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Introduction: The purpose of this research was to provide an update on the accuracy of tooth movement with Invisalign (Align Technology, Santa Clara, Calif). Methods: This prospective clinical study included 38 patients treated with Invisalign Full or Invisalign Teen. All teeth, from the central incisor to the second molar, were measured on digital models created from intraoral scans. Predicted values were determined by superimposing the initial and final ClinCheck models, and achieved values were determined by superimposing the initial Clin-Check models and the digital models from the posttreatment scans. Individual teeth were superimposed with a best-fit analysis and measured using Compare software (version 8.1; GeoDigm, Falcon Heights, Minn). The types of tooth movements studied were a mesial-distal crown tip, buccal-lingual crown tip, extrusion, intrusion, and mesial-distal rotation. Results: The mean accuracy of Invisalign for all tooth movements was 50%. The highest overall accuracy was achieved with a buccal-lingual crown tip (56%), whereas the lowest overall accuracy occurred with rotation (46%). The accuracies for mesial rotation of the mandibular first molar (28%), distal rotation of the maxillary canine (37%), and intrusion of the mandibular incisors (35%) were particularly low. Conclusions: There was a marked improvement in the overall accuracy; however, the strengths and weaknesses of tooth movement with Invisalign remained relatively the same.

Objective: To evaluate the influence of attachments and interproximal reduction on canines undergoing rotational movement with Invisalign. Materials and Methods: In this prospective clinical study, 53 canines (33 maxillary and 20 mandibular) were measured from the virtual TREAT models of 31 participants treated with anterior Invisalign. The pretreatment virtual model of the predicted final tooth position was superimposed on the posttreatment virtual model using ToothMeasure, Invisalign's proprietary measurement software. A one-way analysis of variance (ANOVA) (P Ͻ .05) compared three treatment modalities: attachments only (AO), interproximal reduction only (IO), and neither attachments nor interproximal reduction (N). Student's t-tests (P Ͻ .05) compared the mean accuracy of canine rotation between arches. Results: The mean accuracy of canine rotation with Invisalign was 35.8% (SD ϭ 26.3). Statistical analyses indicated that there was no significant difference in accuracy between groups AO, IO, and N (P ϭ .343). There was no statistically significant difference (P ϭ .888) in rotational accuracy for maxillary and mandibular canines for any of the treatment groups. The most commonly prescribed attachment shape was the vertical-ellipsoid (70.5%). Conclusions: Vertical-ellipsoid attachments and interproximal reduction do not significantly improve the accuracy of canine rotation with the Invisalign system.

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