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Journal of Aligner Orthodontics



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Journal of Aligner Orthodontics 2 (2018), No. 4     21. Jan. 2019
Journal of Aligner Orthodontics 2 (2018), No. 4  (21.01.2019)

Page 295-304

Recommendation of a novel film-thickness sequence, 0.4, 0.5 and 0.75 mm, for aligner systems
Elkholy, Fayez / Lapatki, Bernd G.
Objectives: For experimental evaluation of sequential aligner systems, the conventional sequence of aligner thickness (0.5 to 0.8 mm) and a novel sequence using thinner 0.4- and 0.3-mm films were investigated biomechanically in four mechanical in-vitro studies.
Materials and methods: The first two studies focused on determining mechanical loads exerted during labio-palatal translation of a maxillary central incisor and derotation of a mandibular canine when using aligners with conventional thicknesses of 0.5 to 0.75 mm. The third and fourth studies examined the mechanical load during different movements of a maxillary central incisor by use of 0.3- and 0.4-mm novel, thinner aligners. All experiments were performed on specifically designed test setups equipped with acrylic casts from which the corresponding measurement tooth was separated and mounted on a three-dimensional (3D) movement unit via a 3D force-moment (F/M) sensor.
Results: Even for small movements of < 0.5 mm and < 10 degrees, quite high F/M values, up to 8.4 N and 89.2 Nmm, respectively, were recorded for the 0.5-mm aligner. Use of aligners thermoformed from novel 0.4-mm film resulted in mean reduction in force and moment of 35% and 45%, respectively, for translation and rotation of the maxillary right central incisor (tooth 11). Aligners fabricated from 0.3-mm film showed insufficient form stability during repeated seating and removal from the test cast, and should therefore also be unsuitable for clinical application.
Conclusions: When using the thinnest 0.5-mm film, the risk of overloading the periodontal structures is quite high. Based on these in-vitro experiments, a novel aligner thickness sequence is recommended using 0.4-, 0.5- and 0.75-mm aligners. This sequence substantially reduces the F/M values exerted by the first and thinnest aligner and ensures relatively constant load increases for each individual setup step.

Keywords: aligner sequence, aligner thickness, force, orthodontic aligner, overloading