Table 1.
An overview of the included studies providing information on the experimental designs and settings
| Author (year) | Title | Study design | Setting, treatment duration | Participants (number, sex) | Age of patients (mean age) | Inclusion criteria | Intervention group | Comparison group |
|---|---|---|---|---|---|---|---|---|
| Hennessy et al. [18] (2016) | A randomized clinical trial comparing mandibular incisor proclination produced by fixed labial appliances and clear aligners. | RCT | Setting: n/a Treatment duration: fixed appliance group, 11.3 months; clear aligner group, 10.2 months |
44 patients (17M, 27F) | Invisalign group: 29.1 ± 7.5 years Fixed appliance group: 23.7 ± 7.0 years |
- Age ≥ 18 years - No caries or periodontal disease - Mild Mn crowding (< 4 mm) - Non-extraction orthodontic treatment - Anteroposterior skeletal pattern within the average range (ANB 1–4°) |
22 patients treated with Invisalign | 22 patients treated with fixed appliances (self-ligating brackets) |
| Li et al. [19] (2015) | The effectiveness of the Invisalign appliance in extraction cases using the ABO model grading system: a multicenter randomized controlled trial. | RCT | 2 orthodontic clinics at the Second Affiliated Hospital, Zhejiang University Invisalign treatment duration was 44% longer than fixed appliance treatment |
152 patients (62M, 90F) | Invisalign group: 35.2 ± 7.3 years Fixed appliance group: 32.2 ± 8.3 years |
- Patients aged ≥ 18 years - Extraction treatment - Patients consented to the research procedures and signed - Availability of pre- and post-treatment dental study models and panoramic films with good quality - Classified as being severe in complexity with a score of 25 using the discrepancy index (DI) of the ABO phase III clinical examination - Class I occlusion |
76 patients treated with Invisalign | 76 patients treated with fixed appliances |
| Bollen et al. [20] (2003) | Activation time and material stiffness of sequential removable orthodontic appliances. Part 1: Ability to complete treatment | RCT | University of Washington Regional Clinical Dental Research Center Primary endpoint: completion of initial aligners’ series |
51 patients (15M, 36F) | 34 years (range 19–55) | - Age ≥ 18 years - Ability to attend weekly appointments and to pay for services - Requirement for regular dental and periodontal maintenance program in case of caries or periodontal disease |
51 patients randomly assigned to 4 intervention groups; either to hard/soft plastic appliance and 1 week/2 weeks activation time | The 4 groups were compared to each other |
| Solano-Mendoza et al. [21] (2016) | How effective is the Invisalign® system in expansion movement with Ex30′ aligners? | Prospective | Private clinic in Stuttgart, Germany Mean treatment duration: 657.4 ± 341.4 days |
116 patients (46M, 70F) | 36.57 ± 11.53 years | - Treatment with Ex30 aligner material - Expansion of the posterior upper teeth (from canine to 1st upper molar) - Presence of an initial and final digital model - Definition of the third palatal ruga - No presence of attachments on the initial or final model - No more than two models per patient |
Expansion with Invisalign; 4 groups: (a) G1 (n = 40): expansion ≤ 1.99 mm in intermolar cuspid width (b) G2 (n = 45): expansion ≤ 3.99 mm (c) G3 (n = 14): patients subjected to expansion ≤ 5.99 mm (d) G4 (n = 10): expansion ≥ 6 mm. 7 patients unclassified due to current absence of one or both 1st molars |
Initial and final virtual 3-D ClinCheck® models |
| Buschang et al. [26] (2015) | Predicted and actual end-of-treatment occlusion produced with aligner therapy | Prospective | 1 private practice, Dallas, Texas, USA Treatment duration: n/a |
27 patients (n/a) | n/a | Consecutive patients | 27 consecutive patients treated with Invisalign | Final virtual 3-D ClinCheck® models |
| Castroflorio et al. [22] (2013) | Upper-incisor root control with Invisalign appliances | Prospective | 2 private orthodontic clinics in a metropolitan area of northwest Italy Treatment duration: not reported |
6 patients (2M, 4F) | 26.3 ± 10.2 years | No patient had any record of anterior crossbite, anterior prosthodontic work, previous orthodontic treatment, craniofacial trauma, surgery, TMD, or orofacial pain | Invisalign patients (n = 6; 9 Mx incisors) needing palatal root torque as part of their treatment | Initial and final virtual 3-D ClinCheck® models for each upper incisor |
| Pavoni et al. [23] (2011) | Self-ligating versus Invisalign: analysis of dento-alveolar effects | Prospective | Department of Orthodontics “Tor Vergata,” Dental School, University of Rome Treatment duration: Invisalign group, 18 ± 2 months; self-ligating group, 18 ± 3 months |
40 patients (19M, 21F) were equally divided into 2 groups: Invisalign® group (8M, 12F); self-ligating group (11M, 9F) | Invisalign group: 18.4 years Self-ligating group: 15.6 years |
- Class I malocclusion - Mild crowding in Mn arch (mean: 4.4 ± 0.8 mm) - Permanent dentition - Vertebral maturation more advanced than CS4 (post-pubertal) - No previous orthodontic treatment |
Invisalign + IPR (n = 20) | Fixed appliances (self-ligating; n = 20) |
| Kravitz et al. [5] (2009) | How well does Invisalign work? A prospective clinical study evaluating the efficacy of tooth movement with Invisalign | Prospective | Department of Orthodontics at the University of Illinois, Chicago Primary endpoint: completion of initial aligners’ series. The mean number of aligners per treatment was 10 Mx and 12 Mn with each aligner worn for 2–3 weeks |
37 patients (14M, 23F) | 31 years | - Age ≥ 18 years - Anterior crowding/spacing < 5 mm and adequate buccal interdigitation - Patients with posterior edentulous spaces were included if treatment did not entail space closure (1 participant had mandibular incisor extraction) - Clinicians were allowed to request/refuse IPR, proclination, attachments, and overcorrections on ClinCheck® - Only Invisalign attachments could be used and the tray could not be altered with scissors/thermopliers |
37 patients/401 anterior teeth (198 Mx, 203 Mn) treated with Anterior Invisalign® | Final virtual 3-D ClinCheck® models |
| Kravitz et al. [24] (2008) | Influence of attachments and interproximal reduction on the accuracy of canine rotation with Invisalign | Prospective | Department of Orthodontics, University of Illinois, Chicago Mean duration: 7 months. Primary endpoint: completion of initial aligners’ series |
31 patients (13M, 18F) | ≥ 18 years | Same as Kravitz et al. [5] (2009) | 31 patients/53 canines (33 Mx, 20 Mn) treated with anterior Invisalign® were divided in 3 groups: (a) attachments only (AO) (b) interproximal reduction only (IO) (c) neither attachments nor interproximal reduction (N) |
Final virtual 3-D ClinCheck® models |
| Baldwin et al. [27] (2008) | Activation time and material stiffness of sequential removable orthodontic appliances. Part 3: Premolar extraction patients | Prospective | University of Washington Regional Clinical Dental Research Center Primary endpoint: completion of initial aligners’ series |
24 patients (6M, 18F) | 32.8 (range 18–54) years | Same as Bollen et al. [20] (2003) + at least 1 premolar extraction | 24 patients treated with either hard/soft plastic appliance and 1 week/2 weeks activation time | No control group (pretreatment condition) |
| Vlaskalic and Boyd [25] (2002) | Clinical evolution of the Invisalign appliance | Prospective | University of the Pacific Mean treatment duration: group 1, 20 months; group 2, 27.2 months; group 3, 31.5 months |
40 patients | 14–52 years | - Fully erupted permanent dentition (except for 3rd molars) - Dental health with no immediate need for restorations - Availability for evening appointments - Desire to comply with orthodontic treatment |
3 Invisalign groups based on severity of crowding: group 1 (n = 10 mild cases); group 2 (n = 15 moderate cases), and group 3 (n = 15 severe cases) | The 3 groups were compared to each other |
| Gu et al. [28] (2017) | Evaluation of Invisalign treatment effectiveness and efficiency compared with conventional fixed appliances using the Peer Assessment Rating index | Retrospective | Setting: Division of Orthodontics at Ohio State University College of Dentistry Treatment duration: Invisalign group, 13.35 months; fixed appliance group: 19.1 months |
96 patients (34M; 62F) | Invisalign group: 26 ± 9.7 years Fixed appliances group: 22.1 ± 7.9 years |
- Available pre- and posttreatment records—age ≥ 16 years - No auxiliary appliances other than elastics - Non-extraction patients - No orthognathic surgery or syndromic patients - Full permanent dentition except third molars |
Invisalign (n = 48) | Fixed appliances (straight-wire edgewise appliances; n = 48) |
| Khosravi et al. [29] (2017) | Management of overbite with the Invisalign appliance | Retrospective | Setting: 3 private orthodontic offices; 2 located in the greater Seattle area, Wash and 1 in Vancouver, British Columbia Treatment duration: n/a |
120 patients (36M; 84F) | 33 years (interquartile range: 17) | - Age ≥ 18 years - 11 to 40 aligners used for each arch - A max use of 3 revision sets of aligners - Non-extraction treatment plan - No class II to class I occlusion change - Not significantly changed posterior-transverse relationships - No fixed appliances - Good-quality pre- and post-treatment cephalometric radiographs |
Invisalign; stratified study sample as follows: 68 patients in the normal overbite group, 40 patients in the deep- bite group, and 12 patients in the open-bite group | The 3 groups were compared with each other |
| Houle et al. [30] (2016) | The predictability of transverse changes with Invisalign | Retrospective | Setting: Department of Preventive Dental Science, Division of Orthodontics, School of Dentistry, University of Manitoba - Orthodontic practice in Adelaide, Australia Treatment duration: 56 weeks |
64 patients (23M, 41F) | 31.2 years (range18–61 years) | - Age ≥ 18 years - Non-extraction treatment without any auxiliaries other than Invisalign attachments |
Invisalign (n = 64) | Initial and final virtual 3-D ClinCheck® models |
| Ravera et al. [31] (2016) | Maxillary molar distalization with aligners in adult patients: a multicenter retrospective study. | Retrospective | Orthodontic private practices located in Torino (Italy) and Vancouver (Canada) Treatment duration: 24.3 ± 4.2 months |
20 patients (9M, 11F) | 29.73 ± 6.89 years | - Age ≥ 18 years old - Skeletal class I or II and a bilateral end-to-end molar relationship - Normodivergence on the vertical plane (SN-GoGn angle < 37°) - Mild crowding in the upper arch (≤ 4 mm) - Absence of mesial rotation of the upper 1st molar - Standardized treatment protocol, - Good compliance (wearing aligner time, ≥ 20 h per day) - Absence or previous extraction of the upper 3rd molars - Good quality radiographs |
Invisalign (n = 20) | No control group |
| Duncan et al. [32] (2015) | Changes in mandibular incisor position and arch form resulting from Invisalign correction of the crowded dentition treated nonextraction | Retrospective | Single orthodontic practice Treatment duration: 1st group, 53.6 ± 21.1 weeks; 2nd group, 63.7 ± 20.7 weeks; 3rd group: 71.7 ± 16.3 weeks |
61 patients (17M, 44F) | Adult patients (age n/a) | - Non extraction cases with or without IPR | 3 intervention groups according to pre-treatment crowding of lower dentition (Carey’s analysis): (a) 20 mild (2.0–3.9 mm), (b) 22 moderate (4.0–5.9 mm), and (c) 19 severe (> 6.0 mm) cases | The 3 groups were compared to each other |
| Grünheid et al. [33] (2015) | Effect of clear aligner therapy on the buccolingual inclination of mandibular canines and the intercanine distance | Retrospective | University of Minnesota Mean treatment duration: Invisalign group, 13.4 ± 6.8 months; fixed appliance group: 20.2 ± 5.3 months |
60 patients (30 in each group; 8M, 22F) | Invisalign group: 25 ± 11.8 years; fixed appliance group: 26.3 ± 13.5 years | - Fully erupted permanent dentition including incisors, canines, premolars, and 1st molars - Angle class I malocclusion with normal interarch molar relation - No periodontal attachment loss - Non-extraction orthodontic treatment - Pre- and posttreatment full-field of view CBCT scans - Both mandibular canines clearly visible in the CBCT scans |
Invisalign (n = 30) | Fixed appliances (n = 30) |
| Simon et al. [34] (2014) | Treatment outcome and efficacy of an aligner technique – regarding incisor torque, premolar derotation and molar distalization | Retrospective | Private orthodontic practice in Cologne, Germany Treatment duration: n/a |
30 patients (11M, 19F) initially, but 4 dropped out (n = 26) | 32.9 ± 16.3 years Range 13–72 years |
- Healthy patients - 1 of the 3 following tooth movements required: (1) Upper medial incisor torque > 10° (2) Premolar derotation > 10° (3) Molar distalization of an upper molar > 1.5 mm |
3 Invisalign groups: (a) Incisor torque > 10° (b) Premolar derotation > 10° (c) Molar distalization > 1.5 mm. The groups were subdivided: in the 1st subgroup, movements were supported with an attachment, while in the 2nd subgroup no auxiliaries were used (except incisor torque, in which Power Ridges were used) |
Initial and final virtual 3-D ClinCheck® models |
| Krieger et al. [35] (2012) | Invisalign® treatment in the anterior region. Were the predicted tooth movements achieved? | Retrospective | Setting and treatment duration: not reported | 50 patients (16M, 34F) | 33 ± 11.2 years | Frontal Mx and/or Mn crowding according to Little’s index of irregularity | Invisalign (n = 50) | Initial and final virtual 3-D ClinCheck® models |
| Krieger et al. [36] (2011) | Accuracy of Invisalign® treatments in the anterior tooth region. First results | Retrospective | Setting and treatment duration: n/a | 35 patients (11M, 24F) | 33 (range 15–59) years | - Orthodontic treatment exclusively with Invisalign - Consecutive post-treatment models and patient documentation - Presence of low-moderate Mx and/or Mn crowding |
Orthodontic treatment exclusively with Invisalign (n = 35) | Initial and final virtual 3-D ClinCheck® models |
| Kuncio et al. [37] (2007) | Invisalign and traditional orthodontic treatment postretention outcomes compared using the American Board of Orthodontics Objective Grading System | Retrospective | Private practice in New York City Treatment duration: Invisalign group, 1.7 ± 0.8 years; fixed appliance group: 2.3 ± 0.8 years |
22 patients (11 in each group; 1M, 10F) | 34 years in the Invisalign group 26 years in the fixed applaince group |
Non-extraction cases | Invisalign (n = 11) | Fixed appliances (n = 11) |
| Djeu et al. [38] (2005) | Outcome assessment of Invisalign and traditional orthodontic treatment compared with the American Board of Orthodontics objective grading system | Retrospective | Private practice in New York City Treatment duration: 1.4 years for the Invisalign® group; 1.7 years for the fixed appliance group |
96 patients (gender n/a) | Invisalign®: 33.6 ± 11.8 years Fixed appliances: 23.7 ± 11.0 years |
Non-extraction cases | Invisalign (n = 48) | Fixed appliances (n = 48) |
M male, F female, m.a mean age, Mx maxillary, Mn mandibular, IPR interproximal reduction, CBCT cone-beam computed tomography, n/a not available