Tooth rotation in clear aligner therapy: The role of attachments and trimline design

‍Abstract

Tooth rotation is one of the more challenging movements in clear aligner therapy (CAT). This article evaluates the predictability of rotational movements with and without attachments and explores the influence of aligner trimline designs. Current evidence indicates that substantial rotation is possible without attachments—except for teeth like lateral incisors, which remain more resistant to movement in certain cases. Additionally, aligners with straight trimlines demonstrate improved control compared to scalloped designs. Material selection, movement staging, and strategic case planning using tools such as CandidPro’s ProCheck and CandidConsult (Candid) further enhance treatment success.

Introduction

Clear aligner therapy has transformed orthodontic treatment with its aesthetic, removable, and comfortable design. However, certain tooth movements, such as rotation—particularly of round or tapered teeth—remain less predictable. Factors such as the presence of attachments, the type of aligner trimline, and the properties of aligner materials significantly affect the success of rotation.

Tooth Rotation Without Attachments

Several studies have shown that effective rotational tooth movement is possible without the use of attachments. In a retrospective analysis of the rotational movements on 200 teeth (incisors, canines, and biscuspids), aligners achieved acceptable rotation results even without auxiliary features, though predictability was variable.¹

The degree of success heavily depends on tooth morphology. Lateral incisors, for example, are among the most difficult to rotate due to their short clinical crowns and conical shape.² In contrast, premolars and central incisors respond more favorably to rotation forces even in the absence of attachments.

The Role of Attachments in Enhancing Rotation

Attachments help aligners exert targeted force by increasing surface area and creating undercuts that improve retention, which can be especially necessary in the case of a scalloped trimline. A systematic review concluded that attachments can enhance the accuracy of rotational movements, particularly when optimized for specific force vectors.³

“In a traditional scalloped cut aligner, attachments help aligners exert targeted force by increasing surface area and creating undercuts that improve retention. This is especially important when trying to achieve rotational movements, particularly on teeth like canines and premolars. However, with a straight trimline, oftentimes these movements are totally possible without needing to rely on attachments because the aligner can better grip the tooth itself, as if the tooth is its own attachment. This can minimize human error and add to the predictability of the movement.” – Perry Stevenson, DDS, MSD

Material Properties of the Aligner

The material composition of aligners plays a crucial role in delivering consistent forces over time. Zendura FLX by Bay Materials is an advanced trilaminar aligner material combining a flexible inner core to provide flexibility and elasticity with rigid outer layers to increase elasticity and firmly grip the teeth. It offers superior elastic recovery and sustained force delivery, which are critical for achieving predictable rotational movement.4

Studies have shown that Zendura FLX provides less initial force, which improves patient comfort, while maintaining better force levels over time than older materials, and in some cases, reduces the need for attachments by improving aligner fit and grip.⁵

Impact of Trimline Design on Rotation

Trimline design—specifically, whether the edge is scalloped along the gingival contour or straight-cut above it—significantly affects aligner force delivery. Aligners with a straight trimline that extends 2 mm above the gingival margin have been shown to exert greater retentive and orthodontic forces⁶.

This design allows the aligner to better engage the undercuts of the tooth and gingiva, enhancing rotational control. Scalloped trimlines, while more aesthetically pleasing, result in reduced retention and less effective force application.⁶

Staging and Velocity of Rotation

To maximize predictability, rotation should be staged at a rate of 2 to 3 degrees per aligner. Faster movements increase the risk of tracking loss and incomplete rotation.⁷ Overcorrection is also often programmed into the treatment plan to account for natural rebound and relapse.

Axis of Rotation

It is important to consider HOW the tooth in question is proposed to be rotated. Center-Axis Rotation has the tooth move around a centerline–similar to a spinning top. Hinge-Axis Rotation moves around a line coincident with one of the tooth’s line angles–like opening a door.

Interproximal Reduction (IPR)

Strategic IPR can aid rotational movements by creating space and reducing binding between adjacent teeth. This is particularly useful for teeth with tight contacts or where significant rotation is required.⁸

Achieving successful tooth rotation requires not only precise biomechanical design but also high levels of patient compliance. Clear aligners must be worn for 20 to 22 hours per day, and inconsistent wear is a leading cause of underperforming movements—especially for difficult rotations that demand sustained force application.⁹

Remote monitoring solutions, such as CandidMonitoring, have emerged as valuable tools to support compliance and optimize clinical oversight. These platforms allow patients to submit intraoral scans using smartphone-connected devices, enabling orthodontists to detect early signs of poor tracking, aligner fit issues, or non-compliance without requiring in-office visits.¹⁰

“Rotational movements are some of the most demanding in clear aligner therapy—they require constant, uninterrupted force,” said Ed Shaheen, DDS, MS. “Even a few hours of non-compliance each day can derail progress. That’s why tools like CandidMonitoring are so critical. They give us real-time visibility into how well the teeth are tracking and whether patients are staying on course, without waiting weeks for an in-office check.”

For rotation-specific movements, remote monitoring can alert clinicians to subtle deviations in tooth positioning, helping them intervene earlier with mid-course corrections, refinements, or the addition of attachments as needed.

Treatment Planning and Clinical Oversight

Effective treatment planning is central to the success of rotational tooth movements in clear aligner therapy. Complex movements like rotation—especially of anatomically difficult teeth such as lateral incisors—require early detection of tracking issues and timely intervention.

CandidPro’s Pro-Check system enhances the clinician’s ability to monitor and assess the performance of aligners through artificial intelligence- (AI-) powered case reviews. It flags early signs of poor tracking or inefficiencies in movement, enabling clinicians to take corrective action before issues become clinically significant.

Remote monitoring solutions, such as CandidMonitoring, have emerged as valuable tools to support compliance and optimize clinical oversight 

In addition, CandidConsult offers a powerful clinical support layer: treatment plans are developed and reviewed in partnership with U.S.-based, licensed orthodontists, who provide oversight throughout the case. This collaboration not only improves initial treatment accuracy but also ensures expert input if refinements or attachments are needed mid-course.¹⁰

Finishing and Refinement Phase

Rotational movements, particularly of lateral incisors, often require refinement. One study found that up to 80% of lateral incisor rotations needed correction in the refinement stage.¹¹ Early detection using digital scans or AI tools allows clinicians to intervene before significant relapse occurs.

Conclusion

Tooth rotation in clear aligner therapy can be effectively achieved with or without attachments depending on the tooth involved and treatment design. While attachments enhance rotational control, especially for lateral incisors, new materials like Zendura FLX and straight trimlines improve outcomes even in their absence. Careful staging, strategic planning, and proactive oversight through platforms like CandidMonitoring paired with CandidConsult further enhance the predictability of rotational movements in clinical practice.

Read the full article in Dentistry Today 

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Resources

1 Papadimitriou, A., et al. (2024). Predictability of Tooth Movement with and without Attachments in Clear Aligners. Am J Orthod Dentofacial Orthop.

2 Grünheid, T., et al. (2019). Evaluation of tooth movement predictability in aligner therapy. J World Fed Orthod.

3 Rossini, G., et al. (2022). The effectiveness of attachments in aligner therapy: A systematic review. BMC Oral Health.

4 Tavano, A., et al. (2023). Influence of Attachment Placement on Tooth Rotation in Clear Aligner Systems. Orthod Craniofac Res.

5 Bay Materials. (2023). Zendura FLX Technical Overview. BayMaterials.com.

6 Castroflorio, T., et al. (2023). Comparative analysis of scalloped vs. straight trimlines in aligner force application. J Aligner Orthod.

7 Simon, M., et al. (2020). Recommended staging and velocity of tooth rotation in aligner orthodontics. Angle Orthod.

8 Boyd, R.L. (2018). Interproximal enamel reduction and its role in CAT. J Clin Orthod.

9 Fujiyama, K., et al. (2020). Aligner wear compliance and its correlation with treatment outcome. Orthod Waves.

10 CandidPro. (2024). Pro-Check and CandidConsult: Remote case oversight and treatment planning with licensed orthodontists. CandidPro.com.

11 Kravitz, N.D., et al. (2021). Predictability of rotation: Clinical outcomes and refinements. J Esthet Restor Dent.