7. Dentistry Pain 1

Links to Other Lectures

• Somatic senses

• Pain (nociceptors)

  • Pain 1: Peripheral mechanisms and central pathways

    • Sensory cortex

    • Thalamus

    • Spinothalamic tract

    • Dorsal Root Ganglion (DRG)

    • Temperature/pain/touch & pressure receptors

• Somatosensory cortex

• Sensory homunculus

Structure of This Lecture

• Part A: Nociception

• Part B: Neuropathic pain

• Part C: Psychological aspects of pain

Introduction to Pain

• Importance of pain in medicine

  • Example: Tooth abscess and tooth decay

• International Association for the Study of Pain Definition:

  • Pain as an “unpleasant sensory and emotional experience primarily associated with tissue damage or described in terms of such damage.”

• Concepts:

  • Nociception

  • Subjective response

Nociception

• Nociceptors

  • Widespread distribution in the body

  • Myelinated Neurons (Aδ)

    • Rapid conduction velocity (6 to 30 m/s)

    • Fast pain

    • Characteristics: Sharp, immediate, highly localized, superficial tissue

    • evoked by mechanical and thermal stimuli

  • Unmyelinated Neurons (C)

    • Slow conduction velocity (0.5 to 2 m/s)

    • Slow pain

    • Characteristics: Dull, delayed, hard to locate, affects both superficial and deep tissue, e.g., dental pulp, tongue, gums

    • evoke by mechaical, thermal and chemical stimuli

Types of Stimuli for Pain

• Chemical - slow pain only

• Mechanical - fast, slow

• Thermal - fast, slow

Tooth Pain Stimulators

• Depend on enamel intactness

  • Heat or cold exposure, Application of high forces - enamel

  • Mechanical probing, Drying effects, Application of hypertonic solutions, Hydrostatic pressure - dentine

  • Chemical stimulators - pulp

Nociceptive Pathways

• Ascending pathways from limbs and torso

  • Consideration: Advantageous for the hypothalamus to be informed of injury in harmful situations

  • Hypothalamus involvement in emotion and pain perception

  • Fight or flight response and analgesia

  • Myelinated Aδ fibers release glutamate

  • Unmyelinated C fibers release glutamate and substance P

Ascending Pathways Overview

• Gracile fasciculus

• Cuneate fasciculus

• Posterior spinocerebellar tract

• Anterior spinocerebellar tract

• Anterolateral system

  • Contains spinothalamic and spinoreticular tracts

• Nerve pathways for sensation from the head

  • Trigeminal Nerve (V) pathways include various divisions (V1, V2, V3)

Referred Pain

• Definition: Pain from a visceral organ perceived in a superficial area

• Example: Referred tooth pain

Autonomic Responses to Pain

• Symptoms:

  • Fear, pupillary dilation, pallor, sweating, urination, nausea

• Cardiovascular responses:

  • Bradycardia, hypotension

Acute vs Chronic Pain

• Physiologic Pain

  • Sudden onset, linked to specific event

  • Recedes during healing

• Pathologic Pain

  • Difficult to associate with specific events

  • Persists beyond 3 months, often unresponsive to analgesics

Necessity of Pain

• Pain is a protective mechanism

Sensitization and Pain Presentation

• Variable presentation may include allodynia or hyperalgesia

  • Caused by peripheral and central neuron sensitization

  • Peripheral Sensitization

    • Involves C and Aδ fibers

    • Increased voltage-dependent Na+ channel expression

  • Question: How does increased Na+ channel expression affect nociceptor sensitivity?

    • Higher likelihood of reaching threshold potential

Orofacial Neuropathic Pain

• Result from lesions or diseases in the peripheral or central nervous system

• Part B: Neuropathic Pain

Central Sensitization

• Increased glutamate release due to peripheral sensitization

• Higher expression of NMDA receptor subtype

• Sprouting of Aβ fibers creating new connections

Phantom Limb Pain

• A type of neuropathic pain

• Involves reorganization of the cortex

  • Examples: Phantom limb pain, phantom tooth pain

Psychological Aspects of Pain

• Influence of psychological factors on pain perception

• Connection between chronic pain and depression

• Part C: Psychological Aspects of Pain