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J. Clin. Med. 2021, 10, 3103. https://doi.org/10.3390/jcm10143103 www.mdpi.com/journal/jcm
Article
Factors Influencing Patient Compliance during Clear Aligner
Therapy: A Retrospective Cohort Study
Lan Huong Timm
1,
*
,†
, Gasser Farrag
1,†
, Martin Baxmann
2
and Falk Schwendicke
3
1
Sunshine Smile, Windscheidstraße 18, 10627 Berlin, Germany; gassertarekf@gmail.com
2
Orthodentix, Arnoldstrasse 13 b, 47906 Kempen, Germany; martin.baxmann@orthodentix.de
3
Department of Oral Diagnostics, Digital Health and Health Services Research,
Charité—Universitätsmedizin Berlin, Aßmannshauser Straße 4-6, 14197 Berlin, Germany;
falk.schwendicke@charite.de
* Correspondence: lan.timm@plusdental.de
† Contributed the same.
Abstract: Compliance is highly relevant during clear aligner therapy (CAT). In this retrospective
cohort study, we assessed compliance and associated covariates in a large cohort of CAT patients.
A comprehensive sample of 2644 patients (75.0% females, 25.0% males, age range 18–64 years,
median 27 years), all receiving CAT with PlusDental (Berlin, Germany) finished in 2019, was
analyzed. Covariates included demographic ones (age, gender) as well as self-reported
questionnaire-obtained ones (satisfaction with ones’ smile prior treatment, the experience of
previous orthodontic therapy). The primary outcome was compliance: Based on patients’ consistent
use of the mobile application for self-report and aligner wear time of ≥22 h, patients were classified
as fully compliant, fairly compliant, or poorly compliant. Chi-square test was used to compare
compliance in different subgroups. A total of 953/2644 (36.0%) of patients showed full compliance,
1012/2644 (38.3%) fair compliance, and 679/2644 (25.7%) poor compliance. Males were significantly
more compliant than females (p = 0.000014), as were patients without previous orthodontic
treatment (p = 0.023). Age and self-perceived satisfaction with ones’ smile prior to treatment were
not sufficiently associated with compliance (p > 0.05). Our findings could be used to guide
practitioners towards limitedly compliant individuals, allowing early intervention.
Keywords: orthodontics; corrective orthodontics; removable orthodontic appliance; clear aligners;
malocclusion; remote consultation; telemedicine; teledentistry; teleorthodontics; distance
counseling
1. Introduction
Technological advancements in computers, mobile phones, internet security,
telecommunications, and software allow increased options for networking, information
sharing, and consultation in medicine, facilitating remote and cost-effective (tele-
)healthcare [1–6]. In dentistry, non-contact communication between patients and dentists
has been used for various steps along the clinical workflow including initial diagnosis,
joint treatment planning, follow-up, and intermediate consultations [1–6].
The clear aligner technology (CAT) builds on clear thermoformed plastic aligners to
correct mild to moderately complex forms of malocclusion [7,8] and has gained popularity
in the past years especially for adult orthodontics [9,10]. Although there are a lot of
similarities between different CAT systems, they differ in their range of application,
methods of construction, aligner thickness, the use of bonded resin attachments, the
treatment sequence, and the application duration per aligner. While rapid technological
advances lead to a highly paced evolution of these different systems [7,8], there is often
limited evidence supporting them [7,8,11,12].
Citation: Timm, L.H.; Farrag, G.;
Baxmann, M.; Schwendicke, F.
Factors Influencing Patient
Compliance during Clear Aligner
Therapy: A Retrospective Cohort
Study. J. Clin. Med. 2021, 10, 3103.
https://doi.org/10.3390/jcm10143103
Academic Editor: Theodore Eliades
Received: 18 June 2021
Accepted: 12 July 2021
Published: 14 July 2021
Publisher’s Note: MDPI stays
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Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license
(http://creativecommons.org/licenses
/by/4.0/).
J. Clin. Med. 2021, 10, 3103 2 of 10
Like other orthodontic treatment appliances, CAT moves teeth by applying
compressive and tensile forces to the periodontium. Optimal orthodontic tooth movement
occurs when continuous forces are applied and maintained, while given that teeth are
moved, the initial forces exerted are higher than those later during each aligner step.
Hence, regular change of aligners is needed. In more recent concepts these changes are
suggested to be required after one to two weeks. Regularly changing aligners requires a
high level of patient compliance [13,14]. Such compliance is further needed as they need
to be worn near-permanently (minimum 22 h per day) [15].
Compliance for orthodontic therapy has been found to vary between males and
females [16] as well as between age groups [17], while overall data on compliance and
treatment outcomes in orthodontics are limited and ambiguous [18]. In patients with low
compliance, treatment times increase, and the outcome may be compromised [16,19].
The present study aimed to evaluate the compliance of aligner patients during
remote treatment monitoring and to assess if compliance was associated with
demographic or other covariates (e.g., previous orthodontic treatment experience,
satisfaction with their current smile). Having knowledge on determinants or indicators of
compliance may allow targeted follow-up.
2. Materials and Methods
2.1. Study Design
A retrospective cohort study was conducted using anonymized data provided by
PlusDental, a brand of the Sunshine Smile GmbH (Berlin, Germany). PlusDental is a
Berlin-based health-tech company, specializing in the digitalization of dental treatments
and operating a digital dental care platform for aesthetic orthodontic tooth corrections,
with a network of more than 200 local partner dentists. The platform integrates laboratory
manufacturing of orthodontic aligners as well as treatment monitoring elements enabling
dentists or orthodontists to monitor aligner changes of patients and aligner pressure using
a standardized questionnaire. Among other data, this information is evaluated by the
dentist or orthodontist bimonthly, and patients are provided feedback and individual
instructions on wearing duration, change interval, aligner handling, or oral hygiene by e-
mail or telephone.
Our outcome was compliance of patients with regards to usage of the self-report
(app-based) questionnaire and, within this, the daily aligner wearing time. Patients with
consistent use of the mobile application for aligner check-in and an aligner wear time of
≥22 h on ≥75% of their aligners were classified as fully compliant. Patients with
inconsistent application usage were classified as fairly or poorly compliant based on the
aligner wear time: Patients with aligner wear time of ≥22 h on 50–74.9% of their aligners
were classified as fairly compliant and patients with aligner wear time of ≥22 h on only
<50% of their aligners as poorly compliant. The study was conducted in accordance with
the World Medical Association Declaration of Helsinki and the reporting followed the
STROBE checklist [20]. The data was collected as a part of the treatment and was
anonymized for research use, which according to the Berlin State Hospital Act
(Landeskrankenhausgesetz Berlin) and the recommendations of the Datenschutz und IT-
Sicherheit im Gesundheitswesen (DIG) task force of the German Association for Medical
Informatics, Biometry, and Epidemiology (GMDS) requires neither approval from an
ethics committee nor informed consent.
2.2. Patient Selection
A comprehensive sample of patients who finished the aligner therapy successfully
with the so-called 1-1-2 CAT protocol without attachments or auxiliaries (see subsection:
Orthodontic Treatment Protocol) in 2019 were included in the study. Patients were
selected to conform to the following inclusion criteria: malocclusion in the anterior and
premolar region to be treated with CAT, adults (>18 years) with a permanent dentition,
J. Clin. Med. 2021, 10, 3103 3 of 10
absence of active periodontal disease, absence of local and/or systemic conditions that can
affect bone metabolisms, and with no extractions required for the orthodontic treatment.
These criteria coincide with the treatment scope of PlusDental (i.e., a comprehensive
sample was drawn).
2.3. Clinical Appointment
A complete clinical examination, a full set of digital photographs, and an intraoral
scan were carried out. A basic periodontal examination was performed [21,22], to rule out
periodontal diseases. Added to that, patients were asked to rate their satisfaction with
their current smile on a 10-point Likert scale (1 = very dissatisfied, 10 = very satisfied) and
report if they had previous orthodontic treatment.
2.4. Digital Treatment Planning
Virtual planning of the final desired tooth position and the required tooth
movements were carried out by a dental technician using proprietary digital planning
technology. The data resulting from this process was exported in the form of consecutive
models.
After the treatment plan was finalized and accepted by the dental practitioner, a 3-
dimensional (3D) simulation showing the steps and the virtual final position of the teeth
was sent to the patient to obtain consent on the proposed final result.
2.5. Manufacturing of Aligners
Additive manufacturing of the models was carried out by digital light processing
technology. The aligners were embossed by a patient-specific serial number indicating the
number of the step and the respective jaw to ensure ease of use by the patients. The
thermoformed aligners were trimmed 2 mm above the free gingival margin.
2.6. Orthodontic Treatment Protocol
The treatment protocol consisted of consecutive steps of aligners which might vary
according to the complexity of the case. Each aligner step was divided into three sub-steps,
each with a different foil thickness. The following wear protocol was followed, 7-day wear
time for the 0.5 mm thick and the 0.625 mm thick aligners, and 14-day wear time for the
0.75 mm thick aligners (1-1-2 protocol). Patients were instructed to wear each aligner for
a minimum of 22 h per day, except during meals, hot drinks, and oral hygiene procedures.
2.7. Treatment Follow-Up and Outcome Assessment
The patients were instructed to check-in every aligner change using the app-based
questionnaire (Figures 1 and 2) and to send a set of photos every two months for follow-
up through the PlusDental mobile application. The photos, aligner change date, the
subjective pressure exerted at the start and the end of the aligner wear, the aligner fit, the
current position of the teeth from different angles, and self-reported aligner wear duration
were assessed by a dental practitioner, who then instructed the patient to continue the
treatment, wear an aligner for a longer duration or repeat a step when necessary. Other
comments concerning the treatment, or the oral health condition of the patient were
communicated as well. At the end of the treatment process, the aligner fit, and the tooth
position compared with the virtual treatment plan as well as patients’ satisfaction were
assessed.
J. Clin. Med. 2021, 10, 3103 4 of 10
Figure 1. The PlusDental app-based questionnaire starting with the aligner check-in on the left.
Figure 2. A representation of the patient treatment execution data collected through the app-based
questionnaire.
2.8. Statistical Analysis
Descriptive statistics were carried out and two-sided Chi-square tests were used for
statistical analysis. p-values smaller than 0.05 were regarded as statistically significant. All
calculations were conducted using JASP 0.41.1 (University of Amsterdam, Amsterdam,
The Netherlands)
3. Results
3.1. Sample Characteristics
Data of all patients that finished their treatment successfully based on one intraoral
scan with the 1-1-2 system in 2019 (2644 patients) was available for analysis without
exclusion (comprehensive sample). Of these, 662 (25.0%) were male and 1982 (75.0%)
female. The median age at treatment start was 27 years (range 18–64). When categorized
by age, the largest group were young adults (18–35 years, n = 2223), followed by middle-
aged adults (ages 36–55 years, n = 406). There were only a few older adults (aged older
than 55 years, n = 15) (Table 1).
Table 1. Age group and gender distribution of the overall sample.
18- to 35- Years
Old
36- to 55- Years Old 56- to 64- Years
Old
Total
Male
563 (21.2%)
96 (3.6%)
3 (0.1%)
662 (25.0%)
Female
1660 (62.7%)
310 (11.7%)
12 (0.4%)
1982 (75.0%)
Total
2223 (84%)
406 (15.3%)
15 (0.5%)
2644 (100%)
J. Clin. Med. 2021, 10, 3103 5 of 10
The number of aligners used per patient ranged from 6 to 36 aligners. Out of all
patients, 47 (1.8%) patients were treated by 6 aligners, 434 (16.4%) patients by 9 aligners,
809 (30.6%) patients by 12 aligners, 682 (25.8%) patients by 15 aligners, 441 (16.7%) patients
by 18 aligners, 150 (5.7%) patients by 21 aligners, 72 (2.7%) patients by 24 aligners, and 9
(0.3%) patients by >24 aligners.
A total of 1333/2644 (50.4%) patients reported very strong to medium pressure at the
start of the aligner wear in 100% of their aligners, 345/2644 (13.0%) patients in 90 to 99.9%
of their aligners, 397/2644 (15.0%) patients in 80 to 89.9% of their aligners, 193/2644 (7.3%)
patients in 70 to 79.9% of their aligners, 125/2644 (7.3%) patients in 60 to 69.9% of their
aligners, 100/2644 (3.8%) patients in 50 to 59.9% of their aligners, and 151/2644 (5.7%)
patients in <50% of their aligners.
Most of the patients (2380/2644, 90.0%) reported medium to very weak pressure at
the end of their aligner wear in comparison to the pressure exerted by the aligner at the
start in 100% of their aligners, 111/2644 (4.2%) patients in 90 to 99.9% of their aligners,
95/2644 (3.6%) patients in 80 to 89.9% of their aligners, 24/2644 (0.9%) patients in 70.0 to
79.9% of their aligners, 23/2644 (0.9%) patients in 60.0 to 69.9% of their aligners, and
11/2644 (0.4%) patients in under 60% of their aligners during the treatment. Only 1 patient
reported that the aligner pressure did not change over the course of each checked-in
aligner.
Regarding their current smile aesthetics, 41.2% (577/1401 responders) indicated that
they were “very dissatisfied” to “slightly dissatisfied” (score 1–4) while 535/1401
responders (38.2%) were “neutral” (score 5–6), and 20.6% (289/1401 responders) were
“slightly satisfied” to “very satisfied” (score 7–10).
A total of 1038/2644 (39.3%) patients reported previous orthodontic treatment,
702/2644 (26.6%) reported no previous orthodontic treatment, and 904/2644 (34.2%) could
not answer the question. The patients who indicated previous orthodontic treatment had
removable appliances in 420/1038 (40.5%) cases, fixed appliances in 501/1038 (48.3%)
cases, and both removable and fixed appliances in 117/1038 (11.3%) of the cases.
Patients who had reported a previous orthodontic treatment answered in 847 (81.6%)
of the cases that they did not have any retainer anymore, 98 (9.4%) had a fixed retainer, 87
(8.4%) had removable retainers, and 6 (0.6%) had both removable and fixed retainers.
3.2. Compliance
Patients were classified according to the compliance criteria into full, fair, and poor
compliance. A total of 953/2644 (36.0%) of patients showed full compliance, 1012/2644
(38.3%) fair compliance, and 679/2644 (25.7%) poor compliance.
A total of 1203/2644 (45.5%) patients wore each aligner for 22 h per day throughout
the treatment period, 456/2644 (17.2%) patients deviated in 0.1–25% of their aligners,
306/2644 (11.6%) patients deviated in 25.1–50% of their aligners, 211/2644 (8.0%) patients
deviated in 50.1–75% of their aligners, and 468/2644 (17.7%) patients deviated in >75% of
their aligners.
Compliance was higher in males compared with females (p < 0.05). No significant
differences were found for patient group age in patient compliance (p = 0.097) (Table 2).
J. Clin. Med. 2021, 10, 3103 6 of 10
Table 2. Compliance in different age groups and by gender.
Overall
Sample
Full
Compliance
Fair
Compliance
Poor
Compliance Chi-Square
Gender n (%)
Male
662 (25%)
261 (9.8%)
277 (10.5%)
124 (4.7%)
X2 (2,
n
= 2644) =
22.34
p = 0.000014
(p < 0.05)
Female 1982 (74.9%) 692 (26.1%) 735 (27.8%) 555 (21.0%)
Age group n (%)
18- to 35-
years old
2223 (84%) 794 (30%) 852 (32.2%) 577 (21.8%)
X2 (4, n = 2644) =
7.84
p = 0.097
36- to 55-
years old
406 (15.3%) 156 (5.9%) 156 (5.9%) 94 (3.6%)
56- to 64
years
old 15 (0.5%) 3 (0.1%) 4 (0.2%) 8 (0.3%)
Total
2644 (100%)
953 (36%)
1012 (38.3%)
679 (25.7%)
There were no significant differences in patient compliance when treatments
stretched over different time periods (p = 0.268) (Table 3).
Table 3. Comparisons of compliance by treatment duration.
Overall
Sample
Full
Compliance
Fair Compliance
Poor
Compliance
Chi-Square
Treatment duration n (%)
2 months
47 (1.7%)
20 (0.8%)
14 (0.5%)
13 (0.5%)
X2 (18, n = 2644) =
21.22
p = 0.268
3 months
434 (16.4%)
143 (5.4%)
165 (6.2%)
126 (4.8%)
4 months
809 (30.5%)
308 (11.6%)
285 (10.8%)
216 (8.2%)
5 months
682 (25.7%)
244 (9.2%)
281 (10.6%)
157 (5.9%)
6 months
441 (16.6%) 147 (5.6%) 184 (7.0%) 110 (4.2%)
7 months
150 (5.6%)
60 (2.3%)
53 (2.0%)
37 (1.4%)
8 months
72 (2.7%) 27 (1.0%) 28 (1.1%) 17 (0.6%)
9 months
7 (0.2%)
4 (0.2%)
1 (0.0%)
2 (0.1%)
10
months 1 (0.03%) 0 (0.0%) 0 (0.0%) 1 (0.03%)
12
months 1 (0.03%) 0 (0.0%) 1 (0.03%) 0 (0.0%)
Total
2644 (100%)
953 (36%)
1012 (38.3%)
679 (25.7%)
Compliance was not different for patients with different smile aesthetics satisfaction
before treatment (p = 0.110) (Table 4).
J. Clin. Med. 2021, 10, 3103 7 of 10
Table 4. Patient compliance and smile aesthetics satisfaction.
Total
Responders
Full
Compliance
Fair
Compliance
Poor
Compliance Chi-Square
Smile aesthetics satisfaction n (%)
Very satisfied to
Slightly satisfied
289 (20.6%) 96 (6.9%) 119 (7.0%) 74 (4.4%)
X2 (4, n
= 1401) =
7.54
p = 0.110
Neutral
535 (38.2%)
184 (13.1%)
201 (11.8%)
150 (8.8%)
Slightly
dissatisfied to
Very dissatisfied
577 (41.2%) 217 (15.5%) 237 (13.9%) 123 (7.2%)
Total
1401 (100%)
497 (35.5%)
557 (32.7%)
347 (20.4%)
A significant difference in patient compliance was found for patients regarding
previous orthodontic treatment. Patients without previous orthodontic treatment showed
better patient compliance (p = 0.023) (Table 5).
Table 5. Patient compliance and previous orthodontic treatment.
Total Responders
Full
Compliance
Fair
Compliance
Poor
Compliance Chi-Square
Previous orthodontic treatment n (%)
Yes
1038 (59.7%)
357 (20.5%)
391 (22.5%)
290 (16.7%)
X2 (2, n = 1740) =
7.49
p = 0.023 (p < 0.05)
No 702 (40.3%) 252 (14.5%) 294 (16.9%) 156 (9.0%)
Total
1740 (100%)
609 (35%)
685 (39.3%)
446 (25.6%)
Further analysis of patients with previous orthodontic treatment classified according
to the type of previous treatment showed that patients treated only with removable
appliances were shown to be the most compliant (p = 0.0472) (Table 6).
Table 6. Patient compliance and type of previous orthodontic treatment.
Total
Responders
Full
Compliance
Fair
Compliance
Poor
Compliance Chi-Square
Type of previous orthodontic treatment n (%)
Removable
appliance 420 (40.5%) 158 (15.2%) 165 (15.9%) 97 (9.3%) X2 (4, n
= 1038) =
9.62
p = 0.0472 (p <
0.05)
Fixed appliance
501 (48.3%)
159 (15.3%)
181 (17.4%)
161 (15.5%)
Both removable &
fixed 117 (11.3%) 40 (3.9%) 45 (4.3%) 32 (3.1%)
Total
1038 (100%)
357 (34.4%)
391 (37.7%)
290 (27.9%)
4. Discussion
CAT is increasingly popular for orthodontic corrections but relies heavily on
patients’ compliance. The present study evaluated the compliance and compliance-
associated factors in 2644 CAT patients in 2019. Based on our findings, males were slightly
more likely than females to be compliant while age and pre-treatment satisfaction with
one’s own smile was not associated with compliance. Most significantly, individuals who
had previous orthodontic treatment showed significantly lower compliance. To the
knowledge of the authors, this is the first study evaluating compliance of a large cohort of
J. Clin. Med. 2021, 10, 3103 8 of 10
clear aligner patients using a mobile application during a remote follow-up in terms of
mobile application usage and self-reported wearing hours.
Our findings require some detailed discussion. Gender has been found to be
associated with compliance for orthodontic treatment before, while the direction of any
association remains unclear. For example, Al-Abdallah et al. found female patients to be
more compliant during fixed orthodontic treatment [16], Schäfer et al. found female
patients to be more compliant during removable orthodontic treatment [23], while Crouse
found no difference between males and females [24]. The patients in these studies were
either all below 18 years of age [16,23], or partially under 18 [24], which could be the
reason for the opposite results found in our study where the youngest patients at the start
of the treatment were 18 years old (median = 27). It is possible that in adults, men are more
compliant during orthodontic treatment. This finding, however, needs to be further
confirmed in a sample with a bigger age range including adolescents and children, and
should be explored using qualitative research methods as well to better understand
reasons behind it.
Similarly, age has been ambiguously found to be associated with compliance. For
example, Barbosa et al. showed that adult patients were more compliant with fixed
appliance therapy than adolescents [17], whereas Crouse found that patients in the 14–19
and 20–39 age groups were significantly less compliant with CAT than those younger or
older. The absence of an adolescent age group in the current study could be the reason
why such effect of age on compliance could not be established, together with the small
number of patients (15/2644) in the oldest age group which was expected to be less
compliant using the mobile application. Overall, the comparison of age groups likely
suffered from limited heterogeneity and hence statistical power, as most patients were of
similar age.
The absence of a demonstrable effect of satisfaction with the current smile before
treatment and compliance during the treatment is in line with the findings of Mandall et
al. [18], where concern about the negative impact of teeth appearance was not indicative
of higher compliance during the treatment. This is somewhat counterintuitive, as one may
expect individuals unhappy with their smile to desire an aesthetic improvement more
eagerly than those less unsatisfied, who in turn may be less compliant. It is possible,
however, that all adult patients in our sample where generally relatively interested in
improving their smile aesthetics, mainly demonstrated by them paying out of pocket for
a by-large aesthetic correction.
Notably, patients who had experienced previous orthodontic treatment were shown
to be less compliant during CAT. A possible explanation is that those patients might have
been non-compliant previously, for example with their retention protocol, leading to
relapse in the first place (81.6% of the patients who had previous orthodontic treatment
reported not having retainers at the time of their clinical appointment). A significant
decrease in compliance over time regarding daily retainer wear and/or the wearing hours
is a common finding among orthodontic patients [25], especially for relatively long
orthodontic treatment processes [19]. Individuals who had experienced previous therapy
may perceive the second therapy as especially long and hence become impatient earlier,
impacting on compliance.
It is worth noting that the patients who had previous orthodontic treatment with
removable appliance were found to be more compliant than the patients who had
previous fixed orthodontic treatment. The familiarity with the removable appliances and
their mode of action might have been the reason behind the higher compliance of patients
with previous removable appliance experience during CAT.
Based on the findings in this study, the dental practitioner might be able to identify
potential low compliance CAT patients which would allow for early intervention to try to
improve compliance during remote follow-up. Among many methods, praising the
patient for compliant behavior and patient education about the consequences of poor
compliance were reported by orthodontists to be of high importance in improving
J. Clin. Med. 2021, 10, 3103 9 of 10
compliance [26]. In a remote follow-up CAT context, that could translate into delivering
praise to patients with compliant wear time and consistent application usage and
educating the patient about the consequences of poor compliance prior to treatment and
sending them reminders during treatment when deviation from compliant behavior is
observed. The efficacy of these methods needs to be further studied.
This study comes with a range of limitations. First, the absence of an under 18 years
old (children and adolescents) age group together with the small number of patients in
the oldest age group (above 56 years old) did not allow for a comprehensive
representation of the orthodontic treatment-seeking population, especially those below
the age of 18 years. Second, the aligner wearing hours and the perceived aligner pressure
were recorded using self-reports, which are susceptible to biases such as overstatement
and understatement or distortion of perception and memory [27]. This is why we
classified the patients in this study based on the consistency of mobile application usage
during remote follow-up as a more objective indicator of compliance. Third, compliance
was measured for CAT; inferences on other orthodontic therapies should not be made.
Last, the sample suffered from selection bias; only patients willing to pay a certain amount
of money out-of-pocket from mainly three countries, Germany, Switzerland, and Austria,
for one specific aligner therapy were included. Generalization to other populations should
not be attempted.
Further studies are needed to evaluate the influence of other factors on compliance
such as the type of malocclusion, the aligner thickness, the frequency of aligner breakage,
and the need for IPR.
5. Conclusions
Within the limitations of this study, gender but not age or pre-treatment satisfaction
with one own’s smile was associated with patient compliance during CAT. Most notable,
patients who had experienced previous orthodontic therapy showed significantly lower
compliance. Based on our findings, individuals at-risk should be identified in future
studies and their compliance prospectively recorded. Our findings could be used to guide
practitioners towards limitedly compliant individuals, allowing early intervention.
Author Contributions: Conceptualization, L.H.T. and F.S.; Formal analysis, L.H.T.; Writing—
original draft, L.H.T., G.F. and F.S.; Writing—review & editing, L.H.T., G.F., M.B. and F.S. All
authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: The study was conducted according to the guidelines of the
Declaration of Helsinki. The data was collected as a part of the treatment and anonymized for
research use, which according to the Berlin State Hospital Act (Landeskrankenhausgesetz Berlin)
and the recommendations of the Datenschutz und IT-Sicherheit im Gesundheitswesen (DIG) task
force of the German Association for Medical Informatics, Biometry, and Epidemiology (GMDS) does
not require approval from an ethics committee.
Informed Consent Statement: Patient consent was waived because the data was collected as a part
of the treatment and was anonymized for research use, which according to the Berlin State Hospital
Act (Landeskrankenhausgesetz Berlin) and the recommendations of the Datenschutz und IT-
Sicherheit im Gesundheitswesen (DIG) task force of the German Association for Medical
Informatics, Biometry, and Epidemiology (GMDS) does not require informed consent.
Data Availability Statement: Data available on request due to privacy restrictions.
Conflicts of Interest: Lan Huong Timm and Gasser Farrag declare gainful employment by Sunshine
Smile, the brand owner of PlusDental. Martin Baxmann and Falk Schwendicke are members of the
Scientific Board of the Sunshine Smile GmbH.
J. Clin. Med. 2021, 10, 3103 10 of 10
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