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Has Invisalign improved? A prospective follow-up study on the efficacy of tooth movement with Invisalign

Authors:
  • European University College, Dubai, UAE

Abstract and Figures

Introduction The purpose of this research was to provide an update on the accuracy of tooth movement with Invisalign (Align Technology, Santa Clara, Calif). Methods This prospective clinical study included 38 patients treated with Invisalign Full or Invisalign Teen. All teeth, from the central incisor to the second molar, were measured on digital models created from intraoral scans. Predicted values were determined by superimposing the initial and final ClinCheck models, and achieved values were determined by superimposing the initial ClinCheck models and the digital models from the posttreatment scans. Individual teeth were superimposed with a best-fit analysis and measured using Compare software (version 8.1; GeoDigm, Falcon Heights, Minn). The types of tooth movements studied were a mesial-distal crown tip, buccal-lingual crown tip, extrusion, intrusion, and mesial-distal rotation. Results The mean accuracy of Invisalign for all tooth movements was 50%. The highest overall accuracy was achieved with a buccal-lingual crown tip (56%), whereas the lowest overall accuracy occurred with rotation (46%). The accuracies for mesial rotation of the mandibular first molar (28%), distal rotation of the maxillary canine (37%), and intrusion of the mandibular incisors (35%) were particularly low. Conclusions There was a marked improvement in the overall accuracy; however, the strengths and weaknesses of tooth movement with Invisalign remained relatively the same.
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Has Invisalign improved? A prospective
follow-up study on the efcacy of tooth
movement with Invisalign
Nada Haouili,
a
Neal D. Kravitz,
b
Nikhilesh R. Vaid,
a
Donald J. Ferguson,
a
and Laith Makki
a
Dubai, United Arab Emirates, and South Riding, Va
Introduction: The purpose of this research was to provide an update on the accuracy of tooth movement with
Invisalign (Align Technology, Santa Clara, Calif). Methods: This prospective clinical study included 38 patients
treated with Invisalign Full or Invisalign Teen. All teeth, from the central incisor to the second molar, were
measured on digital models created from intraoral scans. Predicted values were determined by superimposing
the initial and nal ClinCheck models, and achieved values were determined by superimposing the initial Clin-
Check models and the digital models from the posttreatment scans. Individual teeth were superimposed with a
best-t analysis and measured using Compare software (version 8.1; GeoDigm, Falcon Heights, Minn). The
types of tooth movements studied were a mesial-distal crown tip, buccal-lingual crown tip, extrusion,
intrusion, and mesial-distal rotation. Results: The mean accuracy of Invisalign for all tooth movements was
50%. The highest overall accuracy was achieved with a buccal-lingual crown tip (56%), whereas the lowest
overall accuracy occurred with rotation (46%). The accuracies for mesial rotation of the mandibular rst molar
(28%), distal rotation of the maxillary canine (37%), and intrusion of the mandibular incisors (35%) were
particularly low. Conclusions: There was a marked improvement in the overall accuracy; however, the
strengths and weaknesses of tooth movement with Invisalign remained relatively the same. (Am J Orthod
Dentofacial Orthop 2020;-:---)
In 2009, Kravitz et al
1
conducted the rst prospective
clinical study on Invisalign (Align Technology, Santa
Clara, Calif) to evaluate its efcacy. Prior published
data included case reports, material studies, technical ar-
ticles, editorials, surveys, studies comparing Invisalign to
conventional xed appliances, and a systematic review,
none of which provided scientic evidence regarding
the efcacy or limitations of Invisalign.
2-23
Ten years
after Invisalign was introduced, orthodontists were just
beginning to quantify how well it moved teeth.
The landmark study by Kravitz et al
1
evaluated
the accuracy of anterior tooth movements with Invisa-
lign. Measurements were made by superimposing the
predicted and achieved ClinCheck digital models over
the stationary premolars and molars, using ToothMeas-
ure, Align's tooth measurement software.
24
The most
accurate movement was lingual constriction (47%),
and the least accurate movements were incisor extrusion
(18%) and mandibular canine rotation (28%). The
overall mean accuracy of Invisalign was 41%.
In a second study, using the same sample and
methodology, Kravitz et al
25
specically evaluated the
inuence of interproximal reduction (IPR) and ellipsoid
attachments on canine rotation. The mean accuracy of
this rotation with Invisalign was 36%. The authors
reported that canines which received IPR achieved the
highest accuracy (43%). Most importantly, the accuracy
of canine rotation signicantly dropped with rotational
movements greater than 15.
Since these 2 studies were published, signicant
contributions have been made, further evaluating the
efcacy of tooth movement with Invisalign.
In 2012, Krieger et al
26
also evaluated anterior tooth
position with Invisalign, but they studied different
parameters. Rather than assessing individual tooth
movements, the authors evaluated arch length, interca-
nine distance, overbite, overjet, and midlines by
comparing initial and nal plaster casts, which were
measured with digital calipers. They provided a general
a
Department of Orthodontics, European University College, Dubai Healthcare
City, Dubai, United Arab Emirates.
b
Private practice, South Riding, Va.
All authors have completed and submitted the ICMJE Form for Disclosure of Po-
tential Conicts of Interest, and none were reported.
Address correspondence to: Neal D. Kravitz, 25055 Riding Plaza, Ste 110, South
Riding, VA 20152; e-mail, nealkravitz@gmail.com.
Submitted, June 2019; revised and accepted, October 2019.
0889-5406
Ó2020 by the American Association of Orthodontists. All rights reserved. This is
an open access article under the CC BY-NC-ND license (http://creativecommons.
org/licenses/by-nc-nd/4.0/).
https://doi.org/10.1016/j.ajodo.2019.12.015
1
ORIGINAL ARTICLE
conclusion that Invisalign effectively resolved anterior
crowding by incisor proclination, but overbite correction
was difcult to achieve.
In 2014, Simon et al
27
evaluated the inuence of
attachments and power ridges with Invisalign for 3
specic movements: incisor torque, premolar rotation,
and maxillary molar distalization. Predicted digital
models were superimposed over achieved digitized plas-
ter models, using Surfacer software. The least accurate
movement was premolar rotation (40%). Similar to the
ndings by Kravitz et al,
25
this accuracy signicantly
decreased with rotational movements greater than 15.
In 2017, Gr
unheid et al
28
evaluated the efcacy of
tooth movement with Invisalign for all teeth. The pre-
dicted and achieved digital models were superimposed
with a best-t registration, using Compare software
(version 8.1; GeoDigm, Falcon Heights, Minn). Although
the percent accuracy was not calculated, the movements
that had the greatest difference between predicted and
achieved outcomes were molar torque, mandibular
incisor intrusion, and mandibular lateral, canine, and
rst premolar rotation.
In 2018, Charalampakis et al
29
evaluated the efcacy
of incisor, canine, and premolar movements with Invis-
align. The predicted and achieved ClinCheck models
were superimposed over stationary rst and
second molars, using SlicerCFM software. Similar to
the ndings by Gr
unheid et al,
28
the least accurate
movements were mandibular incisor intrusion, followed
by a rotation of the maxillary canines, mandibular
premolars, and mandibular canines.
Since the publication of the 2009 studies,
1,25
the
Invisalign system has undergone signicant changes.
The 2 most notable are the introduction of SmartForce
features (2008), such as optimized attachments, pressure
zones, and customized staging, and the SmartTrack
aligner material (2011), which allows for a better range
of force delivery and t. In addition, physical impressions
have been largely replaced by digital scans. The purpose
of this prospective clinical study is to provide an update
on the accuracy of Invisalign with newer technology.
MATERIAL AND METHODS
The study group comprised 38 patients (13 males, 25
females) with a mean age of 36 years. Twenty-nine
patients received Invisalign Full and 9 received Invisalign
Teen. The mean number of aligners per arch was 21
maxillary and 20 mandibular. Both arches each averaged
6 attachments and less than 1 mm of IPR. The break-
down of malocclusions was as follows: 22 Class I, 13
Class II, and 3 Class III. The average time between the
initial and nal scans was 8.5 months (Table I).
The research protocol was approved by the Institu-
tional Review Board of European University College
(no. EUC-IRB-17.2.11). Invisalign treatment was
provided at a single orthodontic practice in South
Riding, Virginia, and the orthodontist (N.D.K.), who
prescribed all ClinCheck treatment plans, was highly
experienced (Tier-Level Diamond Plus Provider [formerly
Top 1% Elite] with over 2500 Invisalign cases treated).
Unlike the 2009 study,
1
overengineering of tooth
moments was prescribed when deemed necessary to
achieve the best result clinically.
The patients were instructed to wear their aligners for
22 hours per day and change their aligners every 10 days.
At the delivery appointment, the patients understood
that they were part of a research study, and honest
reporting of their compliance was critical. Compliance
was also verbally conrmed at each appointment. The
last data collection was in November 2017.
Inclusion criteria were as follows: (1) treated with
either Invisalign Full or Invisalign Teen, (2) underwent
treatment in both arches, (3) completed an initial and
nal intraoral digital scan, and (4) conrmed good
compliance throughout treatment. Exclusion criteria
were as follows: (1) noncompletion in time for the study,
(2) poor compliance with the aligners, and (3) oral
surgery or dental restorations before the nal scan. A
total of 44 patients were enrolled in the study but 6
were excluded; 3 patients did not complete their
treatment in time for data collection, and 3 patients
had errors in their nal scans.
The digital models were deidentied and imported
into Compare, a tooth measurement software program.
Table I. Sample demographics
Category n
Patients
Male 13
Female 25
Malocclusion
Class I 22
Class II 13
Class III 3
Type of Invisalign
Invisalign Full 29
Invisalign Teen 9
Average number of aligners
Maxillary 21
Mandibular 20
Frequency of attachments
Maxillary 6
Mandibular 6
Average amount of IPR, mm
Maxillary \1
Mandibular \1
2Haouili et al
-2020 Vol -Issue -American Journal of Orthodontics and Dentofacial Orthopedics
All teeth in the arch were evaluated. The total number of
teeth measured was 899 (450 maxillary and 449
mandibular), which was more than twice as many as
the 2009 study.
1
The digital models were evaluated
following the protocol established by Gr
unheid et al.
28
The initial ClinCheck model was segmented into
individual teeth. To provide the predicted values, we
globally aligned the initial ClinCheck model over the
nal ClinCheck model. Then the individual teeth from
the initial model were superimposed over the equivalent
teeth of the nal model, using a best-t algorithm. To
provide the achieved values, we superimposed the
individual teeth from the initial ClinCheck model on
the digital model from the posttreatment scan (Figs,A
and B).
The tooth movements measured were mesial-distal
crown tip, buccal-lingual crown tip, intrusion, extrusion,
and rotation. Although the software measured torque,
in the absence of radiographs, this movement could not
be conrmed and was excluded from this study. The
percent accuracy was determined by the following equa-
tion: percentage of accuracy 5100% ([(predicted
achieved)/predicted] 3100%). The equation accounted
for directionality and ensured that the percentage of
accuracy never exceeded 100% for teeth that achieved
movements beyond their predicted value.
1
To evaluate the clinical relevance of our results, we
printed and assessed the posttreatment scans of half
the sample (19 patients), according to the American
Board of Orthodontics (ABO) cast evaluation system.
30
Patients were randomly chosen using research random-
izer software. Following the protocol of the 2009 study,1
a modied-Discrepancy Index of the pretreatment
malocclusion was calculated, excluding for cephalomet-
rics and skeletal asymmetry scores. The posttreatment
ABO scores were calculated by 2 operators;
subsequently, 10 models were remeasured by the same
examiner to assess intraoperator reliability.
Statistical analysis
The statistical analysis was performed with SPSS
software (version 15; IBM, Armonk, NY). Each tooth
movement was measured separately. Clinical signi-
cance was set for linear movements at \0.25 mm and
angular movements at \2, which is approximately
the amount of maximum movement on a tooth per
aligner. Paired ttests (P\0.05) compared the intraarch
accuracy of tooth movement by direction (ie, buccal
versus lingual), and independent ttests compared the
accuracy of tooth movement by arch (ie, maxillary vs
mandibular).
RESULTS
All predicted linear and angular movements less than
0.1 mm and 1.0were eliminated from analysis to
account for error in model superimposition. Acceptable
sample sizes were attained for all tooth movements,
except for the lingual crown tip of the maxillary rst
molar (n 56), rst premolar (n 53) and second premo-
lar (n 57), as well as the intrusion of mandibular second
premolar (n 58).
The mean accuracy of Invisalign for all tooth move-
ments was 50%. The highest overall accuracy was
achieved with a buccal-lingual crown tip (56%). The
lowest overall accuracy occurred with rotation (46%).
Specically, the most accurate movement was the labial
crown tip of the maxillary lateral incisor (70%), and the
least accurate movements were the mesial rotation of the
mandibular rst molar (28%), followed by intrusion of
the maxillary (33%) and mandibular central incisors
(34%) (Table II).
With regards to directionality, mesial rotation of the
maxillary canine (52%) was signicantly more accurate
than distal rotation (37%), the lingual crown tip of the
maxillary second molar (61%) was signicantly more
accurate than the buccal crown tip (35%), extrusion of
Fig. A, Determining the achieved values. Global alignment of initial ClinCheck model (orange) over the
posttreatment model (white). B, Superimposition of a segmented tooth from the initial ClinCheck model
(green) over the unsegmented posttreatment model (white) using a best-t surface registration.
Haouili et al 3
American Journal of Orthodontics and Dentofacial Orthopedics -2020 Vol -Issue -
the maxillary central incisor (56%) was signicantly
more accurate than intrusion (33%), and intrusion of
the mandibular second molar (51%) was signicantly
more accurate than extrusion (37%).
With regards to accuracy between arches, the distal
crown tip of the maxillary second molar (63%) was
signicantly more accurate than the mandibular
second molar (50%), and the buccal crown tip of the
mandibular second premolar (70%) was signicantly
more accurate than the maxillary second premolar
(61%). Overall, there was little difference in accuracy
between maxillary and mandibular teeth, which was
also found in the 2009 study.
1
The modied-Discrepancy Index score for the
randomly chosen sample was 17. When the posttreat-
ment intraoral scans were 3-dimensional-printed and
graded using the ABO cast evaluation system, 74% (14
of 19) achieved a passing score.
DISCUSSION
In the 2009 study by Kravitz et al
1
evaluating the
efcacy of anterior tooth movement with Invisalign,
the authors reported an overall mean accuracy of 41%.
The most accurate tooth movement was lingual
constriction, whereas the least accurate tooth move-
ments were incisor extrusion, followed by a mandibular
canine rotation. Our current study aimed to determine
whether the accuracy of Invisalign had improved with
newer technology and greater operator experience.
In our study, the mean accuracy of Invisalign for all
tooth movements was 50%. This nding is a notable
increase from the 2009 study,
1
but even more remark-
able considering that the posterior teeth were included,
and the tooth movements were more extensive. Despite
its improved accuracy, the strengths and weaknesses of
tooth movement with Invisalign remained relatively
the same.
The most accurate tooth movement was the buccal-
lingual crown tip (56%). These results are logical, given
that the aligner material primarily exes in a buccal-
lingual direction. Furthermore, aligners move teeth by
pushing, and the buccal and lingual aspects of the crown
provide the largest surface area to push. The improved
accuracy in incisor buccal crown tip could be attributed
to the more exible SmartForce aligner material, as well
as the power ridges, which were used in 71% of the sam-
ple. However, the second molars struggled with buccal
crown tip (36%), likely because of poor aligner grip
around the shorter terminal crown and the decreased
forces on the terminal tooth within the aligner.
The least accurate tooth movement was rotation
(46%), and this movement was particularly challenging
for canines, premolars, and molars. Similar ndings
were observed by Simon et al
27
and Charalampakis
et al.
29
Although the SmartTrack features automatically
placed optimized attachments for rotational movements
greater than 5, rounded teeth still struggled to grip the
aligners. Despite the relatively low accuracy of rotation,
its improvement for the maxillary incisors and canines is
encouraging.
Interestingly, the direction of rotation inuenced the
accuracy of the maxillary canine. Distal rotation (37%)
was signicantly less accurate than mesial rotation
(52%). In 2009, Kravitz et al
25
reported that IPR
improved the accuracy of canine rotation and theorized
that interproximal contact or binding was a major deter-
minant for nontracking. Our results appear to provide
some support. The larger distal contact area and the
mechanical challenges of providing IPR on the distal
aspect of the maxillary canine could explain the lower
accuracy.
One of the most promising ndings of this study was
the improvement in the accuracy of maxillary incisor
extrusion. In the 2009 study,
1
extrusive movement of
the incisors had the lowest accuracy. The authors
advocated combining extrusion with more predictable
movements such as lingual crown tip, which they termed
relative extrusion (resultant extrusion), in contrast to
Table II. Percentage of accuracy of tooth movements
Tooth
Mesial Distal Buccal Lingual Intrusion Extrusion Mesial rotation Distal rotation
Max Min Max Min Max Min Max Min Max Min Max Min Max Min Max Min
Central incisor 57.5 47.8 49.8 45.5 54.2 52.8 57.4 64.0 33.4 33.9 56.4*44.5 61.1 51.3 54.9 43.1
Lateral incisor 47.3 38.5 47.3 51.5 69.9 61.4 54.4 57.4 44.6 36.7 53.7 47.1 54.6 52.6 48.7 41.8
Canine 52.5 53.7 43.8 47.5 58.8 67.9 57.6 54.8 53.3 51.3 42.2 50.6 51.5*55.2 37.2 45.8
First premolar 43.3 45.4 57.1 57.2 66.3 61.1 56.5 57.9 48.4 63.1 51.3 44.5 50.9 43.1 50.0 47.9
Second premolar 64.7 53.6 54.2 62.5 60.5 69.7
y
51.8 51.8 45.5 56.1 38.3 52.5 39.2 44.8 44.7 49.8
First molar 47.8 52.6 58.4 59.2 58.3 53.6 47.2 48.0 35.1 41.2 37.6 45.2 42.9 27.8 43.2 35.4
Second molar 55.4 50.2 62.9
y
50.4 34.8 36.4 61.3*46.0 50.3 51.3*41.5 37.1 42.5 40.4 40.7 33.6
Total 52.7 48.8 53.4 53.4 57.6 57.6 55.2 54.3 44.4 47.7 45.9 45.9 49.0 45.0 45.6 42.5
*Statistically signicant difference in directionality;
y
Statistically signicant difference between arches.
4Haouili et al
-2020 Vol -Issue -American Journal of Orthodontics and Dentofacial Orthopedics
true extrusion in a vertical plane. A plausible explanation
for the improvement in our study may be from the use of
optimized extrusion attachments. Extrusion of the
maxillary incisors (55%) had the highest accuracy,
whereas extrusion of the maxillary and mandibular mo-
lars (40%) had the lowest accuracy.
By contrast, incisor intrusion remained a challenge
and did not improve from the 2009 study, even with
the G5 enhancements. The low accuracy of mandibular
incisor intrusion (35%) was similar to the results
reported by Gr
unheid et al
28
and Charalampakis
et al.
29
One explanation for the lower accuracy of
mandibular incisor intrusion may be the lack of posterior
anchorage. According to the SmartForce protocol,
anchorage (or aligner lift off) is near the last consider-
ation for the software. In contrast, the accuracy of
second molar intrusion (51%) was relatively high.
The higher accuracy of incisor extrusion and molar
intrusion and low accuracy of incisor intrusion and
molar extrusion suggests that Invisalign is more effective
in bite closure, rather than bite opening. Khosravi et al
31
reported that only 1.5 mm of overbite improvement
could be expected with Invisalign, which is half of the
amount typically achieved with xed appliances.
Perhaps deepbite malocclusions that require true
mandibular intrusion and posterior extrusion would
benet from hybrid mechanicsof maxillary Invisalign
with mandibular xed appliances. Nonetheless, when
the results of this study were evaluated to determine
their clinical signicance, 74% of randomly chosen
patients had passing ABO scores. This relatively high
percentage is encouraging when interpreting the results
of the study. In the 2009 study,
1
pretreatment overjet
signicantly affected the accuracy of the labial-lingual
movement. Our results showed a higher accuracy of
individual tooth movement despite treating cases of
greater complexity. Undoubtedly, the Invisalign system
is improving.
The primary limitation with any study using
predicted digital models is that ClinCheck is merely a
graphic depiction of force systems, rather than a predic-
tor of nal tooth position.
32
In other words, the
prescribed nal tooth position on ClinCheck may not
be the desired nal tooth position. For example,
mandibular incisor intrusion achieved a relatively low
accuracy, but likely received the greatest amount of
overengineering. Therefore, a 50% accuracy of predicted
tooth movement does not mean 50% effective from a
clinical perspective.
Other notable limitations include those that rely on
patient compliance, such as wearing the aligners as
prescribed and using intraoral elastics as instructed,
not to mention the inaccuracies associated with patient
self-reporting. There are also doctor-associated limita-
tions because of inaccuracies and imprecision when
placing attachments and performing IPR.
Finally, there is tremendous variation and general
disagreement on attachment design, tooth-movement
sequencing, and extent of overengineering programmed
into ClinCheck plans among orthodontists. This study
relies on clinical decisions by one orthodontic provider.
CONCLUSIONS
1. The overall mean accuracy of Invisalign was 50%.
Although this was a marked improvement from
the 2009 study, the strengths and weaknesses of
tooth movement with Invisalign remained relatively
the same.
2. The highest accuracy was achieved with a buccal-
lingual crown tip (56%).
3. The lowest accuracy occurred with rotation (46%),
and this movement was difcult for the canines,
premolars, and molars.
4. Maxillary incisor extrusion improved, but incisor
intrusion remained a challenge.
5. The percent accuracy determined by a best-t
analysis on a predicted ClinCheck digital model
may underestimate the product's overall clinical
efcacy.
6. As such, the actual number of 50% accuracy may be
less important than the conrmation that the Invis-
align appliance is improving but still struggles with
specic types of tooth movements.
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-2020 Vol -Issue -American Journal of Orthodontics and Dentofacial Orthopedics
... Similarly, in certain studies [8], [10], [11], participants' ratings improved following treatment. While several research [12], [13] claimed that clear aligners made rotation movement harder, this was not the case. ...
... There was a substantial difference between pre and post records when it came to the ABO scores of buccolingual inclination. This was in agreement with certain research [8], [13], but not with others [11], [12], which claimed that there was no improvement in buccolingual inclination ABO scores. ...
... In terms of total ABO scores, the current study found that following treatment with clear aligners, there was a substantial improvement compared to before treatment. Some people agreed with this previous studies [8], [10], [11], [13]. ...
Article
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Keywords: ABSTRACT Aligners, American board of orthodontics grading system, non-extraction orthodontic cases. As the demand and interest toward the clear aligner system continue to grow, questions regarding the efficacy of the system remain. Nowadays, published data include little clinical research on the effectiveness and efficacy of clear aligners. Previous literature primarily included case reports or descriptions of the product, making it difficult to objectively characterize the efficacy of clear aligner systems. This study aimed to assess the treatment outcomes of clear aligners in non-extraction orthodontic cases. This study was carried out upon 7 patients indicated for non-extraction orthodontic treatment with an age ranging from 20 to 40 years old, selected from the outpatient orthodontic clinic, Faculty of Dentistry, Suez Canal University. The assessment was made by using the American board of orthodontics grading system for measuring alignment/rotation, marginal ridges, bucco-lingual inclination, overjet, occlusal contacts, occlusal relationships, interproximal contacts and root angulation using the ABO measuring gauge, cast and panorama. The resulted data revealed that there was a statistically significant difference between before and after treatment values of alignment/rotation, buccolingual inclination, overjet, interproximal contacts and root angulation of teeth, while there was no significant difference between before and after treatment values in marginal ridges, occlusal contacts and occlusal relationship. Based on the results of this study, it was concluded that: The use of clear aligners for treatment of class I non-extraction orthodontic cases was efficient and had clinically accepted treatment outcomes as mostly, all the measured variables improved after treatment according to the ABO assessment. This work is licensed under a Creative Commons Attribution Non-Commercial 4.0 International License.
... In general, both clear aligners and braces effectively treat certain malocclusions. 78 The efficacy and accuracy of tooth movement (difference between predicted and achieved posttreatment outcome) with Invisalign have improved since 2009, from an overall mean accuracy of 41% 63 to 50% in 2020, 79 mainly because of newer technology such as the more flexible SmartForce aligner material, programmed power ridges, overcorrections, and improved operator experience. 79 Although the data indicate that the effectiveness and predictability of individual tooth movements of varying patient complexity with the Invisalign system have improved, 79 doubts remain regarding the accuracy and validity of the data. ...
... 78 The efficacy and accuracy of tooth movement (difference between predicted and achieved posttreatment outcome) with Invisalign have improved since 2009, from an overall mean accuracy of 41% 63 to 50% in 2020, 79 mainly because of newer technology such as the more flexible SmartForce aligner material, programmed power ridges, overcorrections, and improved operator experience. 79 Although the data indicate that the effectiveness and predictability of individual tooth movements of varying patient complexity with the Invisalign system have improved, 79 doubts remain regarding the accuracy and validity of the data. Most studies are based on Invisalign and have several limitations, including (1) methodology: accuracy of predicted tooth movement is not the same as clinical effectiveness, (2) patient compliance and inaccurate reporting of wearing aligners and prescribed intraoral elastic wear, (3) clinician-associated inaccuracies during impression taking, placing composite attachments and performing IPR, (4) aligner system variations, and (5) variability and standardization among clinicians on virtual programming of attachment design, sequencing tooth movement, and overcorrections built into ClinCheck plans. ...
... 78 The efficacy and accuracy of tooth movement (difference between predicted and achieved posttreatment outcome) with Invisalign have improved since 2009, from an overall mean accuracy of 41% 63 to 50% in 2020, 79 mainly because of newer technology such as the more flexible SmartForce aligner material, programmed power ridges, overcorrections, and improved operator experience. 79 Although the data indicate that the effectiveness and predictability of individual tooth movements of varying patient complexity with the Invisalign system have improved, 79 doubts remain regarding the accuracy and validity of the data. Most studies are based on Invisalign and have several limitations, including (1) methodology: accuracy of predicted tooth movement is not the same as clinical effectiveness, (2) patient compliance and inaccurate reporting of wearing aligners and prescribed intraoral elastic wear, (3) clinician-associated inaccuracies during impression taking, placing composite attachments and performing IPR, (4) aligner system variations, and (5) variability and standardization among clinicians on virtual programming of attachment design, sequencing tooth movement, and overcorrections built into ClinCheck plans. ...
Article
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Aggressive promotion by stakeholders and increased public awareness for alternative esthetic orthodontic treatment options have popularized the demand for clear aligner therapy (CAT). Patient demand is driven by appearance, comfort, convenience, and less complicated oral hygiene control. CAT is an important treatment alternative to conventional fixed appliances and a viable alternative for mild-to-moderate malocclusions in nonextraction, nongrowing patients. CAT is less effective and predictable than conventional fixed appliances for complex orthodontic tooth movements and malocclusions. However, the introduction of improved software, aligner materials, and auxiliary devices has enhanced the scope of malocclusions that may be treated. Managing complex tooth movements during CAT requires auxiliaries, overcorrections, and refinements to improve the predictability, effectiveness, and stability of treatment outcomes. The main predictors of treatment outcome are proper patient selection, patient complexity, treatment planning, compliance, clinician experience, and regular monitoring. Currently, there are no evidence-based clinical guidelines for CAT. Aligner technology and therapy are continuously evolving and improving. This literature review aimed to assess and summarize current scientific knowledge and evidence relating to CAT.
... In order to give more clinical relevance to our results, a threshold of 1.0 • can be considered in evaluating the performance index [29]. Although, no significant differences were found on average between Absolute Prescription and Absolute Achieved movement for all the movements, the performance index and the FOPE showed relevant results. ...
... It should be noted, however, that even if some teeth are not moved in the set-up, the anchorage stress can determine a minimal shift on them influencing the reliability of those dental units used as reference structures to perform superimpositions [35]. Finally, also the accuracy of Invisalign system was assessed on 38 patients at the end of treatment, and an average precision of 50% of the predicted movement was achieved [29]. ...
Article
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Background: Clear aligners treatment (CAT) is a common solution in orthodontics to treat both simple and complex malocclusions. This study aimed to evaluate the predictability of CAT, comparing the virtually planned and the achieved tooth movement at the end of stage 15, which is often the time of first refinement. Methods: Seventeen patients (mean age: 28.3 years) were enrolled in the study. Torque, tip and rotation were analyzed in 238 maxillary teeth on digital models at Pre-treatment (T0), at the end of stage 15 (T15) and at virtually planned stage 15 (T15i). Prescription, Achieved movement and performance values were calculated to compare the virtually planned and the clinical tooth position. Data were analyzed by means of Student's t test with a level of significance set at p < 0.05. Results: The largest iper-performance was the torque correction of the second molars (+2.3° ± 3.1°), the greatest under-performance was the tip correction of the first molars (-2.3° ± 3.3°), while rotation corrections of all the teeth showed more accurate performance. No significant differences were found between mean Prescription and mean Achieved movement for all the assessed movements (p < 0.05). Conclusions: An accurate evaluation of CAT after the 15th aligner is fundamental in order to individuate the movements that are not matching the digital set-up.
... capabilities and limitations of appliances and mechanics employed therein [1][2][3][4][5]. ...
... Quantifying the amount of orthodontic tooth movement in digital orthodontics is performed by registration software packages, which are dependent on the registration algorithm used [10,30]. Scholarly literature lacks studies testing accuracy of software packages to compare treatment effects and efficacy [5,8,10,[19][20][21][31][32][33][34][35]. The present study calculated the amount of tooth movement in the three linear directions for the entire maxillary and mandibular dentitions including second permanent molars. ...
Article
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Background: To evaluate the accuracy of three different 3D digital model registration software packages for linear tooth movement measurements, with reference to a 3D digital virtual setup (DS). Methods: Twenty maxillary and mandibular pre-treatment scans of patients undergoing clear aligner therapy were used. Digital Setups were generated from pre-treatment scans using OrthoAnalyzer software. Both the pretreatment digital scans (T1) and Digital Setups (T2) were converted to STL files to be imported to the three studied software packages: Geomagic, OrthoAnalyzer and Compare. Linear changes in tooth positions were calculated for all the registered pairs. Results: The change in tooth position was compared between the calculated tooth movement using each of the registration software packages versus the actual generated tooth movement from the Digital Setups. Continuous data was expressed as mean and standard deviation. Intraclass Correlation Coefficients for agreements between Digital Simulation and each software was used. Intra and Inter-examiner reliabilities were also assessed using Intraclass Correlation Coefficients. Significance of the obtained results was expressed at p ≤ 0.01. Geomagic software showed agreements > 0.90 for maxillary linear tooth movements and between 0.75 and 0.90 for mandibular measurements. OrthoAnalyzer software showed agreements between 0.50 and < 0.75 for maxillary and mandibular measurements. Compare software showed agreements > 0.90 for maxillary and mandibular linear tooth movements, indicating the best consistency. Conclusions: Compare and Geomagic software packages consistently showed maximum accuracy in measuring the amount of tooth movement in the maxillary arch compared to the reference standard. Compare software showed the highest agreements in the mandibular arch. None of the three studied software packages showed poor agreement with the Digital Setup across all tooth movement measurements. Buccolingual tooth movements showed the highest agreements amongst linear measurements.
... What results from the most recent systematic reviews of the efficacy of tooth movement with Invisalign ® , among which the prospective follow-up study by Haouil et al. [17], is that maximum efficiency is obtained in V/L tipping, while the lowest involves the rotation of the canines and premolars. However, though these findings are better than the data obtained in the previous part of To our knowledge, our results may overcome the data already available in the literature, despite the fact strengths and weaknesses of clear aligners proved to be the same. ...
Article
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Background Since their introduction in orthodontics, clear aligners have been appreciated by patients, including adults, for their comfort and low aesthetic impact. Despite the enormous mobilization of financial resources all over the world aimed at producing new product lines, few clinical studies or high-quality evidence have been produced regarding the real effectiveness of such treatment. Given the few limited kinds of research on the subject, this study aims to produce and critically evaluate other data, to establish the concrete reliability of clear aligners in orthodontic therapy. Results Significant sample sizes were obtained for intrusion, vestibulo/lingual (V/L) crown tipping, and rotation. The overall accuracy for rotation resulted in 86%, ranging from 96% for maxillary central incisors to 70.4% for mandibular first premolars. The intrusion was registered only for anterior teeth; mean predictability was 92%, with the worst result being 86.7% for mandibular canines and the best being 98% for mandibular central incisors. V/L tipping was the most accurate movement: 93.1% of the prescribed movement was completed. Maxillary central incisors showed the lowest accuracy (80.7%), while mandibular central incisors were the highest (97.5%). Conclusions The present study provided reassuring data in support of the accuracy of the Invisalign ® system. Vestibulo/lingual tipping was the most predictable movement, while rotation of canines, premolars, and lateral incisors were the least predictable. Intrusion resulted highly predictable up to 2 mm. When careful treatment planning follows a correct diagnosis, together with the use of auxiliary features and refinements, the planned results can be achieved in a clinically successful way. Authors believe that there is a major need for greater samples to overcome bias related to variables if we want to answer the unsolved questions, such as the predictability of severe malocclusions treatment.
Chapter
The biggest difference between the treatment with fixed appliances and treatment with aligners is that most aligner treatments are planned from the first to the last movement in all possible detail. As the demand and need for aesthetic orthodontic treatment alternatives have grown, aligners have secured a firm place in the orthodontic repertoire. Invisalign ® represents the force‐driven approach, whereas the Orthocaps ® system is an effort to utilise the displacement‐driven system. The Invisalign ® system in 1997 claimed that when planned correctly it could achieve desirable treatment results in relation to a majority of malocclusions. A representative of the displacement‐driven system is the Orthocaps ® aligner marketed as the ‘TwinAligner ® ’. Accepting that aligner–tooth interface is mechanically less efficient in transmitting orthodontic forces than systems based on brackets and wires is being addressed by Orthocaps ® in several ways.
Article
Introduction This study aimed to compare the designed and achieved mesiodistal angulation of maxillary canines and posterior teeth (MCPT) for first premolar extraction with clear aligner treatment and identify the main influencing factors for preventing MCPT tipping toward the extraction space. Methods A total of 21 adults with first premolar extraction were recruited. The designed and achieved tooth movement of MCPT was measured by superimposing their respective pretreatment and posttreatment cone-beam computed tomography images and compared with the designed tooth movement in ClinCheck using the paired t test and scatter plot analysis. Influencing factors, including dental arch length change, canine distalization, and initial mesiodistal angulation, were analyzed using the linear mixed-effect model. Results Designed distal crown tipping (second premolar, 10.73 ± 3.22°; first molar, 9.83 ± 3.60°; second molar, 7.18 ± 2.36°) significantly increased the distal inclination of the second premolar (2.50° ± 5.15°; P <0.001), first molar (1.07° ± 4.14°; P <0.001), and second (0.70° ± 3.78°; P <0.001). Furthermore, mesial tipping (8.59° ± 6.03°; P <0.001) achieved appropriate distal crown tipping of canines (−6.43° ± 5.04°; P <0.001). The implemented preliminary formulas showed that shortening of the dental arch length, the distance of canine distalization, and initial mesiodistal angulation were closely related to the antitipping design. Conclusions Designed distal crown tipping of posterior teeth and mesial crown tipping of canines might prevent unwanted crown tipping toward the extraction space during space closure. The proposed preliminary formula could guide antitipping designs in clear aligner treatment.
Poster
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AIM: The Aim of this study was to evaluate the overall efficacy of tooth movement with Invisalign ® , by comparing the amount of predicted tooth movement of the initial ClinCheck ® (Align Technology, Santa Clara, CA) to the actual tooth movement occurred after treatment. MATERIALS AND METHODS: Seventeen patients were treated with Invisalign ® for the movement of the upper and lower anterior teeth. At the beginning of treatment and before the first refinement stage, polyvinylsiloxane impressions were acquired and were sent to Align Technology in order to produce 3D digital casts in STL file format. All STL files were extracted from the ClinCheck ® Software (T1: Initial situation, Tp: ClinCheck ® Prediction Outcome, To: Actual Treatment Outcome). Patients were instructed to wear the aligners 22hrs/7days a week and change them every 2 weeks. The Invisalign ® compliance indicator was included. The T1 digital casts were superimposed over the Tp and the To digital casts using stable structures as reference (posterior teeth that have not moved during treatment). The Tp digital casts were compared with the To digital casts. The Geomagic Control X (3D Systems) software was used for the superimposition and the measurement of anterior tooth displacement between the digital casts. The one-sample t-test was used to compare the Tp vs. To after testing the normality assumption (test value was set to 0). RESULTS: The mean difference for the casts’ comparison of T1-Tp was 1.11 (±0.48), for the T1-To was 1.06 (±0.57) and for Tp-To was 0.51 (±0.17). The mean overall accuracy for the treatment was 83.21% (±14.21). Statistically significant deviation was fount between ideal and actual position (mean deviation=0.51, 95% Confidence Interval (0.45, 0.57), p<0.001). CONCLUSIONS: Our study suggests that the level of accuracy of the prediction outcome has been improved for low severity cases treated with Inisalign ® , although there are still some limitations to achieve the ideal virtual ClinCheck ® predicted outcome.
Article
Objective: The purpose of this study was to examine the effectiveness and mechanism of clear aligner therapy for the correction of anterior open bite in adult nonextraction cases. Methods: Sixty-nine adult patients with anterior open bite were enrolled and classified into Angle's Class I, II, and III groups. Fifty patients presented with skeletal open bite (mandibular plane angle [MPA] ≥ 38°), whereas 19 presented with dental open bite. Fifteen cephalometric landmarks were identified before (T1) and after (T2) treatment. The magnitudes of planned and actual movements of the incisors and molars were calculated. Results: Positive overbite was achieved in 94% patients, with a mean final overbite of 1.1 ± 0.8 mm. The mean change in overbite was 3.3 ± 1.4 mm. With clear aligners alone, 0.36 ± 0.58 mm of maxillary molar intrusion was achieved. Compared with the Class I group, the Class II group showed greater maxillary molar intrusion and MPA reduction. The Class III group showed greater mandibular incisor extrusion with no significant vertical skeletal changes. Conclusions: Clear aligners can be effective in controlling the vertical dimension and correcting mild to moderate anterior open bite in adult nonextraction cases. The treatment mechanism for Class III patients significantly differed from that for Class I and Class II patients. Maxillary incisor extrusion in patients with dental open bite and MPA reduction with mandibular incisor extrusion in patients with skeletal open bite are the most significant contributing factors for open bite closure.
Article
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Objective: To evaluate the accuracy of Invisalign technology in achieving predicted tooth positions with respect to tooth type and direction of tooth movement. Materials and methods: The posttreatment models of 30 patients who had nonextraction Invisalign treatment were digitally superimposed on their corresponding virtual treatment plan models using best-fit surface-based registration. The differences between actual treatment outcome and predicted outcome were computed and tested for statistical significance for each tooth type in mesial-distal, facial-lingual, and occlusal-gingival directions, as well as for tip, torque, and rotation. Differences larger than 0.5 mm for linear measurements and 2° for angular measurements were considered clinically relevant. Results: Statistically significant differences (P < .05) between predicted and achieved tooth positions were found for all teeth except maxillary lateral incisors, canines, and first premolars. In general, anterior teeth were positioned more occlusally than predicted, rotation of rounded teeth was incomplete, and movement of posterior teeth in all dimensions was not fully achieved. However, except for excess posttreatment facial crown torque of maxillary second molars, these differences were not large enough to be clinically relevant. Conclusions: Although Invisalign is generally able to achieve predicted tooth positions with high accuracy in nonextraction cases, some of the actual outcomes may differ from the predicted outcomes. Knowledge of dimensions in which the final tooth position is less consistent with the predicted position enables clinicians to build necessary compensations into the virtual treatment plan.
Article
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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.
Article
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Objective: Based on our previous pilot study, the objective of this extended study was to compare (a) casts to their corresponding digital ClinCheck® models at baseline and (b) the tooth movement achieved at the end of aligner therapy (Invisalign®) to the predicted movement in the anterior region. Materials and methods: Pre- and post-treatment casts as well as initial and final ClinChecks® models of 50 patients (15-63 years of age) were analyzed. All patients were treated with Invisalign® (Align Technology, Santa Clara, CA, USA). Evaluated parameters were: upper/lower anterior arch length and intercanine distance, overjet, overbite, dental midline shift, and the irregularity index according to Little. The comparison achieved/predicted tooth movement was tested for equivalence [adjusted 98.57% confidence interval (- 1.00; + 1.00)]. Results: Before treatment the anterior crowding, according to Little, was on average 5.39 mm (minimum 1.50 mm, maximum 14.50 mm) in the upper dentition and 5.96 mm (minimum 2.00 mm, maximum 11.50 mm) in the lower dentition. After treatment the values were reduced to 1.57 mm (minimum 0 mm, maximum 4.5 mm) in the maxilla and 0.82 mm (minimum 0 mm, maximum 2.50 mm) in the mandible. We found slight deviations between pretreatment casts and initialClinCheck® ranging on average from -0.08 mm (SD ± 0.29) for the overjet and up to -0.28 mm (SD ± 0.46) for the upper anterior arch length. The difference between achieved/predicted tooth movements ranged on average from 0.01 mm (SD ± 0.48) for the lower anterior arch length, up to 0.7 mm (SD ± 0.87) for the overbite. All parameters were significantly equivalent except for the overbite (-1.02; -0.39). Conclusion: Performed with aligners (Invisalign®), the resolvement of the partly severe anterior crowding was successfully accomplished. Resolving lower anterior crowding by protrusion of the anterior teeth (i.e., enlargement of the anterior arch length) seems well predictable. The initial ClinCheck® models provided high accuracy compared to the initial casts. The achieved tooth movement was in concordance with the predicted movement for all parameters, except for the overbite.
Article
Introduction: The purpose of this study was to determine the accuracy of specific tooth movements with Invisalign (Align Technology, Santa Clara, Calif). Methods: The study sample included 20 Class I adult patients treated with Invisalign; they completed their first series of aligners and had to have a "refinement" series. Initial and predicted models were obtained from the initial ClinCheck (Align Technology). The starting point of the refinement ClinCheck was used to create the achieved models. Predicted and achieved models were superimposed over the initial ones on posterior teeth using the 3-dimensional Image Analysis open-source software Slicer CMF. Three hundred ninety-eight teeth were measured for vertical, horizontal, and rotational movements, and transverse widths were measured. The amount of predicted tooth movement was compared with the achieved amount for each movement. Results: Horizontal movements of all incisors seemed to be accurate, with small (0.20-0.25 mm) or insignificant differences between predicted and achieved amounts. Vertical movements and particularly intrusions of maxillary central incisors were found to be less accurate, with a median difference of 1.5 mm (P <0.001). All achieved rotations were significantly smaller than those predicted, with the maxillary canines exhibiting the greatest difference of 3.05° (P <0.001). Conclusions: The most inaccurate movements identified in this study were intrusion of the incisors and rotation of the canines.
Article
Introduction: Most of the published literature on the management of overbite with the Invisalign appliance (Align Technology, Santa Clara, Calif) consists of case reports and case series. Methods: In this retrospective study of 120 patients, we sought to assess the nature of overbite changes with the Invisalign appliance. Records were collected from 3 practitioners, all experienced with the Invisalign technique. The patients were consecutively treated adults (>18 years old) who underwent orthodontic treatment only with the Invisalign appliance. Patients with major transverse or anteroposterior changes or extraction treatment plans were excluded. The study sample included 68 patients with normal overbites, 40 with deepbites, and 12 with open bites. Their median age was 33 years, and 70% of the patients were women. Results: Cephalometric analyses indicated that the deepbite patients had a median overbite opening of 1.5 mm, whereas the open bite patients had a median deepening of 1.5 mm. The median change for the normal overbite patients was 0.3 mm. Changes in incisor position were responsible for most of the improvements in the deepbite and open bite groups. Minimal changes in molar vertical position and mandibular plane angle were noted. Conclusions: The Invisalign appliance appears to manage the vertical dimension relatively well, and the primary mechanism is via incisor movements.
Article
Recent developments in software technology have made it possible to create a virtual three-dimensional (3D) model of the dental arches from digitally scanned impressions of a patient's dentition. This model may then be manipulated with software to produce stages of tooth movement from the initial malocclusion to the final desired occlusion. A stereolithographic model is made for each stage of tooth movement which is the basis for construction of a series of clear, thin, overlay appliances. These appliances are worn full time by the patient to move the teeth according to the programmed stages of movement. Malocclusions involving mild to moderate crowding and space closure have been proven to be successfully treated with this appliance. The present study shows orthodontic treatment of patients with more complex orthodontic problems, requiring dental expansion, Class II and Class III correction, extraction treatment and correction of overbite. Experience with this appliance, thus far, has demonstrated excellent patient compliance with less discomfort, and improved esthetics and oral hygiene, when compared with fixed orthodontic appliances. Orthodontic treatment with this appliance is a potentially useful alternative approach to fixed appliances for treatment of a variety of malocclusions in patients with fully erupted permanent teeth.
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.