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 Spearman's rho correlation coefficient (Experiment 3). The method was sensitive to increasing numbers of chewing cycles (F_5,65 = 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.     

Two‐colour chewing gum mixing ability test for evaluating masticatory performance in children with mixed dentition: validity and reliability study

The unappealing taste of the chewing material and the time‐consuming repetitive task in masticatory performance tests using artificial foodstuff may discourage children from performing natural chewing movements. Therefore, the aim was to determine the validity and reliability of a two‐colour chewing gum mixing ability test for masticatory performance (MP) assessment in mixed dentition children. Masticatory performance was tested in two groups: systemically healthy fully dentate young adults and children in mixed dentition. Median particle size was assessed using a comminution test, and a two‐colour chewing gum mixing ability test was applied for MP analysis. Validity was tested with Pearson correlation, and reliability was tested with intra‐class correlation coefficient, Pearson correlation and Bland–Altman plots. Both comminution and two‐colour chewing gum mixing ability tests revealed statistically significant MP differences between children (n = 25) and adults (n = 27, both P < 0·01). Pearson correlation between comminution and two‐colour chewing gum mixing ability tests was positive and significant (r = 0·418, P = 0·002). Correlations for interobserver reliability and test–retest values were significant (r = 0·990, P = 0·0001 and r = 0·995, P = 0·0001). Although both methods could discriminate MP differences, the comminution test detected these differences generally in a wider range compared to two‐colour chewing gum mixing ability test. However, considering the high reliability of the results, the two‐colour chewing gum mixing ability test can be used to assess masticatory performance in children, especially at non‐clinical settings.     

Factors associated with masticatory performance in community-dwelling older adults: A cross-sectional study

BackgroundDecreased masticatory performance leads to deterioration of overall health among older adults. However, maintaining and improving masticatory performance in ways other than maintenance of natural teeth and appropriate prosthodontic treatment remains unclear. If the factors related to the mixing and shearing abilities for masticatory performance are clarified, it may be possible to maintain and improve the masticatory performance of older adults. We aimed to clarify the association among mixing ability, shearing ability, and masticatory performance-related factors.MethodsOf the 707 community-dwelling older adults in Kusatsu Town, Japan, 344 who had been treated for any dental defects were enrolled in this study. Masticatory performance was evaluated on the basis of mixing ability and shearing ability. The number of natural teeth and artificial teeth, occlusal force, tongue pressure, and oral diadochokinesis /ta/ were measured as masticatory performance-related factors. Their relationship with mixing ability, shearing ability, and masticatory performance-related factors was examined by means of Spearman rank correlation coefficient and path analysis.ResultsAmong masticatory performance-related factors, the number of natural teeth, occlusal force, and tongue pressure were directly associated with both mixing ability and shearing ability. Moreover, mixing ability was also directly associated with shearing ability.ConclusionsTongue pressure, which can be improved by means of training, is a masticatory performance-related factor associated with both mixing and shearing abilities.Practical ImplicationsTraining for tongue pressure after proper prosthetic treatment may provide an effective means of maintaining and improving masticatory performance in older adults.     

A structural equation model relating objective and subjective masticatory function and oral health‐related quality of life in patients with removable partial dentures

Summary The aim of this study was to investigate the relationships between objective masticatory function with respect to masticatory performance and food mixing ability, patients’ perception of chewing ability and oral health‐related quality of life (OHRQoL). Partially dentate patients with removable partial dentures (n = 131, mean age 67·1 year) participated in the study. Four tests were performed to evaluate objective and subjective masticatory function and OHRQoL. Masticatory performance and food mixing ability were assessed using peanuts or a two‐coloured wax cube as test items. Patients’ perception of chewing ability was rated using a food intake questionnaire. OHRQoL was measured using the Japanese version of the oral health impact profile. A structural equation model was constructed based on hypothesis in which objective masticatory function would be related to OHRQoL via perceived chewing ability as a mediator. Structural equation modelling analysis found a statistically significant medium effect of perceived chewing ability on OHRQoL and statistically significant medium or small effects of masticatory performance on perceived chewing ability and OHRQoL (P < 0·05); however, the effect of food mixing ability on perceived chewing ability or OHRQoL was not statistically significant (P > 0·05). A fit index indicated that the model fitted well to the data (Goodness‐of‐fit index = 0·99). These results suggest that perceived chewing ability is a critical factor for OHRQoL and that masticatory performance rather than food mixing ability is important for perceived chewing ability and OHRQoL in patients with removable partial dentures.     

Perceived chewing ability and need for long-term care in the elderly: a 5-year follow-up study

Increasing need for long-term care in older adults is expected with the ageing of Japan's population. The aim of the present study was to show the relationship between perceived chewing ability and long-term care needs for over 5 years in elderly persons. The chewing ability of 812 elderly persons living independently was evaluated at baseline using self-assessed masticatory ability, and it was classified into one of three categories: ability to chew all foods (good masticatory ability), ability to chew only slightly hard food (fair masticatory ability), and ability to only chew soft or pureed food (poor masticatory ability). Participants' care needs were then followed through Japan's long-term care insurance system for over 5 years. The log-rank test and Cox proportional hazard model were used to examine statistical differences in the frequency of care-needs certification between participants with good and fair or poor masticatory ability. Among participants aged 65-79 years, the frequency of care-needs certification was significantly higher in those with fair or poor masticatory ability than in those with good masticatory ability, and the relative hazard ratio was significantly higher in those with fair or poor masticatory ability than in those with good masticatory ability, after adjusting for age, gender, current employment status, educational background, social interaction, chronic medical conditions and dentition status. These relationships were not found among those aged 80-93 years. Impairment in perceived chewing ability may be associated with higher incidence of certification in Japan's long-term care insurance system among elderly persons aged 65-79.     

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

PurposeThe 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.MethodsTwenty 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.ResultsRepeated 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).ConclusionThe 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.     

Mixing ability test compared with a comminution test in persons with normal and compromised masticatory performance

A mastication test was needed with a material that forms a bolus and is soft enough to be chewed by persons with compromised oral function, in particular patients confronted with oral cancer. We therefore developed a wax-mixing ability test and compared it with a comminution test using Optocal as test food. We hypothesized that the mixing ability test would be better at differentiating between groups of persons with compromised masticatory performance than the comminution test. Sixty healthy subjects were recruited in three groups of 20, matched for age and gender: a group with natural dentition; a group with full dentures; and a group with maxillary denture and implant-supported mandibular overdenture. The mixing ability test was found to discriminate better between the two full-denture groups than the comminution test.     

Association between tongue and lip functions and masticatory performance in young dentate adults

Motor functions of masticatory organs such as the tongue, lips, cheeks and mandible are known to deteriorate with age, thereby influencing masticatory performance. However, there are few reports on the relationships between tongue and lip functions and masticatory performance. To investigate the relationship between tongue and lip functions and comprehensive masticatory performance, by evaluating crushing, mixing and shearing abilities in young dentate adults. Participants comprised 51 dentate adults with a mean age of 25 years. Maximum tongue pressure and oral diadochokinesis were measured to evaluate tongue and lip functions. A multiple sieving method using peanuts was performed to evaluate crushing ability. A colour‐changeable chewing gum was performed to evaluate mixing ability. A test gummy jelly was performed to evaluate shearing ability. The relationship between tongue and lip functions and each masticatory performance was assessed using Pearson's correlation coefficients. In addition, stepwise multiple regression analysis was performed to identify predictors of crushing ability. Crushing ability was significantly correlated with maximum tongue pressure and the number of repetitions of the syllables /pa/, /ta/ and /ka/. Maximum tongue pressure and number of repetitions of the syllable /pa/ were identified as significant predictors for crushing ability. Mixing ability was significantly correlated with the number of repetitions of the syllable /pa/. Shearing ability was not significantly correlated with tongue and lip functions. Masticatory performance during the chewing of brittle foods such as peanuts and solid foods such as chewing gum appears to be correlated with tongue and lip functions.     

Gastric and masticatory performances in full‐arch immediate loading rehabilitated patients

Full‐arch immediate loading implant rehabilitations provide patients with compromised dentition an effective treatment to improve their aesthetic and function. Aim of this prospective cohort study was to investigate the correlation between masticatory ability and gastric emptying rates among these patients. Ten subjects (five men and five women) with compromised dentition were tested in two occasions: before treatment and 30 days after the immediate loading rehabilitation. Masticatory ability was evaluated using the sieves test, and the gastric half emptying time (T_1/2) was assessed by means of the ¹³C‐octanoic acid breath test. A statistically significant increment (P < 0·005) in masticatory ability was found only in reference to the particles smaller than or equal to 4·75 mm, whereas the gastric emptying rate showed a statistically significant reduction between pre‐ and post‐treatment (P = 0·003). A moderate negative correlation (rho = 0·64, P = 0·048) between the percentage change in masticatory ability and the percentage change in gastric emptying rate was evidenced. Patients with compromised dentition rehabilitated with full‐arch immediate implant prostheses present a significant improvement of the gastric process.     

Correlation between the median particle size of chewed frankfurter sausage and almonds during masticatory performance test

The correlation between chewing and gastric function is best reflected when the same food type is used during both tests. We proposed frankfurter sausage as test food for masticatory performance as it can also be used in gastric emptying test. The suitability of frankfurter sausage to determine masticatory performance, however, has never been examined. To examine the correlations between the median particle size of frankfurter sausage and almonds (as standard test food) after different numbers of chewing cycles. Twenty‐seven subjects performed masticatory performance tests by chewing 2 types of test foods, that is, a piece of almond or 5‐g frankfurter sausage cubes placed in a sealed latex bag, for 5 and 15 chewing cycles. For each individual, right and left sides were tested separately. Chewed samples obtained from both sides were pooled. Median particle sizes were determined using a multiple sieving method. Spearman’s rank correlation was used to examine any correlation between median particle sizes of the 2 test foods after 5 and 15 cycles. Median particle sizes after 5 and 15 cycles were 2.04 ± 0.87 and 0.95 ± 0.58 mm for almonds and 4.16 ± 0.19 and 3.73 ± 0.25 mm for frankfurter sausage, respectively. Significant correlations were observed between the median particle size of chewed frankfurter sausage after 15 cycles and that of chewed almonds after 5 and 15 cycles (r = .76, P < .01 and r = .52, P = .01, respectively). Frankfurter sausage chewed for 15 cycles may be suitable for the determination of masticatory performance in conjunction with gastric emptying test.     

Validity and reliability of a newly developed method for evaluating masticatory function using discriminant analysis

The objective of the study was to assess validity and reliability of a newly developed method for evaluating mixing ability of masticatory function. A two-coloured paraffin wax cube was used as a test food in the mixing ability test. Eleven full dentate and 33 denture wearers participated in the validity assessment. They were divided into three groups according to their dental state. Validity was assessed by the Spearman's coefficient of correlations between the mixing ability test and the sieving method used as a 'gold standard' test of the masticatory performance. The subjects were asked to masticate the test foods for 5, 7, 10, 15, 20 and 30 strokes in each test. Significant correlations (P < 0.001) were obtained in natural dentition group (r(s) = 0.66), in denture-natural dentition group (r(s) = 0.72) and in denture-denture group (r(s) = 0.56). In the reliability assessment, three full dentate subjects were asked to repeat the mixing ability test a number of times. The intraclass correlation coefficients were 0.94 in interexaminer consistency, 0.98 in intra-examiner consistency, 0.89 in test-retest consistency and 0.99 in measuring consistency. These results indicated that the mixing ability test had the validity and the reliability for evaluation of the masticatory performance.     

Effect of Molar Occlusal Balance on Cognitive Function in the Elderly

BackgroundElderly people with dementia, who are increasing at a rate comparable to the rate at which theelderly population is growing, are becoming a serious social problem in Korea. Therefore, the purpose of this study was to investigate the association between molar occlusal balance and cognitive function among Koreans aged 65 years and older.MethodsA total of 308 participants aged 65 years and older who attended a senior center were recruited for the study with their consent. The Korean version of the Mini-Mental State Examination (MMSE-DS) was used to assess cognitive function, and masticatory ability was measured according to the ability to chew food, the number of remaining teeth, and the self-perceived perceived masticatory function. Relative molar occlusal balance was measured using the T-scan Ⅲ system. All collected data were analysed using SPSS version 23.0.ResultsThere was a significant association between cognitive function and molar masticatory ability (P < .05). The participants with relative molar occlusal balance had a higher MMSE-DS score when compared to those with relative incision occlusal balance, adjusted for sociodemographic factors and number of remaining teeth, subjective masticatory ability, chewing ability, occlusion time, and denture use. Cognitive function was higher when relative molar occlusion was greater compared to anterior occlusion in anterior-posterior teeth balance.ConclusionsCognitive function in elderly people was higher when the relative molar occlusal balance was greater. Mastication with posterior teeth may have a more important effect on stimulation of cognitive function. Therefore, oral health care focusing on maintenance of molar teeth may be crucial for elderly persons.     

Oral tactile sensitivity and masticatory performance are impaired in stroke patients

Oro‐facial impairment following stroke frequently involves reduced chewing performance, that is oral phase dysphagia. The aim was to investigate the sensitivity of oral tissues following stroke and its potential impact on masticatory function. Therefore, hospitalised post‐stroke patients were recruited and compared to healthy controls. Outcome measures comprised masticatory performance employing a colour‐mixing ability, that is a bolus‐kneading test, maximum lip‐ and bite force and the one‐point and two‐point tactile thresholds. Food hoarding and prevalence of dry mouth were evaluated with ordinal scales. Twenty‐seven stroke patients (age 64·3 ± 14·1 years) and 27 healthy controls (age 60·8 ± 14·3 years, P = 0·254) participated in this study. The groups had similar numbers of occluding units. Stroke patients reported more frequently dry mouth sensations and food hoarding. The intra‐oral tactile sensitivity on the contra‐lesional side was significantly lower in stroke patients compared to controls (0·0001 < P < 0·0002), and significant intra‐group side differences were found only in the stroke group (0·0001 < P < 0·0010). For the lip, both sides were less sensitive in the stroke group compared with controls. The experiments confirmed lower masticatory performance and lip force in the stroke group, but the bite force was similar compared to healthy controls. Oral sensitivity was correlated with masticatory performance when a global correlation model was applied. A stroke may affect the sensitivity of the intra‐oral tissues contra‐lesionally, thus potentially affecting chewing function. Rehabilitation should therefore not only focus on motor impairment, but equally stimulate the sensitivity of the oral tissues, employing dry ice application or similar specific treatments.     

Masticatory performance‐related factors in preschool children: establishing a method to assess masticatory performance in preschool children using colour‐changeable chewing gum

A knowledge gap regarding masticatory performance in preschool children exists, which in turn delays intervention for preventive care; therefore, a method to easily assess performance is needed. The purpose of this study is to investigate the feasibility of assessing masticatory performance using colour‐changeable chewing gum and to investigate masticatory performance‐related factors in preschool children. This cross‐sectional survey was conducted in two childcare facilities and our laboratory. First, a one‐third quantity of colour‐changeable chewing gum was masticated by six adults to assess the nature and progression of colour changes in this quantity. Then, masticatory performance in 370 children 4–6 years of age was assessed using the same quantity of colour‐changeable chewing gum (60 chew strokes). The maximum bite force, body height, weight, age and number of healthy teeth were recorded. A t‐test was performed to determine whether gum‐chewing experience or lack thereof produced a significant difference in masticatory performance. The Spearman's rank correlation coefficient was then determined for masticatory performance assessment values and other factors solely for children with gum‐chewing experience. Measurements from 259 children were obtained. Children with gum‐chewing experience demons trated significantly higher assessment values and were deemed to have been correctly assessed. A very weak but significant positive correlation was observed only between masticatory performance and the number of healthy teeth. The masticatory performance of preschool children was easily assessed using colour‐changeable chewing gum. The assessment values demonstrated significant correlation with the number of healthy teeth, but not with maximum bite force, body height, weight or age.     

Changes in Masticatory Performance and Quality of Life in Individuals With Chronic Periodontitis

Background: This study evaluates the effect of periodontitis on masticatory performance and quality of life index. Methods: Patients (n = 24; 23 to 76 years of age) with periodontal conditions ranging from healthy to generalized disease categorized by the alveolar bone height–to–tooth length (AB/T) ratio were separated into the following two groups: control (AB/T >50%) and test (AB/T <50%). The masticatory performance was evaluated through continuous mastication of a special device called a biocapsule. The Brazilian Oral Health Impact Profile (OHIP‐14Br) questionnaire was used to assess the oral health–related quality of life. The Student t test was applied for independent samples (P <0.05) to evaluate the masticatory performance, and the Mann‐Whitney U test was used to determine quality of life (P <0.05) Results: There was a statistically significant difference in masticatory efficiency between groups (P = 0.006). Statistically significant differences were also observed in the following parameters: 1) physical pain (P = 0.003); 2) psychologic discomfort (P = 0.008); 3) physical disability (P = 0.033); and 4) OHIP‐14Br total score (P = 0.001). The control group achieved the best indicators. Both the masticatory performance and quality of life indicators showed significant correlation with the alveolar bone height. Conclusion: The loss of periodontal supporting structures has negative effects on the masticatory performance and quality of life.     

Comparing masticatory performance and mixing ability

Summary Masticatory performance has often been measured by determining an individual’s capacity to comminute a test food. Another method to determine masticatory performance, which is now widely used, evaluates the ability to mix and knead a food bolus. Two‐coloured chewing gum and paraffin wax have been used as test foods for the quantification of the mixing ability. The aim of our study was to compare the results obtained with the comminution of an artificial test food and the results obtained from mixing of a two‐coloured chewing gum. The degree of mixing of the colours of the chewing gum was quantified with an optical method. Twenty young subjects with a natural dentition (average age 24 years) and twenty elderly subjects, mostly with complete dentures (average age 72 years), participated in the study. Significant differences in masticatory performance between the two groups were detected with both methods. However, the comminution test was better in discriminating the masticatory performance of the two groups. The mixing ability test with the two‐coloured chewing gum proofed to be a good method to determine masticatory function in subjects with a compromised masticatory performance (elderly subjects). However, the method appeared to be less suitable for subjects with a good masticatory performance (young subjects).     

Novel software for quantitative evaluation and graphical representation of masticatory efficiency

Blending of chewing gums of different colours is used in the clinical setting, as a simple and reliable means for the assessment of chewing efficiency. However, the available software is difficult to use in an everyday clinical setting, and there is no possibility of automated classification of the patient's chewing ability in a graph, to facilitate visualisation of the results and to evaluate potential chewing difficulties. The aims of this study were to test the validity of ViewGum – a novel image analysis software for the evaluation of boli derived from a two‐colour mixing ability test – and to establish a baseline graph for the representation of the masticatory efficiency in a healthy population. Image analysis demonstrated significant hue variation decrease as the number of chewing cycles increased, indicating a higher degree of colour mixture. Standard deviation of hue (SDHue) was significantly different between all chewing cycles. Regression of the log‐transformed values of the medians of SDHue on the number of chewing cycles showed a high statistically significant correlation (r² = 0·94, P < 0·01). ViewGum eliminates drawbacks of previous two‐colour chewing gum test methods by the simplicity of its application. The newly developed ViewGum software provides speed, ease of use and immediate extraction of clinically useful conclusions to the already established method of chewing efficiency evaluation and is a valid adjunct for the evaluation of masticatory efficiency with two‐colour chewing gum.     

Relationship of masticatory mandibular movements to masticatory performance of dentate adults: a method study

This study evaluated a sieve method for measuring masticatory performance and determined the associations between masticatory performance and masticatory mandibular movements. Ten dentate adults and three complete denture-wearing subjects participated in the study. The masticatory performance indices for these subjects were determined after a 10 s masticatory sequence and another sequence that ended at the swallowing threshold. Almond was used as the test food and almond fragments were sized using a standard 0·65 mm square size brass wire sieve. Masticatory mandibular movements were simultaneously recorded by an optoelectronic device. The reproducibility of the masticatory performance tests was good ( r = 0·98 and 0·82 for the 10 s and swallowing threshold test indices, respectively). The masticatory performance indices were markedly different between dentate and denture-wearing subjects. The 10 s masticatory performance index in the dentate subjects, showed moderate to rather strong correlation with all parameters of mandibular velocity ( r = 0·6–0·7). The 10 s index also showed a strong negative correlation to the duration of the occlusal level phase and the total duration of the chewing cycle ( r = –0·7 to –0·8) in the dentate subjects. This study confirms that masticatory performance levels are relatively stable and associated with the efficacy of specific masticatory mandibular movement parameters.     

Investigation of predictors affecting food mixing ability in mandibulectomy and/or glossectomy patients

PurposeSeveral previous reports have described factors that affect masticatory function. However, there are no known predictors that affect the food mixing ability of the masticatory function, and it has been impossible to predict masticatory function in mandibulectomy and/or glossectomy patients. The purpose of the present study was to develop a numerical formula that could predict the food mixing ability of the masticatory function among mandibulectomy and/or glossectomy patients. The null hypothesis of the study was that five predictors, namely mandibulectomy, mandibular continuity, number of residual mandibular teeth, occlusal units and tongue movement score, were unable to account for the mixing ability index (MAI) in mandibulectomy and/or glossectomy patients.MethodsThe subjects were 20 patients who had undergone mandibulectomy and/or glossectomy. The above-described five predictors were assessed. Tongue movement was evaluated with a tongue movement test and the MAI was evaluated with a mixing ability test. Multiple regression analysis was used to examine whether the five predictors affected the MAI after prosthetic treatment.ResultsA regression equation was determined for the five predictors (R² = 0.83; adjusted R² = 0.77; p < 0.001).ConclusionThe obtained regression equation could successfully account for the MAI in mandibulectomy and/or glossectomy patients.     

Changes in masticatory function after injection of botulinum toxin type A to masticatory muscles

This study examined changes in masticatory function after botulinum toxin type A (BTX‐A) injection using objective and subjective tests during 12 weeks. Also, we compared differences in masticatory function between group in which only masseter muscle (M group) was injected and group in which masseter and temporal muscle (M‐T group) were injected. Forty subjects were assigned into two groups; M group (n = 20) and the M‐T group (n = 20). The Meditoxin^® was used as BTX‐A injection. The mixing ability index (MAI) was used as the objective indicator, and visual analogue scale (VAS) and food intake ability (FIA) index were used as subjective indicators. Overall, the masticatory function drastically declined after 4 weeks and gradually recovered with time. Compared with the pre‐injection state, the masticatory function decreased by 89·2% (MAI), 12·2% (FIA) and 32·2% (VAS) 4 weeks after the injection (P < 0·05). When the results between M group and M‐T group were compared, scores of VAS and FIA were significantly different 4 weeks after the injection (P < 0·05), but the MAI score showed no significant difference between two groups. In conclusion, this study showed that masticatory function was significantly decreased after BTX‐A injection into the masticatory muscle after 4 and 8 weeks from injection. However, masticatory efficiency measured using MAI could completely recover after 12 weeks. Furthermore, after 8 weeks from the injection, the masticatory function measured after injection into only the masseter muscle was similar to that measured after injection into both masseter and temporal muscle.