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Table 1 An overview of the included studies providing information on the experimental designs and settings

From: Clinical effectiveness of Invisalign® orthodontic treatment: a systematic review

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)
  1. M male, F female, m.a mean age, Mx maxillary, Mn mandibular, IPR interproximal reduction, CBCT cone-beam computed tomography, n/a not available