Effectiveness of maxillary arch expansion using clear aligners in adult patients: a systematic review and meta-analysis

1) Pre-treatment digital models created from an iTero scan.

2) Post-treatment digital models created from an iTero scan.

3) Digital models from Clincheck obtained from Align Technology to measure planning accuracy.

1) Canine tip

2) Canine gingival

3) First premolar tip

4) First premolar gingival

5) Second premolar tip

6) Second premolar gingival

7) First molar tip

8) First molar gingival

1) Mean of planned transverse changes

2) Mean difference between the amount of change planned and final outcome

1) Group A (n = 14); Expansion ≤1 mm

2) Group B (n=20); Expansion 1-2 mm

3) Group C (n = 6); Expansion 2 mm

According to baseline torque by root vector analysis by Dolphin software

4) Group D (n = 11); faciolingual inclination -2°

5) Group E (n = 16); faciolingual inclination -2° to 2°

6) Group F (n = 13); faciolingual inclination ≥2° to < 6°

1) Digital models from stereolithography (.stl) files created from plaster models converted from polyvinyl siloxane (PVS) impressions by Optimics scanner (Activity 880, Smart Optics, Germany).

2) To digital dentition models in ClinCheck provided as.stl files from Align Technology (Santa Clara, CA, USA).

3) Conebeam computed tomography (CBCT) records as digital imaging and communications in medicine (DICOM) files, taken by GALILEOS Viewer (Sirona, Germany), in the participant’s natural head position (NHP)

1) Canine

2) First premolar

3) Second premolar

4) First molar

1) Expansion efficiency for crown

2) Efficiency of bodily expansion movement

1) 1 Tooth in crossbite (16.7%)

2) 2 Teeth in crossbite (10.5%)

3) >3 Teeth in crossbite (8.8%)

4) Bilateral crossbite (9.6%)

5) No crossbite (44.7%)

6) Second molar crossbite (9.6%)

1) Diagnostic records obtained using Itero intraoral scanner, at the start and end of first phase of treatment

2) Clincheck registers analyzed at 3 stages

• a) Dimensions recorded at start of first treatment phase (T1)

• b) Dimensions generated by Clincheck software as predicted measurements at end of first treatment phase (T2)

• c) the real dimensions obtained the start of the second treatment phase (also known as “first additional aligners”) (T3)

3) Occlusal images of the maxilla at three stages (T1, T2 and T3)

4) Images were exported to a program (Keynote) designed to measure angulation-

• a) Measuring widths

• b) Measuring the rotation of the first molar

• c) Measuring molar inclination

1) Measuring widths (vestibular (buccal) cusps of canine, first and second premolars, and mesio-vestibular cusps of first and second molars)

2) Measuring the rotation of the first molar (the angle formed by tracing a line from the disto-vestibular to mesio-palatal cusp of the first molars to the perpendicular line that passes through the point of contact of the central incisors and the horizontal line traced from the tip of the mesio-vestibular cusp of both first molars)

3) Measuring molar inclination (he tangent to the vestibular faces of the first molars)

1) Treatment efficacy (differences between means at T3 and T1)

2) Predictability (differences between means at T2 and T3).

1)Pretreatment (T1) digital models (.stl files), created from an iTero scan, were collected

2) Posttreatment (T2) digital models (.stl files), created from an iTero scan, were collected

3) The final position of the ClinCheck representation was collected to establish the predictability of the final virtual model (T2 ClinCheck)

A) The following transverse linear values were measured only on the upper arch for each T1 and T2 model and the T2 ClinCheck model-

• 1) Intercanine width (A)

• 2) First premolar width (B)

• 3) Second premolar width (C)

• 4) Mesial first molar (D)

• 5) Distal first molar width (E)

• 6) Mesial second molar width (F)

• 7) Distal second molar width (G)

• 8) Transpalatal first molar width (H)

• 9) Transpalatal second molar width (I)

B) Angular measurements (inclinations) determined using digital models at T1 and T2 and T2 ClinCheck models

• a) Upper canine

• b) Premolar

• c) First molar

• d) Second molar

1) Pretreatment STL model (T0) of maxillary arch before starting Invisalign treatment.

2) post-treatment STL model (T1) of maxillary arch at the end of the treatment with Invisalign

3) STL model from the final model programmed on the ClinCheck® software (TC)

1) Intercanine cusp width (A)

2) Intercanine gingival width (B)

3) First inter-premolar width (C)

4) Second inter-premolar width (D)

5) First molar mesio-vestibular (buccal) cusp width (E)

6) First molar gingival width (F)

1) Expansion obtained was calculated by the difference between the post-treatment distance with respect to the pretreatment amplitude (T1-T0).

2) Planned expansion was calculated by the difference between the planned distance on the Clincheck with respect to the pretreatment amplitude (TC-T0).

3) Accuracy of expansion was calculated by the difference between planned expansion on the Clincheck with respect to the obtained expansion (TC-T1).

1) For every maxillary measurement, there was a statistically significant difference between Clincheck and the final outcome.

2) The most reliable area to predict transverse changes in the maxilla was the canine cusp tip with 88.9% of the change achieved, a mean difference of 0.22 ± 0.74 mm.

3) For every lower arch measurement, at the gingival margin, there was a statistically significant difference between the Clincheck plan and the final outcome

4) Measurements at the cusp tips in the lower arch showed non-statistically significant differences between Clincheck and the final outcome.

5) Variance was not equal for any of the measurements done either upper or lower, meaning that the amount of change planned was not associated with prediction error.

All of the P values were recorded as significant for the variance ratio tests

1) The mean accuracy for the maxilla is 72.8%

• a) 82.9% at the cusp tips

• b) 62.7% at the gingival margins

2) Invisalign becomes less accurate going from anterior to posterior region.

3) The lower arch presented an overall accuracy of 87.7%

• a) 98.9% for the cusp tips

• b) 76.4% for the gingival margins.

4) All cusp tip post-treatment measurements were found to have a non-statistically significant difference when compared with Clincheck.

5) Clincheck prediction of expansion involves more bodily movement of the teeth than can be seen clinically.

6) But actually more dental tipping was observed.

1) There was no significant difference (P > 0.05) in the transverse dimension variables between the T0 ClinCheck and digital models.

2) There was a significant difference (P > 0.05) between the amount of designed expansion and amount of achieved expansion for the canine, first premolar, second premolar, and first molar

3) The effect of skeletal arch expansion in CBCT

• a) No significant change (P > 0.05) was observed in maxillary basal bone width

• b) The buccal alveolar crest width (BACW) increased significantly by 0.87 mm (P > 0.05)

• c) The lingual alveolar crest width (LACW) increased significantly by 0.75 mm (P > 0.05)

• d) The maxillary alveolar bone width at the level of the most convex point of the buccal alveolar ridge crest (BCPW) showed no significant difference between T0 and T1 (P> 0.05)

• e) The buccolingual inclination of the maxillary molar (HLA) significantly increased by 2.07 after arch expansion

1) The Invisalign system can increase arch width by tipping movement of posterior teeth.

2) The efficiency of bodily buccal expansion for maxillary first molars averaged 36.35%.

3) The preset amount of expansion movement and initial torque are negative correlated with bodily expansion efficiency.

1) Differences between T3 and T1 indicated changes resulting from treatment in the first sequence of transparent aligners.

• a) Widths underwent significant advances as a result of treatment

• b) Maximum expansion was obtained at the pre-molar level, exceeding 8%

• c) Width at the second molar underwent a smaller expansion (+0.54%)

• d) For Inclinations and rotations, the increase in inclination was significant in every case, and variations in rotation were of around 2%

2) Differences between T3 and T1 analyzed by subgroups (no crossbite group and crossbite group)

• a) The only significant differences between the two groups were in inclination of the right and left first molars, and rotation of left first molar.

• b) For all other variables expansion obtained the same efficacy regardless of group

3) Differences between T2 and T3 indicated the precision of Clincheck virtual planning

• a) For all widths, virtual planning obtained prognoses of greater expansion than those actually achieved

• b) All the plan’s estimations, with the exception of the second molar (p = 0.183), were significantly higher than the actual outcomes.

• c) Regarding inclinations, virtual planning was less optimistic for first and second molars, obtaining higher values at T3 than those planned virtually, with significant difference for the upper left first molar.

• d) For rotations, planning overestimated the value obtained at the upper right first molar

4) Differences between T2 and T1 analyzed by subgroups (no crossbite group and crossbite group). No significant differences were observed between the two groups.

1) Aligners are an effective tool for producing arch expansion, being more effective in premolar area and less effective in canine and second molar area.

2) Predictability was reasonable for expansion movement.

3) Based on these results, overcorrection should be considered at the virtual planning stage in order to obtain the expected outcomes.

1) For every maxillary measurement, there was a statistically significant difference between pretreatment values and final outcomes, except for measurements at the second upper molars.

2) A decreasing expansion gradient was observed moving from the anterior to posterior part of the arch.

3) The comparison of T2-T1 angular outcomes showed statistically significant changes in the inclinations of all teeth except for the second permanent molars.

4) The predictability of ClinCheck of the Invisalign software was determined after completion of treatment

• a) For linear measurements, statistically significant differences were detected only for the intercanine width.

• b) Regarding the angular variables, the canine inclinations showed low predictability between the changes predicted by ClinCheck and the changes observed after the completion of treatment. The amount of change planned was not associated with the obtained outcome.

1) The development of the maxillary arch showed a progressive reduction in the expansion rate in the canine, premolar, and posterior regions, with the greatest net increase at the first and second premolars.

2) The Invisalign system can increase arch width by increasing the buccal tipping of maxillary teeth.

3) Buccal tipping followed the same decreasing gradient from anterior to posterior that was observed for transverse width changes.

4) The Invisalign system showed poor predictability between the virtual recreation by ClinCheck and observed treatment outcomes for the maxillary canines.

5) An overcorrection of upper canine movements should be planned during dentoalveolar expansion.

1) The planned expansion (mm) increased progressively from anterior to posterior at the level of the cusps.

2) The planned expansions in millimeters for intercanine and inter-molar gingival width were less than those for the cusp width.

3) The intercanine, inter-premolar, and inter-molar measurements at the level of the cusps, the differences between the expansion obtained and the planned expansion were not statistically significant, while they were statistically significant for gingival measurements.

4) There is more vestibular tipping movement than body movement of the crowns at the level of the canine and of first molars.

1) The efficacy in maxillary arch transverse expansion, on average, is rated at 70%, and is not related to the type of tooth considered but applies overall.

2) Effectiveness is lower at the lingual level, with an average of 55% at the inter-molar level, and 46% at the canine level.

3) Statistically significant differences were found between the efficacy at the cuspal level compared to the efficacy measured at the most apical point of the palatal surface of the tooth, indicating that there is more tipping movement than body movement.

4) The ClinCheck programs a body movement, whereas what we have obtained is a tipping movement