Keywords caries - medicine - masticatory dysfunction - cognitive development - psychomotor
development
Introduction
Oral diseases pose as one of the main worldwide public health issue. Early childhood
caries (ECC) is a significant oral health problem, which is characterized by the existence
of one or more decayed (both cavitated and noncavitated lesions), missing, or filled
teeth in the primary dentition of children aged 71 months or younger.[1 ] It is considered as a chronic infection that most frequently affects children.[2 ]
Considering its unidirectional and bidirectional effects, oral health is considered
one of the essential elements of well-being and general health.[3 ]
[4 ] One of the most interesting factors is the correlation between mastication impairment,
either due to untreated caries or early tooth loss, and cognitive function.[5 ]
[6 ]
[7 ] To date, several studies had discovered its correlation with cognitive function,
specifically in elderly. These studies found that those with more tooth loss are more
susceptible to dementia.[8 ]
[9 ] Fortunately, research on animals found that this effect is reversible with proper
treatment and care.[10 ]
Child development is categorized into four domains, namely physical development, cognitive
development, linguistic development, and socioemotional development. Physical development
includes growth rate, physical fitness, gross and fine motor skills development, and
self-care ability. Cognitive development consists of intellectual processes of analysis,
problem-solving, early mathematical ability, and memory. Linguistic development consists
of babbling, gestures, and pointing in infancy. Socioemotional development denotes
the child's relationship with caregivers and how they build trust to fulfill their
needs.[11 ]
Considering the high number of children suffering from ECC in developing and industrialized
countries,[12 ] especially the socially disadvantaged population, a further understanding of the
effects of ECC on children's general health is necessary.[3 ] One of the significant effects of caries is deterioration in the ability to chew,[13 ] which further affects their nutritional intake, pain, and quality of life.[4 ] In addition, previous studies have found other negative effects of ECC on children's
growth, such as psychomotor function and development,[11 ]
[14 ]
[15 ]
[16 ]
[17 ] cognition,[18 ] speech development,[3 ]
[11 ]
[19 ] as well as their well-being in adulthood.[20 ] Therefore, this article aims to provide a summary of the present literature about
ECC and its effects on masticatory function, cognition, and other aspects of child
development.
Early Childhood Caries
Dental caries is widely known as a preventable disease. However, it immensely affects
disadvantaged groups from the beginning of life through to the elderly. Likewise,
the increase in oral health disparities has caused caries to be declared a silent
epidemic.[21 ] ECC is dental health problem that is commonly found in children, with the incidence
reaching 1.76 billion, regardless of their socioeconomic status.[2 ] Aside from ECC, the following names are also used reciprocally: nursing caries,
rampant caries, early childhood tooth decay, baby bottle-fed tooth decay, comforter
caries, and maxillary anterior caries.[12 ] The problem of children suffered from ECC is not as simple as due to the caregiver
do not maintain their oral health. In addition to dental health disparities, the families
may face certain conditions forcing them to pay less attention to their children's
dental care.[19 ]
ECC that affects children or toddlers is quite distinctive.[12 ] It is characterized with existence of one or more decayed (both cavitated and noncavitated
lesions), missing, or filled teeth in the primary dentition of children aged 71 months
and younger.[1 ] Any signs of caries on the smooth surface of the teeth in children under the age
of 3 are indicators of severe early childhood caries (SECC).[22 ] In addition, any missing teeth due to caries, or restored primary teeth in the maxillary
anterior region, or decay, missing, filling (dmf) scores more than or equal to 4 at
the age of 3, more than or equal to 5 at the age of 4, or more than or equal to 6
at the age of 5 years are also considered as SECC.[12 ] The initiation stage of ECC is indicated by a dull white spot of demineralized enamel
that rapidly advances into noticeable decay along the gingival margin. The first affected
teeth are usually the primary maxillary incisors, all at once. The lesions can be
found on either lingual or labial surfaces or, sometimes, both.[12 ]
Early childhood life denotes one of stage of life that is vulnerable to health problems.
Aside from their independence, it is also difficult for young children to convey what
they need. As a result, their health and well-being heavily rely on the beliefs and
health practices of their primary caregivers.[22 ] One of the triggering factors for the occurrence of ECC is the transmission of the
main bacteria that causes dental caries, namely Streptococcus mutans (S. mutans ). Children acquire the S. mutans from their closest person or caretakers.[23 ] Research shows that the younger a child acquires S. mutans , the higher the risk of the child experiencing caries.[24 ]
Studies have shown that ECC somewhat impacts on children's quality of life, such as
pain arises from the untreated caries, eating difficulties, sleep problems, developmental
issues, school absences, and social self-consciousness.[21 ] The occurrence of dental caries in children is inseparable from the occurrence of
dysbiosis in the oral microbiome, which can also cause dysbiosis in the gastrointestinal
microbiome.[25 ] This, in turn, can lead to various health problems in children. Apart from the child
itself, ECC also affects their family through financial aspect due to dental treatment
expenses and potential time off work to look after the unhealthy children.[3 ]
Previous studies have revealed that high carious activity is associated with various
aspects of general health, such as early tooth decay, orofacial pain,[2 ]
[26 ]
[27 ] reduced dietary intake,[27 ]
[28 ] weight loss, sleep disturbances, hindered school, and learning activities, ultimately
resulting in a poorer quality of life.[29 ] ECC can also cause masticatory dysfunction,[30 ] affecting intellectual development and other developmental milestones.[14 ]
[18 ]
[31 ]
[32 ]
Early Childhood Caries Experience and Masticatory Function
Early Childhood Caries Experience and Masticatory Function
Untreated caries directly affects the mastication unit. Loss of occlusal contact or
tooth extraction may disrupt the permanent teeth alignment, increasing the risk for
orthognathic problems later in life. Mal-aligned teeth and masticatory problems may
subsequently make children more susceptible to periodontal disease.[22 ] Studies have found that cavitated teeth might affect children's ability to chew
food,[26 ]
[33 ]
[34 ] especially in children with a greater number of missing teeth.[20 ]
[26 ] As a result, they prefer to eat soft diets.[35 ] However, a study has revealed that the negative effects of caries on mastication
are reversible.[10 ] Dental restoration treatment for caries is able to restore oral function by increasing
their bite force value.[36 ]
[37 ] Meanwhile, another study suggested that despite the difficulty in chewing due to
extensive tooth extraction, children are able to adapt, and achieve optimal masticatory
function.[35 ]
The mechanism behind the changes in oral function due to caries is that extensive
carious lesions disrupt the tooth structure, leading to open occlusal or proximal
contacts. This results in reduced bite force due to a smaller area for grinding food.
Consequently, this might lead to selective food texture, prolonged chewing time, and
one-sided eating. Likewise, dental pain may also arise during eating, causing sensitivity
and difficulty in chewing.[13 ]
[38 ]
[39 ]
Mastication Impairment and Cognitive Function
Mastication Impairment and Cognitive Function
Children with untreated caries are prone to mastication impairment. There are studies
suggesting the detrimental effects of mastication impairment on hippocampus-related
cognitive function. These effects can occur through both the neural pathways[40 ]
[41 ] and the decrease in blood flow.[42 ] Mastication denotes cyclic, repetitive motions of the jaw, regulated by the feedback
signals from periodontal mechanoreceptors. These receptors are widely recognized as
the main source of signals containing information about the initial contact between
teeth and food. The central nervous system processes this information to control masticatory
muscle and jaw movements.[43 ] While the main purpose of these signals is to control masticatory movements, these
somatosensory inputs also influence the hippocampus through synaptic projections from
the thalamus and cerebral cortex.[44 ] Stimuli from masticatory movements play an important role in maintaining social,
mental, and physical health. The ability to chew is associated with overall health
through nutritional status and daily activities. The two parts of the central nervous
system that regulate cognitive function are the cerebral cortex and hippocampus.[45 ]
The mastication process generates sensory signals that are transmitted through the
trigeminal sensory nerves to various brain regions, including the brainstem reticular
formation, cerebellum, hypoglossal motor nuclei, and trigeminal sensory nuclei.[46 ]
[47 ]
[48 ] The trigeminal sensory nerves later arrive in the ventral posterior thalamic nucleus,
reticular formation, and hypothalamus. The sensory signals from the ventral posterior
thalamic nucleus ultimately reach the somatosensory cortex. Nerve fibers from the
somatosensory cortex project their axons to the somatosensory association area, which
is connected to the entorhinal cortex. The entorhinal cortex is the primary afferent
source for the hippocampal dentate gyrus, allowing sensory signals from the mastication
process to affect the hippocampus via the thalamus and cerebral cortex. The hippocampus
plays a crucial role in regulating the release of various hormones from the hypothalamic-pituitary-adrenal
axis. The hypothalamus produces corticotropin-releasing hormone, which triggers the
anterior pituitary gland to secrete adrenocorticotropic hormone, causing the release
of corticosterone from the adrenal cortex.[6 ]
[40 ] Corticosterone has quick access to the brain. The hippocampus has a large number
of glucocorticoid receptors, triggering the release of stress-related hormones.[49 ] The hippocampus receives projections of noradrenergic, serotonergic, and dopaminergic
fibers from the locus coeruleus, raphe nuclei, and ventral tegmental area, which are
parts of the ascending reticular activating system. Therefore, it can be concluded
that the mastication process can affect the function of the hippocampus through reticular
formation, and the effects of mastication on the hippocampus can arise from several
neural pathways.[41 ]
[49 ]
The mastication process produces sensory signals to the hippocampus.[50 ] If the process does not occur optimally, it will cause disturbances in the morphological
development of the hippocampus, such as a decrease in the number of pyramidal cells.[40 ] Pyramidal cells are cells in the cerebral cortex that send nerve fibers to the spinal
cord and terminate efferent motor neurons that innervate skeletal muscles.[51 ]
In addition to the neural pathways, mastication movements can affect the brain through
an increase in the cortical blood flow, indicating a response from sensory signals
from the masticatory system toward the brain. Furthermore, the increasing partial
pressure of carbon dioxide due to feedback mechanisms from sensory and motor neurons
in the cortex results in dilated capillaries.[42 ]
[50 ]
Mastication has been associated with various cognitive functions, including episodic
memory, verbal fluency, psychomotor function, and delayed word recall. These functions
are regulated by specific parts of the cerebral cortex and hippocampus.[45 ] Observational studies using positron emission tomography and functional magnetic
resonance imaging showed that masticatory muscle activity increases cortical blood
flow and activates areas such as the supplementary motor area, somatosensory area,
insular cortex, cerebellum, and thalamus.[48 ]
[52 ]
[53 ] In addition, an increase in blood supply to the hippocampus and prefrontal cortex
was observed during activities following mastication. This activity is crucial for
the learning and memory process. Finally, the increase in blood flow to the brain
resulting from mastication is considered to have beneficial effects on a wide range
of cognitive functions.[45 ]
Epidemiological studies have shown that the number of remaining teeth, denture wear,
and low bite force are associated with an increased risk of dementia.[41 ] Another study also showed that reduced mastication can lead to mild cognitive decline
in Korean adults.[54 ] Other studies using animals with masticatory impairment due to tooth extraction,[55 ]
[56 ] occlusal bite plane,[57 ]
[58 ] and soft diet[59 ] found that these conditions altered hippocampal function in the spatial memory and
learning ability. However, other studies also found that the declining function of
the hippocampus can be restored by increasing chewing activity.[10 ]
[47 ]
To date, there are studies that have found a correlation between masticatory ion impairment
and specific food texture preferences in both human and animal subjects. However,
to the best of our knowledge, most studies have mainly focused on the elderly, suggesting
that masticatory impairment increases the risk of dementia and worsens their cognitive
function. A study investigating reduced mastication in young mice found a correlation
with low hippocampus activity, causing changes in the morphology of the hippocampus.[7 ]
[60 ] This could result in impaired function in spatial memory and learning ability[7 ] as well as increased vulnerability to mental disorders.[60 ] Although other studies have also found similar effects in post-weaned rats,[44 ] no such evidence in children has been found. Only a few articles mention that caries
in children might affect their cognitive function and neurodevelopment.[18 ]
The chewing patterns of children are different from those of adults. In addition,
several jaw movement parameters change with age. In early life, the sensorimotor control
of jaw movements adapts to morphological changes resulting from growth. Children can
perform adult-like chewing behavior as they reach the late-permanent dentition phase.
Changes in the histological imaging of periodontal mechanoreceptors during human growth
are currently unknown. However, research on animals shows that the density of periodontal
mechanoreceptors in the primary dentition is lower compared with the permanent dentition.
Therefore, it can be assumed that the periodontal mechanoreceptors provide inadequate
and immature sensory inputs during primary and mixed dentition.[43 ] This could explain the lack of published articles investigating the effects of masticatory
ion impairment, specifically due to ECC, on cognitive function and neurodevelopment
in children. Further research regarding the effects of untreated caries, early primary
tooth loss, mastication difficulties on children's cognitive function and neurodevelopment
is required. The summary of the effects of ECC on cognitive function is presented
in [Fig. 1 ].
Fig. 1 The effects of early childhood caries on cognitive function through changes in blood
flow and neural pathway.
Effect of Early Childhood Caries and Psychomotor Function
Effect of Early Childhood Caries and Psychomotor Function
The process of human growth from infancy to adulthood involves both mental and physical
development.[15 ] While cognition refers to the acquisition of knowledge through intellectual processes,
psychomotor function refers to the acquisition of behavior through neuromuscular motor
activities.[61 ] The psychomotor function includes the combination of precise motor responses, attention,
and cognitive problem-solving abilities. Psychomotor development represents children's
growth in terms of cognitive, emotional, social, and motor skills from early life.[62 ]
To date, ECC and psychomotor deficiency appear to be physiologically correlated. Although
somewhat elusive, it can be assumed that high caries activity makes children prone
to reduce chewing and swallowing activities, leading to inefficient digestion, which,
in turn, results in a lack of nutrition required for growth.[14 ] Studies have found that children aged 4 to 6 years old with dmft scores more than
or equal to 4 was significantly associated with psychomotor deficiency (e.g., comprehension-concept
and expressive language). However, children with dmft scores more than 6 showed no
delay in personal, social, and expressive language development.[11 ]
[15 ] Similar results were also discovered by another study, showing that more severe
ECC with dmft scores of between 3 and 8 affected the children's psychomotor development,
specifically in expressive language and comprehension concepts.[16 ] These studies found a negative correlation between caries and psychomotor function,
suggesting that higher dmft scores are associated with less language development.
This might potentially affect both expressive and receptive abilities in growing children.[14 ]
[16 ]
To be able to communicate effectively, children must be able to produce meaningful
sounds, which involve the coordination of respiration, voice, and articulation movements.
To produce correct phonemes, coordinated movements involving the jaw, lips, tongue,
soft palate, teeth, and upper airway (pharynx) are required. Maxillary incisors are
associated with the articulation of l, n, d, and r sounds.[63 ]
Despite the new finding, the mechanisms behind the potential effects of ECC and psychomotor
impairment remain unclear.[14 ]
[15 ]
[16 ]
[17 ] Further research is necessary to determine whether the correlation between ECC and
psychomotor impairment is established directly via the neurophysiological pathways
or other pathways outside the nervous system. However, this correlation can be attributed
to several pathways. ECC can affect children's growth, including physical, psychomotor,
or psychological, due to pain from cavitated teeth or primary tooth loss, which can
alter nutritional intake. This could potentially lead to nutrient loss, low body weight,
sleep disturbances, and ultimately a poorer quality of life. In addition, the presence
of any confounding factors (e.g., gender and age) and comodifiers (i.e., external
behaviors or other environmental factors affecting psychomotor function) should be
further explored to verify their potential impacts on this new finding.[14 ] Another possible mechanism is that severe ECC can compromise mastication forces,
verbal skills, and brain metabolism. These effects, if persist for a long time, may
likely alter the children's interactions with others, and further affect their social
engagement or learning, consequently impacting their language expression, verbal skills,
and communication. Therefore, ECC could likely trigger the related development delays
over time.[14 ]
[15 ]
[16 ]
The pathways showing the effects of ECC on psychomotor function are presented in [Fig. 2 ]. It is expected that children with severe untreated caries are likely to experience
chewing difficulties, resulting in inefficient digestion which further affects their
nutritional intake. The lack of nutrition can subsequently affect their development,
learning, and emotional maturity.[15 ]
Fig. 2 The potential effects of early childhood caries on psychomotor function.
Conclusion
In summary, this study revealed that untreated severe caries in children is negatively
associated with their growth and development. The most apparent effects are masticatory
impairment, nutritional intake, and verbal skills. However, the effects of untreated
severe caries on cognitive function need further exploration to determine whether
masticatory dysfunction affects cognitive function in young children as suggested
by research on animals. The relationship between ECC and psychomotor is complicated,
considering the potential interplay of causal factors, confounding variables, risks,
and interference. Before arriving at a definitive conclusion, further investigation
should focus on how ECC might influence sound distortion, disarticulation, or poor
oral functions, such as physical malocclusion and deficient language development during
maturation.
