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The 'Roller Coaster Effect' in Clear Aligner Premolar Extraction Cases: Posterior Open Bite and Cephalometric Risk
Yujia Zhuo1, Feng Guo2, Shuai Huang1
1Department of Orthodontics, Nanjing Stomatological Hospital, Affiliated Hospital of Medical School, Institute of Stomatology, Nanjing University, Nanjing, China.
Orthodontics & Craniofacial Research
|May 9, 2026
Summary
The roller coaster effect (RCE) in clear aligner therapy (CAT) premolar extraction cases is most pronounced in mild crowding. Smaller ANB angles and increased incisor proclination are risk factors for RCE, necessitating careful case selection.
Area of Science:
- Orthodontics
- Dental Technology
- Biomedical Engineering
Background:
- Clear aligner therapy (CAT) is increasingly used for orthodontic treatment.
- Premolar extractions are sometimes necessary to manage crowding.
- The roller coaster effect (RCE), characterized by posterior tooth movement, can occur in extraction cases.
Purpose of the Study:
- To investigate the occurrence of RCE in premolar extraction cases treated with CAT.
- To identify cephalometric risk factors associated with RCE in these cases.
Main Methods:
- Retrospective analysis of 65 patients treated with CAT after four first premolar extractions.
- Categorization into mild crowding (Mi) and moderate-severe crowding (Mo-Se) groups.
- Measurement of posterior functional cusp distances (FCDs) on digital models using a 3D coordinate system.
Main Results:
- Post-treatment FCDs increased significantly in the mild crowding group, particularly at the first molars.
- The moderate-severe crowding group showed a smaller increase in FCDs.
- Increased upper incisor proclination and smaller ANB angles were positively correlated with greater FCDs increases.
Conclusions:
- Posterior FCDs are a simple indicator of RCE, most evident in mild crowding cases treated with CAT.
- Smaller ANB angles and increased maxillary incisor proclination are independent risk factors for RCE.
- Prudent case selection is crucial for extraction-based CAT to mitigate RCE.
