Cold temperatures cause outflow of fluid
- Hot temperatures cause slow inward movement of fluid (less of an effect)
Mechanical triggers:
- Evaporation from the surface causes outflow of fluid → sensitivity
- Brushing causes direct movement of dentinal fluid → sensitivity
Chemical triggers:
- E.g. acidic substances which often cause erosion
- Acids in fruit juice remove smear layer which has formed to protect the exposed dentine, making the tubules patent to the pulp again.
What factors can increase sensitivity?
- Widening of dentinal tubules (e.g. acid can demineralise peritubular dentine), allows greater outflow of fluid
- Pulpal inflammation which can cause stimulation of C fibres and produce a duller, more persistent pain
Which toothpaste and mouthwash ingredients can reduce sensitivity?
- Strontium salts and potassium salts occlude tubules temporarily, reapplication crucial
- Silica also occludes tubules and is more resistant to acid erosion and mild abrasion than salts so has longer lasting effects
What clinical treatments reduce sensitivity?
- Sodium fluoride varnish (Duraphat 5% NaF) occludes tubules, temporary
- Glass ionomer, permanently bonded to tooth and occludes tubules, resistant to wear
- More extreme: root canal therapy or extraction
Describe the fluid found in dentinal tubules.
It is an ultrafiltrate of the blood from capillaries in the pulp.
