Pain
• It is perhaps the most commonly experienced symptom in dentistry.
• Yet, a precise definition of pain does not exist as pain has a subjective/ psychophysiological aspect (a painful stimuli for one individual may not be painful for another)
• Arbitrarily, pain can be defined as any u...
Review on Local Anesthesiology
By: Dr. Mostafa Lee Mehrafsha
TOPIC I - PAIN
Pain
• It is perhaps the most commonly experienced symptom in dentistry.
• Yet, a precise definition of pain does not exist as pain has a subjective/ psychophysiological aspect (a
painful stimuli for one individual may not be painful for another)
• Arbitrarily, pain can be defined as any unpleasant experiences may it be emotional,
mechanical/physical or chemical with or without tissue damage.
Dual nature of Pain
• Pain like other sensations (touch, hot, cold, etc.) has a physioanatomical aspect which explains the
physiological processes and anatomical parts involved in Pain Perception.
• In addition pain also has a Psychophysiological aspect that is unique to each individual. it explains
the psychological factors associated with Pain Reaction.
Theories of pain
1. Specific theory:
Developed by Descarets in 1644
Describes pain systems as a straight-through channel from the skin to the brain
Presence of specific nerve ending for pain perception called Nociceptors.
These nociceptors once activated carry the unpleasant experience to “Pain Center” within the brain
2. Pattern Theory
• Developed by Goldscheider
• Pain are produced by the summation of sensory input
3. Gate control theory
• – Proposed by Melzack and Wall
• Claims the existence of a so called “gate” in the spinal cord that controls the passage of
information from periphery to brain
• The information that travel faster have higher priority to pass the gate and arrive at brain
4. Hydrodynamic Theory
• Provides explanation for dentinal pain and sensitivity
• Dentinal Sensitive is caused by direct stimulation of sensory nerve ending in the dentin which
are primarily located near the pulp
• Yet the most sensitive part of the tooth is at DEJ where no nerve endings exist
• Hydrodynamic theory suggest that the nerve endings near the pulp are stimulated due to the
movement of dentinal fluids present in dentinal tubules
Classification of Pain
• Acute pain:
• Sudden onset, 1st pain
• Sharp, localized and throbbing
• Information carried through A delta fibers which are large and thinly myelinated neurons
(100m/s)
• Chronic Pain:
• Long lasting pain
• Dull and aching pain
• Information carried through C – fibers which are small and unmyelinated neurons ( 0.5-2m/s)
Pathway of Pain
• Describes how a certain stimuli can travel from periphery ( skin or tooth) to brain and be
interpreted as pain
• Most of painful stimuli in dentistry are mechanical (a stimuli that causes physical injury to
tissue) and can be further aggravated by inflammation and its chemical modifiers
• Explains the Physioanatomical aspect of pain
1 TOPRANK REVIEW ACADEMY- ANESTHESIOLOGY MODULE
, NURSING*RADTECH*DENTISTRY*CRIMINOLOGY*MIDWIFERY*MED
TECH
LET*PSYCHOMET*RESPIRATORY THERAPY*CIVIL
• Encompasses all theories of pain SERVICE*NAPOLCOM
Pathway of Acute Pain
Pathway of pain explains the anatomical and the physiological processes involved in pain
perception. This process of pain perception is similar in all individuals and all throughout the body.
Most dental pains are caused by mechanical stimuli which cause physical injury to tissue and
inflammation.
A mechanical stimulus will cause tissue injury, excitation of nociceptors and inflammation. This
mechanical stimulus will be converted to an electrical impulse through a process called
Mechanotransduction. The electrical impulse travels along the 1 st order neuron (A-delta fibres)
and enter the dorsal horn of spinal cord. All sensory information enter the spinal cord from
the dorsal side. Here the 1st order neuron terminates and its axon forms a Synapse with the
dendrite of the 2nd neuron.
The information which was traveling in form of an electrical impulse through the 1 st order neuron
has to be converted into chemical information to traverse the synapse and converted back to an
electrical impulse to travel along the 2 nd order neuron. This is done by release of neurotransmitters
from the 1st order neuron specifically glutamate for a-delta fibres.
The 2nd order neuron then crosses to the contralateral side of the spinal cord and travels through
the Spinothalamic canal to the thalamus of the brain. Here in thalamus the brain will interpret
the information and generate “PAIN”. However, Thalamus fails to specify where the pain is coming
from. Thus, 3rd order neuron will carry the impulse to the cortex of the brain. In cortex, “ Pain
Localization” occurs and the brain can specify the exact location of the painful stimulus.
Pathway of Chronic Pain
The pathway of chronic pain is almost similar with acute pain with few differences.
First, the neural fibres involve in impulse propagation are C-fibres.
Second, 1st order neuron synapses with an interneuron (located at a part of the dorsal horn of
spinal cord called Substantia Gelatinosa) and then the 2nd order neuron.
Third, the neurotransmitter released at the synaptic joint is Substance P and lastly, the 3 rd order
neuron carries information not only to cortex but also to limbic system where the experience is
remembered for the psychological and emotional aspect of pain.
• Opioid Analgesics have a Supraspinal mode of action where they depress the cortex so the brain
cannot localize the pain.
( cortex= pain localization center)
• Patients taking opioid usually describe it as “the pain is still there but it is not that bad”; this is due to
them not knowing where the pain is coming from.
• How does an impulse travel along the neuron? Watch the video below on Impulse Propagation and
action potential
*https://www.youtube.com/watch?v=OZG8M_ldA1M
Modulatory Pathways of Pain
• Pain is necessary for survival but there are instances that feeling pain can actually lead to worse
consequences.
• For example twisting one’s ankle while being chased by a wild animal. Feeling pain at that instance can
lead to animal bite or death.
• Therefore body needs internal processes to control pain and these are called “Modulatory
Pathways of Pain”
Ascending Modulatory Pathway
• Recall that all sensory information enter the spinal cord at the dorsal horn ( this includes pain,
touch, hot, cold and etc.)
• All their 1st order neurons synapse with their corresponding 2nd order neuron at Substantia
Gelatinosa
• All 1st order neurons produce their own neurotransmitters and saturate the synaptic region.
• Therefore, if two sensory information (for instance pain and touch) compete with each other, the
impulse that travels faster (touch) can produce its neurotransmitter and saturate the synaptic
region.
• Thus the second sensory information(pain) that has arrived late at the synaptic region cannot
activate its corresponding 2nd order neuron and information never reaches the brain and is not
2 TOPRANK REVIEW ACADEMY- ANESTHESIOLOGY MODULE
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