Biomedical subjects

Allahyar Geramy

Publications and source records attributed to Allahyar Geramy.

6 recordsLinked to original sources

PubMed2006

M/F ratios of four different closing loops: 3D analysis using the finite element method (FEM).

BACKGROUND: It has been claimed that the opus loop is capable of delivering a constant and optimum M/F ratio without the need for gable bends. OBJECTIVE: To compare the forces, moments and moment/force (M/F) ratios of the opus loop, L-loop, T-loop and vertical helical closing loop (VHC loop) in a segmented arch with the finite element method (FEM). METHODS: The FEM was used to compare 3D models of closing loops in rectangular (0.016 x 0.022 inch) stainless steel wire. The L-, T- and VHC loops were designed with and without preactivation bends. The opus loop had no preactivation bends. The T-Loops were 10 mm in height and 10 mm in length. The horizontal and vertical forces, the moments and the M/F ratios at the alpha and beta ends were recorded at 0, 0. 1, 0.4, 0.7 and 1 mm intervals. RESULTS: The highest horizontal and vertical forces were produced by the L-loop (with and without preactivation bends) and in most cases the lowest forces were produced by the VHC loop. Loops with preactivation bends produced marked changes in the M/F ratio and loops without preactivation bends low, but relatively constant, M/F ratios over the full range of activation. Of the loops modelled without preactivation bends the opus and T-loop had the highest M/F ratios (7.20 - 7.67 mm at the anterior ends). CONCLUSION: Stainless steel opus and T-loops without preactivation bends had constant M/F ratios, but both loops failed to deliver the optimum M/F ratio of 10:1.

Biomechanical Phenomena↗

PubMed2004

Finite element analysis of three designs of an implant-supported molar crown.

STATEMENT OF PROBLEM: The 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. PURPOSE: The 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 METHODS: Three-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. RESULTS: Mesiodistal 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. CONCLUSION: When the crown was loaded off-center, the double-implant design produced substantially less displacement when compared with either of the single-implant designs.

Biomechanical Phenomena↗

PubMed2002

Optimization of unilateral overjet management: three-dimensional analysis by the finite element method.

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.

Dental Stress Analysis↗

PubMed2002

Initial stress produced in the periodontal membrane by orthodontic loads in the presence of varying loss of alveolar bone: a three-dimensional finite element analysis.

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.

Alveolar Bone Loss↗

PubMedDate not supplied

Abfraction: 3D analysis by means of the finite element method.

OBJECTIVE: Tooth deflections under functional loads are considered to be the etiologic factor of noncarious cervical lesions. There are several studies on the materials used to restore these lesions; however, there are few discussing this phenomenon's etiology from a biomechanic point of view. This study was undertaken to evaluate tooth behavior when forces were applied from different directions. METHOD AND MATERIALS: A 3D finite element model of a maxillary central incisor was designed. A distributed force of 1.5 N was applied on the palatal side of the crown in five stages, with varying directions progressing from tipping to intrusion. Two separate approaches (displacement and stress) were considered to evaluate the cervical area from a stress perspective. RESULTS: The displacement approach resulted in a curved path when compared to a straight line connecting the apical and incisal areas. The maximum deflections were in the cementoenamel junction area. The same area was shown to undergo the maximum of von Mises stress and stress intensity. Patterns of the von Mises stress when evaluated in a mesiodistal direction were in complete agreement with the shape of the cervical lesions (except for the application of the intrusive force, which rules out its effect in producing such lesions). CONCLUSION: Force applications, except for intrusive force, can produce increases in the von Mises stress and tooth deflections that can answer the question of the etiology of noncarious cervical lesions. The highest amounts of deflection and von Mises stress were produced by the 45-degree force application.

Computer Simulation↗

PubMedDate not supplied

Secondary trauma from occlusion: three-dimensional analysis using the finite element method.

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.

Alveolar Bone Loss↗