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Tip back bend in continuous archwire: 3d analysis using finite element method
Abstract
Aim: In spite of different straight wire techniques now available in market, wire bends are still important in daily clinical practice of orthodontics. The main goal of this study was to analyze the effects of different tip back configurations on their force system Material and Method: Six three-dimensional (3D) finite element models were designed. Each model contained a mandibular first molar and was designed with a buccal tube attached to its buccal surface, a segment of rectangular wire 0.4x0.55 mm2 of stainless steel in different designs. Loops were a simple tip back bend, an inverse helix, a vertical loop activated by diverging legs, a vertical loop with equal legs (= 2.5 mm), a vertical loop with a short mesial leg, and a vertical loop with long mesial leg. Tooth occlusal surface was considered to be flat to ease calculations Each model was transferred to the ANSYS Workbench Version 10 Displacements were derived numerically in the level of the mesial and distal marginal ridges to show the differences in the reaction of the molar occlusal table nodes. Vertical displacements were assessed in four parallel planes medio-laterally in molar. In each plane 4 nodes were considered in equal distances mesio distally. Results: Extrusion decrease order is: Apically Activated (1.17) > Simple tip back (1)> Mesial Short (1.05) > Inverse Helix(0.53) > Equal leg(0.49) > Mesial long (0.49) Intrusion decrease order: Simple tip back = Inverse helix (=1) > Mesial Long (0.44) > Equal leg (0.31)> Apically Active (-0.4)> Mesial short (-0.98) Conclusion: Apically activated loop is suggested for bite opening due to higher extrusion in mesio-buccal and lack of intrusion. The highest intrusion in distal side of the teeth is produced by simple tip back.The simple tip back is suggested for anchorage control.
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The aim of this study was to investigate the stress components (S1 and S3) that appear in the periodontal membrane (PDM), when subjected to transverse and vertical loads equal to 1 N. A further aim was to quantify the alteration in stress that occurs as alveolar bone is reduced in height by 1, 2.5, 5, 6.5, and 8 mm, respectively. Six three-dimensional (3D) finite element models (FEM) of a human maxillary central incisor were designed. The models were of the same configuration except for the alveolar bone height. Special attention was paid to changes of the stress components produced at the cervical, apical, and sub-apical levels. In the absence of alveolar bone loss, a tipping force of 1 N produced stresses, which reached 0.072 N/mm2 at the cervical margin, up to 0.0395 N/mm2 at the apex and up to 0.026 N/mm2 sub-apically. In the presence of 8 mm of alveolar bone loss, the findings were -0.288, 0.472, and 0.722 N/mm2, respectively. Without bone loss, an intruding force of the same magnitude produced stresses of -0.0043, -0.0263, and 0.115 N/mm2, respectively, for the same areas and sampling points. In the presence of 8 mm of alveolar bone loss the findings were -0.019, -0.043, and 0.185 N/mm2 for intrusive movement. The results showed that alveolar bone loss caused increased stress production under the same load compared with healthy bone support (without alveolar bone resorption). Tipping movements resulted in an increased level of stress at the cervical margin of the PDM in all sampling points and at all stages of alveolar bone loss. These increased stress components were found to be at the sub-apical and apical levels for intrusive movement.
Clinical effects of forces applied by dental occlusion on the periodontium have been evaluated for decades. Historically, trauma from occlusion has been considered as a major etiologic factor of inflammatory periodontal diseases, while some researchers have interpreted it to be of less importance or without any detectable importance in periodontics. In this study, five three-dimensional models of a maxillary central incisor were created using ANSYS 5.40. The only difference in each model was the height of the alveolar bone that showed from normal height (13 mm of alveolar bone height) to 8 mm of alveolar bone loss (5 mm of alveolar bone height). Five-point forces of 0.3 N summing up to 1.5 N were applied in a parallel line, 1 mm apical to the incisal edge on the palatal side in a palatolabial direction. The maximum (S1) and minimum (S3) principal stresses in the nodes of the labial side of the periodontal ligament (apical to the alveolar crest) were assessed. Analysis was done using the finite element method. An increase of S1 (up to 16 times in the cervical and 11.25 times in the apical area) and S3 (up to 17.13 times in the cervical and 9.9 times in the apical area) in comparison to the normal model was shown. The highest stress levels were traced in the subcervical area, except for the last model (8 mm of the alveolar bone loss). According to the results of this study, 2.5 mm of alveolar bone loss can be considered as a limit beyond which stress alterations were accelerated. Based on the FEM analysis, alveolar bone loss increases stress (S1 and S3) produced in the PDL, in spite of applying the same force vector.
Statement of problemThe optimal method of implant support for a single mandibular molar crown is controversial because commonly used, threaded, root-form implants developed by Branemark were not originally designed to support individual crowns.PurposeThe purpose of this study was to develop a finite element model of a single mandibular first molar crown supported by (1) a standard 3.75-mm–diameter implant, (2) a 5-mm, wide-diameter implant, and (3) double standard-diameter implants, and to compare the induced displacements as a result of various loading conditions.Material and methodsThree-dimensional finite element models were made to simulate the 3 single-molar implant designs. Each model was analyzed with 2 force magnitudes (35 N and 70 N) and with 2 force directions (vertical and 15 degrees to the vertical axis). Displacements in 3-dimensional space as a result of the simulated loading conditions were evaluated along 3 primary axes, mesiodistal, faciolingual, and superior-inferior.ResultsMesiodistal and buccolingual displacements for the crown supported by the 5-mm–diameter implant were reduced by approximately 50% compared with the crown supported by the 3.75-mm implant when the crowns were loaded at the distobuccal cusp tip or the distal marginal ridge. The double-implant design recorded the least mesiodistal displacement with off-center loading of the crown.ConclusionWhen the crown was loaded off-center, the double-implant design produced substantially less displacement when compared with either of the single-implant designs.
The force system generated by a simple V bend in a straight wire was studied by means of the principles for small deflection of a beam and a model developed for the description of the forces and moments. The relationship between the size of the bend and the interbracket position on the force system developed is analyzed and discussed in relation to clinical problems. The parallel between positioning of a V bend and the "geometries" developed between a straight wire and angulated brackets is drawn. Four principally different force systems could be developed by the V bend and a method for the predetermination of the force systems is provided. The general principles are exemplified for wires with different moduli of elasticity, varying materials, and cross-sectional dimensions. Stainless steel and beta titanium (TMA) wires in dimensions of 0.16 inch and 0.017 x 0.025 inch are given as examples.
The force system produced by wires with steps and V bends was studied analytically by means of a small deflection mathematic analysis. Characteristic force relationships were found in both the step and the V bend. Step bands centrally placed between adjacent brackets produce unidirectional couples that are equal in magnitude. Along with these couples, vertical or horizontal forces are produced depending upon the plane of activation. Mesiodistal placement of step bends is not critical because very little alteration in force system occurs if a step is centered or positioned off center. V bends, on the other hand, are very sensitive to the positioning mesiodistally of the apex of the V. If the apex of the V bend is placed on center, equal and opposite couples are produced. As the V-bend apex is moved off center, predictable combinations of moments and forces are created. A method for determination of the relative force system is described that allows for simple interpretation and prediction of the force system from a V bend. The clinical applications of these data and a rational basis for wire bending are presented based on the producing of a desired force system.
The main goal of this research was to study the behavior of initial tooth displacements associated with alveolar bone loss situations when loaded by a force of 1 N. The analysis of displacements was carried out by the finite element method. Six 3-dimensional models of an upper central incisor (designated Geramy 391 to 396) with 1 to 8 mm of alveolar bone loss were formulated and used by the author. Center of rotation and center of resistance were located for the various stages of alveolar bone loss. The results revealed that the moment/force ratio (at the bracket level) required to produce bodily movement increases in association with alveolar bone loss. Bone loss causes center of resistance movement toward the apex, but its relative distance to the alveolar crest decreases at the same time. Greater amounts of displacements of incisal edge and apex were observed with increased alveolar bone loss for a constant applied force. Center of rotation of the tipping movement also shifted toward the cervical line. Among the many differences between orthodontic treatment of an adolescent and an adult patient is the presence of alveolar bone loss in the adult cases. Alveolar bone loss causes center of resistance changes as a result of the alterations in bone support. This necessitates modifications in the applied force system to produce the same movement as in a tooth with a healthy supporting structure.
The main goal of this research was to introduce, evaluate, and mathematically optimize the treatment procedure of unilateral overjet cases. Patients with Class II subdivision malocclusions usually reach a point with canines in a Class I position, and a unilateral overjet remains to be treated at the next stage of treatment. This study tried to prepare an archwire design that combines the midline-shift correction and the unilateral overjet reduction simultaneously. The analyses of displacements were carried out by the finite element method. The upper dental arch was designed three-dimensionally. Three archwire designs that were thought to be useful in these cases were modeled and engaged the dental-arch model separately. Three-dimensional displacements of the mesio- and distoincisolabial point angles of each incisor were assessed. Shortcomings of each design concerning the main treatment objectives were eliminated by optimization. Modeling and optimization of wire ligation methods were the last phase of this study. The use of an archwire containing a closed vertical loop with a helix distal to the lateral incisor on the affected (excess overjet) side and an open vertical loop without a helix distal to the lateral incisor on the normal side (normal overjet) while lacing the four incisors can be suggested as an optimum procedure to treat a unilateral overjet that is combined with a midline shift. The archwire cross-section depends on the initial position of the incisors. This mechanotherapy can be prescribed for both dental arches.