Effect of Three Different Injection Sites on the Success of Anterior Middle Superior Alveolar Nerve Block with 3% Mepivacaine: A Randomized Controlled Trial

AIM

Anterior middle superior alveolar (AMSA) nerve block injection targets the anterior superior alveolar nerve and the middle superior alveolar nerve branches of the infraorbital nerve through nutrient canals. Therefore, the central incisor to the second premolar teeth of one quadrant can be anesthetized. The aim of the present study was to evaluate the efficacy of AMSA nerve block injection with 3% mepivacaine solution at three different injection sites.

MATERIALS AND METHODS

In a double-blind crossover study, 47 volunteers participated and three AMSA nerve block injections of 3% mepivacaine solution without epinephrine were administered at the anterior, posterior, and the most common injection sites with a 1-week interval between injections. Anesthesia of the central incisor to the second premolar of the injected side was evaluated by using an electric pulp tester. The success of the injection was considered as lack of response to two consecutive 80 readings. The generalized estimating equation analytic tests were administered (α = 0.05).

RESULTS

The success rate of the AMSA nerve block injection ranged from 27.5-47.5% for the most common injection site and 22.5-42.5% for both the anterior and posterior injection sites.

CONCLUSION

Changing the injection site did not result in statistically significant improvements (p > 0.05).

CLINICAL SIGNIFICANCE

Changing the injection site anteropos-teriorly did not influence the success rate of the AMSA nerve block injection.

A prospective, randomized comparison of the anesthetic efficacy of the greater palatine and high tuberosity second division nerve blocks

INTRODUCTION

Few clinical studies have evaluated the efficacy of the maxillary second division nerve block. The purpose of this prospective, randomized study was to compare the anesthetic efficacy of the greater palatine second division nerve block and the high tuberosity second division nerve block technique by using 3.6 mL of 2% lidocaine with 1:100,000 epinephrine.

METHODS

Forty subjects randomly received greater palatine nerve blocks and high tuberosity nerve blocks of 3.6 mL of 2% lidocaine with 1:100,000 epinephrine at 2 separate appointments spaced at least 1 week apart. The anterior, premolar, and molar teeth were pulp tested in 4-minute cycles for a total of 60 minutes.

RESULTS AND CONCLUSIONS

Both techniques resulted in a high success rate of pulpal anesthesia (95%-100%) for first and second molars. Around 70%-80% of the second premolars were anesthetized with both techniques. Both techniques were ineffective for profound pulpal anesthesia of the anterior teeth and first premolars.

Forces applied by anterior and posterior teeth and roles of periodontal afferents during hold-and-split tasks in human subjects

Hold-and-split tasks were performed by 20 subjects (12 females and 8 males) using the right central incisors, canines, 2nd premolars, and 1st molars, respectively. Half a peanut was positioned on a transducer-equipped plate and the subject was instructed to hold the plate with the peanut between two antagonistic teeth, and not using more force than necessary. After ca. 3 s the subject was instructed to split the peanut in a natural manner. Each session consisted of a series of three in which the subject performed the hold-and-split task five times for each tooth. Thus, in total, data were obtained from 60 trials for each subject. The magnitude of the forces and the force rates used to split the peanut increased distally along the dental arch. However, the duration of the split phase was similar for the various teeth examined. During anesthesia of the periodontal ligament (four subjects), no significant changes were seen in the split phase. The forces used to hold the peanut between the teeth also increased distally along the dental arch: 0.60 N for the incisor, 0.77 N for the canine, 1.15 N for the 2nd premolar, and 1.74 N for the 1st molar. The difference in hold forces for the various teeth can be explained by the different sensitivity characteristics of the periodontal afferents innervating anterior and posterior teeth. During periodontal anesthesia, the magnitude and variability of the hold forces increased for all types of teeth, thus supporting the suggestion that periodontal afferent information is used in the regulation of the level of forces used to hold and manipulate morsels between the teeth.

Efficacy of anterior and middle superior alveolar (AMSA) anesthesia using a new injection system: the Wand

OBJECTIVE

This study examined the effect of anterior and middle superior alveolar (AMSA) field block of maxillary nerves using a new local anesthetic system--the Wand.

METHOD AND MATERIALS

Twenty healthy volunteers aged 23 to 44 years were used in the study. Either side of the maxillary teeth was randomly selected for AMSA injection; the other side was left as a control. For each side, 1.8 mL of 2% lidocaine solution with 1/80,000 epinephrine was injected by the Wand on a point that bisects the maxillary first and second premolars and is midway between the crest of the free gingival margin and the midpalatine suture. Pain rating score (PRS) and visual analogue scale (VAS) were applied for measurement of puncture, insertion, and injection pain. Electric pulp stimulation was given to each maxillary tooth every 10 minutes for 1 hour after the injection in order to find out the specific tooth on which AMSA injection was effective.

RESULTS

During needle insertion, 14 out of 20 subjects answered moderate pain and VAS showed 27.3 mm (mean). During injection, 11 of 20 revealed no pain and the mean of VAS was 14.5 mm. No one claimed severe pain by PRS. Electric pulp stimulation indicated that lateral incisors, canines, and first and second premolars were more anesthetized than central incisors and first molars.

CONCLUSION

AMSA injection using the Wand method seems to avoid severe injection pain and seems to be very effective for pulpal anesthesia at lateral incisors, canines, and premolars.

Biological interpretation of the correlation of emergence times of permanent teeth

The eruption mechanism is not fully understood. It is known that the dental follicle is essential and that experimentally provoked denervation influence the process of eruption. Accordingly, the purpose of this study was to elucidate the eruption pattern in a human population and relate this pattern to the pattern of jaw innervation. The eruption pattern was evaluated from the correlation between the emergence times of different teeth in the permanent dentition based on longitudinal data from a large national registry (12,642 boys and 12,095 girls). Correlations coefficients were generally high (>0.5) and higher between teeth within the same tooth groups (i.e. incisors, canines and premolars, and molars) than between teeth from different tooth groups. It was shown that the correlation in emergence of teeth closely followed the pattern of innervation of the jaws. Thus the study supported the hypothesis concerning a possible association between eruption and innervation.

Blood flow changes in human dental pulps when capsaicin is applied to the adjacent gingival mucosa

OBJECTIVE

The purpose of this study was to determine whether changes occur in pulpal blood flow when capsaicin is applied to the adjacent gingival or alveolar mucosa in human beings.

STUDY DESIGN

Laser Doppler flowmetry was used to measure changes in pulpal blood flow (PBF) after applying capsaicin to adjacent gingival mucosa in 20 human volunteers. The procedure was repeated on 10 subjects after administration of an ipsilateral inferior alveolar nerve block and on the other 10 subjects after application of topical anesthetic to their adjacent gingival and alveolar mucosa.

RESULTS

PBF increased in 16 subjects and did not change in 4 subjects after capsaicin application. Ipsilateral inferior alveolar nerve block did not alter this effect. Pretreatment with topical lidocaine resulted in no change or decreased PBF in 8 subjects and increased PBF in 2 subjects.

CONCLUSION

Changes occur in the PBF of the mandibular canine teeth of some humans when capsaicin is applied to the adjacent gingival or alveolar mucosa.

Morbidity of harvesting of chin grafts: a prospective study

In a prospective study, 20 patients who underwent harvesting of chin grafts as outpatients, were followed up for 12 months (3 further patients with incomplete follow-up data were excluded from the study). Preoperatively and 7 days, 1, 3, 6 and 12 months postoperatively, follow-up data were assessed. Evaluation of the superficial sensory function of the inferior alveolar nerve was determined by the Pointed-Blunt Test and the Two-Point-Discrimination Test. Sensory disturbances were objectively assessed by testing thermal sensitivity with the "Pain and Thermal Sensitivity" Test (PATH Test). In addition, evaluation of the pulp sensitivity of teeth 35-45 was carried out by cold vitality testing. One week postoperatively, 8 patients were affected by superficial sensory impairment. 8 nerve territories showed hypoaesthetic reactions and 5 showed hyperaesthetic reactions. After 12 months, two patients still suffered from hypoaesthesia of one side of the chin. There was a statistically significant sensitivity impairment of the chin for all patients comparing the preoperative data of the Two-Point-Discrimination Test (left/right median: 8.17/8.17 mm, interquartile range (IQR) 1.00/2.00 mm) with the first postoperative measurement (left/right median 9.00/8.33 mm, IQR 1.67/2.66 mm). Comparing the latter to the last postoperative measurement there was significant tendency for regeneration of a nerve function (left/right median 8.00/7.84 mm, IQR 0.66/2.00 mm). In the PATH Test all hypoaesthetic areas could be identified by a reduction of thermal sensitivity. After the first postoperative examination 21.6% (n=38/176) of the examined teeth had lost their pulp sensitivity. After 12 postoperative months 11.4% (n=20/176) still did not react sensitively. Many of these were canines (n=8/20). Comparing the preoperative to the first postoperative examination, there was a significant reduction of pulp sensitivity. However, statistically significant recovery until the last postoperative follow-up could not be detected. The assessed data show that patients have to be informed extensively about disturbances of the inferior alveolar nerve function lasting longer than 12 months. Moreover, the loss of pulp sensitivity is a very frequent event which has always to be taken into account. Considering the high rate of complications with harvesting of chin grafts, more prospective trials should be done to find out whether there are other donor sites for autogenous bone which put less strain on patients.

Using AMSA and P-ASA nerve blocks for esthetic restorative dentistry

Esthetic restorative dentistry procedures represent an increasing segment of the services provided by the general practitioner. One important assessment criterion for a successful anterior esthetic restoration is how well it harmonizes with the lips to create a pleasing smile line. Unfortunately, traditional local anesthetic techniques interfere with this assessment by distorting the lips and face during anesthesia. The anterior, middle superior alveolar block and the palatal approach anterior superior alveolar block injections represent two recently defined techniques to anesthetize maxillary teeth effectively without numbness of the face, lips, or muscles of expression. Although safety and efficacy studies are only beginning to emerge, these injections appear to be useful additions to local anesthetic techniques, especially when anterior esthetic restorative procedures are being performed.

Anesthetic efficacy of unilateral and bilateral inferior alveolar nerve blocks to determine cross innervation in anterior teeth

OBJECTIVE

The purpose of this prospective randomized study was to measure the degree of anesthesia obtained with unilateral and bilateral inferior alveolar nerve blocks to determine whether cross innervation occurs in anterior teeth.

STUDY DESIGN

Through use of a repeated-measures design, 38 subjects randomly received unilateral or bilateral inferior alveolar nerve blocks at two separate appointments. Each inferior alveolar nerve block used 3.6 mL of 2% lidocaine with 1:100,000 epinephrine. Mandibular anterior teeth were blindly pulp-tested at 4-minute cycles for 60 minutes' postinjection. No response from the subject to the maximum output (80 reading) of the pulp tester was used as the criterion for pulpal anesthesia. Anesthesia was considered successful when 2 consecutive 80 readings were obtained.

RESULTS

One hundred percent of the subjects had lip numbness with each of the inferior alveolar nerve block techniques. Anesthetic success rates of the unilateral inferior alveolar nerve block were 39% for the central incisor, 50% for the lateral incisor, and 68% for the canine. For the bilateral inferior alveolar nerve blocks, success rates were 66% for the central incisor, 74% for the lateral incisor, and 76% for the canine. The bilateral inferior alveolar nerve block success rates were significantly (P <.05) higher for the central and lateral incisors when compared with the success rates of the unilateral inferior alveolar nerve block.

CONCLUSIONS

Cross innervation does seem to occur in mandibular central and lateral incisors. However, the success rates in these teeth with bilateral inferior alveolar nerve blocks were below 75%. The failure of the inferior alveolar nerve blocks to anesthetize the anterior teeth was the overriding reason for failure. Clinically, bilateral inferior alveolar nerve blocks to provide profound pulpal anesthesia in mandibular anterior teeth are not recommended on the basis of the results of this study.

Response of feline intradental nerve fibers to tooth cutting by Er:YAG laser

BACKGROUND AND OBJECTIVE

The aim of this study was to investigate the response of intradental A- and C-fibers during tooth cutting by Er:YAG laser.

STUDY DESIGN/MATERIALS AND METHODS

Bipolar electrical stimulation was applied to the cat's canine to identify functional single nerve fibers of the inferior alveolar nerve. The tip of the canine tooth was cut in 0.5-mm steps until the pulp was exposed. Teeth were alternately cut by using Er:YAG laser (50 mJ, 5 pps) and micromotor under water cooling. The nerve response recorded from the single nerve fibers during laser cutting was compared with that during micromotor cutting.

RESULTS

All 26 A-fibers responded to laser cutting with high frequency of nerve firings. The nerve firing rate was significantly higher during laser cutting compared with that during micromotor cutting of superficial dentin (Chi(2) test, P < 0.05) but was not significantly different at deep dentin (P > or = 0. 05). Nine of 11 C-fibers responded to laser cutting when the deep dentin was cut. Among those nine nerve fibers, three also showed a low frequency response to laser cutting of the superficial dentin.

CONCLUSION

During the tooth cutting, Er:YAG laser was more effective in activating intradental A-fibers compared with micromotor and also caused the activation of intradental C-fibers.

Pulsed Nd:YAG laser irradiation of the tooth pulp in the cat: I. Effect of spot lasing

BACKGROUND AND OBJECTIVE

The purpose of the present study was to evaluate physiologically pulpal nerve responses and to elucidate histopathologically the pulp tissue reactions to "spot irradiation" with a pulsed Nd:YAG laser.

STUDY DESIGN/MATERIALS AND METHODS

Antidromic compound action potentials and the pulpal blood flow (PBF) were recorded from the canine tooth of a sodium pentobarbitone-anesthetized cat. The laser irradiation-induced pulp tissue changes were histologically investigated.

RESULTS

The coronal antidromic compound action potentials disappeared in all the teeth tested during lasing, and the time needed to erase them was significantly shortened with increases in lasing power (P < 0.05). The radicular PBF increased when spot irradiation was performed, and the coronal PBF also temporarily increased with low-powered lasing. Histologic investigation revealed that spot irradiation with the laser produced severe damage in the pulp tissue in a dose-dependent manner.

CONCLUSION

The present study suggests that spot irradiation with a pulsed Nd:YAG laser risks producing nerve injury and irreversible tissue damage in the pulp with lasing for the purpose of desensitizing hypersensitive dentin.

Effect of HeNe and pulsed Nd:YAG laser irradiation on intradental nerve responses to mechanical stimulation of dentine

BACKGROUND AND OBJECTIVE

Our study aimed to determine how lasing affected intradental nerve responses to dentine stimulation. Study Design/Materials and Methods Intradental nerve activity was recorded from canine teeth of anaesthetised ferrets. Dentine exposed at the tip of the tooth was stimulated with a glass probe. After determining baseline responses to mechanical stimulation, dentine was lased using a pulsed Nd:YAG laser at 60-150mJ/pulse and 10-30 pulses/sec (total power = 0.3-3.0 W).

RESULTS

The HeNe aiming beam alone and Nd:YAG laser at 0.3 W (+ HeNe) had no effect on intradental nerve responses to dentine stimulation. Lasing at 0.6-1. 5 W could either enhance or suppress intradental nerve responses. Lasing at more than or equal to 2.0 W or repeated lasing at lower intensities depressed intradental nerve responses. Lasing often induced intradental nerve firing.

CONCLUSION

HeNe lasing had no effect on intradental nerve excitability. The Nd:YAG laser could depress intradental nerve responses to dentine stimulation.

Increased blood flow and nerve firing in the cat canine tooth in response to stimulation of the second premolar pulp

Mustard oil or mechanical stimulation was applied to maxillary second premolar tooth pulps and pulpal blood flow and or intradental nerve activity in the ipsilateral canine tooth were recorded in the cat. Mustard oil application to the second premolar pulp significantly increased blood flow in the canine tooth pulp to 162.0+/-65.8% (n = 16) of the prestimulation flow compared to control data obtained with application of mineral oil (107.0+/-5.1%, n = 6) (Mann-Whitney U-test, p = 0.0009). Sectioning of the infraorbital nerve and its branches on the experimental side (n = 4) did not affect this increase in pulpal blood flow. The paraperiosteal injection of 2% lidocaine (1.0 ml) without vasoconstrictor significantly inhibited the increase in canine pulpal blood flow induced by mustard oil application to the second premolar pulp (109.8+/-6.8% of the prestimulation level, n = 7) (Mann-Whitney U-test, p = 0.0013). Sporadic firing or sometimes bursts of action potentials in the canine pulp nerves were recorded during and/or after the mustard oil application to the second premolar pulp in three of 16 cases. Four single pulp nerve units firing in synchrony with the mechanical stimulation of the second premolar pulp were recorded in two of eight canines, which substantiated the existence of branched afferents innervating both teeth. These findings suggest that stimulation of the second premolar pulp may induce axon reflex-related vasodilation and intradental nerve firing in the canine pulp via branched afferent fibres innervating both the second premolar and canine teeth.

Re-innervation in the canine periodontal ligament of replanted teeth using an antibody to protein gene product 9.5: an immunohistochemical study

The re-innervation process in the periodontal ligament of replanted canine teeth was examined by immunohistochemistry for protein gene product 9.5 (PGP 9.5), a general marker for neurons, and by electron microscopy. Within 1 week of replantation, the periodontal fibers had regenerated, filling the narrow spaces between the alveolar bone and the root surface around the cervical and apical regions. Near the root apex, however, no PGP 9.5-immunopositive nerve fibers were found in the regenerated periodontal ligament except for those in the alveolar half of the ligament. At 2 weeks after replantation, many nerve fibers positive for PGP 9.5 had ascended the periodontal ligament from the thick nerve bundles located near the root apex. Fine nerve endings showing complicated ramification were also present in the apical region. By 3 or 4 weeks after replantation, the vascular network was regenerated and principal periodontal fibers were re-established throughout the entire length of the periodontal ligament. The extensively ramified PGP 9.5-immunopositive structures had increased in thickness and density and showed characteristic tree-like profiles by 3 weeks. Electron microscopy confirmed that most of these structures were Ruffini-like endings, and demonstrated that such nerve terminals were almost regenerated by 4 weeks post-replantation. These results indicated that, in the periodontal ligament of replanted canine teeth, the regeneration of the nerve fibers including mechanosensory receptors first showed signs of regeneration by 2 weeks following tooth replantation and proceeded rapidly thereafter. Regeneration of the periodontal ligament including fiber architecture as well as vascular and neural elements was almost complete by 4 weeks after replantation.

Nerve fibers immunoreactive to calcitonin gene-related peptide, substance P, neuropeptide Y, and dopamine beta-hydroxylase in innervated and denervated oral tissues in ferrets

The effect of sensory and sympathetic denervation on the localization and distribution of nerve fibers immunoreactive (IR) to calcitonin gene-related peptide (CGRP), substance P (SP), neuropeptide Y (NPY), and dopamine beta-hydroxylase (DBH) was studied in the dental pulp, periodontal ligament (PDL), and gingiva in ferrets. Unilateral axotomy was performed by resection of the inferior alveolar nerve (IAN) 10 days before the experiment (Group 1); sympathectomy, by unilateral removal of the cervical ganglion 5 days before the experiments (Group 2). Immunohistochemistry was performed on free-floating sections by the avidin-biotin-peroxidase technique. A considerably higher density of sensory fibers IR to CGRP and SP was found in the dental pulp than in PDL and gingiva. The majority of pulpal fibers were located in the walls of blood vessels. A subodontoblastic network of fibers IR to CGRP and SP was lacking in incisors and canines and was found only in the coronal pulp in premolars and molars. Sympathetic fibers were sparsely distributed in the pulp, and they were mainly confined to large vessels running centrally in the root pulp as well as the larger vessels in apical PDL and alveolar bone. Gingiva was well supplied with CGRP- and SP-IR nerves, and some NPY and DBH fibers were located in association with larger vessels. Round cell-like structures within the basal part of the epithelium were CGRP-IR. Axotomy induced a complete loss of CGRP- and SP-IR fibers in the anterior part of the jaws, whereas sympathectomy caused a reduction, but not a total loss, of NPY- and DBH-IR nerves. It is concluded that, except for some distributional differences, the oral tissues in the ferret have an abundant sensory innervation similar to that found in other species.

Primary somatosensory cortical neuronal activity during monkey's detection of perceived change in tooth-pulp stimulus intensity

To elucidate the functional properties of primary somatosensory cortical neurons for the perception of tooth-pulp sensation, neuronal activity was recorded from the primary somatosensory cortex (SI) in awake behaving monkeys. Monkeys were trained to detect changes in tooth-pulp stimulus intensity applied to the upper canine or incisor tooth pulp. Stimulus intensities applied to the tooth pulp were multiples of the threshold intensity for the jaw opening reflex (1.0 T) elicited by tooth-pulp stimulation. When monkeys pressed a button, baseline electrical pulses (V1: 0.5 T, 1.0 T, 2.0 T, or 3.0 T) were applied to the tooth pulp. After 4-8 s, a V2 stimulus (0.3 T, 0.5 T, 1.0 T, or 2.0 T) was added to V1. Percent escapes at V1 stimulus intensity of 0.5 T and 1.0 T were approximately 10%, 22% at 2.0 T, and 40% at 3.0 T (total of 1,997 trials). A total of 862 single units were recorded from the SI. Thirty-seven SI neurons responded to electrical stimulation of the tooth pulp (tooth-pulp-driven neurons; TPNs), 139 SI neurons responded to tactile stimulation of the lateral face area, 90 to upper lip and 99 to lower lip, 44 to tongue and 102 to periodontal membrane, whereas 351 SI neurons were not responsive to tactile stimulation of the orofacial regions. Thirty of 37 TPNs were recorded long enough to test with V1 stimuli ranging from 0.5 T to 3.0 T. Eleven of 30 TPNs linearly increased their firing frequency following increases in stimulus intensity (encoding TPNs), whereas 19 did not (nonencoding TPNs). Mean first spike latency of encoding TPNs was 24.8 +/- 1.7 ms (n = 11), that of nonencoding TPNs was 23.6 +/- 1.5 ms (n = 19), and that of unclassified TPNs was 24.7 +/- 3.7 ms (n = 7). TPNs were distributed in the areas 1-2, 3a, and 3b within the oral projection area and the transition zone between the face and oral projection areas of the SI. All of them received inputs from the intraoral structures, facial skin, or both. The firing frequency of eight encoding and nonencoding TPNs was correlated with detection latency at stimulus intensities of 0.5 and 1.0 T. On the other hand, when the baseline stimulus was increased to 2.0 T and 3.0 T, the discharge of most TPNs did not increase in firing frequency with the reduction in detection latency. These results indicate that the discharge rates of some SI TPNs are correlated with detection latency at near-noxious threshold and noxious stimulus intensities. These findings suggest that some TPNs are involved in the sensory-discriminative aspect of tooth-pulp sensation in the near-pain threshold and pain ranges.

Quantitative and somatotopic mapping of neurones in the trigeminal mesencephalic nucleus and ganglion innervating teeth in monkey and baboon

Neurones of the trigeminal mesencephalic nucleus (Mes V) and ganglion innervating the periodontium of incisor, canine and molar teeth in 10 monkeys and 10 baboons were counted and mapped using the horseradish peroxidase (Hrp), retrograde axonal transport method. Periodontal afferent neurones of all these teeth were well represented in the Mes V, although the incisors had a significantly higher number of labelled neurones than the canines or molars. The primary cell bodies of the periodontal afferents were located mainly in the caudal part of the ipsilateral Mes V from the level of the inferior colliculus to the floor of the fourth ventricle in the pons. The caudal periodontal Mes V neurones may be favourably located to make collateral connections with the trigeminal motor nucleus for jaw reflexes. Incisors and canines had a large and predominantly ipsilateral representation of Hrp-labelled neurones in the ganglion. In contrast, molar representation in the ganglion was sparse and all labelled neurones supplied ipsilateral teeth. The maxillary and mandibular teeth had a somatotopic distribution within the respective maxillary (middle) and mandibular (posterolateral) compartments of the trigeminal ganglion. It is suggested that the anterior teeth with greater connections to the Mes V and the ganglion may impart greater sensory perception and be involved in jaw reflexes to ensure a good occlusal relation during mastication, while the afferent connections of the molars may initiate complex jaw reflexes during the occlusal phase of mastication.

Pulp interstitial fluid pressure and blood flow after denervation and electrical tooth stimulation in the ferret

The effects of sensory and sympathetic denervation on simultaneously measured interstitial fluid pressure and blood flow in the canine pulp before, during and after electrical tooth stimulation were investigated in 25 ferrets. The micropuncture technique was used to measure interstitial fluid pressure and laser-Doppler flowmetry was used to record pulpal blood flow. Animals with an intact innervation (group 1) served as controls. Sensory denervation was by axotomy of the left inferior alveolar nerve 10 days before the experiment (group 2) and sympathectomy by removal of the left cervical ganglion 5 days before the experiments (group 3). The study was designed to verify whether denervation affected basal pulp blood flow and interstitial fluid pressures during control conditions and/or after tooth stimulation. During control conditions the interstitial fluid pressure averaged 1.32 +/- 0.07 kPa in group 1, whereas the mean was only 0.51 +/- 0.13 kPa in the axotomized animals (group 2). The difference was highly significant, indicating decreased blood or interstitial fluid volume in the pulp after inferior alveolar nerve axotomy. In the sympathectomized group neither the interstitial fluid pressure nor the pulp blood flow was significantly different from those of group 1. Electrical tooth stimulation caused an almost simultaneous increase in interstitial fluid pressure and pulp blood flow in groups 1 and 3, whereas stimulation did not significantly change either variable in the axotomized animals (group 2). It is concluded that a resting nervous vasodilator tone of sensory origin exists in the ferret dental pulp, and that the sensory nerves are responsible for the increased interstitial fluid pressure and pulp blood flow during tooth stimulation.

Direct evidence of parasympathetic vasodilatation in cat periodontal ligament

Sympathetic regulation of periodontal ligament blood flow (PLBF) is well-attested; however, vasodilator responses mediated by parasympathetic nerve fibers have yet to be conclusively demonstrated in the periodontal ligament (PL). The present study was designed to determine whether parasympathetic vasodilator mechanisms do or do not exist in the cat PL. In our cats, the cervical sympathetic trunks were sectioned bilaterally prior to any stimulation in order to eliminate sympathetic effects on the vascular beds under study. Dynamic changes in PLBF, with mandibular lip blood flow (LBF) recorded for comparison, were investigated in cat mandibular canine teeth using laser Doppler flowmetry. The peripheral cut ends of the facial and glossopharyngeal nerve roots, which have been reported to contain parasympathetic nerve fibers to the oral tissues, were electrically stimulated intracranially. Such stimulation caused blood flow to increase in the ipsilateral PL and lip, without an increase in systemic blood pressure. These vasodilator responses in the PL and lip were sensitive to ganglion blockade (with hexamethonium), indicating vasodilation via activation of parasympathetic vasodilator fibers. In contrast, although intracranial stimulation of the trigeminal nerve root also induced increases in both PLBF and LBF, these were unaffected by hexamethonium, but reduced by tripelennamine, indicating antidromic vasodilatation via the trigeminal sensory nerve. These results suggest that parasympathetic vasodilator mechanisms do exist in feline PL.

Insights into maxillary and mandibular growth for a better practice

By understanding the growth mechanisms of the maxilla and mandible and using four key concepts of Neuro-Occlusal Rehabilitation, better treatment can be rendered to the patients with malocclusions and chewing disturbances. This paper relates these concepts with experimental data.

Response characteristics of periodontal mechanoreceptors to mechanical stimulation of canine and incisor teeth in the cat

The alveolar bone that overlies the labial aspect of the root of the right lower canine tooth was pared down until paper thin. Thirty-five periodontal mechanosensitive (PM) units sensitive to stimulation of the canine and incisor and to punctate stimulation through the thinned bone of the periodontal ligament of the canine were recorded from the inferior alveolar nerve rostral to the masseter muscle. The units showed a sustained and directionally selective response to pressure applied to the teeth. The optimal directions of stimulation for each tooth in the receptive field were parallel and oriented linguolabially. When the canine was stimulated mechanically in the optimal stimulus direction, the interspike intervals of the responses were relatively regular in most PM units (91%). The conditioning and test stimuli were applied to the adjacent canine and third incisor. The conditioning stimulus (0.10 N) was given to one of these teeth in the optimal stimulus direction. The test stimulus (0.02 N or 0.05 N) was applied to the adjacent tooth in the opposite direction in order to examine the effect of mechanical spreading of the conditioning stimulus on the adjacent tooth. In most PM units, the spike discharges evoked by the conditioning stimulus given to the incisor were stopped by the test stimulus given to the canine. When the given stimuli were reversed, the firings evoked by the conditioning stimulus were slightly depressed by the test stimulus. After removing the spot-like PM receptor site(s) in the paper-thin area of bone, all units but one did not respond to stimulation. These results provide evidence that neurones with multiple-tooth receptive fields and regular spike-interval responses recorded from the inferior alveolar nerve come from the mechanical spreading effect of the stimulation of one tooth on an adjacent tooth through the trans-septal fibre system and that neurones with irregular-interval responses are due to the ramification of PM fibres peripherally.

A quantitative study on the myelinated fiber innervation of the periodontal ligament of cat canine teeth

The periodontal ligament is richly innervated with mechanosensitive afferent nerve fibers, and the location of the mechanoreceptive terminals within the ligament is of functional significance. In this study, we have obtained quantitative information on mechanoreceptor distribution in the lower canine teeth of the cat. Using light microscopy, we quantified the number of myelinated axons in the periodontal ligament at 1 mm, 3 mm, and 5 mm from the tooth root apex. Grouped axons and axons which were isolated in the cemental half of the ligament (and therefore putative mechanoreceptors) were identified. The mean total number of axons was 1290 (n = 20) at 1 mm from the apex, 1290 at 3 mm, and 814 at 5 mm. The distribution of axons around the tooth root circumference was found to be non-uniform. Near the root apex, the highest numbers of grouped axons were located distally and mesially, and in the middle region of the root, the highest numbers were found mesially. The highest numbers of isolated axons at the apical levels were located distally, and in the mid-root region, mesially. At all levels, the lingual region was the most sparsely innervated by both groups. There was a positive correlation between the number of grouped axons and the width of the ligament in the same region, but this correlation was much weaker for isolated axons, suggesting that their distribution does not result only from the volume of tissue. Variations in the number of axons and, to a lesser extent, the dimensions of the periodontal ligament were considerable.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical detection of S-100 protein in human deciduous dental pulp

S-100 protein was investigated in the temporary dental pulp by the immunoperoxidase technique, using the avidin-biotin complex method. The results showed that there was a strong positive reaction in the Schwann cells ensheathing axons and nerve fibers. The other cells within the pulp were immuno-negative. S-100 protein and the results of the present study are discussed.

The distribution and morphological characteristics of axons innervating the periodontal ligament of reimplanted teeth in cats

Twelve weeks after reimplanting lower canines the distribution and characteristics of myelinated and non-myelinated axons within the periodontal ligament were investigated by light and electron microscopy. The ligament was examined at 2-mm intervals along the length of the root of four reimplanted teeth and of the contralateral canines, which served as controls. In each case the periodontal ligament was reinnervated. In two of the teeth, which showed extensive apical resorption, the innervation was much less than in control teeth. In two teeth showing minimal or no apical resorption the degree of innervation at the most apical level did not differ significantly from controls.

Task-related behaviour of motor units in the human temporalis muscle

Muscle activity patterns in some complex human jaw muscles appear to be task sensitive. However, it is presently uncertain how changes in motor task affect motor unit (MU) behaviour in the human temporalis muscle. In this study, activity was recorded from 40 MUs in the anterior region of the muscle. The lowest sustainable firing frequency (LSFF) was reached by slow increases and decreases in firing rate, then firing was maintained at the lowest possible rate without significant pauses. An array of consecutive interspike intervals (ISI) were sampled digitally and used to measure the LSFF for each task associated with the MU. In a controlled paradigm, MU reflex inhibition was measured during the performance of different tasks. Single electrical pulses of non-noxious intensity were delivered to the gingiva near the maxillary canine tooth. During continuous MU firing at a controlled firing frequency of 10 Hz, series of pulses were delivered with increasing delays, after preselected spikes. The MUs fired continuously during the performance of 1-4 postural and tooth-contact tasks. There were significant differences in LSFFs between tasks in those MUs associated with multiple tasks. In the reflex study, all MUs were inhibited, but the magnitude of the inhibition was highly task dependent. Thus, both LSFF and reflex inhibition of temporalis MUs appear to vary with the motor task and are sensitive to the position of the jaw and the direction and location of tooth contact along the tooth row. This behaviour most likely reflects task-related changes in output from orofacial and muscle afferents.

Properties of periodontal mechanoreceptors supplying the cat's lower canine at short and long periods after reinnervation

1. The properties of periodontal mechanoreceptors innervating the lower canine teeth of cats have been determined 6 weeks and 1 year after sectioning the inferior alveolar nerve. Recordings were made from single fibres dissected from the nerve central to the injury site, whilst forces were applied at right angles to the long axis of the tooth. 2. The range of directions over which each mechanosensitive unit responded (are of sensitivity) was established. Forces were then applied in the direction of maximum sensitivity and the maximum discharge frequency, dynamic index, adaptation rate, and the force threshold at three rates of force application (0.25, 2 and 20 N s-1) were determined. 3. Data from 115 units characterized 6 weeks after nerve section revealed a significantly reduced mean dynamic index and raised mean force threshold to forces applied at 2 and 0.25 N s-1, when compared with the controls. These units were, however, more sensitive than those examined 12 weeks after nerve section in a previous study (Loescher & Robinson, 1989b). 4. Data from 158 units characterized 1 year after nerve section revealed a significantly narrower mean are of sensitivity, reduced mean maximum discharge frequency, lower mean dynamic index and raised mean threshold to forces applied at 0.25 N s-1, when compared with the controls. 5. Bone overlying the roots of the reinnervated teeth was removed in order to localize receptors in the underlying periodontal ligament. Forty-six units were localized 6 weeks after nerve section and thirty-eight 1 year after nerve section. The mean conduction velocity of these units was significantly reduced both 6 weeks and 1 year after nerve section compared to the controls. One unit was found which branched to innervate receptors at two locations within the ligament, and one unit was found which branched to innervate a receptor in the ligament and another in the overlying skin. 6. The higher level of sensitivity of receptors when first reinnervated than at later stages is attributed to their immaturity. This immaturity may also contribute to the paraesthesia which is experienced by patients at a corresponding stage in recovery from nerve injury. The persistent reduction in sensitivity of units 1 year after nerve injury suggests that changes occur which have a permanent effect on their properties.

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.

Central representation of dental structures in the kitten, including projections to the mesencephalic trigeminal nucleus

Horseradish peroxidase (HRP) was injected into either a single maxillary or a single mandibular primary (deciduous) cuspid tooth of 8- to 10-week-old kittens. The large apex of the primary cuspid allowed for some leakage of the HRP from the pulpal chamber to the periodontal ligament (PDL). Thus, the injection procedure resulted in the application of HRP to the PDL as well as to the pulpal tissues. The transganglionic transport of HRP resulted in discrete terminal fields within the spinal trigeminal nucleus (STN) and the main sensory nucleus (MSN). These projections were clearly somatotopically organized within the STN, but less so within MSN. Within pars oralis (PO) and pars interpolaris (PI), mandibular cuspid dental structures (MdCDS) were represented in a dorsal position relative to the maxillary cuspid dental structures (MxCDS), whereas within pars caudalis (PC) and the adjacent reticular formation the somatotopic representation was not dorsoventral, but rather mediolateral, with the MdCDS represented more medially than the MxCDS. Areas of overlap between MxCDS and MdCDS were found within MSN and to a lesser degree within the superficial laminae of PC. In addition, the fiber pathway leading to labeled somata in the mesencephalic trigeminal (Mes V) nucleus was clearly identified. The majority of the fibers traced to the Mes V nucleus exited the spinal trigeminal tract at the level of the transition from PO to the MSN and traversed the nuclear region in a position dorsal to and separate from the trigeminal motor tract. As in STN, fibers within the caudal Mes V tract appeared to be somatotopically organized, with the fibers from the MdCDS generally more dorsal than the ones from the MxCDS. Labeled fibers, some with terminal arbors, were also identified in close association with the trigeminal motor tract. The findings show a complex pattern of central representation in the immature feline central nervous system for deciduous dental structures.

Receptor characteristics of periodontal mechanosensitive units supplying the cat's lower canine

1. Forces have been applied to the lower canine teeth of cats, and the range of directions over which single periodontal mechanoreceptors are sensitive (arc of sensitivity) has been determined. We have further studied the response of each unit to forces applied in the direction of maximum sensitivity and investigated whether there is any relationship between the properties of the unit and its location within the periodontal ligament. 2. Recordings were made from 91 single units dissected from the inferior alveolar nerve in six cats. The mean arc of sensitivity to a 0.5 N force applied at right angles to the long axis of the tooth was 312 degrees. The arc of sensitivity was dependent on the force applied and the threshold of the receptor. 3. More units responded maximally to forces applied in a distolingual direction than would have been expected had the responses been evenly distributed around the tooth. Thirty-four of the units were bidirectionally sensitive, 28 became active when the force was removed, and 20 were spontaneously active. 4. The force threshold decreased with increasing rates of force application. 5. The majority of the units (81%) were slowly adapting. The rapidly adapting units had significantly higher force thresholds. 6. Twenty-eight of the receptors could be localized in the periodontal ligament after removing bone overlying the tooth root. There was no apparent relationship between the distance of the receptor from the fulcrum and its arc of sensitivity, threshold, maximum frequency of discharge, or adaptation properties.

Properties of reinnervated periodontal mechanoreceptors after inferior alveolar nerve injuries in cats

1. The properties of periodontal mechanoreceptors supplying lower canine teeth in cats have been investigated 12 wk after the crushing or sectioning of the inferior alveolar nerve. Forces were applied at right angles to the crown of the tooth and recordings made from filaments dissected from the nerve central to the injury site. Data obtained from 41 units after nerve crush and 65 units after nerve section were compared with those from a series of control animals. 2. The range of directions to which each receptor was sensitive was significantly smaller after both nerve crush and nerve section. There were significantly more rapidly adapting units after both nerve crush (37%) and nerve section (34%) than in the controls (19%). 3. Force thresholds measured at three rates of application (20 N/s, 2 N/s, and 0.25 N/s) were significantly higher after nerve section but not after nerve crush. The maximum frequency of discharge was significantly reduced after both nerve crush and nerve section. 4. Bone was removed from over the roots of the teeth to localize receptors in the underlying periodontal ligament. Seventeen receptors were localized in the nerve crush group and 23 in the nerve section group, and their distribution appeared similar to that found in controls. The conduction velocities of these units were significantly reduced after nerve section but not after nerve crush. One unit in the nerve section group appeared to have branched and innervated receptors in two locations.

Afferent C fibre innervation of cat tooth pulp: confirmation by electrophysiological methods

1. The presence of afferent C fibres innervating the lower canine tooth was investigated in Nembutal-anaesthetized cats. 2. Twenty-five single fibres with conduction velocities (CVp) of less than 2.5 m/s, as calculated from the shortest response latency using monopolar electrical stimulation of the tooth, were recorded from the inferior alveolar nerve. In addition, the extradental conduction velocity (CVn) of the fibres was determined by using bipolar electrical stimulation of the trunk of the inferior alveolar nerve. 3. The mean CVp was 1.4 +/- 0.4 m/s (n = 25; range, 0.6-2.4 m/s); the mean CVn was higher, 1.7 +/- 0.9 m/s (n = 25; range, 0.6-4.0 m/s). For 20% of the fibres CVn exceeded 2.5 m/s; these were slowly conducting A delta fibres. For 80% of the fibres, however, the extradental conduction velocity was in the C fibre range. 4. The relationship between CVp (y) and CVn (x) was y = 0.66 + 0.40x, the correlation coefficient being r = 0.85. According to the present results this implies that for a reliable classification of pulpal C fibres (CVn less than or equal to 2.5 m/s) by monopolar tooth stimulation alone, CVp should be less than 1.7 m/s. 5. For twenty-three of the twenty-five fibres, one to three discrete shortenings of the response latency occurred when the intensity of the tooth stimulation was increased. When the nerve trunk itself was stimulated, a constant response latency was measured at all stimulus intensities applied. 6. For twelve fibres tested, the mean rate of electrical stimulation of the tooth, which the response followed with a constant latency, was 4.1 +/- 2.3 Hz (range, 1.5-10.0 Hz). With higher rates of stimulation the response latency increased until the fibres failed to follow each stimulus pulse. 7. Fifteen of the nineteen fibres tested responded to radiant heat stimulation of the tooth they were innervating. The mean temperature threshold was 41.4 +/- 2.7 degrees C (n = 11; range, 37.4 +/- 46.4 degrees C). 8. For eight heat-sensitive pulpal C fibres the receptive field was determined by mechanical stimulation of the exposed pulp tissue. Four C fibres developed a long-lasting on-going discharge after intense mechanical stimulation of the receptive field. 9. The discharge evoked by heat and mechanical stimulation of the tooth occluded the response evoked by simultaneously applied electrical current pulses to the nerve trunk, indicating that the same fibres were activated by both tooth and nerve stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

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.

A morphological study of the collateral reinnervation of the cat's canine tooth

We examined the morphologic characteristics of the collateral reinnervation of the cat's canine tooth pulp. Collateral reinnervation was stimulated in six adult cats by transecting the ipsilateral inferior alveolar nerve and preventing it from regenerating by sealing the ligated nerve inside a nylon tube. The apices of the canine teeth were examined after 15 weeks using electron microscopy and each axon was counted and measured. Compared with contralateral control teeth, the collateral reinnervation consisted of fewer myelinated fibers and in five animals the number of nonmyelinated fibers was also smaller. In one animal the nonmyelinated count on the operated side exceeded that on the control side. The total number of axons was 33.5% of the number in control teeth, considerably fewer than seen after reinnervation by regenerating fibers in previous experiments. The structural characteristics of the collateral fibers were similar to those of regenerating nerve fibers. Compared with controls the myelinated collateral fibers were smaller and had thinner myelin sheaths. There were more nonmyelinated fibers containing only one axon. More nonmyelinated fibers had exposure of part of their axolemma to the extracellular space and there was also an increase in axoaxonal apposition.

A quantitative electron-microscopic analysis of the axons at the apex of the canine tooth pulp in the dog

The morphology of the dog intradental nerves has not been studied in detail, although dogs have been increasingly used in electrophysiological experiments on pulp nerve function. In this investigation electron microscopy and morphometric analysis were used to study the number and dimensions of the axons at the apex of the dog canine tooth. Two upper and two lower canines, each taken from a different animal, were used. The average number of axons entering a tooth was 2,089 (range: 1,241-3,034), 74.3% (range: 62.2-77.9%) of which were unmyelinated. The mean circumference of the myelinated and unmyelinated axons ranged from 11.1 to 13.9 microns and from 1.3 to 1.7 micron, respectively. Of the myelinated axons 13.7% had a circumference over 19 microns, which is considered to be the upper limit of the A delta-class. Of the unmyelinated axons 13.8% showed apposition to each other and 20% were partly exposed to the extracellular space; these features could, in part, offer the morphological basis for the extreme pain sensitivity of the tooth. The findings of the present study were considered in general to be comparable to the results of earlier histological and electrophysiological studies on pulp nerves of different species. Thus, it seems that the dog tooth is an adequate model for studying the pulp nerve function and morphology.

A comparison of monopolar and bipolar electrical stimuli and thermal stimuli in determining the vitality of autotransplanted human teeth

Of 33 autotransplanted maxillary canines, 13 responded to cathodal monopolar stimuli, 15 to bipolar stimuli and nine to a cold stimulus. Responses returned between seven weeks and 26 months after transplantation and indicated that the coronal pulp was reinnervated. There was no evidence that comparison of monopolar and bipolar stimulation might distinguish between the vitality of the coronal and radicular pulp, probably because monopolar stimuli did not excite nerves within the root. The thresholds to both forms of electrical stimulation were raised; the bipolar threshold was significantly higher than the monopolar. No transplanted teeth which responded to a cold stimulus did not also respond to an electrical stimulus.

Response fields of the periodontal mechanosensitive units in the superior alveolar nerve of the cat

Response properties of periodontal mechanoreceptor primary afferent fibers recorded from the superior alveolar nerve were studied in the cat. The left maxillary canine tooth was stimulated manually in 8 directions and/or in 24 directions in the horizontal plane by a specially designed stimulator. The responses of 328 slowly adapting units observed were affected by the direction of stimulus. These units were classified into three groups according to the shape of the response field: a broad type (more than 180 degrees), a medium type (90 degrees to 180 degrees), and a narrow type (less than 90 degrees). The groups contained 27 units (8.2%), 284 units (86.6%), and 17 units (5.2%), respectively, and the remaining 10 units (10.0%) were unclassified. The shape of each response field was little changed by changes in the stimulus intensity. Every response field investigated showed a unimodal distribution. These results were different from those of Mei et al. (1975) who reported that the response fields of units recorded from a Gasserian ganglion had generally consisted of two parts.

Reinnervation of the canine tooth pulp after section of the inferior alveolar nerve in the cat

The apices of lower canine teeth have been examined 9 weeks after unilateral section of the inferior alveolar nerve. The teeth were extensively reinnervated although there was considerable variation in the number of axons present. The myelinated axons were smaller than normal with thinner myelin sheaths. There were fewer axons per non-myelinated fibre (Remak bundle). The proportions of myelinated and non-myelinated fibres were normal.

Short internodal lengths of canine tooth pulp axons in the young adult cat

Light-microscopical measurements have been made on teased pulpal nerve fibers from young adult cat canine teeth. In the root canal portion (apical to first branching point) the mean internodal length was approximately 250 micron. In the pulpal chamber portion (coronal to the first branching point) the pulpal nerve fibers had a mean internodal length of approximately 125 micron. A local decrease in internodal length was evident at bifurcations and in preterminal regions. These internodal lengths are shorter than in similarly sized stem axons. The possible functional significance of this difference is discussed.

An electrophysiological study of canine, premolar and molar tooth pulp afferents and their convergence on medullary trigeminal neurons

The two main aims of this study were (1) to compare the conduction velocities of tooth pulp (TP) afferents innervating the cat canine, premolar and molar teeth and (2) to determine the degree of convergence of afferent input originating in these different teeth on medullary dorsal horn (MDH) neurons. Experiments were conducted on 10 cats anesthetized with chloralose. Single unit extracellular recordings were obtained from the tooth pulp or the MDH. The distribution of conduction velocities of afferents originating in the mandibular and maxillary canines, premolars and mandibular molar were all found to be similar except that the mean conduction velocity of canine afferents was slightly higher than the means for the other teeth. A total of 48 MDH neurons excited by TP stimulation was studied. Most MDH neurons activated by electrical stimulation of one of the TPs could also be activated by stimulation of one or more of the other TPs. In addition to the marked convergence from different teeth, most of the TP-activated neurons also had convergent inputs from facial skin and/or intraoral mucosa.

Accessory innervation of mandibular anterior teeth in cats: a horseradish peroxidase study

In 10 cats, an ipsilateral section of the inferior alveolar nerve was performed following which horseradish peroxidase was deposited in cavity preparations of either ipsicentral incisors (8) or canines (2). The animals were sacrificed in 24 h, and the ipsilateral nerve to mylohyoid and both semilunar ganglia were prepared histochemically for observation. Labeled axons were found in 6 of 8 cats, whose incisors were prepared, and 4 of the 6 had labeled ganglion cells. In the two remaining cats with incisor preparations, no labeled ganglion cells were found; however, labeled axons were found in the mylohyoid nerve. Neither labeled axons or cells were found in those cats whose canines were prepared. One case of cross-innervation was noted. These results suggest that in addition to the inferior alveolar nerve, the nerve to mylohyoid and possibly other accessory neural pathways are involved in incisor innervation in cats.

Evidence for the persistence of axons at the apex of the cat's lower canine tooth after section of the inferior alveolar nerve

The aim of this investigation was to establish the degree of denervation produced by inferior alveolar nerve section and to provide histological evidence for the presence of pulpal nerve fibres supplying the teeth which do not travel with the inferior alveolar nerve. Four adult cats were used. Each stage of the experiment was carried out under general anesthesia. The left inferior alveolar nerve was exposed and sectioned near the mandibular foramen. After 56 hours and 7 days, respectively, the jaw opening reflex to electrical stimulation of each lower canine was tested. Recordings were made from the left canine during electrical stimulation of the ipsilateral inferior alveolar nerve central and peripheral to the site of section as well as from the ipsilateral and contralateral inferior alveolar nerve during electrical stimulation of the left canine. Recordings were also made from the lingual nerve. After the recordings were completed two animals were perfused 56 hours after inferior alveolar nerve section, two more 7 days after section. Ultrathin sections of the apices of the lower canine teeth were examined in the electron microscope and each nerve fibre photographed. Each axon was examined to determine whether it was degenerating or normal. A jaw-opening reflex could not be elicited by stimulation of the left canine either 2 or 7 days after nerve section, whereas a normal response was evoked by stimulation of the right, control canine. At 2 days small responses could be recorded from the left canine teeth during stimulation of the left inferior alveolar nerve peripheral to the point of section. In one 2-day animal, responses could be recorded in the lingual nerve during stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of some metal ions on the intradental sensory nerves of the cat

Intradental nerve activity from canine teeth of anesthetized cats was recorded during the application of different metal ion solutions in a dentinal cavity. The application of Ag2+, Ca2+, Cd2+, Cr3+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+, Sn2+, and Zn2+ reduced the nerve activity induced by NaCl 0.76 M and compound 48/80. The application of Cu2+ and Co2+ excited the intradental sensory nerves.

Effects of ammonia and organic acids on the intradental sensory nerve activity

Ammonia and organic acids constitute a major part of the bacterial metabolites formed in carious decay. The aim of the present study was to investigate their effect on the intradental sensory nerves. Nerve impulse activity was recorded from canine teeth in cats after application of the test solutions in deep dentinal cavities. Ammonia (17-134 mM) consistently generated nerve impulses, whereas organic acids (0.001-1 M) failed to induce any impulse activity. In contrast, acid application resulted in an inhibition of the ongoing nerve activity induced by various stimuli (hypertonic NaCl solution, mechanical pulp exposure, and compound 48/80). However, acid treatment of the cavities resulted in an enhanced neural response to ammonia stimulation. Thus, the present results demonstrate that these bacterial metabolites can influence intradental sensory nerve activity. It is suggested that they may also modulate the symptoms from decayed teeth.

The number and size of axons at the apex of the cat's canine tooth

Using electron microscopy and morphometric analysis the number and size of axons entering the apex of the cat's mandibular canine tooth have been measured. The total number of axons varied from 761 to 1,903 between different animals but the maximum difference between right and left sides of the same animal was 353. From 56 to 79.6% of the axons were nonmyelinated; the difference in proportion between right and left sides never exceeded 6.4%. The mean circumference of myelinated axons ranged from 10.2 to 18.3 micrometers but again the right and left variation was much less and never exceeded 2 micrometers. In one tooth 38.8% of the myelinated axons were larger than 19 micrometers in circumference and thus outside the A delta range. The proportion was much smaller in other teeth but some "large" fibers were always present. Of all the nonmyelinated axons 19.7% showed some degree of axonal exposure to the extracellular space and 1.7% showed ax-oaxonal apposition. A small proportion of nonmyelinated axons showed evidence of apparent degeneration. Comparison of these data with those from studies at more coronal levels suggests that there is considerable branching and narrowing of fibers during their course through the dental pulp and that the degree of axonal exposure and apposition increases considerably. Some of the pulpal fibers are derived from larger axons than are normally associated with pain. The animal to animal variation in the parameters measured is considerable but right and left sides are similar.

Increased levels of Met-enkephalin-like material in the CSF of anaesthetized cats after tooth pulp stimulation

Tooth pulp stimulation in halothane-anaesthetized cats induced a long lasting (greater than or equal to 3 h) increase in the levels of Met-enkephalin-like material (MELM) in the cisternal CSF. Chromatographic analyses (gel filtration, HPLC) revealed that most of the immunoreactivity was attributable to high molecular weight (mol. wt. greater than or equal to 4000) compounds; in non-stimulated cats, Met-enkephalin (largely in the form of the sulfoxide derivative) only accounted for about 10% of total MELM. In contrast, following tooth pulp stimulation, a large increase in Met-enkephalin (plus Met-Ox5-enkephalin) levels was noted so that the pentapeptide thus represented more than 50% of total MELM. No evidence was obtained for the presence of Met-enkephalin-Arg6-Phe7 in the cisternal CSF of halothane-anaesthetized cats. These data strongly suggest that the activity of enkephalinergic neurons was increased following nociceptive stimulation. This indirectly supports the possible physiological role of enkephalinergic systems in modulating nociceptive inputs.

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

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