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Biomedical subjects

R Orchardson

Publications and source records attributed to R Orchardson.

At least 19 recordsLinked to original sources
PubMed2003

Salivary flow rate and pH during prolonged gum chewing in humans.

Gum chewing for 20 min causes an increase in salivary flow rate and salivary pH. Most people chew gum for longer than 20 min, and our aim was to determine how whole mouth salivary flow rate and pH might adapt during prolonged gum chewing. Resting saliva was collected over 5 min; gum-stimulated saliva was collected at intervals during 90 min, chewing a single pellet (1.5 g) of mint-flavoured, sugar-free gum (n = 19). Subjects chewed at their own preferred rate and style. Both salivary flow rate and pH were increased above resting levels for the entire 90 min. The salivary flow was significantly greater (anovaP < 0.05) than resting flows up to 55-min chewing. The saliva pH remained significantly higher (P < 0.0001) than the resting pH even after 90-min chewing. When the experiment was repeated with the gum pellets replaced at 30 and 60 min (n = 9), similar increases in salivary flow rate and pH were found. In the latter experiment, there was no evidence of any cumulative effects on flow or pH. The persistent increase in salivary pH in particular could be beneficial to oral and dental health.

Adolescent↗
PubMed2001

Differences in the oral size illusions produced by cross-modality matching of peg and hole stimuli by the tongue and fingers in humans.

Individuals overestimate the diameter of 1-mm-deep stimulus holes presented to the tongue when they use their fingers to select a hole of matching diameter. The aim here was to determine whether the oral size illusion evident for 1-mm-deep holes would also occur with 1-mm-high pegs of similar diameters. The illusion was studied in 24 individuals who were blindfolded during the trials. The two sets of test stimuli were (a) 5 cylindrical pegs (1 mm high) and (b) five circular holes (1 mm deep), each of 2.5, 5.0, 7.5, 10.0, 12.5 mm dia. The stimuli were held to the mouth with one hand, while the fingers of the free hand were used to select a matching object from a comparator series of either 1-mm-deep holes or 1-mm-high pegs ranging from 2.0 to 18 mm dia. Each stimulus was presented four times in a random order. The participants overestimated the diameter of the 1-mm-deep stimulus holes when these were matched with 1-mm-deep comparator holes. However, there was no illusion with four out of five 1-mm-high stimulus pegs when matched with 1-mm-high comparator pegs. In the 'reverse' experiment, there was no illusion with four out of five stimulus holes when these were matched with 1-mm-high comparator pegs. However, an illusion was evident for all the 1-mm-high stimulus pegs when these were matched with the 1-mm-deep comparator holes. Regardless of the nature of the stimulus ('hole' or 'peg'), a mismatch between the stimulus and comparator was consistently seen only when the fingers probed comparator holes. The oral size illusion is not due to any intrinsic differences in the sensitivities of the tongue or fingers. Rather, the illusion is due to the inability of the fingertip to access small comparator holes.

Adult↗
PubMed2001

An update on the physiology of the dentine-pulp complex.

The properties of dentine and pulp are closely related and from a functional standpoint these tissues are often referred to as the dentine-pulp complex. In recent years there has been considerable progress in our understanding of the physiology of the dentine-pulp complex. This review describes some of the advances that are relevant to clinical dentistry, including dentine permeability, dentine bonding, dentine sensitivity, the properties of pulpal nerves and blood vessels and the reactions of the dentine-pulp complex to operative dental procedures.

Dental Bonding↗
PubMed2001

The neural mechanisms of oral and facial pain.

Pain is a complex and variable phenomenon that can be influenced by many factors. The neural pathways serving pain are not passive conduits, but are part of a dynamic system which can result in different levels of pain resulting from similar injuries under different circumstances. The passage of signals in these pathways may be inhibited or enhanced at almost any level, from the peripheral sensory receptors to the higher centres of the brain. This review will describe recent developments in our understanding of these mechanisms and how this knowledge may be used in controlling pain.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2000

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.

Action Potentials↗
PubMed2000

The effect of stimulus form and dimensions on the oral size illusion in humans.

Previous work has shown that individuals overestimate the diameter of holes presented to the tongue when they use their fingers to select matching holes from a range of comparators. This disparity is known as the oral size illusion. The hypothesis that this illusion arises from the greater pliability of the tongue surface compared with that of the fingertip was tested here. Two experiments were carried out on 64 participants. In experiment 1 (n=32), the stimuli were two sets of holes, 1 and 5 mm deep and 2.4, 5.6, 8.2, 12 mm dia. , which were presented to the tongue. The comparator was a series of holes 5 mm deep and 0.8-15 mm dia., which were explored manually. Participants significantly overestimated all diameters of the 1- and 5-mm deep stimulus holes (p<0.05). Apart from the 2.4-mm dia. holes, there were no significant differences between the illusions produced with the holes 1 mm and 5 mm deep (p0.7). In experiment 2 (n=32) individuals were tested with small cylinders ('pegs') 1 mm high and 2.6, 5.2. 7.6, 12.6 mm dia. and also with the four 5-mm deep stimulus holes used in experiment 1. The 'peg' stimuli presented to the tongue were matched against a similar set of 1-mm pegs, 2-18 mm dia., explored with the fingers. The comparator series for the 5-mm deep holes was the same as for experiment 1. Participants consistently overestimated the size of the 5-mm holes (p<0.001). However, there was no illusion with the peg stimuli (p=0.08), except for the 7.6-mm dia. stimulus (p<0.05). The results of experiment 1 did not support the experimental hypothesis that the oral size illusion was due to the greater pliability of the tongue surface. The result of experiment 2 suggests that the oral size illusion does not occur when peg stimuli are used instead of holes. The form and diameter of the stimulus is thus important in determining the magnitude of the oral size illusion.

Adolescent↗
PubMed2000

The efficacy of potassium salts as agents for treating dentin hypersensitivity.

Formulations containing potassium salts (e.g., chloride, nitrate, citrate, oxalate) are widely used for treating dentin hypersensitivity (DH). The purpose of this review was to evaluate evidence for the clinical efficacy of potassium salts in reducing DH and also to consider the biologic basis for any effects. Literature searches were used to identify reports of clinical trials of potassium-containing preparations. Searches revealed 3 trials of potassium nitrate solutions or gels; 2 trials of mouthwashes containing potassium nitrate or citrate; 6 trials of potassium oxalates; and 16 double-blind randomized trials of toothpastes containing potassium nitrate, chloride, or citrate. The toothpaste studies provided quantitative data on treatment effects. These outcome measures were expressed as percentage reductions in sensitivity to cold air and mechanical stimulation and the patients' subjective reports. Trials of topically applied solutions yielded inconsistent results. Potassium-containing mouthwashes produced significant reductions in sensitivity. All potassium-containing toothpastes produced a significant reduction in sensitivity to tactile and air stimuli, as well as subjectively reported sensitivity. In most studies, the active agent (potassium) was superior to the minus-active control (placebo), but a few of the more recent trials have demonstrated significant placebo effects. It is postulated that potassium ions released from toothpastes diffuse along the dentinal tubules to inactivate intradental nerves. However, this principle has never been confirmed in intact human teeth. The mechanism of the desensitizing effects of potassium-containing toothpastes remains uncertain at present.

Dentin Sensitivity↗
PubMed1999

Action potential conduction block of nerves in vitro by potassium citrate, potassium tartrate and potassium oxalate.

OBJECTIVES: Potassium salts in desensitising formulations are believed to act by blocking nerve conduction. The aim of this study was to assess the ability of some organic potassium salts to block action potential conduction and to compare their effects with potassium chloride and potassium nitrate. MATERIALS AND METHOD: Potassium citrate, oxalate or tartrate were added to Krebs' solutions to raise the potassium concentration to 8-64 mM. The test solutions were applied to rat spinal nerves in a bath while monitoring the compound action potentials evoked by electrical stimulation. RESULTS: All potassium salts attenuated the compound action potential in a dose-dependent manner. There were no significant differences between the effects of potassium tartrate and potassium citrate solutions (p>0.1) which caused significantly greater compound action potential attenuation than the same concentrations of potassium oxalate (p<0.05). On the basis of the potassium ion concentration required to cause 50% attenuation of the compound nerve action potential, the relative potencies of the potassium salts were: citrate = tartrate> oxalate>chloride =nitrate. CONCLUSION: Potassium citrate and potassium tartrate were more effective than other potassium salts in blocking nerve conduction and may be more effective dentinal desensitising agents.

Action Potentials↗
PubMed1997

Toothache--the 'hell of all diseases'.

Last year was the bicentenary of the death of Robert Burns, who is Scotland's best known poet. January 25, Burns' birth date, is also a well-known celebration to the Scottish-the famous 'Burns Night'. Burns wrote many songs and poems, but his 'Address to the Toothache' is of particular interest to dentists. The poem provides a vivid account of one man's experience of toothache and gives an insight into how people regarded pain two hundred years ago.

England↗
PubMed1997

Effect of pulsed Nd:YAG laser radiation on action potential conduction in isolated mammalian spinal nerves.

BACKGROUND AND OBJECTIVE: Dental lasers are claimed to produce analgesia, but the mechanisms and extent of any effects are uncertain. This study investigated the effects of lasing on nerve conduction in isolated nerves. STUDY DESIGN/MATERIALS AND METHODS: Pulsed Nd:YAG laser energy was applied to spinal nerves in vitro and effects were measured as attenuation of the compound action potential (CAP) evoked by electrical stimulation. RESULTS: Lasing for 1 minute at 0.3-3.0 W caused a dose-dependent attenuation of all components of the CAP (P < 0.03). With 0.3-1.0 W power, the CAP recovered to > 95% of the control levels 7 minutes after lasing; recovery was incomplete after lasing at > 2.0 W. CONCLUSION: Isolated nerves were remarkably tolerant of lasing. The degree of nerve conduction block increased with laser power. The data indicate that lasing could diminish sensations, including pain, mediated by peripheral nerves in soft tissues.

Action Potentials↗
PubMed1997

Guidelines for the design and conduct of clinical trials on dentine hypersensitivity.

Clinical trials on dentine hypersensitivity have been numerous and protocols varied. To date there is little consensus as to the conduct of studies on this poorly-understood yet common and painful dental condition. A committee of interested persons from academia and industry was convened to discuss the subject of clinical trials on dentine hypersensitivity and a consensus report is presented. A double-blind randomized parallel groups design is recommended, although cross-over designs may be used for the preliminary screening of agents. Subjects may have multiple sites scored. Sample size will be determined by estimating the variability in the study population, the effect to be detected and the power of the statistical test to be used. Subject selection is based on a clinical diagnosis of dentine hypersensitivity, excluding those with conflicting characteristics such as currently-active medical or dental therapy. The vestibular surfaces of incisors, cuspids and bicuspids are preferred as sites to be tested. A range of sensitivity levels should be included. Tactile, cold and evaporative air stimuli should be applied. Negative and benchmark controls should be incorporated. Most trials should last 8 weeks. Sensitivity may be assessed either in terms of the stimulus intensity required to evoke pain or the subjective evaluation of pain produced by a stimulus using a visual analog or other appropriate scale. The subject's overall assessment may be determined by questionnaire. Outcomes should be expressed in terms of clinically significant changes in symptoms. Follow-up evaluation is required to determine the persistence of changes. At least 2 independent trials should be conducted before a product receives approval.

Air↗
PubMed1996

A mathematical model of potassium ion diffusion in dentinal tubules.

Desensitizing agents containing potassium ions (K+) are believed to inactivate intradental nerves by raising extracellular [K+]. A mathematical model was used to investigate factors affecting [K+] in dentinal tubules. The most important factors affecting the steady-state tubular [K+] were the tubular fluid-flow velocity, salivary [K+] and the permeability to potassium (k) of the barrier between the tubule and the pulp. Tubular [K+] decreased with increasing outward flow velocity and increasing k. whereas the dimensions of the tubule and odontoblast process had little effect. Following a 1 min simulated application of 500 mmol/1 K+ to the dentine surface, [K+] at the inner end of the tubule increased above steady-state levels for 20-30 min. The maximum [K+] attained at the inner end of the tubule was around 30 mmol/l for an impermeable barrier (k = 0) and flow velocity of 1.4 microns/s, but lower maximum tubular [K+] were achieved when either the outward flow velocity or k was increased. The model suggests that applying potassium-containing preparations to dentine may increase [K+] at the inner ends of dentinal tubules to levels sufficient to inactivate intradental nerves. However, the localized increase in [K+] is transient, and the concentration change will be lessened by conditions that increase the tubular fluid-flow velocity or the permeability of the barrier between the tubule and pulp.

Dentin↗
PubMed1996

Perception of stimulus size in patients with burning mouth syndrome.

Twenty subjects with burning mouth syndrome (BMS) and 20 control subjects were tested for oral size perception. Blindfolded subjects assessed the size of holes (2.38-12.70 mm diameter) presented to the tongue, using their fingers to select a matching hole from a comparator series of 31 holes (0.76-15.87 mm diameter) using first static then phasic touch. Both groups overestimated the size of the holes less than 10 mm in diameter but no systematic disparity was evident with holes greater than 10 mm in diameter. The relationship between the stimulus size and the illusion (expressed as the ratio of apparent size to real size) was hyperbolic, with the illusion tending towards unity for holes greater than 10 mm. No differences were found in object size perception amongst patients with BMS or control subjects. It is therefore unlikely that altered oral size perception is a precipitating factor or accompanying feature in patients with BMS.

Adult↗
PubMed1995

A clinical study of pulsed Nd: YAG laser-induced pulpal analgesia.

The pulsed Nd: YAG laser is advocated as an alternative means of providing analgesia during routine dental procedures. Since the evidence to support this claim is mainly anecdotal, a clinical trial was carried out using an electric pulp tester (EPT) to measure the extent and duration of any analgesic effect induced by pulsed Nd: YAG laser treatment. A double-blind crossover experiment involving laser and sham treatments was used on 21 subjects. A small (3.6 arbitrary units) but statistically significant increase was observed in the mean responses measured 5 min after laser treatment with 113 mJ pulses at 15 pulses s-1 (pps) for 3 min. The pain thresholds returned to baseline values after 60 min. No statistically significant changes in threshold were found with the sham treatment. The order in which laser and sham treatment was received made no difference to the results.

Adult↗
PubMed1995

Effects of potassium ions on action potential conduction in A- and C-fibers of rat spinal nerves.

Potassium ions in dentifrices for treating 'hypersensitive' dentin are believed to act directly on intradental nerves by raising extracellular potassium ion concentration ([K+]o) sufficiently to prevent action potential generation by axonal accommodation. However, the [K+]o necessary to block nerve conduction is not precisely known, nor is it certain that K+ can diffuse from a dentifrice in sufficient amounts to inactivate intradental nerves. To establish more accurately the [K+]o required to block nerve conduction under controlled conditions, we studied the effects of increased [K+]o on the sizes of compound action potentials (CAP) recorded from rat spinal nerves in vitro. [K+]o was increased by the addition of either KCl or KNO3 to Krebs' solutions applied to the central portion of the nerves. CAP attenuation increased in a dose-dependent manner as [K+]o was raised in the 8 to 64 mmol/L range, and complete block was generally produced with solutions containing at least 32 mmol/L K+. CAP attenuation was reversible, and recovery times increased with increasing [K+]o. The effects of KCl and KNO3 solutions were the same for all [K+]o tested. Half-maximal (50%) reduction in the A beta-fiber component of the CAP occurred with 17.4 mmol/L K+, and with 17.8 mmol/L and 19.3 mmol/L K+, respectively, for the A delta- and C-fiber components. Control experiments with glucose and choline chloride confirmed that the conduction block observed with increased [K+]o was not due to increased solution osmolarity or ionic strength.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1994

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

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

Action Potentials↗