Clear Aligners 2021… What does the evidence say?

Improving the predictability of clear aligners.

Bowman, S. Seminars in Orthodontics, 2017 23(1):65-75.

Overview of clinical strategies to enhance the effectiveness and efficiency of clear aligner therapy.

Summary:

1. Patient compliance – one of the main issues with all removeable appliances
  - Informed consent that high level of compliance is required for clear aligner tx to be effective
  - Compliance indicators (colour-fading dot)
  - Risk of forgetting to re-insert aligners after meals or brushing

2. Aligner tracking
  - Research states that 41-57% of predicted tooth movement is realized (issues with impressions/scanning, limitations of plastic material, inconsistent compliance)
  - Certain tooth movements (e.g. extrusion, rotations, torque) esp. for certain teeth (e.g. U3s) require more attention  led to creation of composite attachments for aligners to “grip” onto teeth
  - Use of “chewies” to help seat aligner on teeth which are not tracking

3. Lack of space
  - 2 ways to deal with crowding: (1) create space (expansion) of (2) reduce tooth mass (extraction or IPR)
  - Extraction case considerations: anchorage concerns, torque, tipping, good interproximal contact post-space closure  use of elastics and/or TADs can be valuable in increasing clear aligner tx predictability in exo cases
-  Predictable sequence of space closure requires anchorage control – teeth next to malpositioned tooth to be held stationary/no movement until malpositioned one is moved

4. Rotations (esp. difficult for U2 and U3s)
  - Molded composite attachments have increased rotational control predictability
  - Usually necessary to prescribe 2-3o of over-rotation to attain ideal
  - Detailing pliers – to produce plastic indentations to create rotational couples
- Consider supra-crestal fiberotomy (retention)

5. Torque and root angulation
  - Torque, bodily movement and root parallelism are limitations of clear aligner tx
  - “Torquing ridges” – to enhance palatal root torque (ridges added at facial gingival margin + incisal edge of lingual  rotational couple to tip roots palatally (vice versa if labial root torque required), often want to prescribe over-correction of torque
  - ABO reports that there is often insufficient posterior torque (ideally, there should be no difference between the heights of B and L cusps of molars and PMs)
  - Rem: consequence of anterior torque = loss of posterior anchorage
  - Crowding with deep OB is often associated with upright incisors (obtuse interincisal angle)

6. Extrusion (reported as least accurate tooth movement, 26% efficacy)
  - “Aligner lag” – when plastic slips occlusally/incisally leaving the tooth behind
  - Strategies: add more prominent attachment (“grip”), alleviate tight interproximal contacts (need adequate space around tooth to prevent collisions)

7. Adjunctives
  - Use of elastics, bonded buttons, TADs with clear aligner therapy
  - “Bootstrapping” – bonding buttons at facial and lingual gingival margins  application of elastic from button to button across occlusal surface (e.g. for intrusion)

8. Skeletal discrepancies
  - Use of elastics + aligners for Class II, III and AOB patients
  - Use of precursor adjunctives prior to clear aligner tx: e.g. Carriere, Pendulum/Distal Jet (get posterior teeth into class I occlusion, then clear aligners prescribed to maintain posterior segment while anteriors are retracted, retraction usually supported with class I or II elastics from TADs to prevent anchorage loss)

Management of overbite with the Invisalign appliance

Authors:  Roozbeh Khosravi, Bobby Cohanim, Philippe Hujoel, Sam Daher, Michelle Neal, Weitao Liu, and Greg Huang

Citation:  Khosravi Am J Orthod Dentofacial Orthop 2017;151:691-9

Purpose:

1- To investigate the vertical dimension changes in patients with various pretreatment overbite relationships treated only with Invisalign.
2- To identify the dental and skeletal changes associated with bite closing or opening.

Study Type: Retrospective observational

  • Population: Records were collected from the offices of 3 practitioners, all experienced with the Invisalign technique.
  • Sample: 120 patients (68 with normal overbites, 40 with deepbites, and 12 with open bites). Median age was 33 years and 70% were women.
  • Inclusion criteria: (1) patient 18 years at the beginning of tx (2) tx was completed between Jan 1, 2010, and Jan 1, 2014 (3) 11 to 40 aligners were used for each arch (4) max of 3 revision sets of aligners were used (5) tx plan was non-ex (6) molar AP relationship was not changed (eg, no Class II to Class I change) (7) posterior-transverse relationships were not changed significantly (eg, no correction of posterior crossbite) (8) fixed appliances were not used (9) patient had good-quality pre-tx and post-tx cephs.
  • Data collected: (1) pre-tx and post-tx lateral cephs, (2) Invisalign Tx overview form with info re no. and location of attachments + potential interproximal reduction plans (3) patient's age at start of the tx (4) patient's sex (5) questionnaires filled out by clinicians re their tx strategies.
  • o assess the changes during tx, 9 linear and 3 angular measurements were measured. Palatal, occlusal, and mandibular planes were used as the reference lines.

Results:

- Ceph analyses indicated that the deepbite patients had a median overbite opening of 1.5 mm, the open bite patients had a median deepening of 1.5 mm.
- Invisalign maintained overbite in patients with normal pre-tx overbite.
- The anterior vertical dimension in patients with normal pre-tx overbite showed minimal change (median change was 0.3 mm).
- Changes in incisor position were responsible for most of the improvements in the deepbite and open bite groups.

- Main mechanism of bite opening in deep-bite patients was proclination of the mand incisors
- Overbite correction in open-bite patients was primarily accomplished by extrusion of the max and mand incisors
- Minimal changes in molar vertical position and mandibular plane angle were noted.

Conclusions - Invisalign:

  • Is relatively successful in managing overbite.
  • Maintains overbite in patients with normal overbite.
  • Improves deepbites primarily by proclination of mand incisors. 
  • Corrects mild to moderate anterior openbites, primarily through incisor extrusion.
- These results did not support the idea that posterior teeth intrude during tx with Invisalign.

Title: Clinical effectiveness of Invisalign® orthodontic treatment: a systematic review
Authors: Aikaterini Papadimitriou, Sophia Mousoulea, Nikolaos Gkantidis and Dimitrios Kloukos
Citation: Papadimitriou et al. Progress in Orthodontics (2018) 19:37

Purpose: To systematically search the literature and summarize current scientific evidence regarding the clinical effectiveness of the Invisalign® system as principal therapy to patients of any age treated with this method comparing either among them or those with conventional braces and evaluating the level of efficacy in various malocclusions.

Conclusions:

  • Invisalign might treat faster mild non-ex cases, but requires more time than fixed appliance tx for more complex cases.
  • Invisalign® aligners can safely straighten dental arches in terms of leveling and derotating the teeth(except for canines and premolars, where a small inadequacy was reported). Crown tipping can be easily performed.
  • Teeth inclinations and occlusal contacts seem to be among the limitations of Invisalign®, when accuracy of planned movements achieved with aligners is concerned.
  • Use of additional attachments might be more effective for various types of movement, such as bodily expansion of the maxillary posterior teeth, canine and premolar rotational movements, extrusion of maxillary incisors, and in overbite control.

A systematic review of the accuracy and efficiency of dental movements with Invisalign®

Galan-Lopez et al • Systematic review of clear aligners 2019

CONCLUSION

  • Invisalign® and fixed appliances are able to alter intercanine, interpremolar, and intermolar width in the presence of crowding. Moreover, incisors tend to procline and protrude when crowding is > 6 mm.
  • Vertical movement and derotation are difficult movements to accomplish with aligners. And IPR is recommended, especially in canines.
  • It is not necessary to incorporate an attachment when molar distalization is required in Invisalign® treatment.
  • The expression of the programmed movement is not fully accomplished with Invisalign®.
  • Sex and age affect tooth movement in both modalities.
  • There is better root control with fixed appliances.
  • The majority of tooth movement occurs during the first week with plastic systems.
  • Buccolingual inclination and occlusal contacts are worse with Invisalign®.

Although it is possible to treat complex malocclusions with plastic systems, the results are less accurate than those achieved with fixed appliances.

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