Variable Torque Prescription: State of Art.

Abstract

The variable prescription is widely described under the clinical aspect: the clinics is the result of the evolution of the state-of-the-art, aspect that is less considered in the daily literature. The state-of-the-art is the key to understand not only how we reach where we are but also to learn how to manage propely the torque, focusing on the technical and biomechanical purpos-es that led to the change of the torque values over time. The aim of this study is to update the clinicians on the aspects that affect the torque under the biomechanical sight, helping them to understand how to managing it, following the “timeline changes” in the different techniques so that the Variable Prescription Orthodontic (VPO) would be a suitable tool in every clinical case.

Biomechanical Effects of Torquing on Upper Central Incisor with Thermoplastic Aligner: A Comparative Three-Dimensional Finite Element Study with and Without Auxillaries

“…Biomechanically, the torque is represented by the torsion of a rectangular archwire in the bracket slot. 3 The earliest forms (first generation) of aligner systems were solely reliant on the aligner to achieve their results. No auxiliary elements were incorporated.…”

“…For simulation of the involved structures, their physical characteristics were determined in the following manner: Alveolar bone: A linear elastic, isotropic, and homogeneous behaviour was assumed and mechanical properties were obtained from cancellous bone values taken from previous studies. Differences in rigidity between different bone types were not contemplated, as they were not considered relevant to the objectives of the study (Young modulus of 1.37 × 10 3 ). Teeth: A linear elastic, isotropic, and homogeneous behaviour was assumed and mechanical properties were obtained from previous studies. Differences in rigidity among enamel, dentin, and cement were not contemplated, as they were not considered relevant to the objectives of the study (Young Modulus of 1.96 × 10 4 ). Composite attachments: Assumed as an isotropic homogeneous linear elastic behaviour, with mechanical properties referred by the manufacturers (Filtek TMP60, 3M ESPE, 3M, St. Paul, MN) (Table 1).…”

“…Differences in rigidity among enamel, dentin, and cement were not contemplated, as they were not considered relevant to the objectives of the study (Young Modulus of 1.96 × 10 4 ). Composite attachments: Assumed as an isotropic homogeneous linear elastic behaviour, with mechanical properties referred by the manufacturers (Filtek TMP60, 3M ESPE, 3M, St. Paul, MN) (Table 1). Their location, size, and shape were determined by simulating attachments designed for root control (optimized root control attachments) (Young’s modulus of 12.5 × 10 3 ). Periodontal Ligament (PDL) Assumed to be a nonlinear isotropic elastic and homogeneous material, with a stress–strain function based on the data reported in Toms and Eberhardt. Thermoplastic aligner: A linear elastic, isotropic, and homogeneous behaviour was assumed. The value of Young’s Modulus was established after performing compression tests (using an Instron Universal Testing Machine) on flat samples extracted from a plastic aligner.…”

Fracture strength of monocrystalline and polycrystalline ceramic brackets during archwire torque

“…While there is currently a great range of prescriptions available to the orthodontist 10 , including prescriptions customized for each case 11 , one should still apply archwire torsion forces to obtain the desire torque 12,13 . Some studies have shown that the application of high torque (third-order folds) can fracture ceramic brackets 7,[14][15][16] .…”

“…Ceramics have high friability (no plastic deformation), but also have a high resistance to weariness and corrosion and excellent optical properties 6 . Several factors can influence the torque during orthodontic mechanics, which include the torsion magnitude, wire composition and thickness, slot size and depth, vertical positioning, and bracket 17,18 . This phenomenon occurs more frequently in anterior teeth 10,16 and at the base of the bracket wings, where most tension is present, due to archwire torsion forces inside the slot 19 . The addition of wires and accessories may induce the development and propagation of cracks in the brackets 19 .…”