Mildred Ballin Hecke

Analysis of short implants and lateralization of the inferior alveolar nerve with 2-stage dental implants by finite element method.

AbstractThere are difficulties for dental implant use in posterior mandible when there is little bone height for implant placement. Among the treatment alternatives available, there is no direct comparison between short implants and conventional implants placed with lateralization of the inferior alveolar nerve. The present study aimed to comparatively evaluate the risk of peri-implant bone loss of the above treatments. With this aim, computed tomography scans of mandibles were processed, and implants and prosthetic components were reverse engineered for reconstruction of three-dimensional models to simulate the biomechanical behavior of 3-element fixed partial dentures supported by 2 osseointegrated implants, using simulations with the finite element method. The models of implants were based on MK III implants (Nobel Biocare) of 5- and 4-mm diameter by 7-mm length, representing short implants, and 4- and 3.75-mm diameter by 15-mm length, representing implants used in lateralization of the inferior alveolar nerve. All models were simulated with prestress concerning the stresses generated by the torque of the screw. Axial and oblique occlusal loads at 45% were simulated, resulting in 8 different simulations. The results showed that the risk for bone loss in osseointegrated implants is greater for treatments with short implants.

A method for constructing teeth and maxillary bone parametric model from clinical CT scans

The use of precise geometric models can be of great importance to grant the validity of a computer simulation. Advanced reconstructive techniques must be used to ensure that goal. The authors describe a method to digitally reconstruct a complete model of a toothed maxilla using conventional computerized tomography and manual manipulations based on literature references to correct inaccuracies in the model. The result is a geometric model that can be edited or used as-is in a wide range of research areas such as orthodontics, prosthetic dentistry and restorative dentistry. The model can be downloaded and used freely by the scientific community.

Evaluation of the efficacy and influence of the decontamination and sterilization of FBGs exposed to S. aureus and E. coli

The FBGs (Fibre Bragg Grating) are adequate sensors for measuring strain in biomedical applications. This work evaluates the efficacy of some products and processes, which are used for the decontamination and sterilization of these sensors. Fibre optic samples, partially stripped of the primary coating, were contaminated by E. coli and S. aureus and suffered decontamination processes by autoclave heating, immersion in ethylene oxide, sodium hypochlorite, chloramine T or peracetic acid and illumination ultra-violet radiation. After each process fibre samples were removed, washed in sterile saline and placed individually in BHI broth tubes. Tubes that showed turbidity of the BHI broth were considered positive. The sterilization practices by heating and immersionand avoided the formation of bacteria colonies, whereas illumination processes were not effective to avoid the bacteria colony growth.

The composite element method applied to free vibration analysis of trusses and beams

This work deals with an enrichment technique of the finite element solution to the free vibration problems, called the composite element method [J. Sound Vibration 218 (1998) 619, 659, Key Engrg. Mater. 145-149 (1998) 773]. The enrichment of the solution space is obtained combining the FEM and the high accuracy of closed form solutions from the classical theory. The analytical solutions must be in accordance with some special boundary conditions in such a way they do not change the nodal values of FEM and, also, they must be the solutions to the frequency equation. The CEM can be improved using two types of approach: h and c-versions. The h-version, the same as FEM, consists of the refinement of the element mesh. The c-version is the increase of degrees of freedom related to the classical theory. Truss and beams elements are used in order to verify the numerical efficiency of the CEM. Some examples are presented and the frequencies and mode shapes of vibration obtained by CEM are compared with the FEM solution, and also the classical theory. The numerical results have shown that CEM is more accurate than FEM with the same number of total degrees of freedom. The CEM is also more accurate to determine higher frequencies than the FEM, except for the last ones. The results suggest that, for higher frequencies, numerical instabilities are presented.

An Introduction to the Composite Element Method Applied to the Vibration Analysis of Trusses

This paper introduces a new type of Finite Element Method (FEM), called Composite Element Method (CEM). The CEM was developed by combining the versatility of the FEM and the high accuracy of closed form solutions from the classical analytical theory. Analytical solutions, which fulfil some special boundary conditions, are added to FEM shape functions forming a new group of shape functions. CEM results can be improved using two types of approach: h-version and c-version. The h-version, as in FEM, is the refinement of the element mesh. On the other hand, in the c-version there is an increase of degrees of freedom related to the classical theory (c-dof). The application of CEM in vibration analysis is thus investigated and a rod element is developed. Some samples which present frequencies and vibration mode shapes obtained by CEM are compared to those obtained by FEM and by the classical theory. The numerical results show that CEM is more accurate than FEM for the same number of total degrees of freedom employed. It is observed in the examples that the c-version of CEM leads to a super convergent solution.

Comparative analysis of adhesive failure of orthodontic resins: An in vitro mechanical test with the finite element method

Objective: The purpose of this study was to validate finite element (FE) method as a reliable adhesive shear strength test method by investigating and comparing the results from in vitro mechanical tests and 3-D FE simulations. Materials and Methods: Four groups of teeth ( n =15) using Transbond XT (3M Unitek, Monrovia, CA) and Enlight Ormco (Glendora, CA) with metallic and ceramic brackets (Twin-Edge and InVu, TP Orthodontics, Inc., La Porte, IN) were obtained and submitted to shear bond strength tests. Subsequently, an equivalent geometric model was subjected to FE modeling analysis. ANOVA tests indicated a statistically significant difference ( P Results: FE analysis showed the stress distribution in the adhesive layer and revealed an increased stress distribution in the ceramic brackets. These results were consistent with in vitro detachment experiments. Conclusions: This study establishes that FE sub-modeling can be used to simulate adhesive resistance.