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Since their inception, clear aligners have undergone a multitude of advancements that aimed to make orthodontic treatment less conspicuous. Used for moving teeth for alignment and creating healthy and beautiful smiles, like many other orthodontic appliances, clear aligners have proven to be a much more comfortable and esthetic alternative. The treatment success relies on clinicians’ knowledge and experience with the aligners, proper case selection, and the patients’ adherence to the treatment protocols. The area of exploration of this review is limited to providing an overview of the clear aligner treatment including benefits and limitations, principles and biomechanics of clear aligner treatment, materials used, methods of fabrication, and wear time. Umpteen manufacturers have emerged accounting for the increased demand by patients seeking orthodontic treatment, with the number increasing every year. It is outside the purview of this article to elucidate and compare the array of clear aligner systems available today.
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38 International Journal of Dental and Medical Specialty Vol 7 ● Issue 1 ● Jan-Jun 2020
Aligners: e Science of Clear Orthodontics
Sunegha Kundal1, Tulika Shokeen2
1Specialist Orthodontist, Private Practitioner, Jammu and Kashmir, India, 2Specialist Orthodontist, Private
Practitioner, Delhi, India
Since their inception, clear aligners have undergone multitude of advancements that aimed to make the orthodontic
treatment less conspicuous. Used for moving teeth for alignment and creating healthy and beautiful smiles, like many
other orthodontic appliances, clear aligners have proven to be a much more comfortable and esthetic alternative. The
treatment success relies on clinicians’ knowledge and experience with the aligners, proper case selection, and the patients’
adherence to the treatment protocols. The area of exploration of this review is limited to providing an overview of the clear
aligner treatment including benets and limitations, principles and biomechanics of clear aligner treatment, materials used,
methods of fabrication, and wear time. Umpteen manufacturers have emerged accounting for the increased demand by
patients seeking orthodontic treatment, with the number increasing every year. It is outside the purview of this article to
elucidate and compare the array of clear aligner systems available today.
Key words: Esthetics, clear aligners, orthodontics, tooth movement
Orthodontic treatment has long been synonymous to a
mouth full of “unattractive” wires. The stigma extended
beyond outer appearance, with people perceiving those with
metal braces to have a lower intellect.[1] Introduction of clear
aligners thus came as a respite to the orthodontic patient, for
their esthetic superiority made them more attractive to metal
and ceramic brackets.[2] These are the active clear plastic
trays fitting snugly onto the teeth, each worn for 2 weeks
on an average, and changed sequentially to accomplish the
incorporated tooth movements. From being used for mild
malocclusion cases at the outset to treating vast variety of
cases contemporarily, from minimal crowding to bicuspid
extractions, clear aligners have come a long way and still
continue to evolve.
Contrary to popular belief, clear aligners are not a new
find. The chronology leading up to their present-day use
dates to 1945, when Dr. Harold D. Kesling first advocated
a rubber appliance for moving teeth.[3] In 1964, Nahoum
fabricated the dental contour appliance in what was
to be the first thermoformed plastic sheet for moving
teeth.[4] Sheridan modified the same in 1993, calling it
the Essix Appliance.[5] However, fabricating the appliance
was a laborious process requiring impression-making at
every successive appointment. The solution arrived in
the form of a clear aligner system created digitally by two
Stanford graduates – Zia Chishti and Kelsey Wirth. Called
Invisalign®, it was launched in 1997 by Align Technology©
(Santa Clara, CA) and is credited with bringing a comfortable
alternative to braces to mainstream orthodontics. In 2005,
a competitor emerged in the form of OrthoClear® – a
clear aligner system developed independently by one of the
original founders Zia Chishti. However, it was withdrawn a
year later due to lawsuits alleging patent infringement. Many
practicing clear aligner users suffered as a result, one of whom
was Dr. Willis Pumphrey whose 400 patients were stranded
mid-treatment. He responded by developing ClearCorrect
Address for Correspondence:
Dr. Sunegha Kundal, Specialist Orthodontist, Private Practitioner, Jammu - 180011, Jammu and Kashmir, India. Phone: +91-
Submission: 27 May 2020; Revision: 16 June 2020; Acceptance: 28 June 2020
Review Article
Access this article online
DOI: 10.30954/IJDMS.1.2020.9
Kundal and Shokeen: Clear aligners
International Journal of Dental and Medical Specialty Vol 7 ● Issue 1 ● Jan-Jun 2020 39
(ClearCorrect, Round Rock, TX, USA), an Invisalign®
alternative that quickly gained popularity. An onslaught of
clear aligner systems has since followed that are being used
to correct minor to complex malocclusions.[6]
i. Esthetics: A transparent, clear design that is discreet.
ii. Comfort: Free from brackets or wires and resultant cuts
and ulcerations.
iii. Improved oral hygiene and periodontal health:
Removable nature allows proper brushing and flossing.
iv. No food restrictions: Patients are free to eat or drink
anything during clear aligner therapy (CAT).
v. Predictable treatment time: Digital planning ensures a
precise estimation of treatment time.
vi. Decreased dental office visits: Patients themselves change
their subsequent aligners, requiring fewer office visits.
vii. Minimal emergencies: Significantly reduced emergency
appointments with CAT as compared to fixed orthodontic
viii. Possible to include teeth with structural anomalies and
difficult-to-bond surfaces.
i. Dependency on patient compliance: A wear time of 22
h/day is mandatory for therapy to be effective.
ii. Limited extent of tooth movements by aligners alone:
For complex movements, auxiliaries are required as an
adjunct to aligners.
iii. Higher cost.
iv. Initial slurring of speech: Subsides subsequently after
2–3 days of wear.
v. Breakages: While wearing or removing if the patient
applies excessive force.
vi. Chances of losing the aligners: Removable nature makes
aligners prone to being misplaced.
vii. Inconvenience: Removing aligners every time one eats
or drinks can be a burden.
viii. Manufacturing defects: Results in ill-fitting aligners.
CAT works on two basic principles:[7]
1. Creating space: Through arch expansion, tooth
extraction, or interproximal reduction (IPR).
2. Force/pressure application: Through small incremental
movements incorporated in aligner itself and with
auxiliaries (attachments, dimples, elastics, or digital
power chains). The amount of pressure required for
moving a tooth depends on factors such as tooth shape,
tooth size, type of movement, and periodontal condition.
The mechanism of tooth movement with clear aligners is
centered around two systems:[8,9]
1. Displacement-driven system: Controls tipping and minor
rotations. Aligners are fabricated as per next staged
position; the tooth continues to move till the aligner
becomes passive. No root movement elicited.
2. Force-driven system: The software determines the type
of movement required for an individual tooth, the
mechanical principles needed to achieve that movement,
and aligner shape. Pressure points and attachments are
incorporated into aligners that apply the forces required
for planned movements.
Clear aligner materials have evolved from a single layered
or monophasic plastic to the 2nd generation polyurethane
material, to the currently used 3rd generation multilayered
polyurethane-like material that comprises of hard and
soft layers. While the soft layer imparts the property of
elastic deformation allowing smooth seating of the
aligner, the hard layer ensures strength and durability.[10]
Polyethylene terephthalate glycol modified (PET-G) remains
the commonly used material. Other materials include
polypropylene, polycarbonate, thermoplastic polyurethanes,
and ethylene vinyl acetate.[11] Table 1 enlists popular clear
aligner brands and the material used for aligner fabrication.[12]
Table 1: Clear aligner brands and the material used by them for
aligner fabrication
Code Thickness Product
Manufacture Component
EVA 1.0 mm Bioplast Scheu-Dental,
vinyl acetate
PE 1.0 mm Copyplast Scheu-Dental,
PETG 1.0 mm Duran Scheu-Dental,
PP 0.8 mm Hardcast Scheu-Dental,
PC 0.75 mm Imprelon
A+ 0.040 in. Essix A+ Raintree
Essix, Inc.
C+ 0.040 in. Essix C+ Raintree
Essix, Inc.
stabilizers (<5%)
PUR 0.030 in. Invisalign Align
from methylene
diisocyanate and
Component as obtained from the manufactures’ material safety data sheet
Kundal and Shokeen: Clear aligners
40 International Journal of Dental and Medical Specialty Vol 7 ● Issue 1 ● Jan-Jun 2020
Mechanical Properties
Force delivery of clear aligners depends on:
a. Amount of activation: The extent of movement
prescribed per aligner differs for every clear aligner
system. ClearSmile® system allows 0.5 mm, ClearCorrect
(ClearCorrect, Round Rock, TX, USA) prescribes
0.3 mm, whereas Invisalign (Align Technology, Inc.,
Santa Clara, CA, USA) incorporates 0.25 mm of tooth
movement per aligner.[13,14]
b. Type of material: Pressure formed appliance exerts greater
force systems at higher rates of activation as compared
to vacuum formed ones.[15,16]
c. Thickness of material: Ranges from 0.5 to 1.5 mm; thicker
the material, higher the force.[17,18]
d. Size and shape of adjacent teeth.[16]
Wear resistance of an aligner is indicated by the hardness
of its material; higher the hardness value, better the wear
resistance. Similarly, higher elastic index indicates brittleness
of the material; a high modulus of elasticity increases the
force delivery capacity under constant strain, which is a
desirable property for an aligner material.[19]
Mechanical properties of the aligner material deteriorate
with time. Microcracks, delaminated areas, calcified
biofilm deposits, and loss of transparency were reported
in Invisalign (Align Technology, Inc., Santa Clara, CA,
USA) aligners worn for 2 weeks.[20,21] The residual stresses
decrease in the thermoplastic materials with time.[22] A
change in fit of the appliance and resultant orthodontic
forces can be seen as a result of intraoral hygroscopic
expansion. Water absorption of thermoplastic materials
increases with time, with Invisalign (Align Technology,
Inc., Santa Clara, CA, USA) showing the highest
absorption followed by PET-G.[12]
Thermal Properties
All polymers have a glass-transition temperature (Tg) at
which the rigid state converts to a rubbery state. When
thermal properties of three clear aligners (Invisalign
[Align Technology, Inc., Santa Clara, CA, USA), Simpli5
[Allesee Orthodontic Appliances, Sturtevant, WI, USA],
and ClearCorrect [ClearCorrect, Round Rock, TX, USA])
were compared, all three aligner systems were found to
have a Tg above the accepted oral maximum temperature,
with no significant difference seen before and after
clinical use.[23]
The aligner material should be able to maintain its color
stability and transparency. To avoid pigment adsorption, it
is recommended to remove aligners during eating and while
drinking colored drinks. Color changes in aligners have been
reported on exposure to staining solutions such as coffee,
black tea, and red wine.[24] Invisalign (Align Technology, Inc.,
Santa Clara, CA, USA) was more prone to pigmentation
when exposed to coffee or red wine.[25]
The individual teeth are sectioned and repositioned
sequentially using a wax setup. Once a working cast is
obtained, teeth are removed from cast and moved into
the planned position, with aligners sheets molded onto
the realigned models using pressure molding or vacuum
Digital (CAD-CAM)[27]
• Patients’ impressions obtained digitally by intraoral
scanner and uploaded for virtual treatment planning.
• In case of traditional impressions (polyvinyl siloxane
putty), casts are obtained, scanned, and uploaded.
• Digital models are then analyzed for IPR and expansion
• Teeth are sectioned digitally.
• IPR prescription is reviewed for validity and if acceptable,
IPR is performed digitally and plan is communicated to
the doctor.
• Teeth are then moved into correct alignment digitally
and a digital overlay model is created by superimposing
final model onto the original model.
• Sequence of aligners fabricated using the overlay model.
• The force bumps, attachments, or auxiliaries are then
planned for aiding tooth movements.
Clear aligner should seat completely on insertion and
be properly anchored to the dental arch without any
dislodgement or vertical lifting. A decline in aligner forces
at gum line is seen due to flexibility of gingival margins, thus
impeding the ability to produce certain tooth movements.
The possible margin designs are scalloped, straight cut at the
gingival zenith, and straight cut 2 mm above the gingival
zenith (most retentive) [Figure 1].[28]
Kundal and Shokeen: Clear aligners
International Journal of Dental and Medical Specialty Vol 7 ● Issue 1 ● Jan-Jun 2020 41
Wearing an aligner for 22 h/day for 2 weeks is mandated to
ensure maximum expression of aligner prescription.[29] A
decrease in daily wear time likely decreases the efficacy of
certain incisor movements, reportedly labial inclination and
buccolingual translation of mandibular incisors, rotation of
maxillary central incisors, as well as buccolingual translation
and intrusion of maxillary lateral incisors.[30] However, most
incorporated movements occur within the 1st week, thus
casting doubt over usefulness of the additional 1 week of
aligner wear.[9,31]
Replacing braces with clear polyurethane trays for
orthodontic treatment have raised questions regarding its
efficiency in moving the teeth. Tooth movement obtained
most accurately with clear aligners is retrusion, followed by
rotation, fan-type expansion, and protrusion, respectively.[32]
Acceptable results can be achieved for the buccolingual
inclination of maxillary and mandibular incisors in mild-to-
moderate malocclusions.[33]
CAT is recommended in non-extraction cases with mild-
to-moderate malocclusions in non-growing patients.[34] In
extraction cases, proper root angulations can be attained
with use of suitable attachments and adequate knowledge
of the system.[35] Maxillary molar distalization (2.5 mm)
and premolar extraction space closure (7 mm) are the
most predictable and controlled movements that can be
obtained.[36] To its demerit, as occlusal contacts are lost due
to thickness of aligners, problems with the final settling of
the occlusal plane can arise.[37]
While fixed orthodontic appliances cause root resorption
as a side effect of heavy orthodontic forces, there is no clear
consensus on root resorption with CAT. A lower incidence
and severity of root resorption has been reported, with
incisors being the most affected teeth.[38] The incidence of
root resorption was seen to be comparable between aligners
and light orthodontic forces.[39] Another study revealed
a lower severity and prevalence of root resorption with
Clear aligner treatment has flourished since its introduction
into orthodontics. Continued developments on the
technological front are being adapted to improve its
efficiency, especially in complex cases. Being a removable
appliance, patient compliance is the foremost criteria for
success of treatment with aligners and patient motivation
is indispensable to avail the planned treatment outcomes.
Arrays of companies are manufacturing aligners today,
providing them directly to consumers, or routing through
the dentists; it falls beyond the scope of this article to study
the individual characteristics of each system.
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How to cite this article: Kundal S, Shokeen T. Aligners: The Science of
Clear Orthodontics. Int J Dent Med Spec 2020;7(1):38-42.
Source of Support: None; Conicts of Interest: None
... Clear aligner materials have evolved from single-layered or monophasic plastic to second-generation polyurethane materials, to the currently used third-generation multilayered materials that often comprise hard and soft layers. While the soft layer imparts the property of elastic deformation allowing smooth seating of the aligner, the hard layer ensures strength and durability [55]. ...
Full-text available
Rapid technological improvements in biomaterials, computer-aided design (CAD) and manufacturing (CAM) have endorsed clear aligner therapy (CAT) as a mainstay of orthodontic treatment, and the materials employed for aligner fabrication play an all-important role in determining the clinical performance of clear aligners. This narrative review has attempted to comprehensively encompass the entire gamut of materials currently used for the fabrication of clear aligners and elucidate their characteristics that are crucial in determining their performance in an oral environment. Historical developments and current protocols in aligner fabrication, features of contemporary bioactive materials, and emerging trends related to CAT are discussed. Advances in aligner material chemistry and engineering possess the potential to bring about radical transformations in the therapeutic applications of CAT; in the absence of which, clear aligners would continue to underperform clinically, due to their inherent biomechanical constraints. Finally, while innovations in aligner materials such as shape memory polymers, direct three-dimensional (3D) printed clear aligners and bioactive materials combined with clear aligner materials are essential to further advance the applications of CAT; increased awareness of environmental responsibilities among aligner manufacturers, aligner prescribing clinicians and aligner users is essential for better alignment of our climate change goals towards a sustainable planet.
... It can simulate orthodontic movements and also customize brackets designs for specific malocclusions. [24] Clear aligners [25] Clinical procedure involves accurate impression taking, followed by scanning of the poured casts to obtain a virtual 3D model. This model is studied and the required corrections to treat the particular malocclusion are uploaded by the orthodontist using the software. ...
Full-text available
Background: Manufacturers of orthodontic aligners suggest that users remove appliances every time they consume solid foods or any drink (except water). This is to avoid a color change within the clear thermoplastic material of which they are made. However, limited quantitative evidence exists to guide users and practitioners in this regard. Herein, we evaluated the color stability of the polymer forming three different American brands of aligners and the stain-removal potential of two cleansers to provide such guidelines. Methods: The removable appliances (300 specimens, 100 per brand) were exposed to different staining agents common in a regular diet (coffee, black tea, red wine, cola) or to a control solution in vitro over 12 h or 7 days. The three brands evaluated were Invisalign®, ClearCorrect® and Minor Tooth Movement®. These were then cleaned by using either Invisalign® cleaning crystals or the Cordless Sonic Cleaner combined with a Retainer Brite® tablet. The CIELAB color space approach was used to compare color changes (ΔE) in aligners before immersion (T0), after a 12-h exposure (T1), after a 7-day exposure (T2) and after cleaning (T3). Statistical methods (Levene's test, ANOVA, Brunner-Langer model, Tukey's range test and t-test) were used to identify interactions between the brands themselves or between the brands and the cleaning methods. Statistical analyses were performed at the .05 significance level. Results: A 12-h or 7-day exposure to instant coffee or red wine significantly colored the Invisalign® aligners compared to the two other brands. Black tea created an important extrinsic color change for all three brands after 7 days. Clinically, both cleaning methods showed a better efficacy in removing stains from black tea compared to other staining agents. Conclusions: The Invisalign® aligners were more prone to pigmentation than the ClearCorrect® or the Minor Tooth Movement® devices after an exposure to coffee or red wine. Black tea caused important stains on the surface of the three tested brands. Both cleansing methods performed similarly.
Full-text available
Background: Fixed appliances have been the mainstream for orthodontic treatment, while clear aligners, such as Invisalign system, have become increasingly popular. The prevalence of apical root resorption (ARR) in patients with clear aligners is still controversial. The aim of this study was to investigate and compare the prevalence and severity of ARR in patients treated with clear aligners and fixed appliances using cone beam computed tomography (CBCT). Materials and methods: A total of 373 roots from 70 subjects, with similar baseline characteristics and the ABO discrepancy index scores (i.e., treatment difficulty), were included into two groups: the clear aligners group (Invisalign, Align Technology, California, USA) and fixed appliances group (Victory Series; 3 M Unitek, California, USA). Root length of each anterior tooth was measured on the CBCT images by two blinded investigators. The ARR on each tooth was calculated as the difference of root length before and after orthodontic treatment. Chi-square test and paired t test was used to compare the ARR between the two groups as well as before and after orthodontic treatments. Results: Prevalence of ARR in the clear aligners group (56.30%) was significantly lower than that in the fixed appliances group (82.11%) (P < 0.001). The severity of ARR in the clear aligners group (0.13 ± 0.47 mm) was significantly less than that in the fixed appliances group (1.12 ± 1.34 mm) (P < 0.001). The most severe ARR was found on the maxillary canine (1.53 ± 1.92 mm) and lateral incisor (1.31 ± 1.33 mm) in the fixed appliances group; the least ARR was found on the mandibular canine (- 0.06 ± 0.47 mm) and lateral incisor (0.04 ± 0.48 mm) in the clear aligners group (P < 0.001). Conclusions: The prevalence and severity of ARR measured on CBCT in patients with clear aligners were less than those in patients with fixed appliances.
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As the demand for esthetic treatments is increasing, more people are seeking alternatives to fixed orthodontic appliances. Clear aligners are an esthetic and comfortable option for orthodontic treatment and have gained immense popularity over the last decade. This review will highlight the increasing popularity of clear aligners by describing some aligner systems frequently used today. The scope, limitations, effectiveness, efficacy, and stability of treatment results achieved with this method will be discussed. Further, this paper will assess the possible side effects caused by clear aligner treatment.
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Background Align technology has developed greatly over past few years. Patients tended to prefer clear aligners over conventional brackets because of the superior comfort and esthetics, while the effectiveness of clear aligners was still controversial. The aim of this systematic review was to verify whether the treatment effectiveness of clear aligners was similar to the conventional fixed appliances. Methods A comprehensive search of the Pubmed, Web of Science, Embase, Scopus, and Cochrane Central Register of Controlled Clinical Trials Register databases for studies published through to August 20, 2018 was conducted. Comparative clinical studies assessing the effectiveness of clear aligners compared with braces were included. Results Eight papers were included in this study. Two of the included papers were randomized controlled trials and six were cohort studies. Clear aligners might not be as effective as braces in producing adequate occlusal contacts, controlling teeth torque, increasing transverse width and retention. While no statistically significant difference was found between two groups in Objective Grading System score (WMD = 8.38, 95% CI [− 0.17, 16.93]; P = 0.05). On the other hand, patients treated with clear aligners had a statistically significant shorter treatment duration than with braces (WMD = − 6.31, 95% CI [− 8.37, − 4.24]; P < 0.001). Conclusion Both clear aligners and braces were effective in treating malocclusion. Clear aligners had advantage in segmented movement of teeth and shortened treatment duration, but were not as effective as braces in producing adequate occlusal contacts, controlling teeth torque, and retention.
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Background: Aim was to systematically search the literature and assess the available evidence regarding the clinical effectiveness of the Invisalign® system. Methods: Electronic database searches of published and unpublished literature were performed. The reference lists of all eligible articles were examined for additional studies. Reporting of this review was based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Results: Three RCTs, 8 prospective, and 11 retrospective studies were included. In general, the level of evidence was moderate and the risk of bias ranged from low to high, given the low risk of bias in included RCTs and the moderate (n = 13) or high (n = 6) risk of the other studies. The lack of standardized protocols and the high amount of clinical and methodological heterogeneity across the studies precluded a valid interpretation of the actual results through pooled estimates. However, there was substantial consistency among studies that the Invisalign® system is a viable alternative to conventional orthodontic therapy in the correction of mild to moderate malocclusions in non-growing patients that do not require extraction. Moreover, Invisalign® aligners can predictably level, tip, and derotate teeth (except for cuspids and premolars). On the other hand, limited efficacy was identified in arch expansion through bodily tooth movement, extraction space closure, corrections of occlusal contacts, and larger antero-posterior and vertical discrepancies. Conclusions: Although this review included a considerable number of studies, no clear clinical recommendations can be made, based on solid scientific evidence, apart from non-extraction treatment of mild to moderate malocclusions in non-growing patients. Results should be interpreted with caution due to the high heterogeneity.
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Background Root resorption (RR) is described as a permanent loss of tooth structure from the root apex. Many reports in the literature indicate that orthodontically treated patients are more likely to have severe apical root shortening, interesting mostly maxillary, followed by mandibular incisors. The aim of the study was to investigate the incidence and severity of RR in adult patients treated with aligners. The study group consisted of 71 class I adult healthy patients (mean age 32.8 ± 12.7) treated with aligners (Invisalign®, Align Technologies, Santa Clara, CA, USA). All incisors, canines, upper first premolars, and first molars were assessed. Root and crown lengths of 1083 teeth were measured in panoramic radiographs at the beginning (T0) and at the end (T1) of clear aligner therapy. Individual root-crown ratio (RCR) of each tooth and therefore the relative changes of RCR (rRCR) were determined. A decrease of rRCR was assessed as a reduction of the root length during treatment. Results All patients had a minimum of one teeth affected with a reduction of root length, on average 6.38 ± 2.28 teeth per patient. Forty one, 81% of the 1083, measured teeth presented a reduction of the pre-treatment root length. A reduction in percentage of >0% up to 10% was found in 25.94% (n = 281), a distinct reduction of >10% up to 20% in 12.18% (n = 132) of the sample. 3.69% (n = 40) of the teeth were affected with a considerable reduction (>20%). Conclusions Orthodontic treatment with Invisalign® aligners could lead to RR. However, its incidence resulted to be very similar to that described for orthodontic light forces, with an average percentage of RR < 10% of the original root length.
Objective: To analyse through a systematic review the effectiveness of clear aligners by assessing: (a) predictability of clear aligners and (b) treatment outcome comparison of clear aligner therapy with fixed appliance therapy. Methods: An electronic search was made from January 2014 to April 2019 using MEDLINE, Embase, Web of Science and LILACS databases without any limitations on language. Three reviewers independently assessed the articles. Quality assessment of observational studies and randomized control trial was done by using the ROBINS tool and Cochrane risk of bias tool, respectively. GRADE instrument was used to assess certainty level for each identified outcome. Results: Seven eligible articles (one randomized controlled trial and six retrospective cohort) were included in our systematic review. Most of the studies (six out of seven) had a moderate risk of bias and one had a high risk of bias. Conclusions: 'Low to moderate level' of certainty in regard to specific clear aligner therapy tooth movements' efficiency was identified. Clear aligners may produce clinically acceptable outcomes that could be comparable to fixed appliance therapy for buccolingual inclination of upper and lower incisors in mild to moderate malocclusions. However, not all potential clinical scenarios have been assessed in the included studies. Most of the tooth movements may not be predictable enough to be accomplished with only one set of trays with clear aligners despite the recent advances in technology.
OBJECTIVE To update the scientific evidence related to the efficacy of clear aligner treatment (CAT) in controlling orthodontic tooth movement (OTM). MATERIALS AND METHODS International medical databases were searched to identify all peer-reviewed papers potentially relevant to the review. The quality of evidence was ranked using the Swedish Council on Technology Assessment in Health Care Tool criteria. RESULTS 20 relevant articles were selected and the quality of evidence was high for 3 studies, moderate for 12 studies and low for 5 studies. Mesio-distal tooth movement revealed the highest predictability, with a molar distalization up to 2.5 mm and space closure of 7 mm performed with good control. Arch expansion is predictable up to 2 mm on molars. Improvements in Little’s and PAR Index were reported in mild to severe malocclusions. CONCLUSIONS The overall quality of available evidence was of moderate/high level. CAT aligns and levels the arches even in severe cases, with efficient control of incisors inclination. Arch expansion and tooth bodily movement are efficiently achievable movements with CAT.
Objectives: The objective of this study was to perform a systematic review of the orthodontic literature with regard to efficiency, effectiveness and stability of treatment outcome with clear aligners compared with treatment with conventional brackets. Methods: An electronic search without time or language restrictions was undertaken in October 2014 in the following electronic databases: Google Scholar, the Cochrane Oral Health Group's Trials Register, Scopus, CENTRAL, MEDLINE via OVID, EMBASE via OVID and Web of Science. We also searched the reference lists of relevant articles. Quality assessment of the included articles was performed. Two authors were responsible for study selection, validity assessment and data extraction. Results: Four controlled clinical trials including a total of 252 participants satisfied the inclusion criteria. We grouped the trials into four main comparisons. One randomized controlled trial was classified as level 1B evidence, and three cohort studies were classified as level 2B evidence. Clear aligners appear to have a significant advantage with regard to chair time and treatment duration in mild-to-moderate cases based on several cross-sectional studies. No other differences in stability and occlusal characteristics after treatment were found between the two systems. Conclusions: Despite claims about the effectiveness of clear aligners, evidence is generally lacking. Shortened treatment duration and chair time in mild-to-moderate cases appear to be the only significant effectiveness of clear aligners over conventional systems that are supported by the current evidence.