Orthodontic treatment with clear aligners and apical root resorption

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Ugnė Sadauskienė1, Vilija Berlin1

1Vilnius University hospital Zalgiris clinic, Vilnius, Lithuania

 Abstract

            Background and aim:  The aim of this systematic review was to evaluate the link between clear aligner therapy and apical root resorption and to compare the amount of apical root resorption using different orthodontic appliances – clear aligners and fixed orthodontic treatment.

            Materials and methods: Electronic and manual search for articles was carried out with specific inclusion and exclusion criteria. All selected studies had to be published in English between 2009 and 2019.

            Results:  6 articles met the criteria and were selected for this systematic review. 3 of 6 studies presented comparisons between results of clear aligner therapy and fixed appliance treatment. The external root resorption after treatment with clear aligners was similar or significantly lower than with use of fixed appliances. Other 3 studies were only investigating results of treatment with clear aligners. The incidence of root resorption ranged between 46% and 81%. However, only 3,69% to 6,31% of all teeth were affected by considerable root length reduction (>20%).

            Conclusion: Both incidence and severity of apical root resorption are lower after clear aligner therapy compared with root resorption results using fixed orthodontic treatment.

            Key words: Orthodontic treatment; Clear aligners; Apical root resorption.

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Medical Sciences 2020 Vol. 8 (14), p. 35-47
Orthodontic treatment with clear aligners and apical root
resorption
Ugnė Sadauskienė
1
, Vilija Berlin
1
1
Vilnius University hospital Zalgiris clinic, Vilnius, Lithuania
Abstract
Background and aim: The aim of this systematic review was to evaluate the link between clear
aligner therapy and apical root resorption and to compare the amount of apical root resorption using different
orthodontic appliances – clear aligners and fixed orthodontic treatment.
Materials and methods: Electronic and manual search for articles was carried out with specific
inclusion and exclusion criteria. All selected studies had to be published in English between 2009 and 2019.
Results: 6 articles met the criteria and were selected for this systematic review. 3 of 6 studies
presented comparisons between results of clear aligner therapy and fixed appliance treatment. The external
root resorption after treatment with clear aligners was similar or significantly lower than with use of fixed
appliances. Other 3 studies were only investigating results of treatment with clear aligners. The incidence
of root resorption ranged between 46% and 81%. However, only 3,69% to 6,31% of all teeth were affected
by considerable root length reduction (>20%).
Conclusion: Both incidence and severity of apical root resorption are lower after clear aligner
therapy compared with root resorption results using fixed orthodontic treatment.
Keywords: Orthodontic treatment; Clear aligners; Apical root resorption.
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1. INTRODUCTION
Orthodontically induced external apical
root resorption (ARR) is a permanent loss of
tooth structure (cementum and/or dentin) and
pathological side effect of orthodontic treatment
[1]. This complication results from combination
of individual biologic variability, genetic
predisposition and the effect of mechanical
factors [1,2,3]. Orthodontic appliance and
treatment technique can be important factors in
the degree of ARR because of different treatment
duration, amount of tooth movement and strength
of applied forces [1].
During the last decade, clear aligner
therapy (CAT) is becoming increasingly popular
among patients and doctors. Orthodontists are
treating young and adult patients by application
of CAT because of its better esthetics and comfort
during the treatment compared to fixed appliance
treatment (FAT) [4,5]. The majority of studies
and review articles investigated ARR as a result
of orthodontic treatment when fixed orthodontic
appliances were used. Whereas the data about the
frequency and amount of ARR caused by aligner
therapy is scarce.
Because of recent trend to widely use
CAT for orthodontic treatment, the aim of this
systematic review was to evaluate the link
between CAT and ARR, to compare the amount
of OIEARR using different orthodontic
appliances - CAT and FAT.
2. MATERIALS AND METHODS
2.1 Search strategies
The electronic and manual search for
articles was carried out in the following data
bases: PubMed, Wiley, Science Direct, Cochrane
Library. Applied keywords in MeSH were
[aligners AND root resorptions].
2.2 Inclusion and exclusion criteria
We included articles that met all the following
criteria:
1. Randomized controlled trials (RCTs),
non-randomized controlled trials,
prospective and retrospective studies
2. Studies published in English between
2009 and 2019
3. Studies evaluating the incidence and the
severity of apical root resorption during
treatment with orthodontic aligners
alone or compared with fixed appliance
treatment
4. Studies that analyzed orthodontic
treatment in humans
Exclusion criteria was:
1. Case reports
2. Literature reviews
3. Studies only involving fixed appliance
treatment
3. RESULTS
3.1 Search results
Based on selected keywords, a total of
23 articles were selected from four data bases. 15
articles were selected after title review and
abstract analysis. Following the evaluation of full
article, 6 articles were accepted for this
systematic review (Figure 1).
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Figure 1: Flow diagram of the studies that were included in this systematic review
Additional records
found after manual
search (n = 6)
Screening
Abstracts after screening
(n = 62)
Eligibility
Evaluation of full-length
articles for eligibility
(n = 14)
Abstracts excluded
(n = 49)
Selected
Studies selected for systematic
review (n = 6)
Full-length articles
excluded
(n = 8)
4 studies examining resorption
after orthodontic treatment
using clear aligners
2 studies comparing root
resorption between aligners
and fixed appliances
Identification
Records identified by
electronic database search
(n = 84)
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3.2 Study characteristics
Systematized and detailed information
about selected studies is shown in Table 1. 2 of 6
included studies were retrospective cohort
studies, one non-randomized clinical trial, one
case-control genetic association study, one
prospective and one pilot study.
3 of 6 studies were comparing CAT and FAT
results:
-pilot study by Eissa et al. (Tanta University,
Egypt) measured teeth length, using CBCT scans,
before and after treatment with Smart Track®
clear aligners, SL Damon brackets and 3M
regular edgewise brackets [6]. The results show
that patients treated with regular edgewise
brackets are characterized by significantly higher
resorption than those treated with aligners
(P<0.05). No significant difference was noted
between SmartTrack and Damon groups
(P>0.05);
-retrospective cohort study by Yi et al. (Sichuan
University, China) compared panoramic
radiographs before and after treatment for
patients that were treated with clear aligners
(CAT group) and fixed brackets (FAT group) [7].
The mean value of EARR in CAT g ro up
(5.13±2.81%) was significantly less than in FAT
group (6.97±3.67%);
-case-control genetic association study by
Iglesias-Linares et al. (Complutense University
of Madrid and University of Seville, Spain) also
compared root resorption after CAT and FAT [8].
They concluded that a similar apical root
resorption predisposition was identified using
either removable aligners or fixed appliances.
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Other 3 studies were investigating CAT results
alone:
-non-randomized clinical trial by Krieger et al.
(Johannes Gutenberg University, Germany)
measured 1600 teeth after treatment with clear
aligners [9]. More than half (54%) of all teeth
showed no measurable reduction of root length.
Only 6.31% of all teeth showed 20% or more
reduction of root length;
-retrospective cohort study by Farouk et al. (Al-
Ahzar University, Egypt) compared and
measured CBCT scans before and after clear
aligner treatment [10]. Patients were divided in
two groups according to treatment protocol:
Group I consisted of patients treated with
Invisalign SmartTrack® clear aligners and high
frequency mechanical vibration (HFV) device
VPro5, Group II consisted of patients that were
in treatment only with Invisalign SmartTrack®
clear aligners, without additional HFV device.
Researchers concluded that Group II showed a
statistically significant reduction of tooth lengths
compared to the Group I, which did not show
statistically significant root resorption after the
treatment.
-prospective study of Gay et al. (University of
Torino, Italy) found that 81% of the 1083
measured teeth treated using clear aligner therapy
presented a reduction of tooth length [11]. But
average root length reduction after the treatment
was less than 10% of original tooth length.
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4. DISCUSSION
The aim of this systematic review was
to evaluate the link between CAT and ARR, to
compare the amount of ARR using different
orthodontic appliances - CAT and FAT. As ARR
is very common complication among
orthodontically treated patients and it is a
multifactorial pathological event, it is very hard
to find one leading factor for this complication [2,
12, 13].
4.1 Teeth affected by ARR and evaluation tools
In three of the selected studies only
maxillary incisors were evaluated, in other three
studies maxillary incisors were evaluated
together with other teeth. The main reason why
only maxillary incisors are taken into
consideration is because in previous studies it
was determined that these teeth are most
susceptible to resorption during orthodontic
treatment using fixed appliances [13, 14, 15, 16,
17, 18]. But none of the included studies in this
analysis reported that maxillary incisors are the
most vulnerable to ARR during orthodontic
treatment.
Also, in older studies when cone-beam
computed tomography (CBCT) was not so
widespread tool, researchers were measuring
only single-rooted teeth length on panoramic or
periapical radiographs because it is very hard to
accurately measure the length of multi-rooted
teeth only using this radiographs. So later studies
concluded that the amount of ARR seems to be
underestimated in panoramic or periapical
radiographs compared to CBCT [19, 20]. Despite
this, Krieger et al. and Gay et. al. included multi-
rooted teeth into observation and calculated teeth
length from panoramic radiographs before and
after treatment [9, 11]. To avoid distortion of
results due to different degrees and magnification
of panoramic radiographs, both authors
calculated root-crown ratio before and after
orthodontic treatment.
Now CBCT has been widely applied to
dental field and it is accurate and reliable
measuring tool because it allows for measuring of
tooth’s length in all three dimensions [21]. But
still only two studies included in this review were
using CBCT for teeth length measuring and they
both are the latest researches from all 6 included
studies [6, 10].
4.2 Different mechanical approaches between
CAT and FAT may influence different results of
ARR
One of the main differences between
CAT and FAT from patient’s perspective is that
they can remove aligners before eating and
toothbrushing. This frequent removal and
insertion of aligners creates intermittent forces
for teeth and it was already concluded that this
irregular pressure to surrounding periodontal
structures allow cementum to heal during the
absence of pressure [22, 23, 24]. Meanwhile
during FAT, continuous forces and intense
mechanical stimulations are created and usually
we are not able to accurately measure the amount
of force that is applied to one tooth [25, 26]. This
leads to a long-term impairment of blood
circulation in periodontal structures, which
consequently results in higher risk of ARR [15,
23, 26].
CAD/CAM technologies allows us to
plan and forecast the direction, amount of teeth
movement and fabricate the aligners accordingly.
This helps to distribute the light forces in every
aligner, which is 0,2 mm of movement every 7-
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14 days [27, 28]. However, treatment using fixed
appliances usually generates 1 mm of movement
per month [29, 30]. Also, accurate planning of
teeth movement with aligners can generate less
tipping, unwanted proclination during leveling
phase compared to treatment with conventional
appliances. These types of movements create
excessive force to the periodontium, cortical
bone and later, after initial alignment with braces,
we create back-and-forth movement, while this
rarely happens during CAT [31, 32, 33]. And this
difference between CAT and FAT can explain
why studies with aligner treatment usually show
less ARR than studies with fixed appliances [6, 7,
28, 34].
4.3 Connection between complexity and
duration of the treatment and amount of ARR
Back-and-forth movement that was
mentioned before is usually more frequent when
using orthodontic appliances and this is one of
many reasons why FAT treatment becomes
prolonged and usually needs longer than
expected pre-treatment. And many studies have
already stated that the longer the duration, the
more severe the root resorption is [7, 32, 35, 36,
37].
The other reason why researchers find
less ARR after treatment with aligners than fixed
appliances may be different treatment complexity.
3 of 6 studies that were included in this analysis
examined patients in clear aligner therapy only,
not including fixed appliances for comparison [9,
10, 11]. In all of these three studies only class I
malocclusion with anterior crowding was
included. Two other studies that were comparing
CAT and FAT also excluded class II, III and tooth
extraction cases (except for the third molar
extraction) [6, 7]. One study did not separate
patients into classes of malocclusion or different
treatment [8]. Investigation of only class I cases
compromised the results of ARR amount and
severity after the treatment. In order to receive
more reliable results, comparison of the results of
ARR before and after the treatment should be
carried out with more complex and longer
treatment and cases requiring extraction.
Based on results of this systematic
review, we can conclude that apical root
resorption during and after the orthodontic
treatment with clear aligners is not unavoidable.
But both incidence and severity of ARR are lower
after clear aligner therapy compared with ARR
results with fixed orthodontic treatment.
However, these conclusions should be
accepted critically, because CAT cases included
in studies are relatively mild or easy. To get more
accurate results, researchers should include
extraction and other complex cases for CAT, as
clear aligner companies are now able to offer
protocols for extraction treatment.
5. ACKNOWLEDGEMENTS AND
DISCLAIMERS
This work was not supported by any
company. The authors declare that they have no
conflict of interest.
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