Third-order torque and self-ligating orthodontic bracket-type effects on sliding friction

Area of Science:

• Orthodontics and Dental Mechanics
• Biomaterials Science

Background:

• Kinetic friction is a critical factor in orthodontic treatment efficiency.
• Self-ligating brackets aim to reduce friction compared to conventional ligation.
• Understanding the impact of third-order torque on bracket friction is essential for optimizing treatment.

Purpose of the Study:

• To investigate how third-order torque influences kinetic friction in active and passive self-ligating brackets during sliding mechanics.
• To compare frictional forces across different bracket systems under varying torque conditions.

Main Methods:

• Quantified wire-slot frictional forces in five bracket/tube sets within a simulated posterior dental segment.
• Applied torque ranging from -15 to +15 degrees to the second-premolar bracket.
• Pulled a working archwire through the bracket slots to measure friction.

Main Results:

• Increasing torque from 0 to +/-15 degrees significantly elevated frictional resistance across all bracket sets.
• At low torque (0 to +/-5 degrees), passive self-ligating brackets exhibited less friction than active ones; conventional elastomeric ligation showed the highest friction.
• At higher torque (+/-10 to +/-15 degrees), wire-slot clearance was reduced, leading to similar or significantly increased frictional resistances, depending on bracket design and specific torque values.

Conclusions:

• Third-order torque substantially increases frictional resistance in self-ligating brackets during archwire sliding in posterior dental segments.
• Passive self-ligating brackets offer lower friction than active ones at lower torque angles, though bracket design plays a role.
• Substantial friction occurs irrespective of ligation type when wire-slot torque exceeds the bracket's third-order clearance.