Electrophysiological analysis of rhythmic jaw movements in the freely moving mouse

Although rhythmic jaw movement in feeding has been studied in mammals, such as rats, rabbits and monkeys, the cellular and molecular mechanisms underlying it are not well understood. Transgenic and gene-targeting technologies enable direct control of the genetic makeup of the mouse, and have led to the development of a new category of reagents that have the potential to elucidate the cellular and molecular mechanisms of neural networks. The present study attempts to characterize rhythmic jaw movements in the mouse and to demonstrate its relevance to rhythmic jaw movements found in higher mammals using newly developed jaw-tracking systems and electromyograms of the masticatory muscles. The masticatory sequence of the mouse during feeding was classified into two stages, incision and chewing. Small and rapid (8 Hz) open-close jaw movements were observed during incision, while large and slow (5 Hz) open-close jaw movements were observed during chewing. Integrated electromyograms of the masseteric and digastric muscles were larger during chewing than those observed during incision. Licking behavior was associated with regular (8 Hz), small open-close jaw movements with smaller masseteric activity than those observed during mastication. Grooming showed variable patterns of jaw movement and electromyograms depending on the grooming site. These results suggest that there are neuronal mechanisms producing different frequencies of rhythmic jaw movements in the mouse, and we conclude that the mouse is useful for understanding rhythmic jaw movements in higher mammals.     

Different corticostriatal projections from two parts of the cortical masticatory area in the rabbit

The cortical masticatory area (CMA) elicits rhythmic jaw movements in response to repetitive stimulation and is involved in the control of mastication. Based on jaw movement patterns, the CMA is divided into two parts. One is the part of the CMA in which a T-pattern similar to jaw movements during food transport in natural mastication is evoked by electrical stimulation. The other is more dorsomedially located, and during chewing a C-pattern similar to jaw movements can be induced. However, it is still not known which region of the putamen receives projections from the CMA and whether projections originate from both parts of the CMA. In this study, electrophysiological and histological experiments were undertaken in rabbits to investigate projections from the CMA to the putamen. Both experiments showed that the ventral region of the putamen received projections from the CMA. The density of the projections from the CMA area inducing the T-pattern seemed to be higher than that from the area inducing the C-pattern. Furthermore, the peak latency of the evoked potentials from stimulation of the CMA area inducing the T-pattern was shorter than that from stimulation of the area inducing the C-pattern. The data obtained from the present study indicate the functional role of the ventral region of the putamen in the regulation of mastication, and further suggest that the corticostriatal pathway is involved in the transition between behavioral jaw movement patterns.     

An electromyographic method for the assessment of naloxone-induced abstinence in morphine-dependent rats

Summary The electromyographic (EMG) activities of suprahyoideal muscle were recorded to measure naloxone-precipitated abstinence signs in morphine-dependent rats anesthetized with urethane (1 g/kg). Rats were rendered dependent on morphine by implanting 2 morphine pellets (75 mg each) and abstinence signs were induced by intravenous injections of various doses of naloxone at different times after pellet implantation. Three precipitated abstinence signs, a) myoclonic twitch activity (MTA), b) mastication, and c) body shakes were observed on EMG recordings after the injection of naloxone. Of these symptoms, only the MTA induced by naloxone (10 g/kg) occurred 4 h after pellet implantation and its sensitivity to naloxone increased with prolonged pellet implantation. Both mastication and precipitated shakes could be induced at 24 h. However, higher doses of naloxone were required to produce the shakes than is required to induce mastication. There appears to be a positive correlation between the intensity of naloxone-induced MTA and the degree of physical dependence on morphine. Since the MTA and mastication can be induced by low doses of naloxone in morphine-dependent rats, we suggest that these two parameters may be used to detect morphine abstinence signs in this species.Deceased February 13, 1979     

An index for the evaluation of 3D masticatory cycles stability

ObjectivesTo introduce an index (Masticatory Stability Index, MSI) to analyze the stability of chewing cycles in standardized conditions and test it in a group of patients with subclinical mild temporomandibular disorder (TMD).Design23 subjects with mild subacute TMD and 21 healthy subjects were involved; they all responded to a questionnaire about signs and symptoms of TMD (ProTMDmulti) and underwent a myofunctional orofacial evaluation with scores, using the protocol of orofacial myofunctional evaluation with scores (OMES). Their mandibular kinematics was assessed with a 3D motion capture system during deliberate unilateral gum chewing. The MSI was computed synthesizing the information contained in nine kinematics parameters into a single global figure. Patients’ and controls’ MSI were compared considering the preferred and non-preferred chewing side using a 2-way ANOVA (factors: group, side).ResultsTogether with a lower total score of myofunctional orofacial status, the TMD group showed a reduced stability based on MSI (p < 0.05).ConclusionsThe MSI is an efficient method to measure the stability of the masticatory cycles. These preliminary results encourage validating the index on a larger sample. The variability in the motor behavior of chewing can impair the objectivity of its evaluations in several types of patients, including those with TMD. The MSI could be useful to complement clinical assessments, providing data for planning the rehabilitation of masticatory function in these patients.     

A new evaluation of masticatory ability in patients with dysphagia: The Saku-Saku Test

ObjectiveIn the elderly and patients with dysphagia, masticatory problems often cause aspiration or choking. Although simple methods to predict aspiration and silent aspiration exist, methods for evaluating the masticatory function of patients with dysphagia are lacking. Accordingly, we developed a simple test to assess the chewing and swallowing ability of patients with dysphagia.MethodsOne hundred and five patients with dysphagia were included. We used the Saku-Saku Test (SST), in which patients were asked to eat a rice cracker, and evaluated the quality of mandibular rotation during mastication. We studied the participants’ ability to grind, aggregate, and swallow using videoendoscopic evaluation (VE) and investigated its association with mandibular rotation.ResultsThe SST showed good reliability between two examiners, with a kappa coefficient of 0.80. 92.4% of the patients ate the rice cracker without aspiration. The SST showed a high sensitivity of 73.3% and specificity of 93.3% for the degree of grinding. The degree of food bolus aggregation had a sensitivity of 45.0% and specificity of 90.6%, and aspiration had a sensitivity of 25.0% and specificity of 84.5%, both of which showed high specificity.ConclusionsThe results of this study suggested that the SST might be simple and useful for identifying patients with dysphagia who are able to masticate, even if they do not eat foods that need chewing and could be used before starting these patients on foods that need chewing.     

Chronic pain related to first bite syndrome: report of two cases

First bite syndrome is the classic symptomatology of pain in the parotid region that occurs in response to the first bite of a meal. We report two cases of this syndrome in patients after operations to the parapharyngeal space.     

Increasing the Number of Chews before Swallowing Reduces Meal Size in Normal-Weight,Overweight, and Obese Adults

Eating slowly contributes to a lower risk of obesity, probably because it could aid appetite control. Chewing thoroughly is an effective strategy to reduce eating rate; however, insufficient data are available to demonstrate the relationship between such an eating behavior and energy intake. To investigate the effect of increasing the number of chews before swallowing on meal size, a randomized cross-over trial was conducted in 18- to 45-year-old normal-weight, overweight, and obese participants (n=45) who were recruited from the local community (Ames, IA). After assessment of baseline number of chews, participants were asked to attend three test sessions to eat pizza for lunch until comfortably full by chewing each portion of food either 100%, 150%, or 200% of their baseline number of chews before swallowing. Two-way analysis of variance was used to test the effect of treatment and body-weight status, as well as their interactions on food intake, meal duration, eating rate, and appetite at meal termination. Appetite data during 60 minutes were analyzed by repeated measures analysis of variance. Food intake in the sessions with 150% and 200% of their baseline number of chews was reduced significantly, by 9.5% and 14.8%, respectively, compared with the 100% session. Increasing the number of chews also prolonged meal duration and reduced eating rate. However, subjective appetite at meal termination or during the immediate postprandial period did not differ. These data indicate that increasing the number of chews before swallowing might be a behavioral strategy to reduce food intake and potentially aid body-weight management.     

Reorganization of muscle activity in patients with chronic temporomandibular disorders

ObjectiveTo investigate whether reorganization of muscle activity occurs in patients with chronic temporomandibular disorders (TMD) and, if so, how it is affected by symptomatology severity.MethodsSurface electromyography (sEMG) of masticatory muscles was made in 30 chronic TMD patients, diagnosed with disc displacement with reduction (DDR) and pain. Two 15-patient subgroups, with moderate (TMDmo) and severe (TMDse) signs and symptoms, were compared with a control group of 15 healthy subjects matched by age. The experimental tasks were: a 5 s inter-arch maximum voluntary clench (MVC); right and left 15 s unilateral gum chewing tests. Standardized sEMG indices characterizing masseter and temporalis muscles activity were calculated, and a comprehensive functional index (FI) was introduced to quantitatively summarize subjects’ overall performance. Mastication was also clinically evaluated.ResultsDuring MVC, TMDse patients had a significantly larger asymmetry of temporalis muscles contraction. Both TMD groups showed reduced coordination between masseter and temporalis muscles’ maximal contraction, and their muscular activity distribution shifted significantly from masseter to temporalis muscles. During chewing, TMDse patients recruited the balancing side muscles proportionally more than controls, specifically the masseter muscle. When comparing right and left side chewing, the muscles’ recruitment pattern resulted less symmetric in TMD patients, especially in TMDse. Overall, the functional index of both TMDmo and TMDse patients was significantly lower than that obtained by controls.ConclusionsChronic TMD patients, specifically those with severe symptomatology, showed a reorganized activity, mainly resulting in worse functional performances.     

Properties of a color-changeable chewing gum used to evaluate masticatory performance

PurposeTo clarify the basic properties of a color-changeable chewing gum to determine its applicability to evaluations of masticatory performance under different types of dental status.MethodsTen participants with natural dentition aged 26–30 years chewed gum that changes color during several chewing strokes over five repetitions. Changes in color were assessed using a colorimeter, and then L*, a*, and b* values in the CIELAB color system were quantified. Relationships between chewing progression and color changes were assessed using regression analysis and the reliability of color changes was assessed using intraclass correlation coefficients. We then measured 42 dentate participants (age, 22–31 years) and 47 complete denture wearers (age, 44–90 years) to determine the detectability of masticatory performance under two types of dental status.ResultsRegression between the number of chewing strokes and the difference between two colors was non-linear. The intraclass correlation coefficients were highest between 60 and 160 chewing strokes. Dentate and edentulous groups significantly differed (Wilcoxon rank sum test) and values were widely distributed within each group.ConclusionsThe color of the chewing gum changed over a wide range, which was sufficient to evaluate the masticatory performance of individuals with natural dentition and those with complete dentures. Changes in the color values of the gum reliably reflected masticatory performance. These findings indicate that the color-changeable chewing gum will be useful for evaluating masticatory performance under any dental status.     

Fabrication of maxillary single complete denture in a patient with deranged mandibular occlusal plane: A case report

Construction of a single complete denture (SCD) is a challenging clinical situation especially when the opposing natural dentition is not in a normal plane of occlusion. Mal-aligned, tilted or supra-erupted teeth in the opposing arch are some of the problems that should be corrected to achieve a balanced occlusion in patients who require SCD. Achieving harmonious occlusal plane is a primary objective of any restorative procedure to facilitate natural mandibular movements and ease of mastication. Establishment of normal occlusal plane in opposite arch is pre-requisite to maintain the stability of the SCD. This clinical report describes restoration of mandibular teeth (with severe attrition and deranged occlusion) by establishing normal plane of occlusion with the help of custom made occlusal plane template (OPT) followed by construction of a complete denture in maxillary arch.