E. Yoshida

Association between food mixing ability and electromyographic activity of jaw‐closing muscles during chewing of a wax cube

The purpose of this study was to clarify association between food mixing ability and activity of jaw-closing muscles during chewing of a wax cube. Twenty subjects with complete dentitions (mean age 24.1 years) were directed to chew a two-coloured paraffin wax cube for 10 strokes on preferred chewing side. Surface electromyograms (EMG) were recorded from the right and left masseter and anterior temporalis muscles during chewing of the wax cube. Maximum voltage, duration and muscle work for burst of each chewing cycle were measured on integrated EMG in each muscle. Food mixing ability was estimated as mixing ability index determined from the colour mixture and shape of the chewed wax cube. Some EMG parameters of all muscles except for masseter muscle on non-chewing side showed significant positive correlations with the mixing ability index (r = 0.45-0.56, P < 0.05). However, most of the EMG parameters correlated with one another. As a result, only muscle work of masseter muscle on the chewing side was identified as a significant predictor accounting for 28% interindividual variation in the mixing ability index (P < 0.01). These results suggest that activity of jaw-closing muscles during chewing the wax cube seems to be weakly related to food mixing ability.

A structural equation model to investigate the impact of missing occlusal units on objective masticatory function in patients with shortened dental arches

The aim of this study was to investigate the impact of missing occlusal units (MOUs) on objective masticatory function with respect to food comminuting and mixing ability. Sixty partially dentate patients (mean age, 64·1 years) with shortened dental arches participated in the study. Food comminuting ability was assessed using a masticatory performance test with peanuts as a test food. Food mixing ability was assessed using a mixing ability test with a two-coloured wax cube. Maximum bite force (MBF) was measured using a pressure-sensitive film as a mediator for food comminuting and mixing ability. A structural equation model was constructed based on a hypothesis that MOUs would be associated with reduced MBF and impairment of food comminuting and mixing ability. Structural equation modelling analysis found significant direct effects of MOU on median particle size and mixing ability index (MAI) (P < 0·001). In addition, MOU had significant indirect effects on median particle size and MAI with MBF as a mediator (P < 0·05). These results suggest that decrease in occlusal platform area and reduced MBF because of MOUs are associated with the impairment of food comminution and mixing in patients with shortened dental arches.

Two‐colour chewing gum mixing ability: digitalisation and spatial heterogeneity analysis

Many techniques are available to assess masticatory performance, but not all are appropriate for every population. A proxy suitable for elderly persons suffering from dementia was lacking, and a two-colour chewing gum mixing ability test was investigated for this purpose. A fully automated digital analysis algorithm was applied to a mixing ability test using two-coloured gum samples in a stepwise increased number of chewing cycles protocol (Experiment 1: n = 14; seven men, 19-63 years), a test-retest assessment (Experiment 2: n = 10; four men, 20-49 years) and compared to an established wax cubes mixing ability test (Experiment 3: n = 13; 0 men, 21-31 years). Data were analysed with repeated measures anova (Experiment 1), the calculation of the intraclass correlation coefficient (ICC; Experiment 2) and Spearmans rho correlation coefficient (Experiment 3). The method was sensitive to increasing numbers of chewing cycles (F5,65 = 57·270, P = 0·000) and reliable in the test-retest (ICC value of 0·714, P = 0·004). There was no significant correlation between the two-coloured gum test and the wax cubes test. The two-coloured gum mixing ability test was able to adequately assess masticatory function and is recommended for use in a population of elderly persons with dementia.

Association between occlusal curvature and masticatory movements with different test foods in human young adults with permanent dentitions

OBJECTIVE Occlusal curvatures such as the curve of Spee, curve of Wilson and Monsonss sphere exist in the human adult mandibular arch. A previous study showed that human young adults with flatter occlusal curvatures had higher ability of food comminution and mixing. The aim of this study was to clarify functional significance of occlusal curvatures in terms of masticatory movements. This study investigated the association between occlusal curvature and mandibular movements while chewing a variety of food items. DESIGN Forty-six young adults with complete dentitions (mean age, 25.0 years) participated in the study. Sphere radius of occlusal curvature was determined by a three-dimensional analysis of the mandibular arch based on the Broadrick flag method. Mandibular movements during unilateral chewing of six test food items (chewing gum, cheese, kamaboko, boiled beef, gummy jelly and raw carrot) until the subjects felt ready to swallow were recorded using a six-degrees-of-freedom mandibular movement recording system, and 11 parameters for masticatory movements of a lower incisal point of the mandible were analysed. RESULTS Linear regression analyses identified the sphere radius as a significant predictor for closing velocity in all test food items, occluding/cycle duration in 3 items, opening velocity, closing duration and chewing time in 2 items, and opening duration in 1 item (P<0.01). The results suggest that subjects with larger sphere radius (flatter occlusal curvature) in the mandibular arch could prepare food bolus effectively for swallowing. CONCLUSION Occlusal curvature seems to be associated with masticatory movements in young adults with permanent dentition.

Association between occlusal curvature and food comminution and mixing in human young adults with permanent dentitions

OBJECTIVE Occlusal curvatures in human adult dentition such as the curve of Spee, curve of Wilson and Monsonss sphere provide clinical guidance for prosthetic rehabilitation and orthodontic treatment. However, association between occlusal curvature and masticatory function is not known. The aim of this study was to investigate the association between occlusal curvature and food comminuting and food mixing ability in human young adults with permanent dentitions. DESIGN Fifty young adults with complete dentitions (mean age, 25.0 years) participated in the study. Occlusal curvature was determined by a three-dimensional analysis of the mandibular arch according to the Broadrick flag method. Food comminuting ability was assessed using a masticatory performance test with peanuts as test food and it was scored as median particle size. Food mixing ability was assessed using a mixing ability test with a two-coloured wax cube and it was scored as mixing ability index. RESULTS A linear regression analysis identified the sphere radius of occlusal curvature as significant predictor for both median particle size and mixing ability index after controlling for maximum bite force (P<0.001). These results indicated that subjects with a flatter curvature (larger sphere) in the mandibular arch showed better food comminuting and mixing ability. Coefficient of determination (R(2)) of occlusal curvature related to median particle size and mixing ability index was comparable to that of maximum bite force. CONCLUSION Occlusal curvature seems to be associated with food comminuting and mixing ability in human young adults with permanent dentitions.

Effects of delayed-onset muscle soreness on masticatory function

The aim was to clarify the effects of experimentally provoked delayed-onset muscle soreness (DOMS) in the jaw-closing muscles on subjective and objective measures of masticatory function. Twenty-one dentate female subjects, without pain-related signs and symptoms of temporomandibular disorders, participated. Delayed-onset muscle soreness was provoked with eccentric and concentric contractions of the jaw-closing muscles using a custom-made apparatus. At baseline, and 24 h and 1 wk after the exercises, data were gathered on the subjective measures of muscle fatigue, muscle pain, and masticatory chewing ability using visual analogue scale (VAS) scores, on the maximum voluntary bite force (MVBF), and on the food Mixing Ability Index (MAI). After 24 h, muscle fatigue and muscle pain had increased and the MAI had decreased. All had returned to baseline levels after 1 wk. There were no significant changes found in the chewing ability VAS scores and in the MVBF over time. After correction for its baseline value, the MAI after 24 h was found to be significantly related to the muscle pain after 24 h. In conclusion, DOMS in the jaw-closing muscles can cause a decrease in the objectively scored chewing ability, while the subjectively scored chewing ability remained the same.

Comparison of electromyographic activity of jaw-closing muscles between mixing ability test and masticatory performance test

PURPOSE The purpose of this study was to compare the muscle activity of jaw-closing muscles during chewing of a wax cube used for mixing ability test with that of peanuts used for masticatory performance test. METHODS Twenty subjects with complete dentitions (mean age 24.1 years) were directed to perform a mixing ability test and a masticatory performance test. Surface electromyograms (EMGs) were recorded from the masseter and temporalis muscles on right and left sides. Muscle work, maximal voltage and duration were measured on the integrated EMG signal in each muscle. In addition, muscle work was normalized with EMG activity during maximum voluntary clenching at centric occlusion. The mean of the 2nd to 5th cycle in each parameter was employed for statistical analysis. RESULTS Repeated measures one-way multiple analysis of variance found a significant effect of chewing test on muscle work, normalized muscle work and maximal voltage (P<0.002), but no significant effect on duration (P=0.07). Muscle work, normalized muscle work and maximal voltage for the mixing ability test were significantly less than for the masticatory performance test in all muscles (paired t-test, P<0.006). CONCLUSION The results of this study suggest that muscle activity of jaw-closing muscles in the mixing ability test is less than that in the masticatory performance test using peanuts as test food.