Presurgical orthodontic decompensation with clear aligners

Abstract

Introduction: Orthodontists, surgeons, and patients have taken an interest in using clear aligners in combination with orthognathic surgery. This study aimed to evaluate the accuracy of tooth movements with clear aligners during presurgical orthodontics using novel 3-dimensional superimposition techniques.

Methods: The study sample consisted of 20 patients who have completed presurgical orthodontics using Invisalign clear aligners. Initial (pretreatment) digital dental models, presurgical digital dental models, and ClinCheck prediction models were obtained. Presurgical models were superimposed onto initial ones using stable anatomic landmarks; ClinCheck models were superimposed onto presurgical models using surface best-fit superimposition. Five hundred forty-five teeth were measured for 3 angular movements (buccolingual torque, mesiodistal tip, and rotation) and 4 linear movements (buccolingual, mesiodistal, vertical, and total scalar displacement). The predicted tooth movement was compared with the achieved amount for each movement and tooth, using both percentage accuracy and numerical difference.

Results: Average percentage accuracy (63.4% ± 11.5%) was higher than in previously reported literature. The most accurate tooth movements were buccal torque and mesial displacement compared with lingual torque and distal displacement, particularly for mandibular posterior teeth. Clinically significant inaccuracies were found for the buccal displacement of maxillary second molars, lingual displacement of all molars, intrusion of mandibular second molars, the distal tip of molars, second premolars, and mandibular first premolars, buccal torque of maxillary central and lateral incisors, and lingual torque of premolars and molars.

Conclusions: Superimposition techniques used in this study lay the groundwork for future studies to analyze advanced clear aligner patients. Invisalign is a treatment modality that can be considered for presurgical orthodontics-tooth movements involved in arch leveling and decompensation are highly accurate when comparing the simulated and the clinically achieved movements.

Figure 1.

Superimposition of presurgical (yellow) onto the initial (white) DDMs. (A) Landmarks used for upper arch superimposition. (B) Lower arch superimposition of non-extraction cases is completed using 10 landmarks: between molars, the molar and the second premolar, between premolars, between the first premolar and the canine, and between the canine and the lateral incisor on both the right and left sides. (C) Lower arch superimposition of extraction cases is completed using 6 landmarks referencing the buccal frenum attachments.

Figure 2.

ClinCheck^® models (blue) are converted to solids using Meshmixer to eliminate virtual root stumps (A); ClinCheck^® and presurgical (yellow) models are segmented via the DSCI neural networks (B), then superimposed using surface-based best-fit in SlicerCMF (C).

Figure 3.

Placement of landmarks for quantification of tooth movement. (A) An initial (pretreatment) DDM (grey) with five fiducial points placed for each tooth. The molar close-up is showing each of the five fiducials: (1) central occlusal, (2) mid-gingival lingual, (3) mid-gingival buccal, (4) disto-occlusal, and (5) mesio-occlusal. Midpoints between landmarks (2) and (3) are shown in aqua. The same points were then placed for each tooth (consistently at the same location across models) on (B) the presurgical DDM (yellow), and (C) the ClinCheck^® model (blue). After superimposition of the three models (D), the displacement of the landmarks is measured in each model relative to the other two models for each patient.

Figure 4.

Examples of angular measurements: (A) the yaw angle between two lines from the mesial to the distal occlusal landmarks measures clinical crown rotation; (B) the pitch angle between the occlusal and mid-gingival landmarks measures buccolingual angulation; and (C) the roll angle between the occlusal and mid-gingival landmarks measures mesiodistal angulation.

Figure 5.

Median percentage accuracy (A and B) and differences between predicted and achieved (C and D) for each tooth and angular movement types combination. Only points with statistically significant differences between predicted and achieved movements are colored in B and D. The pink dotted line represents the 2.5° clinical significance threshold (C and D). Negative percentages mean the difference between predicted and achieved movements was greater than the predicted movement in magnitude (A and B). Negative numeric differences mean achieved movement was greater than predicted (C and D).

Figure 6.

Median percentage accuracy (A and B) and differences between predicted and achieved (C and D) for each tooth and linear movement types combination. Only points with statistically significant differences between predicted and achieved movements are colored in B and D. The pink dotted line represents the 0.5mm clinical significance threshold (C and D). Negative percentages mean the difference between predicted and achieved movements was greater than the predicted movement in magnitude (A and B). Negative numeric differences mean achieved movement was greater than predicted (C and D).

Figure 7.

Mann-Whitney U test of pooled angular and linear measurements to compare between arches and to compare between opposite directions of the same movement category. Error bars represent 1 median absolute deviation. For the angular measurements, P values are from left to right: 0.0085, 0.0097, <0.0001, 0.0091, <0.0001 (green asterisks). For the linear measurements, P values are from left to right: <0.0001, 0.0111, 0.0030 (blue asterisks), <0.0001, 0.014, 0.0017 (green asterisks), 0.0026, 0.0051.