Research Article| Volume 11, ISSUE 4, P107-113, August 2022

Evaluation of the effectiveness of modified aligner appliance with nickel-titanium springs in treatment of mild crowding of lower incisors: A randomized controlled clinical trial


      • Modified aligner appliances with nickel titanium springs (MAAs) were effective in lower incisor decrowding.
      • Using MAAs did not significantly reduce alignment duration.
      • Using MAAs increased the alignment improvement percentage in the first 6 weeks of treatment.
      • Using MAAs decreased the amount of change in the lower incisor proclination after treatment.



      This study aimed to evaluate the effectiveness of modified aligner appliances with nickel-titanium springs (MAAs) in treating mild mandibular crowding and assess the overall alignment treatment duration, alignment improvement percentage, and mandibular incisor proclination.


      This two-armed, parallel-group randomized controlled trial included 36 patients (7 men, 29 women) with mild mandibular incisor crowding according to Little's Irregularity Index. Patients were randomly assigned to two groups: the MAA group (mean age = 22.56 ± 3.50 years) and the conventional fixed bracket group (control group; mean age = 20.89 ± 2.90 years). The duration of alignment treatment of the lower anterior teeth was calculated. The progress of alignment was evaluated every 2 weeks on the study casts, which were taken at fixed intervals: pretreatment (T0) and 2 (T1), 4 (T2), 6 (T3), and 8 (T4) weeks after beginning the treatment. Change of mandibular incisor proclination was evaluated by measuring and comparing pretreatment and postalignment lateral cephalograms.


      No statistically significant difference was detected between the two groups in terms of alignment treatment duration (P = 0.097), whereas a significant difference was observed in the alignment improvement percentage at T1 (P = 0.000), T2 (P = 0.001), and T3 (P = 0.022). In addition, the MAA group had a lower change of mandibular incisor proclination than the control group (P = 0.000).


      The clinical application of MAAs may be effective in lower incisor decrowding, with a reduction in lower incisor inclination compared with conventional fixed brackets. This trial was registered at (identifier: NCT04988373).


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