Response properties of periodontal mechanosensitive neurones in the rat trigeminal sensory complex projecting to the posteromedial ventral nucleus of the thalamus.

Unitary discharges from periodontal mechanosensitive (PM) neurones responding to mechanical stimulation of the tooth were recorded from the trigeminal sensory complex in the rat brainstem. Of the PM units recorded, 22% were activated by antidromic stimulation of the contralateral (20%) or ipsilateral (2%) posteromedial ventral nucleus of the thalamus. Although thalamic-projecting neurones were recorded extensively throughout the trigeminal sensory complex, they originated most often in the region from the caudal main sensory nucleus to the rostral subnucleus oralis of the trigeminal spinal tract nucleus. The response latencies of the rostral nucleus units to orthodromic stimulation of peripheral receptive fields and antidromic stimulation of the thalamus were significantly shorter than those of the caudal nucleus units. More than half were single-tooth units originating from incisor teeth. They responded continuously when pressure was applied to the tooth. The magnitude of the response varied with the direction of the stimulus. Maximal responses were obtained when the stimulus was applied labiolingually or vice versa. The threshold for mechanical stimulation of the tooth was less than 0.05 N. The rostrocaudal distribution and response properties of thalamic-projecting PM neurones were very similar to those of non-thalamic-projecting PM units that were not activated by antidromic stimulation of the thalamus.     

The effect of inflammation on Fos expression in the ferret trigeminal nucleus

We have previously carried out detailed characterization and identification of Fos expression within the trigeminal nucleus after tooth pulp stimulation in ferrets. The aim of this study was to determine the effect of pulpal inflammation on the excitability of central trigeminal neurons following tooth pulp stimulation. Adult ferrets were prepared under anesthesia to allow tooth pulp stimulation, recording from the digastric muscle, and intravenous injections at a subsequent experiment. In some animals, pulpal inflammation was induced by introducing human caries into a deep buccal cavity. After 5 d, animals were re-anaethetized, and the teeth were stimulated at 10 times the threshold of the jaw-opening reflex. Stimulation of all tooth pulps induced ipsilateral Fos in the trigeminal subnuclei caudalis and oralis. All non-stimulated animals showed negligible Fos labeling, with no differences recorded between inflamed and non-inflamed groups. Following tooth pulp stimulation, Fos expression was greater in animals with inflamed teeth than in animals with non-inflamed teeth, with the greatest effect seen in the subnucleus caudalis. These results suggest that inflammation increases the number of trigeminal brainstem neurons activated by tooth pulp stimulation; this may be mediated by peripheral or central mechanisms.     

The effect of tooth extraction on periodontal ligament mechanoreceptors represented in the mesencephalic nucleus of the cat

When a force is applied to a tooth, mechanoreceptors in the periodontal ligament are stimulated. When teeth are extracted the remnants of the periodontal ligament break down and disappear, but it is not known what happens to the mechanoreceptor neurones that innervated it. The present study seeks to determine the effect of tooth extraction on the population of periodontal ligament mechanoreceptor neurones represented in the mesencephalic nucleus of the fifth cranial nerve. The incisor and canine teeth were extracted from adult cats; terminal experiments were performed between 7.5 months and 2 yr later. Recordings were made in the mesencephalic nucleus with microelectrodes, and neurones were identified in the inferior alveolar nerve that previously innervated the periodontal ligament of one of the extracted mandibular teeth. The majority of these neurones responded only to electrical stimuli applied to the edentulous ridge of the mandible in the area where the incisor or canine teeth had previously been. It was not possible to stimulate them mechanically, despite the use of large forces. A small number had reinnervated new soft-tissue sites. They could be mechanically stimulated and were found adjacent to the area in which the mandibular incisor and canine teeth had been. Thus the population of periodontal ligament mechanoreceptor neurones represented in the mesencephalic nucleus do not all degenerate after tooth extraction. As the majority of those still present do not appear to reinnervate new tissues in which they can be mechanically stimulated, it is unlikely that they have any functional role after tooth loss.     

Physiological properties of periodontal mechanosensitive neurones in the posteromedial ventral nucleus of rat thalamus

Unitary discharges of periodontal mechanosensitive (PM) neurones responding to mechanical tooth stimulation were recorded from the posteromedial ventral nucleus (VPM) of rat thalamus. PM neurones are distributed in the ventromedial area in the rostral two-thirds of the VPM nucleus. Maxillary and mandibular tooth-sensitive neurones are arranged in dorsoventral sequence. Of the PM neurones, 36% were slowly adapting to pressure applied to the tooth and 67% were rapidly adapting. The majority of PM units were sensitive to the contralateral incisor tooth. Response magnitudes of the slowly adapting neurones varied with stimulus direction and were directionally selective to mechanical tooth stimulation. The optimal stimulus direction was labiolingual or linguolabial. Rapidly adapting neurones were directionally non-selective to tooth stimulation. The threshold for mechanical stimulation was <0.05 N. Mean response latencies evoked by electrical stimulation of the peripheral receptive fields were 4.6 ms in the slowly adapting neurones and 5.8 ms in the rapidly adapting neurones.     

Activation of carotid sinus baroreceptors reduces pain sensations evoked by electrical and cold stimulation of human teeth

Activation of carotid sinus baroreceptors (CSBs) has been shown to have an influence on the perception of pain evoked by electrical stimulation of the skin. The present work was carried out to study to what extent dental pain can be modulated by simultaneous activation of CSBs. In 19 healthy voluntary human subjects, activation of CSBs was induced by application of negative pressure to an air tight collar fitted around the neck of the subjects (neck suction). Dental pain was evoked by electrical stimulation of the tooth (determination of the pain threshold) and by cold stimulation of teeth (ratings of the pain intensity). Neck suction resulted in an elevation of the dental pain thresholds and a reduction of the ratings of the cold-evoked dental pain. The present findings support the suggestion of the interaction of cardiovascular control systems with trigeminal nociceptive systems.     

Deciduous dentition in the rabbit (Oryctolagus cuniculus). A roentgenographic study

The sequence and chronology of deciduous tooth eruption and exfoliation in the rabbit was studied roentgenographically. In the mandible, two molars are erupted at 25 days gestation age. Root resorption of these teeth is apparent by the 7th postnatal day and both have been exfoliated by the 30th day. Development is more variable in the maxillary arch. Two molars and the second incisor tooth are erupted at 25 days gestation age and a third, more anteriorly placed, molar erupts by the 7th postnatal day. All of the maxillary teeth have been exfoliated by the 35th day. Transitory predecessors of the large permanent anterior incisor teeth in both jaws, reported in the literature, were not seen radiographically in our series. The deciduous dental formula, including the first incisors, may be stated: $\text{I}\text{(}\text{ab}\text{a}\text{)}\text{C}\text{(}\text{o}\text{o}\text{)}\text{M}\text{(}\text{def}\text{ef}\text{)}$, with $\text{d}$ the late erupting maxillary molar. The dentition of the rabbit differs from that of other commonly used laboratory animals in two important respects: (a) the deciduous dentition persists for about 1 month postnatally before being completely exfoliated; and (b) all of the permanent teeth are of the continuously erupting variety.     

Facilitatory effect of jaw opening on somatosensory (SI) cortical neurones sensitive to tooth pressure in the cat

In anaesthetized cats, an upper canine tooth was stimulated mechanically at two different levels of jaw opening, the resting position and an open position with 20 ± 2 mm between the upper and lower canines. The evoked field potentials and neuronal discharges were recorded from the caudal part of the contralateral coronal gyrus (SI cortex). The waveforms of the evoked potentials appeared in a positive-negative sequence. There were no significant changes in them when the jaws were open. Discharge patterns elicited in the cortical neurones by mechanical stimulation of the teeth consisted of initial ‘burst’ discharges, inhibitory pauses and/or large after-discharges. Jaw opening did not influence any phases of these responses to suprathreshold stimulation, spontaneous activities, or the sizes of the receptive fields. However, jaw opening did affect the initial ‘burst’ phase of the response to threshold stimulation, i.e. that which caused the neurones to fire with a probability of 30–50% with the jaw closed. Jaw opening enhanced this response probability in half (6/12) of the units that had very small receptive fields restricted to the canine tooth, but did not influence it in the majority (21/24) of the units that had larger receptive fields including the oral mucosa and the facial skin. There was no difference in distribution in the coronal gyrus between the two groups of neurones categorized by whether or not they were influenced by jaw position.     

Response properties of slowly and rapidly adapting periodontal mechanosensitive neurones in the primary somatosensory cortex of the cat

Periodontal mechanosensitive neurones in the primary somatosensory (SI) cortex are classified as either slowly or rapidly adapting. The responses of cortical neurones and their projection pathways were studied using mechanical and electrical stimulation of the teeth and electrical stimulation of the thalamic posteromedial ventral (VPM) nuclei and contralateral SI cortex. A total of 247 periodontal mechanosensitive units were recorded from the SI cortex in 35 anaesthetized cats, distributed mainly in area 3b: 14% were slowly adapting and 86% rapidly adapting units; 62% of the slowly adapting and 9% of the rapidly adapting units were single-tooth units sensitive to stimulation of only one tooth. The incidence of slowly adapting units with an ipsilateral receptive field was almost equal to that of slowly adapting units with a contralateral receptive field, and more than half of the units were directionally selective to mechanical tooth stimulation. The majority of rapidly adapting units had their receptive field in the contralateral teeth and were directionally non-selective to tooth stimulation. The latencies of the cortical responses of the slowly and rapidly adapting units were 7.3 and 10.7 ms, respectively, on electrical stimulation of the contralateral teeth, and 1.8 and 2.0 ms, respectively, on electrical stimulation of the ipsilateral VPM nucleus. From these findings, it is inferred that slowly adapting neurones are useful for discriminating the tooth stimulated, the stimulus direction, the stimulus intensity and the change of pressure applied to the tooth, while rapidly adapting neurones could function to signal initial contact with food or the opposing teeth.     

Effect of transcutaneous electrical nerve stimulation on pain perception threshold and pain tolerance level of human teeth subjected to electrical stimulation

Abstract The effect of low current, sub-sensation transcutaneous electrical nerve stimulation on pain threshold and pain tolerance level of human teeth subjected to stimulation with an electrical pulp tester was studied. Electrodes were attached to the patients via a patch between the thumb and first finger and a damp cotton roll in the vestibule over the apex of the tooth to be tested. No significant differences between the values for the baseline, experimental and placebo pain perception thresholds were found. Nor were significant differences found between the average experimental and placebo values concerning pain tolerance level. However, in 1 individual the pain tolerance level was not reached at the highest level of stimulation from the electrical pulp tester.     

Effect of resveratrol on the hyperexcitability of nociceptive neurons associated with ectopic hyperalgesia induced by experimental tooth movement

The present study investigated whether, under in vivo conditions, systemic administration of resveratrol attenuates the experimental tooth movement-induced ectopic hyperalgesia associated with hyperexcitability of nociceptive trigeminal spinal nucleus caudalis (SpVc) neurons. The threshold of escape from mechanical stimulation applied to the ipsilateral whisker pad in rats exposed to experimental tooth movement was significantly lower than seen in control rats from day 1 to 3 following movement of the right maxillary first molar tooth. The lowered mechanical threshold in the rats exposed to experimental tooth movement had almost returned to the level of sham-treated naïve rats at day 3 following administration of resveratrol. The mean mechanical threshold of nociceptive SpVc neurons was significantly lower after experimental tooth movement but the lower threshold could be reversed by administration of resveratrol. The higher discharge frequency of nociceptive SpVc neurons for noxious mechanical stimuli observed in rats exposed to experimental tooth movement was statistically significantly lower following resveratrol administration. These results suggest that resveratrol attenuates experimental tooth movement-induced mechanical ectopic hyperalgesia via suppression of peripheral and/or central sensitization. These findings support the idea that resveratrol, a complementary alternative medicine, is a potential therapeutic agent for the prevention of experimental tooth movement-induced ectopic hyperalgesia.     

An electrophysiological study of the central connections of primary afferent nerve fibres from the dental pulp in the cat

Supramaximal electrical stimuli were delivered to the pulps of the canine teeth through bipolar electrodes and recordings were made of the field potentials and single unit activity evoked in the trigeminal sensory nucleus. While some activity was elicited in the subnucleus caudalis, much more was encountered in the main sensory nucleus and subnucleus oralis. The significance of this distribution with respect to pain is discussed.     

Deciduous incisor teeth of the mouse (Mus musculus)

A vestigial tooth, apparently a deciduous incisor, was found in the maxilla of all mice of 4 strains (AKR, Swiss-Webster, Hale-Stoner and an albino strain of unknown origin) ranging in age from $\text{12}\text{1}\text{2}\text{-}\text{day}\text{-}\text{embryos}$ to 15 days after birth. This tooth reaches its maximum development in $\text{15}\text{1}\text{2}\text{-}\text{day}\text{-}\text{foetuses}$, and consists of a cup-like shell of dentine with a maximum diameter of 40–60 μm, with some small, irregular masses of dentine between the odontoblastic cells. No enamel organ is formed and no enamel. The odontoblasts degenerate at the time of birth, and the internal dentine disappears. The tooth does not erupt, but sinks deeply into the connective tissue. It disappears, presumably by resorption, about the fifteenth day after birth.A mandibular counterpart is occasionally formed in the Swiss-Webster and the mice of unknown origin, but was never seen in the other strains and never develops to the extent of the maxillary deciduous incisor. There is clear differentiation of the adjacent epithelial cells, forming a single layer of columnar epithelial cells in which the nuclei migrate as in ameloblasts of normally developing teeth. The mesenchymal cells are irregular in shape, and only rarely is dentine formation seen.This deciduous tooth resembles, in many ways, some very primitive teeth seen in Ornithorhynchus and some reptiles.     

Mouth-opening Exercises Produce a Decrease in Pain Perception in Patients with Disk Displacement with Reduction

This study was intended to determine whether mouth-opening exercise reduces pain sensitivity in remote regions as well as in the trigeminal region. Seven female subjects with disk displacement with reduction were asked to perform a three-minute repetitive mouth opening and closing exercise (exercise A) and a three-minute continuous mouth opening exercise (exercise B) on two separate days. Sensory/nociceptive perception thresholds were measured at the point over the right masseter and the skin overlying the volar aspect of the right forearm immediately after exercises A and B, and were compared to data in which no exercise was performed (baseline). Significant elevation in the heat-induced pain threshold was seen as a result of both exercises in the cervical region and in the trigeminal region. Also, a significant elevation in the cold-induced pain threshold was seen after exercise B in the cervical region. Further, there was a tendency toward a higher warm sensation threshold after exercise A in the cervical region. These results indicate that mouth opening training produces non-segmental analgesic effects mediated by C fiber and Adelta fiber.     

The response of caries-free, unfilled teeth to electrical excitation: a comparison of two new pulp testers

Summary. A total of 845 sound teeth in 54 patients were stimulated by one of two new electric pulp testers to obtain pain perception threshold values. The age range of the patients was 18 to 27 years and only incisor, canine and premolar teeth were studied. Both testers were found to produce threshold responses over a wide range of control settings in groups of similar teeth. From the results it is clear that there is no consistent threshold excitation value for teeth with intact-uninflamed pulps.     

Effect of transcutaneous electrical nerve stimulation on pain perception threshold of human teeth: a double-blind, placebo-controlled study

In this double-blind, placebo-controlled study, we studied the effect of three different transcutaneous electrical nerve stimulation (TENS) devices with extra- and intraoral electrodes on the pain perception thresholds of 234 unrestored, caries-free human teeth of 66 healthy individuals subjected to stimulation with an electric pulp tester. A placebo control collective of 64 healthy subjects received no electrical stimulation, since an inactive TENS device was used. In all tooth types tested (maxillary and mandibular incisors and premolars), the use of the active TENS devices resulted in an increase of 16.3–32.5% versus baseline in the pain perception threshold. The differences between active TENS and baseline were statistically significant for both TENS devices using extraoral electrodes (P<0.05). No statistically significant differences were found between the different devices tested (P>0.05). In the placebo collective, the increase in the pain perception threshold ranged between 6.4% and 10.3% versus baseline. There were no significant differences between placebo TENS and baseline on the one hand and between placebo TENS and the active TENS devices on the other hand (P>0.05). The findings suggest that, as an alternative to local anesthetics, TENS seems not to be useful in the case of painful dental interventions, since it offered only minor advantages over a placebo. Received: 23 November 1999 / Accepted: 21 December 1999     

Associations between Pain Severity,Clinical Findings,and Endodontic Disease: A Cross-Sectional Study

IntroductionThorough pain assessment and thermal and mechanical testing are the primary diagnostic tools used to assess the status of pulp and periapical tissues in teeth with potential endodontic pathology. This study evaluated predictors of acute odontogenic pain to better understand the relationship between endodontic pain, clinical testing, endodontic disease, and diagnoses.MethodsParticipants (N = 228) presenting with acute odontogenic pain underwent standardized clinical testing and reported their pain intensity. Univariate and multiple regression analyses were performed to evaluate the predictors of acute endodontic pain. Chi-square tests with Bonferroni adjustments were conducted to measure the frequency of endodontic diagnostic test findings and clinical observations in patients with different pulpal diagnoses.ResultsA negative response to cold stimulation on the causative tooth and percussion hypersensitivity on the healthy adjacent tooth were the strongest predictors of higher levels of acute endodontic pain. Percussion hypersensitivity on the healthy adjacent tooth was present in a quarter of the cohort and was reported with equal frequency in teeth diagnosed with irreversible pulpitis, necrotic pulp, and previously initiated/treated teeth. Although painful percussion on the causative tooth was more frequently reported in teeth diagnosed with necrotic pulp, painful palpation was more frequently reported on teeth diagnosed with previously initiated/treated teeth.ConclusionsPercussion hypersensitivity on the healthy adjacent tooth may reveal a lowered pain threshold and heightened pain sensitization. It is also possible that the 2 commonly performed mechanical sensory tests, percussion and palpation hypersensitivity, may detect different aspects of endodontic pathophysiology and pain processing.     

正畸牙齿移动刺激信息传导通路的动物实验研究

研究丘脑腹后内侧核（ＶＰＭ）是否接受来自三叉神经脊核尾业核传入的牙齿移动性刺激信息,从而探讨牙齿动引起的伤害性刺激信息在中枢神经系统内的感觉传导通路。方法：用微量注射器将２％荧光金ＦＧ）注入大鼠ＶＰＭ４－６ｄ后,进行对侧的实验性牙齿移动２ｈ,用ＦＯＳ蛋白免疫化方法观察Ｖｃ内神经元对ｃ－ｆｏｓ的表达以及是否存在ＦＧ与ＦＯＳ双重阳性的神经元。结果ＦＯＳ阳性神经元密集分布于同侧Ｖｃ浅层,呈带状,背外侧居     

Tooth injury increases expression of the cold sensitive TRP channel TRPA1 in trigeminal neurons

Objective

Transient receptor potential (TRP) channels, a family of structurally related proteins have been implicated in the sensation of pain and hyperalgesia caused by exogenous and endogenous agonists, as well as touch, pH, and temperature. The objective of this study was to determine the effects of tooth injury on the expression of the cold sensitive channel TRPA1, in the trigeminal ganglion, the primary source of sensory and nociceptive innervation of teeth.

Design

We analyzed TRPA1 expression in a rodent model of tooth injury, by Western blot analyses of proteins extracted from trigeminal ganglia.

Results

We found that TRPA1 was selectively increased in trigeminal ganglia innervating injured teeth when compared to TRPA1 expression in trigeminal ganglia innervating healthy teeth.

Conclusions

Our results provide the first evidence of increased expression of a cold-sensitive TRP channel in trigeminal ganglia after pulp exposure, and are consistent with the possibility that increased expression and function of TRPA1 in trigeminal neurons contributes to hyperalgesia and allodynia following tooth injury.     

Cortical activation resulting from painless vibrotactile dental stimulation measured by functional magnetic resonance imaging (FMRI)

There have been few investigations on hemodynamic responses in the human cortex resulting from dental stimulation. Identification of cortical areas involved in stimulus perception may offer new targets for pain treatment. This initial study aimed at establishing a cortical map of dental representation, based on non-invasive fMRI measurements. Five right-handed subjects were studied. Eight maxillary and 8 mandibular teeth were stimulated after the vibratory perception threshold was determined for each tooth. Suprathreshold stimulation was repeated thrice per session, in a total of three sessions performed on three consecutive days. Statistical inference on cluster level identified increased blood-oxygen-level-dependent signal during vibratory dental stimulation, primarily in the insular cortex bilaterally and in the supplementary motor cortex. No significant brain activation was observed in the somatosensory cortex with this stimulation protocol. These results agree with previous findings obtained from invasive direct electrical cortical stimulation of the human insula.     

Pulp responses to precise thermal stimuli in dentin-sensitive teeth

The purpose of this study was to determine whether pulpal responses to cold temperatures applied to enamel, using a method that precisely controls the intensity of the cold stimulus or measures the response time, could distinguish dentin-sensitive teeth from nonsensitive teeth. Eighteen human subjects were stimulated with cold temperatures decreasing in 5 degree C intervals (and with tetrafluoroethane) on exposed root and enamel of a dentin-sensitive tooth and enamel of a contralateral nonsensitive tooth. Pain threshold, intensity of pain, time to pain onset, and duration of pain at baseline, 4 h, 8 h, and 1 week were measured. Responses to enamel stimulation of sensitive teeth compared with the nonsensitive teeth usually were highly correlated and not significantly different. The exception was a longer duration of pain in the dentin-sensitive teeth (4.62 +/- 0.47 s) compared with nonsensitive teeth (2.92 +/- 0.49 s; p = 0.016) after enamel stimulation with tetrafluoroethane. Longitudinal studies are necessary to determine whether these slight increases in pain duration indicate an increased probability of pulpal degeneration or need for dentin protection.