Sensory mechanisms in mammalian teeth and their supporting structures

Tardive dyskinesia affected by occlusal treatment--a case report

The following is a case report of occlusal treatment for involuntary mandibular movement occurring in a 79-year old woman. This was diagnosed as sulpiride-induced tardive dyskinesia. The patient had been treated with sulpiride to improve gastrointestinal symptoms for five years until the onset of involuntary mandibular movement. The involuntary movement worsened even after discontinuation of the drug for 10 weeks. The dyskinesia improved in the course of treatment with an occlusal splint placed over her upper denture. After wearing the new denture with increased occlusal vertical dimension, the dyskinesia disappeared almost completely. Sirognathographic observation showed that previous denture wear evoked remarkable involuntary movement of the mandible once again. It is uncertain whether such improvement may result from discontinuation of the drug or from the occlusal treatment. However, it appears that occlusal factors played an important role in orofacial manifestation of tardive dyskinesia (TD) in this case.

Physiological properties of periodontal mechanosensitive neurones in the trigeminal (Gasserian) ganglion of the rat

Periodontal mechanosensitive (PM) primary afferent neurones were recorded from the rat trigeminal ganglion and their response to mechanical tooth stimulation studied. The majority (95%) of PM afferents were single-tooth units and most were sensitive to mechanical stimulation of the incisor. They had a sustained response to pressure applied to the tooth, and showed a directional selectivity to the stimulation. Only a small number (5%) of units were multi-tooth sensitive; their receptive fields were restricted to the molars. When the incisor was stimulated mechanically in 12 directions in a plane perpendicular to the axis of the tooth crown, the predominant response fields of the PM units were of the medium type (90-180 degree response angle) or the broad type (180-360 degrees). Each unit had single optimal stimulus direction oriented predominantly in the rostrocaudal or caudorostral direction. About 60% of the PM units responded to tooth stimulation at irregular spike intervals, whereas the remaining 40% fired at relatively regular intervals. When the tooth was stimulated at a force of 0.05 N, the mean spike interval and rate of spike-interval fluctuation [percentage of the standard deviation (SD) of the interval distribution to the mean interval (mean); SD/mean x 100] were 29.2 ms and 38.1% for the regular-interval units, and 15.1 ms and 8.8% for the irregular-interval ones. The mean spike interval of the regular units was significantly longer than that of the irregular ones.

Reflex responses to periodontal and auditory stimulation in human masseter

An investigation was made of the reflex responses evoked in the human masseter by periodontal mechanoreceptors. Weak taps were applied to the labial surface of a central incisor tooth by an electromechanical stimulator with a flexible probe (von Frey hair). Forces as low as 0.2 N evoked inhibitory reflex responses in the surface electromyograms of both masseter muscles. These reflexes were modulated to markedly different extents in different subjects by auditory white noise, which always reduced the amplitude of the inhibition. The reflexes were abolished when local anaesthesia was infiltrated around the stimulated tooth and white noise was played into the ears. Evidence is presented that the sound of the tap on the tooth, transmitted through the air, is in itself sufficient to evoke an inhibitory reflex in masseter which is qualitatively similar to that from the periodontal receptors. Thus, in the absence of auditory masking, the total reflex evoked by tooth taps is the result of the summation of the inputs from both periodontal mechanoreceptors and auditory receptors.

Monitoring of the discrimination threshold for interocclusal thicknesses in rehabilitated edentulous patients

Thirty-seven white Caucasian subjects with unsatisfactory dentures were tested for interocclusal thickness discrimination threshold. New dentures were prepared and the test was repeated on days 1, 4 and 90 (from delivery). Eight patients whose situation was still unsatisfactory were given osseointegrated implant anchored dentures and the test repeated at the same intervals. Results were analysed statistically. Improved denture fit was found to increase interocclusal sensitivity. Decreased sensitivity during follow-up might indicate the need to check denture fit.

Factors affecting nerve excitability and conduction as a basis for desensitizing dentine

Nerve excitability is principally determined by the state of membrane sodium channels, which can be influenced by factors such as drugs or the ionic composition of the extracellular fluids. The excitability of isolated nerves is increased by lowered extracellular calcium and hydrogen ion concentrations, and similar effects are seen on intradental nerve excitability. This is of interest as some agents used to desensitize hypersensitive dentine are believed to act by reducing intradental nerve excitability. A variety of ions, including potassium and divalent cations, have been shown to reduce intradental nerve excitability when applied in relatively high concentrations to dentine close to the pulp. However, these conditions do not mimic the clinical situation, where agents are applied to outer dentine, up to 2 mm from the pulp. Also, when agents are applied to dentine it is difficult to quantify the precise changes in extracellular fluid composition, and there is the additional complication of possible interactions between the agents and dentine. These problems can be minimized by using isolated nerves, which allow better control over the conditions and ionic concentrations necessary to achieve nerve conduction block. Such methods can provide a convenient way to screen potential desensitizing agents before evaluation in vivo or in clinical trials.

Effects of calcium phosphate solutions on dentin permeability

Calcium phosphate solutions at various concentrations and pH levels were used to obstruct the dentinal tubules. The effects were evaluated by measurements of permeability through dentin discs and by scanning electron microscopy. Precipitation kinetics were followed by pH changes in the solutions and products were determined by X-ray powder diffraction. The solutions were applied in two ways: (a) calcium and phosphate solutions were mixed before application and (b) one solution (calcium or phosphate) was applied first followed by the other solution. Three kinds of human dentin discs were used; one with smear layer and the other two with tubules exposed by sonication or etched by acid. The high concentration calcium phosphate solutions at pH = 9.5 rapidly precipitated amorphous calcium phosphates that obstructed the dentinal tubules and decreased dentin permeability by 85% or more. At pH = 5.6, the calcium phosphate solutions precipitated large crystals of dicalcium phosphate dihydrate. In this case, the effectiveness in obstructing dentinal tubules was found to be procedure sensitive.

The immediate effect of the variation of anteroposterior laterotrusive contacts on the elevator EMG activity

A unilateral maxillary splint divided into three occlusal blocks was built for eight healthy young adults. The three blocks allowed the anteroposterior location of the laterotrusive contacts to vary and to distribute the occlusal force over equivalent periodontal surfaces. The ipsilateral masseteric and temporalis electromyogram (EMG) activities were recorded with surface electrodes during maximal voluntary clenching. The elevator EMG activity with the anterior occlusal block in place was significantly lower than with the intermediate or posterior blocks. The reduction for both elevators with the intermediate block in place did not show a significant variation in comparison to the posterior block of the three blocks inserted. The elevator activity with the three occlusal blocks did not differ from that recorded with the posterior block alone. Neurophysiologic and biomechanical explanations are given related to this laterotrusive elevator muscular behavior.

Assessment of pain in cervical dentinal sensitivity studies. A review

Traditionally cervical dentinal sensitivity (CDS) has been evaluated mainly subjectively on the basis of the individual patient's subjective response, e.g., in the form of verbal rating and visual analogue scales and questionnaires. The stimuli used for evaluating this response can be grouped into 4 main categories: mechanical, chemical, electrical and thermal. This review of the literature, however, indicates that there are problems in evaluating patient subjective response to these various test stimuli used in the assessment and treatment of CDS. Opinions also vary as to the reliability of some of these methods of assessment, although recently, efforts have been made to develop controlled reproducible stimuli more suited to the evaluation of CDS. Currently no single method of eliciting and assessing CDS may be considered ideal. Further research is required to evaluate suitable methodology for the quantification of realistic test stimuli under controlled clinical conditions, whereby the subjective response may be objectively measured by the investigator.

Identification and characterization of afferent periodontal A delta fibres in the cat

1. The presence and responsiveness of afferent periodontal A delta fibres was studied in pentobarbitone-anaesthetized adult cats. 2. Extracellular single fibre recordings were made from fine nerve filaments split from the proximally cut end of the inferior alveolar nerve. Periodontal nerve fibres were identified by constant current stimulus pulses applied via platinum wire electrodes inserted into the periodontal space of the lower canine tooth. 3. Of a total of 252 periodontal nerve fibres, 97 (37%) were classified as A delta fibres according to their conduction velocities (CV) (> 2.5 m s-1, < 30 m s-1) as determined by electrical stimulation of the periodontal ligament. The mean (+/- S.D.) conduction velocity was 11.0 +/- 7.7 m s-1 (n = 97; range: 2.6-28.2 m s-1). 4. A good exponential correlation (r = 0.85) was found between the electrical thresholds of the A delta fibres and their conduction velocities. 5. For four A delta fibres a complete stimulus-duration curve was determined. It followed rather well the I = I0/(1-et/tau) law, where I represents the stimulus amplitude, t the stimulus duration, I0 the rheobasic current and tau the time constant. 6. In the intact tooth none of the identified periodontal A delta fibres showed any ongoing activity in the absence of intentional stimulation. 7. The responses of sixteen electrically identified periodontal A delta fibres were tested by mechanical, thermal and chemical stimuli applied to the periodontal space. Seven of nine periodontal A delta fibres tested responded to mechanical forces applied to the tooth from different directions of which none could be activated by slight touch. A rudimentary directional sensitivity was seen. When a human tooth was stimulated by a mechanical stimulus of similar strength the sensation evoked was described as a dull, poorly localized pain. 8. Six periodontal A delta fibres were activated by heat and/or cold and/or chemical stimulation. Two of eight periodontal A delta fibres tested responded to heat and four of six A delta fibres tested responded to cold stimuli applied to the alveolar bone overlying the periodontal ligament; none of them responded to both types of thermal stimuli. Two of seven periodontal A delta fibres tested were activated by a saturated solution of potassium chloride applied locally to the periodontal ligament; two of these responded also to cold. 9. The response behaviour of periodontal afferent A delta fibres observed in this study suggests that they may play a role in periodontal nociception.

Central connections of trigeminal primary afferent neurons: topographical and functional considerations

This article reviews literature relating to the central projection of primary afferent neurons of the trigeminal nerve. After a brief description of the major nuclei associated with the trigeminal nerve, the presentation reviews several early issues related to theories of trigeminal organization including modality and somatotopic representation. Recent studies directed toward further definition of central projection patterns of single nerve branches or nerves supplying specific oral and facial tissues are considered together with data from intraaxonal and intracellular studies that define the projection patterns of single fibers. A presentation of recent immunocytochemical data related to primary afferent fibers is described. Finally, several insights that recent studies shed on early theories of trigeminal input are assessed.

Thalamic nociceptive mechanisms in cats, influenced by central conditioning stimuli

Field potentials and single cell activity evoked by tooth pulp (TP) stimulation were studied in the ventrobasal (VB) complex of the cat. The experiments were performed using a conditioning-test paradigm. Evoked cell activity or field potentials following TP stimulation was used as a test. Conditioning stimulus was given to different regions of the thalamic central lateral nucleus (CL). Conditioning electrical stimulation in medial (ML 2.8-3.6 mm) parts of CL induced a depression of the TP evoked response in 10 cells. Stimulation sites in lateral CL (ML 3.6-4.2 mm) induced facilitation in eight cells and decreased activity in seven cells. Tooth pulp evoked field potentials in thalamus were facilitated by a preceding stimulation in lateral CL. Cells in the lateral parts of CL are suggested to induce an increased activity in cells in the VB complex which mediate nociceptive information. This effect is suggested to be mediated via a CL induced disinhibition at a reticular thalamic (RE) or at a VB complex level. The medial parts of CL seem to give a traditional feedback inhibition on VB cells. Such an effect is also suggested to be mediated via the RE complex. The importance of these findings are discussed with relation to changes in the thalamus that may occur following long lasting nociceptive stimulation.

Morphology of neural endings in the human periodontal ligament: an electron microscopic study

The ultrastructure of sensory nerve endings in the human periodontal ligament from 43 extracted teeth was studied using serial sections. Three types of nerve endings were found: free nerve endings (FNE), Ruffini-like endings and lamellated corpuscles. Free nerve endings stem from unmyelinated or from myelinated nerve fibers. The endings contain neurotubuli, neurofilaments and vesicles. Ruffini-like receptors were mostly found in the apical part of the periodontal ligament. In these Ruffini-like receptors a particularly abundant concentration of mitochondria appears. In some cases desmosome-like junctions are present between neurite and ensheathing cell. Lamellated corpuscles were also found in the periodontal ligament. The lamellae are extremely endocytotic and are in close contact with each other.

Sensitizing effects of leukotriene B4 on intradental primary afferents

Previous studies have established that leukotriene B4 (LTB4) sensitizes cutaneous nociceptors. In this study the effects of LTB4 on spontaneous and stimulus-evoked nerve activity from primary afferents innervating the dentin of canines in adult cats were examined. LTB4 treatment (25 micrograms/ml) significantly enhanced stimulus-evoked intradental nerve activity (INA) for at least 20 min after the removal of the compound from the recording preparation. Teeth treated with LTB4 demonstrated enhanced spontaneous nerve activity following the removal of hypertonic saline used to evoked INA. These findings provide additional evidence that LTB4 is able to sensitize nociceptors and may be a long-lasting hyperalgesic factor which may contribute to pain of pulpal origin.

Identification and characterization of afferent periodontal C fibres in the cat

The presence of afferent periodontal C fibres was studied in pentobarbitone-anaesthetized cats. Extracellular single-fibre recordings were made from fine nerve filaments split from the proximally cut end of the inferior alveolar nerve. Periodontal nerve fibres were identified by constant-current stimulus pulses applied via platinum wire electrodes inserted into the periodontal space. Of 260 periodontal nerve fibres, 142 (55%) were classified as C fibres according to their conduction velocities (less than or equal to 2.5 m/sec) as determined by electrical stimulation of the periodontal ligament (c.v.p). The mean (+/- S.D.) c.v.p was 1.2 +/- 0.6 m/sec (n = 142; range: 0.3-2.5 m/sec). In addition, the axonal conduction velocity of 14 periodontal C fibres was determined by bipolar electrical stimulation of the trunk of the inferior alveolar nerve (c.v.n). On average the c.v.n was 42% higher than the c.v.p; the mean value was 1.7 +/- 0.8 m/sec (n = 14; range: 0.6-3.9 m/sec). Nevertheless, the classification of nerve fibres based on c.v.p proved to be reliable; only 1 fibre had a c.v.p less than 2.5 m/sec and a c.v.n greater than 2.5 m/sec and a c.v.n greater than 2.5 m/sec and was therefore reclassified as an A delta fibre. The responses of 30 electrically identified periodontal C fibres were tested by mechanical, thermal and chemical stimuli applied to the periodontal space. Thirteen of 19 periodontal C fibres tested responded to a strong mechanical force applied to the tooth from different directions while none could be activated by slight touch. A rudimentary directional sensitivity was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of periodontal stimulation on VHM neurones in anesthetized rats

In anesthetized rats, mechanical stimulations, the direction and intensity of which could be modified, were applied to the superior incisive while single neurone activities were recorded within the VHM region by means of extracellular glass microelectrodes. The great sensitivity of periodontal receptors to the direction and the intensity of the stimulations was demonstrated at this level. This finding, which is reported here in detail for the first time, suggests that the periodontal afferents might be involved in physiological mechanisms including food intake regulation and osteomorphogenesis.

Distribution of axons showing calcitonin gene-related peptide- and/or substance P-like immunoreactivity in the sensory trigeminal nuclei of the cat

Distribution of axons with calcitonin gene-related peptide (CGRP)-like and/or substance P (SP)-like immunoreactivity (LI) within the sensory trigeminal nuclei was examined in the cat before and after trigeminal rhizotomy. Axons with CGRP-LI or SP-LI were seen throughout the principal sensory trigeminal nucleus (Vp) and spinal trigeminal nuclei, including the medullary dorsal horn (MDH). They were densely distributed particularly in the dorsolateral part of the dorsal subnucleus of the Vp, ventromedial marginal zone of the ventral subnucleus of the Vp, dorsomedial and ventromedial parts of the oral spinal trigeminal nucleus, ventromedial and lateral marginal zones of the interpolar spinal trigeminal nucleus, and lamina I, outer part of lamina II and lamina V of the MDH. Most of the CGRP-LI axons exhibited SP-LI, while many SP-LI axons did not show CGRP-LI. After trigeminal rhizotomy, almost all CGRP-LI axons disappeared from the ipsilateral sensory trigeminal nuclei, while a considerable number of SP-LI axons remained intact throughout the nuclei; these SP-LI axons did not show CGRP-LI. The results indicate that CGRP-LI axons within the sensory trigeminal nuclei exhibit SP-LI and are of peripheral origin, and that SP-LI axons without CGRP-LI are of central origin.

Blocking of periodontal afferents with anesthesia and its influence on elevator EMG activity

The effect of anesthetic blocking of the periodontal afferents of the canine teeth was studied in order to determine its influence on any changes in the jaw elevation activity. Unilateral integrated EMG recordings were made of the masseter and anterior temporal muscles during maximal voluntary clenching in centric occlusion and laterotrusive position with canine contact. After anesthetic blocking of the periodontal afferents of one or both ipsilateral canines, a significant increase was observed of the EMG activity of both jaw elevator muscles studied, in centric occlusion as well as with canine contact. The elevator activity increase was of a greater magnitude when antagonistic canines were anesthetized. These findings thus support the hypothesis that high threshold periodontal receptors exert an inhibitory effect on jaw elevator muscular activity.

A human periodontal ligament fibroblast clone releases a bone resorption inhibition factor in vitro

The conditioned media (CM) obtained from three lines of cloned human periodontal ligament (PDL) cells were analyzed to determine whether they altered the parathyroid hormone (PTH)-stimulated resorption rates (45Ca release) in 48-hour cultures of 45Ca-labeled rat long bones. One PDL cell line, PDL-5, produced a heat-resistant factor in its CM that inhibited the PTH-stimulated resorption by 43.8 +/- 9.7 (SE) percent (p less than or equal to 0.02), whereas the CM from the other cell lines were without statistically significant effect. The CM from the PDL-5 line did not diminish organ culture viability, as determined by 3H-thymidine incorporation, and did not enhance or diminish the resorption-inhibiting activity of calcitonin added to the PTH-stimulated cultures. The addition of CM from PDL-5 did not alter the bone-resorbing effect of interleukin-1 (IL-1). These results indicate that CM from PDL-5 inhibits only the PTH-induced and not the IL-1-mediated resorption processes, whose mechanisms are therefore likely to differ.

Gap junctions between odontoblasts revealed by transjunctional flux of fluorescent tracers

Cell communication between odontoblasts was investigated with the use of fluorescent-dye tracers; Lucifer Yellow CH (molecular weight = 457.3), and dextran-Lucifer Yellow CH (average molecular weight = 10,000). Dyes were injected into cell bodies of individual odontoblasts via an intracellular microelectrode or into a group of cells through their processes, and passage to adjacent cells was examined with a fluorescence microscope. Lucifer Yellow CH appeared to diffuse very easily among odontoblasts, while dextran-Lucifer Yellow remained within the injected cell or cells. This efficient migration of Lucifer Yellow CH can be considered a functional manifestation of gap junctions between odontoblasts.

Influence of variation in anteroposterior occlusal contacts on electromyographic activity

A full upper stabilization splint divided into three pairs of occlusal bilateral blocks was made for eight healthy young adult subjects. The three pairs of blocks allowed the location of the centric occlusal contacts to vary and to be distributed over equivalent periodontal surfaces. The electromyographic activity of the masseter and temporal muscles was recorded with surface electrodes during maximum voluntary clenching over the centric occlusal blocks. The electromyographic activity from the elevator muscles with the anterior blocks was significantly less than with the intermediate and posterior occlusal blocks. With use of the intermediate blocks, the activity from the elevator muscles was significantly less than with the posterior blocks. The elevator activity with the posterior blocks was similar to that with the full coverage splint.

The effect of vibration on the discharge of periodontal ligament mechanoreceptors to controlled loading of the cat canine tooth

This study observes the maximum 1:1 following frequencies of these mechanoreceptors, as well as their response characteristics before and after vibratory stimuli. Mechanical stimuli were applied to the tip of the crown of the left mandibular canine tooth in cats anaesthetized with alpha-chloralose while recordings were made from functionally single fibres teased from the inferior alveolar nerve. Vibratory stimuli were applied at various frequencies and durations at twice the threshold to that stimulus. Controlled ramp-plateau forces were applied before and after the period of vibration. A temporary rise in the receptor discharge was recorded and the threshold to ramp-plateau stimuli fell to about one-third of its original value. The increased post-vibration response was dependent on the frequency and duration of the stimulus. It is suggested that vibration has some temporary effect on the receptor environment.

Comparison of trigeminal receptor location and structure in the periodontal ligament of different types of teeth from the rat, cat, and monkey

The periodontal ligament is richly innervated by mechanoreceptors whose cell bodies are located either in the trigeminal ganglion (TG) or the mesencephalic (MS) trigeminal nucleus. Both are sensitive to stretch of the ligament induced by tooth movement, but their thresholds, central connections, and functional significance differ. This study compared the location of TG and MS receptors in the periodontal ligament of cat teeth after labeling each by anterograde axonal transport. We also compared the location and ultrastructure of the feline TG receptors with labeled TG receptors in the periodontal ligament of monkey teeth and rat incisors in order to determine their location and ultrastructural properties. We found that the MS and TG receptors had a different distribution in the periodontal ligament of cat teeth; the MS terminals were concentrated below and next to the base of the roots, whereas the TG receptors were most numerous around the middle of the roots. The TG receptors of monkey teeth had a similar location to the feline TG receptors, but those of rat incisors were very different. Rat incisors are curved, continuously erupting teeth, and their TG receptors were located primarily on the lingual side in the alveolar (nonerupting) portion of the ligament. Ultrastructural comparisons found that most mechanoreceptors in the periodontal ligament of all the teeth had an unencapsulated branched Ruffini-like structure. The TG receptors in the rat incisor ligament were the largest; those of monkey had the most varied form. Some coiled or encapsulated receptors were found in the monkey and cat ligament, but not in the rat incisor ligament. The TG receptors appear to be located at sites that would be most easily stretched during tooth contact. The different sites and intensity of the stretch forces occurring during the use of different types of teeth may determine the variations in the size and location of the TG mechanoreceptors and of their associated support cells. The different distribution of MS receptors may contribute to their response thresholds and static properties, which differ from those of TG receptors.

Dual somatosensory representation of the periodontium in nucleus ventralis posteromedialis of the cat thalamus

The distribution of periodontal units within the nucleus ventralis posteromedialis (VPM) was studied in urethane-chloralose-anesthetized cats. Recordings were made from a total of 63 periodontal units. Of these, 55 received contralateral input, the rest receiving ipsilateral input. The periodontal units receiving contralateral inputs were located in the medial part of the VPM proper, whereas those receiving ipsilateral inputs were found in the lateral subdivision of the nucleus ventralis posteromedialis parvocellularis (VPMpcl).

The role of periodontal receptors in the jaw-opening reflex in the cat

1. In anaesthetized cats, graded electrical stimulation of the inferior alveolar nerve at just above threshold for the largest afferent fibres caused inhibition of jaw-closer motoneurones. Stimulus strength had to be increased to 1.5 times threshold with double shocks to cause reflex contraction of the digastric muscle. 2. Inhibition of jaw-closer muscles and excitation of digastric muscle resulted from transients of force applied to the upper canine tooth. However, the threshold for the digastric response was approximately 11 times higher than that of the periodontal afferent units recorded in the mesencephalic nucleus of the fifth nerve (MesV). Vibration of the upper canine at 50 Hz, with amplitude adequate to excite periodontal afferents, caused no digastric contraction. 3. Stimulation in the caudal part of the MesV so as to excite periodontal afferents caused no digastric reflex, provided that the stimulus did not spread to other parts of the fifth nerve nuclei. 4. It is concluded that under these conditions the low-threshold periodontal mechanoreceptors cause inhibition of jaw-closer muscles, but no significant excitation of jaw-opener muscles. 5. These findings are discussed from the point of view of the control which periodontal mechanoreceptors may exert over the biting force during mastication.

Changes in dental blood flow following electrical tooth pulp stimulation--influences of capsaicin and guanethidine

The responses of rat incisors microcirculation to electrical pulp stimulation was examined. A fast initial decrease was followed by a long lasting increase in blood flow due to activation of sympathetic efferents and nociceptive afferents, respectively. Both constituents of the response could be abolished differentially by the use of guanethidine (sympathectomy) and capsaicin (C-deafferentiation), respectively. The results point to a role of both C-efferents and peptidergic C-afferents in the control of tooth pulp circulation.

Arterial hypertension is associated with hypalgesia in humans

An association between increased blood pressure and hypalgesia has been reported in several studies in animals and in a few reports in humans. We investigated the relationship between hypertension and pain perception by comparing the response to graded electrical stimulation of the tooth pulp, which is thought to represent an exclusively nociceptive system. The test was performed with a commercial tooth pulp tester in a large series of subjects with borderline or established hypertension and in three groups of normotensive controls: volunteers, nonhypertensive patients, and medical students with a well-established or no family history of hypertension. Subjects had to report when they started to feel pulp stimulation (sensory threshold) and when this became painful (pain threshold). Sensory and pain thresholds were obtained as means of the measurements on four healthy, unfilled teeth. Sensory thresholds were significantly higher in subjects with borderline or established hypertension than in two of the three normotensive groups (volunteers and normotensive patients), whereas no significant difference was observed between the two hypertensive groups. The results for the pain threshold were qualitatively similar but less clear and less amenable to statistical analysis because this parameter could not be determined with accuracy in a number of subjects in whom the subjective pain threshold was above the upper range of stimulation of the instrument. The association between blood pressure levels and pain perception was further confirmed by the highly significant correlation found for the overall data between mean arterial blood pressure and both thresholds.(ABSTRACT TRUNCATED AT 250 WORDS)

Intradental nerve activity and jaw-opening reflex in response to mechanical deformation of cat teeth

Mechanical stress was applied to canine teeth in anaesthetized cats to excite intradental A-fibres and to produce digastric muscle EMG responses. Activity in the intradental sensory units was recorded by two electrodes, one inserted in a dentinal cavity, the other in contact with the gingival sulcus. A pneumatically driven piston was used to cause a mechanical stress (10-150 N) on the stabilized tooth crown for 30 s, with instantaneous onset and release. Application of a load of 30 N produced a momentary burst of impulses in 2 of 12 teeth; 8 out of 10 teeth responded when 150 N was used. Digastric EMG responses were obtained at and above 60 N. Removal of the coronal pulp or cooling of the tooth crown with ethyl chloride abolished this reflex, whereas percussion of the tooth still produced a digastric response. Our results suggest that load-induced deformation of teeth activates intradental sensory mechanisms and a reflex withdrawal reaction unrelated to periodontal stimulation.

The ability of a mathematical model to evaluate the effects of two pain modulating procedures on pulpal pain in man

The ability of a mathematical model to evaluate the effects of two different pain modulating procedures (partial nerve block and vibration) on acute experimental pulpal pain was studied. The results were also compared with placebo procedures and it was shown that the model could accurately quantify the parameters that determine the pain response following cold-induced intradental nerve impulse activity (INA). The most effective pain relieving method was found to be partial nerve block which induced significant parameter alterations reflecting decreased pain sensation and increased reaction time. Thus, it was shown that the present mathematical model is a useful tool enabling detailed analysis of differences in pain relieving procedures on human pulpal pain mediated by nerves of the A type.

Periapical innervation of the ferret canine and the local retrograde neural changes after pulpectomy

The amputation of the dental pulp severs a population of axons that are predominantly in the A delta and C fiber size range and are principally involved in nociception. Local periapical neuromas, if they are formed after pulpectomy, may be the sites of spontaneous nervous activity that may, in some circumstances, be involved in the genesis of chronic pain. The periapical tissues from the mandibular canines of four ferrets were examined 3 months after pulpectomies. Silver-stained paraffin sections were examined in three dimensions at the light microscope level. Ultrathin sections were examined at the electron microscope level. Compared with contralateral and independent controls, the principal changes were the loss of the periodontal plexus around the root apex, the extension of damage well below the apical foramen, and the persistence of inflammation 12 weeks postoperatively. While a somewhat disorderly mass of nerve fibers develops subapically, the arrangement has only some of the features usually associated with neuromas.

The response characteristics of mechanoreceptors related to their position in the cat canine periodontal ligament

The relation between threshold, adaptation properties and position of these receptors was studied in anaesthetized cats. Electrophysiological recordings were made from functionally single fibres teased from the inferior alveolar nerve as forces were applied to the tip of the left mandibular canine tooth. Receptors were located within the periodontal ligament by paring away the overlying bone. Threshold and adaptation properties were related to the receptor position relative to the fulcrum and apex of the tooth. These results support the hypothesis that there is only one type of periodontal-ligament mechanoreceptor, and that their response characteristics depend on position.

The effect of rate of force application on the threshold of periodontal ligament mechanoreceptors in the cat canine tooth

Mechanical stimuli in the form of ramp-plateau forces were applied to the tip of the crown of the left mandibular canine tooth in cats anaesthetized with alpha-chloralose. Electrophysiological recordings were made from functionally single fibres teased from the inferior alveolar nerve. The force threshold was determined for 34 periodontal ligament mechanoreceptors at different controlled rates of force application. Force threshold was dependent on the rate of force application to the crown tip. Rate sensitivity was present for all receptors across the range from rapidly to slowly adapting; the degree of rate sensitivity was graded according to the adaptation rate of the receptor. The results suggest that the velocity of mechanical stimulus application to teeth needs to be considered in studies involving periodontal mechanoreceptor responses and their reflexes.

Intrapulpal nerve stimulation in the rat

Electrical stimulation of the rat incisor pulp has been frequently used as a method to study the mechanisms of pain. However, several of the techniques used to stimulate nociceptive nerves in these teeth also tend to excite non-nociceptive nerves in adjacent tissues. This report deals with the development and verification of a procedure which selectively stimulates pulpal nerves over a wide range of stimulus intensities. The methods consisted of placing electrodes in labial cavities of each of the two lower rat incisors, 1 mm distal to the level of the crest of the interdental papilla. Each cavity had a diameter of 0.5 mm and a depth of about three-quarters fo the crown diameter. Each electrode consisted of a Ag/AgCl filling compacted onto the end of a 0.1 mm silver wire. Constant current stimuli were passed between the two electrodes. EMG was monitored to detect reflex activation of the digastric muscle in response to intradental or extradental afferent excitation. The response consisted of two components. One was a long latency potential (LLP) (37 ms latency) (89 microA ave TH); the other was a short latency potential (SLP) (12 ms latency) (650 microA min TH). In all animals that LLP was abolished by bilateral sectioning of the tooth pulp 7 mm below the level of the labial gingival margin. The SLP was not abolished. This would indicate that the LLP was due to stimulation of pulpal fibers, and the SLP to excitation of extrapulpal fibers. This may prove to be a helpful method for nociceptive researchers to easily verify that they are actually stimulating pulpal afferents.

Direct and relayed projection of periodontal receptor afferents to the cerebellum in the ferret

Field potentials in the cerebellar cortex of the ferret have been studied in response to stimulation of alveolar, muscular and cutaneous branches of the trigeminal nerve. Responses from the alveolar nerves are unusual in their very short latency. Evidence based on latency analysis, frequency following and comparison with other well-known inputs supports the view that the earliest field potentials are due to direct, unrelayed afferents, which terminate as mossy fibres. There is, in addition, a monosynaptically relayed afferent path via mossy fibres. The alveolar nerve afferents concerned with the direct projection are shown to come from periodontal mechanoreceptors and not from cutaneous receptors. No such connections are found from jaw-muscle spindle afferents. The direct and relayed periodontal pathways are both ipsilateral and crossed. They terminate in the cerebellar cortex in the parvermal region of lobules IV, V and VI. The functional significance of the direct periodontal afferent projection is considered particularly in the light of parallels with the vestibular system, which also has direct and relayed cerebellar projections.

Alpha adrenoceptor modulation of the jaw-opening reflex

In the present study, the nature, role and location of the alpha-adrenoceptors, modulating the tooth pulp stimulation (TPS)-evoked jaw-opening reflex (JOR), was investigated. Clonidine, a lipophilic alpha 2-adrenoceptor agonist, rapidly, reversibly and significantly elevated the threshold of the digastric electromyogram (dEMG) evoked by tooth pulp stimulation which was antagonized by yohimbine or piperoxane (two alpha 2-adrenoceptor antagonists) but not by prazosin (an alpha 1-adrenoceptor antagonist). 4-Hydroxyclonidine and ST-91 non lipophilic alpha 2 adrenoceptor agonists, were ineffective on the tooth pulp stimulation-evoked threshold of the digastric electromyogram. Clonidine was ineffective upon digastric muscle stimulation (DMS)-evoked threshold of the digastric electromyogram of the curarized digastricus and mylohyoid (motor) nerve stimulation (MNS)-evoked digastric EMG. It is concluded that modulation by clonidine of the tooth pulp stimulation-evoked jaw-opening reflex is devoid of a peripheral efferent component and that such modulation is predominantly expressed through interactions with centrally located alpha 2 adrenoceptors.

Psychophysical experiments of thermoperception in human teeth

Clinically inconspicuous anterior teeth of subjects 18-53 years of age were stimulated by means of an electrically controlled thermode of 0.5 degree C, 35 degrees C and 71 degrees C for 60 s. In two sets of experiments testing vital anterior teeth the cold stimuli were correctly identified significantly above chance level, making the existence of cold receptors inside the tooth probable. No evidence of a corresponding warm perception in human anterior teeth was found. These results were corroborated in a third experiment by comparative testing of 75 anterior teeth--25 devital and 50 vital--for a possible stimulus spread to other than intradental neural structures. Local surface anaesthesia of the tissues adjacent to the teeth significantly reduced the subject's ability to correctly identify cold stimuli. Investigating the effect of cold stimulus temperatures (0.5 degree C, 15 degrees C and 25 degrees C), no significant difference in correct cold perception was found when the two lower temperatures were applied, while with the 25 degrees C stimulus correct cold perception was at chance level. The latency of correct cold responses increased significantly when stimuli of 15 degrees C instead of 0.5 degree C were applied (t-test p less than 0.05). The latency of correct cold responses (0.5 degrees C) was not significantly influenced by surface anaesthesia. It increased significantly, however, when devital teeth were tested with the 0.5 degree C stimulus (t-test; p less than 0.01).

The neurobiology of facial and dental pain: present knowledge, future directions

This review outlines recent research which has identified critical neural elements and mechanisms concerned with the transmission of sensory information related to oral-facial pain, and which has also revealed some of the pathways and processes by which pain transmission can be modulated. The review highlights recent advances in neurobiological research that have contributed to our understanding of pain, how acute and chronic pain conditions can develop, and how pain can be controlled therapeutically. Each section of the review also identifies gaps in knowledge that still exist as well as research approaches that might be taken to clarify even further the mechanisms underlying acute and chronic oral-facial pain. The properties of the sense organs responding to a noxious oral-facial stimulus are first considered. This section is followed by a review of the sensory pathways and mechanisms by which the sensory information is relayed in nociceptive neurones in the brainstem and then transmitted to local reflex centers and to higher brain centers involved in the various aspects of the pain experience--namely, the sensory-discriminative, affective (emotional), cognitive, and motivational dimensions of pain. Reflex and behavioral responses to noxious oral-facial stimuli are also considered. The next section provides an extensive review of how these responses and the activity of the nociceptive neurones are modulated by higher brain center influences and by stimulation of, or alterations (e.g., by trauma) to, other sensory inputs to the brain. The neurochemical processes, involved in these modulatory mechanisms are also considered, with special emphasis on the role of neuropeptides and other neurochemicals recently shown to be involved in pain transmission and its control. The final section deals with recent findings of peripheral and central neural mechanisms underlying pain from the dental pulp.

Characteristics of periodontal mechanosensitive neurons in the first somatosensory cortex of the cat

Response properties of periodontal mechanosensitive (PM) units which were activated by the mechanical stimulation of canine teeth were studied in the oral area of somatosensory cortex S I (anterior coronal gyrus) of the cat. Spike discharges of PM units were recorded as post-stimulus time histograms (PSTHs). Most PM units showed more or less spontaneous activity and phasic response properties to the trapezoid waveform stimulation. When the rate of stimulus application was increased, the initial peak value of the PSTH increased and its crest time decreased. Direction-selective PM units which changed their response discharge rates according to the direction of the stimuli applied to the canine teeth were found in this cortical area. Posterior-directed mechanical stimulation was more effective for eliciting the spike discharges of PM units than anterior-directed stimulation. Applying the test and conditioning stimuli to the contralateral or ipsilateral canine teeth, interactions of afferent inputs received by the mechanoreceptors of the periodontal tissues of different teeth were studied. Test responses of PM units were inhibited for 20-50 ms after the onset of the conditioning stimuli.

Influence of group function and canine guidance on electromyographic activity of elevator muscles

A comparative EMG study was done between two types of occlusal guidances: group function and canine guidance. The purpose was to determine which of the two occlusal schemes causes a greater reduction in muscle activity and thereby a decrease in muscle tension in eccentric mandibular positions. Full-coverage occlusal splints were made for six test subjects with normal function of the stomatognathic system. Left- and right-side integrated EMG recordings were made of the masseter and temporal muscles during static (clenching) and dynamic (lateral excursion and clenching) maximal contractions. The results showed an EMG activity reduction of the elevator muscles with group function relative to their activity in centric occlusion. A more marked reduction was observed on the mediotrusive side, mainly in the temporal muscle. With canine guidance, the reduction in elevator muscle activity is much greater, more significant, and mainly in the temporal muscle of the mediotrusive side. The clinical implications of this study suggest the use of canine guidance in laterotrusion for therapy with full-coverage occlusal splints.

Thresholds of hypersensitive teeth to 2 forms of controlled stimulation

2 new methods are described for measuring the sensitivity of dentine to mechanical (probe) and cold-air stimulation. The methods are suitable for clinical use and could be used in the evaluation of desensitising treatments. In addition to qualitative differences in the pattern of sensitivity of teeth to these stimuli, considerable variation was observed in the distribution of pain thresholds to probe and air stimulation. Thresholds were not significantly affected by the age or sex of the subjects, but mean thresholds of teeth sensitive to only one stimulus were significantly greater than thresholds of teeth sensitive to both stimuli; these differences were most marked in female subjects. Factors such as the qualitative differences in sensitivity to various stimuli and quantitative differences in the degree of sensitivity to the stimuli require to be considered in clinical evaluation of desensitizing treatments.

Is electrical stimulation of the rat incisor an appropriate experimental nociceptive stimulus?

The purpose of this study was to determine whether or not tooth pulp stimulation in the rat can selectively activate the pulp nerve fibers without excitation of the periodontium and to decide if the nerve fibers situated in the pulp of the rat's incisor are involved in the nociceptive reactions caused by an intrapulpal stimulation. The experiments were carried out on 20 awake and freely moving Sprague-Dawley rats. Bipolar stimulating electrodes were inserted into the pulp of the left lower incisor and in the right incisor after removal of the pulp. Special cares were taken to avoid, on the right side, direct stimulation of the stump of the apical nerve. The jaw opening reflexes were recorded from the digastric muscles ipsilaterally to the stimulated teeth and the thresholds were compared. Using the same animals, four typical and reproducible nociceptive behavioral reactions caused by a long tooth pulp stimulation were also observed (shock of 0.5 ms at 50 Hz during 1 s). The stimulus intensity was progressively increased, and the threshold of each reaction was recorded. For each of the 20 rats tested, the jaw opening reflex and the nociceptive reactions did not disappear after removal of the pulp, but the threshold of the responses to the stimulation of the nonvital tooth were significantly above the threshold of the responses to the stimulation of the vital incisor. The conclusion was tooth pulp stimulation activates the periodontal nerve fibers in the rat, and stimulation of the incisor pulp is significant in pain study in the rat because the thresholds of the jaw opening reflex and the nociceptive reactions were increased after the tooth pulp tissue was removed.

Cortical cells driven by the low-threshold tooth pulpal afferent in cats

The input pattern and spatial distribution of tooth pulp-driven neurons (TPNs) in the cat cortex were studied by recording the unitary activities of these neurons. Stimulation was applied to the upper and lower canine and molar tooth pulps. It was possible to record activities of TPNs in the deep layers of the areas 3a and 3b of the coronal gyrus of cerebral cortex. TPNs driven by the ipsilateral tooth pulp stimulation were distributed more anteroventrally than those driven by contralateral stimulation. Cells driven by bilateral pulp stimulation were situated between these two neurons. The threshold intensity for TPNs in the area 3a was lower than that for neurons in 3b. The majority of TPNs in the area 3a of the anterior part of the coronal gyrus received inputs from low-threshold masseteric muscular afferents as well as from tooth pulp afferents. The findings suggest that TPNs in the area 3a may have a relation to orofacial motor functions.

Alpha 2 adrenoceptors modulate the nociceptive jaw-opening reflex in rats

The jaw-opening reflex in lightly anesthetized rats induced by intrapulpal (left maxillary) electrical tooth pulp stimulation and quantified by the electromyograms (threshold values) recorded from the ipsilateral digastric muscle was used as the experimental pain index. The threshold for the jaw-opening reflex was significantly elevated by clonidine (12.5 to 50 micrograms/kg, i.v.) and was inversely correlated with the frequency of stimulation. The analgesia elicited by clonidine was antagonized by pretreatment with the alpha 2-adrenoceptor antagonist yohimbine (1 mg/kg, i.v.). All doses of clonidine produced an initial transient pressor response followed by a sustained hypotension and bradycardia. However, there was no direct correlation between the antinociceptive and cardiovascular effects of clonidine. It is proposed that clonidine modulates jaw-opening reflex analgesia by specifically activating alpha 2-adrenoceptors.

Is the jaw-opening reflex a valid model of pain?

Tooth pulp shock does not produce only pain; low intensity stimulation results in a non-painful sensation that is termed pre-pain. In animals low intensity tooth pulp shock does not evoke escape behavior; the similarity of the animal escape/detection threshold ratio with the human pain/pre-pain threshold ratio is evidence that pre-pain and pain may be present in animals as in humans. Both pre-pain and pain may arise from the activation of a common afferent modality. The TP-JOR does not correlate with the degree of pain experienced under all conditions. The TP-JOR threshold is at or near the sensory detection threshold, at stimulation intensities which evoke pre-pain. Under normal conditions both the magnitude of the TP-JOR response and the degree of pain experienced increase with increasing stimulation intensity. The TP-JOR and the tooth pulp-evoked pain are affected in parallel by sensory habituation and both appear to relay in the rostral trigeminal complex. There are no cases where the TP-JOR is suppressed and pain is still experienced from tooth pulp shock; the suppression of the TP-JOR may therefore be an accurate index of analgesia. However, in humans treatments that produce analgesia have not been shown to produce suppression of the TP-JOR. Thus, the TP-JOR that persists following analgesic treatments is not a reliable index of either analgesia or pain.

Physiological properties of intradental mechanoreceptors

A major role of tooth receptors in signaling overt or impending tissue damage (nociception) has been previously established by substantial evidence from mechanical, thermal and chemical stimulation of exposed dentin. We report evidence showing that some intradental receptors in canine teeth of the cat detect mechanical transients applied to intact enamel. This new finding suggests that dental innervation may play an important non-nociceptive role in oral function such as detecting tooth contact during mastication and swallowing.