Controlling incisor torque with completely customized lingual appliances.

Area of Science:

• Orthodontics
• Biomechanical analysis
• Dental imaging

Background:

• Accurate control of tooth movement is crucial in orthodontics.
• Understanding the relationship between the center of rotation (CROT) and center of resistance (CRES) is essential for predictable outcomes.
• Angle class II division 2 malocclusions present unique challenges for incisor retraction.

Purpose of the Study:

• To evaluate the deviation between the CROT and CRES during space closure in Angle class II division 2 subjects.
• To assess the efficacy of a completely customized lingual appliance (CCLA) with class II elastics and elastic chains in controlling incisor movement.
• To test the null hypothesis of no significant difference between CROT and CRES.

Main Methods:

• Retrospective study of 29 Angle class II division 2 patients treated with a CCLA.
• Maxillary incisor root inclination assessed via X-ray superimpositions before and after treatment.
• CROT determined by incisor axis intersection; CRES defined at 36% of incisor length.

Main Results:

• The null hypothesis was rejected, with a significant mean CROT-CRES difference (52.6%, p < 0.001).
• The mean CROT was located significantly incisal to the CRES (88.6% of incisor length).
• Most CROT positions (93.1%) were between the alveolar crest and incisal edge, or beyond.

Conclusions:

• CCLA treatment in Angle class II division 2 cases results in a significant deviation between CROT and CRES.
• CCLAs can achieve palatal root torque of upper incisors, even when forces are applied incisal to the CRES.
• This suggests effective control over incisor inclination during space closure with this appliance system.