ABSTRACT
Objective To study the effects of different root control attachment on root control and periodontal ligament （PDL） stress during canine distal translation in plastic aligner-based orthodontic treatment. Methods Through three-dimensional (3D) finite element technology, 11 models composed of 4 attachments and 3 kinds of loading were established. Namely, attachment A: no attachments; attachment B: traditional vertical rectangular attachment; attachment C: 1/4 spherical double optimized attachment; attachment D: double optimized door arch attachment; load a: 0.15 mm distal translation of the canine; b: load a+ application of 30 N·mm counterclockwise torque to stress surface of the attachment; load c: load a+ application of 30 N·mm counterclockwise torque to the entire crown. The root control effect of distal translation of the right maxillary canine was simulated with plastic aligner under different loads. Results Displacement modes of all models were distally tipped translation. The double optimized door arch attachment showed the optimal root control effect during canine distal translation. The root control effect for two groups of double optimized attachment was better than that of traditional rectangular attachment. The effect of adding attachments on root control of the canine was better than that of applying only counterclockwise couple. The PDL stress mainly appeared in distal alveolar ridge and root apex without attachment, while the PDL stress mainly appeared in distal alveolar ridge with attachment. Conclusions The most suitable measure to improve the effect of root control during canine distal translation is to use the double optimized door arch attachment in clinic.
ABSTRACT
Objective To study the influence of different moment-to-force ratios (M/F) and forces on canine displacement and periodontal ligament (PDL) stress. Methods A three-dimensional (3D) mandibular model was established based on CT images. The orthodontic force systems without a moment and with various M/F were applied to the canine for numerical calculation of its translation. An optimum force system to realize canine translation was validated by analyzing translation displacement of the canine in each case. Results The PDL stress increased with an increase in force magnitude in all cases. The PDL stress first decreased with an increase in the M/F before the M/F reached the optimum value (M/F=10.1 mm), and then increased with an increase in the M/F. The initial displacement of the canine was inclined movement, which was most close to translation when the precise optimum M/F was applied. Conclusions The canine movement requires an appropriate force to prevent root absorption, whereas the translation movement requires an optimal M/F value which is within the physiological range. Understanding the influence of force and moment on tooth translation can help to apply more reasonable orthodontic force system and design more reasonable orthodontic device.