Clinical outcomes of arch expansion with Invisalign: a systematic review
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Clinical outcomes of arch expansion with Invisalign:
a systematic review
SONGYANG MA MA
Stomatological Hospital of Chongqing Medical University
YUNJI WANG WANG ( YUNJI1986@126.COM )
Stomatological Hospital of Chongqing Medical University
Research Article
Keywords: Invisalign, aligner, expansion, efficacy, predictability
Posted Date: February 8th, 2023
DOI: https://doi.org/10.21203/rs.3.rs-2532028/v1
License: This work is licensed under a Creative Commons Attribution 4.0 International License.
Read Full License
Page 1/12Abstract
Objective: To assess the scientific evidence related to the clinical outcomes of Invisalign therapy in
controlling orthodontic tooth movement.
Materials and Methods: An electronic search was conducted in Pubmed，Cochrane Library，Web of
Science，Embase，and Scopus from November 2015 to November 2022 to identify all articles.
Methodological shortcomings were highlighted and the quality of the studies was ranked using the
Cochrane Tool for Risk of Bias Assessment.
Results: Three prospective, and twelve retrospective studies were included. Besides, the risk of bias was
moderate for thirteen studies and unclear for the others. There’s statistically significant difference
between the prettreatment and posttreatment arches. The average expansion was significantly different
from that predicted for each type of tooth in both the maxilla and mandible. Furthermore, the efficiency
decreased from the anterior area to the posterior area in the upper arch.
Conclusion: Despite the fact that arch expansion with Invisalign® is not ideally predictable, clear
treatment is considerable option to resolve dentition crowding. The efficacy of expansion performs
greatest in the premolar area. More researches focusing on the treatment outcome with different
materials of aligners should be conducted in the future. Overcorrection should be considered when
planning arch expansion with Invisalign. In maxilla, the expansion rate decreases from anterior to
posterior. In maxilla, presetting sufficient buccal root torque of posterior teeth may result in better
efficiency of expansion.
1. Introduction
In recent decades, orthodontic technology has been making continuous progress. Since invisalign
appliance came out in 1997, it has become an important choice of orthodontic treatment[1]. Compared
with traditional fixed orthodontic appliance, clear treatment has certain advantages, including fewer
clinical emergencies, better aesthetic effect, more comfort, favouring periodontal health and lack of
stimulating to the soft tissue. Now, CAT has become an increasingly common orthodontic treatment
option[2, 3].
Expanding dental arch is one of the existing choices to solve transverse problems, and it’s divided into
rapid maxillary expansion and slow maxillary expansion. According to the different degree of maxillary
compression, clinicians could choose different expansion method such as dentoalveolar expansion or
jaw expansion, which is conducted by aligners or fixed orthodontic appliance[4, 5]. However, aligners are
not accuracy as the traditional fixed orthodontic appliance in the arch expansion on the transverse
dimension[6, 7].
ClinCheck software can simulate the dentition models before or after the treatment, which are used to
analyze the efficiency and accuracy of the tooth movement, and the measurement can be based on the
Page 2/12crown[8]. The most accurate type of tooth movement produced by aligners is the buccolingual tipping
movement, which is logical, because the materials of the appliance are mainly bent in the buccolingual
direction[9].
Even though the available body of literature pertaining to clear treatment, its clinical performance has
been analyzed less thoroughly and a synthesis of the results still remains vague. Five systematic reviews
about the clinical outcomes of clear aligners exist in the literature: They not only focused on the oblique
movement of the teeth, but also on other types of tooth movement during the treatment[1, 10–13].
However, there are only a few studies on the efficiency of arch expansion with aligners. Therefore, the
purpose of the present review was to systematically search the literature and summarize the current
available scientific evidence regarding the effectiveness of arch expansion with the Invisalign system.
2. Materials And Methods
2.1. Eligibility criteria
Inclusion criteria and exclusion criteria are as follows:
Types of studies
Prospective and retrospective studies were considered eligible for inclusion in this review. These studies
concerned to the outcomes of arch expansion with Invisalign. Only studies published in English were
included.
Types of participants
Orthodontic adult patients with permanent dentition who have expanded the dental arch after Invisalign
therapy.
Types of interventions
Studies using Invisalign therapy to expand the dental arch were included. All other aligner systems have
been excluded.
Outcome
Any effect on clinical efficiency, predictability of ClinCheck, treatment outcomes, movement accuracy
after arch expansion. Studies which evaluated arch width on actual and virtual models were included.
2.2. Exclusion criteria
Studies older than 15 years, patients with mixed dentition, studies written in a language other than
English, animal studies, case reports, studies that did not provide the data, or reviews of literature.
Page 3/122.3. Information sources, search strategy, and study
selection
An electronic search was conducted in Pubmed, Cochrane Library, Web of Science, Embase, and Scopus,
until November 30, 2022. An additional manual search of references in the included studies was also
conducted. We used the search terms combination ((((aligner[Title/Abstract]) OR (invisalign
system[Title/Abstract])) OR (invisalign[Title/Abstract])) OR (orthodontic appliances,
removable[Title/Abstract])) AND ((expansion[Title/Abstract]) OR (arch development[Title/Abstract])).
Selection of studies
An initial screening through titles and abstracts was conducted independently by two reviewers, who then
cross checked and reviewed the text in full to decide whether they were eligible. Disagreements were
resolved through discussion, when necessary, by seeking the opinion of a third reviewer.
3. Results
3.1. Study selection
An independent search was performed by two of the authors (Ma and Wang). Study selection procedure
was comprised of title-reading, abstract-reading, and full-text-reading stages. After exclusion of not
eligible studies, the full report of publications considered eligible for inclusion by either author was
obtained and assessed independently. Disagreements were resolved through discussion, when necessary,
by seeking the opinion of a third reviewer. Finally, 15 articles were included in the analysis. (Fig. 1)
3.2. Characteristics of included studies
Data collection forms were used to record the desired information. The following data were collected on a
customized data collection form: title, year of publication, names of the authors, study design, number of
participants, type of intervention, comparative groups, clinical outcomes and conclusions. (Table 1)
3.3. Quality assessment
To determine the methodological quality and level of evidence, the classification system described by the
Swedish Council on Technology Assessment in Health Care was applied[27]. And each study received a
judgment according to the criteria in Table 2.
Definitions of evidence level was showing in Table 3. The methodological quality was moderate for
twelve included studies[4, 9, 14–16] and limited for the rest three studies[17, 22, 25], showing in Table 4.
Therefore, conclusions obtained from this review were based on a limited level of evidence. The most
recurrent sources of bias were related to the study type and the lack of blinded outcome assessment.
However, only two retrospective studies and one prospective study were rated as evidence of low value.
Page 4/12Furthermore, the reason why they were rated as low was the lack of reproducibility tests or well-defined
patient material.
Table 2
Swedish Council on Technology Assessment in Health Care (SBU) Criteria for Grading Assessed Studies
Grade A Grade B Grade C
High value of evidence Moderate value of evidence Low value of
evidence
All criteria should be met: All criteria should be met: One or more of the
conditions below:
-Randomized clinical study or a -Cohort study or retrospective case series -Large attrition
prospective study with a well with defined control or reference group
-Unclear diagnosis
defined control group -Defined diagnosis and endpoints and endpoints
-Defined diagnosis and -Diagnostic reliability tests and -Poorly defined
endpoints reproducibility tests described patient material
-Diagnostic reliability tests and
reproducibility tests described
-Blinded outcome assessment
Table 3
Definitions of Evidence Level
Level Evidence Definition
1 Strong At least two studies assessed with level “A”
2 Moderate One study with level “A” and at least two studies with level “B”
3 Limited At least two studies with level “B”
4 Inconclusive Fewer than two studies with level “B”
Page 5/12Table 4
Grading of included Studies
Author, year Grade
Duncan et al. (2016) B
Grünheid et al. (2017) B
Houle et al. (2017) B
Solano-Mendoza et al. (2017) B
Zhao et al. (2017) B
Haouili et al. (2020) B
Deregibus et al. (2020) C
Morales-Burruezo et al. (2020) B
Zhou et al. (2020) B
Lione et al. (2021) B
Riede et al. (2021) C
Bernardez et al. (2021) B
Goh et al. (2022) B
Lione et al. (2022) C
Tien et al. (2022) B
3.4. Clinical findings
Efficacy of expansion
In all included studies, by comparing the pretreatment and posttreatment models the analysis of the
efficacy of expansion with invisalign can be conducted. And, it’s obvious that there’s statistically
significant difference between the prettreatment and posttreatment arches, indicating that Invisalign
actually had the function of expanding dental arch[4, 8, 9, 17–25]. Deregibus concluded that Invisalign class
II treatment resulted in a significant increase in arch width at the molar and premolar level in both
arches[17]. However, in Morales-Burruezo’ s study, expansion was more effective in premolar area and less
effective in canine and second molar area[21]. Furthermore, the efficacy was different between the upper
and lower arches[4].
Predictability of expansion
The predictability of expansion which meant the ability of predicting final outcome at the beginning of
invisalign treatment was also called the efficiency or the accuracy of arch expansion, which could be
Page 6/12examined by comparing the difference between the virtual posttreatment digital model simulated on the
ClinCheck software and the actual digital model obtained by scanning the posttreatment model. Among
the included studies, thirteen of them focused on the predictability of arch expansion with invisalign[4, 9,
14, 15, 17–19, 21–26]
. The average expansion was significantly different from that predicted for each type of
tooth in both the maxilla and mandible, and both underexpansion and overexpansion were observed[15].
However, in the contrary, no statistically significant changes between the ClinCheck model and the
posttreatment model were discovered in Lione’ s study[25]. Notably, in Zhou’ s study the efficacy of crown
expansion movement in the upper arch for the canine, first premolar, second premolar, and first molar
were 79.75%, 76.10%, 73.27%, and 68.31%, respectively[20]. Obviously, the efficiency decreased from the
anterior area to the posterior area in the upper arch, which was similar to the Lione’ s finding[23].
Types of material
Invisalign appliances made of different materials were used to examine whether there was difference in
the predictability of dental arch development. As described by Riede, the effectiveness of achieving
transverse values as planned was generally not increased with SmartTrack compared to the previously
used Ex30 material[22]. However, the Invisalign system aligners (SmartTrack material) offer high degree of
predictability both in the upper and lower arches in Bernardez’s study[4]. Furthermore, during orthodontic
treatment with Ex30 aligners the predictability of expansion depending on the magnitude of the planned
expansion was not predictable, while canine depth, arch depth, molar inclination, and molar rotation
showed to be predictable[19].
Other findings
When treating crowded dentition, buccal arch expansion and interproximal reduction were important
clinical tools[16]. Besides, carefull planning with overcorrection and other auxiliary methods of expansion
should be taken into concern, resulting in reducing the rate of midcourse corrections and refinements[14].
The Invisalign system can increase arch width by tipping movement of posterior teeth, and no significant
change was observed in maxillary basal bone width[20]. What’s more, the preset expansion amount and
initial maxillary first molar torque were significantly negatively correlated with efficiency of bodily
expansion movement[20].
4. Discussion
Among the collected literatures including those of which full text cannot be obtained, most of them have
been published in the past three years, indicating that there is a trend that dental arch expansion has
been a hot spot of the research of clear treatment. Up to now, six systematic reviews on invisalign are
available[1, 10–13, 28], with three of them evaluating the efficiency of arch expansion[1, 11, 12]. However, they
did not pay much attention to the changes in transverse dimension, with their selected literatures
published earlier than ours. Therefore, we decided to write this review. Furthermore, our review is more
precise and involve more innovative clinical findings.
Page 7/12In fact, 12 retrospective studies and 3 prospective studies were included in this review. After assessment
of the quality of the included studies, limited conclusions were drawn as the existing of more than two
studies grading B.
Two retrospective studies[18, 20] have reported that the expansion effect of dental arch was mainly caused
by tipping movement of teeth, which was manifested as the change of transverse width. Furthermore,
Duncan et al.[16] mentioned that the arch expansion achieved by buccal tipping movement of teeth which
is a kind of transversal movement is one of the significant pathways to resolve dentition crowding. In
Duncan’s research[16], it’s noteworthy that the greatest expansion efficacy performs in the premolar area.
And Zhou et al.[20] and Morales-Burruezo et al.[21] agree with that. In the results of one retrospective
study[17] and one prospective study[25] it is shown that for patients who have underwent class II clear
treatment, a significant increase of arch width and functional and stable outcomes are observed.
Lione et al.[25] and Grünheid et al.[15] state that though maxillary arch expansion may not be fully
achieved, in nonextraction cases invisalign is able to achieve predicted tooth positions with high
accuracy. Aligners made of different materials do not have significant difference in efficacy[22]. However,
Solano-Mendoza[19] and Vidal-Bernardez[4] disagree with that. Among patients treated with Ex30 aligners
the predictability of upper arch expansion is not predictable [19], but on the contrary among those with
SmartTrack material the predictability is shown to be high in both upper and lower arches[4]. Therefore,
more researches focusing on the materials of aligners should be conducted.
In the statement of Morales-Burruezo et al.[21], Lione et al.[23] and Tien et al.[24], there were statistically
significant differences between the predicted and actual treatment outcomes, overcorrection should be
considered on ClinCheck in order to obtain the expected outcomes. Furthermore, discretion was required
when overcorrecting to compensate for expansion inaccuracy. Notably, a progressive reduction in the
expansion rate from the anterior area to the posterior region in upper arch is observed in three
retrospective studies[18, 20, 23] and one prospective study[23]. The reasons for this may be differences in
root anatomy and cortical bone thickness, the higher occlusal load, the greater soft tissue resistance in
the posterior region, and the decline of mechanical efficiency from anterior to posterior[20]. Furthermore,
the preset expansion amount and initial maxillary first molar torque are significantly negatively correlated
with efficiency of expansion movement. Thus, presetting sufficient buccal root torque of posterior teeth is
a considerable strategy to improve the efficiency of expansion[20].
5. Conclusions
Despite the fact that arch expansion with Invisalign® is not ideally predictable, clear treatment is
considerable option to resolve dentition crowding.
The efficacy of expansion performs greatest in the premolar area.
More researches focusing on the treatment outcome with different materials of aligners should be
conducted in the future.
Page 8/12Overcorrection should be considered when planning arch expansion with Invisalign.
In maxilla, the expansion rate decreases from anterior to posterior.
In maxilla, presetting sufficient buccal root torque of posterior teeth may result in better efficiency of
expansion.
Declarations
Authors’ contributions
All authors have read and approved the manuscript. Ma and Wang reviewed and compiled evidence and
wrote the manuscript. Ma formulated the search strategy, compiled evidence and reviewed the
manuscript. All authors read and approved the final manuscript.
Funding
No funding was obtained for this study.
Availability of data and materials
Not applicable.
Ethics approval and consent to participate
No ethics approval and consent to participate was required for this manuscript.
Consent for publication
No consent for publication was required for this manuscript.
Competing interests
The authors do not have any financial and non-financial competing interests to declare for this
manuscript.
Acknowledgment
Not applicable.
Contributor information
Songyang Ma, Email: 673013113@qq.com.
Yunji Wang, Email: yunji1986@126.com.
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Tables
Table 1 is available in the Supplementary Files section.
Figures
Page 11/12Figure 1
Studies flow diagram
Supplementary Files
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Table1.docx
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