Introduction
Control of overbite is considered essential in achieving ideal orthodontic outcomes. Questions have been raised regarding the accuracy of ClinCheck software (Align Technology, Santa Clara, Calif) in predicting posttreatment outcomes with Invisalign, with the paucity of well-researched literature available on this topic. This research aimed to investigate and determine the accuracy of Invisalign (Align Technology) in correcting a deep overbite by comparing the outcomes predicted by ClinCheck with achieved posttreatment outcomes.
Methods
A retrospective study was conducted using pretreatment and posttreatment intraoral scans and predicted outcome (ClinCheck) stereolithography files of 42 adult patients consecutively treated with Invisalign from January 2014 and completed before July 2018, selected from the files of 1 experienced orthodontist. Patients included in the study were treated without extractions and with a minimum of 14 dual arch Invisalign aligners using a 2-weekly aligner change protocol. The pretreatment, posttreatment, and predicted outcome stereolithography files for each patient were imported into Geomagic Control X (3D Systems, Rock Hill, SC) software to measure overbite.
Results
The deeper the patient’s initial overbite and the greater the amount of programmed reduction in overbite according to ClinCheck, the greater the discrepancy in overbite expression posttreatment. ClinCheck over-predicted overbite reduction in 95.3% of patients in which, on average, only 39.2% of the prescribed overbite reduction was expressed.
Conclusions
Overbite reduction may result in suboptimal outcomes when using the Invisalign appliance unless remedial measures are employed. The deeper the initial overbite, the more challenging it is to achieve the prescribed posttreatment overbite.
Highlights
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Correcting deep overbite with Invisalign appliances is challenging.
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Overbite results predicted with ClinCheck are not consistently achieved.
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The deeper the overbite, the lower the likelihood ideal overbite will be achieved.
Kesling, in 1945, introduced the tooth positioner, an appliance employed to help achieve ideal outcomes during the finishing stages of orthodontic treatment. The tooth positioner was fabricated by repositioning the teeth on study models and forming the positioner over the adjusted tooth positions. The concept of sequentially moving teeth with removable appliances regained interest in the 1970s. Since then, the idea has evolved and gained popularity, and in the last 2 decades, clear aligners have increasingly been implemented for orthodontic tooth movement. ,
In 1998 Align Technology (Santa Clara, Calif) introduced Invisalign (Align Technology), the first sequential clear aligner appliance that utilized computerized 3-dimensional technology for treatment planning and the fabrication of clear aligners, using TREAT software (Performance Systems Development, Ithaca, NY), which is then relayed to the clinician via the software program ClinCheck (Align Technology). Initially, Invisalign was recommended for correction of only mild malocclusions, but with advances in technology, materials, auxiliaries, and attachments, Invisalign has been increasingly employed for treatment of more complex malocclusions, including correction of deep overbite. In 2013, Align Technology introduced SmartTrack, a new material used for Invisalign aligners. According to in-house studies at Align Technology, the material has increased control for tooth movement and is more comfortable for patients. At the time of this review, more than 6.4 million patients have been treated with Invisalign, and an unknown number have been treated with aligner products from other companies.
The vertical dimension is considered an important aspect of occlusion, and it is well known that orthodontic correction of a deep overbite is challenging. Deep overbites can cause occlusal trauma to the anterior segment resulting in tooth mobility, loss of attachment, , and interferences in lateral excursive movements. , Although there are many ways to correct a deep overbite using conventional orthodontics, , , the choice of biomechanics must be made on an individual case-by-case basis. Reducing a deep overbite orthodontically can be achieved by the intrusion of anterior teeth, passive eruption of the buccal segments, extrusion of posterior teeth, a combination of posterior extrusion and anterior intrusion, or by flaring of maxillary and mandibular incisors. , ,
The consensus among clinicians is that ClinCheck plans do not accurately reflect the patient’s final occlusion on completion of Invisalign treatment. In 2009, Kravitz et al compared programmed tooth movements on ClinCheck to actual tooth movements with Invisalign and found that overall the mean accuracy with Invisalign was 41% in moving teeth to the programmed tooth positions. The programmed outcomes of Invisalign treatment using ClinCheck have been questioned because of the uncertainty of accuracy compared with actual post-Invisalign treatment outcomes, , especially regarding the extent of clinical expression of correction of a deep overbite, extrusive movements, rotations, torque, and bodily movements. Given that no orthodontic appliance delivers 100% of the movement prescribed and that Invisalign ClinCheck software is effectively analogous to archwire design with fixed appliances, the under expressions of planned tooth movements are not unexpected.
Since the introduction of the Invisalign system, there has been conflicting evidence in the literature regarding the efficacy of Invisalign appliances in the correction of deep overbite. , , Questions have been raised regarding the ability of clear aligners to effectively extrude teeth, and clinicians have reported concerns that the presence of material between the maxillary and mandibular posterior teeth may cause posterior dental intrusion. In addition, studies have found extrusion with aligners appears more challenging than other orthodontic mechanics to correct deep overbites. Therefore, this study aimed to investigate and determine the predictive accuracy of ClinCheck software in estimating overbite reduction with the Invisalign appliance by comparing the predicted outcome from ClinCheck to the actual posttreatment outcome.
Material and methods
This study was approved by the University of Queensland School of Dentistry Ethics Committee under project no. 1837. The subjects included in this study were patients treated within the private orthodontic practice in Brisbane, Australia. The orthodontist (T.W) is an experienced Invisalign provider who has been treating patients with Invisalign since early 2004.
To perform a power analysis and determine the appropriate sample size for this study, an estimated mean and standard deviation of the results would be required. Because there is minimal scientific literature on the accuracy of clinical expression of overbite using Invisalign, a pilot study was performed on 20 patients to determine the mean and standard deviation. The pilot study found the mean overbite posttreatment was 3.24 ± 1.21 mm and that ClinCheck had estimated a mean overbite of 1.84 ± 0.84 mm. As these measures should be similar, an equivalence testing protocol using two 1-sided t tests and agreement analysis using limits of agreement was used. Based on the results of the pilot study, the sample size of 20 was adequate for the equivalence testing protocol with 90% power assuming an equivalence limit of ±0.5 mm. From this, it was determined to use a sample size of 42 participants to improve the precision of the limits of agreement.
The criteria for inclusion for patients were as follows: (1) aged ≥ 18 years before orthodontic treatment to help eliminate the effects of growth, (2) dual arch Invisalign treatment, (3) completed initial Invisalign treatment with a minimum of 14 aligners, (4) commenced Invisalign treatment from January 2014 using SmartTrack, (5) completed Invisalign treatment before the end of July 2018, (6) availability of pretreatment and progress digital scans, (7) Class I malocclusion (Angle’s classification), (8) overbite >0-8 mm, (9) nonextraction Invisalign orthodontic treatment, (10) the presence of maxillary first and second molars, and (11) patients in which overbite reduction was prescribed in the ClinCheck treatment plan. Exclusion criteria were as follows: (1) the use of vertical elastics, bite ramps, cross elastics, or fixed appliances; (2) poor scans with uncaptured teeth; (3) interproximal enamel reduction was performed; (4) patients who required orthognathic surgery, restorative occlusal or anterior build-ups; (5) patients with identified centric relation-centric occlusion discrepancies or incisal or canine interferences; (6) patients with refinement scans taken 4 weeks after completion of initial clear aligners; (7) uncooperative patients; and (8) patients with deep overbites >8 mm. Patients were considered uncooperative if they presented with poor-fitting aligners and/or required an early refinement scan.
The first 42 patients were chosen via alphabetical order from the orthodontist’s (T.W) Align patient databases that met the inclusion criteria previously described were de-identified by the orthodontist and included in the study. Patient pretreatment, posttreatment, and predicted outcome stereolithography files were exported from ClinCheck and imported into the Geomagic Control X software (version 2017.0.3; 3D Systems, Rock Hill, SC). To eliminate the error of bias, an examiner (H.L.B) was blinded to the patient’s name, gender, and age. To accurately measure overbite depth on the pretreatment, posttreatment, and ClinCheck digital models, the examiner (H.L.B) aligned the digital study models to a horizontal reference plane adapted from Grünheid et al, the midpoint of the superior margin of the incisive papilla and the interproximal papilla between the maxillary first and second molars being used to define the horizontal reference plane ( Fig 1 ). Once the digital models were aligned to the horizontal reference plane, using a vector, the midpoint between the incisal edges of the mandibular left central and lateral incisors and the midpoint of the incisal edge of the maxillary left central incisor were identified ( Figs 2 and 3 ). The vertical linear distance between these 2 points was used to measure the depth of overbite for the pretreatment, posttreatment, and predicted outcome digital models for all 42 patients included in the study ( Fig 4 ).
Statistical analysis
Statistical analyses of all data were performed using Microsoft Excel (Microsoft Office 2016; Microsoft, Redmond, Wash) and Stata (version 14.1; StataCorp, College Station, Tex). The intraexaminer reliability for overbite measurement was tested using the test-retest method of 20 randomly selected patients remeasured 2 weeks apart. The same 20 patients were then used to form the sample for the initial pilot study. Interexaminer reliability of overbite measurements of 10 randomly selected patients was tested by 2 clinicians with experience with Geomagic Control X (version 2017.0.3.69; Geomagic, Morrisville, NC) using the same method described above. The data were analyzed using the interclass correlation coefficient 2-way random-effects model for continuous data. The level of agreement was based on the lower 95% confidence interval value, in which >0.80 is excellent agreement, >0.60 is moderate, and <0.60 is fair-poor reliability.
Two 1-sided t tests were used to test for equivalence in the predicted final overbite by ClinCheck and the actual posttreatment overbite with a clinically relevant difference in measurements being set at 1 mm. A Bland-Altman plot was also used to evaluate the bias between ClinCheck predicted and posttreatment overbite. This was further explored using linear regression with the posttreatment measurement used as the explanatory variable and the difference in measurements as the outcome variable.
Results
A total of 42 patients were included in this study. The results for intraoperator and interoperator error for overbite measurement showed excellent agreement ( Tables I and II ). The mean overbite measurements of the sample population for pretreatment, posttreatment, and predicted outcome (ClinCheck) are displayed in Table III , in which 50% of patients presented with overbites >4 mm pretreatment.
