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8/10/2019 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:
Journal of Texture Studies 35 (2004) 395-414. All Righfs Reserved.
oCopyright
2004 by
Food Nurr i t ion Press Inc.
Trumbull
Connecticut.
395
8/10/2019 Khoyama and Mioche, 2004 (Masticacion )
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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,
8/10/2019 Khoyama and Mioche, 2004 (Masticacion )
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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
8/10/2019 Khoyama and Mioche, 2004 (Masticacion )
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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