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Reliability of torque expression by the Invisalign® appliance: A retrospective study

Raj Gaddam
Raj Gaddam
, 
Elissa Freer
Elissa Freer
, 
Brett Kerr
Brett Kerr
 und 
Tony Weir
Tony Weir
   | 13. Juli 2021
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Article Category: research-article
Online veröffentlicht: 13. Juli 2021
Seitenbereich: 3 - 13
DOI: https://doi.org/10.21307/aoj-2021-001
© 2021 Raj Gaddam et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Figure 1.

Generation of long axis of the tooth.
Generation of long axis of the tooth.

Figure 2.

Generation of reference plane.
Generation of reference plane.

Figure 3.

Measurement of torque.
Measurement of torque.

Figure 4.

Best-fit superimposition (global and fine).
Best-fit superimposition (global and fine).

Figure 5.

The best fit superimposition with a common transverse reference plane for both pretreatment and predicted post-treatment STL files.
The best fit superimposition with a common transverse reference plane for both pretreatment and predicted post-treatment STL files.

Figure 6.

Measurement of interincisal angle.
Measurement of interincisal angle.

Figure 7.

Box-whisker plot showing the distribution of torque and IIA differential.
Box-whisker plot showing the distribution of torque and IIA differential.

Figure 8.

Mean accuracy of the torque expression and interincisal angle change resulting from prescribed torque.
Mean accuracy of the torque expression and interincisal angle change resulting from prescribed torque.

Calculation of torque, interincisal angle (IIA) differential and mean accuracy.

Predicted change in torque = torque at T1 – torque at T0Achieved change in torque = torque at R – torque at T0Torque differential = predicted change in torque – achieved change in torque
Predicted change in IIA = IIA at T1 – IIA at T0Achieved change in IIA = IIA at R – IIA at T0IIA differential = predicted change in IIA – achieved change in IIA
Mean accuracy for torque or IIA = 100 – (predicted change-achieved change/predicted change) X 100

Criteria for sample selection.

Inclusion criteria: Non-growing patientsComplete permanent dentitionOrthodontic treatment with Invisalign (SmartTrack)All subjects finished the initial aligner wear as determined by ClinCheckTwo-week aligner wear protocolSimple Class I malocclusion comprising spacing (< 4 mm) to crowding (< 6 mm)Non – extraction treatmentNo interproximal reductionNo intermaxillary elasticsNo orthognathic surgeryNo restorative treatment to incisors and distal most molars during orthodontic treatmentAll the subjects included in this study met the criteria of compliance
Exclusion criteria:Periodontally compromised patientsMedications which alter bone metabolism (e.g.: Bisphosphonates, PG inhibitors)Patients treated with Power Ridges

Descriptive statistics and paired student t-test values for torque, IIA differential.

Group N Predicted change (Mean ± SD) (°) Achieved change (Mean ± SD) (°)(Mean ± SD) (°) Differential (predicted change – achieved change) (°) t P-value
Median (°) 95% CI
Lower (°) Upper (°)
Labial CT UC 56 8.16 ± 7.78 1.73 ± 5.22 6.43 ± 7.09 5.94 4.50 8.36 6.78 <0.001*
UL 51 5.99 ± 6.26 0.93 ± 4.49 5.06 ± 7.32 3.94 2.96 7.16 4.94 <0.001*
LI 112 7.77 ± 5.11 5.03 ± 5.94 2.75 ± 5.70 2.40 1.65 3.84 5.10 <0.001*
Lingual/Palatal CT UC 24 4.49 ± 3.38 5.22 ± 4.01 -0.73 ± 3.31 -0.71 -2.16 0.70 -1.08 >0.05
UL 29 4.90 ± 4.28 4.54 ± 4.38 0.36 ± 4.41 0.81 -1.36 2.08 0.44 >0.05
LI 48 4.73 ± 5.39 5.40 ± 5.50 -0.67 ± 6.06 -0.45 -2.49 1.15 -0.77 >0.05
Labial CT – IIA 61 13.80 ± 10.69 4.80 ± 8.74 9.00 ± 10.73 7.50 6.20 11.8 6.55 <0.001*
Lingual/Palatal CT– IIA 19 9.79 ± 11.70 13.20 ± 9.44 -3.40 ± 7.90 -2.45 -7.39 0.59 -1.88 >0.05

Liner regression analysis.

Group Unstandardised coefficients Standardised coefficients
Constant B (R 2 )
Labial CT UC -2.27 0.49 0.53
UL -1.21 0.36 0.25
LI -2.21 0.93 0.64
Lingual/Palatal CT UC 1.18 0.90 0.58
UL 1.33 0.66 0.41
LI 1.76 0.77 0.57
Labial CT – IIA -3.08 0.57 0.49
Lingual/Palatal CT – IIA 6.39 0.70 0.74
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