Robert C. Canfield

Cerebral responses to electrical tooth pulp stimulation in man An objective correlate of acute experimental pain

The pulp of individual teeth of 17 normal adult volunteers was electrically stimulated via pairs of electrodes implanted into dentine. Computer-summated responses recorded from the surface of the head were composed of two concurrent sequences of events, one of which was seen maximally over midline areas and the other over the lower portions of the postcentral regions. Appropriate tests demonstrated that these wave forms represented cerebral tooth pulp-evoked potentials. Because tooth pulp-evoked potentials represent objective, quantifiable, nonverbal concomitants of central events associated with the perception of noxious stimuli, they may prove helpful in investigating acute experimental pain in man.

Transganglionic degeneration in the spinal trigeminal nucleus following removal of tooth pulps in adult cats

It is generally thought that transganglionic degeneration of central axons following lesions of their peripheral processes does not occur in adult nervous systemS, 6. For this reason there has been a lack of anatomical descriptions of the central distribution of specific groups of peripheral sensory axons. We, however, have found reproducible axonal and terminal degeneration in specific regions of the spinal trigeminal nucleus in adult cats following tooth pulpectomies 12. Healthy adult cats were used and the absence of dental pathology was confirmed prior to operation and in the controls. Under pentobarbital anesthesia and using appropriate aseptic dental procedures, the pulps were completely removed from all of the teeth on one side of 12 animals. Following postoperative survival times of 7, 9, 11, 14, 21, 28 and 100 days the animals were perfused with 4~o formaldehyde in a phosphate buffer 11. Transverse frozen sections through the brain stem, including the major parts of the spinal trigeminal nucleus, were stained by either the NautaGygax v or the Fink-Heimer (I) 4 technique. Two normal, unoperated animals were sacrificed and processed in the same fashion to serve as controls. Fig. 1 illustrates the pattern of degeneration observed at 1 l days. Unequivocal axonal and terminal degeneration (Fig. 2) is seen predominantly in the ventral half to one-third of the subnucleus interpolaris of the spinal trigeminal complex, near and immediately rostral to the obex, with very much less in the adjacent subnuclei (caudalis and oralis). The distribution is bilateral, but heaviest on the side of the lesion. The occurrence of contralateral degeneration is surprising in view of what is known of the organization of this system 2, but it is a consistent finding here. A crossing pathway of degenerating fibers cannot be identified with certainty. The amount of degeneration is less at shorter or longer survivals, but the pattern is similar in each. Control animals, with healthy teeth, show no degeneration.

Each canine tooth projects to all brain stem trigeminal nuclei in cat

Abstract The aim of this study was to determine in cats the precise sites of representation in the brain stem for specific teeth and their periodontal structures. Horseradish peroxidase was implanted in the pulpal chambers of either maxillary or mandibular canines and its transganglionic transport to the brain stem was studied light microscopically in tetramethyl benzidine preparations. The findings showed some differences between projections of maxillary and of mandibular canines, but a much more extensive ipsilateral central representation than previously reported for the individual teeth. The results are discussed in relation to previous anatomic and physiologic studies.

Projections from dental structures to the brain stem trigeminal complex as shown by transganglionic transport of horseradish peroxidase

Horseradish peroxidase (HRP) was implanted in one maxillary canine of cats and the transganglionic transport to the brain stem studied and mapped. HRP-positive fibers and terminal granules are distributed ipsilaterally to each subdivision of the trigeminal complex but are heaviest in the main sensory nucleus, adjacent pars oralis and pars interpolaris near obex with somewhat less in the rest of pars oralis and least in pars caudalis. The distribution indicates a wider central representation than previous anatomical reports and corresponds well with certain physiological studies.

Electrical stimulation of tooth pulp in humans. I. Relationships among physical stimulus intensities, psychological magnitude estimates and cerebral evoked potentials

Abstract Brief electrical pulses were applied to the pulp of individual pre‐molar teeth of 14 healthy, adult volunteers via wire electrodes implanted and sealed in dentine. The sensation threshold was estimated in each individual by the Two‐Alternative Forced‐Choice Staircase (2AFCS) method. Seven, 5 or 4 stimulus intensities were employed which were equally spaced in a logarithmic scale between 10 &mgr;A above threshold and 500 &mgr;A. Magnitude estimates of the subjective intensity of the sensation produced by individual dental excitations were obtained. Cerebral tooth pulp‐evoked potentials were simultaneously recorded in 11 subjects. The growth of psychological sensory magnitude with increasing strength of electrical stimulus conformed to the general psychophysical power law. Individual power function exponents varied from 0.204 to 0.907 with a mean of 0.475 and a standard deviation of 0.190. The amplitude of TPEPs, measured between components N135 and P293, also was a power function of stimulus intensity. The exponents of individual TPEP amplitude‐intensity functions ranged from 0.055 to 0.362 with a mean of 0.144 and a standard deviation of 0.100. These last exponents were substantially smaller than those describing the growth of psychological magnitude estimates. Neither magnitude estimation nor TPEP amplitude‐intensity functions displayed abrupt changes in slope which might accompany transition from one operating sensory mechanism to another and/or changes in qualities of subjective sensations from ‘innocuous’ to ‘uncomfortable’ to ‘painful.’ The result of our psychophysical and electrophysiologic experiments indicate That: (1) albeit highly specialized both morphologically and functionally, human tooth pulp has certain fundamental properties in common with other sensory systems and (2) late midline TPEP components may provide measures of central events that, within a range of stimulus itensities, are associated with the perception of pain, but should not be looked upon as specific indicators of pain processes.

Ultrastructural study of transganglionic degeneration following dental lesions

SummaryTransganglionic degeneration in the trigeminal main sensory nucleus (MSN) and pars interpolaris (PI) was studied in cats following dental lesions. At early survival times, three types of terminal alteration were seen in both MSN and PI: (1) flocculent degeneration, (2) neurofilamentous hyperplasia and, (3) glycogen accumulation. With longer survival times, the magnitude of these terminal alterations increases. Electron dense degeneration was only seen in the ventral half of PI. Phagocytosis of the altered terminals was also observed. The study suggests a plausible explanation for the variations observed in the CNS projection of primary afferents with degeneraton and with HRP transport studies.

electrical stimulation of tooth pulp in humans. II. Qualities of sensations

Abstract Individual premolar teeth of 22 normal volunteers were stimulated via intradentinal electrodes using brief electrical pulses. Questionnaires were used to determine the qualities of sensations produced by this stimulation. Operationally defined “innocuous’ sensations predominated between 1 and 10 dB SL, and were absent above 30 dB SL. Similarly defined ”painful’ sensations were observed throughout the range of suprathreshold intensities but were most common above 20 dB SL.‘Uncomfortable’ sensations were especially frequent between 1 and 20 dB SL. These findings demonstrate that non‐painful sensations can arise from electrical tooth pulp excitation in circumstances in which spread of the stimulating current to periodontal and gingival structures is most unlikely. Two interpretations of these results are considered: (1) that tooth pulp afferents may have some unspecified sensory function besides mediation of painful sensations and (2) that they may be specialized in the mediation of nociceptive impulses but may give rise to innocuous sensations under special circumstances.

Normal loss of milk teeth causes degeneration in brain stem

Abstract Transganglionic axonal and terminal degeneration occurred reproducibly in the brain stem spinal trigeminal nucleus at specific ages in kittens during shedding of deciduous and eruption of permanent teeth. The distributional pattern and sequence of degeneration is similar to that in adult cats after tooth pulp extirpations. Comparative representation for tooth afferent fibers in the brain stem implies the possibility of central plasticity associated with peripheral changes in innervation during tooth eruption.

Ultrastructure of degenerative changes following ricin application to feline dental pulps

SummaryThe ultrastructure of degenerative changes within the ipsilateral trigeminal ganglion, and partes caudalis and interpolaris of the spinal trigeminal nucleus in the cat is described following the application of the potent toxin ricin to the tooth pulps of unilateral maxillary and mandibular posterior teeth, including the cuspids. Survival times ranged from 6 to 10 days. Typical changes identified within the ipsilateral trigeminal ganglion included myelin fragmentation and ‘compartmentalization’ of the axoplasm of medium-sized myelinated axons, while small myelinated and unmyelinated axons underwent a more variable response ranging from electron-lucent to electron-dense changes. The affected cell body was characterized by the presence of swollen, electron-lucent mitochondria, a reduction of cytoplasmic ribosomes and a filamentous hyperplasia. Other changes often included an eccentric nucleus and satellite cell proliferation. Degenerative changes often occurred in isolated elements surrounded by normal profiles, suggesting specificity of ricin within the trigeminal ganglion. Changes within brainstem axons showed both an electron-dense and a lucent, fragmenting type of axonal alteration. Terminal changes ranged from electron-dense to lucent and also included filamentous hyperplasia and ‘hyperglycogenesis’. The altered axonal knobs contained round synaptic vesicles that were presynaptic to dendritic profiles and postsynaptic to terminals containing flattened synaptic vesicles. The above brainstem alterations were identified specifically in the following areas: ventrolateral, medial and dorsomedial pars interpolaris; the ventrolateral and mid-dorsal to dorsomedial areas of the marginalis and outer substantia gelatinosa layers of pars caudalis; and in ventral pockets corresponding to lamina V of the medullary dorsal horn. Dense alterations within terminals containing flattened synaptic vesicles that are typically presynaptic to primary afferents in these areas were rare findings, but along with vacuolization of dendritic profiles suggest a trans-synaptic effect possibly due to the exocytosis of ricin. The results are discussed in relation to different reports of dental projections and with regards to patterns of transganglionic degeneration.

Cerebral responses to electrical stimulation of tooth pulp in man.

In seven normal, adult paid volunteers, the bare tips of two tungsten wire electrodes 0.07 mm in diameter were sealed with silver amalgam restorative material in small cavities drilled without anesthesia into the dentin of a lower canine or lateral incisor on opposite surfaces of the tooth. A quick-setting resinous material provided continuity between the insulation of the wires and the exposed tooth surface. A rubber dam kept the tooth dry. Monophasic square waves of 0.5 msec duration and 1.5 mA intensity were delivered by an electrical stimulator at intervals of 2.7 to 4.9 seconds. Each stimulus elicited brief, sharp pain of moderate intensity. Fifty consecutive electroencephalographic (EEG) responses recorded simultaneously between each of six exploring electrodes and a reference lead at the inion (head diagram) were amplified, stored on magnetic tape, summated by a computer, and graphed by a plotter. The band pass of the system was 0.16 Hz to 2.5 KHz (-3dB). The tooth was restored conventionally after the study. Tooth pulp-evoked potentials (TPEPs) consisted of two temporally related sequences of events. One sequence was best developed over the vertex area and was represented by five successive waves of alternating polarity, the initial component being negative. Peak latencies of 38, 72, 134, 234, and 315 msec were measured at electrode 4 in the Illustration. Another sequence of potentials was most prominent over the inferior portion of the postcentral region contralateral to the tooth that was stimulated and consisted of an initial negative deflection followed by a positive wave. The peak latencies of these potentials were 74 and 108 msec respectively at electrode 1 in the Illustration. These responses were followed at times by a rhythmic after-discharge of frequency close to that of the spontaneous EEG activity. Appropriate maneuvers (CltAcco and BicKFoiw, Arch Neurol 18, 52-68, 1968) demonstrated that these TPEPs were not myogenic in origin. Mandibular block anesthesia with 2% mepivacaine hydrochloride abolished them. We believe that to the extent that TPEPs represent objective, quantifiable, nonverbal concomitants of central events associated with the perception of pain, they hold promise as a method of investigating acute, experimental dental pain in man.