Efficiency and side effects of a novel method for maxillary central root torque (a horizontal box loop of round wire) in comparison with the conventional rectangular wire: A finite element study

Abstract

Applying root torque using conventional methods (rectangular wire) has side effects such as inverse and destructive forces, undesirable torque on adjacent teeth, heavy forces that are limited in range and duration, and needing too many sessions. We introduce a new method (a horizontal box loop [HBL]) that is designed to reduce many of these side effects; we tested its efficiency and side effects using finite element analysis. An HBL was created from a 0.018-in round stainless steel archwire, in the form of an equilateral triangle of 7mm sides, for the permanent maxillary left central incisor. As a control, a SS rectangular wire (19×25-in) was used. First, a pilot simulation was performed to standardize the torque in both models as 31.099Nmm. The extent of twisting by the rectangular wire, of which the same amount of moment would be applied, was estimated at 28.282°. The main study evaluated the effects of the 31.099N.mm moments applied by both models to the left central incisor on stresses, dental movements (buccolingually, mesiodistally, and extrusive or intrusive), and intercanine or intermolar widths. Under standardized conditions, the HBL causes a greater palatal root torque of the central incisor than the rectangular wire. The HBL does not apply reverse root torque on adjacent teeth, whereas the rectangular wire causes reverse root torque in neighboring teeth. The HBL also causes less extrusion and expansion in the molar area than does the rectangular wire. The HBL increases intercanine width, whereas the rectangular wire might not change it. HBL of round wire seems an appropriate appliance and hence its clinical assessment is recommended.