Clinical efficacy of the Invisalign mandibular advancement appliance: A retrospective investigation

Introduction

This retrospective investigation aimed to determine whether the achieved changes in the treatment of Class II malocclusion were the same as those planned after the prescribed wear of an initial phase of Invisalign treatment with the mandibular advancement appliance (MAA) (Align Technology, Santa Jose, Calif).

Methods

All patients treated with the MAA and who satisfied inclusion/exclusion criteria were selected from a database of 16,500 patients treated with clear aligners by 16 orthodontists. The pretreatment, planned, and achieved overjet measurements were documented from data provided in Align Technology’s software facility, ClinCheck. Changes in intermaxillary anteroposterior (AP) first permanent molar (FPM) relationships were evaluated using Geomagic Control X (3D systems, Rock Hill, SC) metrology software.

Results

Most of the 195 patients who satisfied the inclusion criteria were females (n = 104; 53.3%). The mean age was 12.62 ± 2.20 years. The pretreatment overjet was reduced from 6.49 ± 2.86 mm to 4.61 ± 2.22 mm after prescribed MAA wear, which was 42.5% of the planned outcome. The pretreatment AP FPM reduced from 3.14 ± 1.95 mm to 2.24 ± 2.51 mm, which was 31.3% of that planned. Thirty-eight (19.5%) patients experienced an increase in overjet where a reduction was planned.

Conclusions

Less than half of the planned overjet reduction and less than a third of the planned AP FPM correction were achieved with the MAA. Almost 20% of patients completed the MAA phase of treatment with an increased overjet despite a reduction being planned.

Highlights

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We studied the efficacy of Invisalign’s mandibular advancement appliance.
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The mean achieved overjet reduction with the appliance was less than that planned.
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Just 31% of the planned anteroposterior first permanent molar changes occurred.
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Almost 20% experienced an increase in overjet after prescribed wear of the appliance.

The provision of clear aligner therapy (CAT) for the treatment of malocclusion is increasing among orthodontists, with recent studies indicating that the use of the Invisalign (Align Technology, San Jose, Calif) appliance is commonplace globally. In 2017, Align Technology introduced Invisalign with mandibular advancement appliance (MAA) to aid Class II correction in growing patients. The MAA uses buccally positioned inclined planes (precision wings), which are built into the maxillary and mandibular aligners to posture the mandible forward.

Purported advantages of the MAA over traditional functional appliance treatment (FT) include the ability to align the teeth while correcting the Class II malocclusion, superior control of mandibular incisor angulation and molar extrusion, in addition to ease of use, patient comfort, and superior esthetics. ^, ^, Reported limitations included issues concerning patient compliance with wear protocols, discomfort, and an initial period in which the patient must learn to posture their mandible forward in a correct manner to enable effective engagement with the precision wings. ^,

An additional advantage is the ability to use the digital facility, ClinCheck, provided by Align Technology for treatment planning. The facility enables the clinician to formulate a treatment plan to achieve a desired occlusal outcome via the use of a series of removable thermoplastic aligners. Each aligner is modified slightly from the aligner preceding it to incrementally move the teeth to the planned position. Patients are required to wear their aligners for approximately 22 hours daily and renew the aligner every 7-14 days until the wear of all aligners in the series has been completed.

The facility also enables the clinician to visualize the planned outcome from treatment planning processes via the use of digital models representing the patient’s intraarch and interarch occlusion and to avail of data such as pretreatment and planned overjet measurements. In addition, it can facilitate the prescription of ≥1 additional series of aligners if treatment goals have not been satisfactorily achieved with the initial prescribed series of aligners. Additional series of aligners are frequently required as planned treatment objectives appear not to be commonly achieved. Furthermore, the presence of the initial and planned digital models within the facility lends itself readily to academic research with metrology software.

Studies regarding the clinical efficacy of the MAA are limited. Current evidence suggests that treatment responses to MAA therapy are similar to FT, with predominantly dentoalveolar and limited skeletal effects being observed. ^, ^, ^, Some evidence exists regarding the overjet changes with the MAA. ^, ^, However, most studies related to MAA treatment are based on the analysis of the changes in lateral cephalometric radiographs. ^, ^, Information regarding how closely the achieved overjet outcome corresponds to the outcome planned by the ClinCheck facility in growing patients is limited in growing patients. Furthermore, research comparing the changes in the anteroposterior (AP) relationship between the first permanent molar (FPM) in the maxilla and the corresponding molar in the mandible resulting from treatment with the MAA is minimal.

Global epidemiologic studies have indicated a high prevalence of Class II malocclusion. ^, With the increasing ubiquity of CAT, investigation regarding the clinical efficacy of the MAA is likely to be of value to the clinician, patient, researcher, and aligner provider. This retrospective investigation aimed to determine whether the achieved changes in overjet and the AP relationship between the FPM in the maxilla and the FPM in the mandible were the same as those planned after the prescribed wear of an initial series of the MAA appliance in growing patients. The null hypothesis was that there was no difference between the planned and achieved outcomes.

Material and methods

Ethical approval for this study was granted by the University of Adelaide Human Research and Ethics Committee.

The patient records used for this investigation were obtained from the Australasian Aligner Research Database (AARD), a database containing information on patients treated with the Invisalign appliance by 16 orthodontists experienced in its use in 3 countries. It is a requirement of the participating orthodontists that they provide the information of all patients they have treated with appliances provided by Align Technology.

At the time of data acquisition, AARD held the Invisalign treatment information of approximately 16,500 patients. All patients within the database consented to the use of their records for research purposes before beginning their CAT.

Patient records were included for assessment in the present study if they satisfied the following criteria: (1) an initial treatment phase carried out with the MAA, (2) complete stereolithography (STL) digital records of the dental arches at the commencement of treatment and the end of the first treatment phase, (3) compliant with MAA wear protocols according to the treating clinician, and (4) necessitating an additional series of aligners to facilitate assessment of the treatment outcome at the end of the initial series of MAA aligners. Records were excluded if patients had a craniofacial syndrome.

Data regarding patient gender, age at the beginning of treatment, and the number of prescribed MAA aligners were recorded onto a Microsoft Excel (Microsoft, Redmond, Wash) spreadsheet. In addition, the pretreatment, planned, and achieved overjet measurements were recorded from the data provided in the ClinCheck interface. Changes in intermaxillary AP FPM relationships were recorded using the Geomagic Control X (3D systems, Rock Hill, SC) metrology software system. The patients’ STL models were imported into Geomagic, and a plane was generated by drawing a line from the buccal groove of the mandibular left FPM to the buccal groove of the mandibular right FPM ( Fig 1 ).

The mesiobuccal cusp tips of the maxillary FPMs were identified as points for the maxillary STL model, and the linear measurement from each of these points to the constructed plane was recorded ( Fig 2 ). Measurements in which the mesiobuccal cusp points were located anterior to the plane were recorded as positive values, whereas those posterior to the plane were recorded as negative values.

Statistical analysis

Statistical analyses were calculated using SPSS software (version 25; IBM, Armonk, NY) and R (version 4.0; R Core Team, Vienna, Austria). Descriptive statistics were expressed in means and percentages.

Normality testing with the Shapiro-Wilk test signified that the data followed a normal distribution. Two 1-sided t tests were used to test for equivalence in ClinCheck planned overjet and AP FPM relationship outcomes and achieved overjet and AP FPM relationship outcomes. Bland-Altman plots were used to determine the bias between the ClinCheck planned outcomes and the achieved overjet and the AP FPM relationship changes. Proportional bias was further investigated via linear regression, with the achieved outcome measurement as the explanatory variable and the difference in measurements as the outcome variable.

Results

Figure 3 shows that 195 patient records satisfied the inclusion and exclusion criteria. The sample size for the regressions for the Bland-Altman plots and the regressions used in data calculation was 195. For all practical effect sizes, the power of the tests for regression slope significance was at least 0.99. That is, a sample size of 195 was almost certain to detect a nonzero slope when it exists, thus precluding the requirement for a post-hoc sample size calculation.

Almost 2% (n = 298; 1.8%) of the AARD comprised patients treated with the MAA. Most patients were females (n = 104; 53.3%), and the mean age of the sample was 12.62 ± 2.20 years. There was no difference between the mean age of males (12.84 ± 2.15 years) and females (12.5 ± 2.27 years) ( P >0.05). The mean number of MAA aligners prescribed in the initial phase was 40.2 ± 10.7. Table I shows that the initial overjet reduced from a mean of 6.49 mm to a mean of 4.61 mm after the initial sequence of aligners, which was 42.5% of its planned outcome. Almost half (47.7%) of the patients had an overjet >4 mm at the end of the initial series of aligners compared with 74.4% before treatment. The AP FPM correction was 31.3% of what was planned.

Table I

Pretreatment, achieved, and planned overjet and AP FPM relationships

Variables	Overjet (mm)	AP FPM Relationships (mm)
Variables	Overjet (mm)	Left	Right	Overall
Pretreatment	6.49 ± 2.86	3.08 ± 1.99	3.20 ± 1.93	3.14 ± 1.95
Achieved	4.61 ± 2.22	2.23 ± 2.54	2.26 ± 2.50	2.24 ± 2.51
Planned	2.07 ± 0.68	−0.14 ± 1.43	−0.35 ± 1.50	0.26 ± 1.46

Note. Values are presented as mean ± standard deviation. Mesiobuccal cusp points located anterior to the plane formed from the buccal groove of the mandibular left FPM to the buccal groove of the mandibular right FPM were recorded as positive values, whereas those posterior to the plane were recorded as negative values.

Figure 4 provides a visual representation of the difference between the achieved and planned overjet measurement values of the patients included in the study, and Figure 5 and Table II suggest that the greater the pretreatment overjet, the greater the difference between the planned and the achieved posttreatment outcome. Tables III and IV indicate that the greater the linear discrepancy of the left and right AP FPM relationship, the greater the difference between the planned and the achieved outcomes.

Table II

Estimated discrepancies between planned and achieved overjet for selected values of pretreatment and planned measurement values

Planned overjet (mm)	Pretreatment overjet (mm [95% confidence interval])
Planned overjet (mm)	0	3	6	9	12
0	1.01 (−2.70 to 4.72)	2.36 (−1.32 to 6.03)	3.71 (0.04 to 7.37)	5.06 (1.39-8.73)	6.40 (2.71-10.10)
1	0.34 (−3.31 to 3.99)	1.69 (−1.93 to 5.30)	3.04 (−0.57 to 6.64)	4.38 (0.77-7.99)	5.73 (2.10-9.37)
2	−0.33 (−3.96 to 3.29)	1.02 (−2.58 to 4.61)	2.36 (−1.22 to 5.94)	3.71 (0.13-7.30)	5.06 (1.45-8.68)
3	−1.00 (−4.65 to 2.64)	0.35 (−3.27 to 3.96)	1.69 (−1.90 to 5.29)	3.04 (−0.56 to 6.65)	4.39 (0.76-8.02)
4	−1.67 (−5.37 to 2.02)	−0.33 (−3.99 to 3.34)	1.02 (−2.63 to 4.68)	2.37 (−1.29 to 6.03)	3.72 (0.04-7.40)
5	−2.35 (−6.14 to 1.44)	−1.00 (−4.75 to 2.76)	0.35 (−3.39 to 4.10)	1.70 (−2.05 to 5.45)	3.05 (−0.72 to 6.82)