Selective stimulation of human tooth-pulp with a new stable method: responses and validation.

INTRODUCTION: The aims of this study were to establish a safe technique for selective stimulation of nerves in human tooth-pulp during long experiments and to validate its use even with stimuli of high intensities. METHODS: A custom-made veneer containing 2 silver wire-conductive cream electrodes was attached with cement to the labial surface of an upper central incisor tooth. A variety of stimulus intensities were applied, and sensory and reflex responses from jaw-closing muscles were recorded. RESULTS: In 15 participants, the stimuli evoked predominantly sharp or painful sensations and reflex inhibitions of activity in the jaw muscles. Stimulation of 3 non-vital teeth evoked no sensations or reflexes, even at intensities that evoked maximal reflexes in vital teeth. The electrodes had reasonably stable resistances throughout experiments lasting up to 90 min. CONCLUSION: The method described enables responses to low- or high-intensity stimulation of human pulpal nerves to be investigated in long experiments.

Forces, movements and reflexes produced by pushing human teeth.

Pushing a tooth results in movement of the tooth and reflex inhibition of activity in jaw-closing muscles. The aims of this study were to determine how much tooth movement is required to elicit such reflexes and whether this is dependent on the point of force application to the tooth. Eight experiments were performed on six volunteer subjects. Electromyograms (EMGs) were recorded from a masseter muscle while the subjects produced approximately 12.5 % of the EMG associated with maximal clenching. Reflexes were evoked by pushing at two positions (incisal and cervical) on an upper central incisor. The forces applied and the resulting movements of the tooth were recorded. There was a linear relationship between force and movement regardless of whether the force was incisal or cervical (Pearson's r = 0.91 and r = 0.93 respectively). There were no differences between the slopes or intercepts for these relationships (ANCOVA p = 0.42, p = 0.46 respectively). There were linear relationships between the logarithms of force or movement and the resulting inhibitory reflexes (r = 0.81, 0.79, 0.81 and 0.74 for incisal and cervical forces and incisal and cervical movements, respectively). Again, there were no significant differences between the slopes for these relationships (ANCOVA p = 0.75, p = 0.46 for force and movement, respectively). There were no significant differences between the reflex thresholds for incisal and cervical stimuli in terms of force (0.23 and 0.25 N, ANCOVA p = 0.1) or movement (9.7 and 8.5 µm, ANCOVA p = 0.22). Thus, it appears that neither tooth movements nor jaw reflexes are dependent on the point of force application to a tooth.

3D Technology Development and Dental Education: What Topics Are Best Suited for 3D Learning Resources?

The aim of this study is to identify topics (knowledge and skills) from the dental curricula that would benefit from having a 3D learning resource using an exploratory sequential design method. The first phase targeted stakeholders from a Scottish dental school. Seven focus groups and three interviews disclosed 97 suitable topics for 3D technology development. These results were used to construct a survey that was sent to final year dental students, newly dental graduates and academics from three Scottish universities. The survey asked participants to rank each item based on the perceived benefit that a 3D learning resource would have for dental education. Results revealed that detailed anatomy of the temporomandibular joint, dental anaesthesiology, dental clinical skills techniques, dental occlusion and mandibular functioning were top priorities. Gender differences only appeared in relation to 'Extraction techniques: movements and force' (p < 0.05), this topic was considered to be more beneficial by females than by males. No statistical difference was found when comparing results of graduates with undergraduates. These results serve as a starting point when developing a new 3D technology tool for dental education, considering users demands and perceived needs has the potential to benefit dental students and dental education directly.

Differences between inhibitory jaw reflexes evoked by stimulation of tooth pulp and across the adjacent alveolar process in man.

OBJECTIVE: In humans, stimulation of nerves in or around teeth can evoke inhibitory jaw reflexes. Previous studies had suggested that there may be subtle differences in the timings of the responses. The aim of the present study was to investigate this by comparing reflexes evoked by electrical stimulation of a tooth and of the adjacent tissues in individual subjects. DESIGN: Experiments were performed on 9 volunteers (3 male, 6 female). EMG recordings were made from the masseter muscle ipsilateral to the stimuli, whilst the subjects maintained a steady level of activity in the muscle. Reflexes were evoked by applying stimuli to an incisor tooth (pulpal stimuli) or across the adjacent alveolar process (transalveolar stimuli), using bipolar electrodes. RESULTS: Two inhibitory responses were evoked in most (8/9) subjects. The first occurred at a shorter latency after transalveolar than after pulpal stimulation (12.3+/-0.5 ms vs 19.4+/-1.5 ms; P=0.0014, paired t-test). For technical reasons, it was not possible to make such comparisons for the second inhibitory responses in all the subjects. In 5 subjects where such a comparison was possible, the mean latency of the transalveolar-evoked response was again shorter than that of the pulpal-evoked response (56.4+/-2.8 ms and 58.8+/-5.3 ms, respectively), but this difference was not significant (P=0.5). CONCLUSIONS: It appears that inhibitory jaw reflexes evoked from around the teeth are faster than those from the dental pulp. This observation could be due to differences between the peripheral afferent and/or the central pathways mediating the reflexes.

An audit of dentine hypersensitivity treatments in six general dental practices in Scotland.

AIMS: This investigation sought to: (a) determine the agents used by nine dentists to treat dentine hypersensitivity and measure their effectiveness; (b) evaluate the adoptive ease and apparent success of the most effective treatment when used by all nine dentists; and (c) validate a novel categorical ranking score for dentine hypersensitivity. METHODS: A clinical audit methodology was used in the setting of general dental practice. In the initial data-collection round, patients presenting with dentine hypersensitivity were treated using the dentist's favoured regimen. Evaluation of agent effectiveness was made by patient completion of a pre- and post-treatment visual analogue scale (VAS) for the frequency (f) and severity (s) of hypersensitivity. A four-point categorical ranking scale (CRS) was also used to assess the impact of hypersensitivity upon lifestyle (L) (1=No sensitivity/effect on what I eat/drink; 2=Sometimes sensitive, rarely interfering with what I eat/drink; 3=Sometimes sensitive, occasionally interfering with what I eat/drink; 4=Always sensitive, always interfering with what I eat/drink). The most successful treatment was determined and used by all participating dentists. Its effectiveness was then assessed using the same criteria. RESULTS: Four agents were routinely used to treat hypersensitivity: (Duraphat (D) (Colgate), Duraphat & Sensodyne (DS) (GlaxoSmithKline), Sensodyne (S) (GlaxoSmithKline), Seal & Protect (SP) (De Trey, Dentsply). All produced statistically significant (P<0.001) reductions in VAS (Tukey) and CRS (Kruskal-Wallis) scores, except for DS and S. Of these, the greatest percentage reduction was seen for SP (f=72.01%, s=71.19%, L=45.98%). When SP was applied by all dentists, similar percentage reductions were seen (f=68.74%, s=75.85%, L=38.33%). The CRS, in both data-collection rounds, correlated well with the corresponding VAS scores (Spearman R for f=0.77 (P<0.001) and for s=0.80 (P<0.001). CONCLUSION: For the dentists in this audit, the use of SP was found to be reliable and predictable. The CRS provided a simple and reliable measure of dentine hypersensitivity. Subject to validation in a larger study, this could be used in a future audit as an alternative to multiple VAS scores.

Functional roles of oral reflexes in chewing and biting: phase-, task- and site-dependent reflex sensitivity.

Because loading during chewing is not totally predictable and jaw-closing muscles are strong and act over short distances, feedback from oral receptors is important in the control of mastication. Information on such feedback can be obtained by studying reflexes in jaw muscle EMGs. This review will deal with the contribution of reflex mechanisms to modifying motor neuron activity during chewing, and the dependency of reflex sensitivity on motor task, phase of movement, and site of stimulation.

Differentiation of nociceptive- from stress-induced modulatory influences on human reflexes.

This paper describes a new protocol that addresses the question of whether, in human experiments, modulatory effects of remote nociceptive conditioning stimuli on reflex responses are mediated by the stress induced by the conditioning stimuli. The protocol has been illustrated by a study into the effect of a remote nociceptive conditioning stimulus on an inhibitory jaw reflex. Electromyograms were recorded from an active masseter muscle and inhibitory reflexes were evoked by applying electrical stimuli to the upper lip. This protocol utilised the application of discrete electrical conditioning stimuli applied to the sural nerve prior to the test stimulus. A preliminary experiment determined that the optimal interval between the conditioning and test stimuli, which produced modulatory effects was 100 ms. In the definitive study, computer software was used to deliver control and conditioned sweeps in a double-blind randomised sequence. This resulted in a "stress-equal" protocol in which the level of stress would be the same for both control and conditioned sweeps. Therefore any observed modulatory effects on the reflexes could not have been wholly secondary to stress. This protocol could be adapted to the study of the modulation of other reflexes or evoked sensations by nociceptive conditioning stimuli.

Quantification of jaw reflexes evoked by natural tooth contact in human subjects.

Inhibitory jaw reflexes are believed to be important for protecting the teeth and temporo-mandibular structures from damage during sudden or forceful biting or mastication. Accordingly, alterations in these reflexes are sometimes implicated in aetiologies proposed for oro-facial pain syndromes, although the association is not well-established. We now aim to develop a method for quantifying objectively inhibitory jaw reflexes evoked by natural tooth contact. In the longer term, this may provide a new approach to examining the association of altered reflexes and clinical conditions. Eighteen subjects gave their written, informed consent, and were recruited to participate in this study. They were instructed to clench their teeth together in response to visual cues. They performed two such tasks twenty times: from the jaw postural position and from a more open position with the jaws set 10mm apart. Both tasks produced a rapid rise then stabilisation in electromyographic activity in the masseter muscle. This was always interrupted by a large inhibitory reflex starting 11.1±1.5 ms (mean±SD) after tooth contact. The inhibitions produced during the second task were similar but of significantly longer duration (24.3±6.4 vs 18.4±6.5 ms, P=0.0003, paired t-test) and greater magnitude (measured as an integral of the waveform: 1577±478 vs 1279±425%.ms, P=0.007, paired t-test). Interestingly, in a minority (13%) of the tasks, a second inhibition with a longer latency (50.9±0.9 ms) was also observed. Thus reflex responses in the masseter muscle to natural tooth contact usually consist of single inhibitory periods. In this respect they are like those induced by externally applied tooth pushing although occasionally there is a second inhibition, reminiscent of that seen with externally applied tooth taps.

Modulation of an inhibitory jaw reflex by remote noxious stimulation: effects of spatial conditioning factors.

In humans, inhibitory jaw reflexes can be depressed by painful stimulation of remote parts of the body. The underlying mechanisms may involve diffuse noxious inhibitory controls (DNIC). Animal experiments have shown that the neurons which may mediate DNIC show spatial encoding (i.e. their responses vary in relation to the size of the body area being stimulated). The aim of this study was to investigate whether the modulation of an inhibitory jaw reflex shows similar spatial dependency. Electromyographic recordings were made in 9 subjects, from a masseter muscle that was activated to a level equivalent to 10% of that obtained during a maximum voluntary contraction. Reflex inhibitions were evoked by electrical stimuli to the upper lip, either alone (controls) or during the application of conditioning stimuli (47 degrees C water) to the fingers, the hand, the half forearm or the whole forearm. Conditioning stimuli applied to the larger but not to the smaller areas resulted in significant modulations of the reflex. There was a significant correlation between stimulus area and reflex magnitude. These results demonstrate a spatial dependency for the modulation of an inhibitory jaw reflex by painful stimuli -- a further parallel with DNIC as studied on single neurons in animals.

Dissociation of nociceptive modulation of a human jaw reflex from the influence of stress.

In human beings, inhibitory jaw reflexes can be depressed by painful stimulation of remote parts of the body. Since similar effects can be produced by the stress of anticipating pain, we wished to investigate whether the effects of remote painful stimuli are dependent on stress. EMG recordings were made from a masseter muscle while subjects maintained activity in the muscle at approximately 12.5% of maximum using visual feedback. The protocols involved three sequences: (1) "standard controls" in which reflexes were evoked by electrical test stimuli applied to the upper lip; (2) "standard conditioning" in which painful electrical conditioning stimuli were applied over the sural nerve 100 ms before the test stimuli; (3) "random sequences" in which test-only and conditioning-test combinations were employed in a double-blind, random, order. Data are presented as means +/- SEMs. In the standard controls, the stimuli evoked clear inhibitory reflexes (latency 37 +/- 1.3 ms, duration 62 +/- 5.6 ms; n = 10) in all the subjects. During standard conditioning, the reflex magnitude was reduced significantly (by 50.0 +/- 8.5%, P = 0.0002, one-sample t-test). When the test-only and conditioning-test responses were extracted from the random sequences, there was also a significant reduction in the reflex magnitude following conditioning (by 34.6 +/- 5.5%, P = 0.0002, one-sample t-test) albeit less so than between the standard sequences (P = 0.03, paired t-test). A second series of experiments suggested that these lesser effects during the random sequences were not substantially due to any loss of temporal summation of the conditioning mechanisms. The evidence for this was that application of pairs of conditioning stimuli did not produce a significantly greater effect than single conditioning stimuli within a random sequence (39.9 +/- 9.6% as opposed to 32.7 +/- 9.1% reductions in the reflex, P = 0.117, paired t-test). Therefore since any stress in the random sequences would not have been "tied" to the conditioned responses alone, the effects of remote painful stimuli on this inhibitory jaw reflex cannot be entirely secondary to stress.

Remote noxious stimuli modulate jaw reflexes evoked by activation of periodontal ligament mechanoreceptors in man.

The purpose of the study was to investigate whether jaw reflexes evoked by selective stimulation of periodontal ligament me canoreceptors are susceptible to modulation by remote noxious stimulation. Experiments were performed on 10 volunteer subjects. Skin surface recordings were made from the jaw-closing masseter muscle. The subjects activated the muscle to approximately 10% of maximum by biting on a rubber impression of their molar teeth while they received visual feedback of the electromyogram (EMG) of the muscle. Reflexes were produced by the application of gentle mechanical stimuli to an upper central incisor tooth. The stimuli were in the form of 'ramp and hold' forces with a 5 ms rise-time and a 1.5 N plateau which lasted 350 ma. The resulting reflexes were recorded both under control conditions and while the subjects received a remote noxious stimulus (immersion of a hand in water at 3 degrees C). In all 10 subjects, the stimuli produced a single period of inhibition of masseteric activity (latency, 12.8 t 04 ms; duration, 18.1+/-1.3 ms; means +/- S.E.M.), which was usually followed by a period of increased masseteric activity. The period of inhibition constituted a downward wave in full-wave rectified, averaged signals. The integrals of such waves were significantly smaller (by 17+/- 6.5 %; P = 0.027; Student's t test) when the reflex was evoked during remote noxious stimulation rather than under control conditions. As such reflexes are beLieved to play a modulatory role during normal oral function this finding maybe relevant to disorders of mastication associated with pain.