Hilbert W. van der Glas

Force-deformation properties of artificial and natural foods for testing chewing efficiency

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.

Infraorbital nerve function following treatment of orbitozygomatic complex fractures. A multitest approach.

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 patients 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.

Information on infraorbital nerve damage from multitesting of sensory function

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 patients 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.

Oral Function After Oncological Intervention in the Oral Cavity: A Retrospective Study

PURPOSE 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. PATIENTS AND METHODS 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. RESULTS 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. CONCLUSIONS 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.

Maximal bite force and surface EMG in patients with myasthenia gravis

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.

A selection model to estimate the interaction between food particles and the post-canine teeth in human 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 particle sizes do not depend upon the numbers of the particles in the mixture.

Mechanisms underlying the effects of remote noxious stimulation and mental activities on exteroceptive jaw reflexes in man.

Abstract 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°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 subjects 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<0.01) than that on the QR segment. By contrast, MEx induced similar effects on both segments. Regression analyses were performed for the relationship between condition‐induced changes in amplitude of the excitatory waves and their control amplitudes. These analyses were performed to reveal any condition‐induced inhibition or facilitation of the tap‐induced influences on the motoneurons. Overall, the evidence suggested that: (1) mental exercise induced a similar degree of inhibition of the two tap‐induced inhibitory jaw reflexes and a facilitation of the excitatory ones, and (2) remote noxious stimulation induced an inhibition of the second tap‐induced inhibitory reflex which was greater than that of the first one, and an inhibition of the first excitatory reflex. Thus, although factors related to altered mental activity could play a role in the modulation of jaw reflexes by RNS, the differences between the effects of MEx and RNS suggest that alternative or complementary mechanisms are also likely to be involved.

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

The purpose of the study was to investigate whether jaw reflexes evoked by selective stimulation of periodontal ligament mechanoreceptors 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 ms. 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 °C). In all 10 subjects, the stimuli produced a single period of inhibition of masseteric activity (latency, 12.8 ± 0.4 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; Students 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 may be relevant to disorders of mastication associated with pain.

Long-term reliable change of pain scores in individual myogenous TMD patients

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 49 mm. 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.

Statistically and clinically important change of pain scores in patients with myogenous temporomandibular disorders

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 Cohens ES as the ratio between mean change and SD of baseline values. The SDDs were 2–3units (40–60% of the scale range) for test–retest intervals of 1–13 days. CID was 1.13units (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.