Rate Limiting Teeth in Clear Aligner Therapy

The staging of clear aligner treatment can be affected by many factors. Staging is the path of tooth movement and sequence necessary to avoid collisions and sufficient force per aligner. It determines the number of aligners created for treatment and can affect the timing of attachments, force features, and interproximal reduction. When the software determines the number of stages of a clear aligner treatment plan, we have to consider the amount of movement determined by the final tooth positions and the concept of the rate-limiting teeth. The rate limiting teeth more often dictate the total number of stages in the digital treatment plan.

Multi-tooth Staging

As teeth travel from their initial presentation to the desired result, we manage adjacent intra-arch and occlusal collisions. We design treatment with a clear aligner system setting the end goal and the movement path during the aligner therapy. That path is rarely linear, and CAD software will manage it using a multi-tooth staging algorithm. The linear and rotational movements of many teeth in the arch will involve dynamic staging while opening visible space or interproximal reduction to handle collisions.

Staging Visualization

Treating doctors can visualize the staging on the ClinCheck software staging panel. These patterns can vary and follow some treatment protocols, and the most common staging pattern is simultaneous staging. Although all teeth move simultaneously, the multi-tooth staging process can involve many different paths of tooth movement at the same time. The TREAT software manages this with the Invisalign System, and technicians can manually adjust staging patterns.

The Rate Limiting Tooth

The rate-limiting tooth determines the total number of stages in a single arch. Taking note of the tooth with the most significant movement helps doctors determine why the number of aligners is higher or lower than expected. The ClinCheck tooth movement table underlines the leading tooth in the arch. Reducing the movement on the rate-limiting tooth will decrease the number of aligners. Increasing linear or rotational changes within the arch will increase the number of aligners when the rate-limiting tooth is affected.

Tooth Movement Assessment and the Rate Limiting Tooth

The TMA can be a helpful tool to reduce noise during the systemized ClinCheck review and preparation. It is a graphical display of tooth movement data without loading the tooth movement table. For many doctors, it can help guide decisions to give focus and attention to tooth movements of greater magnitude and ensure proper force systems. The TMA will highlight severe movements (>1mm) in black and moderate changes (0.5-1 mm) in blue.

In the latest update of ClinCheck Pro, the Tooth Movement Assessment (TMA) tool can reveal the rate-limiting tooth within the graphical interface. Hovering the cursor over the leading movements tool will summarize the relevant movements in a pop-up display along with the movement assessment available with the TMA tool. This visualization can help highlight the tooth that has the most significant impact on the staging of the treatment plan. Any modification in the magnitude of movement to this leading tooth will affect the number of stages. This new release will help us treatment plan staging better without manually requesting a specific number of aligners.