Evaluation of the Effect of Retightening and Mechanical Cycling on Preload Maintenance of Retention Screws

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Obturator for Rehabilitation of Cleft Palate With Implant-Supported Retention System

Objective: Surgical reconstruction and prosthetic obturation are alternatives for the treatment of cleft in the soft palate.Design: The present case reports the rehabilitation of a patient presenting cleft palate with obturator prosthesis associated with implant-supported retention system.Conclusions: The use of ball attachment system improved speech, masticatory efficiency, swallowing, and social behavior of the patient.

The Effect of Mechanical Cycling and Different Misfit Levels on Vicker's Microhardness of Retention Screws for Single Implant-Supported Prostheses

Purpose: The aim of this study was to evaluate the effect of mechanical cycling and different misfit levels on Vicker's microhardness of retention screws for single implant-supported prostheses.Materials and Methods: Premachined UCLA abutments were cast with cobalt-chromium alloy to obtain 48 crowns divided into four groups (n = 12). The crowns presented no misfit in group A (control group) and unilateral misfits of 50 mu m, 100 mu m, and 200 mu m in groups B, C, and D, respectively. The crowns were screwed to external hexagon implants with titanium retention screws (torque of 30 N/cm), and the sets were submitted to three different periods of mechanical cycling: 2 x 10(4), 5 x 10(4), and 1 x 10(6) cycles. Screw microhardness values were measured before and after each cycling period. Data were evaluated by two-way ANOVA and Tukey's test (p < 0.05).Results: Mechanical cycling statistically reduced microhardness values of retention screws regardless of cycling periods and groups. In groups A, B, and C, initial microhardness values were statistically different from final microhardness values (p < 0.05). There was no statistically significant difference for initial screw microhardness values (p > 0.05) among the groups; however, when the groups were compared after mechanical cycling, a statistically significant difference was observed between groups B and D (p < 0.05).Conclusions: Mechanical cycling reduced the Vicker's microhardness values of the retention screws of all groups. The crowns with the highest misfit level presented the highest Vicker's microhardness values.

Evaluation of Different Retention Systems on a Distal Extension Removable Partial Denture Associated With an Osseointegrated Implant

The aim of this study was to evaluate the biomechanical behavior of a mandibular distal extension removable partial denture (DERPD) associated with an implant and different retention system, by bidimensional finite element method. Five hemimandible models with a canine and external hexagon implant at second molar region associated with DERPD were simulated: model A, hemimandible with a canine and a DERPD; model B, hemimandible with a canine and implant with a healing abutment associated to a DERPD; model C, hemimandible with a canine and implant with an ERA attachment associated to a DERPD; model D, hemimandible with a canine and implant with an O'ring attachment associated to a DERPD; and model E, hemimandible with a canine and implant-supported prosthesis associated to a DERPD. Cusp tips were loaded with 50 N of axial or oblique force (45 degrees). Finite element analysis was performed in ANSYS 9.0. model E showed the higher displacement and overload in the supporting tissues; the patterns of stress distribution around the dental apex of models B, C, and D were similar. The association between a DERPD and an osseointegrated implant using the ERA or O'ring systems shows lower stress values. Oblique forces showed higher stress values and displacement. Oblique forces increased the displacement and stress levels in all models; model C displayed the best stress distribution in the supporting structures; healing abutment, ERA, and O'ring systems were viable with RPD, but DERPD association with a single implant-supported prosthesis was nonviable.

Effect of Misfit on Preload Maintenance of Retention Screws of Implant-Supported Prostheses

The aim of this study was to evaluate the effect of unilateral misfit at different levels on a crown-implant-retention screw system of implant-supported crowns. Hexagon castable UCLA abutments were cast in Co-Cr alloy to fabricate 48 metallic crowns divided into four groups (n = 12). Group A: crowns did not present misfit; Groups B, C and D: crowns were fabricated with unilateral misfit of 50, 100, and 200 mu m, respectively. The crowns were attached by titanium retention screw with 30 N/cm to external hexagonal osseointegrated implants embedded in acrylic resin. After 2 min, the retention screw of each replica was submitted to detorque evaluation by an analogic torque gauge. Three retention screws were used to perform detorque evaluation at each replica and the procedure was repeated twice with each screw. Each group was submitted to 72 detorque measurements. Data were evaluated by ANOVA and Tukey test (P < 0.05). All groups exhibited significant decrease (P < 0.05) in preload and the lowest decrease occurred in Group A. Groups B, C, and D were statistically significant different from Group A (P < 0.05), but there was no statistically significant difference between Groups B and D (P > 0.05). Crowns with unilateral misfit presented higher preload decrease than crowns completely fitted to osseointegrated implants.

Effect of Different Light-Curing Modes on Degree of Conversion, Staining Susceptibility and Stain's Retention Using Different Beverages in a Nanofilled Composite Resin

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Comparison of space analysis performed on plaster vs. digital dental casts applying Tanaka and Johnston's equation

OBJETIVO: comparar medidas de tamanhos dentários, suas reprodutibilidades e a aplicação da equação de regressão de Tanaka e Johnston na predição do tamanho dos caninos e pré-molares em modelos de gesso e digital. MÉTODOS: trinta modelos de gesso foram escaneados para obtenção dos modelos digitais. As medidas do comprimento mesiodistal dos dentes foram obtidas com paquímetro digital nos modelos de gesso e nos modelos digitais utilizando o software O3d (Widialabs). A somatória do tamanho dos incisivos inferiores foi utilizada para obter os valores de predição do tamanho dos pré-molares e caninos utilizando equação de regressão, e esses valores foram comparados ao tamanho real dos dentes. Os dados foram analisados estatisticamente, aplicando-se aos resultados o teste de correlação de Pearson, a fórmula de Dahlberg, o teste t pareado e a análise de variância (p < 0,05). RESULTADOS: excelente concordância intraexaminador foi observada nas medidas realizadas em ambos os modelos. O erro aleatório não esteve presente nas medidas obtidas com paquímetro, e o erro sistemático foi mais frequente no modelo digital. A previsão de espaço obtida pela aplicação da equação de regressão foi maior que a somatória dos pré-molares e caninos presentes nos modelos de gesso e nos modelos digitais. CONCLUSÃO: apesar da boa reprodutibilidade das medidas realizadas em ambos os modelos, a maioria das medidas dos modelos digitais foram superiores às do modelos de gesso. O espaço previsto foi superestimado em ambos os modelos e significativamente maior nos modelos digitais.

Retention of particulate organic matter in a tropical headstream

Retention of particulate organic matter was investigated over a range of water discharges in pool and riffle zones of a tropical stream (Itauna Stream, São Paulo, Brazil). A closed-system leaf release and capture method was used to quantify leaf retention in a 50-m reach of the stream. Instantaneous retention rates (k) were calculated by a negative exponentialmodel and specific retention rates (ke) computed for each 1m interval. The mean k was 0.0161 +/- 0.0101 (S.E.) and ranged from 0.005 to 0.036 during the study period. This suggests a low retention of particulate matter. The evidence provided by this study shows that there was a relationship between retention and discharge. At low discharges, greater percentages of leaves were retained in a 3-h period while high discharges resulted in low retention percentages within the studied reach. In the Itauna Stream, no significant difference (p < 0.05) was found between the ke values of pool and riffle zones.

MATHEMATICA notebook for computing tetrahedral finite element shape functions and matrices for the Helmholtz equation

A MATHEMATICA notebook to compute the elements of the matrices which arise in the solution of the Helmholtz equation by the finite element method (nodal approximation) for tetrahedral elements of any approximation order is presented. The results of the notebook enable a fast computational implementation of finite element codes for high order simplex 3D elements reducing the overheads due to implementation and test of the complex mathematical expressions obtained from the analytical integrations. These matrices can be used in a large number of applications related to physical phenomena described by the Poisson, Laplace and Schrodinger equations with anisotropic physical properties.

Edge detection and noise removal by use of a partial differential equation with automatic selection of parameters

This work deals with noise removal by the use of an edge preserving method whose parameters are automatically estimated, for any application, by simply providing information about the standard deviation noise level we wish to eliminate. The desired noiseless image u(x), in a Partial Differential Equation based model, can be viewed as the solution of an evolutionary differential equation u t(x) = F(u xx, u x, u, x, t) which means that the true solution will be reached when t ® ¥. In practical applications we should stop the time ''t'' at some moment during this evolutionary process. This work presents a sufficient condition, related to time t and to the standard deviation s of the noise we desire to remove, which gives a constant T such that u(x, T) is a good approximation of u(x). The approach here focused on edge preservation during the noise elimination process as its main characteristic. The balance between edge points and interior points is carried out by a function g which depends on the initial noisy image u(x, t0), the standard deviation of the noise we want to eliminate and a constant k. The k parameter estimation is also presented in this work therefore making, the proposed model automatic. The model's feasibility and the choice of the optimal time scale is evident through out the various experimental results.

A Decomposition and Noise Removal Method Combining Diffusion Equation and Wave Atoms for Textured Images

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Oxidative Stability and alpha-Tocopherol Retention in Soybean Oil with Lemon Seed Extract (Citrus Limon) under Thermoxidation

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

The effects of extrusion conditions and the addition of volatile compounds and flavour enhancers to corn grits on the retention of the volatile compounds and texture of the extrudates

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Solutions of the Fokker-Planck equation for a Morse isospectral potential

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)