Evaluation of femur of orchiectomized guinea pigs by bone densitometry using dual-energy x-ray absortiometry (DXA) and mechanical testing

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Effect of cold plasma treatment on mechanical properties of PET/PMMA composites

Mechanical strength of polyethylene terephthalate (PET) fibres and polymethyl methacrylate (PMMA) matrix composites were studied with particular interest on the effects of oxygen and argon plasma treated fibres. PET. fibres were treated in a radio frequency plasma reactor using argon or oxygen for different treatment times to increase the interface adhesion. Fibre volume fraction was measured through digital image analysis. Elastic moduli resulted between 3 GPa for untreated to 6 GPa for treated composites. Tensile tests on PET fibres showed that plasma treatment caused a decrease in average tensile strength compared to untreated fibres. Fracture analysis confirmed the increase in interfacial adhesion due to plasma treatment. (c) 2004 Elsevier Ltd. All rights reserved.

Influence of thermal and mechanical cycling on the flexural strength of ceramics with titanium or gold alloy frameworks

Objectives: The aim of this study was to evaluate the effect of thermal and mechanical cycling alone or in combination, on the flexural strength of ceramic and metallic frameworks cast in gold alloy or titanium. Methods: Metallic frameworks (25 mm × 3 mm × 0.5 mm) (N = 96) cast in gold alloy or commercial pure titanium (Ti cp) were obtained using acrylic templates. They were airborne particle-abraded with 150 μm aluminum oxide at the central area of the frameworks (8 mm × 3 mm). Bonding agent and opaque were applied on the particle-abraded surfaces and the corresponding ceramic for each metal was fired onto them. The thickness of the ceramic layer was standardized by positioning the frameworks in a metallic template (height: 1 mm). The specimens from each ceramic-metal combination (N = 96, n = 12 per group) were randomly assigned into four experimental fatigue conditions, namely water storage at 37 °C for 24 h (control group), thermal cycling (3000 cycles, between 4 and 55 °C, dwell time: 10 s), mechanical cycling (20,000 cycles under 10 N load, immersion in distilled water at 37 °C) and, thermal and mechanical cycling. A flexural strength test was performed in a universal testing machine (crosshead speed: 1.5 mm/min). Data were statistically analyzed using two-way ANOVA and Tukey's test (α = 0.05). Results: The mean flexural strength values for the ceramic-gold alloy combination (55 ± 7.2 MPa) were significantly higher than those of the ceramic-Ti cp combination (32 ± 6.7 MPa) regardless of the fatigue conditions performed (p < 0.05). Mechanical and thermo-mechanical fatigue decreased the flexural strength results significantly for both ceramic-gold alloy (52 ± 6.6 and 53 ± 5.6 MPa, respectively) and ceramic-Ti cp combinations (29 ± 6.8 and 29 ± 6.8 MPa, respectively) compared to the control group (58 ± 7.8 and 39 ± 5.1 MPa, for gold and Ti cp, respectively) (p < 0.05) (Tukey's test). While ceramic-Ti cp combinations failed adhesively at the metal-opaque interface, gold alloy frameworks exhibited a residue of ceramic material on the surface in all experimental groups. Significance: Mechanical and thermo-mechanical fatigue conditions decreased the flexural strength values for both ceramic-gold alloy and ceramic-Ti cp combinations with the results being significantly lower for the latter in all experimental conditions. © 2007 Academy of Dental Materials.

Hybridization effect on the mechanical properties of curaua/glass fiber composites

The aim of this paper was to evaluate the effect of hybridizing glass and curaua fibers on the mechanical properties of their composites. These composites were produced by hot compression molding, with distinct overall fiber volume fraction, being either pure curaua fiber, pure glass fiber or hybrid. The mechanical characterization was performed by tensile, flexural, short beam, Iosipescu and also nondestructive testing. From the obtained results, it was observed that the tensile strength and modulus increased with glass fiber incorporation and for higher overall fiber volume fraction (%Vf). The short beam strength increased up to %Vf of 30 vol.%, evidencing a maximum in terms of overall fiber/matrix interface and composite quality. Hybridization has been successfully applied to vegetable/synthetic fiber reinforced polyester composites in a way that the various properties responded satisfactorily to the incorporation of a third component. © 2013 Published by Elsevier Ltd. All rights reserved.

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.

Shear bond strength of metal-ceramic repair systems

Statement of problem. When clinical fractures of the ceramic veneer on metal-ceramic prostheses can be repaired, the need for remake may be eliminated or postponed. Many different ceramic repair materials are available, and bond strength data are necessary for predicting the success of a given repair system.Purpose. This study evaluated the shear bond strength of different repair systems for metal-ceramic restorations applied on metal and porcelain.Material and methods. Fifty cylindrical specimens (9 X 3 mm) were fabricated in a nickel-chromium alloy (Vera Bond 11) and 50 in feldspathic porcelain (Noritakc). Metal (M) and porcelain (P) specimens were embedded in a polyvinyl chloride (PVC) ring and received I of the following bonding and resin composite repair systems (n=10): Clearfil SE Bond/Clearfil AP-X (CL), Bistite II DC/Palfique (BT), Cojet Sand/Z100 (Q), Scotchbond Multipurpose Plus/Z100 (SB) (control group), or Cojet Sand plus Scotchbond Multipurpose Plus/Z100 (CJSB). The specimens were stored in distilled water for 24 hours at 37 degrees C, thermal cycled (1000 cycles at 5 degrees C to 55 degrees C), and stored at 37 degrees C for 8 days. Shear bond tests between the metal or ceramic specimens and repair systems were performed in a mechanical testing machine with a crosshead speed of 0.5 mm/min. Mean shear bond strength values (MPa) were submitted to 1-way ANOVA and Tukey honestly significant difference tests (alpha=.05). Each specimen was examined under a stereoscopic lens with X 30 magnification, and mode of failure was classified as adhesive, cohesive, or a combination.Results. on metal, the mean shear bond strength values for the groups were as follows: MCL, 18.40 +/- 2.88(b); MBT, 8.57 +/- 1.00(d); MCJ, 25.24 +/- 3.46(a); MSB, 16.26 +/- 3.09(bc); and MCJSB, 13.11 +/- 1.24(c). on porcelain, the mean shear bond strength values ofeach group were as follows: PCL, 16.91 +/- 2.22(b); PBT, 18.04 +/- 3.2(ab); PCJ, 19.54 +/- 3.77(ab); PSB, 21.05 +/- 3.22(a); and PCJSB, 16.18 +/- 1.71(b). Within each substrate, identical superscript letters denote no significant differences among groups.Conclusions. The bond strength for the metal substrate was significantly higher using the Q system. For porcelain, SB, Q, and BT systems showed the highest shear bond strength values, and only SB was significantly different compared to CL and CJSB (P <.05).

In Vitro Study of Fracture Load and Fracture Pattern of Ceramic Crowns: A Finite Element and Fractography Analysis

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Biomechanical in vitro evaluation of three stable internal fixation techniques used in sagittal osteotomy of the mandibular ramus: a study in sheep mandibles

Among the osteotomies performed in orthognathic surgery, the sagittal osteotomy of the mandibular ramus (SOMR) is the most common, allowing a great range of movements and stable internal fixation (SIF), therefore eliminating the need of maxillomandibular block in the postoperative period. Objectives: The purpose of this study was to evaluate the biomechanical resistance of three national systems used for SIF in SOMR in sheep mandibles. Material and methods: The study was performed in 30 sheep hemi-mandibles randomly divided into 3 experimental groups, each containing 10 hemi-mandibles. The samples were measured to avoid discrepancies and then subjected to SOMR with 5-mm advancement. In group I, 2.0x12 mm screws were used for fixation, inserted in an inverted "L" pattern (inverted "L" group). In group II, fixation was performed with two 2.0x12 mm screws, positioned in a linear pattern and a 4-hole straight miniplate and four 2.0x6.0 mm monocortical screws (hybrid group). In group III, fixation was performed with two-hole straight miniplates and eight 2.0x6.0 mm monocortical screws (mini plate group). All materials used for SIF were supplied by Osteosin - SIN. The hemimandibles were subjected to vertical linear load test by Kratos K2000MP mechanical testing unit for loading registration and displacement. Results: All groups showed similar resistance during mechanical test for loading and displacement, with no statistically significant differences between groups according to analysis of variance. Conclusion: These results indicate that the three techniques of fixation are equally effective for clinical fixation of SOMR.

Novel production method of porous surface Ti samples for biomedical application

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

Investigação da Interface Metal-Porcelana da Liga Ni-Cr-Mo Soldada a LASER

The interface formed between the metal and the porcelain of a LASER welded Ni-Cr-Mo alloy was studied. The characterization was carried out through optical microscopy, scanning electron microscopy, X-ray dispersive spectroscopy-EDS and mechanical testing by three-point flexion test-TPE in the region LASER welded with and without the porcelain. The porcelain adhesion with the alloy alone is possible after the oxidation of the metallic surface and subsequent application of an adhesive called opaco. The applied porcelain, on the base metal and fusion zone presented some distinct behaviors. After the TPF test the base metal presented fractures while that in the fusion zone was completely gone. One noticed that the region submitted to the LASER welding showed less porcelain adhesion than the region of the base metal due to the microestructural refinement of the fusion zone. These results can be evidenced by the EDS of the studied regions. The TPF had demonstrated that the Ni-Cr-Mo alloy submitted to the LASER welding, undergone significant alterations in its mechanical properties after the application of the porcelain.

A utilização de diferentes configurações de molas T para a obtenção de sistemas de forças otimizados

OBJETIVO: determinar as características mecânicas de molas T e T com helicóides, quando da incorporação de variações na liga metálica (aço inoxidável e beta-titânio), na intensidade de dobras de pré-ativação (0º e 40º/180º) e na secção transversal do fio utilizado para a construção destas molas (0,017 x 0,025 e 0,019 x 0,025). METODOLOGIA: foram submetidas ao ensaio mecânico 80 molas para fechamento de espaços, sendo estas centralizadas em um espaço de 21mm. As magnitudes de força horizontal, proporção momento/força e relação carga/deflexão produzidas pelos corpos de prova foram quantificadas utilizando-se um transdutor de momentos acoplado ao módulo indicador digital para extensiometria e adaptado a uma máquina universal de ensaios Instron. As molas foram submetidas a uma ativação total de 5mm, sendo registrados os valores a cada 1mm de ativação. No tratamento estatístico dos dados obtidos, foi realizada a análise de variância, sendo esta complementada pelo teste de comparações múltiplas de Tukey, considerando o nível de significância de 5%. RESULTADOS E CONCLUSÕES: os resultados demonstraram que, de maneira geral, as molas T com helicóides produziram menores magnitudes de força horizontal e relação carga/deflexão do que as molas T. Na presença de pré-ativação, as molas produziram altas proporções momento/força, enquanto, na ausência de dobras de pré-ativação, as mesmas geraram baixas proporções momento/força. Dentre todas as variáveis analisadas, aquela que apresentou uma maior influência na força horizontal e na relação carga/deflexão produzidas pelas molas foi a liga metálica. Já a proporção momento/força mostrou ser influenciada em maior grau pela pré-ativação das molas de fechamento.

Hindlimb unloading producing effects on bone biomechanical properties in mature male rats

Aging is associated with decline in muscle mass and strength and reduced bone density. Age-related bone loss is a primary factor in osteoporosis and all individuals are potential candidates for osteoporosis because bone loss with aging occurs in men and women, but less studied in men. To examine the appropriateness of hindlimb elevation, by tail suspension as a model for diminished mechanical loading, and to determine the influence of age on bone responsiveness to skeletal unloading, we use dual X ray absorptiometry (DXA) and digital radiographic images to analyze the response of the femur from mature rats to biomechanical loads. Femurs from male Wistar rats (9-mo-old) were scanned using DXA and DIGORA and measures obtained in ephipyseal and diaphyseal regions of interest. The mechanical testing was divided into compression load to fracture the head and a three-point bending load to fracture the femur middiaphysis. In femoral epiphysis from hindlimb unload (HU), animals presented significant differences between mineral bone content and density assessed by DXA. Detailed regions of femoral epiphysis (head, throcanteric fossa, throcanter and metaphysis) presented significant lower values from radiographic density. Only compressive load necessary to fracture the femoral head neck was also significantly diminished in HU animals. Disuse induced, as in elderly patients, deterioration of the trabecular bone architecture with critical effect on bone fragility. Rats with 21 days of hindlimb unloading can simulate disuse, suggesting that certain sub-regions of their aging bones are more susceptible to fracture, while other, i.e. diaphyses, are not.

Effect of toothbrushing with different manual toothbrushes on the shear bond strength of orthodontic brackets

The aim of this study was to evaluate the effect of brushing with a Colgate 360° or Oral B Indicator 35 toothbrush on the shear bond strength of orthodontic brackets bonded to extracted human teeth. The bristle wear and bristle tip morphology were also examined after simulated tooth-brushing. Orthodontic brackets (Roth-P/1 st and 2 nd pre-molar S/D- Slot 0.18) were bonded (Transbond XT ®) to the smoothest surface of each of 45 extracted human molar and premolar teeth. Test specimens were randomly divided into three groups: Group 1, control group with no brushing; Group 2, brushing with the Oral B Indicator 35; Group 3, brushing with the Colgate 360°. Samples were adapted to a machine that simulated tooth-brushing. The bond strength of each bracket to each tooth was assessed with a mechanical testing machine. The bristle wear and bristle tip morphology indices were also assessed. Statistically significant differences were defined for p ≤ 0.05. The average bond strengths (range: 90.18-90.89 kgf/cm 2) did not differ among the three groups. The Colgate 360° showed less bristle wear and a better bristle tip morphology than the Oral B Indicator 35 toothbrush. However, use of either toothbrush did not decrease the bond strength of the orthodontic brackets. Therefore, patients undergoing orthodontic therapy can safely use either toothbrush.

In vitro biomechanical evaluation of sagittal split osteotomy fixation with a specifically designed miniplate

Recent studies have evaluated many methods of internal fixation for sagittal split ramus osteotomy (SSRO), aiming to increase stability of the bone segments while minimizing condylar displacement. The purpose of this study was to evaluate, through biomechanical testing, the stability of the fixation comparing a specially designed bone plate to other two commonly used methods. Thirty hemimandibles were separated into three equal groups. All specimens received SSRO. In Group I the osteotomies were fixed with three 15 mm bicortical positional screws in an inverted-L pattern with an insertion angle of 90°. In Group II, fixation was carried out with a four-hole straight plate and four 6 mm monocortical screws. In Group III, fixation was performed with an adjustable sagittal plate and eight 6 mm monocortical screws. Hemimandibles were submitted to vertical compressive loads, by a mechanical testing unit. Averages and standard deviations were submitted to analysis of variance using the Tukey test with a 5% level of significance. Bicortical screws presented the greatest values of loading resistance. The adjustable miniplate demonstrated 60% lower resistance compared to bicortical screws. Group II presented on average 40% less resistant to the axial loading. © 2012 International Association of Oral and Maxillofacial Surgeons.

Effect of the number of screws on the stability of locking mandibular reconstruction plates

Atrophic mandible fractures are frequently a challenge to stabilize. This study evaluated, through mechanical testing in vitro, the number of locking screws that is sufficient to withstand loading when applied with a locking reconstruction plate in the fixation of atrophic mandible fractures. Polyurethane mandibles with a simulated linear fracture at the midline were used as substratum. Results show that resistance of the fixation is poor when one and two screws are used on each side of the fracture. Three screws on each side of the fracture significantly increases the resistance to displacement. However, no additional strength is added to the construct when more than three screws per side are used. © 2013 International Association of Oral and Maxillofacial Surgeons.