Orofacial pain Prof. MUDr. M. Kukletova Fig. 4.1 Schematic drawing presenting the innervation of the dental pulp. Several branches from the alveolar nerve enter the apical area of the tooth. A part of the nerve bundles innervate the periodontal tissues. Multiple bundles enter the pulp in close proximity to the blood vessels through the apical foramen; they branch further on their way to the tooth crown. Most of the intradental axons have their terminals in the pulp/dentine border of the coronal pulp, which is the most densely innervated area in the tissue (a). There are fewer nerve endings in the cervical area (b) and the pulp/dentine border in the root pulp is sparsely innervated (c). Fig. 4.2 A schematic drawing showing a nerve bundle entering the pulp chamber in the apical area of the tooth. The nerve bundle contains both unmyelinated and myelinated axons of variable sizes. Fig. 4.3 Innervation of the pulp/dentine border in the coronal pulp. The nerve fibers entering the area form a dense network known as the plexus of Raschkow. The fibers form free nerve endings in the peripheral pulp and in the odontoblast layer. Many nerve terminals are also located in the dentinal tubules. Some fibers branch to innervate the adjacent blood vessels (see text for details). Dentinal fluid flow Tissue deformation Stimulus Nerve activation Fig. 4.5 The hydrodynamic mechanism of pulp nerve activation. Any stimulus capable of removing fluid from the outer ends of the dentinal tubules activates hydrodynamic fluid movement. The lost fluid is replaced by an immediate outward flow due to the high capillary forces in the dentinal tubules. The fluid flow causes mechanical distortion of the tissue with the nerve endings in the pulp/dentine border. Table 3-2. Classification and function of fibers in peripheral nerves Fiber Diameter |»im| Conduction velocity (speed of Impulse. m/sec| Function A-alpha (a) A-bcta (ß) 6 to 20 5 to 12 15 to 80 (myelinated) 30 to 70 Afferent fibers for touch, pressure, proprioception, vibration (mcchanoreccptors) A-gamma (7) A-dclta (5) 1 to 5 2 to 30 (myelinated) Afferent fibers for pain and temperature B 1 to 3 3 to 15 'myelinated) Visceral afferent fibers: preganglionic visceral efferent fibers C 0.4 to 1.0 0.4 to 2 (nonmyelinated) Afferent fibers for pain and temperature; postganglionic visceral efferent fibers Table 3-3. Pain fibers in the pulp (nociccptive/algogenic) A-delta (8) fibers C fibers Diameter (u.m) 2 to 5 0.3 to 1.2 Measurement of parent fiber, which Remain this diameter throughout their includes myelin sheath; smaller termi- length nal processes (telodendrites) emerge from parent fiber. Conduction velocity 5 to 30 0.4 to 2 (m/scc)—speed of As many as eight smaller terminals (tel- electrical impulse odendrites) feed into one larger my- or action potential elinated parent fiber to produce greater traveling along velocity because of increased diame- nerve ter. Myelinated Yes—parent axons located in cell-rich No and central zones Jelly roll spirals of Schwann cell mem- No—myelination lost by terminal branes are absent. branches of parent axon in dentinoblas- Fibers are enveloped by Schwann cells tic and subdentinoblastic zones but not with myelin. Location of terminal.; Superficial—terminals in dentin tubules Probably near blood vessels throughout in dentinoblastic and subdentinoblastic pulp; small C fibers difficult to differ- zones (pulp-dcntin border zones) entiate from other cell processes. Pain characteristics Sharp, pricking and unpleasant but bear- Throbbing, aching, and less bearable; lin- able (fast and momentary) gering and extremely unpleasant sen- sation Stimulation threshold Relatively low—doesn't take much to High stimulation threshold \cj stimulate initiate (fire) an impulse; can be stimu- these fibers; stimulus may nave to be lated without injury to tissue so intense that tissue is damaged; from a pathologic standpoint, pain is associ- ated with inflammatory process (exu- dative lesion and tissue damage). • í Enamel Dentin Predentin Dentinoblastic zone Cell-free zone Cavity preporotion (primary irritant) C fibers 4 ■~"*~Acut"e~*"--x inflammation ' Arterioles Dental pulp Coi (conscious of p tex recognition oin) Thal« 3mus Peripheral sensory units Sensory (afferent) Vasomotor control (efferent sympathetic) Medulla Sympathetic nerve chain Spinal cord Central nervous system B Fig. 3-20, cont'd. B, Afferent-efferent pathway for sensory arid vasomotor impulses as a result of severe dentinal stimulation. Sealed margin i i ' ////'///V Normal dentin Protective base or liner Sclerosis of tubules Irritation dentin K 'd ' ' \\$' C' . / -—— Acid filling material [>;.. cement ''A\ * \'j-''J/ h— leaking margin íiwtňnfMtíi Increased permeability of tubules Irreversible denlinoblastic injury '•^J^S^^T'tv'^ ' Irritation dentin absent Inflammation of pulp Fig. 3-34. Reaction of pulpodcntinal complex to mild and severe injury. Following cavity preparation and insertion of an inert filling, mild acute injury produces tubular sclerosis and irritation dentin. However, severe prolonged injur)' causes irreversible denlinoblastic injur)1, which in turn initiates pulpal inflammation. (From Massler, M: Dent Clin North Am, March 1965.) 9999 Postcentrol gyrus of cerebrol cortex Tholomo- corlicol Iroct Moxillory orlery> Inferior olveolor ortery' Internal carotid ortery' External carotid! ortery ' Postganglionic sympathetic neuron Preganglionic U* I Superior cervical sympathetic ganglion sympathetic"} I [ Middle neuron / i \ cervical S» 1 I Inferior cervicar sympathetic ganglion Dorsal root Substantia gelatinosa sympathetic ganglion j _li First thoracic ganglion Spinal nerve ramus communicans Ventral root Trigeminal I (gasserian) ganglion of fifth cranial nerve Spinal nucleus of V Fig. 3-20. A, Afferent-efferent pathway for sensory and vasomotor impulses. E, Enamel; D. dentin; P. predentin. Db. dentinoblast; LH, lateral horn (upper thoracic region); ....., efferent nerves;_, afferent nerves; /. 2, 3, sensory neuron sequence. \ Referred pain pathways from leetli involved with pulpalgia to other teeth as well as to immediate area. Black signifies tooth with pulpalgia; Stippled MOM, site of referred pain. A, Maxillary canine may refer lo maxillary first or second premolars and/ or first or second molars; also to mandibular first or second premolars. B, Maxillary premolars may refer pain lo mandibular premolars. Reverse is also true. C, Mandibular incisors, canine, and first premolar may refer pain into mental area. 0, Mandibular second premolar may refer pain into menial and midramus area. f, Mandibular first or second premolars may also refer pain into maxillary molars, f, Mandibular molars may refer pain forward to mandibular premolars. (Adapted with permission from Click, D.H.: Oral Surg., J5:613, May, 1962.) Pain referred from pulpalgia (o structures remote from involved tooth. Black indicates teeth involved in pulpalgia; stippled areas, remote areas of referred pain. A, Maxillary incisors may refer pain to frontal area. B, Maxillary canine and first premolar may refer pain into nasolabial area and into orbit. C, Maxillary second premolar and first molar may refer pain to maxilla and back to temporal region. D, Maxillary second and third molars may refer pain lo mandibular molar area and occasionally into car. 5, Mandibular first and second molars may commonly refer pain to ear and to angle of mandible. F, Mandibular third molar may refer pain to ear and occasionally to superior laryngeal area. (Adapted with permission from Click, D.H.: Oral surg., (5:613, May, 1962.) Table 3-10. Referred pulpal pain Site of pain referral Tooth pulp initiating pain Frontal (forehead) region Maxillary incisors Nasolabial area Maxillary canines Maxillary premolars Maxillary region above maxillary molars Maxillary second premolars Maxillary first molars Temporal region Maxillary second premolars Mandibular area below mandibular molars Maxillary second and third molars Ear Mandibular molars Maxillary second and third molars (occasionally) Mental region of mandible Mandibular incisors, canines, and premolars Angle of mandible Mandibular first and second molars Midramal region Mandibular second premolars Superior laryngeal area Mandibular third molars Maxillary premolars Maxillary canines Maxillary molars Maxillary canines Mandibular premolars Mandibular premolars Maxillary canines Maxillary premolars Mandibular first premolar Mandibular first and second molars Primary afferent nociceptive fibers of the trigeminal nerve (cranial nerve V) synapse in the nucleus caudalis of the spinal trigeminal tract. The nucleus caudalis descends as low as C3-4 in the spinal cord. Many nociceptors from deep cervical structures synapse on the same second-order pain transmission neurons as the trigeminal nerve. This may explain why cervical pain disorders are often perceived as facial pain or headache. Local Pathosis of Extracranial Structures Structures Diseases Tooth pulp, periradicular structures Inflammation Periodontium, gingiva, mucosa Infection Salivary glands Degeneration Tongue Neoplasm Ears, nose, throat, sinuses Obstruction Eyes Referred Pain from Remote Pathologic Sites Structures Diseases Heart Thyroid Carotid artery Cervical spine Muscles Angina pectoris, myocardial infarction Inflammation Inflammation, other obscure causation Inflammation, trauma, dysfunction Myofascial trigger points Inflammation of nasal mucosa causes swelling of turbinate and blocks off ostium of maxillary sinus. Pain referred to maxillary teeth may then develop. (With permission from Bal-lenger, J.J.: Diseases of the Nose, Throat, and Ear. 11th Ed. Philadelphia, Lea & Febiger, 1969.)