Keywords
dentin hypersensitivity - patient - health - questionnaire - regression analysis -
surveys
Introduction
Due to its painful characteristics, dentin hypersensitivity (DH) has been shown to
impact on the patient's quality of life.[1] A systematic review estimated that the prevalence of DH is 11.7% worldwide and affects
more women and young adults.[2]
[3] Yet, despite the importance of preventing and treating this condition, studies reported
that dentists commonly control its symptoms without, in fact, controlling its etiological
factors.[4]
[5]
[6]
Previous studies on the knowledge of dentists about the management of DH have been
published.[4]
[5]
[6]
[7]
[8]
[9]
[10] For example, Zeola et al[5] reported that dentists are already attentive and concerned about controlling the
predisposing factors for the development of DH, although Francisconi-dos-Rios et al[6] and Exarchou et al[9] reported that the professionals' and students' knowledge on this topic still required
improvement. Moreover, although several dental schools have included teaching on DH
and noncarious cervical lesions (NCCLs) in their curricula, communication with the
local lay community was often neglected by the profession. In these cases, even though
the dentist can perform the treatment, patients do not seek dental care because they
either do not identify this condition as treatable or consider the condition as a
relatively minor inconvenience not requiring treatment.[4]
[9]
Several factors have also been reported to be associated with DH, such as orthodontic
treatment, frequency of daily toothbrushing, use of dietary supplements by athletes,
gastroesophageal disorders, use of illicit drugs, and even parafunctional habits.[11]
[12]
[13]
[14]
[15]
[16] Some of these factors are daily habits unknown or overlooked by the population.
Therefore, to practice person-centered care, the patient should be made aware of these
habits to make the process of prevention and treatment easier, simpler and to reduce
the costs related to the maintenance of oral health.[17] Thus, it is necessary to identify what self-reported habits can serve as predictors
for DH for dentists to modify or eliminate these factors when considering the prevention
and treatment of the condition.
Therefore, the aim of this study was to assess the knowledge of a sample of the Brazilian
population regarding prevention, diagnosis, and treatment of DH, and to identify what
self-reported factors are associated with it and can serve as predictors of the presence
of DH.
Materials and Methods
The CHERRIES (Checklist for Reporting Results of Internet E-Surveys)[18] and the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology)[19] guidelines were used to report this observational cross-sectional study.
Study Design and Ethical Aspects
This study was conducted using a voluntary online questionnaire open survey with a
convenience sample. The questionnaire was specifically developed for this study and
was composed by sociodemographic questions, followed by 22 questions about DH and
its etiological factors. This study was performed following approval by the local
Human Research Ethics Committee (CAAE: 46103021.3.0000.5417).
Development and Testing
The questionnaire was developed by two researchers based on the complaints and on
the clinical signs and symptoms detected by dentists during the care of patients with
DH at the university dental clinics.
After developing it, the questionnaire was revised by independent experts regarding
its content and clarity (content validity analysis). These experts reported to the
developers what questions were not clear and/or irrelevant, so the questionnaire could
be modified until all the questions were unanimously considered clear and relevant.
Then, the questionnaire usability and technical functionality were pretested with
a small sample composed of lay citizens (not related to the dentistry field) and dentists
using different electronic devices. Considering their answers and feedback, the questionnaire
was once again adjusted to better fit the aims of the authors and to improve its clarity,
comprehensiveness, and acceptability. Thereafter, due to the modifications made to
the questionnaire after the pretest, the data generated during the pretest were discarded
before the commencement of the study.
Questionnaire Characteristics
The questionnaire was developed through the Google Forms platform. Before answering,
the participants were educated about DH and informed that the estimated time required
to complete all questions was 10 minutes. The participants were also informed on the
purpose of the study, who were the investigators, and that their answers and e-mail
addresses would be stored only for the purpose of the study. Questionnaire responses
were kept confidential, and participants were kept anonymous, but an e-mail account
was necessary to prevent duplicate entries. No cookies nor IP checks were used. No
incentives were offered, and data were kept secure in a Google Drive account, which
could be accessed only by this study's investigators.
The questionnaire (unvalidated English version available as Appendix 1) was structured
in four main pages: (1) the first page involved six sociodemographic questions, (2)
the second page (with seven questions) addressed the participants' perception of their
own oral health (with pictures available for consultation); (3) the third page (two
questions) included specific questions related to the impact of other dental treatments
on DH; and (4) the final page (seven questions), specific questions about DH prevention
and treatment.
All questions were set as mandatory, and the questionnaire could not be submitted
without its completion. The questions and the alternatives were not randomized for
each participant and no consistency or integrity check was performed before the questionnaire
was submitted. The participants were able to revise and, if necessary, modify their
answers before submission.
Sample Size Calculation
The sample size was estimated according to Faul et al,[20] whose model containing f
2 = 0.15, α error = 0.05 and power (1 − β) = 0.95 estimated that a sample with n = 178 was necessary when considering 11 independent variables inserted in a multiple
linear regression model.
Sample Acquisition
Social media were used to recruit participants from all regions of Brazil. The posts
and invitations contained a description of the study and the link to access the questionnaire.
In total, 227 people accessed the questionnaire; however, one person did not consent
to participate in the study, so the sample consisted of 226 participants who completed
the questionnaire between July and December 2021.
Eligibility Criteria
The sample was composed of Brazilian citizens from all parts of Brazil who were at
least 18 years old and did not graduate as dentists or were currently enrolled in
a dentistry course. Individuals without a resident visa in Brazil were not included
in the sample.
Data Interpretation
Data interpretation(s) were comparable to the methodological interpretation used by
Foratori-Junior et al,[21] for example, the educational level was categorized from 0 to 5 as: 0, illiteracy;
level 1, incomplete high school; level 2, complete high school; level 3, incomplete
higher education; level 4, complete higher education; and level 5, complete postgraduation
degree.
Monthly household income was organized into six categories according to the minimum
wage (MW) approved by the Brazilian government for the year 2021 as R$ 1,100.00 (approximately
USD 199): level 1, up to 1 MW; level 2, between 1 and 2 MW; level 3, between 2 and
3 MW; level 4, between 3 and 4 MW; level 5, between 4 and 5 MW; and level 6, more
than 5 MW.
All answers to the questions that evaluated the frequency with which a certain situation
occurred were ordered in a modified Likert scale, with score 0 assigned to the answers
“never”; 1 to “rarely”; 2 to “sometimes”; 3 to “often”; and 4 to “always.” Based on
these scores, the answers to the questions related to the frequency with which the
participants experienced DH when (1) ingesting cold water, (2) talking in windy environments,
(3) ingesting a cold drink, (4) ingesting acidic foods, and (5) brushing their teeth
were added and grouped in the variable “frequency of DH,” with a minimum score of
0 and a maximum of 20. The “frequency of DH” score was categorized into nonexistent
(score 0), low (between 1 and 6), moderate (between 7 and 13), and high (between 14
and 20).
Similarly to that stated earlier, the score of the questions related to the frequency
with which the participant (1) consumed acidic foods or drinks, (2) felt stressed
or anxious, (3) gritted teeth, (4) pressed tongue against teeth, (5) bit lips, cheeks,
or tongue, (6) chewed on objects (such as pens, glasses, or nail), (7) brushed their
teeth vigorously, and (8) brushed their teeth with a medium-bristled toothbrush were
summarized and grouped in the variable “modulating factors,” with a minimum score
of 0 and a maximum of 32. The score was also categorized into nonexistent (score 0),
low (between 1 and 10), moderate (between 11 and 20), and high (between 21 and 32).
The score for the answers to questions related to the frequency with which the participants
reported (1) difficulties opening their mouth upon waking up, (2) headaches, (3) pain
or tension in the neck, and/or (4) pain near the ears were added and grouped in the
variable “symptom of parafunction,” with a score minimum of 0 and maximum of 16. The
score was categorized into nonexistent (score 0), low (between 1 and 5), moderate
(between 6 and 10), and high (between 11 and 16).
Statistical Analysis
Data were organized and a qualitative descriptive analysis was performed, expressing
the data in absolute numbers, percentages, and means. Also, the participants' answers
for variables “frequency of DH,” “modulating factors,” and “symptom of parafunction”
were subjected to a reliability analysis using Cronbach's alpha test.
A multiple linear regression analysis was performed (backward method), in which the
dependent variable was the “frequency of DH” (score between 0 and 20). The analysis
of the residues was performed, and the independency of the residues, presence of outliers,
normal distribution, multicollinearity, and homoscedasticity were checked. A significance
level of 5% was adopted. The independent variables included in the regression model
were gender, age, educational level, household monthly income, presence of NCCLs,
presence of carious lesions, frequency of daily toothbrushing, use of orthodontic
appliances, use of a product for DH, modulating factors, and symptom of parafunction.
All tests were conducted using the IBM SPSS Statistics v25 (IBM Corp, Armonk, New
York, United States) software.
Results
All 226 participants were residents of the Northeast, Midwest, South, and Southeast
regions of Brazil and presented ages between 18 and 74 years (mean: 35.1 ± 12.2).
The sociodemographic characteristics are displayed in [Table 1]. The Cronbach's alpha test retrieved a value of α = 0.726, therefore was considered
acceptable.
Table 1
Sample sociodemographic characteristics (n = 226)
|
Sociodemographic
|
n
|
%
|
|
Gender
|
|
Females
|
138
|
61.1
|
|
Males
|
88
|
38.9
|
|
Educational level
|
|
Illiterate
|
0
|
0
|
|
Incomplete high school
|
4
|
1.8
|
|
Complete high school
|
25
|
11
|
|
Incomplete higher education
|
51
|
22.6
|
|
Complete higher education
|
58
|
25.7
|
|
Postgraduation degree
|
88
|
38.9
|
|
Household monthly income
|
|
Less than 1 minimum wage
|
27
|
11.9
|
|
Between 1 and 2 minimum wages
|
33
|
14.6
|
|
Between 2 and 3 minimum wages
|
32
|
14.2
|
|
Between 3 and 4 minimum wages
|
20
|
8.9
|
|
Between 4 and 5 minimum wages
|
26
|
11.5
|
|
More than 5 minimum wages
|
88
|
38.9
|
|
Dental care
|
|
In the private sector
|
192
|
84.9
|
|
In the public sector
|
16
|
7.1
|
|
In both sectors
|
18
|
8
|
As for the “frequency of DH” score ([Table 2]), the mean value among the participants was 4.2; therefore, it was classified as
low. The situations that the participants reported triggering DH episodes more frequently
were, respectively, when (1) ingesting cold foods, (2) brushing their teeth, (3) ingesting
some hot food, (4) ingesting acidic foods, and (5) speaking in windy environments.
Table 2
Participants' self-perception of oral health and previous dental treatments
|
Self-perception of oral health and previous dental treatments
|
n
|
%
|
|
Frequency of DH scores
|
|
Nonexistent (score 0)
|
22
|
9.8
|
|
Low (scores 1–6)
|
158
|
69.9
|
|
Moderate (scores 7–13)
|
43
|
19
|
|
High (scores 14–20)
|
3
|
1.3
|
|
Modulating factors scores
|
|
Nonexistent (score 0)
|
0
|
0
|
|
Low (scores 1–10)
|
58
|
25.7
|
|
Moderate (scores 11–20)
|
148
|
65.5
|
|
High (scores 21–32)
|
20
|
8.8
|
|
Parafunction symptom scores
|
|
Nonexistent (score 0)
|
10
|
4.4
|
|
Low (scores 1–5)
|
133
|
58.8
|
|
Moderate (scores 6 to 10)
|
70
|
31
|
|
High (scores 11–16)
|
13
|
5.8
|
|
Presence of carious lesions
|
|
Yes
|
60
|
26.5
|
|
No
|
120
|
53.1
|
|
Do not know
|
46
|
20.4
|
|
Presence of NCCLs
|
|
Yes
|
50
|
22.1
|
|
No
|
133
|
58.9
|
|
Do not know
|
43
|
19
|
|
Used product for DH
|
|
Yes
|
43
|
19
|
|
No
|
182
|
80.5
|
|
Do not know
|
1
|
0.5
|
|
Frequency of daily toothbrushing
|
|
Do not brush their teeth
|
0
|
0
|
|
Once a day
|
9
|
4
|
|
Twice a day
|
62
|
27.4
|
|
Thrice a day
|
108
|
47.8
|
|
More than three times a day
|
47
|
20.8
|
|
Using/used orthodontic appliances
|
|
Yes
|
162
|
71.7
|
|
No
|
64
|
28.3
|
Abbreviations: DH, dentin hypersensitivity; NCCL, noncarious cervical lesion.
Most of the sample also reported not having carious lesions nor NCCLs ([Table 2]). Also, 80.5% of the participants reported not using any DH product. Among the participants
who reported using a product for DH, 79.1% (n = 34) used it after being prescribed by a dentist, 7% (n = 3) used products recommended by friends or family, 7% (n = 3) by advertisements on television or social media, and 7% (n = 3) by other communication vehicles.
When asked about the frequency with which they used DH products, 64.6% (n = 146) reported never using these products without their dentist's instructions,
15.9% (n = 36) reported doing so rarely; 10.2% (n = 23) sometimes; 7.1% (n = 16) frequently; and 2.2% (n = 5) always. However, when asked about the frequency with which they scheduled an
appointment with a dentist following experiencing DH episodes, 21.2% (n = 48) reported never doing it; 30.1% (n = 68), rarely; 23.9% (n = 54), sometimes; 15% (n = 34), frequently; and 9.7% (n = 22), always.
The results for the frequency of daily toothbrushing and use of orthodontic appliances
are displayed in [Table 2]. Of those participants who wore orthodontic appliances (n = 162), 83.9% (n = 136) did not use any product for DH; 15.4% (n = 25) used at least one product for DH, and 0.6% (n = 1) did not know if the product they used was for DH. On the contrary, those participants
who never wore orthodontic appliances (n = 64), 71.9% (n = 46) did not use any product for DH, whereas 28.1% (n = 18) did. The frequency of DH score of those who wore orthodontic appliances and
of those who never did were both 4.2 and classified as low.
When the modulating factors were measured ([Table 2]), the mean value among the participants was 14.2. Hence, the frequency of DH scores
of the sample was classified as moderate. Habits that patients reported more frequently
were, respectively, (1) consumption of acidic foods, (2) feeling stressed and/or anxious;
(3) grinding or clenching teeth; (4) brushing teeth with force; (5) biting lips, cheeks,
or tongue; (6) pressing the tongue against the teeth; (7) chewing on objects; and
(8) using a toothbrush with medium or hard bristles.
In respect of parafunctional habits ([Table 2]), the mean value among the participants was 4.8; therefore, it was classified as
low. The symptoms that patients reported most frequently were as follows: (1) neck
pain or tension, (2) headaches, (3) pain near the ears, and (4) difficulty in opening
the mouth upon waking up.
Overall, 63.3% of the participants answered they acknowledged DH could be prevented
([Table 3]), and 81.4% reported knowing that DH could be treated. Also, 60.2% believed that
DH treatment is temporary in nature. The participants' answers for the use of toothpastes,
laser, orthodontic appliances, and professional products on the treatment of DH are
displayed in [Table 3].
Table 3
Participants' answers about DH prevention and treatment
|
DH prevention and treatment
|
n
|
%
|
|
Knew that DH can be prevented
|
|
Yes
|
143
|
63.3
|
|
No
|
83
|
36.7
|
|
Knew that DH can be treated
|
|
Yes
|
184
|
81.4
|
|
No
|
42
|
18.6
|
|
The treatment is
|
|
Definitive
|
32
|
14.2
|
|
Temporary
|
136
|
60.2
|
|
I do not know
|
58
|
25.6
|
|
Can toothpastes be used in the treatment of DH
|
|
Yes
|
197
|
87.2
|
|
No
|
8
|
3.5
|
|
I do not know
|
21
|
9.3
|
|
Can lasers be used in the treatment of DH
|
|
Yes
|
56
|
24.8
|
|
No
|
31
|
13.7
|
|
I do not know
|
139
|
61.5
|
|
Can orthodontic appliances be used in the treatment of DH
|
|
Yes
|
32
|
14.2
|
|
No
|
88
|
38.9
|
|
I do not know
|
106
|
46.9
|
|
Can professional products be used in the treatment of DH
|
|
Yes
|
188
|
83.2
|
|
No
|
8
|
3.5
|
|
I do not know
|
30
|
13.3
|
Abbreviation: DH, dentin hypersensitivity.
Regarding the multiple linear regression, multicollinearity (tolerance values >0.772;
Variance Inflation Factor (VIF) values <1.295) and outliers were not detected, and
the residuals were independent (Durbin–Watson <1.899). This analysis resulted in a
statistically significant final model (F [5,220] = 12.047; p < 0.001; R
2 = 0.215) with the independent variables (1) presence of NCCLs, (2) frequency of daily
toothbrushing, (3) use of any product for DH, (4) modulating factors, and (5) symptoms
of parafunction present in the final model as possible predictors of the dependent
variable ([Table 4]).
Table 4
Final multiple linear regression model indicating the predictive variables related
to the dependent variable
|
Dependent variable
|
Independent variable
|
Standardized β
|
t
|
p-Value
|
|
Frequency of DH
|
–
|
–
|
–
|
–
|
|
Presence of NCCLs
|
0.126
|
2.092
|
0.038
|
|
Frequency of daily toothbrushing
|
−0.101
|
−1.667
|
0.097
|
|
Use of desensitizing product
|
0.262
|
4.334
|
<0.001
|
|
Modulating factors
|
0.220
|
3.231
|
0.001
|
|
Symptom of parafunction
|
0.168
|
2.497
|
0.013
|
Abbreviation: DH, dentin hypersensitivity, NCCLs, noncarious cervical lesions.
Discussion
This study identified that 36.7% and 18.6% of the population did not know that DH
can be prevented or treated, respectively. Moreover, despite the participants having
a low frequency of DH episodes and symptoms of parafunctional habits, the presence
of habits that can lead to the development of DH was moderate in nature. Finally,
the study also reported on some of the predictors of the frequency with which patients
experienced episodes of DH, such as: (1) presence of NCCLs, (2) frequency of daily
toothbrushing, (3) use of products for DH, (4) presence of modulating factors, and
(5) parafunctional habits symptoms.
As reported by Gillam et al,[22] DH can only be diagnosed by excluding other potential causes for dental pain. Therefore,
the information collected during screening and clinical examination stages are essential
to exclude other conditions with similar pain characteristics, including dental caries,
pulpitis, molar–incisor hypomineralization, fractured/chipped restorations/teeth,
and gingival inflammation.[13]
[22]
[23]
[24]
[25]
[26] In the present study, the presence of carious lesions did not remain in the final
regression model, which also indicated that patients were relatively able to differentiate
the presence of carious lesions from the symptoms of DH, also validating the final
regression model. Yet, the results must be interpreted with caution, given that this
is a self-reported study and that patients often consider that they have carious lesions
because of a stained area in their teeth while ignoring areas of white spot lesions.
Furthermore, as suggested by other previous studies,[27]
[28]
[29] despite DH being a symptom arising from the exposure of dentin to the oral environment
and NCCLs being considered a structural defect, these two conditions are closely related.
Que et al[27] reported that 15% of the evaluated teeth had NCCLs, while 4.7% had DH. However,
63.3% of the teeth with DH also presented NCCLs, indicating the close relationship
between these two conditions. This relationship is relevant since both NCCLs and DH
share some etiological factors,[9]
[27]
[30] and the presence of NCCLs often lead to exposure of dentin, which, in turn, may
lead to the onset of DH. This justifies the presence of NCCLs being a predictive factor
in the final regression model in the present study (p = 0.038). This finding agrees with other published studies, where an association
between DH and NCCLs was also observed.[27]
[28]
[31]
In a systematic review,[32] the worldwide prevalence of NCCLs is estimated at 46.7%, contrasting with the 22.1%
observed in the present study. Nevertheless, as previously mentioned, data collected
in this study were self-reported, and 19% of the sample could not indicate whether
they had any type of NCCL, even though NCCLs images were available during the completion
of the questionnaire. This suggests that, if NCCLs were identified during a clinical
examination, the prevalence of NCCLs in the present study could have been closer to
that reported in the systematic review.
Previous studies also reported an association between dental erosion and DH.[9]
[15]
[33] In the present study, the presence of habits related to the consumption of acidic
foods or drinks presented the highest frequency values between the modulating factors
of DH. This observation agreed with the studies of Exarchou et al[9] and O'Toole and Bartlett,[15] in which patients with erosive eating habits had a higher prevalence of DH symptoms
(p < 0.001) and corroborated the fact that the independent variable “modulating factors”
remained as a predictor in the final regression model (p = 0.001) in the present study.
However, although an acidic diet may be an etiological factor for DH,[9]
[15]
[22]
[33] some associated habits appeared to increase this loss, such as the use of abrasive
toothpastes[33]
[34]
[35] and the habit of sipping or holding the drink in the mouth for several seconds.[15] Brushing frequency and force, as well as brush stiffness, are also able to act as
cofactors in the development of NCCLs,[30]
[36] which justifies the fact that the brushing frequency remained in the final regression
model in this study. However, as described by O'Toole and Bartlett,[15] the frequency of brushing appeared to have a lower relevance for the development
of DH than the stiffness of the brush bristles and the use of abrasive toothpastes,
which may explain the fact this variable did not show statistical significance within
the final regression model (p = 0.097).
When considering the importance of this condition, it is important that desensitizing
toothpastes are recommended by a dentist. In the present study, although 87.2% of
the participants stated knowing that toothpastes could be used to control DH and 19%
used a desensitizing product, 20.9% of the participants reported that the products
they used had not been recommended by a dentist. These data agree with the conclusions
by Medeiros et al,[28] in which an association was detected between the use of desensitizing toothpastes
and the presence of NCCLs, and with Gillam et al,[4] where 23.3% of participants reported using a desensitizing dentifrice. These data
are particularly important to the present study because the use of desensitizing products
was one of the predictive variables in the final regression model (p < 0.001).
The desensitizing product that the participants reported knowing the most about was
a toothpaste, with the use of lasers being the least known. This is probably due to
the easy access of this sample population to the former, but it is also possible that
the lack of knowledge of other resources is either related to the lack of communication
between the dentist and the patient or to the fact that only 15% and 9.7% of patients
frequently and always, respectively, scheduled an appointment with a dentist upon
experiencing a DH episode. This observation agrees with a previous study, where 48%
of patients reporting sensitivity never consulted a dentist.[37] Other published studies have reported that DH is not perceived as a severe problem[9]; therefore, patients do not seek treatment,[4] making it particularly difficult to manage the symptoms and educate them.
Moreover, contrary to the study of Medeiros et al,[28] the use of orthodontic appliances did not remain as a predictive factor in the final
regression model of the present study. However, the relationship between orthodontic
treatment and DH is widely discussed in the published literature, as there is evidence
that the use of orthodontics in patients with gingival recession due to trauma appears
to reduce gingival recession following bone remodeling during tooth movement.[38] Conversely, there is also evidence that orthodontic movement increases the prevalence
of gingival recession in patients with anteversion of the lower anterior teeth and
in patients requiring maxillary arch expansion.[39] Future studies are therefore required to investigate the association of orthodontic
movement with DH. Thus, as orthodontic movement can be beneficial or harmful for gingival
recession depending on its causal factor, and while the causal factor of recession
was not investigated in each participant, it is possible that these factors were canceled
out, justifying the absence of an association with the frequency of DH in this study.
The present study also has its limitations, for example, the questionnaire was based
on self-reported answers, and therefore, the participants could have had different
interpretations of a particular question, which in turn could influence their answers.
Furthermore, despite the questionnaire being answered anonymously, the existence of
the Hawthorne effect cannot be ignored, especially in questions related to (1) the
frequency of daily toothbrushing, (2) if the participants scheduled an appointment
with the dentist following experiencing an DH episode, and (3) if they used products
with their dentist's advice.
In addition, the cross-sectional model and the representativeness of the sample are
also limited, since most study participants had an average household monthly income
more than 5 MW, which differs from the data reported by the Brazilian Institute of
Geography and Statistics (Instituto Brasileiro de Geografia e Estatística [IBGE]),
where the average income of the Brazilian population in 2021 was close to 2 MW.[40]
Despite these limitations, understanding the population's knowledge on DH is also
important to practice the person-centered care approach,[17] as this helps professionals to understand which habits may be related to onset of
the disease and what information helps the patient to become an active part in their
own treatment. This approach may therefore help make the process of prevention and
treatment easier and cheaper, which increases the possibility of a longer lasting
result.
Conclusion
In conclusion, 36.7% of a Brazilian population sample were unaware that DH can be
prevented, whereas 18.6% were also unaware that DH can be treated. Furthermore, the
presence of NCCLs, frequency of daily toothbrushing, use of products for DH, presence
of DH modulating factors, and presence of symptoms of parafunctional habits were identified
as predictive factors of the frequency of DH episodes.
