Dr Haylea Blundell, Tony Weir,

Brett Kerr & Elissa FreerDiscipline of Orthodontics,

University of Queensland

THE UNIVERSITY

OF QUEENSLAND

AUSTRALIA

INTRODUCTIONCorrecting the vertical dimension in orthodontics

is challenging.1,2

Clear aligner therapy is becoming increasingly

demanding by patients, however there is currently

insufficient evidence to support the efficacy of

clear aligners to correct a deep overbite.

ClinCheck® software (Align Technology®) is used

by clinicians to treatment plan Invisalign® cases.3

The predicted outcomes of Invisalign® treatment

using ClinCheck® have been questioned due to

uncertainty of accuracy when compared with

actual post-treatment outcomes. 3-7

Since the introduction of Invisalign® in 1998, there

has been limited and conflicting evidence in the

literature regarding the efficiency of this appliance

in deep overbite correction. 8-11 Therefore, the aim

of this study was to investigate and determine the

accuracy of Invisalign® in correcting deep overbite

by comparing the predicted outcome from

ClinCheck® to the actual post-treatment outcome.

The null hypothesis states there is no difference

in overbite when comparing ClinCheck® and

achieved post-treatment overbite

SUBJECTS &

METHODOLOGYA retrospective study involving 42 adult (>18years old)

patients with pre-treatment and post-treatment intra-oral scans

using an iTero Element scanner treated with Invisalign® by Dr

Tony Weir at his private orthodontic practice in Brisbane,

between January 2013 - July 2018.

Additional inclusion criteria included compliant patients, the

presence of second maxillary molars, dual arch Invisalign

treatment, patients treated with a minimum of 14 aligners,

non-extraction treatment plan with an overbite depth up to

8mm. Patients treated with IPR, anterior build-ups,

orthognathic surgery treated, or in combination with auxiliaries

such as vertical elastics, anterior bite ramps, cross elastics or

fixed appliances were excluded from the study.

A pilot study was performed to determine the sample size.

Pre-treatment, predicted (ClinCheck®) and actual post-

treatment overbite for each patient were imported into

Geomagic® Control X software (Version 2017.0.3.69;

Geomagic, Morissville, NC, USA) and compared.

The models were aligned to a horizontal reference adjusted

from Grunheid et al7 (Fig. 1) using the interproximal papillae

instead of the occlusal surfaces. Overbite depth was

measured from the mid point of the 21 incisal edge (Fig. 2) to

the mid point of a vector from the 31 and 32 incisal edges

(Fig. 3). Intra-operator error was measured using 20 randomly

selected patients at two intervals, two weeks apart. Inter-

operator error was measured on 10 patients by an operator

with experience with Geomagic® Control X.

Figure 1 Reference points for the horizontal

reference plane adapted from Grunheid et al (2017)

Figure 2 Models aligned to the horizontal reference

line with the mid-point of 21 incisal edge and the

vector between 21-32.

Figure 3 Linear measurement of overbite between

the incisal edge of the 21 and the vector between

31-32

RESULTS

• Intra- and inter-operator error for overbite measurement showed excellent agreement (> 0.997).

• In 40/42 cases, ClinCheck over-predicted the post-treatment reduction in overbite (Fig. 4)

• 50% of the sample groups overbite was >4.0mm pre-treatment and 30% of patients post-treatment still

had an increased overbite >4.0mm post-treatment. (Table 1)

• Overall, only 39.2% of the prescribed overbite reduction was achieved using the Invisalign ® appliance

Table I. Frequency and percentage of overbite

Overbite Depth

Overbite Mean Normal Moderate Deep

± SD 0 to 2mm 2 to 4mm >4mm

mm n(%) n(%) n(%)

Pre-treatment overbite 3.9 ± 1.4 5 (12) 17 (38) 21 (50)

Post-treatment overbite 3.3 ± 1.3 7 (17) 23 (55) 12 (30)

Predicted (ClinCheck) overbite 1.9 ± 0.7 25 (60) 17 (40) -

0

1

2

3

4

5

6

7

1.6

8

1.8

1.8

1.8

6

1.8

7

2.2

2

2.3

5

2.3

7

2.5

1

2.7

2.7

2.8

5

2.8

6

2.9

3.1

7

3.2

9

3.4

2

3.6

3

3.7

2

3.8

3

3.9

4.0

8

4.1

4.4

4.4

3

4.5

3

4.5

4

4.6

4.6

4.6

6

4.7

4

4.8

2

4.9

5

5.0

6

5.1

7

5.3

3

5.3

3

5.6

4

5.7

1

6.1

3

6.2

3

7.7

2

Ove

rbit

e (

mm

)

Pre-treatment overbite (mm)

ClinCheck predicted overbite Post-trearment overbite

Figure 4 Difference between predicted (ClinCheck) and post-treatment overbite

RESULTS

Table II. Estimate post-treatment overbite with Invisalign® treatment (95%CI)

ClinCheck (mm)

0 1 2 3

Init

ial O

verb

ite

(m

m)

4 2.9 3.2 3.4 3.6

(2.0, 3.8) (2.7, 3.6) (3.1, 3.7) (3.1, 4.2)

5 3.5 3.8 4 4.2

(2.5, 4.5) (3.1, 4.4) (3.7, 4.3) (3.7, 4.7)

6 4.1 4.3 4.6 4.8

( 3.0, 5.3) ( 3.6, 5.2) (4.1, 5.1) ( 4.3, 5.4)

7 4.7 5.0 5.2 5.5

(3.4, 6.1) (4.0, 6.0) (4.5, 5.9) (4.8, 6.1)

• Table II highlights the greater overbite correction (mm) required, the larger the discrepancy between the

predicted (ClinCheck ®) and the achieved overbite post-treatment.

• The regression coefficient analysis shows that on average, only 30.5% of overbite reduction will be

achieved when reducing an initial 4.0 – 7.0mm overbite to 0mm. (Table II)

DISCUSSION

In the present study all patients had a prescribed reduction (ClinCheck®) in overbite to less than

4.0mm. However, clinically 30% of patients still had a deep overbite (>4.0mm) post-treatment,

highlighting the shortfall of overbite reduction using the Invisalign® appliance, where ClinCheck®

over-predicted overbite reduction in 95.3% of the patients in the sample.

Two patients produced greater overbite correction than prescribed on ClinCheck®. The reason

for this was not investigated within this study, however this could be due to individual biological

response to orthodontic tooth movement. It is also important to note that as these two outliers

were included in the overall data, therefore the overall accuracy of achieved overbite using the

Invisalign appliance® has been affected in the current sample of patients.

Overall, the data showed a general, positive linear trend between prescribed overbite reduction

and the actual post-treatment overbite depth. Using the linear regression analysis we were able

to predict overbite reduction depending on the initial pre-treatment overbite depth (Table II).

Reducing a pre-treatment overbite of 7mm to 0mm on ClinCheck® as estimated, would produce

a post-treatment overbite of 4.7mm, where only 32.9% of the prescribed overbite reduction is

achieved. From the available data, the overall clinical expression of overbite reduction using the

Invisalign® appliance is 39.2%. This finding is considerably lower than previously published

articles by Drake et al12 (72%), Chisari et al13 (57%) and Brenner14 (51.9%) although similar to

the results presented by Kravitz et al15 (41%).

It is worth noting that the use of bite ramps and intermaxillary elastics were exclusion criteria,

and these may assist aligners in achieving improved overbite correction. Equally, the exclusion

of cases which had extractions, interproximal reduction or space closure eliminated the role of

relative extrusion which could further challenge overbite correction outcomes.

The authors acknowledge the flaws in any retrospective study, where there is an inherent risk of

selection bias.

Further investigations to determine the reasons for the inability of aligners to correct overbites

to the prescribed amount should be carried out. An investigation into the role of arch

depth/incisor flaring in determining final overbite in the current sample is presented in a

separate poster.

CONCLUSIONS

AcknowledgementsThis project wouldn’t have been possible without the support

from the University of Queensland and the ASO-FRE.

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1. On average, the Invisalign appliance expressed 39.2% of the

programmed overbite reduction when compared to the prescribed

outcome in the ClinCheck Software.

1. The deeper the overbite is pre-treatment, the more challenging it may

be to express the overbite reduction with Invisalign aligners alone

2. ClinCheck overestimated bite opening in 95.3% of cases. Therefore,

programmed movement in ClinCheck software may not be a clinically

useful determinant of the expression of overbite reduction