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Biomedical subjects

A Woda

Publications and source records attributed to A Woda.

At least 19 recordsLinked to original sources
PubMed2006

Adaptation of healthy mastication to factors pertaining to the individual or to the food.

Mastication is a physiological process controlled by the central nervous system and modulated by inputs from the mouth. Both the intrinsic characteristics of the subject and the extrinsic characteristics of the chewed food are responsible for variations of the masticatory function. Age, gender and dental state constitute the most studied intrinsic factors whereas hardness, rheological characteristics such as plasticity or elasticity, and food size are the better known extrinsic factors. These factors cause physiological adaptations which can occur during individual cycles or the whole sequence of mastication. Electromyographic and jaw movements (kinematic) recordings are commonly used to study mastication, from which, several variables can be measured. Vertical and lateral amplitudes and, velocities of jaw movements, are only given by kinematic recordings. Bioelectrical activities per cycle or per sequence are closely linked to masticatory forces and are measured from electromyographic recordings. Number of cycles, sequence duration and masticatory frequency can be measured from both types of recordings. The objective of this review is to provide an overview of the variations of the measured masticatory variables that occur when mastication adapts to changes in characteristics of the individual or the food.

Adaptation, Physiological↗
PubMed2006

The regulation of masticatory function and food bolus formation.

This review emphasizes the following points: 1. The values of the physiological parameters of mastication (number of cycles and total electromyographic activity in the sequence, sequence duration, cycle frequency in the sequence, kinetic characteristics of the cycles) are characteristic of each individual and vary widely from one individual to another. In a given individual their modification reflects an adaptation of mastication to the size of the food bolus, and the hardness and rheological characteristics of the food. 2. The ready-to-swallow food boluses produced by different individuals nevertheless display similar particle size distributions. 3. Ageing entails adaptation of the masticatory function and does not impair swallowing. 4. Observed increase in total electromyographic activity shows that more energy is expended in mastication by full denture wearers. Despite this increased muscle activity, loss of teeth, even if compensated for by complete dentures, hinders the formation of a normal bolus. The food boluses made by denture wearers thus contain many large-size particles. The impaired mastication observed in denture wearers approaches the masticatory disabilities found in persons with neuromotor deficiencies.

Aging↗
PubMed2006

Effect of texture of plastic and elastic model foods on the parameters of mastication.

Mastication is continually modified throughout the chewing sequence in response to the texture of the food. The aim of this work was to compare the effects of an increase in hardness of two model food types, presenting either elastic or plastic rheological properties, on mastication. Each model food type consisted of four products of different hardness. Sensory testing experiments conducted with one group of 14 subjects showed significant perceived differences between products in terms of their increasing hardness. Fifteen other volunteers were asked to chew three replicates of each elastic and plastic product during two sessions. EMGs of masseter and temporalis muscles were recorded simultaneously with jaw movement during chewing. Numerous variables were analyzed from these masticatory recordings. Multiple linear regression analyses were used to assess the respective effects of food hardness and rheological properties on variables characterizing either the whole masticatory sequence or different stages of the sequence. Muscle activities were significantly affected by an increase in hardness regardless of the food type, whereas the shape of the cycles depended on the rheological properties. The masticatory frequency was affected by hardness at the initial stage of the sequence but overall frequency adaptation was better explained by a change in rheological behavior, with plastic products being chewed at a slower frequency. A dual hypothesis was proposed, implicating first a cortical-brain stem preprogrammed mechanism to adapt the shape of the jaw movements to the rheological properties of the food, and second, a brain stem mechanism with mainly sensory feedback from the mouth to adapt muscle force to the food hardness.

Adaptation, Physiological↗
PubMed2004

Impact of teaching requirements for students on the activity of a university dental hospital.

OBJECTIVES: This study aimed at investigating the influence of teaching requirements on the clinical activity of a dental hospital. METHOD: The annual clinical activity of seven classes of fifth-year students (n = 294) was monitored between 1994 and 2001 within the conservative dentistry and endodontic departments of a French dental hospital. The variables chosen were: (i) the mean number of procedures performed per student, and (ii) the proportion of different types of treatment within the global activity (i.e. endodontic treatment, anterior, and posterior restorations). These data were analysed in relation to changes in student assessment criteria over time. RESULTS: Quantitative clinical teaching requirements were removed for the academic year 1998-99 and student clinical activity subsequently decreased by 32.7%, going from 51.9 +/- 12.2 dental procedures on average per student in 1997-98, to 29.1 +/- 7.2 in 2000-01. The mean number of patients treated per student also declined significantly during this period. The size of the minimum clinical requirement altered over the years prior to being removed altogether and a positive correlation existed between the volume of activity and the minimum requirement over this time. The types of treatment provided changed independently from the assessment criteria over the study period. There was a decrease in the percentage of amalgams placed and an increase in the number of posterior composites. A negative correlation existed between the evolution of these two types of treatment. CONCLUSION: This study demonstrates that the clinical activity of a department in a dental teaching hospital is directly related to the assessment criteria fixed by the university. This may have repercussions for hospital services.

Analysis of Variance↗
PubMed2004

Particle size distribution of food boluses after mastication of six natural foods.

There is a large variability between and among individuals in the physiology of mastication, but it is not known whether this produces a similar variability in the particle sizes of food boluses at the end of the chewing process. Food boluses obtained just before swallowing were analyzed in ten subjects (aged 36.7 +/- 9.5 yrs) with normal dentition. Food samples of 3 nuts (peanut, almond, pistachio) and 3 vegetables (cauliflower, radish, and carrot) were chewed and expectorated after self-estimated complete mastication. Measurements with sieving and laser diffraction methods indicated that particles were much larger in vegetables than in nuts. Particle size distributions were similar among nuts and among vegetables. Surprisingly, no inter-individual variability was observed in the particle distributions for the 6 foods, although several sequence variables differed markedly. A need for a bolus to be prepared with a precisely determined texture before it can be swallowed may explain the inter-subject variability of the masticatory function.

Deglutition↗
PubMed2003

Gonadectomy induces site-specific differences in nociception in rats.

High prevalence of chronic orofacial pain in women and its relationship with ovarian states suggest that ovarian hormones may be involved in the control of orofacial nociception. Since the interaction between ovarian hormones and nociception seems more evident in the orofacial area than in many other parts of the body, a possible site specificity of an ovarian hormone effect on nociception was tested in rats. Two nociceptive tests were applied to three groups of male rats (n=46) and three groups of female rats (n=46), that were gonadectomised (n=17), sham-operated (n=15) or intact (n=14). Each rat in each group received a local subcutaneous injection of formalin in the upper lip and in the hindpaw. Upper lip injection resulted in an increased occurrence of upper lip rubbing for more than 45 min and hindpaw injection resulted in an increased occurrence of hindpaw licking for about 1h. The duration of the nociceptive behaviours was measured at 3 months after surgery. No significant difference was found between intact and sham-operated animals. A significant increase (54%) in the upper lip rubbing but not the hindpaw licking was observed in gonadectomised females. No difference was observed in castrated males for upper lip rubbing, but a tendency towards an increased duration (102%) of hindpaw licking was noted. The depletion in gonadal hormones was confirmed 3 months after gonadectomy and after the sacrifice of the animals, by the observed decline in the bone mineral density measured on the femur of 40 rats belonging to the six groups. A role of ovarian hormones was also suggested after immunostaining of oestrogen receptors in the lamina II of Caudalis subnucleus of the trigeminal sensory complex and cervical (C1-C2) spinal dorsal horn. The number of cells expressing oestrogen receptors displayed a small (13.6%) but significant (P=0.037) increase in ovariectomised compared with sham-operated rats. These results suggest that the lack of ovarian hormones induces a site-specific increase in the sensitivity to orofacial nociceptive stimulation, and that an up-regulation of oestrogen receptors in the Caudalis subnucleus and C1-C2 dorsal horn may be one of the factors involved in this effect.

Animals↗
PubMed2002

Ascending connections from the caudal part to the oral part of the spinal trigeminal nucleus in the rat.

The brainstem trigeminal somatosensory complex, while sharing many common aspects with the spinal somatosensory system, displays features specific to orofacial information processing. One of those is the redundant representation of peripheral structures within the various subnuclei of the complex. A functional redundancy also exists since a single sensory modality, e.g. nociception, may be processed within different subnuclei. In the present study, we addressed the question whether anatomical connections from the caudal part to the oral part of the spinal trigeminal nucleus may support topographical and functional redundancy within the rat trigeminal somatosensory complex. The retrograde tracer tetramethylrhodamine-dextran was injected iontophoretically into the oral subnucleus of anaesthetised rats. Cell bodies labelled retrogradely from the oral subnucleus were observed in laminae III-IV and V of the ipsilateral caudal subnucleus consistently, and to a lesser degree in lamina I. Such a distribution of retrogradely labelled cells suggested that specific subsets of neurones may relay nociceptive information, and others non-nociceptive information. Furthermore, intratrigeminal connections conserved the somatotopic distribution of primary afferents in the two subnuclei. First, injections of tracer in the dorsomedial and ventrolateral parts of the oral subnucleus resulted in retrograde labelling of the dorsal and ventral parts of the caudal subnucleus respectively. Second, animals that received tracer into the ventrolateral oral subnucleus displayed more caudal labelling than animals that were injected into the dorsomedial oral subnucleus. These findings show the existence of anatomical connections from the caudal part to the oral part of the spinal trigeminal nucleus in the rat. The connections conserve the somatotopic distribution of primary afferents in the two subnuclei. They provide an anatomical substrate for the indirect activation of trigeminal oral subnucleus neurones by somatosensory stimuli through the caudal subnucleus.

Animals↗
PubMed2001

A human oral capsaicin pain model to assess topical anesthetic-analgesic drugs.

Repeated application of capsaicin on the tongue has been used as a human oral pain model to assess topical anesthetic-analgesic drugs. The reliability of the model was evaluated by observing the variability of the response to repeated applications of capsaicin after three successive sessions at 1 day intervals. No session effect was observed for the time course of the visual analogue scale (VAS) scores and the area under the curve, but a significant decrease of VAS peak scores was noted from the first to the third session. The sensitivity of the model was assessed by mouth rinses with three doses of lidocaine (0.25, 0.5 and 1%). Lidocaine significantly reduced the burning pain. This effect was rapid, reversible and dose dependent. It is concluded that the oral capsaicin pain model displays good reliability and sensitivity and allows safe evaluation of candidate topical analgesic and anesthetic drugs.

Administration, Topical↗
PubMed2001

Effects of increased hardness on jaw movement and muscle activity during chewing of visco-elastic model foods.

When food is chewed, sensory feedback adapts the motor program to the characteristics of the food. However, the relationship between the physical properties of different foods and the motor response is poorly understood. In this study, we developed edible and well-controlled model foods in order to describe some of the stimulus-response functions of the food-mastication loop. Four gelatine-based visco-elastic model foods identical in shape and size but differing in hardness were prepared. They displayed reproducible sensory and physical characteristics and were distributed on a wide hardness scale. Electromyographic activity of masseter and temporalis muscles and jaw movements in the frontal plane were simultaneously recorded during mastication in 15 young men with intact dentition and good oral status. Almost all EMG and jaw movement parameters were clearly affected by increasing hardness of model foods. However, it is possible to summarise the results by reducing the number of parameters to three: the number of chewing cycles, EMG activity of any one of the two temporal or the two masseter muscles and the amplitude of the opening mandibular movements. Indeed, these were the best transcriptors of the hardness range of the model foods used in this study. As inferred from these parameter recordings, the food hardness modifications were strongest during the first five strokes, began as early as the first stroke and lasted for the whole sequence.

Adult↗
PubMed2001

Low doses of N-methyl-D-aspartate antagonists in superficial laminae of medulla oblongata facilitate wind-up of convergent neurones.

In this study, a trigeminal model was used in which high threshold C-fibre-evoked activities of convergent neurones located in the subnucleus oralis of the trigeminal complex are modulated through the superficial part, the substantia gelatinosa, of the subnucleus caudalis. The two subnuclei are located 3 mm apart, therefore, it was possible to inject dizocilpine, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, into either the superficial or the deep parts of subnucleus caudalis without interfering with ongoing recording of convergent neurones in subnucleus oralis. A differential NMDA-dependent modulation of wind-up was observed according to the dose and the injection target. (1) The injections of small non-diffusible doses (0.12 microg) of dizocilpine into the superficial part of subnucleus caudalis facilitated wind-up. The effect peaked at 25 min with a mean increase above control of 173+/-31%. Injection (0.5 microg) of either the less active enantiomer dizocilpine or saline into superficial subnucleus caudalis had no significant effect on subnucleus oralis convergent neurones. This suggests that NMDA-dependent interneurones, probably located in substantia gelatinosa of subnucleus caudalis, exert, in normal conditions, an inhibitory control on wind-up of convergent subnucleus oralis neurones. (2) The injection of larger doses (0.5 microg) into the superficial part of subnucleus caudalis induced a predominant inhibitory effect on wind-up. The mean peak effect at 15 min was 46+/-7% compared to control (100%). Small and large doses of dizocilpine injected into the deep part of subnucleus caudalis had a predominant inhibitory effect. The inhibition of wind-up of subnucleus oralis neurones after injection of NMDA receptor antagonists in superficial or deep subnucleus caudalis indicates that wind-up may be due, at least in part, to NMDA activation at synapses that do not involve the recorded convergent neurones.

Animals↗
PubMed2001

Superficial and deep convergent nociceptive neurons are differentially affected by N-methyl-D-aspartate applied on the brainstem surface of the rat medullary dorsal horn.

The activation of N-methyl-D-aspartate receptors is implicated in the spinal and trigeminal processing of nociceptive information conveyed by convergent (wide dynamic range) neurons and particularly in C-fiber-evoked responses elicited by repetitive and high-intensity electrical stimulation of the neuronal receptive field. In this study, the effects of intrathecal NMDA application on the electrically evoked nociceptive responses of trigeminal subnucleus caudalis convergent neurons have been investigated. The total C-fiber-evoked activity triggered by 30 successive stimuli was divided into two components: the C-fiber input response and the 'wind-up' response. Application of 0.1 microg (in 50 microl) of NMDA evoked a bi-directional effect on the total C-fiber-evoked activity of 19 neurons tested. A significant increase in the total C-fiber-evoked activity was observed 15-25 min after the NMDA application for nine neurons located in superficial laminae II and III. In contrast, a significant decrease in the total C-fiber-evoked activity was observed 5-25 min after the NMDA application for 10 neurons located more deeply, in lamina V. The NMDA-induced modifications seen in the total C-fiber-evoked activity were likely a reflection of a significant increase or decrease in neuronal activity evoked by the C-fiber input rather than wind-up of the responses since the latter was not significantly modified by the NMDA application. These results provide evidence for a possible inhibitory role for NMDA-dependent interneurons of the superficial laminae of the medullary dorsal horn on the nociceptive activity of deep convergent neurons.

Animals↗
PubMed2001

Regulation of mandibular postures: mechanisms and clinical implications.

This review argues that (1) the habitual mandibular position is constantly variable and so cannot be considered as a craniomandibular reference point, (2) there is no unique centric relation, (3) mandibular posture greatly depends on head posture, (4) clinical evaluation of the occlusal vertical dimension is mostly empirical, and (5) neither the vertical dimension at rest nor the centric relation can be determined by means of existing instrument-based clinical methods. However, some physiological conditions exist that facilitate the recording of craniomandibular position.

Centric Relation↗
PubMed2001

[Orofacial idiopathic pain: clinical signs, causes and mechanisms].

Atypical facial pain, stomatodynia, atypical odontalgia, masticatory muscle and some temporomandibular joint disorders are grouped together under the category of orofacial idiopathic pain as they reveal numerous common clinical features. For each of these entities, problems of definition and terminology are discussed. Epidemiological and demographic data and a semiological description are given. Proposed diagnostic criteria and some of the causes or mechanisms common to these entities are also described in this article. Firstly, the rôle of female hormones in the physiology and treatment of certain patients is suggested with regard to the marked prevalence of changes in oestrogen levels in patients with orofacial idiopathic pain. Postmenopausal osteoporosis and the hypothesis of neuralgia due to the presence of cavities of osteonecrosis are placed within the context of atypical facial pain. A neuropathic component is suggested for these pain entities. These latter may be linked to a phenomenon of central sensitisation that is induced and maintained by activity in the peripheral tissues. Clinical features of both atypical facial pain and atypical odontalgia have led several authors to advocate the existence of a sympathetic mechanism in the physiopathology of these entities. Moreover, some arguments emphasize similarities with Complex Regional Pain Syndromes of limbs. Lastly, psychosocial components are also considered as a common factor, but it is currently impossible to determine if the pain is the cause or the result of psychosocial problems. Currently, none of these mechanisms can be considered as a single established etiological factor. Indeed, each of these mechanisms can be observed in all types of orofacial idiopathic pain. This leads to the hypothesis that these different mechanisms may act on each target tissue but the details of interaction are still unknown.

Arousal↗
PubMed2000

Variability of the masticatory process during chewing of elastic model foods.

Many studies show a consistent individual chewing pattern; chewing being governed by a pattern generator and regulated by sensory feedback. The aim of this study was to determine the variation in chewing between sessions, replicates and subjects using elastic model foods. Fifteen young male subjects were selected to chew four food products differing in hardness. Four sessions were performed at 1-wk intervals for each subject and, within each session, the four model foods were presented 3 times each. Jaw movement was recorded simultaneously with masseter and anterior temporalis electromyographic activities. Several chewing characteristics increased progressively from one session to the next; the largest increase occurred from the 1st to the 2nd session, with little difference between the last two sessions. No differences were observed between the samples of the same food product within a session. As mastication progressed, the amplitude and speed of the cycles and the muscular work decreased progressively. The first cycle appeared to be very different from the subsequent for all parameters except for occlusal duration. Thus, under our experimental conditions, the origin and amount of variation in chewing patterns were identified and provide information to improve the accuracy and comparability of results in studies of mastication.

Adult↗
PubMed2000

A unified concept of idiopathic orofacial pain: pathophysiologic features.

Atypical facial pain, stomatodynia, atypical odontalgia, and some forms of masticatory muscle and temporomandibular joint disorders all seem to belong to the same group of idiopathic orofacial pain illnesses. The many common clinical features they display have been discussed in a preceding paper. Some of their common pathophysiologic mechanisms are reviewed in this article. The role of female hormones is suggested as a risk factor by the strong female prevalence and by the effects of physiologic and therapeutic modification of estrogen levels in patients with these pain conditions. Osteoporosis, which appears with menopause, and neuralgia-inducing cavitational osteonecrosis have been linked to atypical facial pain. Similar clinical features have also prompted a comparison between atypical facial pain and complex regional pain syndrome of the limbs. The presence of psychosocial factors is also a common feature, but it is not known whether these are causal or whether the pain induces the psychosocial problem. Local inflammatory, infectious, or mechanical irritation as well as minor nerve trauma are frequently reported in these conditions and can also be considered as risk factors. However, none of the above factors can currently be considered as the sole etiologic factor, and instead the following hypothesis is proposed: the idiopathic pain entities depend on one or several neuropathic mechanisms, the development of which is triggered or favored by one or several events or risk factors. Different neuropathic mechanisms may be at work: nociceptor sensitization, phenotypic changes and ectopic activity from the nociceptors, central sensitization possibly maintained by ongoing activity from initially damaged peripheral tissues, sympathetic abnormal activity, alteration of segmental inhibitory control, and hyper- or hypoactivity of descending controls. Research directions that are suggested include epidemiologic approaches to improve the clinical definition of these conditions, studies to test for the factors and mechanisms proposed, and definition of mechanism-based diagnostic and treatment strategies.

Complex Regional Pain Syndromes↗
PubMed1999

Effects of pre-emptive local anaesthesia on tooth pulp deafferentation-induced neuroplastic changes in cat trigeminal brainstem neurones.

Previous work has shown increased excitability of brainstem neurones in the trigeminal (V) subnucleus oralis following the deafferentation produced by tooth-pulp removal. The present study was designed to determine if the changes in oralis neuronal properties seen in cats 1-2 wk after the deafferentation could be blocked by local anaesthesia of the Vth nerve proximal to the sites of pulp injury just before the actual deafferentation. The response properties of neurones recorded in V subnucleus oralis were determined in anaesthetized cats. One or two weeks before neuronal recording, the pulps of the posterior mandibular teeth were removed under local mandibular anaesthesia in one group of cats (group A) and without local anaesthesia in a second group (group B); a third group (group C) had no pulp removal but received local anaesthesia. Consistent with the earlier data, there was a significantly increased incidence of neurones having an enlarged mechanoreceptive field, spontaneous activity and habituating tap sensitivity in group B compared to group C, but no significant differences were found between the two deafferented groups (A and B). As local anaesthesia did not prevent the development of pulp deafferentation-induced changes in the oralis neurones, it is unlikely that an afferent barrage of impulses induced by the deafferentation procedure was responsible for the neuroplastic changes that subsequently developed in the V subnucleus oralis.

Anesthetics, Local↗
PubMed1999

A unified concept of idiopathic orofacial pain: clinical features.

The main features of atypical facial pain, stomatodynia, atypical odontalgia, and masticatory muscle and temporomandibular joint (TMJ) disorders are compared in this article, which included a search of articles indexed in MEDLINE. The fact that their terminology has been the subject of many debates can be considered a consequence of taxonomic difficulties and uncertainties. Epidemiologic studies indicate marked female predominance for all types of idiopathic orofacial pain. There is also a difference in the age of maximal prevalence between masticatory muscle and TMJ disorders and the other entities. The clinical presentations display several symptoms in common. Pain is oral, perioral, or facial and does not follow a nervous pathway. It has been present for the last 4 to 6 months or has returned periodically in the same form over a period of several months or years. The pain is continuous, has no major paroxysmal character, and is present throughout all or part of the day. It is generally absent during sleep. Clinical, radiographic, or laboratory examination does not reveal any obvious organic cause of pain. There is also a frequent presence of certain psychologic factors, personality traits, or life events. Based on these shared characteristics, a unified concept is proposed. Each of these entities belongs to a group of idiopathic orofacial pain and could be expressed in either the jaws, the buccal mucosa, the teeth, the masticatory muscles, or the TMJ.

Chronic Disease↗