This document provides an overview of pain, including its definition, pathways, and theories. It discusses how pain was conceptualized in ancient times and defines pain as an unpleasant sensory and emotional experience associated with actual or potential tissue damage. It describes the specificity, pattern, and gate control theories of pain and discusses neural pathways and structures involved in pain processing, including primary afferent neurons, secondary neurons, and higher brain centers. It also covers sensory receptors, fiber types, spinal cord laminae, and ascending pain pathways.

1. PAIN
Guided by Dr. G.K Thapliyal
Moderated by Dr. Himanshu Bhutani
Presented by Dr. Nishant Kumar

2. Contents-
• Introduction
• Definition
• Pathways
• Theories
• Evaluation
• Differential diagnosis
• management

3. In 19th century, MUELLER, VAN FREY,
GOLDSCHEIDER hypothesized the
concepts of neuroreceptors,
nociceptors, and sensory input.
Early Hebrews considered pain to be a
manifestation of concerns that lead to
grief and sorrow.
Aristotle distinguished five physical
senses, considered pain to be a “
passion of soul” that resulted from the
intensification of other sensory
experience
Plato contended that pain and
pleasure arose from within the body.
In ancient times, Homer thought pain
was due to arrows shot by god.

4. Pain is a vital function of the nervous system in providing the body with a warning
of potential or actual tissue damage.
It is both a sensory and emotional experience, affected by psychological factors such as
past experiences, beliefs about pain, fear or anxiety.
Pain is one of the most commonly experienced symptom . It is often spoken of as a
protective mechanism since it is usually manifested when an environmental change occurs
that causes injury to responsive tissue

5. The word pain is derived from the Latin word Peone and the Greek word Poine
meaning penalty or punishment
Definition-
Pain is defined by The International Association for the Study of Pain as an
unpleasant sensory and emotional experience associated with actual or potential
tissue damage, or described in terms of such damage.
An unpleasant emotional experience usually initiated by noxious stimulus and
transmitted over a specialized neural network to the CNS where it is interpreted as
such. MONHEIM’S local anesthesia and pain control in dental practice C. Richard
Bennett 7th edtion

6. Theories of pain conduction
Specificity theory
• Descartes in 1644
• Pain system as a straight through channel from the skin to
the brain.
• Von Frey developed the concept of specific cutaneous
receptors for the mediation of touch, heat, cold and pain.
• Free nerve endings were implicated as pain receptors.
• A pain “center ” was thought to exist within the brain
which was responsible for all overt manifestations of the
unpleasant experience.

7. Pattern theory
• Goldscheider in 1894
• Stimulus intensity and central summation are the critical determinants of pain.
• The theory suggested that particular patterns of nerve impulses that evoke pain
are produced by summation of sensory input within the dorsal horn of the spinal
column.
• Example touch plus pressure plus heat might add up to cause pain
PAIN
TOUCH
HEAT PRESSURE

8. Gate control theory
• Melzack and Wall in 1965
• According to this theory, the pain stimuli transmitted by afferent pain fibres are blocked
by GATE MECHANISM located at the posterior gray horn of the spinal cord.
• If the gate is open pain is felt, and if the gate is closedpain is suppressed.
• Impulses in smaller fibres can be blocked by modulated by large diameter nerve fibers
activity that can selectively block impulses from being transmitted to
the transmission cells in the spinal cord and then to CNS resulting in no pain.

9. • Gate control theory postulates the following
• Information about the presence of injury is transmitted to the central nervous
system by small peripheral nerves.
• Cells in the spinal cord or nucleus of the fifth cranial nerve, which are excited by
these injury signals, are also facilitated or inhibited by other large peripheral
nerves that also carry information about innocuous events.
• Descending control systems originating in the brain modulate the excitability of
cells that transmit information about injury

10. Transcutaneous electric nerve stimulation
• The chief product of the gate control theory as a therapeutic modality.
• Early Egyptians used electric fish to minimize pain.
• In 1858,Francis used forceps charged with electricity to extract teeth with less
pain.
• The rationale of TENS is based on the antinociceptive effect of stimulating
cutaneous sensory nerves.
• The stimulation is usually below what is required to activate A-delta and C
nociceptive fibers.

11. Level of pain processing
• Nociception refers to the noxious stimulus originating from the sensory receptor.
This information is carried into the CNS by the primary afferent neuron.
• Pain is an unpleasant sensation perceived by the cortex usually as a result of a
nociceptive input. The CNS has the ability to alter or modulate nociceptive input
before it reaches the cortex for recognition.
• The term suffering refers to how the human reacts to the perception of pain.
• Pain behavior refers to the individuals audible and visual actions that
communicate his or her suffering to others.
• Pain behavior is the only communication the clinician receives regarding the
pain experience.

12. Neural pathways of pain
• Fields has described that the subjective experience of pain arises by four distinct
processes-
• Transduction-process where noxious stimuli lead to electrical activity in the
appropriate sensory nerve endings.
• Transmission refers to the neural events that carry the nociceptive input into the
central nervous system for proper processing. There are three basic components
to the transmission system.

13. • The first component is primary afferent neuron-carrying nociceptive input
from the sensory organ into the spinal cord.
• The second component is second order neuron, which carries the input to
the higher centers to the thalamus.
• The third component represents interactions of neurons between the
thalamus, cortex and the limbic system as the nociceptor input reaches
these higher centers.
• Third process is modulation which is the ability of the central nervous system to
control the pain transmitting neurons.
• The final process is perception, which immediately initiates a complex
interaction of neurons between the higher centers of the brain .

14. Neural structures
• Nerve is a cordlike structure that has the ability to convey electrical and
chemical impulses.

15. Neuron

16. Depending on location and function, neurons are designated as
• Afferent neuron-conducts the nervous impulse toward the CNS.
• Sensory or receptor, afferent in type.
• The first sensory neuron is the primary or first order neuron.
• Second and third order neuron are internuncial.
• Efferent neuron conducts the impulses peripherally.
• Motor or efferent neuron convey neurons impulses to produce muscular or secretory effects.
• Internuncial neurons or interneurons lie wholly within the CNS.

17. Sensory receptors
• At the distal terminals of afferent nerves are specialized sensory receptors that
respond to physical or chemical stimuli.
• Specific for certain types of stimuli
• Classified in three main groups
• Exteroceptors
• Proprioceptors
• Interoceptors

18. • Exteroceptors-stimulated by immediate external environment and are appropriately
fashioned and located so as to be exposed to the organisms environment.
Some examples of this type of receptors are:
• Merkel’s corpuscles-tactile receptors in the submucosa of the tongue and oral mucosa.
• Meissner’s corpuscles-tactile receptors in skin.
• Ruffini’s corpuscles-pressure and warmth receptors.
• Krause’s corpuscles or end-bulbs-cold receptors.
• Free nerve endings-perceive superficial pain and touch.

19. • Proprioceptors provide information from the musculoskeletal structures
concerning the presence, position and movement of the body.
Some examples of this type of receptors are:
• Muscle spindles present between the skeletal muscle fibers that responds to
passive stretch of the muscle, signaling muscle length, and are responsible for
the myotactic reflex.
• Golgi tendon organs mechanoreceptors in the tendons of the muscle that signal
both in contraction and stretching, probably responsible for nociceptive and
inverse stretch reflexes.
• Pacinian corpuscles concerned with the perception of pressure
• Periodontal mechanoreceptors which respond to biomechanical stimuli.
• Free nerve endings for perceiving deep somatic pain and other sensations.

20. • Interoceptors are sensory receptors that are located in and transmit impulses
from the viscera of the body
Some examples of this type of receptor include the following
• Pacinian corpuscles concerned with perception of pressure.
• Free nerve endings perceive visceral pain and other sensations.

21. • The axons of these first order neurons are found to have varying thickness.
• A general classification of neurons dividing the large fibers(A fibers) from the
smaller ones (C fibers)
• Type A fibers are further divided into
Alpha fibers-size 13 to 20 µm in diameter;
velocity 70 – 120 m/s.
Beta fibers-size 6 to 13 µm in diameter;
velocity 40 – 70 m/s.
Gamma fibers-size 3 to 8 µm in diameter;
velocity 15 – 40 m/s.
Delta fibers- size 1 to 5 µm in diameter;
velocity 5 – 15 m/s.
• Type C fibers- size 0.5 to 1 µm in diameter;
velocity 5 – 15 m/s.
• There is also a relationship between fiber size and type of impulse transmitted.

22. Second order neuron
• Sometimes also called as a transmission neuron, since it transfers impulses on
to higher centers.
• The synapse of the primary and second order neuron occurs in the dorsal horn
of the spinal cord.
• Three types of second order neuron-
• The low threshold mechanosensitive neurons(LTM)-light touch, pressure and
proprioception.
• The nociceptive specific neurons(NS) exclusively carry noxious stimuli.
• The wide dynamic range neuron(WDR) respond to a wide range of stimulus
intensities from non noxious to noxious.

23. • The dorsal horn of the spinal cord is subdivided into different laminae.
• Studies suggest that nociceptive input enters dorsal horn through NS and WDR
neurons in the area of laminae I,II and V.
• Within the dorsal horn there are inhibitory and excitatory neurons present in
laminae II and III and this region is collectively called substantia gelatinosa.

24. • Nociceptive input is predominantly carried by the anterolateral system or
anterolateral spinothalamic tract , where once impulses that have been
transferred from the primary afferents the second order neurons cross to the
opposite side of the spinal cord which ascends to the higher centers.
• This system is composed of smaller myelinated and unmyelinated fibers that
transmit signals at velocities ranging from a few meters per second up to 40
m/s.
The anterolateral system is divided into two tracts
• The neospinothalamic tract that caries A delta nociceptive inputs directly to the
higher centers
• The paleospinothalamic tract predominantly carries the slower C fiber
nociception and travels through many other centers before reaching the brain.

25. • The higher centers of the central nervous system can be subdivided into
the following four regions from the most inferior to the most superior:
a) The brain stem made up of the medulla oblongata , the pons and the
midbrain (or mesencephalon).
b) The cerebellum.
c) The diencephalon is made up of the thalamus and hypothalamus.
d) The cerebrum made up of the cerebral cortex, the basal ganglia and the
limbic structures.

26. THE TRIGEMINAL SYSTEM
• Somatic input from the face and oral
structures enter the spinal cord by the
way of the trigeminal nerve.
• The cell bodies of the trigeminal afferent
neurons are located in the large
gasserian gangelion.
• Impulses carried by the trigeminal nerve
enter directly into the brain stem in the
region of the pons to synapse in the
trigeminal spinal nucleus.

27. A graphic depiction of the trigeminal nerve entering the brain stem at the level of the
pons.
The primary afferent neuron (1st N) enters the brain stem to synapse with a second-
order neuron (2nd N) in the trigeminal spinal tract nucleus (STN of V).
The spinal tract nucleus is divided into three regions; the subnucleus oralis (nso),
the subnucleus interpolaris (sni), and the subnucleus caudalis (snc).
The trigeminal brain stem complex is also composed of the motor nucleus of V (MN
of V) and the main sensory nucleus of V (SN of V).

29. Pain Diagnosis
• For the clinician to fully classify the pain disorder, he or she must consider both
the somatosensory input and the psychosocial input.
• A complete pain classification must assess the pain condition on two axes-
• Axis I will depict physical factors
• Classified according to the tissues that produce the nociception
• Axis II will depict psychologic factors

31. Diagnosing a pain complaint consists of three major steps.
a) Accurately identifying the location of the structure from which the pain
emanates.
b) Establishing the correct pain category that is represented in the
condition under investigation.
c) Choosing the particular pain disorder that correctly accounts for the
incidence and behavior of the patient’s pain problem.

32. Evaluating the Pain Condition
When a patient reports with pain, information must be gathered so that the clinician
can determine the proper pain diagnosis.
This information is gathered in two forms:
The history and the clinical examination.
The main objective of the history and the clinical examination is to locate the true
source of the pain that relates to the patients chief complaint.

33. Preliminary interview
• At the preliminary interview, sufficient data should be collected to help determine the
future course of the examining procedure.
• Some overall idea of the location, inception, duration, and clinical behaviour of the
complaint should be obtained.
• It is important to evaluate the patients pain in terms of what it means to him or her.
• In his McGill pain Questionnaire, Melzack arranged descriptive adjectives in several
groups.
• Each series of words is arranged in an order of increasing intensity.
• The patient is instructed to select one word in each series, the word that best
describes the complaint

34. The first group of is composed of sensory descriptions that help describe what the
discomfort feels like to the patient:
1. Temporal: flicking, quivering, pulsing, throbbing, beating, pounding
2. Spatial: jumping, flashing, shooting
3. Punctate pressure: pricking, boring, drilling, stabbing, lancinating
4. Incisive pressure: sharp, cutting, lacerating
5. Constrictive pressure: pinching, pressing, gnawing, cramping, crushing
6. Traction pressure: tugging, pulling, wrenching
7. Thermal: hot, burning, scalding, searing
8. Brightness: tingling, itchy, smarting, stinging
9. Dullness: dull, sore, hurting, aching, heavy
10. Miscellaneous: tender, taut, rasping, splitting

35. The second group consists of affective descriptors that yield information about how
the patient is reacting to the pain:
1. Tension: tiring, exhausting
2. Autonomic: sickening, suffocating
3. Fear: fearful, frightful, terrifying
4. Punishment: punishing, grueling, cruel, vicious, killing
5. Miscellaneous: wretched, blinding

36. • The third group is a series of evaluative descriptors that tend to classify the intensity of
pain:
1. annoying, troublesome, miserable, intense, unbearable.
• A fourth group of general descriptors has been added to the questionnaire:
1. Spreading, radiating, penetrating, piercing
2. Tight, numb, drawing, squeezing, tearing
3. Cool, cold, freezing
4. Nagging, nauseating, agonizing, dreadful, torturing

37. History for orofacial pain-
• An accurate history is the most important aspect in the diagnosis obscure pain.
• Two forms – oral or written
• An oral history provides some advantage over the written history provides some
advantages over the clinician to meet the patient and establish important rapport.
• Oral history taking allows the clinician to gain information in a logical sequence, asking
appropriate questions as needed.
• The major disadvantage of the oral history is that it relies on the clinicians ability to
remember all aspects of the history so that no important information is missed.
• A written history can eliminate this concern.

38. D. Aggravating and alleviating factors
1. Physical modalities
2. Function and parafunction
3. Sleep disturbances
4. Medications
5. Emotional stress
E. Past consultation and/or treatments
F. Relationship to other complaints
II.Past medical history
III.Review of systems
III.Psychologic assessment
Features to include in a Orofacial pain history
I.The chief complaint(perhaps more than one)
A. Location of pain
B. Onset of Pain
1. Associated with other factors
2. Progression
C. Characteristics of pain
1.Quality of pain
2.Behavior of pain
a. Temporal
b. Frequency
c. Duration
3.Intensity
4.Concomitant symptoms
5.Flow of the pain

39. III. Masticatory evaluation
A. Range of mandibular movement
1. Measurements
2. Pain
B. Temporomandibular joint evaluation
1. Pain
2. Dysfunction
C. Oral structures
1. The mucogingival tissues
2. The teeth
3. The periodontia
4. The occlusion
Other diagnostic tests
A. Imaging
B. laboratory tests
C Psychologic provocation tests
Orofacial pain clinical examination
I. General examination
A. Vital signs
1. Blood pressure
2. Pulse rate
3. Respiration rate
4. Temperature
B. Cranial nerve evaluation
C. Eye evaluation
D. Ear evaluation
E. Cervical evaluation
F. Balance and coordination
II. Muscle examination
A. Palpation
1. Pain and tenderness
2. Trigger points and pain referral

40. Establishing pain category
• Is the pain acute or chronic?
• Pain may be considered chronic if it continues after normal healing time.
• The class definition of chronic pain is pain that lasted longer than 6 months.
• If the patient is experiencing chronic pain, some Axis II disorders are almost
always present even if it is only the category Psychologic Factors Affecting a
Medical Condition.

41. Is the Pain Neuropathic or Somatic?
• The next diagnostic issue is whether the pain stems from somatic structures
supplied by normal neural elements (somatic pain) or from abnormal neural
structures (neuropathic pain).
• Neuropathic pains include the following clinical characteristics:
1. Burning type pains that arc spontaneous. triggered, or ongoing and unremitting
2. Pains that occur disproportionately to the stimulus
3. Pains that are accompanied by other neurologic symptoms
4. Pains that are initiated or accentuated by efferent sympathetic activity in the
area
Neuropathic
pain
Episodic pain
Paroxysmal
neuralgia pain
Neurovascular
pain
Continuous pain
Neuritis pain
Deafferentatoin
pain
Sympathetically
maintained pain

42. Is the pain primary or secondary?
• Secondary pains are not increased by local provocation unless it is a site of
secondary hyperalgesia.
• Secondary pain that is felt superficially as a touchy or sensitive area (secondary
hyperalgesia) is not arrested by a topical anesthetic applied where the pain is
felt.
• Primary pain is present when local provocation of the site of pain increases the
pain.
• Primary somatic pain emanating from superficial skin or the mucogingiva is
arrested by a topical anesthetic applied at the site of pain. Primary somatic pain
emanating from musculoskeletal or visceral structures and felt as tenderness to
manual palpation or functional manipulation is arrested by analgesic blocking of
that area.

43. Is the pain superficial or deep?
• Superficial somatic pain displays the following clinical characteristics by which it can be
recognised:
1. The pain Is a bright, stimulating sensation that is precisely located by the patient.
2. Response to local provocation is faithful in location, duration, and intensity.
5. The pain remains clean-cut without secondary manifestations such as reference,
secondary hyperalgesia, autonomic symptoms, and/or muscle effects.
4. The pain is arrested by topical anaesthesia at the site of pain.

44. • Deep somatic pain displays the following clinical characteristics by which it can be
recognized:
1. The pain is a duller, more depressing sensation that is less precisely located by the
patient.
2. Response to local provocation is less faithful, especially with regard to location and size.
3. The pain frequently and expectantly exhibits secondary manifestations such as referred
pain, secondary hyperalgesia, autonomic symptoms, and/or muscle effects.
4. The pain is arrested by analgesic blocking of the site of pain.

45. Is the pain musculoskeletal or visceral?
• Pain with musculoskeletal origin exhibits two characteristic clinical features:
1. It relates intimately to biomechanical function
2. Response to provocation is a gradient reaction that is proportionate to the
stimulus.
• Pain from visceral structures exhibit two characteristic features:
1. It occurs irrelevant to biomechanical function.
2. It is relatively non responsive to local provocation until a threshold level is
reached.

46. Is the pain inflammatory?
• Inflammatory pain can usually be recognized by clinical features:
1. Concomitant signs of inflammation such as swelling, redness, heat, and
dysfunction are present.
2. The pain reflects the type, intensity, location, and phase of inflammatory
reaction.
3. The pain follows an inflammatory time frame. This means that it requires time
to develop, plateau, and resolve.

47. Confirming the clinical diagnosis.
• There are four methods that can help confirm the diagnosis
1. Diagnostic analgesic blocking
2. Utilization of diagnostic drugs
3. Consultations
4. Trial therapy

48. General considerations in managing orofacial pains.
Modalities for Managing Orofacial Pain Disorders
I. Pharmacologic therapy
A. Analgesic agents
1. Non-narcotic agents
2. Narcotic agents
3. Adjuvant analgesics
B. Anesthetic agents
1. Topical anesthetic
2. Injectable local anesthetic
C. Anti-inflammatory agents
D. Muscle relaxants
E. Antidepressants
F. Antianxiety agents
G. Vasoactive agents
H. Norepinephrine blockers
I. Antimicrobial agents
J. Antiviral agents
K. Antihistamine agents
L. Anticonvulsive agents
M. Neurolytic agents
N. Uricosuric agents
0. Dietary considerations

49. II. Physical therapy
A. Modalities
1. Sensory stimulation
2. Ultrasound
3. Electrogalvanic stimulation (EGS)
4. Deep heat
B. Manual techniques
1. Massage
2. Spray and stretch techniques
3. Exercise
4. Physical activity
III. Psychological therapy
A. Counseling
B. Behavioral modification training
1. Stress reduction training
2. Relaxation training

50. THANK YOU