J.P. Gouvêa

Mechanical testing and finite element analysis of orthodontic teardrop loop

INTRODUCTION Understanding how teeth move in response to mechanical loads is an important aspect of orthodontic treatment. Treatment planning should include consideration of the appliances that will meet the desired loading of the teeth to result in optimized treatment outcomes. The purpose of this study was to evaluate the use of computer simulation to predict the force and the torsion obtained after the activation of tear drop loops of 3 heights. METHODS Seventy-five retraction loops were divided into 3 groups according to height (6, 7, and 8 mm). The loops were subjected to tensile load through displacements of 0.5, 1.0, 1.5, and 2.0 mm, and the resulting forces and torques were recorded. The loops were designed in AutoCAD software(2005; Autodesk Systems, Alpharetta, GA), and finite element analysis was performed with Ansys software(version 7.0; Swanson Analysis System, Canonsburg, PA). Statistical analysis of the mechanical experiment results was obtained by ANOVA and the Tukey post-hoc test (P < .01). The correlation test and the paired t test (P < .05) were used to compare the computer simulation with the mechanical experiment. RESULTS AND CONCLUSIONS The computer simulation accurately predicted the experimentally determined mechanical behavior of tear drop loops of different heights and should be considered an alternative for designing orthodontic appliances before treatment.

Sensitivity analysis of the ECAE process via 2 k experiments design

In this work the theoretical solutions based upon the upper-bound theorem recently proposed by Perez and Luri [Mech. Mater. 40 (2008) 617] for the equal channel angular extrusion process (ECAE) are analyzed by performing a 25 central composite factorial analysis. The uniaxial mechanical properties of commercial pure aluminium are considered by assuming isotropic nonlinear work-hardening combined to von Mises and Drucker isotropic yield criteria to predict the ECAE load and the effective plastic strain. From the proposed 25 factorial analysis, the main parameters affecting the ECAE pressure may be ranked as: (1) Friction factor, (2) die channels intersection angle, (3) outer and (4) inner die corners fillet radii and lastly, (5) plunger velocity. Alternatively, the effective plastic strain is mainly controlled by the die channels intersection angle and, in a less extent, by the outer and inner die corners fillet radii.

Análise do movimento inicial de molares superiores submetidos a forças extrabucais: estudo 3D

OBJECTIVE: To analyze maxillary molar displacement by applying three different angulations to the outer bow of cervical-pull headgear, using the finite element method (FEM). METHODS: Maxilla, teeth set up in Class II malocclusion and equipment were modeled through variational formulation and their values represented in X, Y, Z coordinates. Simulations were performed using a PC computer and ANSYS software version 8.1. Each outer bow model reproduced force lines that ran above (ACR) (1), below (BCR) (2) and through the center of resistance (CR) (3) of the maxillary permanent molars of each Class II model. Evaluation was limited to the initial movement of molars submitted to an extraoral force of 4 Newtons. RESULTS: The initial distal movement of the molars, using as reference the mesial surface of the tube, was higher in the crown of the BCR model (0.47x10-6) as well as in the root of the ACR (0.32x10-6) model, causing the crown to tip distally and mesially, respectively. On the CR model, the points on the crown (0.15 x10-6) and root (0.12 x10-6) moved distally in a balanced manner, which resulted in bodily movement. In occlusal view, the crowns on all models showed a tendency towards initial distal rotation, but on the CR model this movement was very small. In the vertical direction (Z), all models displayed extrusive movement (BCR 0.18 x10-6; CR 0.62 x10-6; ACR 0.72x10-6). CONCLUSIONS: Computer simulations of cervical-pull headgear use disclosed the presence of extrusive and distal movement, distal crown and root tipping, or bodily movement.

Evaluation of Bonding Resistance after Surface Treatment of Two Glass-Ceramics Used in Dentistry

The goal of this study was to evaluate the bonding resistance of two dental ceramics. The samples, one of each type of ceramics, were split into 4 groups (n=4) separated from those from control group, the others were conditioned with 5% hydrofluoric acid, according to the times of 20, 40 and 60 seconds. Cylindrical pins of resin cement were applied in each sample. After a shearing test, the obtained results showed that experimental groups has given higher bonding strength values than the control groups for both ceramics. For the e.max ceramic, the highest values were observed with timings of 20 and 40 seconds and for the Suprinity ceramic the conditioning timings were insignificant. The authors concluded that the surface treatment with hydrofluoric acid improved the bonding strength for both ceramics; and the e.max ceramic showed higher bonding values than the Suprinity.

Evaluation of Load Parameters and Hold Time of a Vickers Ultra-Micro Hardness Tester for Measure of Hardness and Modulus of Elasticity of Dental Composites

The aim of this study was to standardize the parameters for testing the hardness and elastic modulus for dental composites. It used the equipment Dynamic Ultra Micro Hardness Tester DUH-211 / DUH-211S (Shimadzu) varying the load and the hold time. two composites were used with various inorganic particles that were embedded and sanded for the assay. one Vickers indenter was used being held nine rows with ten penetrations. For each composite loads were used (20, 50 and 100gf) and times (zero, five and ten seconds). The results showed that the effect of the load and the hold time had influence on the modulus and hardness values of the studied composites. The authors concluded that loads and hold larger team showed greater stability of hardness values and modulus of elasticity for the studied composites and these values for both hybrid composites as for nanoparticulate were dependent on load and time.

Evaluation of Mechanical Properties of Composite Materials Used in Dentistry Varying the Inorganic Composition

The aim of this study was to determine the hardness and the elasticity modulus of the two composite resins base of BISGMA with different inorganic particles: a nanoparticulated with a ceramic withload, (Filtek Z350XT-3M) with and without thermal activation and a microhybrid with no ceramic load (Opallis-FGM). The samples were prepared and subjected to the tests of Vickers hardness (Shimadzu HMV) and acoustic excitation pulse (Sonelastic ®). The samples were divided into three groups: G1-Filtek Z350 XT; G2-Filtek Z350XT MO (subject to further polymerization microwave) and G3-Opallis. The results showed that the hardness of G2 was significantly higher than the groups G1 and G3. The elastic modulus was higher than the G2 to G1 and G3. One can conclude that the resins filled with inorganic ceramic filler showed higher hardness and elastic modulus. The thermal activation increased the hardness and the elasticity modulus of the resin with ceramic load.

Evaluation of Morphology and Roughness of the Surface of a Ceramic Based on Lithium Disilicate, after Conditioning with Acid Hydrofluoric the 5% and 10%

The aim of the study was to evaluate the difference in the surface of dental ceramics, the basis of lithium disilicate, varying the concentration and time of application of the acid. Samples of IPS e.max Press (Ivoclar) were divided into: G1-control; G2 hydrofluoric acid 10% - 20 sec; G3 hydrofluoric acid 10% - 40 sec; G4 hydrofluoric acid 5% - 20 sec G5 and hydrofluoric acid 5% - 40 sec. The samples were analyzed under SEM (Carl Zeiss) confocal microscope and (Carl Zeiss). The qualitative morphologic analysis showed that 40 seconds of conditioning promoted the dissolution of the vitreous component and the ceramic crystal display for the two concentrations. Hydrofluoric acid 10% showed higher values of roughness. One can conclude that conditioning for 40 seconds is more effective than the 20 seconds for the two concentrations hydrofluoric acid and 10% promoted a higher surface roughness in the ceramic.

Numerical Modelling of a High-Pressure Type 2 Cylinder for Storing Natural Gás for Vehicles

ISO 11439 standards considers 4 types of high-pressure cylinders to storing natural gas for vehicles applications. Among them the type 2, metal-lined hoop wrapped cylinder, is the aim of this work. It describes a numerical model built using ANSYS application to determine stress on the metal liner and on the composite material applied on the liner via filament winding process. Using design criterion for laminate composites, the total thickness of the composite layer has been evaluated to get an optimized value. Employing the element shell multilayer of ANSYS 8.1 and a model of the type 2 cylinder, the stress state in the metal liner and in each layer of the composite system of epoxy-glass fibre has been studied. The failure criterion of Hill-Tsai for composite laminates was used to analyse failure of each layer. The results are analysed considering the performance of the cylinder under test conditions of loading of 30 MPa.