Predictability of Orthodontic Tooth Movement With Invisalign Aligners
Condition: Tooth Crowding; Malocclusion; Malocclusion, Angle Class II; Malocclusion, Class I/II
MeSH terms: Malocclusion; Malocclusion, Angle Class II; Overbite
Study type: Observational

Summary: 
      Together with the increased adult patient demand for orthodontic treatment and the push
      toward increasingly personalized treatment, technology developments have resulted in a
      growing worldwide demand for clear aligners, to the point that they are now an essential part
      of any orthodontic practice.

      Despite the widespread use of the technique, the existing literature about reliability of
      orthodontic tooth movement with Invisalign aligners seems not encouraging. Several papers
      have demonstrated that what is virtually planned is not what is clinically achievable.
      However, it should be considered that clear aligner orthodontics techniques are customized
      not only for the patients but for orthodontists too. Therefore, virtual treatment plan
      design, in terms of attachments' design and placement, orthodontic tooth movement (OTM)
      staging and aligner deformation overengineering, or in other words aligners biomechanics
      knowledge, plays a crucial role in defining the quality of the orthodontic treatment with
      Invisalign aligners.

      Based on these considerations the present study was designed to answer two research-clinical
      questions: 1) which are the less predictable orthodontic movements with Invisalign aligners
      when the treatment plan is designed by expert operators? and 2) which is the impact of the
      orthodontist experience, in terms of patient motivation, on the predictability of orthodontic
      tooth movement with Invisalign aligners? To answer those questions, the predictability of OTM
      in a sample of Invisalign patients treated by expert operators was compared with the
      predictability of OTM in a sample treated by post-graduate students.

      The null hypothesis for question 1 is that all the prescribed orthodontic tooth movements are
      predictable, while the null hypothesis for question 2 is that the reliability of orthodontic
      tooth movement is not affected by operator experience.

      98 patients (31 M, 67 F; mean age 28 ± 12 years) were selected among those in treatment at
      the Department of Orthodontics of the University of Turin, which is the coordinating center,
      and at 5 private orthodontics offices across Italy. The inclusion criteria for practitioners
      were as follows: orthodontist with huge and renewed experience in Invisalign treatments; has
      the ability to scan plaster model or to collect intraoral scans and upload (via internet) the
      files obtained to a central repository; affirms that the practice can devote sufficient time
      in patient scheduling to allow focused recording of all data required for the study; and does
      not anticipate retiring, selling the practice, or moving during the study. Signed, written
      informed consent was required before inclusion in the trial.

      All participants included in this prospective observational study had Class I or mild Class
      II malocclusion with mild to moderate crowding or spacing in the maxillary and mandibular
      dental arches (nonextraction cases). Interproximal enamel reduction was performed as
      prescribed in each patient's virtual treatment plan.

      The average treatment time was 10 ± 5 months. The sample considered a total of 2716 teeth
      that were analyzed overlapping the real post-treatment .stl file obtained with the final
      intra-oral scan to the planned post-treatment .stl file obtained exporting the final stage of
      the virtual setup.

      Every virtual treatment plan was designed by orthodontists with a huge and renewed experience
      in Invisalign treatments. While in the private practices the treatment was directly conducted
      by 5 expert orthodontist (mean age 45.6 ± 8.2) who controlled the patient at every
      appointment, in the University setting the treatment was conducted by 5 post-graduate
      students at the last year of their program (mean age 26.4± 1.4). Control appointments were
      fixed at 6 weeks interval in both the University and the private settings.

      Posttreatment digital models and final virtual treatment plan models were exported from
      ClinCheck® software as stereolithography files and subsequently imported into Geomagic
      Qualify software (3D Systems(r), Rock Hill, South Carolina, USA), in order to compare
      individual tooth positions between digital models of each patient. The dental arches were
      superimposed using the landmark-based method and the surface-based method (Best Fit
      Alignment). So that the differences between the tooth positions could be calculated, 3
      reference planes were identified on the virtual treatment plan model. Differences between the
      actual treatment outcome and the predicted outcome were calculated and tested for statistical
      significance for each tooth in the mesial-distal, vestibular-lingual, and occlusal-gingival
      directions, as well as for angulation, inclination, and rotation. Differences greater than
      0.5 mm for linear measurements and 2° for angular measurements were considered clinically
      significant. In addition, the statistical significance of categorical variables was tested
      for each previously calculated difference in tooth movement.
    


Intervention name(s): Aligner
Intervention type(s): Device
Intervention description(s): A method of straightening teeth without fixed braces
Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        orthodontic patients affering to the department of Turin and patients affering to 5 private
        orthodontics offices across Italy
      
Keywords: Biomechanics; Aligner orthodontics; Adult patients; Orthodontic Tooth Movement predictability