Osmotic stimulation of human dentine and the distribution of dental pain thresholds

Evaluation and Comparison for the Efficacy of 810 nm Diode Laser, Nano Carbonate Apatite and Their Combination Over Dentinal Tubules Occlusion: An In Vitro Scanning Electron Microscopic Study

BACKGROUND

Dentin hypersensitivity (DH) involves sensitive symptoms, because of exposure of the dentinal tubules. Various materials have been utilized to occlude dentinal tubules for the treatment of DH. Here is a comparative evaluation of nano-carbonate apatite (n-CAP), diode laser, and their combination over the occlusion of dentinal tubules.

MATERIALS AND METHOD

Ten intact first premolars were used in this study, out of which 40 dentin disk specimens were obtained by hard tissue microtomy. Four study groups were formulated out of which one was the control group and the remaining three were test groups. Scanning electron microscopy (SEM) was done to evaluate the diameter of the dentinal tubules in each group.

RESULTS

On examining data, it was observed that the mean diameter of dentinal tubules in four study groups of control, laser, n-CAP, and n-CAP + laser was found to be 3.40, 2.00, 0.46, and 0.02 respectively. This shows the significant reduction in the diameter of dentinal tubules in the test groups when compared with the control group.

CONCLUSION

Among all the measures used to see for a reduction in the diameter of dentinal tubules, the combination group was found to be most occluding, though each of the groups also had a significant reduction in the diameter of dentinal tubules. The present study showed that combination therapy offers a promising means of treating DH in a clinical setting when compared with the treatment of DH n-CAP containing dentifrice or laser irradiation alone.

TRPM8 Mediates Hyperosmotic Stimuli-Induced Nociception in Dental Afferents

Hyperosmolar sweet foods onto exposed tooth dentin evoke sudden and intense dental pain, called dentin hypersensitivity. However, it remains unclear how hyperosmolar stimuli excite dental primary afferent (DPA) neurons and thereby lead to dentin hypersensitivity. This study elucidated whether TRPM8, which is well known as a cold temperature- or menthol-activated receptor, additionally mediates nociception in response to hyperosmolar stimuli in adult mouse DPA neurons, which are identified by a fluorescent retrograde tracer: DiI. Single-cell reverse transcription polymerase chain reaction revealed that TRPM8 was expressed in subsets of DPA neurons and that TRPM8 was highly colocalized with TRPV1 and Piezo2. Immunohistochemical analysis also confirmed TRPM8 expression in DPA neurons. By using Fura-2-based calcium imaging, application of hyperosmolar sucrose solutions elicited calcium transients in subsets of the trigeminal ganglion neurons, which was significantly abolished by a selective TRPM8 antagonist: N-(3-Aminopropyl)-2-[(3-methylphenyl)methoxy]-N-(2-thienylmethyl)benzamide (AMTB) hydrochloride. When we further examined changes of c-fos expression (a neuronal activation marker) in the spinal trigeminal nucleus after hyperosmolar stimulation onto exposed tooth dentin, c-fos mRNA and protein expression were increased and were also significantly reduced by AMTB, especially in the spinal trigeminal interpolaris-caudalis transition zone (Vi/Vc). Taken together, our results provide strong evidence that TRPM8 expressed in DPA neurons might mediate dental pain as a hyperosmosensor in adult mice.

Neurochemical properties of dental primary afferent neurons

The long belief that dental primary afferent (DPA) neurons are entirely composed of nociceptive neurons has been challenged by several anatomical and functional investigations. In order to characterize non-nociceptivepopulation among DPA neurons, retrograde transport fluorescent dye was placed in upper molars of rats and immunohistochemical detection of peripherin and neurofilament 200 in the labeled trigeminal ganglia was performed. As the results, majority ofDPA neurons were peripherin-expressing small-sized neurons, showing characteristic ofnociceptive C-fibers. However, 25.7% of DPA were stained with antibody against neurofilament 200, indicating significant portion of DPA neurons are related to large myelinated Aβ fibers. There were a small number of neurons thatexpressed both peripherin and neurofilament 200, suggestive of Aδ fibers. The possible transition of neurochemical properties by neuronal injury induced by retrograde labeling technique was ruled out by detection of minimal expression of neuronal injury marker, ATF-3. These results suggest that in addition to the large population of C-fiber-related nociceptive neurons, a subset of DPA neurons is myelinated large neurons, which is related to low-threshold mechanosensitive Aβ fibers. We suggest that these Aβ fiber-related neurons might play a role as mechanotransducers of fluid movement within dentinal tubules.

Prostaglandin E2 enhances bradykinin-evoked iCGRP release in bovine dental pulp

Mediators produced during inflammation are responsible for hyperalgesia and expression of neurotransmitters and receptors in the nervous system. The production of bradykinin (BK) and the prostaglandins (PGs) may regulate initiation of pain. This study tested the hypothesis that BK and prostaglandin E2 (PGE2) have a positive interaction in evoking neurosecretion of immunoreactive calcitonin gene-related peptide (iCGRP). Bovine dental pulp was prepared and stimulated by the superfusion method with BK alone and in combination with PGE2. Kinin receptor antagonists to bradykinin-evoked release of iCGRP were also tested. Also tested was the hypothesis that dental pulp contains either the B1 or B2 or both BK receptors. Results showed that PGE2 enhanced BK-evoked iCGRP release by more than 50%. Western immunoblots revealed detectable B2 receptor protein with no detectable B1 receptor protein. We conclude that BK evokes iCGRP release from bovine dental pulp which is enhanced by a positive interaction with PGE2. Neurosecretion is evoked from isolated terminals of dental pulp fibers via the bradykinin B2 receptor-dependent mechanism.

Isolation and culture of rat sensory neurons having distinct sensory modalities

We have recently published papers in which sensory neurons that innervate either the tooth pulp or masseter muscle spindles were labelled in vivo and later identified and studied in primary tissue culture (Taddese et al., 1995; Cook et al., 1997). Here, we provide detailed descriptions of cell labelling and tissue culture methods that we used. The purpose of the preparations is to compare nociceptive and non-nociceptive sensory neurons in vitro. The spindles in mastication muscles are the only muscle afferents whose cell bodies reside in the mesencephalic nucleus (MeN5) of the fifth nerve (Corbin and Harrison, J Neurophysiol, 1940; Cody et al., J Physiol, 1972). Thus, labelling neurons projecting to the masseter muscle and dissecting the MeN5 isolates muscle spindle afferents. Pain is the only conscious sensation elicited by physiological stimulus of tooth pulp (Anderson and Matthews, 1967; Edwall and Olgart, 1977; Ahlquist et al., 1984; Narhi et al., 1994); there may be unconscious sensations that arise from the pulp, but these have never been demonstrated. Thus, tooth pulp afferents represent at least a highly enriched, and possibly a pure, population of nociceptors. In broad outline, the methods of labelling and tissue culture are standard, but we have honed many details in order to obtain practical yields.

HIPERSENSIBILIDADE DENTINÁRIA: DIAGNÓSTICO E TRATAMENTO

A hipersensibilidade é a sensibilidade exagerada da dentina quando exposta ao meio bucal, que se torna permeável à ação de estímulos agressivos. O diagnóstico é feito através da anamnese e da inspeção clínica minuciosa. O tratamento pode ser feito pelo profissional ou pelo próprio paciente sob orientação, dependendo do caso. Ela ocorre comumente no final da terceira década, sendo ligeiramente mais freqüente nas mulheres do que nos homens.

Distinct ATP receptors on pain-sensing and stretch-sensing neurons

The initial pain from tissue damage may result from the release of cytoplasmic components that act upon nociceptors, the sensors for pain. ATP was proposed to fill this role because it elicits pain when applied intradermally and may be the active compound in cytoplasmic fractions that cause pain. Moreover, ATP opens ligand-gated ion channels (P2X receptors) in sensory neurons and only sensory neurons express messenger RNA for the P2X3 receptor. To test whether ATP contributes to nociception, we developed a tissue culture system that allows comparison of nociceptive (tooth-pulp afferent) and non-nociceptive (muscle-stretch receptor) rat sensory neurons. Low concentrations of ATP evoked action potentials and large inward currents in both types of neuron. Nociceptors had currents that were similar to those of heterologously expressed channels containing P2X3 subunits, and had P2X3 immunoreactivity in their sensory endings and cell bodies. Stretch receptors had currents that differed from those of P2X3 channels, and had no P2X3 immunoreactivity. These results support the theory that P2X3 receptors mediate a form of nociception, but also suggest non-nociceptive roles for ATP in sensory neurons.

Encoding of the subjective intensity of sharp dental pain

This paper is a review and a discussion of our own pain research over the last decade. It is of a methodological and theoretical character and deals with preparation technique, choice of electrodes, control experiments involving pulpotomy and reliability tests of psychophysical methods for pain measurements, and the neuronal population encoding of sharp dental pain. The electrophysiological recording technique selectively picks up electrical activity induced in pulpal A-delta nerve fibers. The sensation of pain was quantified by means of an intermodal matching technique, finger span (PAS), in combination with sensory verbal descriptors covering a range from very, very weak to maximal pain. When a cold stimulus, ethyl chloride, was applied on the tooth surface a close agreement was demonstrated between intradental A-delta nerve activity (INA) and the sensation magnitude of pain (PAS) with respect to curve amplitude and time course. The high covariation of the neural and perceptual response measures indicated a good internal validity and confirmed also the basic soundness and the applicability of the procedures employed. For the purpose of further analyzing the functional relation of INA to PAS we studied specifically the effect of cold stimuli of different intensity on the integrated nerve response. Only sharp, shooting pain was accepted as a sensorial, perceptual correlate of the intradental A-delta nerve activity. Since an increase in amplitude was generally accompanied by an increase in duration of the responses, the fundamental question was raised how to best describe and characterize the neural and perceptual responses so that they most adequately reflect the information processing of the intensive aspect of sharp dental pain.(ABSTRACT TRUNCATED AT 250 WORDS)

The neurophysiological basis and the role of inflammatory reactions in dentine hypersensitivity

Recent studies indicate that intradental A-type nerve fibres are responsible for the sensitivity of dentine and are activated by fluid movements in dentinal tubules (hydrodynamic mechanism). The patency of the tubules affects dentine sensitivity to a great extent. Both A delta- and A beta-type nerve fibres respond to dentinal (hydrodynamic) stimulation in a similar way. Only a few studies have been made on the regional sensitivity of dentine or the receptive areas of intradental nerve fibres. The results indicate that the fibres innervating different parts of coronal dentine are equally sensitive to dentinal stimulation but those in the cervical area may be less responsive. Inflammation in the pulp can considerably alter dentine sensitivity. In dog teeth with chronically exposed dentine, nerve responses to hydrodynamic stimulation were reduced although other functional changes indicated nerve sensitization. This may be due to spontaneously occurring changes in the exposed dentine that block the tubules. In acute experiments on cat and dog teeth with open dentinal tubules, certain inflammatory mediators increase the sensitivity of the responding nerve fibres. It seems that intradental C-fibres do not respond to hydrodynamic stimulation of dentine. They are polymodal and activated when external stimuli reach the pulp proper. They could perhaps mediate the dull pain connected with pulpitis. However, they might also have an important modifying effect on dentine sensitivity because they can release neuropeptides, which function in the inflammatory reactions.

Morphological features of dentine and pulp related to dentine sensitivity

This review considers those structural features of the pulp and dentine relevant to an understanding of dentine sensitivity. It does not discuss innervation, or microvasculature, which are covered in other contributions. The sensitivity of dentine is directly related to the size and patency of the dentinal tubules. Tubular occlusion by peritubular dentine deposition or the formation of other intratubular material would reduce the flow of fluid and diffusion of molecules through dentine. Irregular (reparative) secondary dentine would, because its tubules are not continuous with those of primary dentine, be expected to reduce permeability and fluid flow and decrease sensitivity. Regular secondary dentine would have little or no effect other than by increasing diffusion distances. The odontoblast layer is of limited permeability and could restrict the access of materials diffusing through the dentinal tubules to pulpal axons. Odontoblasts are not involved in the sensory process as special sensory receptors but may, by modifying the local ionic environment, alter the threshold of intradentinal nerves.

Distribution of zinc ions from orthophosphate cements at the cement-tooth interface in fixed dental prosthesis

Cast metal prostheses are considered to be one of the best ways to restore the morphology and function of missing teeth. However, the success of fixed prosthesis therapy is mainly to be judged on its durability. It is therefore important to know how cemented prostheses behave in the mouth. A protocol for an in vivo study was set up to analyse the influence of time on the release of zinc ions from zinc orthophosphate cements used at the tooth-prosthesis interface.

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.

Selectivity of lingual nerve fibers to chemical stimuli

The cell bodies of the lingual branch of the trigeminal nerve were localized in the trigeminal ganglion using extracellular recordings together with horseradish peroxidase labeling from the tongue. Individual lingual nerve fibers were characterized with regard to their conduction velocities, receptive fields, and response to thermal, mechanical, and chemical stimuli. Fibers were classified as C, A delta, A beta, cold, and warm. The chemical stimuli included NaCl, KCl, NH4Cl, CaCl2, menthol, nicotine, hexanol, and capsaicin. With increasing salt concentration the latency of the response decreased and the activity increased. The responses elicited by salts (to 2.5 M), but not nonpolar stimuli such as menthol, were reversibly inhibited by 3.5 mM of the tight junction blocker, LaCl3. These data suggest that salts diffuse into stratified squamous epithelia through tight junctions in the stratum corneum and stratum granulosum, whereupon they enter the extracellular space. 11 C fibers were identified and 5 were characterized as polymodal nociceptors. All of the C fibers were activated by one or more of the salts NaCl, KCl, or NH4Cl. Three C fibers were activated by nicotine (1 mM), but none were affected by CaCl2 (1 M), menthol (1 mM), or hexanol (50 mM). However, not all C fibers or even the subpopulation of polymodals were activated by the same salts or by nicotine. Thus, it appears that C fibers display differential responsiveness to chemical stimuli. A delta fibers also showed differential sensitivity to chemicals. Of the 35 characterized A delta mechanoreceptors, 8 responded to NaCl, 9 to KCl, 9 to NH4Cl, 0 to CaCl2, menthol, or hexanol, and 2 to nicotine. 8 of 9 of the cold fibers (characterized as A delta's) responded to menthol, none responded to nicotine, 8 of 16 were inhibited by hexanol, 9 of 19 responded to 2.5 M NH4Cl, 5 of 19 responded to 2.5 M KCl, and 1 of 19 responded to 2.5 M NaCl. In summary, lingual nerve fibers exhibit responsiveness to chemicals introduced onto the tongue. The differential responses of these fibers are potentially capable of transmitting information regarding the quality and quantity of chemical stimuli from the tongue to the central nervous system.

Dentine hypersensitivity: the measurement in vitro of streaming potentials with fluid flow across dentine and hydroxyapatite

Stimulus transmission across dentine, in conditions such as dentine hypersensitivity, is considered to occur via a hydrodynamic mechanism. This fluid flow in dentine may then induce a mechanoreceptor response in pulpal nerves. However, when fluid flows through a porous structure electrical potentials are also generated. The aim of this study was to develop a reproducible model system to measure streaming potential across dentine and hydroxyapatite and determine the influence of pressure. Using an acrylic cell, with silver electrodes, streaming potentials were recorded across dimensionally standardized dentine and hydroxyapatite specimens, over a pressure range of 1-6 atmospheres. Streaming potentials were found to be directly proportional to pressure and dependent on the electrical conductivity of the saline used in the cell. The results confirm the limited existing data on streaming potentials across dentine and indicate that at these low pressures excitation of pulpal nerves would not occur. However, if, as may be the case, stimuli applied to dentine create very high pressures, the resultant potentials generated could indeed evoke a neural response. The model system is worthy of further use to study this phenomenon and the factors which may influence it.

Decreasing intradental nerve activity in the cat with potassium and divalent cations

Nerve activity was recorded from deep dentinal cavities in the canine teeth to assess the possible influence of potassium and divalent cations in decreasing this activity in hypersensitive teeth. The decreased activity after the topical application of 0.756 mol/l KCl to the cavity was primarily due to the cation. KCl elicited a biphasic response from intradental nerves, an initial transient excitatory response followed by a prolonged inhibitory period. During the inhibitory period 3 mol/l NaCl, an effective excitatory stimulus, failed to evoke intradental nerve activity. However, with time the response to 3 mol/l NaCl eventually recovered to its previous control level. Close, intra-arterial injection of KCl showed the same biphasic response and time-course of intradental nerve activity as with topical application. Therefore, whether KCl was applied topically or injected its effectiveness in altering the nerve activity was similar. Pretreatment of the dentinal cavity with CaCl2, MgCl2 or SrCl2 greatly reduced the response of intradental nerves to KCl. Therefore these divalent cations seem to have a depressant action on pulpal nerve fibres. The mechanism of action of KCl seems to be an alteration of K+ concentration immediately surrounding the intradental nerves which presumably depolarizes the nerve fibre membrane and elicits an initial firing of action potentials. Because of the persisting high levels of extracellular potassium a sustained depolarized state occurs that results in an inactivation of the action potential. Divalent cations appear to depress the excitability of the nerve cell membrane without altering membrane potential. Such ionic agents could be used in conjunction with KCl as a possible treatment for hypersensitive teeth.

Acute and chronic reactions of dental sensory nerve fibers to cavities and desiccation in rat molars

We have studied the effects of air drying of exposed, acid etched dentin on the sensory innervation of rat molars. In the acute series of experiments, trigeminal nerve fibers were labeled by axonal transport of radioactive protein prior to the dentin exposure and desiccation, the anesthetized rats were fixed by aldehyde perfusion 10 min later, and the teeth were prepared for autoradiography. The results confirmed the hydrodynamic theory by showing outward movement of labeled nerve material in response to dentinal drilling and desiccation. It also showed that some odontoblasts could be separated from the dentinal nerve fibers. In the chronic series, teeth were injured 25 h, 5-7 days, or 21 days prior to fixation and nerves were labeled during the last 24 hours; the surviving vital nerve fibers were evident because of their axonal transport of the radioactive label. In that series, sensory nerve fibers were found to have been lost from areas with newly-formed reparative dentin, or from dentinal tubules that had lost their odontoblasts. In the teeth injured 25 h, 5-7 days, or 21 days earlier, an abnormal nonneuronal labeling occurred 0.2-0.3 mm into injured dentin. Our results are discussed in relation to the hydrodynamic theory, nerve-odontoblast interactions, differences between shallow and deep cavity injuries, altered nerve location in response to pulpal or dentinal injury, and characteristics of the pulp-dentin border.

Effects of ionic and non-ionic solutions on intradental nerve activity in the cat

Intradental nerve activity (INA) was recorded from cat canine teeth to determine whether solutions altering intradental nerve sensitivity were strongly correlated to the osmotic concentration of the solution or via a more direct action on intradental nerve excitability. The effects of various ionic and non-ionic solutions were tested in both deep and shallow dentinal cavities. With saline in the deep dentinal cavity a very low firing rate or resting nerve spike (action potentials) activity was recorded. When 3 M NaCl was placed in the same or similar cavity a high discharge rate of nerve spike activity was obtained. This 3 M NaCl elicited activity was utilized to determine the inhibitory or excitatory effects of various test agents on the intradental nerves. The following agents: MgCl2, MgSO4, and CaCl2 were inhibitory to the INA response elicited by 3 M NaCl. Non-ionic solutions of urea or sucrose failed to evoke INA and they were also minimally effective in altering 3 M NaCl elicited activity. Shallow cavities were utilized to maintain the tubular structure of dentin relatively intact. In the shallow cavity preparations hypertonic sucrose or urea failed to evoke INA, even when dentin was etched with 50% citric acid for 2 min. The results suggest that the osmolarity of these solutions is a poor indicator of the INA.

The response of dog intradental nerves to hypertonic solutions of CaCl2 and NaCl, and other stimuli, applied to exposed dentine

Responses of single nerve units from the canine and incisor pulps of anaesthetized beagles to CaCl2 (3.5 M, 4.9 M and saturated) and NaCl (2.5 M and 4.0 M) were recorded. The sensitivity of these nerve units to drilling and probing of dentine, and to drying with air blasts, was also studied. Twenty-one out of 22 units responded immediately, either with a few spikes or, sometimes, with a 2-5 s train of impulses, to hypertonic CaCl2 when applied to superficial dentine. Deep in dentine, CaCl2 induced immediately responses in 15 out of 21 units. There were responses to hypertonic NaCl in 15 out of 19 units, but only when applied deep in dentine. This firing had a latency of 15-300 s (mean 94 s) and continued until the solution was washed away. Units sensitive to CaCl2 also responded to drilling, probing and drying. When applied to the exposed pulp, CaCl2 never induced nerve activity, but hypertonic NaCl induced responses in all units tested (n = 19); the latencies were 0-300 s (mean 34 s). The mechanism of nerve activation in response to hypertonic CaCl2 is probably hydrodynamic, and common to several other stimuli as in drilling, probing and air drying. Responses to hypertonic NaCl may have been induced by a direct excitatory effect of Na+-ions on the nerve endings or axons in the pulp-dentine border.

The effect of dentinal stimulation on pulp nerve function and pulp morphology in the dog

The effect of dentinal stimulation on pulpal nerve responses and pulp morphology has been studied in the dog. Canine tooth (n = 25) dentin was stimulated by drilling, probing, and air-blasting for from two to five hours. Acid-etching was used to open dentinal tubules. All test teeth showed disruption of the odontoblast layer and its separation from the predentin; also, dislocation of odontoblast nuclei into dentinal tubules was found in most cases. Single-fiber (n = 14, conduction velocity = 24.3 +/- 7.4 (SD) m/s) recordings of the responses of canine tooth pulpal nerves to dentinal stimulation were made in ten of the stimulated teeth. No changes in the sensitivity of the nerves to dentinal stimulation could be detected. It is concluded that pulpal nerve function and morphological changes of the pulp are not clearly correlated. The condition of the dentin surface seems to be the important factor.

Effects of opioids and opioid peptide on the release of substance P-like material induced by tooth pulp stimulation in the trigeminal nucleus caudalis of the rabbit

The superficial layer in subnucleus caudalis of the brain-stem trigeminal sensory nuclear complex (SpVc) in the rabbit was perfused with artificial cerebrospinal fluid using a push-pull perfusion cannula system. Immunoreactive substance P (iSP) and [Met5]enkephalin (iME) released into the perfusates following electrical stimulation of the lower incisor pulp were measured. An increase in the release of iSP and iME lasting for 1 h or more was observed following electrical stimulation with 40 V. The increase in iSP release depended on the intensity of stimulation. Systemic morphine (10 mg/kg i.v.) completely inhibited the stimulus-evoked iSP release and this inhibition was antagonized by pretreatment with naloxone (5 mg/kg i.v.). The stimulus-evoked iSP release was also inhibited by local application of morphine (10(-6) M) or the opioid peptide [D-Ala2,Met5]enkephalinamide (10(-4) M). However, the local application of naloxone (5 X 10(-7) M) only partially antagonized the inhibitory effects of locally applied morphine and the opioid peptide. These results suggest that there is a functional interaction between SP and enkephalin systems in the superficial layer of SpVc for the regulation of dental pain transmission.

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.

Responses of feline intradental sensory nerves to hyperosmotic stimulation of dentin

The responses of intradental sensory nerves to hyperosmotic solutions of sucrose (4M) and calcium chloride (6M) applied in dentinal cavities were studied in anesthetized cats. Nerve impulse activity was recorded from canine teeth after application of the test solutions in shallow and deep cavities. In shallow cavities (thickness of remaining dentin, about 500 micron) sucrose and calcium chloride caused an immediate and transient excitation of the nerves in 3 out of 15 teeth and in 8 of 12 teeth, respectively. Treatment of such cavities with lactic acid (1M) increased the frequency of nerve responses to 100%. When applied in deep cavities (thickness of remaining dentin, 0-50 micron), sucrose induced a burst of impulses followed by continuous nerve activity, whereas calcium chloride decreased the nerve excitability. Our results support the hypothesis that solutions exerting an effective osmotic pressure excite the intradental nerves by an indirect mechanism when applied on the dentin and that they exert a direct effect on nerves when in contact with the pulp. In addition, it is suggested that acids produced in carious dentin may facilitate the induction of pain by hyperosmotic stimuli.

Responses of intradental nerve fibres to stimulation of dentine and pulp

In the present work responses of intradental nerve fibres to stimuli that induce fluid flow in dentinal tubules as well as to direct mechanical irritation of the exposed pulp were studied on 9 young adult beagle dogs. Under pentobarbitone anesthesia 31 single functional intradental fibre units were dissected from the mandibular nerve. Stimuli were applied to the lower left canine tooth. Exposed dentine surface was irritated by scraping, air blasts and dry absorbent paper and the pulp mechanically with a von Frey hair. Ten fibre units responded to stimulation of dentine. Six of them were also tested with mechanical irritation of the pulp and were all responsive. Fifteen of twenty fibres responded to mechanical stimulation of the pulp. The mechanosensitive nerve fibres were all A-type according to conduction velocities (mean 25.6 +/- 8.1 (SD) m/s). It is concluded that there exist mechanosensitive intradental A-nerve fibres in the dog which are activated by stimuli that induce fluid flow in dentinal tubules. Nerve fibres of this type could be responsible for dentine sensitivity in man. Consequently, the present study gives support to the hydrodynamic hypothesis of dentine sensitivity. Moreover, mechanosensitive nerve fibres could also be responsible for the pain symptoms of pulpal inflammation, because pulpitis may also create suitable circumstances for their activation.

Cultural, clinical and physiological aspects of pain: a review

A review is given of selected cultural, clinical and physiological issues pertaining to the human experience of pain. Special attention is devoted to the modern gate control theory of pain as it applies to the sensory pathways of the fifth cranial nerve; that is, facial pains and some of their associated symptoms and signs.

Enamel structure in some therapsids and mesozoic mammals

The distribution of enamel tubules, the shapes and arrangements of prisms, and the orientation of crystals in ground sections from several therapsids and mesozoic mammals have been investigated by conventional and polarizing microscopy. Along each of three separate phylogenetic lines which evolved occluding teeth, there was a progressive increase in the numbers of enamel tubules. In the investigation, the arcade-shaped prisms typical of recent mammals were first seen in material from the Cretaceous period. All the enamels investigated from the Triassic contained columns of crystals, which were deduced as hexagonal. The inner ends of the crystals within each column deviated towards the center of the column. It is concluded that the existence of an interprismatic region provides the most important distinction between prismatic enamels and the hexagonal columns of crystals in the Triassic material.

Features peculiar to the trigeminal innervation

The aspects of trigemina! sensory structure and function which are uniquely different from spinal systems are reviewed in this paper.

In the periphery, several unique arrangements of sensory receptors are seen, and appear to have unique sensory functions. The receptors in the cornea, the nasal mucosa, and the tooth pulp are morphologically unspecialized and are associated with “protopathic” sensory experiences. The important sensory functions of the mammalian vibrissae are also discussed, as well as their relationship to the anatomically distinctive cortical “barrels”.

Aspects of trigeminal proprioception are also of interest. The absence of spindles in some muscles and the unique central organization of trigeminal proprioceptive afférents in the jaw and extraocular muscles are of functional significance in the motor function of the jaw and the eye.

Trigeminal afférents are also involved in several complex autonomie reflexes. Characteristic changes in cardiovascular and respiratory function are elicited by various patterns of trigeminal sensory stimulation. These reflexes include the diving reflex, the oculo-cardiac reflex, naso-cardiorespira-tory reflexes, and the trigeminal depressor response. The clinical significance of these reflexes is discussed.

Several coordinated behavioral responses including suckling are also elicited from trigeminal afférents. The evidence implicating trigeminal afférents in eating and drinking behavior is presented.

Dentin permeability: determinants of hydraulic conductance

A technique is described which permits measurements of the ease with which fluid permeates dentin. This value, the hydraulic conductance of dentin, increased as surface area increases and/or as dentin thickness decreases. It increased 32-fold when dentin was acid etched due to removal of surface debris occluding the tubules.

The sensory mechanism in human dentin as revealed by evaporation and mechanical removal of dentin

Dentinal pain in connection with mechanical stimulation i.e. probing, chiseling and initial drilling may be due to removal of fluid from the dentinal tubules. Loss of fluid due to "normal" evaporation from exposed dentin may produce an outward flow in the dentinal tubules rapid enough to cause pain and within a few minutes odontoblast aspiration.

Sensation evoked by bipolar intrapulpal stimulation in man

Bipolar intrapulpal stimulation was applied to human teeth using the same procedure as in animal experiments. The effects of variation of stimulus parameters on the quality of sensation were studied. A prepain sensation exists which cannot be explained by diffusion of the stimulus to periodontal tissues. When the intensity of stimulation is increased, the prepain sensation is gradually replaced by a pinprick sensation. With long, high intensity stimulation, an acute long lasting very painful sensation appears. To evoke a pinprick sensation the best stimulation seems to be a 50 msec train (0.5 msec, 300 Hz, 0.5 mA). Longer train duration and a higher intensity of current are necessary to evoke a long lasting, acute very painful sensation. Since the exclusively Adelta and C nerve fiber content of the dental pulp is well documented and since it is possible to avoid current diffusion outside the dental pulp cavity, the tooth pulp implantation seems to be a good technic for studying pain, as long as the investigator uses adequate stimulation.

Responses of intradental nerves to electrical and thermal stimulation of teeth in dogs

1. Experiments were carried out to investigate the mechanism whereby thermal stimul excite nerves to produce pain from teeth. 2. Recordings have been made from single fibres dissected from the inferior dental nerve in dogs during thermal stimulation of the lower canine tooth. 3. In preliminary experiments, no units were found with thresholds close to the thresholds for pain in man (45 and 27 degrees C) and subsequently test stimuli of 55 degrees C, applied for up to 15 sec, and 0-5 degrees C were used. 4. Of 117 fibres tested, forty-three responded to cooling but not to heating and nine responded to heating but not to cooling. 5. By applying thermal stimuli direct to the saphenous nerve in cats, it was shown that these responses might have been due to direct excitation of nerves and not to stimulation of specialized receptors. 6. Some units responded to electrical stimulation of the tooth pulp with a latency which decreased abruptly at a critical intensity as the stimulus was increased above threshold. Evidence was obtained which suggested that this was due to branching of the fibres.

Responses of intradental nerves to chemical and osmotic stimulation of dentine in the cat

Recordings have been made of the neural responses evoked by stimulation of dentine with solutions of NaCl, NH4Cl and dextrose. Stimulation of the outer dentine produced no response. From the inner dentine, a smaller number of impulses were recorded with solutions of NaCl than with corresponding concentrations of NH4Cl, but a much larger number than with solutions of dextrose. The discharge evoked by a solution increased in mean frequency and decreased in latency as the thickness of dentine was reduced. The responses suggest that the receptors were in the innermost dentine or the pulp and that they were excited by changes in extracellular fluid composition rather than by osmotic effects. The properties of the receptors appear to be different from those involved in pain from dentine in man.

Evidence on the origin of impulses recorded from dentine in the cat

1. Recordings have been made from dentine at the tip of the canine teeth of cats using a large Ag/AgCl electrode.2. All-or-none action potentials with complex shapes were recorded when single nerve fibres from the dental pulp were stimulated electrically outside the tooth.3. The wave forms of these action potentials changed when the stimulation rate was increased from 1/sec to 10/sec, when the temperature of the tooth surface was changed between 17 and 42 degrees C, when the thickness of the dentine was reduced, and when local anaesthetic was applied to the dentine. Only a small, monophasic, positive potential remained after transection of the pulp in the crown of the tooth.4. The latency of the action potentials was not affected by these same procedures.5. It is suggested that each wave form represented a compound action potential produced by impulses invading the main branches and terminals of a single nerve in the pulp. Some of the terminals may have penetrated the innermost layers of the dentine.6. There was no spontaneous discharge from pulpal nerves.7. A discharge of impulses was recorded from dentine when 2.5 mol/l. NaCl was applied beneath the electrode at the tip of the tooth. By recording simultaneously from dentine and from single fibres from the tooth pulp, it was shown that impulses recorded from dentine were associated with propagated nerve action potentials.