Curve of Spee Leveling by Using Three Different Clear Aligner Systems: A Comparative Analysis

Aim: To evaluate the leveling of the curve of Spee (COS) of the lower arch in deep-bite patients by using three different clear aligners: Invisalign® Align Technology® Inc. (Santa Clara, CA, USA), Spark™ Clear Aligner System Ormco™ (Brea, CA, USA) and Angel Aligner™ Technology Inc. (Shanghai, China). Material and Methods: Sixty-nine patients were selected based on specific criteria and subdivided in three different groups based on clear aligner systems used for their treatment: Invisalign® Aligner (I group), Spark™ Clear Aligner (S group), and Angel Aligner™ (A group). All patients were treated from 2021 to 2025 by the same orthodontist with extensive experience in the aligner technique, following a standardized protocol for deep-bite resolution. The STL files of the lower arch were analyzed using MeshLab software at three specific time points: pre-treatment (ID), post-treatment (AC), defined as the result achieved after the first set of aligners, and digital planning (EC). In all three groups, the differences between AC-ID and EC-AC were examined by means of the T-test; intergroup variations were also compared using the ANOVA test. Results: The study revealed that aligners were only minimally effective at leveling the COS. The planned dental movements were not fully achieved, leading to a low accuracy of the treatment. The highest mean accuracy was detected in the Angel Aligner™ group (39%). Conclusions: The clear aligner treatment for leveling the COS presents limits in terms of biomechanics of the device. The study shows that no clinically and statistically significant differences emerged across the three systems used.