Evaluation of the Rate of En-masse Retraction in Orthodontic Patients with Maxillary Protrusion Using Friction versus Frictionless Mechanics: A Randomized Clinical Trial

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Abstract Background The purpose of this 2-arm parallel study was to compare the rate of en-masse retraction using friction versus frictionless mechanics. Anchorage loss, molar rotation, changes in the incisor position, and pain was additionally assessed. Methods Twenty-eight patients were randomly allocated into two en-masse retraction groups using friction or frictionless mechanics. Eligibility criteria included maxillary dentoalveolar protrusion requiring maxillary 1st premolars extraction with maximum anchorage. Randomization was done in a 1:1 allocation ratio into either friction (A) or frictionless (B) groups. In group A, power-chains of 200 g retraction force on 0.017” x 0.025” st.st archwire were utilized. Group B comprised of T-loops using the same gauge TMA archwires and comparable force. Measurements were made on scanned 3D models, superimposed on one another, as well as pre-treatment and post-retraction cephalograms. Results It was a single-blinded study where the outcome assessors were blinded. For the friction group, the rate of retraction was 0.63 ± 0.18 mm per month, with a total retraction of 4.04 ± 1.41 mm spanning over 6.42 ± 1.08 months. The frictionless group was 0.75 ± 0.23 mm per month with a total retraction of 4.13 ± 1.44 mm, over 5.67 ± 1.5 months. Conclusion Frictionless mechanics was only slightly faster than friction mechanics regarding the rate of retraction, not enough to make a significant difference between the two groups. Frictionless mechanics is not recommended in cases with great anchorage needs, as the molars tend to move and rotate mesially during retraction, regardless of the presence of miniscrews. Trial registration: Trial was registered on clinicaltrials.org, with the reference number NCT04902430.

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