Introduction
The purpose of this study was to compare predicted anterior teeth intrusion measurements with the actual clinical intrusion measurements using cone-beam computed tomography. Understanding the precision of the software in anticipating changes may help practitioners predict the need for overcorrection.
Methods
Twenty-two patients, with a mean age of 23.74 years, who underwent Invisalign (Align Technology, Santa Clara, Calif) clear aligners treatment for both arches only after having completed treatment with an initial series of aligners were included in this study. The pretreatment and posttreatment cone-beam computed tomography scans after the initial series were acquired by a single orthodontist practitioner. ClinCheck measurements were recorded with Align Technology. The long axis of the anterior tooth intrusion movement was measured in 142 teeth. A comparison between the predicted and actual measurements of anterior intrusion of the teeth was performed, and the intraclass correlation coefficients showed an almost perfect agreement in the linear measurements.
Results
A statistically notable difference between the predicted and actual measurements of anterior intrusion. The predicted intrusion movement of the maxillary canines ( P = 0.001), maxillary lateral incisors ( P <0.0001), and maxillary central incisors ( P <0.0001) significantly differed from the actual values. Similarly, the intrusion movement in the mandibular teeth seemed to be inaccurate, with significant differences in the mandibular canines ( P <0.0001) and mandibular lateral and central incisors ( P <0.0001).
Conclusions
The mean precision of true anterior intrusion with Invisalign clear aligners was 51.19%, and the mean amount of correction was 48.81%. The use of other supplementary methods of anterior teeth intrusion may be helpful to reduce the rate of midcourse corrections and refinements.
Highlights
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Pre and posttreatment CBCT was measured to evaluate the Invisalign anterior intrusion.
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Dolphin Imaging software was used to measure the anterior intrusion.
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Predicted intrusion movements differed significantly from actual values.
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Auxiliary methods of anterior intrusion may help reduce the need for refinement.
The treatment of misaligned teeth with Invisalign (Align Technology, Santa Clara, Calif) involves the sequential use of software-fabricated, clear plastic aligners that fits over the buccal, palatal (lingual), and occlusal surfaces of the teeth and move specific teeth to their appropriate positions. The appliances are removable and made of 0.75 mm dense polyurethane. Patients are instructed to wear the aligners for a minimum of 20 hours per day on a 1-2 week basis before progressing to the next step. Every aligner is designed to adjust specific teeth by approximately 0.25-0.3 mm. ,
The Invisalign technique is used to manufacture tailored aligners from a very accurate impression or an intraoral 3-dimensional (3D) image scanned in the dental office. This process allows the replication of a patient’s teeth as a 3D model, which can be operated on and practically amended by an orthodontist using advanced propriety software; the treatment designed by the orthodontist is then implemented by Invisalign clear aligners appliances. The ClinCheck (Align Technology) online software program allows clinicians to view virtual models showing a range of conditions from malocclusion to correction in small increments.
The Invisalign clear aligners were initially proposed to treat orthodontic patients of moderate severity. , However, intricate orthodontic case reports of patients who are effectively managed with Invisalign clear aligners treatment are still being published in the literature. The Invisalign clear aligners appliance was recently modified to include the latest treatment alternatives comprising calculated attachments and virtual bite ramps to specifically control movement in the vertical dimension and reduce deep overbites.
Align Technology has developed numerous techniques over the past 17 years to control deep overbites better. Passive optimized deepbite attachments are usually placed on the buccal surface of the first or second premolar to increase retention and provide anchorage for the intrusion of the anterior teeth, whereas active optimized deepbite attachments deliver extrusive forces to the premolars to achieve posterior extrusion and level the curve of Spee. Precision bite ramps operate similarly to anterior bite planes or bite turbos. These bite ramps are placed onto the palatal surface of the maxillary incisors and make contact with the mandibular incisors to separate the posterior teeth as a patient brings his or her teeth together.
In recent years, numerous methods, including the American Board of Orthodontics objective grading system, peer assessment rating systems, and other objective occlusal criteria, have been used by scholars to evaluate the quality of orthodontic treatment with Invisalign clear aligners. The conclusions were that Invisalign clear aligners are not an effective removable appliance for managing overbites, occlusal contacts, occlusal relationship. Although they have some limitations, and they do not explain the etiology of unsatisfactory results in depth.
There are limited studies on the level of inconsistency between the predicted and actual measurements of the movement achieved with Invisalign clear aligners. The average precision of tooth movement in the anterior region was 41% with Invisalign clear aligners. An in-house study from Align Technology found that approximately 80% of the desired tooth movement is achieved, as measured by ClinCheck. To comprehend how the Invisalign clear aligners appliance manages the intrusion of anterior teeth, studies with various sample sizes and sophisticated designs are required.
Most of the studies performed before Invisalign clear aligners launched their SmartTrack material and deep overbite protocol used different methods to evaluate the accuracy of Invisalign clear aligners, such as 2-dimensional (2D) cephalometric and 3D models. The major limitations of these 2 methods are that the contours and shapes change, and a stable anatomic structure is missing. Furthermore, the etiology of unsatisfactory results cannot be determined with these methods. Studies with 3D images can provide valuable information for efficient treatment planning with ClinCheck. For instance, if the precision percentage of a specific tooth movement is known, overcorrecting it by the appropriate amount may result in the desired outcome.
Cone-beam computed tomography (CBCT) allows an orthodontist to rapidly and accurately create patient-specific 3D software models that can be used for diagnoses, treatment planning, and evaluations. Accurate measurements can be made for any part of the anatomy, and the tooth sizes can be measured. Therefore, the true anatomic measurements for each patient can be determined.
Studying treatment results using CBCT can be useful because CBCT scans provide authentic quantitative data permitting images to be compared with accuracy and precision and without magnification. Furthermore, these scans enable volumetric measurements of an object and the assessment of changes in the contours and shapes of objects, which are often limited in 2D cephalometry. In addition, these scans provide more information than 2D images. ,
This study aimed to compare predicted anterior teeth intrusion measurements with the actual clinical intrusion measurements using CBCT. Understanding the precision of the software in anticipating changes may help practitioners predict the need for overcorrection, thereby reducing the need for midcourse modifications and the treatment time.
Material and methods
An endorsement certificate was issued by the Wuhan University Hospital of Stomatology Ethics committee at Wuhan University (no. B20) for this retrospective study. Patients being treated in the Department of Orthodontics in Wuhan University Hospital of Stomatology, Wuhan, China, under the guidance of an experienced orthodontist who certified in Invisalign treatment, were included in this study. The patient’s identification, age, sex, treatment duration, crowding, overbite, and molar relationships, as well as the 5 files required to determine the predicted treatment and achieved treatment (the difference from before and after treatment), were recorded. The study population was composed of 22 patients, including 142 teeth, 12 females and 10 males with a mean age of 23.74 years (range from 16 years to 46 years 8 months). All patients had both arches treated with Invisalign clear aligners only. The average treatment period was 19.27 months (range from 11 months to 29 months). Mild crowding ranged from 0.00 to 3.00 mm in 6 subjects, moderate crowding ranged from 3.00 to 5.49 mm in 14 subjects, and 2 subjects had spacing (3.92-4.76 mm). The overbite status was normal in 8 patients (ranged from 1.80 to <4.00 mm), and 14 patients had a deep overbite with a mean of 4.18 mm (standard deviation, 1.51 mm; range, 4.00-8.50 mm). The Angle classifications of malocclusion were as follows: 19 patients had Angle Class I malocclusion, 2 patients had Class II malocclusion, and 1 patient had a Class III malocclusion. The patients had to wear each aligner for 14 days.
Each patient in this study started treatment in 2016 or later after Align Technology introduced the SmartTrack material and launched their deepbite protocol. This protocol was developed to improve the predictability of deepbite correction with clear aligner treatment via several innovations, including specific pressure areas and optimized deepbite attachments. In this study, we used passive optimized deepbite attachments.
The study focused only on the initial series of aligners. No refinement was included. We defined the inclusion criteria as follows: (1) the patient underwent treatment in both arches, (2) the patient successfully completed treatment with an initial series of aligners, (3) the patient attended their appointments and had good compliance with consistent aligner wear, (4) the patient had a minimum of 1 mm or more of intrusion of the anterior teeth, (5) the patient started treatment in 2016 or later, (6) the treatment plan was nonextraction, and (7) the patient had good-quality pretreatment and posttreatment CBCT scans after the initial series. We defined the exclusion criteria as follows: (1) an initial series of aligners unsuccessfully completed, (2) the absence from appointments or poor compliance, (3) extraction cases or 1 arch extraction, (4) bite ramps or the extrusion of posterior teeth, and (5) missing before or after CBCT scans.
The CBCT scans were obtained by NewTom VGI (Quantitative Radiology, Verona, Italy). The volume data were exported in the DICOM format for Dolphin Imaging software (version 11.95 premium; Dolphin Imaging and Management Systems, Chatsworth, Calif) to perform 3D analysis with reference lines and landmarks for evaluation. In the axial view, each tooth was adjusted from the midpoint of the crown in the buccolingual and mesiodistal directions ( Fig 1 ). In addition, 2 reference planes in the sagittal view on each CBCT scan were used to determine the maxillary anterior teeth palatal plane from the right side to the left side shows the Video 1 , available at www.ajodo.org (plane constructed by projecting a line through points ANS and PNS) ( Fig 2 ) and the mandibular anterior teeth mandibular plane Me-Go from the right side to the left side shows the Video 2 , available at www.ajodo.org (plane between the left gonion, right gonion and menton) ( Fig 3 ). , The CBCT scans taken before and after the treatment were superimposed to assess the reference planes and landmarks positions. The linear measurements included the UT-PP, expressed as the distance in millimeters from the intersection point between the palatal plane and tip of the maxillary anterior teeth ( Fig 2 ). The LT-MP was defined as the distance in millimeters from the intersection point between the mandibular plane and tip of the mandibular anterior teeth ( Fig 3 ).
