khoyama and mioche, 2004 (masticacion )

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CHEW ING BEHAVIOR OBSERVED AT DIFFERENT STAGES

OF MASTICATION FOR SIX FOODS, STUDIED BY

ELECTROMYOGRAPHY AND JAW KINEMATICS IN

YOUNG AND ELDERLY SUBJECTS

KAORU KOHYAMA'

National Food Research Institute

2-1

I 2 Kannondai

Tsukuba Ibaraki 305-8642 Japan

AND

LAURENCE MIOCHE

Institut National de l Recherche Agronomique

Station

de

Recherches sur

la

Viande

63122 Their, France

(Manuscript received February 17 , 2004 ; in final form June 14, 2004)

ABSTRACT

The chewing patterns measured w ith ja w kinematics and electromyography

(EMG) of ten young adults and ten healthy elderly subjects chewing six food

products (rice, beeJ cheese, crispy bread, apple, and peanut) were compared.

The chewing sequence was divided into

f ive

periods by number of chewing

cycles, each corresponding to

20

of the entire chewing sequence, Elderly

subjects exhibited lower EMG amplitudes and longer jaw-closing duration than

younger subjects, but the maximal venical and lateral displacements

o

the jaw

were not significantly different at any period of mastication. EMG amplitudes,

muscle activities during the jaw-closing phase, duration of con traction, and

vertical ja w movements decreased in the mastication process. M uscle activities

during occlusion and inter-burst duration increased in the later period. Food

properties modified EMG activities and jaw-kinem atics more significantly in the

earlier stage of mastication, but the food effects continued until the latest stage.

Generally, the eflects of the mastication period and the food type on the

masticatory variables except maximal EMG amplitude were similar fo r both

ages. The amplitude decreased significantly while m astication proceeded fo r

Correspon ding author. National Food Research Institute. 2-1-12 K annond ai, Tsukuba, Ibarak i 305-

8642. Japan. TEL : +8 1-29-838-8031; FAX: +81-29-838-7996;

EMAIL:

[email protected]

Journal of Texture Studies 35 (2004) 395-414. All Righfs Reserved.

oCopyright

2004 by

Food Nurr i t ion Press Inc.

Trumbull

Connecticut.

395


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396

K.KOHYAMA

and

L.

MIOCHE

young subjects but stayed unchanged

for

elder ly. This suggests that the elderly

found i t more difficult

to

adapt their chewing force

to

changing thefood exture

during

i n

mouth

degradation.

INTRODUCTION

Mastication is a physiological process whereby food taken into the mouth

is processed into a food bolus Prim nd Lucas 1995). The masticatory sequence

is the whole set of movements from food ingestion to swallowing. Rabbits show

three types of chewing cycles

in

jaw kinematics: (1) preparatory,

(2)

reduction

and (3) preswallowing series (Lund 1991). Similarly, the masticatory sequence

of humans can be divided into three phases: (1) ingestion ransfer of food to

between the teeth by the tongue,

(2)

comminution sequence hythmic chewing

in

which the food is comminuted and the bolus formed, and (3) clearance and

swallowing (Hiiemae et af . 1996; Heath and

Pnm

1999). We aim to study

textural changes during the second, comminution sequence of chewing which is

the longest for many foodstuffs and may determine the masticatory way

corresponding to

food

texture, although all three phases contributes to texture

evaluation.

Hutchings and Lillford (1988) developed a tridimensional model for

understanding mastication that included the degree of structure, degree of

lubrication, and time. The degree of structure must fall below a certain level and

the degree of lubrication be sufficient in order to swallow a bolus. Foods with

differing textures exhibit different chewing paths before forming a bolus.

Electromyography (EMG), which records muscle activities, can be used to

study the influence of food texture on jaw-closing muscles throughout

oral

processing (Sakamoto et al. 1989; Mathevon er al. 1995; Agrawal et al . 1998;

Kohyama et al. 1998,

2000,2002;

Shiozawa et al. 1999a, b,

2002;

Mathonihe

et al. 2000; Mioche et al. 2002a, 2003). Its use is frequently associated with

mandibular kinematics (Horio and Kawamura 1989; Takada et al. 1994; Brown

et al. 1998; Lassauzay et al. 2000; Nakazawa and Togashi 2000; Peyron et al .

2002).

Humans exhibited higher muscle activity, longer EMG duration, and slower

chewing cycles when they masticate harder chewing

g u m

(Plesh

et

al.

1986).

More recently, Anderson et al.

(2002)

stated that jaw-excursion and velocities

increased with harder

gum,

but cycle duration did not change. Hardness of

chewing gum is practically constant during chewing , but physical properties of

real foodstuffs dynamically change. Previous studies dealing with physical

attributes of foods have shown the influence of the initial food texture

instrumentally measured before consumption on the masticatory patterns of

humans.

Those properties underwent dramatic changes during chewing,


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AGE AND TEXTURE EFFECTS ON MASTICATION STAGES 397

including the breakdown of solid food into smaller particles by compression and

shear forces under bite loads, the incorporation of saliva, adaptation to in-mouth

temperature, the agglomeration and homogenization of foodcomponents, and the

shaping into a bolus suitable for swallowing Prim and Lucas 1995; Mioche

ef

al.

2003). The original textural differences between foods were more sign ificant

during the early stage of mastication and tended to decrease during intra-oral

transformation, although the time course of these temporal changes and their

consequences

on

the chewing behavior were poorly documented (Lucas ef al.

1985; Heath 1991; Kilcast and Eves 1991; Brown er al. 1998; Kohyama ef af.

1998, 2000; Peyron

er d

2002; M ioche ef al. 2003). Different properties of

each

food

were still observed at the moment of swallowing (Shiozawa

ef

al.

1999b, 2002). It suggests that swallowing threshold is varied by original food

texture unlike the model of Hutchings and Lillford (1988).

In

our

previous works (Kohyama

et al.

2002, 2003), we examined the

effects of subjects age on EMG variables for various kinds of food (apple,

cheese, cooked rice, hard bread, peanut and cooked beef).Aging significantly

decreases the muscle activity used to overcome food resistance during the

comminution chewing sequence, but the elderly appear to compensate for this

weakness by increasing the chewing duration, and in the end, age had

no

effect

on

the total m uscle activity required until swallowing. In addition, people having

less number of paired, postcanine teeth, had an impaired mastication which

decreased the muscle activity per chew and in turn increased the number of

chewing cycles (Kohyama ef al. 2003).

Food

products affected

both

the total

number of chewing cycles during comminution and muscle activity per chew

(Kohyama et

al.

2002). However, age effects on chewing behavior were less

obvious for an easy-to-chew food such as cooked rice. Effects of food were

observed for the total or mean values

of

whole mastication, but we have not yet

examined these variations at different stages of the chewing process.

Previous results showed that total muscle activity for chewing a food

product until swallowing was not significantly different among groups

of

subjects (Kohyama

ef al.

2002, 2003). In contrast, the weight of a chew in the

whole mastication process, which was estimated by the ratio of muscle activity

of one chew to the total muscle activity, depended highly on both subject and

food. For a given food, the number of chewing cycles required before

swallowing varied between subjects up to a factor of seven, although the

variation observed in an individual was much less (within 10 in most cases).

Generally, the mean number of chewing cycles was higher in the elderly

subjects than in the young, except for rice and cheese, in which a similar

number was observed (Kohyama

er

al. 2002). Food varied from 5 chewing

cycles for apples to 117 for meat. Therefore, the weight of a single chew was

about 0 .2 for the former and less than 0.01 for the latter. The relative value of

masticatory variables, expressed

as

a percentage of the mastication sequence,


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398

K.

KOHYAMA

and L .

MIOCHE

allowed appropriate comparison between subjects and samples rather than to

compare variables in a given number of chews. We divided the comminution

sequence into five stages amenable to the smallest number, each of them

representing 20 of the number of chewing cycles for the entire sequence,

regardless of its length.

The purpose of this study was to characterize different stages of mastication

regarding variation in food texture and subject age. We re-examined the

previous EMG results and the newly analyzed jaw-kinem atics data, while elderly

and young subjects chewed six food products

so

as to display the effects of food

texture on the dynamics of mastication.

MA lXRIALS AND

METHODS

ubjects and Samples

Ten elderly subjects

(7

female and 3 male, mean

65.8

years, range

58-71

years) and 10 young adults 4 female and 6 male, mean 28.8 years, range 23-36

years) voluntarily participated in this experiment. They were also subjects of the

previous study (Kohyama et al 2002).

All

gave their informed consent before

the recording sessions. Though the ratio

of

female to male subjects differed in

both age groups, no significant gender effect was found in all masticatory

variables for

all

foodstuffs tested.

Five grams of cooked

rice

(Uncle Ben'sN Masterfoods, Orleans, France),

cooked beef,

Edam

cheese, and raw apple (var. Golden Delicious), and

2

g of

crispy bread (Wasan, Barilla, Stockholm, Sweden) and natural peanuts were

served

as

previously (Kohyama er al 2002; 2003). The physical properties of

each food were reported elsewhere (Kohyama ef al 2002). The six products

displayed a large range of textures. Rupture stress increased from cheese, to

bread, rice, apple, and then became very high for meat and peanuts. Stress at

a small strain, equivalent to the elastic modulus, increased in the order of

cheese, meat, rice, apple, and bread, and was extremely high for peanuts as

rupture strain varied approximately in a reverse order.

Recording Session

E M G activities were recorded from both sides of the temporal and masseter

muscles as previously reported (Kohyama er af 2002). Two-dimensional jaw

movements

of

the subjects were recorded using an Articulograph AGlOO

(Carsrens Medizinelektronlk GmbH, Gottingen, Germany) by affixing two

micro-coils of 3 x

3

x 2 rnm on mandibular and maxillary teeth with

cyanoacrylate adhesive (Peyron ef af 1996). The subject's head was placed in

the middle of the magnetic field made by three transmitter coils fixed on a


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AGE AND TEXTURE EFFECTS

ON

MASTICATION STAGES

399

frame. Subtracting the position of the mandibular coil to that of the maxillary

at 100Hz, to allow for head movements, provided the vertical and lateral

movements of the mandible

on

the frontal plane of the subject. The zero points

for both vertical and lateral axes were set to the initial mandibular position of

each subject. EMG and jaw-movement recordings were synchronized.

Data

Analysis

Spike2 software (Cambridge Electronic Design, Cambridge, UK) with

customized procedures (Mathevon ef al. 1995; Peyron

et

al.

1996) was used to

analyze the data.

Figure 1 s an example of the mastication recording. Jaw-kinem atics clearly

indicated the comminution sequence where the rhythrmcal chewing was

performed. The first EMG signal often associated with a large jaw opening was

due to food ingestion, that is the ingestion phase, where the food is transferred

from the front of mouth to between the back teeth by the tongue (Heath and

Prinz 1999). Clearance and swallowing phase (Heath and Prinz 1999) was

shown after the first identified swallow not followed by a rhythmical jaw

movement activity (arrow E). We averaged the four rectified EMG signals as

the subjects freely chose the chewing side and sometimes

used

both sides. The

complete, rhythmical chewing sequences (between arrows

B

and E in Fig. 1) for

the averaged EMG activities and lateral and vertical jaw movements chew by

chew were analyzed.

From the mean of EMG activities of the four muscles, (1) mean voltage,

2)maximum voltage or amplitude,

3)

muscle activity, which is the integrated

area of EMG voltage (mean voltage x burst duration), 4) burst duration, and

5 ) inter-burst duration were calculated for each chewing cycle. From

mandibular kinematics,

(6)

aw opening duration,

(7)

jaw closing duration, and

(8)

occlusion duration, (9) maximum lateral displacement, and the

(10)

maximum vertical displacement were measured for each cycle. Muscle activity

was divided into 11) jaw closing and (12) occlusion period. The occlusion

period was defined as the duration when the linear velocity of the vertical jaw

movement was below a constant threshold (noise level) defined for all

recordings. Closing duration was the time elapsed between maximal vertical

opening and the beginning of occlusion.

To

analyze the different stages of mastication, the whole chewing sequence

was divided into five equivalent stages based on the number of chew ing cycles

(see stages 1 to

5

in Fig. 1). Stage 1 was from the beginning to 20 of the total

number of chews, stage 2 from 20 -

40 ,

tage 3 from 40 - 6 0 , stage

4

60

80 , and stage 5 from 80 to the last chew. The first EMG burst is often

accompanied by a large jaw opening. Such bursts were not included in the


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AGE AND TEXTURE EFFECTS ON MASTICATION STAGES

40

of the means using the Tukeys multiple comparisons for food effect,

as

determined by paired t-tests with Bonferronis correction for stage effect w ithin

the subject

as

posr

hoc

analysis. Statistical significance was set at

P

khoyama and mioche, 2004 (masticacion )

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