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Treatment outcome and efficacy of an aligner technique – regarding incisor torque, premolar derotation and molar distalization

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Background The aim of this study was to investigate the efficacy of orthodontic treatment using the Invisalign® system. Particularly, we analyzed the influence of auxiliaries (Attachment/Power Ridge) as well as the staging (movement per aligner) on treatment efficacy. Methods We reviewed the tooth movements of 30 consecutive patients who required orthodontic treatment with Invisalign®. In all patients, one of the following tooth movements was performed: (1) Incisor Torque >10°, (2) Premolar derotation >10° (3) Molar distalization >1.5 mm. The groups (1)-(3) were subdivided: in the first subgroup (a) the movements were supported with the use of an attachment, while in the subgroup (b) no auxiliaries were used (except incisor torque, in which Power Ridges were used). All tooth movements were performed in a split-mouth design. To analyze the clinical efficacy, pre-treatment and final plaster cast models were laser-scanned and the achieved tooth movement was determined by way of a surface/surface matching algorithm. The results were compared with the amount of tooth movement predicted by ClinCheck®. Results The overall mean efficacy was 59% (SD = 0.2). The mean accuracy for upper incisor torque was 42% (SD = 0.2). Premolar derotation showed the lowest accuracy with approximately 40% (SD = 0.3). Distalization of an upper molar was the most effective movement, with efficacy approximately 87% (SD = 0.2). Conclusion Incisor torque, premolar derotation and molar distalization can be performed using Invisalign® aligners. The staging (movement/aligner) and the total amount of planned movement have an significant impact on treatment efficacy.
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Treatment outcome and efficacy of an aligner technique - regarding incisor
torque, premolar derotation and molar distalization
BMC Oral Health 2014, 14:68 doi:10.1186/1472-6831-14-68
Mareike Simon (mareike.simon@uniklinik-freiburg.de)
Ludger Keilig (ludger.keilig@uni-bonn.de)
Jörg Schwarze (s@dr-schwarze.com)
Britta A Jung (britta.jung@uniklinik-freiburg.de)
Christoph Bourauel (bourauel@uni-bonn.de)
ISSN 1472-6831
Article type Research article
Submission date 14 December 2013
Acceptance date 2 June 2014
Publication date 11 June 2014
Article URL http://www.biomedcentral.com/1472-6831/14/68
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© 2014 Simon et al.
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Treatment outcome and efficacy of an aligner
technique – regarding incisor torque, premolar
derotation and molar distalization
Mareike Simon1,2,*
Email: mareike.simon@uniklinik-freiburg.de
Ludger Keilig1
Email: ludger.keilig@uni-bonn.de
Jörg Schwarze3
Email: s@dr-schwarze.com
Britta A Jung2
Email: britta.jung@uniklinik-freiburg.de
Christoph Bourauel1
Email: bourauel@uni-bonn.de
1 Oral Technology Medical Faculty, Dental School, University of Bonn,
Welschnonnenstr, 17 53111 Bonn, Germany
2 Department of Orthodontics, University Medical Center, Hugstetter. Str. 55,
79106 Freiburg, Germany
3 Private Practice, Richard-Wagner-Str. 9-11, 50674 Köln, Germany
* Corresponding author. Department of Orthodontics, University Medical Center,
Hugstetter. Str. 55, 79106 Freiburg, Germany
Abstract
Background
The aim of this study was to investigate the efficacy of orthodontic treatment using the
Invisalign® system. Particularly, we analyzed the influence of auxiliaries (Attachment/Power
Ridge) as well as the staging (movement per aligner) on treatment efficacy.
Methods
We reviewed the tooth movements of 30 consecutive patients who required orthodontic
treatment with Invisalign®. In all patients, one of the following tooth movements was
performed: (1) Incisor Torque >10°, (2) Premolar derotation >10° (3) Molar distalization
>1.5 mm. The groups (1)-(3) were subdivided: in the first subgroup (a) the movements were
supported with the use of an attachment, while in the subgroup (b) no auxiliaries were used
(except incisor torque, in which Power Ridges were used). All tooth movements were
performed in a split-mouth design. To analyze the clinical efficacy, pre-treatment and final
plaster cast models were laser-scanned and the achieved tooth movement was determined by
way of a surface/surface matching algorithm. The results were compared with the amount of
tooth movement predicted by ClinCheck®.
Results
The overall mean efficacy was 59% (SD = 0.2). The mean accuracy for upper incisor torque
was 42% (SD = 0.2). Premolar derotation showed the lowest accuracy with approximately
40% (SD = 0.3). Distalization of an upper molar was the most effective movement, with
efficacy approximately 87% (SD = 0.2).
Conclusion
Incisor torque, premolar derotation and molar distalization can be performed using
Invisalign® aligners. The staging (movement/aligner) and the total amount of planned
movement have an significant impact on treatment efficacy.
Background
In 1999, the Invisalign® system was introduced to the orthodontic market as a system of
treating mild malocclusions, such as minor crowding and space closure [1]. In the following
years, the system developed: different attachment designs and auxiliaries such as Precision
Cuts and Power Ridges were designed to enable additional treatment of difficult
malocclusions. According to the manufacturer, Invisalign® can effectively perform major
tooth movements, such as bicuspid derotation up to 50 degrees and root movements of upper
central incisors up to 4 mm [2]. In reference to the literature, however, there is no consensus
about the exact indications of this system’s treatment [3]. This may be because little is known
about orthodontic therapy with removable thermoplastic appliances (RTAs). Prior
publications on Invisalign® mainly cover technical aspects, materials studies and case reports
[4,5]. Only a few studies have concentrated on the efficacy of the treatment: Kravitz et al. [6]
evaluated the accuracy of anterior tooth movement using the Invisalign® system and reported
a mean accuracy of 41%. The most effective movement was lingual constriction (47.1%), and
the least accurate movement was extrusion (29.6%).
To date, no published data could be found concerning the efficacy of tooth movements such
as molar distalization and incisor torque with removable thermoplastic appliances. Some
authors doubt whether bodily movements or torque can be accomplished at all by RTA and
therefore recommend using RTA only in cases where tipping movements are needed [7].
Consequently, the purpose of this clinical and experimental study was to investigate the
treatment efficacy of Invisalign® aligners for the following three predefined tooth
movements: incisor torque >10°, premolar derotation >10°, molar distalization >1.5 mm.
For this purpose, the amount of tooth movement predicted by ClinCheck® (=software
developed by Align Technology in order to provide the doctor a virtual 3-D simulation of the
planned orthodontic treatment based on the patients beginning situation and the doctor’s
predescribed treatment plan) was compared with the amount achieved after treatment.
Furthermore, the influence of auxiliaries (attachments/Power Ridge) as well as the staging
(movement/aligner) and the patient’s compliance on the treatment were evaluated.
Methods
Study design and patients
Models of 30 patients were retrospectively assessed in the period between 2011 and 2012.
The Invisalign system is a worldwide well known and accepted orthodontic appliance, and
due to the retrospective character of the study, the local ethical committee of the University
of Bonn granted us exempt status for our retrospective study.
Inclusion criteria were healthy patients, treated with Invisalign® and one of the three
following tooth movements were required:
1) upper medial incisor torque >10°,
2) premolar derotation >10°,
3) molar distalization of an upper molar >1.5 mm.
Exclusion criteria were patients with systemic disease, syndromes and cleft lip and palate. All
patients’ malocclusions were exclusively treated with Invisalign® aligners in a private
orthodontic practice in Cologne, Germany. The influence of auxiliaries, such as attachments
(temporarily bonded composite buttons) and Power Ridges (pressure lines close to the
gingival margin), on the above-mentioned tooth movements was investigated:
For carrying out upper incisor torque (group 1), (a) a ‘horizontal ellipsoid attachment’ or (b)
power ridges were used according to the manufacturer’s information. In group 2 (premolar
derotation) (a) optimized rotation attachment’ or (b) no auxiliary and in group 3 with a (a)
‘horizontal bevelled gingival attachment’ or (b) no auxiliary was used. In all, 60 tooth
movements (20 in each main group, 10 in each subgroup) were determined using a split-
mouth design. Furthermore, the tooth movement was performed in isolation in the
ClinCheck® thus it could be analyzed exclusively.
Attachments and staging
The attachments were engineered by Align Technology to achieve predictable tooth
movements and placed according to the Align technology attachment protocol (horizontal
ellipsoid attachment, horizontal gingival bevelled attachment) [8] or automatically placed by
the software (optimized rotation attachment). Regarding the treatment protocol of Align
technology, velocities up to 2 degrees/aligner for rotation, up to 1 degree/aligner for incisor
torque and up to 0.25 mm/aligner for distalization are possible. To investigate the influence
of the staging on the treatment efficacy, the tooth movements were planned to be partly
slower and partly faster (Table 1).
Table 1 Amount of planned movement
Tooth Movement
Possible staging
* Maximal amount of
movement **
Mean movement
/
aligner **
Mean staging
/
aligner**
Premolar Derotation w Att 2.0 ° 30.0 ° 17.8 ° 1.1 °
Premolar Derotation w/o Att 2.0 ° 35.0 ° 20.1 ° 1.2 °
Distalization w Att 0.25 mm 3.2 mm 2.7 mm 0.2 mm
Distalization w/o Att 0.25 mm 3.2 mm 2.6 mm 0.2 mm
Incisor Torque w Att 1.0 ° 28.0 ° 16.1 ° 1.2 °
Incisor Torque w PR 1.0 ° 30.0 ° 15.9 ° 1.1 °
w Att. = with Attachment; w/o Att. = without Attachment; w PR = with Power Ridge.
* Possible staging according to the treatment protocol of Align technology.
** Amount of planned movement according to ClinCheck / the technician.
Scanning, segmentation and superimposition
To document the clinical outcome, alginate impressions (Tetrachrom Alginat, Kaniedenta
GmbH & Co. KG, Herford, Germany) of the intraoral conditions prior to the start of the
movement (T1) and immediately after finishing this treatment phase (T2) were taken. The
produced plaster cast models (Snow White Plaster, Kerr GmbH, Karlsruhe, Germany) were
digitalized using a laser scanner (Micromeasure 70®, Microdenta Sensorik, Linden,
Germany). Fixed on a motor-driven positioning table, the plaster casts were scanned on the
basis of laser triangulation from four different predefined angles to cover all relevant areas
and to prevent shadowing effects due to undercuts (Figure 1). The measuring points were
registered by a charge-couple device (CCD) camera with an accuracy of approximately 20
µm according to the manufacturer’s data [9]. Thereafter, the individual scans were matched
and merged into a single cloud of points by the computer to gain one single 3-D data set.
Figure 1 Laser scanner used in this study.
The ClinCheck® data at the time T2 (after finishing the investigated treatment phase)
represented the virtual treatment goal. It was provided by AlignTechnology as a virtual 3-D
model using the ClinCheck® database (Clin T2).
The point of cloud of the pre-treatment (T1), of the final plaster cast model (T2) as well as the
virtual 3-D ClinCheck® model (Clin T2) were fed into the software Surfacer 10.0
(Imageware/Siemens PLM Software, Plano, Texas, USA). In the next step, each point of the
cloud of (T1), (T2) and (Clin T2) were segmented into the individual teeth (Figure 2). The cloud
points of the untreated teeth of the initial situation (T1) defined a global coordinate system for
each patient and were used as a corresponding structure to merge the cloud points of the
initial and final conditions. One after another, the clinically moved teeth of the final
conditions (T2 and Clin T2) were superimposed with the initial situation (T1) using a surface/surface
matching algorithm (Figure 2). In doing so the predicted movement by the ClinCheck® (Clin T2
T1) as well as the clinical achieved tooth movement (T2 T1) was determined exactly by the
translational (Tx,Ty,Tz) and rotational (Rx, Ry, Rz) new coordinate components relative to
the initial position [10].
Figure 2 Superimposition of the scans. 2a) The plaster cast models of the beginning
conditions are digitised using a laser scanner. 2b) The models are segmented into single teeth.
2c) The predicted tooth movement in the ClinCheck (extracted from the dataset from Align
Technology). 2d) Superimposition of the plaster cast of the beginning conditions with the
ending conditions in the ClinCheck to determine the predicted tooth movement.
To evaluate treatment efficacy, the difference between the parameters of the clinically
achieved tooth movement (T2 – T1) with the expected amount of tooth movement predicted by
ClinCheck®(Clin T2-T1) was calculated.
Coordinate system
To describe the tooth movement in all three spatial dimensions and to compare the predicted
tooth movement with the achieved tooth movement, a reference coordinate system was set up
(Figure 3): In the right-handed coordinate system, the axes were defined so that the x- and y-
axes described movements in the horizontal plane and the z-axis described movements along
the vertical plane. Thus, the tooth movement could be described by three translations (Tx,y,z)
and three rotations (Rx,y,z) around the axes of this coordinate system. For the investigated
tooth movements, that mean that an upper incisor torque was a rotation around the y-axis,
premolar derotation was a rotation around the z-axis and molar distalization was a translation
on the x-axis.
Figure 3 Definition of the coordinate system used in this work. The distalization is
described as a translation on the x-axis, incisor torque as a rotation around the y-axis, and
premolar derotation is described as a rotation around the z-axis.
Statistical analysis
The statistical evaluation included the analysis of the measured values as well as a minimum,
a maximum, means and standard deviation of the mean. As the results were normally
distributed according to the Shapiro-Wilk test, student’s paired t-test was used to analyze
statistical difference between T2 (clinical achieved tooth movement) and ClinT2 (predicted
tooth movement) values in each group (1–3: incisor torque, premolar derotation, molar
distalization) for each subgroup (a: using an attachment, b: no attachment / using Power
Ridge). A value of p 0.05 was considered statistically significant. The statistical evaluation
was undertaken with the Statistical Package for Social Sciences, version 20.0 (SPSS Inc.,
Chicago, Illinois, USA).
Results
Clinical outcome
Of 30 patients (n = 11 male, n = 19 female; aged between 13 and 72 years, mean age 32.9
years, SD = 16.3), a total of 60 tooth movements were investigated (20 movements in each
main group (1–3), 10 in each subgroup (a-b)).
However, 4 patients (13.3%) dropped out because:
one patient moved away
one patient discontinued orthodontic therapy
impressions could not be taken from two patients directly after the investigated treatment
phase (T2), since they did not re-attend at this point.
Therefore, the total amount of analyzed tooth movements revealed forty-nine:
14 in the incisor torque group (1), 7 in each group (a) and in group (b)
20 in the premolar derotation group (2), 10 in each group (a) and in group (b)
15 tooth movements in the distalization group (3), 7 in group (a) with attachment, 8 in
group (b) without the support of an auxiliary.
Altogether, patients’ compliance was quite positive, with the exception of two patients who
reported wearing their aligners for only 8 h per day, all patients followed the alignment
technology treatment protocol of wearing their aligners the prescribed time of 22 h per day.
Measurement outcome
Figure 4 illustrates the treatment efficacy of the different tooth movements. The overall
efficacy for all tooth movements amounted to 59.3% (SD = 0.2). The highest accuracy was
achieved in the group of molar distalization, while the lowest accuracy was in the group of
premolar derotation (Table 2). In the group of upper incisor torque (1) as well as in the group
of premolar derotation (2) there was a statistical significant difference between the planned
movement in the ClinCheck® and the clinical achieved movement (Table 2).
Figure 4 Boxwhisker plots showing the treatment efficacy of incisor torque, premolar
derotation and molar distalization. w. Att = with Attachment, w/o Att = without
Attachment, w. PR. = With Power Ridge.
Table 2 Accuracy of tooth movements
Movement Mean accuracy
(%) Highest accuracy
(%) Lowest accuracy
(%) Standard
deviation
p
-
value
Premolar Derotation w Att 37.5 80.6 - 2.9 0.3 0.00
Premolar Derotation w/o Att 42.4 79.8 23.6 0.3 0.02
Distalization w Att 88.4 108.7 56.4 0.2 0.38
Distalization w/o Att 86.9 104.2 61.0 0.2 0.46
Incisor Torque w Att 49.1 71.6 29.9 0.2 0.00
Incisor Torque w PR 51.5 75.1 27.4 0.2 0.00
w Att. = with Attachment; w/o Att. = without Attachment; w PR = with Power Ridge.
p-value = clinically achieved tooth movement (T2) – tooth movement predicted by ClinCheck (Clin
T2), p < 0.05.
Group 1: upper central incisor torque >10°:
No substantial differences were observed if the upper central incisor torque was supported
with a horizontal ellipsoid attachment or with a Power Ridge. Measurements of incisor torque
with Power Ridges (b) achieved a mean accuracy of 51.5% (SD = 0.2). The highest accuracy
in this group was 75.1%, while the lowest accuracy amounted to 27.4%. In the group
supported by an attachment (a), the mean accuracy amounted to 49.1% (SD = 0.2), the
highest accuracy was 71.6%, and the lowest accuracy was 29.9%.
Group 2: premolar derotation >10°,
Also in the group of the premolar derotation no statistically significant difference could be
found with regard to them being conducted in conjunction with an attachment. The mean
accuracy achieved using an attachment (a) was 37.5% (SD = 0.3). The highest accuracy in
this group amounted to 80.6%, and the lowest accuracy was −2.9%. This patient had poor
compliance and claimed to have worn the aligner only 8 h per day. In the group of premolar
derotation without the support of an attachment (b), the mean accuracy was 42.4% (SD =
0.3). The highest accuracy amounted to 79.8%, while the lowest accuracy was 23.6%. The
efficacy of premolar derotation was further evaluated according to the amount of tooth
movement as well as the amount of staging planned in the ClinCheck®: The results show that
the accuracy was significantly reduced for predicted rotations greater than 15° as well as for
rotations with a planned staging > 1.5°/aligner (Tables 3 and 4).
Table 3 Accuracy of premolar derotation according to the amount of planned tooth
movement
Planned Movement Mean accuracy
(%) Highest accuracy
(%) Lowest accuracy
(%) Mean Standard
deviation
Premolar Derotation < 15° 43.3 72.5 16.8 0.24
Premolar Derotation > 15° 23.6 76.9 −2.9 0.15
Table 4 Accuracy of premolar derotation according to the staging (movement/aligner)
Movement
planned staging
/
aligner
Mean accuracy
(%) Mean Standard deviation
Premolar Derotation < 1.5° 41.8 0.3
Premolar Derotation > 1.5° 23.2 0.2
Group 3: molar distalization of an upper molar >1,5 mm.
The distalization of upper molars was the most effective movement, irrespective of the use of
an attachment. The mean accuracy of molar distalization supported with an attachment (a)
was 88.4% (SD = 0.2). The highest accuracy achieved was 108.7%, while the lowest
accuracy was 56.4%. Without the support of an attachment (b), the mean accuracy for upper
molar distalization amounted to 86.9% (SD = 0.16). The highest accuracy in this group was
104.2%, while the lowest accuracy was 61.0%.
Discussion
It was the aim of our investigation to evaluate the treatment efficacy of three predefined tooth
movements (translation, rotation and incisor torque) with aligners using the Invisalign®
system, with respect to the influence of attachments/Power Ridges, the staging and the
patients’ compliance.
In our study, the overall efficacy amounted to 59.3%. It should be noted, however, that the
total efficacy in our study was composed of the efficacy of the three investigated movements:
premolar derotation, molar distalization and incisor torque. Thus, it does not reflect the
efficacy of complete orthodontic treatment.
Some authors doubt that bodily movements (especially incisor torque) can be accomplished
using removable plastic appliances [7]. To generate the needed force systems, Invisalign®
provides the use of an attachment or Power Ridge. As the results of our study indicate, both
are practicable; nevertheless, a loss of torque up to 50% must be considered. However, it
must be noted that the efficacy of fixed orthodontic appliances does not reach 100% either:
Conventional orthodontic brackets and wires do not completely fill the bracket slots, so that
the wire is able to twist, leading to a loss of moment, known as the so-called “torque play.”
Moreover, the size and quality of the wire, the wire edge bevelling, the bracket material
(polycarbonate brackets vs. metal and ceramic brackets) and bracket design, the interbracket
distance, the vertical positioning of the bracket as well as the mode of ligation all influence
the torque movement of conventional fixed appliances [11]. Due to this large amount of
variation, it is almost impossible to calculate how much loss of torque expression exists with
the use of a fixed appliance.
As described in the literature, one of the most difficult movements to perform with an aligner
is the derotation of a cylindric tooth, as thermoplastic appliances tend to lose anchorage and
slip off due to the presence of few undercuts and a round tooth shape [12,13]. This is
reflected by the published results for premolar and canine derotation, which range between
29.1% to 49.7% [6,14-16]. In our study, the mean accuracy for premolar derotation (group 2)
was 42.4% without and 37.5% with the support of an attachment. The lower efficacy in the
group supported with an attachment was mainly due to poor patient compliance, which
significantly reduced the treatment efficacy. It seems that if the aligner fitting is reduced but
there is no attachment on the tooth’s surface, the rotational force transfer just decreases,
whereas with an attachment, counter-moments can occur, leading to tooth movement in the
opposite direction. If one was to exclude the patient’s poor compliance, a mean accuracy of
47.3% would be achieved. Overall, the amount of derotation influenced the accuracy
significantly: If rotations greater than 15° were attempted, the mean accuracy of premolar
derotation decreased by 46%, from 43.3% to 23.6%. These results were in accordance with
those of Kravitz et al., who reported a significant reduction of up to 52.5% in the accuracy of
canine derotation for rotations greater than 15° [6]. In addition to the amount of derotation,
the staging (amount of derotation/aligner) also has a considerable impact on the treatment
efficacy: for premolar derotations with a staging <1.5°/aligner, the total efficacy was 41.8%
(SD = 0.3), whereas with a staging >1.5°/aligner, the accuracy decreased to 23.2% (SD =
0.2).
Among clinicians, one very important aspect is if and to what extent anterior-posterior
movements can be performed using RTAs because this significantly increases the indications
and allows for usage in even more complex malocclusions. Some authors reported a low
accuracy of Invisalign® in correcting large anterior-posterior discrepancies [17]. To date, no
scientific study has evaluated the exact efficacy of molar distalization using RTA. In our
study, the molar distalization revealed the highest accuracy, approximately 87%. None of the
patients used class II elastics during treatment. However, it should be noted that we measured
the accuracy of distalization using a maximal amount of desmodontal anchorage: no anterior
teeth were moved during the distalization of single molars. Furthermore, the anchorage lost in
the posterior region during the retrusion of anterior teeth was not considered because the
impressions were taken directly after the distalization of the second/first molar (T2). It
remains to be investigated what impact simultaneous distalization of anterior teeth has on the
overall efficacy of molar distalization, if the use of interarch elastic enhances distalization,
and what amount of anchorage lost in the posterior region occurs during the retrusion of
anterior teeth.
This study exhibited some limitations:
Because the data from the final tooth position in the ClinCheck® did not show the palatal
surface, we used the untreated teeth as reference points for superimposition. Although only
one tooth per hemiarch was moved, leaving enough teeth as a reference structure, relative
movements of the reference teeth could not be excluded due to periodontal anchorage.
Furthermore, the aligner material we used in our study was the so-called the Exceed30
(EX30), the original aligner material from Align Technology. From the first quarter of 2013,
a new aligner material called SmartTrack™ (LD30) was introduced to the orthodontic market
by Align Technology. To what extent the new aligner material influences the treatment
efficacy needs to be investigated.
Our evaluation focuses on the treatment efficacy of the three tooth movements during a
certain set of aligners (on average 18) because during regular orthodontic treatment, the
amount of aligners used to treat patients’ malocclusion is greater. In turn, the overall efficacy
may be greater as the tooth movements are performed more slowly throughout the entire
treatment time.
Another methodological deficit of this study was the low number of study participants,
recruited from one single orthodontic practice. The treatment outcome using the Invisalign®
appliance is strongly influenced by the experiences of the clinicians, so that the study results
are not generally valid. To provide more accurate results on the treatment efficacy, a follow-
up study with a larger sample size from several orthodontists would be useful.
Finally it must be said that we only investigated the efficacy of orthodontic treatment using
the Invisalign® system with regards to the influence of auxiliaries (Attachment/Power
Ridge), the staging (movement per aligner), as well as patient’s compliance. No comparison
was made between the Invisalign® system and other orthodontic systems such as
conventional fixed appliances, lingual appliances or other removable thermoplastic appliance
systems. Further studies should compare treatment efficacy between different orthodontic
treatment systems to find out which system is most appropriate for different dental
malocclusion.
Conclusions
This study showed that bodily tooth movements such as molar distalization, incisor torque, as
well as premolar derotation can be accomplished using the Invisalign® system. Especially the
efficacy of premolar derotation significantly depends on the velocity as well as the total
amount of planed tooth movement. Upper incisor torque and pure premolar derotation are
challenging movements using removable thermoplastic appliances - users should take into
account that overcorrections or case refinements may be needed, since in these cases the
ClinCheck® simulation could predict more movement than what may result clinically.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
CB is the designer, supervisor and conductor of this project. MS participated in the project in
all its phases (design, implementation, evaluation). LK supervised the experimental set up
and the statistics. JS offered the patients’ models, BAJ is co-investigator and reviewed the
manuscript. All authors read and approved the final manuscript.
Acknowledgements
The article processing charge was funded by the German Research Foundation (DFG) and the
Albert Ludwigs University Freiburg in the funding programme Open Access Publishing by
the Albert Ludwigs University Freiburg.
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14. Nguyen CV, Chen J: Chapter 14: Three-Dimensional Superimposition Tool. In The
Invisalign System. Edited by Tuncay OC. New Malden, UK: Quintessence Publishing Co,
Ltd; 2006:121–132.
15. Durrett SJ: Efficacy of Composite Tooth Attachments in Conjunction With the Invisalign
System Using Three-Dimensional Digital Technology. University of Florida; 2004. Available
at: http://etd.fcla.edu/UF/UFE0004566/durrett_s.pdf. Accessed May 2004.
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... In the beginning, the aligners were limited only to mild malocclusions, such as anterior crowding, or to periodontal patients; through the years, thanks to advances in technology and clinical trials, clear aligners have effectively performed major tooth movements, e.g. premolar derotation as well as molar distalization [1]. Despite the predictability of the treatment, its clinical potency remains debatable; opponents have remarked on the need to require mid-course correction or case refinement, especially when treating complex malocclusions, whereas advocates have remained convinced of successful outcomes at the end of the therapy [2]. ...
... In literature, the outcomes regarding the torque variation appear to be discordant: this is due to methodological heterogeneity. Some studies analyzed torque without planning for optimized attachments, auxiliaries, or power ridges [25]; others used different materials, even materials no longer used today [1]. Different material properties and aligner production processes affect the force levels and, thus, the predictability of tooth movements [26]. ...
... In addition, there are studies [1] which evaluated the torque only on a small number of aligners and, for this reason, concluded that a greater number of aligners or a torque overcorrection should be required to achieve the desired dental movements. In the present research, the refinements and power ridges have also been included. ...
Article
Full-text available
This study aimed to investigate the efficacy of torque movement and the incidence of root resorption in the maxillary and mandibular teeth with clear aligner therapy using cone-beam computed tomography. The sagittal root positions, the faciolingual inclinations, and the root lengths of 672 teeth, from central incisors to first molars for each arch, were measured and compared on virtual cross sections from pre-treatment and post-treatment cone-beam computed tomography of 28 patients who received comprehensive orthodontic treatment with clear aligners. An improvement of root position was found in incisors, canines, and premolars of the upper and lower arches: over 78% of their root was centered in the alveolus at the end of orthodontic treatment. There was a statistically significant torque increase for incisors, canines, and first premolars at the end of therapy. The most considerable torque changes were achieved in incisors and canines, while the lowest was in posterior teeth. The maxillary and mandibular central incisors achieved 3.26 ± 1.95° and 2.97 ± 2.53° of mean torque increase, respectively. The root length loss was greater in the upper and lower central incisors. All teeth showed mild resorption (<10%) except for two upper lateral incisors, which showed moderate resorption (10.79% and 10.23%). Comprehensive treatment with clear aligners improved sagittal root position and increased torque, especially in the anterior teeth. Most teeth showed mild resorption after clear aligner therapy, and only two showed moderate resorption.
... including three studies on treatment efficacy with different aligner stiffnesses and wearing protocols [5][6][7] , six studies comparing Invisalign treatment with fixed appliances, [8][9][10][11][12][13] nine studies comparing actual tooth movement with predictions, [14][15][16][17][18][19][20][21][22] two studies on outcomes with different treatment strategies, 23,24 three retrospective studies on the treatment effects of Invisalign, [25][26][27] and two studies on treatment efficacy in patients with different amounts of crowding or overbite. 28,29 The comparison group and outcome measures of each study were also varied which were summarized in Table 3 and Table 4. ...
... Invisalign treatment with fixed appliances 6 [8][9][10][11][12][13] Actual tooth movement with predictions 9 [14][15][16][17][18][19][20][21][22] Outcomes of different treatment strategies 2 23,24 Before and after study of Invisalign treatment 8 5-7, 25-29 Table 4. Outcome measures of each study in the review. ...
... Simon et al. found that the accuracy of premolar de-rotation with optimized rotation attachment was even lower (37.5%). 23 These findings should be interpreted carefully. Sampling ...
... However, it has shown an accuracy of 87% for molar distalization. 4,5 The key to nonextraction treatment of Class II malocclusion is maxillary molar distalization. As previously reported, CAT is able to provide molar distalization with high accuracy through sequential movement. ...
Article
Objectives To analyze the effects of maxillary tooth distalization by clear aligner (CA) treatment with variations in the angular direction of the distalization force, presence of attachments, and force-application method used. Materials and Methods A finite element model containing alveolar bone, dentition, and periodontal ligament was constructed. Analytical model groups were as follows: (1) distalization with buttons (without attachments), (2) buttons on canines (with attachments), (3) precision cuts on the canines (without attachments), and (4) precision cuts on the canines (with attachments). A distalization force of 1.5 N was applied to the button or precision cut at −30°, −20°, −10°, 0°, 10°, 20°, and 30° to the occlusal plane. Results As the direction of force approached +30°, the dentition inclined posteriorly. The posterior movement pattern was significantly influenced by the presence of an attachment and the direction of force, rather than the area where the force was applied. Distal inclination was dramatically reduced with attachments. A disengagement or deformation of the CA may reduce the distalization efficiency of the dentition or move the dentition in an inappropriate direction. Conclusions Attachments for efficient distalization by the CA are necessary. The use of miniscrews in the direction of force parallel to the occlusal plane is more advantageous than the use of Class II elastics. Due to CA deformation, distalization with the button on the canines can be more effective for distal movement of the maxillary dentition.
... Currently, in the scientific literature analysis of this type of treatment is lacking, there are just few case reports. The predictability of maxillary molar distalization using aligners is high (88%) and well demonstrated by Simon et al. [30]. The paper published by Ravera et al. [31] confirmed these results. ...
Article
Full-text available
Background: Lower molar distalization is considered to be one of the most difficult movements to obtain with clear aligners. The aim of this study was to evaluate the possibility to distalize the lower molars using clear aligners in adults without miniscrews. Material and methods: rx cephalograms of 16 patients (8 males, 8 females; mean age of 25.6 years), who underwent lower molar distalization, were analyzed. Cephalograms were taken before the beginning of treatment (T0) and after the end of treatment (T1). Dental and skeletal changes between T0 and T1 were evaluated. The level of significance was set at p < 0.05. Results: At T1, the lower second molar moved distally 2.47 mm, but there was a significant tipping (p = 0.027); the same result was found at the first molar, with a mean distal movement of 1.16 mm and a significant tipping (p = 0.003). No significant changes were detected on the sagittal and vertical skeletal variables. Conclusion: Clear aligner therapy can provide more distal tipping than bodily movement in the lower molars when a distalization is programmed. This movement could be sufficient to correct the initial malocclusion and gain a class I molar relationship.
... 1999'da Invisalign sistemi, yalnızca hafif maloklüzyonları tedavi etmek için ortodonti pazarına sunulmuştur; ancak, farklı ataşmanların ve yardımcıların geliştirilmesi sayesinde Invisalign sistemi ile büyük diş hareketleri gerçekleştirilmekte ve küçük azı çekimi vb. işlemler gerektiren karmaşık vakalar tedavi edilmektedir (Gu et al., 2017;Simon et al., 2014b;Wong, 2002). Invisalign sistemindeki hizalayıcılar, CAD-CAM teknolojisi (Barone et al., 2017) kullanılarak tasarlanmakta ve üretilmektedir. ...
... Nevertheless, the influence of attachment on the movement pattern of molar distalization, which is either bodily movement or tipping movement, could not be clarified. 34 Regarding to the effectiveness of vertical tooth movement with CAT, Rossini et al. in the systemic review indicated that CAT could be only recommended for mild deep overbite correction but not for treatment of open bite. CAT had less effects on controlling the vertical movement of incisors. ...
... This was further elaborated by a systematic review in 2019 concluding that attachment incorporation is not necessary when molar distalization is planned. 13 Furthermore, Simon et al 19 highlighted the importance of staging in increasing the predictability of distalization. This was also observed in our case, where sequential distalization was planned on 24 stages of aligner treatment, hence achieving the highest predictability of distalization. ...
Article
Full-text available
To describe an esthetic orthodontic treatment using aligners in an adult patient with dental class II malocclusion associated with crowding. A 25‐year‐old female patient with skeletal class I, bilateral class II relation, increased overjet and overbite and crowding in both arches presented for orthodontic treatment. The patient refused conventional fixed multibracket treatment in favor of aligners. Pre‐ and post‐treatment records are presented. Treatment objectives were achieved in 10 months, and the patient was satisfied with the functional and esthetic outcomes. Combining aligners with appropriate attachment location and geometry is an efficacious means of resolving orthodontic issues such as class II malocclusion in a time frame comparable to that of conventional fixed orthodontics. Staging in distalization increases the predictability of movement. Furthermore, this system is associated with optimal oral hygiene and excellent esthetics.
... The primary outcome lack of correction (LC) and the exposure prescribed movement (PM) were normalized by means a logarithmic transformation *The variable was normalized conducting a logarithmic transformation of the data † The reference category is angulation ‡ The reference category is maxillary central incisor § The reference category is absence of attachment aligners. Several in vivo and in vitro studies confirmed the clinical experience of the poor predictability of rotational movement of rounded shaped teeth, with maxillary canines being the most affected teeth [8,13,15,39,40]. According to some reports, canines demonstrate a mean rotational discrepancy between predicted and finally achieved movement of approximately 3.8° [41]. ...
Article
Full-text available
Abstract Backgrounds The present study was designed to define: (1) which are the less predictable OTM with Invisalign aligners when the treatment plan is designed by expert operators, (2) if the presence and shape of attachments influence the predictability of OTM and (3) if patients’ demographics influence OTM predictability. The sample comprises 79 prospectively recruited patients (mean age 30.8 years; SD 12.0; 23 M, 56 F), treated by expert operators with an average of 27 aligners (SD 15) in the maxillary arch and 25 aligners (SD 11) in the mandibular arch. Post-treatment digital models and final virtual treatment plan models were exported from ClinCheck® software as STL files and subsequently imported into Geomagic Qualify ®software, to compare final teeth positions. The differences were calculated and tested for statistical significance for each tooth in the mesial–distal, vestibular–lingual and occlusal–gingival directions, as well as for angulation, inclination and rotation. In addition, the statistical significance of categorical variables was tested. Results The lack of correction was significant for all movements and in all group of teeth (P
... A prospective study conducted on 53 canines of 31 subjects assessed a mean accuracy for canine rotation of 35.8% [10] . Simon et al. revealed a high predictability (88%) of the distalization movement of upper molars [11] . ...
Preprint
Full-text available
Objective The objective of this study was to detective the accuracy of model superimposition and automatic analysis for upper and lower dentition width in Invisalign Progress Assessment during the process of clear aligners. Methods 19 cases were included in this study. Pre-treatment dental cast(T0) and post-treatment dental cast after staged treatment(T1) were available for three-dimensional model superimposition. Subsequently, movements of maxillary teeth in horizontal plane (cross section) after staged treatment, width of upper and lower dentition were measured by three-dimensional model superimposition in real world and Invisalign Progress Assessment separately. Consequently, the data collected from these two methods was compared. Results In Invisalign Progress Assessment, movements of maxillary teeth in horizontal plane after staged treatment was 2.31(1.59,3.22) (median (upper quartile, lower quartile)) millimeter (mm), while in three-dimensional model superimposition, the result was 1.79(1.21,3.03)mm. The difference between two groups is significant(P<0.05). Intercanine width upper, intermolar width upper, intercanine width lower, and intermolar width lower were 36.55±2.76mm, 56.98±2.62mm, 28.16±1.85mm, 53.21±2.72mm separately in Invisalign Progress Assessment and were 36.48±2.78mm, 56.89±2.58mm, 28.05±1.85mm, 53.16±2.64mm separately in three-dimensional model analysis, which were no significant difference among these groups (P>0.05). Conclusions The data from Invisalign Progress Assessment was not in parallel with what achieved from model superimposition with palate as reference completely. The accuracy of model superimposition in Invisalign Progress Assessment needs further investigation, whereas the accuracy of model analysis in Invisalign Progress Assessment was accurate. Thereby, results from Invisalign Progress Assessment should be interpreted with caution by the orthodontist in clinic.
Article
Introduction: The objective of this study was to investigate the predictability of overbite correction in patients with deepbite using the clear aligners (Invisalign, Align Technology, San Jose, Calif) and examine the accuracy of vertical movement and inclination change of individual teeth. Methods: This retrospective study included 24 deepbite patients (10 males and 14 females; aged 32.8 ± 11.9 years; an initial overbite of 5.20 ± 0.95 mm; an average treatment period of 11.04 ± 4.14 months) consecutively treated from September 2016 and completed before August 2021. SmartTrack materials were used for all patients. The initial, predicted, and achieved final models were exported from ClinCheck and superimposed via best-fit surface-based registration using Slicer CMF (version 4.9.0; cmf.slicer.org). The overbite correction, changes in vertical movement, and inclination for individual teeth were measured. Descriptive statistics and a paired t test or Wilcoxon signed-rank test were performed. P <0.05 was considered statistically significant. Results: Mean overbite correction was 33%, with a 1.15 mm improvement after the first set of aligners. All teeth demonstrated statistically significant differences between planned and achieved amounts in vertical movement and inclination change, with the largest difference in maxillary central incisors. Mandibular incisor intrusion and mandibular premolar extrusion had similar accuracies. Regarding inclination change, maxillary central incisors showed the lowest accuracy of 13.3%. Conclusions: Clear aligner treatment showed an average of 33% overbite correction. Overcorrection and additional refinement treatments are needed in most patients with a deepbite.
Article
Full-text available
The force moment providing rotation of the tooth around the x-axis (buccal-lingual) is referred to as torque expression in orthodontic literature. Many factors affect torque expression, including the wire material characteristics. This investigation aims to provide an experimental study into and comparison of the torque expression between wire types. With a worm-gear-driven torquing apparatus, wire was torqued while a bracket mounted on a six-axis load cell was engaged. Three 0.019 x 0.0195 inch wire (stainless steel, titanium molybdenum alloy [TMA], copper nickel titanium [CuNiTi]), and three 0.022 inch slot bracket combinations (Damon 3MX, In-Ovation-R, SPEED) were compared. At low twist angles (<12 degrees), the differences in torque expression between wires were not statistically significant. At twist angles over 24 degrees, stainless steel wire yielded 1.5 to 2 times the torque expression of TMA and 2.5 to 3 times that of nickel titanium (NiTi). At high angles of torsion (over 40 degrees) with a stiff wire material, loss of linear torque expression sometimes occurred. Stainless steel has the largest torque expression, followed by TMA and then NiTi.
Article
The Invisalign System (Align Technology, Santa Clara, CA) is a new treatmentmethod using computer virtual treatments to create a series of clear, removable, esthetic appliances that can treat a wide range of malocclusions. We present the treatment of a patient who presents with a deep bite, upper incisor flaring, and deep curve of Spee with Invisalign.
Article
The purpose of this prospective clinical study was to evaluate the efficacy of tooth movement with removable polyurethane aligners (Invisalign, Align Technology, Santa Clara, Calif). The study sample included 37 patients treated with Anterior Invisalign. Four hundred one anterior teeth (198 maxillary and 203 mandibular) were measured on the virtual Treat models. The virtual model of the predicted tooth position was superimposed over the virtual model of the achieved tooth position, created from the posttreatment impression, and the 2 models were superimposed over their stationary posterior teeth by using ToothMeasure, Invisalign's proprietary superimposition software. The amount of tooth movement predicted was compared with the amount achieved after treatment. The types of movements studied were expansion, constriction, intrusion, extrusion, mesiodistal tip, labiolingual tip, and rotation. The mean accuracy of tooth movement with Invisalign was 41%. The most accurate movement was lingual constriction (47.1%), and the least accurate movement was extrusion (29.6%)- specifically, extrusion of the maxillary (18.3%) and mandibular (24.5%) central incisors, followed by mesiodistal tipping of the mandibular canines (26.9%). The accuracy of canine rotation was significantly lower than that of all other teeth, with the exception of the maxillary lateral incisors. At rotational movements greater than 15 degrees, the accuracy of rotation for the maxillary canines fell significantly. Lingual crown tip was significantly more accurate than labial crown tip, particularly for the maxillary incisors. There was no statistical difference in accuracy between maxillary and mandibular teeth of the same tooth type for any movements studied. We still have much to learn regarding the biomechanics and efficacy of the Invisalign system. A better understanding of Invisalign's ability to move teeth might help the clinician select suitable patients for treatment, guide the proper sequencing of movement, and reduce the need for case refinement.
Article
It is the aim of presurgical infant orthopedics (PSIO) to reduce the width of the cleft and to achieve optimal alignment of the cleft palate segments within the first few months of infancy prior to any surgical cleft closure. The question about the amount that PSIO can stimulate and steer the growth of the maxilla using a Hotz and Gnoinski passive appliance has not yet been satisfactorily answered. In this study, a 3-dimensional digital computer-aided procedure was developed to analyze metrically and to visualize the growth of the edentulous maxilla of cleft lip and palate in infants. In a pilot study, a series of digital scans of consecutive plaster casts was carried out. 5 infants with complete unilateral cleft lip and palate (UCLP), who had been treated with passive appliances were evaluated. Impressions were taken at the age of one week and after 3, 6 and 12 months. Following digitizing, the casts were computer-reconstructed and segmented perpendicular to the alveolar crest, the reference points being C1, C1', C2, C2' and I. The volume of the resulting segments was ascertained. Computer superimposition of reconstructed consecutive casts was employed to facilitate a visualization of the extent and direction of morphological changes. Our first results have shown that with our method it is possible to quantify the growth rate of defined segments of the maxilla. The 3-dimensional analysis presented here will be the basis for further studies to objectify PSIO.
Article
Am J Orthod Dentofacial Orthop 2002;121:540-1
Article
This article describes the Invisalign technique. It is based on the author's personal experience of over 60 cases started in the private practice setting. The technology behind Invisalign and its development is reviewed. The Invisalign clinical technique is described, and the advantages and disadvantages of using Invisalign are highlighted.
Article
Orthodontic tooth movements are described as the differences between initial and final tooth positions. A computer based method for determination of tooth movements for different treatment methods was developed. A total of 20 casts of the upper jaw of patients treated with tooth positioners or fixed appliances were used as a basis for this study. Tooth movement was analysed on casts before (Ci) and after treatment (Cf). The casts were digitized either with a COMT or 3D laser scanning systems. After digitization, the models were superimposed in the palate by using a surface-surface matching algorithm. Tooth surfaces of the orthodontically moved teeth were segmented and determination of tooth movement was accomplished by matching the moved teeth from Ci to Cf. The resulting transformations delivered three dimensional information on translations and rotations. An accuracy of 0.2 mm in translations and 1 degree in rotations could be demonstrated, showing the different efficiency of treatment schemes.