Search

International audience; A large number of methodological procedures and experimental conditions are reported to describe the masticatory process. However, similar terms are sometimes employed to describe different methodologies. Standardisation of terms is essential to allow comparisons among different studies. This article was aimed to provide a consensus concerning the terms, definitions and technical methods generally reported when evaluating masticatory function objectively and subjectively. The consensus is based on the results from discussions and consultations among world-leading researchers in the related research areas. Advantages, limitations and relevance of each method are also discussed. The present consensus provides a revised framework of standardised terms to improve the consistent use of masticatory terminology and facilitate further investigations on masticatory function analysis. In addition, this article also outlines various methods used to evaluate the masticatory process and their advantages and disadvantages in order to help researchers to design their experiments.

Objectives Following chewing a solid food, the median particle size, X50, is determined after N chewing cycles, by curve-fitting of the particle size distribution. Reduction of X50 with N is traditionally followed from N ≥ 15–20 cycles when using the artificial test food Optosil®, because of initially unreliable values of X50. The aims of the study were (i) to enable testing at small N-values by using initial particles of appropriate size, shape and amount, and (ii) to compare measures of chewing ability, i.e. chewing efficiency (N needed to halve the initial particle size, N(1/2-Xo)) and chewing performance (X50 at a particular N-value, X50,N). Design 8 subjects with a natural dentition chewed 4 types of samples of Optosil particles: (1) 8 cubes of 8 mm, border size relative to bin size (traditional test), (2) 9 half-cubes of 9.6 mm, mid-size; similar sample volume, (3) 4 half-cubes of 9.6 mm, and 2 half-cubes of 9.6 mm; reduced particle number and sample volume. All samples were tested with 4 N-values. Curve-fitting with a 2nd order polynomial function yielded log(X50)-log(N) relationships, after which N(1/2-Xo) and X50,N were obtained. Conclusions Reliable X50-values are obtained for all N-values when using half-cubes with a mid-size relative to bin sizes. By using 2 or 4 half-cubes, determination of N(1/2-Xo) or X50,N needs less chewing cycles than traditionally. Chewing efficiency is preferable over chewing performance because of a comparison of inter-subject chewing ability at the same stage of food comminution and constant intra-subject and inter-subject ratios between and within samples respectively.

Following chewing, the particle size distribution (PSD) by cumulative volume is characterized by X50, and b. Volume data are lacking when using less time-consuming optical scanning instead of sieving for characterizing PSDs. The aim was to transform 2D scanning data to 3D ones. Optosil® and almond were used as artificial and real solid foods, and minimal Feret-diameter (min-FD) as a measure of particle size. Border min-FDs were calibrated as a function of sieve aperture to determine size classes. Flakes produced by chewing were considered as ellipsoids. The ratio between the largest and the intermediate ellipsoid's radius was known by scanning. The ratio between the smallest and the intermediate radius was adjusted with Solver of Excel® to minimize the difference between the estimated total volume of the particles, and the known total volume. Estimated values of X50 and b from scanning closely approached those from sieving, the ‘gold standard’.

Studies on relationships between chewing ability (CA) and flavor perception that use different test foods to determine both functions, include three assumptions: (1) inter-subject ratios of any CA measure are invariant to the test food, (2) CA is invariant to the subject’s amount of attention to the food, and (3) the value of CA is invariant to the nature of the flavor released. The present study used chewing efficiency (CE), the number of chewing cycles needed to halve the initial particle size, as a measure of CA with specific inter-subject ratios. The aim was to examine whether CE is affected by perceiving solely the release of flavor during habitual chewing, and by the combination of perceiving the release and its scoring of Time Intensity (TI), with attention to TI anyhow. CE was determined for 12 subjects in three sessions, using Optosil® as an artificial solid model food. Unflavored taste-less Optosil was used in session-1, with habitual chewing. Optosil flavored with 0.3% of the sweetener Neotame was used in session-2, with habitual chewing without TI scoring of flavor release. Flavor was released and TI was scored in session-3. The effect of flavor release and TI scoring on CE was highly significant (p = 0.0008; one-way ANOVA; paired observations). With respect to unflavored Optosil, CE improved 14.0% for habitual chewing on flavored Optosil, and 23.2% for additionally scoring TI of flavor release. Common conditions of test food, flavor and scoring are required for determining unbiased relationships between CE and perceived flavor release.

Objectives Food comminution during chewing is due to intra-oral particle selection and subsequent breakage. Under conditions of habitual chewing and a nearly complete selection, the influence of initial breakage on particle size reduction was studied in trials with a first chewing cycle (N = 1) from a sequence of randomized trials with various cycle numbers. Furthermore, relationships were examined between degree of fragmentation from breakage (r-fr), molar maximal bite force (MBF) and chewing efficiency (the number of cycles needed to half the initial particle size, N(1/2-Xo)). Design Thirty-one subjects with a natural dentition chewed samples of 2 half-cubes (9.6 × 9.6x4.8 mm) of Optosil®, using sequences with 1-7 cycles, in 2-10 randomized trials; 10 trials with one cycle. Particle size distributions by underweight, characterized by median particle size, X50, were obtained using sieving. N(1/2-Xo) was derived from the log(X50)-log(N) relationship. and r-fr from the cumulative distribution of underweight fractions of damaged particles for N = 1. MBF was determined on both sides of the jaw using a force transducer and averaged. Conclusions A strong, decreasing regression occurred in X50 at N = 1 with r-fr (R2 = 0.934, p

A test using a solid food is relevant to measure chewing ability (CA) as (a) it includes an integrated functioning of all oral structures involved, (b) an impairment of chewing a solid food causes inevitably diet restrictions, and (c) chewing efficiency (CE) can easily be defined. CE is the number of chewing cycles, N(1/2-Xo), needed to attain a particular chewing outcome (a median particle size, X 50 , which is half the initial particle size Xo) whereas chewing performance (CP) is a state of chewing outcome (X 50 ) at an arbitrary number of chewing cycles. The use of CE is preferable for CA because inter-subject ratios are constant regardless of the initial conditions of the test food. Furthermore, the inter-subject variation is two times larger for CE values than for CP ones, yielding a better inter-subject differentiation of CA. However, a determination of CP needs only one N-value, and that of CE at least two N-values for enabling an interpolation of N(1/2-Xo). Using samples of only two half-cubes (9.6 x 9.6 x 4.8 mm; limiting test load) of Optosil (an artificial test food), and detailed previous information on log(X 50 )-log(N) relationships (Liu et al., Archives of Oral Biology, 2018, 91, 63-77) as a "gold standard," a short procedure has been developed for a priori choosing two appropriate N-numbers, and the subsequent determination of a subject's CE. This procedure has been developed using results from 20 young adults (23.7 years, SD 1.1) and was validated in 10 middle-aged and older adults (52.3 years, SD 10.1), where impairments in the dentition were reflected in the CE-values. Our short procedure to determine CE will improve studies on relationships between CA and food preference, or between CA and dental factors and/or physiological factors. The first type of relationship may be of interest for food industry whereas the second type may be of interest for population studies in rapidly aging societies and for clinical studies in dentistry. Results can be compared between subjects and studies without bias by using CE rather than CP as a measure of CA.

Objectives With an increasing number of elderly in China, it becomes imperative to establish a comprehensive understanding of their physiological capabilities and investigate fundamental mechanisms underpinning the discrepancies between Chinese individuals and other ethnical groups, which will facilitate government policymaking, design and development of special food products. Design In this study, 100 healthy Chinese subjects in the eastern region of China (22–89 years old) were recruited with full consent, then divided into young adult, middle-aged and elderly groups. Subjects’ maximum biting force (MBF), maximum tongue pressure (MTP), maximum oral volume (MOV), and saliva flow rate were recorded. Unstimulated (US) and stimulated (SS) saliva were collected. Subjects were then objectively clustered into 3 different levels of oral processing capability. A total of 10 young subjects from two different clusters were selected for chewing efficiency (CE) determination. Conclusions With increased age, there is a decline in subject’s dental status, MBF and MTP. Gender affects greatly on MOV; males have larger MOV. No significant effects on SS and US flow rate were found with age and gender. The finding of a similar CE and differences in overall capability in relevant physiological variables (MBF and MOV in young adults) suggest that the degree of CE is not determined by a total capability of various oral physiological variables. In contrast, the findings suggest that CE will be non-impaired as long as each of the relevant physiological variables (i.e. dental status, MBF) operates at a supra-threshold level.

Objectives Food particles are intra-orally locked up between antagonistic posterior teeth, during each chewing cycle. Food locking up (FL) may enhance selection of particles for subsequent breakage, hence chewing efficiency (CE). The two aims were to determine FL, and to examine the relationship between FL and CE. Design A spherical gum bolus (volume: 1.3 cm3) that undergoes plastic deformation rather than breakage, was used to determine FL in 20 young adults. Chewing such a bolus with initially a width-length ratio of 1, decreases this ratio, the more locking up elongates the bolus to a greater extent by pressing from the tongue, teeth, and a cheek. Before and after chewing randomly for 2–6 cycles (3 trials each), the bolus was scanned and its width-length ratio was determined using imaging. The number of chewing cycles needed to attain a width-length ratio of 0.5, N(0.5 W-L ratio) was a measure of FL. CE corresponded with the number of cycles needed to halve the initial particle size, N(1/2-Xo), when chewing samples of 2 half cubes (9.6 × 9.6 × 4.8 mm; sample volume: 0.88 cm3) of a solid artificial model food. Conclusions N(0.5 W-L ratio) and N(1/2-Xo) were on average 3.21 cycles (SD 1.14) and 4.04 cycles (SD 1.87) respectively. Whereas a relationship between CE and FL was lacking for subjects whose CE was worse than the median, a pronounced quadratic U-shaped relationship (R2 = 0.75; p

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. Muscle Nerve, 48: 256–264, 2013

Background Temporomandibular Disorders (TMD) may be characterized by pain and restricted jaw movements. In the absence of somatic factors in the temporomandibular joint, mainly myogenous, psychobiological, and psychosocial factors may be involved in the aetiology of myogenous TMD. An occlusal appliance (splint) is commonly used as a basic therapy of the dental practice. Alternatively, a type of physiotherapy which includes, apart from massage of sore muscles, aspects of cognitive-behavioural therapy might be a basic therapy for myogenous TMD. Treatment outcome of physiotherapy (Ph-Tx) was evaluated in comparison to that of splint therapy (Sp-Tx), using the index Treatment Duration Control (TDC) that enabled a randomized controlled trial with, comparable to clinical care, therapy-and-patient-specific treatment durations. Methods Seventy-two patients were randomly assigned to either Ph-Tx or Sp-Tx, with an intended treatment duration between 10 and 21 or 12 and 30 weeks respectively. Using TDC, the clinician controlled treatment duration and the number of visits needed. A blinded assessor recorded anamnestic and clinical data to determine TDC-values following treatment and a 1-year follow-up, yielding success rate (SR) and effectiveness (mean TDC) as treatment outcomes. Cohen’s d, was determined for pain intensity. Overall SR for stepped-care was assessed in a theoretical model, i.e. a second of the two studied therapies was applied if the first treatment was unsuccessful, and the effect of therapy sequence and difference in success rates was examined. Results SR and effectiveness were similar for Ph-Tx and Sp-Tx (long-term SR: 51–60%; TDC: −0.512– −0.575). Cohen’s d was 0.86 (Ph-Tx) and 1.39 (Sp-Tx). Treatment duration was shorter for Ph-Tx (on average 10.4 weeks less; p

Color- and form-labeled particles of Optosil (version 1980, a silicone rubber, Bayer, Leverkusen, Germany) have been used previously to quantify the underlying processes of food comminution, i.e., selection and breakage, in subjects with normal dentitions. The aim of this present study was to develop a weakened Optosil that is suitable for the study of selection and breakage in subjects with impaired chewing ability. Half cubes (4.8 × 9.6 × 9.6 mm) were subjected to load tests to determine the force, deformation and work at particle fracture for periods of up to 6 months. Methods of modifying Optosil were (1) heat-treating the base material to produce “Optosoft”; (2) mixing the base of Optosil or Optosoft with a nonprescribed catalyst (Verone, Davis Schott Lander & Davis Ltd, Herts, England) to produce “Optoweak” or “Optosoft-weak” and (3) heating half cubes that were preweakened. A weakened and stable test food that is suitable for labeling and reuse has been obtained by color-dyeing the Optosoft base and using Verone (“dyed-Optosoft-weak”). PRACTICAL APPLICATIONS Every chewing cycle begins with selection, in which food particles have a chance to be placed between the teeth in such a way that they are at least damaged, if not broken, by the subsequent breakage process. Bite force is reduced in certain patients, e.g., patients with neuromuscular diseases, following orthognathic surgery and in full denture wearers, and the action of the tongue and cheeks differs when compared with healthy individuals. Both factors are important in selection and breakage. The artificial test food Optosil has a large fracture force so that it is difficult to chew for subjects with an impaired chewing ability. This problem has been solved by developing a weaker test food, i.e., “dyed-Optosoft-weak.” This test food allows the study of selection and breakage in general with color- and form-labeled particles and to determine the effect of medication, orthognathic surgery or oral implants on these processes.

The influence of auditory and/or visual information on the neuromuscular control of chewing a crispy food was investigated. Participants chewed biscuits of three different levels of crispness under four experimental conditions: no masking, auditory masking, visual masking, and auditory plus visual masking. The order of the four masking condition blocks was randomized. The sound of chewing was masked by loud sounds on a headphone, and visual masking of the food was achieved by closing the eyes. Mechanical tests were performed on the biscuits to determine their characteristics, yield force, and sound production. Skull vibration, jaw-muscle activity, and jaw movement were measured while the subjects chewed and swallowed the food. Auditory and/or visual masking did not have a significant effect on skull vibration, muscle activity, and number of chewing cycles until swallowing. However, auditory and/or visual masking significantly increased the chewing cycle duration, but only for the participants who started the experiments with auditory and/or visual masking. The other participants were not influenced by masking. The memory of the unmodified stimuli helped these subjects to maintain their habitual chewing rate in later trials.

A within-patient change in pain score after treatment is statistically 'reliable' when it exceeds the smallest detectable difference (SDD). The aims of the present study were to: (i) determine SDDs for VAS-scores of pain intensity, for sufficiently long test-retest intervals to include most biological fluctuations, (ii) examine whether SDD is invariant to baseline score, and (iii) discuss the value of reliable change (RC) for detecting clinically important difference (CID) or as a possible indicator of successful treatment. SDDs were determined using duplicate data from 118 patients with myogenous Temporomandibular disorders: (1) VAS-scores of pain intensity from the masticatory system in a pre-treatment diary, and (2) VAS-scores of pain intensity from the hand (cold-pressor test). RC was determined in VAS-scores from a pre- and post-treatment questionnaire. The long-term SDD was 49mm. A regression analysis on duplicate VAS-scores showed that SDD was largely invariant to the baseline level. Because RC (change>SDD) exceeded CID, it might serve as an indicator of successful treatment. However, only 17% of the patients showed RC after treatment, mainly because the baseline was smaller than SDD in 67% of the patients thus making detection of any treatment effect impossible. For patients with possible detection (33%), the frequency of RC was 51%. If the detection threshold would be avoided by provoking pain in patients with a low baseline, a long-term RC in VAS-scores might occur in about half of all myogenous TMD patients and might then serve as an indicator of cases of treatment success.

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.

Studies of the masticatory process show that besides the rhythmic character of the chewing cycles much variability in the movement trajectories can be observed. This is related to differences in food texture, but even in chewing one type of food there are considerable variations between chewing cycles in movement trajectories, cycle time and muscle activity of cycles. This indicates that sensory information in actual cycles plays a role in the control of jaw muscle activity during chewing. Notwithstanding the differences between cycles a force always has to be built up to overcome the food resistance or to fragment the particles to smaller ones. Before the next cycle starts, the bite force has to stop. Muscle spindles and periodontal mechanoreceptors are important in the jaw muscle response to loading. This was demonstrated in experiments with anesthetized rabbits where chewing movements were evoked by cortical stimulation and a hard object was placed between opposing molars. In our own observations in humans, where a resisting force disturbed cyclic open-close movements in the closing phase (simulated chewing), the role of muscle spindles and periodontal receptors was confirmed. When jaw closing suddenly accelerates after a decrease in load, such as during unloading of a static bite force, the muscle force quickly decreases. This jaw muscle response, preceding the neuromuscular response, is mainly due to intrinsic muscle properties. Although there is some understanding of the main processes that control muscle force during chewing, the fine tuning of the muscle activity and many details of the control are still object of investigation.

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.

Comminution of food is the composite result of selection and breakage. Selection is characterised by the chance that a food particle will at least be damaged by the teeth during chewing. For any size, this chance equals the ratio between the weight of damaged or broken particles and that of all initial particles. The breakage process refers to fracturing of selected particles. The aim was to examine whether a reduced chewing performance of pre-orthognathic surgery patients is due to an impairment of selection, breakage or both. Eight cubes of 8.0 mm of the silicone-rubber Optosil " were used as a test food to determine chewing efficiency for 12 patients (skeletal Angle Class II and dental Angle Class II, subdivision 1) and 12 controls (class I molar relation). Selection and breakage were determined in one-chew experiments using various particle sizes. Chewing efficiency was significantly lower for the patients than for the controls. The selection chance was significantly smaller for the patients, in particular for smaller (< or = 4.8 mm) particles. The degree of breakage was lower for the patients, in particular for medium-sized particles of 4.8 mm. These findings suggest that the reduced chewing performance of pre-orthognathic surgery patients is due to an impairment of both selection and breakage.

Mastication was evaluated in patients with bulbar myasthenia gravis and compared with that of patients with ocular myasthenia gravis, patients in remission who previously suffered from bulbar symptoms, and healthy controls. Bulbar myasthenia gravis may impair mastication due to weakness of the masticatory muscles. The aim of the study was to objectively evaluate the influence of myasthenia gravis on mastication. The subjects chewed a piece of breakfast cake and chewed 1 min on a piece of chewing gum. Surface EMG of the masseter muscle, temporalis muscle and jaw opener muscles was recorded. Statistical analysis revealed that bulbar patients produced significantly less EMG activity in the closing phase of a chewing cycle in both experiments. The EMG of the masseter muscle expressed as percentage of the maximum EMG during maximal clenching showed significantly higher values in the bulbar group than in the other groups. This was not found for the temporalis muscle. It was suggested that bulbar patients use a strategy of limited effort to produce a bolus that can be swallowed. The ocular patients and the patients in remission showed no subclinical impairments in muscle function during chewing.

Many patients with myasthenia gravis who experience bulbar symptoms show a vertical smile, which may have a considerable, and often underestimated, impact on social life. Peri-oral muscle function can be quantified by calculating lip-length and snout indices, which indicate the degree to which a person is capable of smiling and of pursing the lips, respectively. In the present study patients with bulbar myasthenia gravis were compared to patients with ocular myasthenia gravis, patients now in remission (but previously suffering from bulbar myasthenia gravis), and healthy subjects. The lip-length and snout indices of patients with bulbar myasthenia gravis were significantly lower than those of the other groups. The facial impairments were no longer detectable in patients with bulbar myasthenia gravis in remission and no subclinical impairments in lip-length and snout indices were found in the ocular myasthenia gravis group. These findings were consistent with the patients' reports of impairment of smiling and other oral functions. The patients suffering from a vertical smile or other oral impairments were well aware of their condition, most probably because of the social consequences of being unable to smile. The indices could be of importance in the longitudinal evaluation of therapy in individual patients and in pharmacotherapeutical research. We found a low correlation between the lip-length and snout indices, which reflects the capricious pattern of involvement of separate muscles in myasthenia gravis. Therefore both indices deserve special attention if they are used for monitoring myasthenic symptoms.

Successive inhibitory, excitatory, inhibitory and excitatory reflexes (the Q, R, S and T waves of the post-stimulus electromyographic complex (PSEC)), evoked by applying non-painful taps to an incisor tooth, were recorded from the jaw-closing muscles of 15 subjects. The effects on these reflexes of the subjects undertaking mental exercises (MEx) in the form of arithmetic calculations were compared with those of remote noxious stimulation (RNS; application of 3 degrees C to a hand). This was done to investigate whether the previously established effects of RNS were likely to be related to a change in the subject's mental state and/or to direct nociceptive mechanisms. Both MEx and RNS caused increases in EMG activity around the Q-R and S-T transitions of the PSEC, which resulted principally from shortenings of the inhibitory Q and S waves. Reducing the intensity of the tap stimuli, which mimicked condition-induced disinhibition, caused shortenings of the inhibitory waves at latencies similar to the shortenings induced by MEx or RNS. The magnitude of the RNS-induced effect on the ST segment of the PSEC was greater (P

Masticatory muscle strength was quantified in patients with bulbar myasthenia gravis and compared with that of patients with ocular myasthenia gravis, patients in clinical remission (whether or not pharmacological) who previously suffered from bulbar myasthenia gravis, and healthy subjects. Maximal bite force and maximal activity of the masseter and temporalis muscles and of the submental muscle complex were measured. Bite force was decreased in the patients with bulbar myasthenia gravis, but was normal in the patients in the clinical remission group and in the ocular group. These findings were consistent with the results of electromyographic data. Although subjective reports of masticatory muscle weakness provide valuable information, quantitative measurements provide more information about the degree of muscle weakness of individual muscles. This is especially important for longitudinal evaluation of therapy in individual patients and for pharmacotherapeutic research.

In man, the principal exteroceptive reflexes evoked by intra-oral stimulation involve the jaw-closing muscles and include inhibitory and excitatory responses [H.W. van der Glas, A. De Laat, D. van Steenberghe, Oral pressure receptors mediate a series of inhibitory and excitatory periods in the masseteric post-stimulus EMG complex following tapping of a tooth in man, Brain Res. 337 (1985) 117-125.]. These reflexes can be observed in electromyograms (EMGs) recorded with bipolar surface electrodes. The likelihood that these reflexes play important roles in the integrative actions of the jaw has led to interest in the physiological control mechanisms by which they may be modulated. It has been reported recently that the complex series of jaw reflexes evoked by non-painful tapping on human teeth can be modulated by the application of noxious stimulation to the hand [S.W. Cadden, H.W. van der Glas, F. Lobbezoo, A. van der Bilt, Effects of remote noxious stimulation on exteroceptive reflexes in human jaw closing muscles, Brain Res. 726 (1996) 189-197.] or by exercises which produce a change in mental state [S.W. Cadden, H.W. van der Glas, F. Lobbezoo, A. van der Bilt, The influence of attentional factors on short- and long-latency jaw reflexes in man, Arch. Oral Biol. 41 (1996) 995-998.]. The effects of remote noxious stimuli and mental exercises usually involved transient increases in electromyographic (EMG) activity around the interfaces between the successive inhibitory and excitatory reflexes. As the mechanisms underlying the tap-induced inhibitory and excitatory reflexes may show some temporal overlap [H.W. van der Glas, A. De Laat, D. van Steenberghe, Oral pressure receptors mediate a series of inhibitory and excitatory periods in the masseteric post-stimulus EMG complex following tapping of a tooth in man, Brain Res. 337 (1985) 117-125.], these condition-induced increases in EMG activity could, in the simplest hypothesis, have been due to either (i) a condition-induced inhibition of the tap-induced inhibitory influences on the motoneurones (i.e., disinhibition) and/or (ii) a condition-induced facilitation of the tap-induced excitatory influences underlying the subsequent excitatory reflexes. In the present protocol, we describe how it is possible to differentiate between these different underlying mechanisms. The method includes a regression analysis of the relationship between condition-induced changes in amplitude of a reflex and the reflex amplitude under control conditions after taking account of the effect of chance. The analysis is applied on reflex data pooled from various subjects. Although this method of data analysis is illustrated with trigeminal reflexes, it is potentially of use for other complex extracellular recordings including those in other fields of motor control (e.g., EMGs from muscles other than jaw ones).

Sensory disturbance following orbitozygomatic complex fractures was studied in 65 patients from 4 treatment groups which represented potentially varying degrees of sensory disturbance. The fracture-type-dependent treatments were: no surgical intervention ( n =20), closed reduction with or without wire fixation ( n =17), open reduction with miniplate fixation ( n =15) and/or reconstruction of the orbital floor ( n =13). In order to assess the sensory function of different classes of afferent fibres, several methods of sensory testing were applied. On average 6.3 months after treatment, the patient's report was obtained, and tests regarding touch, two methods of two-point discrimination, and cold were applied on the cheek and upper lip. The degree of sensory disturbance was method-dependent. In patients who underwent closed reduction, pronounced levels of positive correlation occurred between results from different tests or from both test sites. The levels of these correlations were, in general, low for all other treatments. These findings suggest that afferent fibres of both large and small diameter tended to be permanently damaged in the patient group with closed reduction. In contrast, the types of sensory afferent fibres that were involved in the trauma and/or their recovery were highly variable within patients and sites for all other treatment groups.

Sensory disturbance following orbitozygomatic complex fractures was studied in 65 patients in relation to type of fracture and method of treatment. The fracture-type-dependent treatments were: no surgical intervention (n=20), closed reduction with or without wire fixation (n=17), open reduction with miniplate fixation (n=15) and/or reconstruction of the orbital floor (n=13). Several methods were applied to assess sensory function, on average 6.3 months after treatment, i.e. the patient's report and tests regarding touch, two methods of two-point discrimination, and cold, all applied on the cheek and upper lip. The various examinations indicated that, on average, the long-term sensory disturbance was most pronounced and severe in patients who underwent closed reduction without miniplate fixation. As the sensory disturbance of patients with open reduction and miniplate fixation approached the base-line level of patients for whom surgical intervention was not indicated, open reduction with miniplate fixation can be recommended as treatment for frontozygomatic suture fractures. The degree of sensory disturbance of patients who underwent orbital floor reconstruction was intermediate compared to patients with closed and open reduction respectively.

Skinfold measurements by means of calipers and the use of linear regression functions, representing relationships between maximal EMG activity and skinfold thickness, provide a simple and non-invasive procedure to diminish the influence of the thickness of the subcutaneous tissues overlying jaw-elevator muscles on electromyographic data of the maximal voluntary contraction (MVC) level. This method, which allows an improved comparison between different subject or muscle groups in terms of neuromuscular capacity, has been applied to MVC values from the masseter and the anterior temporal muscles (surface EMG) of 21 healthy males, 14 healthy females, and 14 females suffering from myogenous temporomandibular disorders (TMD). Non-corrected MVC values from both muscle groups were larger for the male controls than for the female controls. As the skinfold thickness was smaller for males than for females, these MVC levels did not differ significantly after correction for skinfold thickness. As the skinfold thickness was very similar for the female TMD patients and the controls, the correction method did not appreciably change the lower MVC values of the TMD patients.

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.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.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.The method described enables responses to low- or high-intensity stimulation of human pulpal nerves to be investigated in long experiments.

The influence of auditory and/or visual information on the neuromuscular control of chewing a crispy food was investigated. Participants chewed biscuits of three different levels of crispness under four experimental conditions: no masking, auditory masking, visual masking, and auditory plus visual masking. The order of the four masking condition blocks was randomized. The sound of chewing was masked by loud sounds on a headphone, and visual masking of the food was achieved by closing the eyes. Mechanical tests were performed on the biscuits to determine their characteristics, yield force, and sound production. Skull vibration, jaw-muscle activity, and jaw movement were measured while the subjects chewed and swallowed the food. Auditory and/or visual masking did not have a significant effect on skull vibration, muscle activity, and number of chewing cycles until swallowing. However, auditory and/or visual masking significantly increased the chewing cycle duration, but only for the participants who started the experiments with auditory and/or visual masking. The other participants were not influenced by masking. The memory of the unmodified stimuli helped these subjects to maintain their habitual chewing rate in later trials.

The force-deformation characteristics of two artificial test foods (Optosil and Optocal) for measurements of food comminution during mastication were investigated in a bite simulator and compared with those of carrots and peanuts. The influence of cusp geometry was evaluated by use of a flat plate and three cusp forms. The forces at the yield point were lower for Optocal than for Optosil artificial test food. The forces needed for Optocal overlapped those needed for carrots and peanuts. The natural foods showed more variation in the force and percentage of deformation at the yield point than the artificial foods. The artificial foods reflected the differences in cusp form better than did the natural foods. The use of artificial foods fulfills a need for standardization and warrants consideration in studies of mastication.

Food comminution during chewing is the composite result of selection and breakage. In the selection process, every food particle has a chance of being placed between the antagonistic post-canine teeth and being subjected to subsequent breakage. The selection chance, being the ratio between the number of selected and offered particles, has been mathematically described as a function of the number of particles offered, in terms of the number of breakage sites available on the teeth and particle affinity, i.e. the fraction of breakage sites occupied by one particle. The assumption has been made that particles are successively selected during a jaw-closing phase and that the selection chance of subsequent particles having the opportunity to occupy a breakage site proportionally decreases with the unoccupied fraction of the breakage sites left. The number of selected particles of a single size then asymptotically approaches the total number of breakage sites available for that size, when the number of particles offered increases. The critical particle number, derived from the measure of particle affinity, indicates the number of particles by which the breakage sites become saturated. The selection model for single particle sizes has been successfully applied to describe one-chew experiments, using various numbers and sizes of particles made of a silicone-rubber. After pseudo-chewing movements the subjects were unexpectedly instructed to carry out a real chew on particles (half-cubes). Undamaged, hence non-selected half-cubes could afterwards be distinguished from broken particles. The model has been extended to a particle mixture to describe the selection of particles of a certain size while other particles of different sizes are present. If a two-way competition between smaller and larger particles is assumed, the model predicts that the ratios of the selection chances between different particles sizes do not depend upon the numbers of the particles in the mixture.

To assess self-perceived oral function of patients with oral cavity cancer at different stages of treatment, ie, before oncologic intervention, 5 weeks after intervention, and 5 years after intervention.A cohort of 158 patients with malignancy in the oral cavity treated by surgery in 1999 or 2000 was included. From this cohort we interviewed 69 patients by telephone in 2005 and collected data on dental status, disorders of chewing and swallowing, xerostomia, preference of food consistency, tube nutrition, weight loss, and speech for different stages of treatment.For patients treated in the maxilla region we observed a significant (P.05) recovery of perceived chewing ability after 5 years to the level experienced before oncologic intervention. Patients treated in the mandible region reported a deteriorated dental state, chewing ability, lip competence, and xerostomia after 5 years. Patients treated in the tongue and mouth-floor region experienced deterioration for dental state, chewing ability, and xerostomia after 5 years compared with the level before the oncologic intervention.Our telephone interview on oral function provided supplementary information on how patients experienced their problems with oral function during various phases of oncologic treatment. A retrospective interview may thus help to add information to incomplete retrospective data.

Maximum voluntary bite force has often been studied as an indicator of the functional state of the masticatory system. Bilateral, as well as unilateral, methods have been used to determine bite force. Only a few studies have compared the outcomes of both methods. The aim of this study was to measure bite force and jaw-muscle activity during bilateral as well as unilateral maximum clenching in a large number of healthy subjects, so that the results could be compared. In a group of 81 dentate subjects we observed an average bilateral bite force of 569 N. The average unilateral bite force was significantly lower, being 430 N (right) and 429 N (left). Masseter and anterior temporal muscle activities were also significantly lower during unilateral clenching as compared with bilateral clenching. The masseter muscles showed no difference in activity between the ipsilateral side and the contralateral side during unilateral clenching. In contrast, the activity of the anterior temporal muscle on the ipsilateral side was significantly higher than on the contralateral side. Thus, the change in the forces acting on the jaw during unilateral clenching compared with bilateral clenching leads to a different response in the temporal muscles than in the masseter muscles.

A within-patient change in pain score after treatment is statistically ‘reliable’ when it exceeds the smallest detectable difference (SDD). The aims of the present study were (i) to determine SDD for scoring pain behavior on a 0–5 point adjectival scale, and (ii) to explore the relationship between SDD, clinically important difference (CID) and effect size (ES) following treatment of known efficacy, and to compare these parameters of pain behavior with those of VAS-scores of pain intensity [van Grootel RJ, van der Bilt A, van der Glas HW. Long-term reliable change of pain scores in individual myogenous TMD patients. Eur J Pain 2007;11:635–43]. SDD was determined using duplicate scores on pain behavior from a pre-treatment diary that was completed by 118 patients with myogenous temporomandibular disorders (TMD). CID was determined as the mean change in score following treatment, and Cohen’s ES as the ratio between mean change and SD of baseline values. The SDDs were 2–3 units (40–60% of the scale range) for test–retest intervals of 1–13 days. CID was 1.13 units (22.6%) and ES was 1.38. The normalized SDD and CID values and ES were similar for VAS-scores of pain intensity, i.e., 38–49% (SDD), 24.2% (CID) and 1.09 (ES). Because reliable change (change > SDD) exceeds CID, the responsiveness of scoring of pain variables is low for detecting CID. The finding of ES values that are larger than 0.5 (ES for patients with chronic degenerative diseases [Norman GR, Sloan JA, Wyrwich KW. Interpretation of changes in health-related quality of life. The remarkable universality of half a standard deviation. Med Care 2003;41:582–92]) suggests that for myogenous TMD (chronic pain not caused by somatic disease and with a large chance on recovery following treatment), there are higher expectations of what constitutes important change.

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.

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.

Purpose Previous studies have shown that patients with mandibular retrognathism who were scheduled for orthognathic surgery have a lower maximum bite force and an impaired chewing performance. Surgical correction of this deformity is supposed to lead to an improvement of these oral functions. One year after surgery, no significant changes could be shown in these patients. However, a longer follow-up might demonstrate an improvement after all. Patients and Methods Maximum bite force and chewing performance were determined in 12 patients with a mandibular retrognathism before mandibular advancement surgery and at least 5 years after surgery. Chewing performance (median particle size) was determined with a sieving method after chewing 15 strokes on an artificial test food. Maximum bite force was recorded bilaterally at the level of the first molars. Results Five years after surgery, chewing performance was improved, especially in patients with a poor performance before treatment. An increase of the maximum bite force could not be shown. Conclusion Surgical correction of mandibular retrognathism had a positive effect on oral function 5 years after surgery, although it could not be detected 1 year after surgery. However, the function of the masticatory system was still impaired when compared with controls.

Objectives: Myogenous temporomandibular disorders are characterized by jaw muscle pain. The aims were: 1) to characterize this pain generally in terms of intensity, frequency, duration, and behavior across a period of 2 weeks; 2) to identify main intraday pain patterns and to examine whether subgroups of patients in this respect differed in clinical, demographic, pain and sleep variables, psychosocial factors, and use of medication; and 3) to investigate some possible interday trends of pain intensity at a group level. Method: One hundred thirty-three patients with myogenous temporomandibular disorders completed a 2-week diary, rating pain intensity (100 mm Visual Analog Scale [VAS]), duration, behavior (verbal 6-point scale), and medication use on 4 times of the day. Furthermore, questionnaires were completed to score pain period before seeking treatment, spread of pain, and demographic, psychosocial, and sleep variables. Results: In the diary, pain intensity, frequency, daily pain duration, and the score of pain behavior were on average 29.1 mm, 69% of the scoring times, 5.5 hours, and 1.8 points (approaching pain present, but I can ignore it at times), respectively. Pain intensity was, on average, maximal late in the day (before dinner or bedtime) for the majority of patients (79%) and early in the day (before breakfast or lunchtime) for the minority (21%). The larger subgroup had a significantly higher daily pain intensity, more frequently a widespread pain and problems with falling asleep at bedtime, agreed more about the role of a physician as an external health locus of control, and had a more distancing coping style. Both subgroups were similar for other variables, most notably in the level of state anxiety and depressive mood, and in a sparse use (7.8% of all possible times) of over-the-counter medication. Daily mean VAS scores, averaged across patients, were approximately constant for the various diary days. Both the daily mean and maximal VAS score were not related to a specific day of the week. Conclusions: Two main daily pain patterns occur in patients with myogenous temporomandibular disorders (79%: maximal pain late in the day; 21%: early in the day), which might be related to differences in processes that influence pain sensitivity and patterns of jaw muscle activation. The interday similarities in pain level suggest that a sustained influence of counseling after the intake or an influence of a common behavioral pattern with a cycle duration of a week are not involved.

Purpose Mandibular retrognathia is a dentofacial deformity that can be surgically corrected. The purpose of this study was to evaluate the influence of orthognathic surgery on masticatory function in a sample of retrognathic patients and to compare these findings with those of controls. Patients and methods Eleven retrognathic patients were tested before and 1 to 1.5 years after mandibular advancement surgery and compared with 12 controls. The median particle size after chewing a silicon rubber test food, the maximum bite force, and the electromyographic activity (EMG) of the anterior temporalis and the masseter muscles during isometric clenching and during chewing were determined. Patients, before and after treatment, and controls were statistically compared by analysis of variance. Results Surgical correction of mandibular retrognathia did not change chewing efficiency, maximum bite force, EMG during maximal clenching, EMG during chewing, or the EMG/bite-force relationship. Compared with controls, the chewing efficiency, maximum bite force, EMG during maximal clenching, and EMG during chewing values were lower. No difference for the EMG/bite-force ratio at maximal clenching was found, indicating similar muscle efficiency for patients and controls. However, in the range of 10% to 40% of the maximum bite force, the slope of the EMG/bite-force regression line was steeper for the patients than for the controls, indicating decreased muscle efficiency for patients. Conclusions The results of this study suggest that in retrognathic patients, function of the masticatory system is impaired. Oral function was not influenced by mandibular advancement surgery.

When an interside comparison is hampered, for example, in cases of bilateral trauma, normal threshold values of two-point discrimination from healthy subjects might be used to delineate abnormal from normal sensory function in patients. To determine threshold pin distances, two devices, the Disk-Criminator and the Aesthesiometer, have often been applied in a clinical setting. Because these devices are hand-operated, the force of applying a device might vary considerably. The general applicability of normal threshold values from the literature may therefore be questioned. Five subjects participated in experiments with two observers, in which a hand-operated device with a constant pin distance (5 or 10 mm) was pushed on a facial site, until the point at which blanching of the skin started, and the applied force was recorded. To that end, the devices were modified by providing them with force transducers. These recordings revealed a considerable variation in force variables (level, duration, and rate). Significant differences in mean force level, duration, and rate occurred, particularly between devices, pin distances, and/or sites (cheek, upper and lower lips, and mental region) and also in mean duration between observers (p < 0.01 to 0.001, analysis of variance). However, the observed force levels were always at an extremely supra-threshold stimulus intensity. The threshold pin distances in subsequent experiments (four subjects, the two devices and two sites: cheek and mental region) were therefore almost invariant to the difference in the extreme low and high force levels that were applied, using acoustic feedback on the force signal. Furthermore, these thresholds were also similar when one or two observers performed repeated measures on groups of 15 to 18 subjects under the influence of a usual variation of force level, using an interval of at least 1 week and both nonmodified devices. Because of invariance, normal values of threshold pin distance are generally applicable to any well-trained observer and are related to the density of afferent nerve fibers. In contrast, recently reported force thresholds determined at a constant pin distance might not be related to fiber density only. The findings regarding dependency on site and pin distance of the force level suggest that force thresholds will also be related to tissue stiffness and to the extent to which a pair of pins co-operate mechanically.

1. To test the colour pattern hypothesis ofE-vector orientation in the honeybee (van der Glas, 1975) menotactic orientation to unpolarized overhead patterns, in which the colours blend in a gradual transition from one to the other (Fig. 2; stimulus field: 17.7°), has been studied by observation of bees dancing on a horizontal comb. 2. When the patterns are of colours of short wavelength, dances are well oriented with relatively small variance but the angle between the indicated feeding place and the sun's bearing is usually transposed by 180° (Fig. 11). Therefore an unpolarized colour pattern evokes directional dances specifically oriented as if the pattern provided a clue to the sun's bearing. 3. In contrast, when the patterns are made up of bee white (including UV) of different brightness levels (with gradual transition between “light” and “dark”), dance orientation is poor. Hence orientation to the coloured patterns cannot be just a response to brightness or a result of differential stimulation of R9 or the other UV receptors in different overhead areas independent of other receptor types. 4. Evidence is given that the oriented response to the experimental overhead short wavelength colour patterns does not indicate that natural colour- and UV patterns in the sky are used. 5. The fact that bees do orientate to unpolarized colour patterns along with previous data on integrational processes between different types of spectral receptors inE-perception (van der Glas, 1975, 1976), are consistent with a perception mechanism for sky polarization by means of colour coding. On the other hand, the result of the bees' transposition by 180° of the angle between the indicated feeding place and the sun's bearing cannot yet be finally interpreted with any current model for celestial orientation.

Poststimulus EMG complexes (PSECs), consisting of a series of inhibitory and excitatory waves in full-wave rectified and averaged electromyogram (EMG), were elicited in the masseter muscles of 7 subjects following controlled tapping of a tooth, at a controlled clenching level. Applying local anaesthesia to this tooth decreased the total surface of the waves, on average by 89%. The excitatory and the inhibitory waves were similarly affected, indicating that mainly pressure receptors in the periodontium mediate the entire PSEC. In 4 subjects, who were exposed to acoustic noise to exclude a contribution of acoustic receptors, the recovery of the PSEC waves from local anaesthesia was tracked. In 3 subjects, one wave (the first inhibitory or the first excitatory one, respectively) recovered differently from the other waves, indicating that they are not necessarily mediated by one type of afferent axons. The evidence, nevertheless, suggests that the different PSEC waves in man reflect the projection of the periodontal afferents upon several brain structures, involved in the control of the activity of the masseteric motorneurones, as: (1) inhibitory and excitatory control requires different groups of interneurones; and (2) a mediation of the first inhibitory wave by slower conducting axons than the second inhibitory wave, or a mediation of both waves by axons of similar type, is not compatible with common interneurones.

Out of a total of 139 area 19 cells, 87 were examined quantitatively for their responses to stimuli moving at a wide range of velocities. The results were compared with those obtained on a sample of 106 area 17 cells (out of a total of 172) tested in the same way. It was found that both areas 19 and 17 prefer slow stimulus movement. However, area 17 responded well to velocities up to 4 degrees/s while response amplitudes of area 19 cells started to decrease for stimulus velocities over 0.3 degrees/s. In both areas, responsiveness to fast stimuli improved at higher eccentricities. The most frequently encountered velocity type in area 19 was the 'velocity broad band' (VBB) type, lacking velocity preference, while the rarest type was the 'velocity tuned' (VT) type. As in area 17 very few area 19 cells were found to prefer high velocities (velocity high pass type, VHP) and those that were encountered had peripheral receptive fields (RFs). Cells preferring exclusively low velocities (velocity low pass type, VLP) were less frequent in area 19 than in area 17 and were considerably more sluggish. Area 19 was also less direction and orientation selective than area 17. In contrast, end-stopping was very common in area 19 (66%) and more units were binocular as compared to area 17. On average firing rate during optimal stimulation was lower in area 19 than in area 17. These results are consistent with the notion that area 19 receives predominantly W-type input and is involved in form discrimination (low spatial frequencies) during fixation.

Post-stimulus electromyogram (EMG) complexes (PSECs) were studied in the full-wave rectified and averaged EMGs of the masseter muscles in 15 subjects, who clenched at a controlled level. The PSECs, a series of downward- and upward-going waves reflecting inhibitory and excitatory influences upon the masseteric motoneurones, were elicited by mechanical stimulation of a tooth. The stumuli selectively activated mechanoreceptors in the periodontium and, by bone-conduction, acoustic receptors. Application of acoustic masking during the periods of stimulation revealed a series of inhibitory and excitatory acoustic influences in the PSEC, which were absent after local electrical stimulation of receptors in the periodontium or their afferents. By applying local anaesthesia to the periodontium of a mechanically stimulated tooth, the durations of the acoustic influences were on the average reduced by 76%. In subjects whose PSECs consistently included a second inhibitory period, the duration of the acoustic influences with respect to that of the PSEC (30%) was larger than otherwise (13%), suggesting a central gating of periodontal pathways which can block both periodontal and acoustic influences. The acoustic influences, of which the appearance in the PSEC largely depends upon activated periodontal pathways, represent a new finding of audio-motor reflexes.

A total of 139 cells from area 19 along with a comparison sample of 172 cells from area 17 were classified using a system proposed by Orban and Kennedy, following Henry and consisting of 4 basic cell ‘families’, namely S,C,A and B, each having an end-stopped member: HS, HC, HA and HB. The two basic parameters separating the 4 families are firstly spatial overlap of ON and OFF subregions and secondly receptive field (RF) width. Spatial overlap was studied quantitatively in a number of these cells using multiple presentations of stationary slits or moving light and dark edges. RF width was determined quantitatively using bars moving at different velocities across the RF. It was found that cells with spatially nonoverlapping and overlapping subregions are present in both areas. S and HS cells, which shows similarities with simple cells, were encountered in area 19 but they constituted only 18% of the population as opposed to 55% in area 17. C and HC cells, reminiscent of complex cells, were about as common in area 19 as in area 17. In both areas C cells were the only group which consistently discharged equally well or better in response to diffuse light turned on and off than when presented with light bars. A and B families formed a minority in both areas. Area 19 contained a larger proportion of nonoriented and undriveable units, as well as a special category of cells preferring stimuli with a width larger than the length (‘rectangle cells’). RF width was generally larger in area 19 than in area 17 and its distribution in area 19 showed distinct peaks. In the part of area 19 subserving central vision these peaks appeared with a periodicity of 0.8°, suggesting that cells in this zone are supplied by one or more rows of a uniform set of afferents having a RF cetner diameter of about 0.8°. The identification of this population as W-relay cells is supported by the long latencies found in cells from this part of area 19. It is concluded that the basic principles underlying the structure of the RF are similar in both areas 19 and 17.

Background Treatment duration varies with the type of therapy and a patient’s recovery speed. Including such a variation in randomized controlled trials (RCTs) enables comparison of the actual therapeutic potential of different therapies in clinical care. An index, Treatment Duration Control (TDC) of outcome scores was developed to help decide when to end treatment and also to determine treatment outcome by a blinded assessor. In contrast to traditional Routine Outcome Monitoring which considers raw score changes, TDC uses relative change. Methods Our theory shows that if a patient with the largest baseline scores in a sample requires a relative decrease by treatment factor T to reach a zone of low score values (functional status), any patient with smaller baselines will attain functional status with T. Furthermore, the end score values are proportional to the baseline. These characteristics concur with findings from the literature that a patient’s assessment of ‘much improved’ following treatment (related to attaining functional status) is associated with a particular relative decrease in pain intensity yielding a final pain intensity that is proportional to the baseline. Regarding the TDC-procedure: those patient’s scores that were related to pronounced signs and symptoms, were selected for adaptive testing (reference scores). A Contrast-value was determined for each reference score between its reference level and a subsequent level, and averaging all Contrast-values yielded TDC. A cut-off point related to factor T for attaining functional status, was the TDC-criterion to end a patient’s treatment as being successful. The use of TDC has been illustrated in RCT data from 118 chronic pain patients with myogenous Temporomandibular Disorders, and the TDC-criterion was validated. Results The TDC-criterion of successful/unsuccessful treatment approximated the cut-off separating two patient subgroups in a bimodal post-treatment distribution of TDC-values. Pain intensity decreased to residual levels and Health-Related Quality of Life (HRQoL) increased to normal levels, following successful treatment according to TDC. The post-treatment TDC-values were independent from the baseline values of pain intensity or HRQoL, and thus independent from the patient’s baseline severity of myogenous Temporomandibular Disorders. Conclusions TDC enables RCTs that have a variable therapy- and patient-specific duration.