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A posterior cross-bite is defined as an abnormal bucco-lingual relationship between opposing molars, pre-molars or both in centric occlusion. Although it has been reported that patients with unilateral posterior cross-bite often show unique chewing patterns, the relationship between the form of cross-bite and masticatory jaw movement remains unclear in adult patients. The objective of this study was to investigate masticatory jaw movement among different forms of cross-bite. One hundred and one adults were recruited in this study: 27 had unilateral first molar cross-bite ( MC group); 28, unilateral pre-molar cross-bite ( PC group); 23, anterior cross-bite ( AC group); and 23, normal occlusion (control group). Masticatory jaw movement of the lower incisor point was recorded with six degrees of freedom jaw-tracking system during unilateral mastication. Our results showed that the reverse chewing ratio during deliberate unilateral mastication was significantly larger in the MC group than in the PA ( P < 0·001), AC ( P < 0·001) and control ( P < 0·001) groups. These findings suggest that compared to the anterior or pre-molar cross-bite, the first molar cross-bite is more closely associated with a higher prevalence of a reverse chewing cycle. [ABSTRACT FROM AUTHOR]

Efficient mastication of different types and size of food depends on fast integration of sensory information from mechanoreceptors and central control mechanisms of jaw movements and applied bite force. The neural basis underlying mastication has been studied for decades but little progress in understanding the dynamics of bite force has been made mainly due to technical limitations of bite force recorders. The aims of this study were to develop a new intraoral bite force recorder which would allow the study of natural mastication without an increase in the occlusal vertical dimension and subsequently to analyze the relation between electromyographic (EMG) activity of jaw-closing muscles, jaw movements and bite force during mastication of five different types of food. Customized force recorders based on strain gauge sensors were fitted to the upper and lower molar teeth on the preferred chewing side in fourteen healthy and dentate subjects (21-39 years), and recordings were carried out during voluntary mastication of five different kinds of food. Intraoral force recordings were successively obtained from all subjects. anova showed that impulse of bite force as well as integrated EMG was significantly influenced by food ( P < 0·05), while time-related parameters were significantly affected by chewing cycles ( P < 0·001). This study demonstrates that intraoral force recordings are feasible and can provide new information on the dynamics of human mastication with direct implications for oral rehabilitation. We also propose that the control of bite force during mastication is achieved by anticipatory adjustment and encoding of bolus characteristics. [ABSTRACT FROM AUTHOR]

Summary The aim of this study was to investigate the influence of chewing force on salivary stress markers (alpha-amylase activity, salivary cortisol level and secretory immunoglobulin A secretion rate) as indicators of mental stress. Participants comprised 20 healthy men. The first set of saliva specimens (S1) was collected at immediately after a 20-min rest to evaluate stress markers. As stress loading, the participants were required to perform arithmetic calculations for 20 min, after which the second set of saliva specimens (S2) was collected. Each participant was then required to chew a piece of tasteless gum for 10 min, after which the third set of saliva specimens (S3) was collected. After a 20-min rest, the fourth set of saliva specimens (S4) was collected. Weak, habitual and strong chewing forces were assigned. Change rates of stress markers between S2 and S3, and S2 and S4 were calculated. A significant difference was observed in the change rate of cortisol levels between S2 and S3. Cortisol level decreased more under strong chewing than under weak chewing. No significant differences were observed in the change rate of amylase activity or s-IgA secretion rate among the three chewing forces. The results suggest that differences in chewing force influence the salivary cortisol level of the three stress markers, and that a strong chewing force induces a greater reduction in mental stress than a weak one. [ABSTRACT FROM AUTHOR]

Summary 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. [ABSTRACT FROM AUTHOR]

Summary The aim of the present study was to elucidate whether self-assessed masticatory ability (masticatory ability) is significantly related to muscle strength of the body evaluated as handgrip strength and skeletal muscle mass of the whole body (kg) (SMM) after adjusting for confounding variables, including, age, gender, height, weight, employment status, type of household, educational background, social interaction, chronic medical conditions, smoking habit, drinking habits and dentition status among the elderly. A total of 381 persons aged 67-74 years were enrolled. Masticatory ability was classified into one of three categories: ability to chew all kinds of food, ability to chew only slightly hard food or ability to chew only soft or pureed food. Handgrip strength was measured, and bioimpedance analysis was used to estimate SMM. One-way analysis of variance and Bonferroni methods were used to examine differences in handgrip strength and SMM among the three groups of masticatory ability. An ordinal regression model was conducted with masticatory ability as the dependent variable and handgrip strength as the principal independent variable. Handgrip strength was significantly lower in those individuals who could chew only soft or pureed food than in those individuals who could chew all kinds of food. No significant difference in SMM was found among the three groups of masticatory ability. Masticatory ability was significantly related to handgrip strength after adjusting for SMM, dentition status and background factors. Chewing ability may be related to muscle strength of the body evaluated as handgrip strength, but not evaluated as SMM. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The purpose of this study was to reveal the relationship between chewing-side preference and anterior disc displacement (ADD) of the TMJ. Thirty-two healthy subjects with ages ranging from 26 to 34 years were selected from volunteer students at the Okayama University Dental School. Subjects were asked to chew freely with two kinds of test foods, beef jerky (hard food) and chiffon cake (soft food), thus expecting different amounts of mechanical loading on the TMJ. One, 4, and 7 s after starting the mastication, subjects were asked to open their mouth momentarily to have a digital image of their mouth taken. The bolus placement area was measured by processing the digital images, calculated as the number of pixel of bolus area. Area asymmetry index was used for the determination of preferred chewing side (PCS). Oblique sagittal MRI scanning in the closed mouth position was taken to evaluate the articular disc position. In asymptomatic subjects with ADD, a significant predominance of the PCS on the ipsilateral side of ADD was observed during the mastication of hard food. On the contrary, no correlation was found between unilateral ADD and PCS for the soft food. From the results of this study, it is suggested that ADD is the associating factor of PCS for hard food. Therefore, it would be necessary to break down the concept of PCS into at least two categories, one for hard food and one for soft food, considering the mechanical loading on the TMJ. [ABSTRACT FROM AUTHOR]