The 'roller coaster effect' in premolar extraction cases: clear aligners vs. straight-wire appliance

Area of Science:

• Orthodontics
• Dental Biomechanics

Background:

• The 'roller coaster effect' (RCE) is a challenging phenomenon in orthodontic treatment.
• Quantifying RCE in premolar extraction cases treated with clear aligner therapy (CAT) or straight-wire appliance (SWA) is crucial for understanding treatment outcomes.

Purpose of the Study:

• To quantitatively investigate and compare the roller coaster effect (RCE) in patients undergoing premolar extraction treated with CAT versus SWA.
• To identify potential factors influencing RCE in these treatment modalities.

Main Methods:

• Inclusion of protrusion cases with bilateral first premolar extraction.
• Measurement of the bending angle of the occlusal plane (BAOP) using pre- and post-treatment cephalograms to quantify RCE.
• Comparison of BAOP changes between the CAT and SWA groups.

Main Results:

• Both CAT and SWA groups showed a significant decrease in maxillary BAOP, with a greater reduction in the CAT group.
• The SWA group exhibited no significant change in mandibular BAOP, while the CAT group showed a significant decrease.
• Post-treatment BAOP was significantly lower in the CAT group compared to the SWA group for both dentitions.
• Mandibular canine crown length was positively correlated with post-treatment mandibular BAOP in the CAT group.

Conclusions:

• Clear aligner therapy (CAT) results in a more pronounced roller coaster effect (RCE) in premolar extraction cases compared to straight-wire appliance (SWA) treatment.
• The bending of the anterior occlusal plane significantly contributes to RCE in the CAT group.
• Longer mandibular canine crown length may serve as a mitigating factor for mandibular RCE in patients treated with CAT.