What are differences in chewing performance of healthy children and children with cerebral palsy.

Chewing is a rhythmic oral motor activity, in which the coordination of mouth
muscles and joints are controlled by the central nervous system (Forster et
al., 2006; Lund et al., 2006). An efficient chewing process requires repetitive
movements of the mandible in combination with rotational movements of tongue
combined with motor activity of lips and cheeks (Sakaguchi et al., 2003; Rogers
et al., 2005). The development of the chewing is completely developed at the
age of about 6 years (Le Révérend et al., 2013).

Children with cerebral palsy (CP) have constrains in coordination and control
of muscles. This results not only in reduced gross motor movement, but also in
decreased oral motor movements (Rosenbaum, 2007). One of the consequences is a
reduced masticatory function. Children with CP show in their chewing ability:
- reduced chewing speed, with result that eating chewable food costs more time
- reduced coordination with as result less chewed food
- due to the reduced coordination and additional restrictions, these children
are at greater risk of choking, impaired digestion and reduced natural dental
cleaning.
As a result, children with CP are limited in managing solid food compared to
healthy peers (Bell et al., 2010, Matsuo et al., 2008). This has social
consequences (participation level), for example, not being able to eat treats
or eating at a restaurant.

In clinical practice of speech/language therapists working with children with
CP, there is a need for instruments to diagnose and/or evaluate chewing
problems during development or after intervention. However, tongue movements
and muscle activity of the masseter muscles and jaw movements cannot
objectively be measured by observation. To measure mastication, studies with
ultrasound, electromyography (sEMG) and kinematics are performed in adults and
children. De Felicio et al. (2013) were able to distinct different movements
patterns in adults with temporomandibular joint problems compared to healthy
subjects using sEMG and kinematics. Also in children from 6 years of age a
combination of sEMG and kinematics were used for chewing movements in open bite
subjects (e.g. Piancino et al., 2009). Kinematics of jaw movement is applied in
infants from 7 months of age (Wilson et al., 2012). These studies concern
mostly jaw movement during chewing and present no data of tongue movements. In
addition, there are few studies using natural food or studying the reliability
of methods and/or to distinguish the minimal differences. Ultrasound is
frequently used for images of the tongue during swallowing and articulation
(Blissett et al. (2007); Bressmann et al. (2010) . The tongue movement during
chewing are limited described with ultrasound. Also, little is known about the
methodology used and the methods of analysis.

Previous to this study, an observation instrument to measure the ability to
manage solid foods in childen is developed by the researchers.The reliability
and discriminative validity of the mastication observation and evaluation
instrument (MOE) is determined. Subsequently, the test-retest reliability of
measurement of the jaw movement and muscle activity using kinematics and sEMG
is established. sEMG makes it possible to determine changes in the activity of
individual muscles and the cooperation between the oral muscles (m. Masseter,
m. Temporalis and m. Digastricus). With kinematics, the jaw movements (size,
direction and speed) are measured in three directions. In addition, a method
using ultrasound to determine tongue movements is developed.

Results of the preliminary studies
1. Mastication Observation and evaluation (MOE).
The Mastication Observation and evaluation (MOE) instrument was developed using
three Delphi rounds with 15 experts. The final instrument consists of 8 items,
to be scored on a 4-point ordinal scale. Based on three bites of bread and
three bites of a biscuit of 59 healthy children (6-48 months of age) and 38
CP-children (24-72 months of age), the MOE is assessed on (i) interrater
agreement (Gwet's Agreement coefficient = 0.51-0.98), (ii) internal consistency
(Cronbach's alpha >. 70), (iii) construct validity (relationship MOE score-age;
r = 0.73; p = 0.23 for healthy children and r < 0.01; p = 0.05 for CP-children)
and (iv) floor and ceiling effects; which were absent (Remijn et al., 2013;
Remijn et al., 2014). The MOE is appropriate for assessing chewing. However,
the scores give insufficient reliable results on the intra-oral tongue movement
during chewing, such as lateral tongue movement and the number of times needed
for swallowing the bolus.
(This research was approved by the Medical ethics committee of READE to
Amsterdam (number: EN 40472.048.12)

2. Surface electromyography (sEMG)) and kinematics
sEMG and kinematics research is simultaneously used in 12 adult subjects. The
aim of this research was to understand normal chewing movements and to
establish the test-retest reliability of the relevant parameters. During this
study 5 pieces of bread and biscuit in 2 different sizes (large and small) were
eaten. Chewing cycles 2-5 were used for the analyses. We looked whether
different food consistencies gave different outcomes. The results showed a good
test-retest reliability with ICC (two-way random, agreement, average
measurement) = 0.80-0.98. For all parameters a Bland & Altman analysis is
calculated and Minimal Detectable Differences (MDD) are established. In this
pilot the maximum sEMG is measured using the maximum bite force on a plastic
tube. This provided a large variation between subjects in the% sEMG of the
bites. We expect to determine the maximum bite force more stable with a bite
force measurement instrument (Koc et al., 2010).

Ultrasonography (Ultrasound).
Ultrasound measurements of the tongue movement during chewing were established.
Ultrasound movements of the transverse and sagittal cross section of the tongue
are shown at the same time (see Figure 2). The transverse and sagittal section
of ultrasound measurements of four healthy subjects and two persons with CP (3
trials per person) are manually drawn by two raters. The value of the ICCs
showed a good intra-and inter-rateragreement (0.79-0.91 or 0.75-0.87) for
drawing of the contour lines. There are indications of differences in the
transverse tongue movements between healthy subjects and adults with CP
concerning the movement and speed of displacement of the highest point of the
tongue and the frequency of up and down movement and left-right movement. The
sagittal tongue movements showed limited differences on these parameters. The
moment of swallowing is determined afterwards in the analysis. As a result, the
duration of the analysis is not sufficiently reliable. To increase the
reliability of duration of chewing it is necessary to determine the start of
the swallowing phase objectively. Hereby we propose to use an acoustic signal
for the setting of the swallowing phase in a further study (Borr et al.,
2007). (Remijn, Weijers, Nijhuis-van der Sanden, Groen & de Korte; paper in
progress)

Using a variety of methods, we try to determine the dynamics of the chewing
movements in typically developing children and children with CP. The methods
are, in some degree, complementary to each other. Given the limitations of the
methods we need all methods to complete the insight in the mastication process.
In clinical practice the MOE is the most accessible and feasible instrument, so
we want to validate the MOE with the other methods.

Research questions:
1. Is it possible to measure chewing movements in healthy children and children
with CP with MOE, sEMG, kinematics and ultrasound?
2. Is it possible to discriminate between normal and abnormal chewing movements
with the results of the MOE and objective measurement methods (sEMG, kinematics
and ultrasound) ?

Children visit once the SMK for the measurements. Two sessions will take place.
Per session 5 (2 reserve) pieces of wheat bread and pate or chocolate spread
(depending on the taste preference) and 5 (2 reserve) pieces of a biscuit are
offered. The reserve pieces are offered if necessary to obtain at least 5 to
analyse. The size of the pieces of bread and biscuit is 1.5 cm2 . In total, 3/4
slice of bread without crusts and 1* biscuit will be eaten. In addition, the
child will chew 20 times on a waxtablet (a kind of chewing gum) (plasticine
modelling wax, non-toxic DIN en-71). The consistency of the waxtablet does not
change during mastication. This value is considered as a reference value for
the chewing movements of bread and biscuit. After 20 chewing movements, the
waxtablet is removed from the mouth. There is no health risk when the waxtablet
is accidentally swallowed. In a previous study in children (5-12 years) with a
muscular disorder this waxtablet was already used. Parents are asked to be
present during the entire session and are asked to offer the food. Between both
sessions there is a short break for relaxation. The order of the sessions are
presented ad random.

Session 1: Ultrasound in combination with video recording for the observation
tool MOE. The transducer of the ultrasound is held under the chin and the
stethoscope is held on the side of the neck against the larynx during eating.
Both devices provide a minimal pressure on the chin and neck and do not
influence the chewing. Simultaneously a video is recorded for post-hoc
analysis of the mastication with the MOE. This session will take approximately
20 minutes.
Session 2. Att first, the kinematics markers and sEMG boxes are fixed on the
head. The maximum bite force is determined by the bite force measurement as a
reference value for the relative muscle activity. The stethoscope is held next
to the larynx during swallowing. This replaces the sEMG sticker under the chin.
This session will take approximately 45 minutes due to fixing process of the
markers.

The burden for the children is 2 hours for the research. The children are asked
to eat for them well-known products, namely bread and biscuit. The parent is
allowed to be present during the session and are asked to offer the food to
the child. EMG markers are placed on the face of the child. The markers are
associated with a for the child attractive cartoon character. In addition, the
child has to chew on a waxtablet. The risk of choking is equal to the risk of
choking in the regular mealtimes at home. No additional activities are executed
in the mouth. There is no interference of the research session with the
treatment. Parents and child have to visit the Sint Maartenskliniek once.