DENTAL PAIN WABeresford Dental pain enters consciousness (HURTS) & becomes a major aspect of dentistry What is the innervation of the tooth & periodontium? How are these nerve fibers and endings related to dental pain? How do the stimuli - heat, inflammatory mediators, etc - activate the nerve fibers? What are the central pathways, structures, & interactions bringing pain to conciousness? DENTAL SENSITIVITIES SENSITIVE?
Enamel Dentine Pulp Cementum PDL PULP INNERVATION 1 Nerves: autonomic Sub-odontoblastic plexus in cell-poor zone of Weil 2
3 Nerves: sensory (V) to 1 PULP 2 ODONTOBLASTS 3 DENTINAL TUBULES Blood vessels EXTENT of TOOTH INNERVATION Sub-odontoblastic plexus of Raschkow Most fibers branch Hundreds of nerve fibers per tooth
Fibers grow in during development & some transfer to 2 0 tooth, so 20s have more nerves fibers than 10s FIBER CALIBER & MODALITY 80 % unmyelinated C fibers Hundreds of nerve fibers per tooth 10 % myelinated Ad fibers < 1/2% Ab fibers No specialized receptors
NOCICEPTION - pain - sensory modality for pulp & dentine FIBER FUNCTIONS NOCICEPTION - pain - the sensory modality for pulp & dentine Hundreds of nerve fibers per tooth But what do these do? < 1/2% Ab fibers Any trophic effects on pulp
from sensory fibers? Autonomic roles PNS: AUTONOMICS Sympathetic fibers Pulp vessel Other targets? V Sup Cervical Ganglion Branch of external carotid A
PNS:CNS Sensory relations Superior alveolar nerves Spinal nucleus of V CNS Inferior alveolar nerves Trigeminal ganglion Convergence from several teeth onto one CNS neuron PAIN QUALITY ACUTE, SHARP DULL ACHE myelinated Ad fibers
unmyelinated C fibers POOR LOCALIZATION Convergence Spinal nucleus of V CNS Inferior alveolar nerves Trigeminal ganglion PERIODONTAL LIGAMENT INNERVATION Sup Cervical Ganglion Sympathetic
Free ending Ruffini receptors V Ganglion CNS Mesencephalic nucleus of V Mechanoreceptors for stretch Modalities: PROPRIOCEPTION & pain CNS: Dental pain pathways SENSORY CORTEX
Parietal lobe Thalamic VPM Reticular formation Periaqueductal grey (PAG) Spinal N V Spinal V tract Mesencephalic N of V Sensory V Nucleus TRIGEMINAL NERVE CNS
CNS: Dental pain pathways SENSORY CORTEX Thalamic VPM Reticular formation Spinal N V Spinal V tract Mesencephalic N Sensory V Nucleus TRIGEMINAL NERVE Periaqueductal grey
(PAG) can inhibit ascending pain signals by using endorphins, enkephalins RETICULAR FORMATION: Roles Reticular formation sends signals everywhere Cortex - arousal Hypothalamus autonomic responses Limbic system emotions Motor nuclei - reflexes Sensory relays - Inhibition of incoming & ascending sensory signals NERVE-FIBER:STIMULI RELATIONS I Direct pulp
stimuli ODONTOBLASTS Worn dentine brings stimuli nearer to pulp Pulp Enamel 2 3 Heat Cold Pressure Chemicals? Axons in tubules Axons around
odondoblast bodies Sub-odontoblastic plexus ODONTOBLAST as sensory transducer ? NERVE-FIBER:STIMULI RELATIONS II ODONTOBLASTS Worn dentine brings stimuli nearer to pulp Pulp Enamel 2 3
Axons in tubules Axons around odondoblast bodies Pulp fibers sensitized by factors released because of inflammation or previous activity Heat Cold Pressure Chemicals NERVE-FIBER:STIMULI RELATIONS III ODONTOBLASTS Dentine Enamel Axons in tubules
Axons around odondoblast bodies HYDRODYNAMIC hypothesis of sensitivity Heat Cold Pressure Stimuli move fluid back & forth in the tubule stimulating tubule axons &/or odontoblasts NERVE-FIBER:STIMULI RELATIONS IV
ODONTOBLASTS Dentine Enamel Axons around odondoblast bodies Heat Cold Pressure Stimuli move fluid back & forth in the tubule HYDRODYNAMIC hypothesis of sensitivity
with distortion of the odontoblast possibly causing it to release ATP, and thus chemically exciting the axon - Alavi AM et al. Immunohistochemical evidence for ATP receptors in human pulp. J Dent Res 2001;80:476-483 HYDRODYNAMIC hypothesis of sensitivity ODONTOBLAST as sensory transducer ? Stimuli move fluid back & forth in the tubule with distortion of the odontoblast possibly causing it to release ATP, and thus chemically exciting the axon - Alavi AM et al. Immunohistochemical evidence for ATP receptors in human pulp. J
Dent Res 2001;80:476-483 DENTAL PAIN: Unknowns Stimulation mechanisms in pulp - normal & diseased Reticular formation - what happens centrally Patterns of firing - relation to perceptions PAIN: Difficult to study First Anatomy Journal about 1860; first Pain journal 1973 Animal cannot tell of pain; humans reluctant to let you hurt them or do invasive investigations, e.g., nerve recordings Allowed to work on animals only if pain is prevented or minimised Many small nerve fibers used for other purposes, e.g., autonomic
No specialized pain endings? Defining pain stimuli? Complex chemistry with tissue injury Poorly understood dynamic interactions between CNS & PNS - Pain is in the mind & usually in the body (CNSPNS interactions: compare sexual arousal)
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