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European Journal of Orthodontics, 2016, 393–397
doi:10.1093/ejo/cjv092
Advance Access publication 14 December 2015
Original article
Evaluation of masticatory parameters in
overweight and obese children
Darlle Santos Araujo*, Maria Carolina Salomé Marquezin*,
Taís de Souza Barbosa*, Maria Beatriz Duarte Gavião* and
Paula Midori Castelo**
*Department of Pediatric Dentistry, Piracicaba Dental School, University of Campinas (UNICAMP), Brazil and
**Department of Biological Sciences, Federal University of São Paulo (UNIFESP), Diadema, Brazil
Correspondence to: Paula Midori Castelo, Departamento de Ciências Biológicas, Universidade Federal de São Paulo
(UNIFESP), R. São Nicolau, 210 – 1. Andar, Diadema – SP, Brasil 09913-030. E-mail: [email protected]
Summary
Objectives: Mastication is an essential function that prepares the food for swallowing and
digestion and may be related to nutritional status. Thus, the aims of this study were to evaluate the
masticatory parameters in overweight and obese children and the relation between bite force and
anthropometric evaluation, food consistency, breast/bottle-feeding, and occlusion. Materials and methods: The sample consisted of 204 children of both genders, age range
8–10 years, divided into normal weight, overweight, and obese. Unilateral bite force was
measured using a digital gnatodynamometer with 10 mm force fork. Anthropometric and
nutritional evaluation involved the measurements of body mass index and skeletal muscle mass
using bioelectric impedance analysis. Occlusion was evaluated as regards orthodontic treatment
need and food consistency was analysed using a structured questionnaire. In addition, the time
of breast- and bottle-feeding was investigated. The results were submitted to chi-square and
correlation tests, analysis of variance, and multiple linear regression to determine the relation
between bite force and the independent variables under study (α = 0.05). Results: Statistical analysis showed that the time of breast- and bottle-feeding and food consistency
did not differ among groups. The regression model showed that body mass index, orthodontic
treatment need, and body skeletal muscle mass contributed significantly to the variation in bite
force.
Conclusions: Breast- and bottle-feeding behaviour and food consistency did not differ in normalweight, overweight, and obese children. However, bite force was dependent on body skeletal
muscle mass, body mass index, and orthodontic treatment need.
Introduction
Chewing is an important function of the stomatognathic system; it
consists in biting, grinding, and breaking foods into smaller particles,
and preparing them with saliva for swallowing and digestion (1). An
efficient mastication is acquired with the action of teeth and proper
mandibular movements, co-ordinated by the neuromuscular system
(2). In addition to mechanical functions, chewing is also related to
the pleasure provided by the food flavours. Proper chewing favours
the first stages of digestion by stimulating saliva production and activation of cephalic control, which starts food assimilation (3).
Recent studies have suggested that chewing slowly or increasing
the number of chewing cycles during the meal is associated with a
lower body mass index (BMI), probably because it interferes in appetite control (4). The relationship between physical constitution and
masticatory function in the elderly people has been studied, since
loss of body skeletal muscle mass resulting from ageing may have an
© The Author 2015. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved.
For permissions, please email: [email protected]
393
394
influence on the masticatory ability of these individuals (5, 6), thus
influencing their nutritional status. However, in children this subject
has received little attention.
Chewing difficulties lead to alterations in food preference, being
foods with soft (versus hard) and with smooth (versus rough) properties the most preferred; they are easier to chew, but high in calories.
In this way, the unbalanced intake of foods may also increase the
risk of diseases related to nutritional deficiencies (7) and tooth decay
(8). Foods with harder and more fibrous consistency have a positive
influence on the development of stomatognathic structures, such as
masticatory muscles, periodontal supporting tissues, and the maintenance of bone integrity. Foods with soft consistency may have an
atrophic effect on the bones and muscles, contributing to the appearance of malocclusion and loss of muscle force (9, 10).
The strength of the jaw muscles determines the amount of available force to cut or crush the food. Masticatory muscle strength can
be evaluated by measuring the maximum bite force (1), which varies
within the region of the oral cavity and is greater in the region of the
first permanent molars (11). Previous studies have shown that bite
force is associated with the stomatognathic system integrity, as well
as with the morphology and efficiency of the muscles, bones, joints,
and dentition, (12–14) and may be useful as a parameter of masticatory function.
Previous studies have emphasized the positive influence of good
masticatory ability on oral health, food’s digestion, and nutritional
status. The hypothesis to be tested was whether masticatory parameters would be different among children with different nutritional status and would be related with body composition. In this way, the aims
of this study were to evaluate masticatory parameters in overweight
and obese children and the relationship between bite force and anthropometric evaluation, food consistency, breast-feeding, and occlusion.
Materials and methods
Sample
A convenience sample was selected and consisted of 204 prepubertal
subjects from 8 to 10 years of age, from public schools of Piracicaba
(SP, Brazil). Each subject and his parent/guardian gave voluntary
consent to participate in this research by signing an informed assent
form and a parental/guardian consent form, respectively, after having their questions and concerns addressed, in accordance with the
Research Ethics Committee of the Piracicaba Dental School Dental
School criteria (protocol No.017/12).
The sample size calculation was based on previous results from
our laboratory, in which bite force was evaluated in subjects of the
same age group, using the same methodology (unpublished work).
Considering a correlation coefficient between bite force and BMI
equal to 0.19, power = 0.80, and α level 0.05, it was found that 215
subjects would satisfy the criteria adopted.
A questionnaire was sent to the children’s parents/guardians in
order to gather information concerning socioeconomic indicators,
medical and nutritional history (time of breast- and bottle-feeding, birth weight, delivery type, childhood diseases), comorbidities
(hypertension, diabetes mellitus, dyslipidemia), treatments and use
of health services, and history/presence of non-nutritional sucking
habits (fingers, pacifier, and/or lips). This information was useful to
check the homogeneity of the sample and exclusion criteria.
The exclusion criteria adopted were: presence of systemic disorder, such as neurological disorders, cerebral palsy, diabetes, hypertension, and others; use of medicines which interfere in the central
nervous system (anxiolytics, antidepressants, anticonvulsants), girls
European Journal of Orthodontics, 2016, Vol. 38, No. 4
who had gone through the first menstrual cycle, and subject’s refusal
to participate in the research.
Clinical oral examinations
The oral examination was performed at the school, using a clinical
mirror with LED light, exploratory probe, mouth retractors, after
performing biofilm control. Caries experience was evaluated by
determining the number of decayed, missing, and filled primary and
permanent teeth (DMFT and dmf-t, respectively).
The individuals were classified according to their stage of dentition as follows: early mixed, intermediate mixed, final mixed, and
permanent dentition. Occlusal evaluation was performed using
the Index of Orthodontic Treatment Need (IOTN)-Dental Health
Component (DHC), which is based on the contribution of various
occlusal characteristics to the orthodontic treatment need. The DHC
measurements were obtained with the use of a periodontal probe,
and individuals were classified on a scale of 5 degrees in ascending
order of orthodontic treatment need: 1. no need for treatment, 2. little need, 3. moderate need/borderline, 4. great need, and 5. very great
need (15).
Evaluation of food consistency
Food consistency was evaluated using a questionnaire developed
previously for children, in which the parents/guardians answered to
eight questions with dichotomous responses (yes/no) with reference
to the child’s eating habits (for example, “Does your child eat beef
steak?) (16). In this study, the total score was used to grade the foods
from soft to hard consistency.
Evaluation of maximum unilateral bite force
The maximum unilateral bite force was measured by means of a
digital gnatodynamometer (model DDK, Kratos Equipamentos
Industriais Ltda., Cotia, SP, Brazil), with a 10 mm force fork connected to a digital appliance, which provided the maximum bite
force values in Newtons (N). During the evaluation, the subject
remained seated, with the head in a relaxed position. The fork was
placed between the maxillary and mandibular arches, in the permanent first molars region. The child was instructed and trained before
to bite it with maximum force, and two measurements were made
for each side of the dental arches (left and right). The maximum
value of the two measurements on each side was considered as final
value, with an approximation of 0.1N.
Physical examination
Anthropometric and nutritional evaluations involved the measurements of height, weight, and body skeletal muscle mass, by means of
a digital stadiometer scale and bioelectric impedance analysis. Body
mass index (BMI = kg/m2) was determined in order to classify the
selected sample into three groups, according to the reference data
BMI-for-age and gender (5–19 years) into: normal weight, overweight, and obese (17).
To quantify the body skeletal muscle mass, bioelectric impedance analysis was used (InBody 230, Biospace Co. Ltd., Gangnan-gu,
Seul, South Korea). The measurement system is tetra-polar with eight
tactile electrodes: two sets of electrodes in metal plates for each foot
on which the subject was placed; at the top part of the scale column,
there are two devices for the hands, which were held by the subject
at the time of analysis. The children were in a standing position, with
the arms and legs extended, in accordance with the manufacturer’s
instructions. Analyses were performed in the morning, without the
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D. S. Araujo et al.
subject having done exercise or eaten before this (at least 2 hours
after the last meal).
Statistical analysis
The data collected were statistically analysed using the BioEstat 5.3
(Mamirauá, Belém, PA, Brazil) and SigmaPlot 11.0 (Systat Software
Inc., San Jose, California, USA) statistical software packages. The
Kolmogorov–Smirnov test was used to examine distribution of the
variables; for those that presented deviation from normal distribution, non-parametric tests or logarithmic transformation were used.
A P-value <0.05 was adopted.
A pilot study was conducted before beginning the data collection to verify the reproducibility of the measurements made, and
later calculation of agreement (kappa test) and intraclass correlation
coefficient (ICC). In addition, the questionnaire used for food consistency evaluation was tested to check the clarity of the questions.
The questionnaire was applied to a group of 10 parents/guardians
who were not included in the final sample, and the alternative “I
did not understand” was added to each question for identifying the
questions that were not understood by them.
The descriptive statistics consisted of means, standard deviation,
median, interquartile range, and percentages. The proportion of
individuals in different stages of dentition (early mixed, intermediate
mixed, late mixed, and permanent) and the distribution of genders
in each group (normal weight, overweight, and obese) was tested for
differences by means of the chi-square test. The differences in mean
age, time of breast- and bottle-feeding, scores of food consistency,
and skeletal muscle mass among groups were analysed using analysis of variance (ANOVA) or Kruskal–Wallis test, where appropriate.
The correlation between bite force and the studied variables was
analysed by means of Pearson or Spearman correlation tests. This
test was applied before the multiple regression analysis was performed, because if there were two or more variables with very strong
correlation (r equal to or higher than 0.95), they would interfere in
the multiple regression model.
Thus, to evaluate which of the variables under study contributed
to the variation in bite force magnitude, a multiple linear regression model with backward stepwise elimination was used. The stepwise procedure was employed to choose the model with the highest
adjusted R2 and the variance inflation factor (VIF) at or near 1.0.
The following independent variables were added to the initial model:
age, gender, stage of dentition, BMI, time of breast/bottle-feeding,
presence of sucking habit, food consistency, IOTN score, dmf-t and
DMFT, and skeletal muscle mass. The variables gender, IOTN scores,
dmf-t, and DMFT were forced to remain in the final model with
the aim of controlling these confounding variables. The independent
variables were thus eliminated step-by-step until those that attained
a P-value <0.05 remained in the final model.
Results
Table 1 shows the measures of reproducibility obtained in the pilot
study and their interpretation. The food consistency questionnaire
was applied to the parents/guardians in the pilot study and it has
demonstrated no significant difficulty in understanding the questions
(the number of responses “I did not understand/not applicable” was
less than 15%, which was deemed acceptable).
The demographic data of the three groups are shown in Table 2.
Statistical analysis showed that the three groups were not significantly different in regard to gender (P = 0.285), age (P = 0.279),
and stage of dentition (P = 0.643). The total time of breast-feeding
Table 1. Measurements of reproducibility for the variables evaluated in the pilot study. DMFT, index of decayed missing and filled
permanent teeth; dmf-t, index of decayed, exfoliated and filled
primary teeth; IOTN-DHC, Index of Orthodontic Treatment NeedDental Health Component.
Variables
n
Test
Values
Interpretation
DMFT/dmf-t
20
Kappa
0.97
IOTN-DHC
Bite force
24
15
Intraclass correlation
Intraclass correlation
0.88
0.97
Almost perfect
agreement
Excellent to perfect
Excellent to perfect
(P = 0.402) and exclusive breast-feeding (P = 0.792), as well as
time of bottle-feeding (P = 0.635) did not differ significantly among
groups. Also, no significant difference was observed in food consistency scores (P = 0.643).
Table 3 shows the correlation coefficients obtained between bite
force and the clinical and physical variables. According to the correlation coefficients found, it was observed that there was significant
positive correlation between bite force and age and skeletal muscle
mass. As these variables could concomitantly be correlated with the
other variables under study, a multiple linear regression analysis was
performed.
Table 4 shows the results obtained using the multiple linear
regression model. It was observed that the independent variables
BMI, orthodontic treatment need, and body skeletal muscle mass
significantly contributed to the variance in bite force magnitude.
Higher BMI and orthodontic treatment need were related to lower
bite force, whereas greater body skeletal muscle mass was related to
greater bite force. The ANOVA validated the model (F = 3.452 and
P-value = 0.004). In addition, this model explains 17.2% of the variance in bite force, with the remaining being explained by variables
that were not included in the study.
Considering the sample size calculation, 215 subjects would
satisfy the criteria adopted for the present study; although, due to
the loss of some of the volunteers, the final sample consisted of 204
subjects. The power of the regression model was above the satisfactory level (99%), which demonstrates that the sample included was
sufficient.
Discussion
Chewing may provide beneficial effects on satiety and appetite controls (4, 18). However, over the last years, changes have occurred
in the eating habits, in which the home meal rich in fibres has been
replaced by processed food, poor in fibres, and complex carbohydrates, but rich in simple carbohydrates and lipids, with soft and
highly palatable consistency (19). Although the use of a specific
questionnaire did not find significant differences in food consistency
among children with different nutritional status, it is clear that there
is a need for further studies to assess the relation between food’s
characteristics, consistency, palatability, and nutritional status.
The development of the stomatognathic system begins at birth,
with the maturation of sucking, breathing, and swallowing. Breastfeeding promotes greater stimulus to the orofacial muscles in comparison with bottle-feeding (20). It may also be related to lower
rates of overweight/obesity, since the use of formulas in the first
years has been shown to be associated with greater weight gain and
increased skin folds (21). The findings of the present study showed
no significant difference in the time of breast- and bottle-feeding in
normal-weight, overweight, and obese individuals. However, one
European Journal of Orthodontics, 2016, Vol. 38, No. 4
12.7
(2.6)
14.1
(2.4)
15.8
(4.7)
267.6
(97.1)
285.6
(116.6)
277.4
(95.9)
16.3
(1.4)
19.9
(1.4)
24.3
(2.4)
Bite force
Age
BMI
Breast-feeding
time
Food
consistency
Skeletal
muscle mass
r
P-value
0.16
0.024
0.11
0.132
0.09
0.310
−0.03
0.768
0.23
0.001
Table 4. Final multiple linear regression model with backward
stepwise elimination used to verify the relation between bite force
and the independent studied variables. Ln, logarithmic transformation; BMI, body mass index; IOTN, Index of Orthodontic Treatment Need; DMFT, decayed. missing, filled permanent teeth; dmf-t,
decayed exfoliated and filled primary teeth.
Model
Bite force
Coefficient
P-value
Constant
Gender
Ln (BMI)
IOTN score
dmf-t
DMFT
Ln (skeletal
muscle mass)
332.179
3.379
−8.779
−31.266
−1.257
36.898
13.219
—
0.855
0.010
0.002
0.846
0.367
0.005
F
(P-value)
3.452
(0.004)
R2
0.172
Power 5%
0.994
0
12.9
45
37
Overweight
Obese
122
Normal weight
204
64♀
58♂
29♀
16♂
18♀
19♂
111.7
(13.5)
110.2
(10.9)
107.8
(13.4)
8.0
(4–17)
7.5
(2–12)
6.5
(4.5–11.5)
5.0
(3–6)
5.0
(1.75–6)
4.0
(3.25–6)
3.0
(2–5)
3.5
(2–4)
2.0
(2–4.5)
9.9
3.0
(3–4)
4.0
(3–4)
4.0
(3–4)
Mean
(SD)
Mean
(SD)
Mean
(SD)
Median
(25–75%)
Mean
(SD)
Median
(25–75%)
Median
(25–75%)
Median
(25–75%)
(%)
Skeletal muscle mass
(kg)
Bite force (N)
Food consistency
(total score)
Age (months)
Breast-feeding
(months)
Exclusive Breastfeeding (months)
Bottle-feeding
(months)
Presence of sucking
habit
BMI (kg/m2)
Table 3. Correlation coefficients obtained between bite force and
physical and clinical studied variables. BMI, body mass index; r,
correlation coefficient.
Gender
n
Table 2. Demographic data and physical and clinical variables of the studied sample, divided in accordance with body mass index for age and gender. BMI, body mass index; SD, standard
deviation.
396
should consider the multifactorial nature of obesity, in which several
variables may influence this condition and may be relevant to the
subject’s nutrition, such as hereditary, family environment, sedentarism, among others (19). A published meta-analysis showed that
breast-feeding was associated with a lower BMI when compared to
artificial feeding (22), although this difference was small and vulnerable to confounding factors.
In this study, a trend towards bite force being dependent on BMI
was observed, while past studies have failed to establish a relationship between BMI and bite force, in both adults and young individuals (21, 23). Taking into consideration a possible alteration in
the obese individuals’ diet, it may be suggested that the increase in
processed foods ingestion, with soft consistency and rich in carbohydrate and fat, would promote reduced stimulation of the masticatory
muscles than those rich in fibres, such as grains and fruits (24). In a
previous study (13), BMI contributed 1.3% to the variation in maximum bite force in adolescents and young adults. In the elderly, this
relationship appears to be clearer as past studies observed an association between gastrointestinal and masticatory function alterations,
loss of teeth and appetite, and a compromised nutritional status (6,
25). However, the relationship between BMI and masticatory force
and performance may not be linear in all ages, therefore the difficulty
in obtaining evidence that supports the importance of masticatory
function for the adequate digestion and absorption of nutrients (25).
Variations in the normal position of teeth are able to change
facial appearance and occlusal function and, possibly, make chewing
difficult (26). The IOTN is not cumulative and takes into account
the most severe occlusal feature, which reflects the functional, dental health, and/or aesthetic impairment. In this way, the present
study observed that the severity of malocclusion related with lower
bite force magnitude, corroborating previous studies conducted
in children (27, 28). Occlusal alterations may lead to changes in
D. S. Araujo et al.
mandibular posture to an unfavourable position, which affects muscle biomechanics and force production.
Bioelectric impedance analysis has been shown to be valid and
reliable in the evaluation of body composition, even in children. It is
a fast and non-invasive exam, appropriate for epidemiological studies. As far as we know, this is the first study that described the role
of body skeletal muscle mass in the variation of bite force in children using bioelectric impedance analysis. This result supports the
hypothesis that bite force is dependent on the muscular integrity of
the body, and previous studies have shown that masticatory ability is
related to body muscle force and physical performance in the elderly
population (5, 29).
The model used explained only 17.2% of the variance in bite
force, with the remaining being explained by variables that were
not included in this study, such as craniofacial morphology, occlusal
contacts, and other. The study design—cross-sectional—also limits
generalization of the results, but the results found showed important
trends to be evaluated in future longitudinal studies.
In the studied sample, the time of breast- and bottle-feeding and
the characteristics of food did not differ among normal-weight,
overweight, and obese children. It was also observed that bite force
was dependent on body skeletal muscle mass, BMI, and orthodontic
treatment need.
Funding
State of São Paulo Research Foundation, Brazil (2011/15621–5,
2012/04492-2).
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