Pierre Bourdiol

Chewing behaviour and bolus formation during mastication of meat with different textures

During chewing, meat is mashed under compression and shear bite forces whilst saliva is incorporated. The resulting mixture is shaped into a cohesive bolus by agglomeration of small particles, and triggers a swallow. This study aimed to investigate the relationship between chewing behaviour and bolus formation of meat with different textures. Twenty-five consenting young adults participated in this study. Electromyographic activity was recorded from surface electrodes on the elevator muscles (masseter and temporalis) during mastication of cold beef. Two different textures (T(1): tough and dry; T(2): tender and juicy) were studied, and subjects were asked to chew the beef and then spit out the bolus either: (1) after a constant chewing period of 7s or (2) when the bolus was ready to be swallowed. Meat samples were weighed before and after chewing to determine weight changes due to saliva incorporation and the release of meat juice. Cutting tests were applied to measure the maximum shear force. The mechanical shear force was maximal for meat before chewing (T(1)=124 N/cm(2); T(2)=83 N/cm(2)) and decreased with increased chewing duration. Texture differences analysed from mechanical measurements remained significant even when the boli were ready for swallowing (T(1)=39 N/cm(2); T(2)=32 N/cm(2)); the toughest meat gave the toughest bolus. Muscular activity adapted to the texture of the meat as soon as chewing began, and remained constant over the observed chewing period. Mean muscular activity was higher during the chewing of tough meat than during the chewing of tender meat. As a consequence, by the time a bolus was ready to be swallowed, more saliva had been incorporated into the tough meat samples (mean weight increase: 36%) than the tender meat samples (mean weight increase: 30%).

Influence of age on mastication: effects on eating behaviour

The present review covers current knowledge about the ageing of oral physiology related to mastication and its effects on eating behaviour. Mastication is the first process undergone by a food during feeding. It has a key role in the maintenance of nutritional status in two respects. First, the perceptions of foods sensory properties elicited during chewing and swallowing are one of the major determinants of the pleasure which drives us to eat; second, the properties of the swallowed bolus are affected by oral conditions and this may modulate the subsequent phases of digestion. Ageing in healthy dentate subjects induces moderate changes in oral physiology. Changes in neuromuscular activity are partly compensated by changes in chewing behaviour. No clear age effect is seen in texture perception, although this does impact on food bolus properties. In contrast, great alterations in both chewing behaviour and food bolus properties are observed when ageing is associated with a compromised dentition, general health alterations and drug intake. Eating behaviour is far more complex than just chewing behaviour and the concerns of the elderly about food cannot be explained solely by oral physiology. Discrepancies are often noticed with older subjects between various objective measurements of oral performance and corresponding measures of self-perception. In addition, although more foods are recognised as hard to chew with increasing age, there is no clear shift in preference towards food that is easy to chew. Food choices and food consumption are also driven by memory, psychology and economic factors. Advances in the understanding of food choice in the elderly need a sustained collaborative research effort between sensory physiologists, nutritionists, and food scientists.

Changes in jaw muscles activity with age: effects on food bolus properties.

Bolus formation depends on chewing process that evolves with age. This study aims to analyze the effect of age on chewing behavior (recorded by EMG) and the consequences on bolus formation for meat products. Twenty-five young adults (age range: 25-30) and 20 healthy elderly (age range: 68-73) having at least six pairs of natural postcanine teeth participated. From two different textures of bovine meat, boli were characterized by shear force measurements. Saliva incorporated into the bolus was quantified. Chewing duration was significantly longer in the elderly group for both textures, but muscle activity was significantly lower for the toughest texture only. Moreover, muscle activity was less accurately adapted to food texture in elderly than in young. In order to control that changes in EMG reflect changes in bite force, EMG was recorded during static bite forces. Slopes were fairly similar for both groups suggesting that EMG/bite force relationships do not vary with age. Elderly subjects could partly compensate for a weaker chewing efficiency by increasing the number of chewing cycles before swallowing. It is hypothesized that lengthening of chewing duration results from a decrease in muscle activity during healthy aging. After chewing, the mechanical resistance of the bolus was always higher for the elderly than for the young subjects. No significant age effect was found on the amount of saliva incorporated in the bolus. Elderly subjects, despite the lengthening of the chewing sequence, were less efficient to comminute a meat bolus than young subjects and swallowed less comminuted boli.

The relationship between chewing activity and food bolus properties obtained from different meat textures

During chewing, a meat sample is mashed under compression and shear bite forces whilst saliva is incorporated. The resulting mixture is shaped into a cohesive bolus by agglomeration of small particles to trigger a swallow. This study aims to investigate the relationship between meat structure before chewing and texture after various chewing durations, according to the subjects chewing behavior. Twenty-five young adults participated. Electromyography activity (EMG) was recorded from surface electrodes on the elevator muscles during mastication of cold beef (5 g). Two different meat textures were obtained by varying aging and cooking temperature. Subjects were asked to chew and then to spit out the bolus either after a constant chewing duration (7 s) or when the bolus was ready to be swallowed. Boluses were then weighed to determine saliva incorporation. Cutting tests were applied to measure maximum shear force and to assess bolus structure homogeneity. From EMG recordings, temporal and amplitude parameters were analyzed. The mechanical shear force was maximal for meat before chewing and decreased for the bolus with the lengthening of the chewing duration. Significant texture differences were found for samples before chewing and for two types of bolus but differences were larger for the bolus after 7 s chewing than for the bolus when ready to be swallowed. The amount of saliva incorporated into the bolus increased with both chewing muscular activity and chewing duration. Finally, the more chewing cycles before swallowing, the more comminuted the meat bolus (lower shear force) and the more saliva was incorporated in it. These results fit with one of the major roles of the saliva, that is, to provide cohesion between particles [Nature 391 (1998) 329] and with the intra-oral management of meat during chewing as analyzed by videofluorography [Arch. Oral Biol. 47 (2002) 267].

Age‐related changes in mastication

The paper reviews human mastication, focusing on its age-related changes. The first part describes mastication adaptation in young healthy individuals. Adaptation to obtain a food bolus ready to be swallowed relies on variations in number of cycles, muscle strength and volume of emitted saliva. As a result, the food bolus displays granulometric and rheological properties, the values of which are maintained within the adaptive range of deglutition. The second part concerns healthy ageing. Some mastication parameters are slightly modified by age, but ageing itself does not impair mastication, as the adaptation possibilities remain operant. The third part reports on very aged subjects, who display frequent systemic or local diseases. Local and/or general diseases such as tooth loss, salivary defect, or motor impairment are then indistinguishably superimposed on the effects of very old age. The resulting impaired function increases the risk of aspiration and choking. Lastly, the consequences for eating behaviour and nutrition are evoked.

Is the tongue position influenced by the palatal vault dimensions

The influence of the palatal vault dimensions on tongue position is here studied through evaluation of the in-mouth air cavity (IMAC) volume when the mandible is in maximal intercuspal position. A sample of 35 women (mean age 21.2 +/- 1.0) and 15 men (mean age 22.1 +/- 0.9) was selected. The sagittal cross-section area of the IMAC, which is modulated by the tongue position, was measured on lateral cephalograms. Dental casts were used to measure the palatal vault volume, which was defined by the occlusal plane, the hard palate and the posterior face of the second molars. Palatal vault volume allowed deduction of the IMAC volume through a rule of three procedure relating volume to area ratios. No IMAC could be calculated from cephalograms of 10 subjects who had the tongue stuck to the palate. For the 40 other subjects, the IMAC volume was 8.9 +/- 4.8 mL. It was 2 mL larger in men (n = 14) than in women (n = 26) and was the largest in skeletal Class III and the smallest in skeletal Class II (P > 0.05). IMAC volume was strongly correlated with palatal vault height but neither with palatal width nor length. It was thus assumed that the height of the palatal vault could influence the most observed position of the tongue but this does not exclude a possible growth influence of the tongue on its surrounding skeletal structures.

Only severe malocclusion correlates with mastication deficiency

OBJECTIVES The relation between level of dentofacial deformity and extent of masticatory deficiency was studied. DESIGN Three groups of human young adults were formed: (i) subjects needing orthodontics plus orthognathic surgery (SevDFD, n=18), (ii) subjects needing orthodontic treatment only (ModDFD, n=12), and (iii) subjects needing no treatment (NoDFD, n=12). For mastication tests, carrot boluses were collected at the deglutition time. Bolus particle size range was expressed as d50 value, which was compared with the Masticatory Normative Indicator (MNI). Index of treatment need (IOTN), global oral health assessment index (GOHAI) and chewing kinematic characteristics were also recorded. We used a general linear model univariate procedure followed by a Student-Newman-Keuls test. RESULTS All the SevDFD subjects showed impaired mastication with MNI above the normal limit (d50 mean=7.23mm). All the ModDFD subjects but one were below this limit (d50 mean=2.54mm), and so could adapt to a low level of masticatory impairment as also indicated by kinematics. IOTN indicated a treatment need for ModDFD (3.7±0.5) and SevDFD (4.3±0.6) groups, while GOHAI values were unsatisfactory only for SevDFD (42.6±9.2 vs. 55.3±1.9). CONCLUSIONS Our findings emphasize the need for an objective evaluation of masticatory function to discern truly deficient mastication from mild impairment allowing satisfactory adaptation of the function. However, malocclusions are known to worsen with time justifying thus their corrections as early as possible.

Mood-induced variations of mandible and tongue postures

Twelve young adults in a good general health were observed during habitual posture of tongue and jaw in different emotional conditions induced by watching three video sequences. The position of the mandible was tracked by the displacements of an electromagnetic sensor glued to the chin. The tongue-to-palate distance was obtained by 2-D location of three electromagnetic sensors placed on the tongue upper midline surface. Head displacements were evaluated with a sensor fixed to an upper central incisor and were subtracted from corresponding displacements of tongue and chin sensors to obtain the real tongue and mandible positions during continuous recording sequences. Emotional conditioning by a fear movie influenced the vertical position of the mandible: the mean interarch distances during the fear movie (2·34 ± 0·24 mm) were significantly different from those measured during the tender (3·13 ± 0·35) and neutral (3·42 ± 0·80) movies, respectively (anova repeated measure, SNK; P < 0·05). anova repeated measure indicated that the tongue-to-palate distance differed significantly when the subjects were watching the conditioning movies (P = 0·003), the tip of the tongue taking a lower position during the fear movie than during the tender and neutral movies.