Keywords
deglutition - mastication - smoking - stomatognathic system
Introduction
Chewing performs an active role in craniofacial growth, favoring the development of
muscle action, of the temporomandibular joint, as well as periodontal development.[1] Chewing and swallowing are physiologically interconnected, since they share motor
structures and supranuclear regions for its execution,[2] involving a sensorimotor synchrony capable of coordinating the following processes
involved in swallowing. Swallowing is the earliest acquired stomatognathic function
during the embryonic period and coordinates with the other abilities from the association
between cortical, subcortical and brainstem areas.[2] Related to the motor control, it can be divided into four phases: preparatory oral,
oral, oropharyngeal, and esophageal.[3]
The oral preparatory phase involves chewing, which performs the mechanical grinding
of the food into small fragments,[4] with closure of the lips and tongue movements as important aspects for the proper
positioning of the food bolus.[5] The oral phase begins with the tongue movements to place the food bolus on the posterior
region through its wave movements, to direct it to the pharyngeal and esophageal phases.[3] Structural and sensitivity disorders during the oral preparatory and oral phases
can interfere in the efficacy of swallowing.[6] Intrinsic and extrinsic factors can contribute to alter these processes, characterizing
them as atypical by the presence of compensatory events. Regarding extrinsic factors,
tobacco consumption results in structural alterations, such as tooth loss[7] and modification of sensory perception,[8] which cause disorders in the functionality of the stomatognathic system, which adapts
to the structure presented.[9]
From the data of the same sample included in the present study, it was observed greater
occlusal alteration associated to the masticatory performance,[7] besides the reduction of the olfactory and gustatory perception associated with
muscular compensations during the oral phase of swallowing[8] in smokers. Nevertheless, the relationship between masticatory performance and muscular
deglutition compensations in this population has not yet been elucidated to evaluate
whether these adaptations are directly associated with smoking or if they are from
a deviated masticatory behavior. Thus, the objective of the present study is to analyze
the masticatory and swallowing patterns of smokers and nonsmokers and to verify if
there is an association between masticatory behavior and the presence of muscular
swallowing compensations in smokers.
Methods
This is a comparative cross-sectional study, which was approved by the Research Ethics
Committee of the institution of origin under the protocol number 3636/11. All of the
participants agreed to participate in the study and signed the informed consent form
after being explained the study objectives and procedures. The sample consisted of
48 subjects, divided into 2 study groups equally distributed, paired by gender and
age in a 1:1 ratio: smokers and individuals who never smoked and were not exposed
to passive consumption of the substance ([Fig. 1]). Smokers were recruited from the pulmonology clinic of the institution, and nonsmokers
volunteered to participate.
Fig. 1 Pairing of individuals in the study groups.
As inclusion criteria, the subjects should not have diagnosis of neurodegenerative
or systemic diseases, salivary alterations, disorders in the upper airways, be using
medication or treatments for the stomatognathic system, or present with congenital
or genetic alterations of the sensorimotororal system.
Aiming to establish the characteristics and the association of mastication and swallowing
functions, we have performed an evaluation of these functions through clinical observation
by a single professional with experience in the area.
To perform the evaluation of the masticatory function, the subject was asked to ingest
bread in the usual way. During mastication, the following parameters were recorded
from an adapted protocol[10]: food grinding, performed with the posterior teeth, with the anterior teeth or with
the tongue; masticatory pattern, classified in alternating bilateral, unilateral right,
unilateral left or simultaneous bilateral; masticatory speed, considered adequate,
increased or decreased; presence or absence of atypical muscle contractions; besides
lip closure during the masticatory act, considered as adequate or with partial closure.
After the masticatory evaluation, the muscular behavior of the perioral region was
analyzed during swallowing. Thus, aspects of contraction of the orbicular and mental
musculature were evaluated. To delineate orbicularis muscle compensation, this variability
was graded into four aspects: absent, when there was no movement of this musculature
during swallowing; mild, when only contraction of the labial commissures was present;
medium, contraction of the labial commissures associated with slight contraction in
the center of the lips; and accentuated contraction of the labial commissures associated
with intense contraction of the center of the lips. To describe the compensation of
the mental muscle contraction, it was defined as: absent, when there was no movement
of this musculature during swallowing; mild, when there was only muscle elevation;
medium, slight contraction; and accentuated, intense contraction. In addition, aspects
of head movement during swallowing and presence of oral residues after swallowing
were also observed.
The data were analyzed through descriptive statistics and statistical tests. The Fisher
exact test was used to compare masticatory and swallowing variables between groups
and to evaluate the relationship between time and amount of smoking aspects with masticatory
variables and the association between chewing and swallowing aspects. The results
were considered significant at a maximum significance level of 5%, and the statistical
software used for the analysis was IBM SPSS Statistics for Windows, Version 21.0 (IBM
Corp. Armonk, NY, USA).
Results
Comparing the sample by masticatory behavior ([Table 1]), it was observed that nonsmokers perform grinding of food with the posterior teeth,
while smokers present a pattern of kneading of food with the tongue. In addition,
the masticatory speed of smokers was decreased compared with nonsmokers, and there
was no difference between the groups for other masticatory variables. There was no
association between masticatory performance with time and amount of tobacco consumption,
stratifying the sample in 20 years and 20 cigarettes per day of consumption, respectively
(p> 0.05).
Table 1
Comparison between groups regarding masticatory behavior
|
Variable
|
Category
|
Group
|
p-value
|
|
Nonsmokers
|
Smokers
|
|
n
|
%
|
n
|
%
|
|
Food griding
|
Posterior teeth
|
22
|
91.7
|
13
|
54.2
|
0.011[*]
|
|
Anterior teeth
|
2
|
8.3
|
7
|
29.2
|
|
|
With tongue
|
−
|
−
|
4
|
16.7
|
|
|
Masticatory pattern
|
Bilateral
|
15
|
62.5
|
9
|
37.5
|
0.287NS
|
|
Unilateral right
|
5
|
20.8
|
6
|
25.0
|
|
|
Unilateral left
|
1
|
4.2
|
4
|
16.7
|
|
|
Simultaneous bilateral
|
3
|
12.5
|
5
|
20.8
|
|
|
Masticatory speed
|
Adequate
|
16
|
66.7
|
13
|
54.2
|
0.048[*]
|
|
Increased
|
5
|
20.8
|
1
|
4.2
|
|
|
Decreased
|
3
|
12.5
|
10
|
41.7
|
|
|
Atypical muscle contractions
|
Absent
|
18
|
75.0
|
22
|
91.7
|
0.245NS
|
|
Present
|
6
|
25.0
|
2
|
8.3
|
|
|
Lip clousure
|
Adequate
|
21
|
87.5
|
23
|
95.8
|
0.609NS
|
|
Partial
|
3
|
12.5
|
1
|
4.2
|
|
NS, Not Significative.
*
p < 0.05.
Regarding swallowing performance ([Table 2]), there was a difference between the groups in mental contraction, which was absent
when associated with nonsmokers, and with mean contraction among smokers, with no
statistically significant difference for other variables.
Table 2
Comparison between the groups regarding the swallowing behavior
|
Variable
|
Category
|
Group
|
p
|
|
Non-Smokers
|
Smokers
|
|
n
|
%
|
n
|
%
|
|
Contraction of the orbicular muscle
|
Absent
|
2
|
8,3
|
−
|
−
|
0,130NS
|
|
Mild
|
11
|
45,8
|
6
|
25,0
|
|
Medium
|
7
|
29,2
|
9
|
37,5
|
|
Accentuated
|
4
|
16,7
|
9
|
37,5
|
|
Contraction of the mentual muscle
|
Absent
|
10
|
41,7
|
1
|
4,2
|
0,003[*]
|
|
Mild
|
11
|
45,8
|
13
|
54,2
|
|
Medium
|
−
|
−
|
5
|
20,8
|
|
Accentuated
|
3
|
12,5
|
5
|
20,8
|
|
Head movement
|
Absent
|
21
|
87,5
|
17
|
70,8
|
0,286NS
|
|
Present
|
3
|
12,5
|
7
|
29,2
|
|
Oral residues after swallowing
|
Absent
|
22
|
91,7
|
19
|
79,2
|
0,416NS
|
|
Present
|
2
|
8,3
|
5
|
20,8
|
NS, Not Significant.
*
p < 0,05.
No relationship was observed between masticatory findings on muscle compensations
during the oral phase of swallowing of smokers in any of the analyzes performed (p > 0.05).
Discussion
The impact of smoking on stomatognathic functions in the absence of tumor lesions
is still poorly described in the literature. Therefore, the results obtained in the
present study, although restricted, allow analyzing the influence of this habit on
oral myofunctional changes. These modifications occur insidiously, and probably because
of this, are not even associated to tobacco consumption by users and even by health
professionals.
The results obtained allowed to observe the variability of food grinding between the
groups, revealing that smokers use the tongue as a compensatory mechanism to crush
food. This compensation is associated with a higher prevalence of dental losses in
smokers.[11]
[12] The lack of these elements can alter the masticatory balance,[13] causing a compensation in the abilities of stomatognathic functions.[14] Regarding the masticatory difficulty, tooth loss is directly related to this alteration,
since, in the absence of teeth, the tongue interposes in the edentulous place, modifying
the pattern.[14]
Considering the masticatory speed, it was verified that smokers have a slower pattern.
It occurs due to the reduction of dental pieces, which increases the time spent for
adequate preparation of the food before swallowing. As the efficiency of the masticatory
pattern is decreased, since it is performed by tongue kneading,[7] it is expected that the masticatory speed will be in deficit. In addition, the gustatory
capacity of smokers is reduced due to structural changes caused by smoking.[8] This difficulty to taste the food properly can decrease the masticatory speed, since
the process occurs without adequate sensorial stimulation.[15]
[16]
It is considered that an inefficient masticatory pattern will allow the ingestion
of fragments that are larger and less moistened by the saliva, resulting in a greater
effort during swallowing that can be accompanied by compensatory movements of the
head and facial musculature.[11] In smokers, it was not possible to establish an association between the masticatory
pattern and the appearance of swallowing compensations, since the increased muscular
compensations are due to other factors related to smoking that influence this motor
activity response.[8]
[17] It is important to point out that, since there is no association between the masticatory
characteristics of time and the amount of tobacco consumption, the inference that
this deviant masticatory pattern is due to an adaptation of the system to structural
alterations, such as tooth loss and reduction of perception, and not directly related
to tobacco exposure, becomes plausible, corroborating the findings previously described.
Based on the data collected in the present sample and on other studies in the literature
that corroborate these findings, the present study group proposes a qualitative hypothesis
model[18] that associates tobacco consumption to the stomatognathic functions, which is presented
in [Fig. 2]. It is believed that the formulation hypothesis model should be analyzed in longitudinal
studies with large sample sizes, an adequate methodology to establish causality, to
confirm or refute these association findings, which would allow an in-depth analysis
on the risks to the stomatognathic functions associated with smoking.
Fig. 2 Hypothesis model of influence of tobacco consumption in stomatognathic functions
disorders.
Conclusion
The present study allowed us to observe changes in the pattern of mastication and
swallowing behavior in smokers, with atypical patterns in both functions compared
with nonsmokers. It was observed that the masticatory characteristics are not associated
with time and amount of tobacco consumption, but it is a consequence of the structural
alterations of the stomatognathic system. In addition, the appearance of muscular
compensations during swallowing are associated with the smoking habit and not with
the masticatory pattern itself, as described in a previous study of this sample.
