FEM is a mathematical method in which the shape of complex geometric objects and their physical properties are computer-constructed. However, the finite element method (FEM) described by Zienkiewicz has been used to investigate a wide range of dentistry topics, including tooth structure, biomaterials and restorations, and dental implants and root canals, and may elucidate the reaction of the teeth, periodontal ligament, alveolar bone, etc. Although a variety of traditional analytical and experimental methods for analyzing dental stresses, such as photoelasticity, interferometric holography, and strain gauges, have shed some light on the mechanism of orthodontic tooth movement, they have been unable to clarify the micro-environmental changes around the periodontal ligament (PDL) and within the bone. It is very difficult to measure clinically the stress induced at various locations within the root by different types of orthodontic tooth movement.
That being said, mesial movement of the posterior teeth is known to be more problematic in lingual orthodontics than in the labial technique, as the periodontal stresses generated by orthodontic forces are transferred to the alveolar bone, leading to resorption in compressed regions and apposition where the bone is under tensile stress. This clinical procedure appears to offer better anchorage on the lower posterior teeth than labial treatment, due to the different point of force application. In particular, for aesthetic reasons, the six anterior teeth are generally retracted as a unit in the lingual technique, so as not to create any space between canines and lateral incisors. Nevertheless, lingual appliances have their own peculiar biomechanics, distinct from that of conventional orthodontics, and special care must be taken in their application.
Lingual appliances marked a great leap forward in aesthetic orthodontics, thanks to their unobtrusiveness, and recent improvements in terms of indirect lingual bracket bonding, new archwire materials, and computerized planning systems have made the technique even simpler and more precise. labial bracket placement influences the pattern of tooth movement, but the stress that occurs around the teeth can be accurately mapped using a 3D FEM model. At the premolars and first molars, intrusion, lingual movements, and lingual tipping were seen with the labial archwire, while intrusion was accompanied by labial movements, mesial tipping, and buccal rotation with lingual mechanics. Lingual tipping and extrusion of the anterior dentition occurred with both archwires. The Algor program (Algor Inc., Pittsburgh, PA, USA) was used to calculate the strains and displacements at each nodal point. The type of finite element used in the analysis was an eight-noded brick element. En masse retraction was simulated by applying 300 g of distal force from the canine to the second premolar on the 0.016 × 0.022-in.
SS labial (Tru-Arch form, small size) and lingual (mushroom) archwires. GAC Roth Ovation labial and Ormco 7th Generation lingual brackets were virtually bonded to the lower teeth and threaded with 0.018 × 0.025- and 0.016 × 0.022-in. MethodsĪ 3D FEM of each lower tooth was constructed and located as appropriate to Roth's prescription. The aim of this study was to compare displacements and stress after en masse retraction of mandibular dentition with lingual and labial orthodontics using three-dimensional (3D) finite element models (FEM).