Orofacial pain Flashcards
Define noxious stimuli, allodynia and hyperalgesia
- Noxious stimuli: A stimulus that is painful
- Allodynia: Pain due to a non- noxious (non painful) stimuli, for example, pain due to touch
- Hyperalgesia: A state of increased pain to a noxious (painful) stimuli
Explain the process of pain perception (nociception) in terms of nerve fibres and the general pathway of pain transmission
There are two types of afferent nociceptive nerve fibres:
• Aδ fibres: myelinated thus sharp, pricking pain that’s well localised
• C fibres: unmyelinated, thus dull pain that is poorly localised. It is a secondary or slow pain
General pathway involved in the transmission of pain:
• First, the fibres detect pain and transmit this information to second order neurons into dorsal horn of the spinal cord, then this is transmitted to the thalamus of the brain
Explain the process of orofacial pathway of pain transmission
- Trigeminal nociceptive nerve fibres in the TMJ, PDL or orofacial muscles will travel to the trigeminal ganglion as “first order neurones”.
- From here, they travel to the trigeminal sensory complex in the brainstem.
- These first order will synapse with second order neurones in the “subnucleus caudalis”
- Second order neurones ascend to the nucleus of the thalamus.
- Here, second order neurons synapse with third order neurons in higher order centres in the brain , which will discriminate where the pain is coming
Explain peripheral sensitisation in the scenario of tissue damage (e.g. tooth abscess)
- This is known as an increased sensitivity to a stimuli that is received by afferent nerves (nerves that travels from the skin to the brain)
- Injury/ cell damage recruits mast cells, macrophages and neutrophils
- These immune cells releases chemicals such as H+, bradykinin, interleukin and pro-inflammatory cytokines
- These chemicals bind to nociceptors, which has two effects
- Firstly, it causes an action potential strong enough that it will travel to the brain = pain sensation
- Secondly, it sensitises nociceptors by bringing their membrane potential closer to the depolarization threshold. This up-regulates ion channels, causing an influx of ions -> fast and/or prolonged depolarisation -> action potential -> pain
Provide 3 oral examples of peripheral sensitisation
- Abscessed tooth painful to bite upon, painful to percussion
- Ulcer/sore spot under over-extended denture flange
- Tender jaw muscles; tender TMJ
Explain central sensitisation, and how this can also contribute to allodynia
- An increased responsiveness of nociceptors in the central nervous system
- The brain has adapted toover reactto the normal signals of movement/pressure/temperature etc and the brain misinterprets this information and sends a protective signal: pain - results in hyperalgesia and allodynia
- 2nd order neurones are much more likely to be involved in this. A very strong response from first order neurones could cause a barrage of chemicals that result in constant depolarisation of second order neurones, thus continually firing off action potentials that go to the brain
- Low inputs may end up easily activating second neurones
- Tactile input can also illicit pain because 2nd order neurones not only conduct nociception, but also are responsible for tactile input/ pressure/ temperature
Explain why an abscessed tooth is tender to touch
- The patient is experiencing allodynia
- The nociceptive pathway to higher centres of the brain is being activated
Mechanisms involved in allodynia:
• Peripheral sensitization of nociceptive endings (inflammatory changes etc.)
• Central sensitization of neurons conveying information along the nociceptive pathway to higher centres - their subnucleus caudalis is sensitised
• Combination of both
State why central sensitisation is considered a disease entity
- Possibility where periphery heals but central brain changes perpetuate the pain
- This is why peripheral nociceptive input is blocked during GA surgery; it reduces the chances of central sensitisation
Explain the mechanism of referred pain in the orofacial region
- Referred pain is pain felt at a site distant from the site of injury
- Nociceptive afferents from different orofacial regions may converge onto the same 2nd order neurone. These are known as “silent connections”
- This is the case for the temporalis muscle, where its nociceptors converge with forehead and upper molars nociceptors
- Prolonged and/or intense noxious stimulus in the temporalis muscle (star) could sensitise/ activate these “silent connections” with other neurones. The brain is therefore confused as to which nociceptive afferent is the source of the problem
- Thus, pain source may not be the pain site
List the the management of referred pain (4)
Reduce pain
Restore comfortable jaw function
Improve quality of life by addressing stressors
Long term management
Explain the possible mechanism behind persistent pain in a patient where the suspected source of pain is removed
- Central sensitization helps explain these somewhat bizarre signs and symptoms –changes have occurred in the excitability of 2nd order (and higher) neurones in the Trigeminal Brainstem Sensory Nuclear Complex
- Tactile input is eliciting pain because 2nd order neurones not only conduct nociception, but also are responsible for tactile input/ pressure/ temperature
- Therefore, even though the periphery has calmed down, the changes in the 2nd order neurones is causing nociception
Describe the management of central sensitisation
- Short term management goals: pain reduction, improvement of psychosocial factors and restoration of function
- Medications: Amitriptyline (Tricyclic antidepressants) 10 mg at bedtime or capsaicin 0.075% cream (apply to the skin of the cheek where pain is)
- Commence exercises and muscle relaxation techniques
- Further psychological assessment and cognitive therapy and strategies for coping with the pain and improving family relationships.
Explain the possible mechanism behind TMJ pain. (refer to TMJ lecture notes)
Peripheral sensitisation:
• Excessive stretching of the jaw can be injurious
• Injury/ cell damage recruits mast cells, macrophages and neutrophils
• These immune cells releases chemicals such as H+, bradykinin, interleukin and pro-inflammatory cytokines
• These chemicals bind to nociceptors which has two effects
• Firstly, it causes an action potential strong enough that it will travel to the brain = pain sensation
• Secondly, it sensitises nociceptors by bringing their membrane potential closer to the depolarization threshold. This up-regulates ion channels, causing an influx of ions -> fast and/or prolonged depolarisation -> action potential -> pain
Central sensitisation:
• An increased responsiveness of nociceptors in the central nervous system
• The brain has adapted toover reactto the normal signals of movement/pressure/temperature etc and the brain misinterprets this information and sends a protective signal: pain - results in hyperalgesia and allodynia
• 2nd order neurones are much more likely to be involved in this. A very strong response from first order neurones could cause a barrage of chemicals that result in constant depolarisation of second order neurones, thus continually firing off action potentials that go to the brain
• Low inputs may end up easily activating second neurones
• Tactile input can also illicit pain because 2nd order neurones not only conduct nociception, but also are responsible for tactile input/ pressure/ temperature
• This is thought to be one of the main mechanisms of chronic pain; Possibility where periphery heals but central brain changes resulting in hyperexcitable 2nd order neurones perpetuate the pain
Describe the concept of “reducing pain”
- Education of problem and the pain
- Awareness of habits/jaw use patterns; clenching, grinding, jaw posturing
- Diet modifications
- Positioning of jaw to avoid tooth contact habit
- Avoid wide jaw openings
- Moist heat/ice or
- Analgesics: moderate pain = NSAID + codeine, severe pain = opioid
Describe the concept of “restoring comfortable jaw position” and “improving quality of life by addressing stressors”
Restore comfortable jaw function:
• Jaw exercises/heat packs to increase jaw mobility
Improve quality of life by addressing stressors:
• Chronic pain is often associated with severe physical and/or emotional stresses
• Relaxation strategies; deep breathing, muscle relaxation
• Reduction of work stressors; improve work station ergonomics, discuss with employer work goals
