Primary Tooth Enamel Loss After Manual and Mechanical Microabrasion

Purpose: This study's purpose was to assess the amount of dental enamel loss on primary incisors after manual or mechanical microabrasion with a phosphoric acid/pumice poste. Methods: Ten exfoliated primary maxillary incisors were bisected faciolingually and the resulting 20 halves were randomly assigned to 2 groups: group 1 (N=10) manual technique (plastic spatula); and group 2 (N=10) mechanical technique (rubber cup attached to a low-speed handpiece). Microabrasion was performed on the buccal surface using an abrasive paste prepared with 37% phosphoric acid and pumice. Ten 20-second applications alternated with 20-second risings were performed in each group. Enamel thickness measurements made under stereomi-croscopy before and after microabrasion were analyzed statistically by analysis of variance and pairwise t test. Results: There was a statistically significant difference (P=.003) between the manual and mechanical techniques. The mechanical technique produced a mean enamel loss of 274.16 mu m (66% of total enamel thickness), while the mean enamel loss with the manual technique was 152.59 mu m (39% of total enamel thickness). Conclusion: Manual microabrasion using a plastic spatula removed less enamel, but was sufficient to eliminate most superficial stains and defects, and may be a viable option for the microabrasive technique on primary teeth. (Pediatr Dent 2008;30:420-3) Received March 15, 2007 / Lost Revision September 19, 2007 / Revision Accepted October 19, 2007

Influence of thermal and mechanical stresses on the strength of intact and relined denture bases

Statement of problem. Denture bases may become increasingly weaker as a result of thermal stress and flexural cyclic loading. Information regarding this potential problem and its relationship to the denture base reline is limited.Purpose. This study evaluated the influence of thermal and mechanical stresses on the strength of intact and relined denture bases.Material and methods. Twenty-eight microwave-polymerized (Acron MC) intact denture bases were prepared in the shape of a 3-mm-thick maxillary denture. Additionally, fifty-six 2-mm-thick denture bases were relined with 1 mm of autopolymerizing resin (Tokuyama Rebase Fast II or New Truliner) (n = 28). Intact and relined specimens were divided into 4 groups (n = 7) as follows: without stress (control); a mechanical stress at 0.8 Hz for 10,000 cycles; 5000 thermal cycles between 5 degrees C and 55 degrees C; or a combination thermo-mechanical stress. The specimens were vertically loaded in compression with a rounded rod at 5 mm/min until failure, using a universal testing machine. Data on maximum fracture load (N), deflection at fracture (%), and fracture energy (N-mm) were analyzed by 2-way analysis of variance and Student-Newman-Keuls tests (alpha = .05).Results. The strength of the denture bases relined with New Truliner was not significantly affected by any of the experimental conditions, but comparing the control groups, New Truliner exhibited the lowest maximum fracture load values. The maximum fracture load of intact denture bases (P = .002) and those relined with Tokuyama Rebase Fast II (P = .01) showed a significant decrease after thermal stress. Additionally, cyclic loading significantly decreased the maximum fracture load (P < .001), deflection at fracture (P = .025), and fracture energy (P < .001) of intact denture bases and those relined with Tokuyama Rebase (P values of .002, .039, and .001, respectively).Conclusion. Thermal and mechanical stresses exert deleterious effects on the strength of intact and/or relined denture bases, which vary according to the relining material used.

Electrical and mechanical effects of hyoscine butylbromide on the human stomach: a non-invasive approach

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Dynamics of experimental populations of native and introduced blowflies (Diptera: Calliphoridae): mathematical modelling and the transition from asymptotic equilibrium to bounded oscillations

The equilibrium dynamics of native and introduced blowflies is modelled using a density-dependent model of population growth that takes into account important features of the life-history in these flies. A theoretical analysis indicates that the product of maximum fecundity and survival is the primary determinant of the dynamics. Cochliomyia macellaria, a blowfly native to the Americas and the introduced Chrysomya megacephala and Chrysomya putoria, differ in their dynamics in that the first species shows a damping oscillatory behavior leading to a one-point equilibrium, whereas in the last two species population numbers show a two-point limit cycle. Simulations showed that variation in fecundity has a marked effect on the dynamics and indicates the possibility of transitions from one-point equilibrium to bounded oscillations and aperiodic behavior. Variation in survival has much less influence on the dynamics.

Karyotype plasticity in crickets: Numerical, morphological, and nucleolar organizer region distribution pattern of Anurogryllus sp.

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

Evaluation of interface characterization and adhesion of glass ceramics to commercially pure titanium and gold alloy after thermal- and mechanical-loading

Objectives. This study evaluated the effect of thermal- and mechanical-cycling on the shear bond strength of three low-fusing glassy matrix dental ceramics to commercial pure titanium (cpTi) when compared to conventional feldspathic ceramic fused to gold alloy.Methods. Metallic frameworks (diameter: 5 min, thickness: 4 mm) (N = 96, n = 12 per group) were cast in cpTi and gold alloy, airborne particle abraded with 150 mu m aluminum oxide. Low-fusing glassy matrix ceramics and a conventional feldspathic ceramic were fired onto the alloys (thickness: 4mm). Four experimental groups were formed; Gr1 (control group): Vita Omega 900-Au-Pd alloy; Gr2: Ticeram-cpTi; Gr3: Super Porcelain Ti-22-cpTi and G4: Vita Titankeramik-cpTi. While half of the specimens from each ceramic-metal combination were randomly tested without aging (water storage at 37 C for 24h only), the other half were first thermocycled (6000 cycles, between 5 and 55 C, dwell time: 13 s) and then mechanically loaded (20,000 cycles under SON load, immersion in distilled water at 37 C). The ceramic-alloy interfaces were loaded under shear in a universal test machine (cross-head speed: 0.5 mm/min) until failure occur-red. Failure types were noted and the interfaces of the representative fractured specimens from each group were examined with stereo microscope and scanning electron microscope (SEM). in an additional study (N = 16, n = 2 per group), energy dispersive X-ray spectroscopy (EDS) analysis was performed from ceramic-alloy interfaces. Data were analyzed using ANOVA and Tukey's test.Results. Both ceramic-metal combinations (p < 0.001) and aging conditions (p < 0,001) significantly affected the mean bond strength values. Thermal- and mechanical-cycling decreased the bond strength (MPa) results significantly for Gr3 (33.4 +/- 4.2) and Gr4 (32.1 +/- 4.8) when compared to the non-aged groups (42.9 +/- 8.9, 42.4 +/- 5.2, respectively). Gr1 was not affected significantly from aging conditions (61.3 +/- 8.4 for control, 60.7 +/- 13.7 after aging) (p > 0.05). Stereomicroscope images showed exclusively adhesive failure types at the opaque ceramic-cpTi interfacial zone with no presence of ceramic on the substrate surface but with a visible dark titanium oxide layer in Groups 2-4 except Gr1 where remnants of bonder ceramic was visible. EDS analysis from the interfacial zone for cpTi-ceramic groups showed predominantly 34.5-85.1% O(2) followed by 1.1-36.7% Aland 0-36.3% Si except for Super Porcelain Ti-22 where a small quantity of Ba (1.4-8.3%), S (0.7%) and Sn (35.3%) was found. In the Au-Pd alloy-ceramic interface, 56.4-69.9% O(2) followed by 15.6-26.2% Si, 3.9-10.9% K, 2.8-6% Na, 4.4-9.6% Al and 0-0.04% Mg was observed.Significance. After thermal-cycling for 6000 times and mechanical-cycling for 20,000 times, Triceram-cpTi combination presented the least decrease among other ceramic-alloy combinations when compared to the mean bond strength results with Au-Pd alloy-Vita Omega 900 combination. (c) 2008 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Effect of Acid Neutralization and Mechanical Cycling on the Microtensile Bond Strength of Glass-ceramic Inlays

Objectives: To evaluate the hypothesis that a process of hydrofluoric acid precipitate neutralization and fatigue load cycling performed on human premolars restored with ceramic inlays had an influence on microtensile bond strength results (MTBS). Methods: MOD inlay preparations were performed in 40 premolars (with their roots embedded in acrylic resin). Forty ceramic restorations were prepared using glass-ceramic (IPS Empress). The inner surfaces of all the restorations were etched with 10% hydrofluoric acid for 60 seconds, rinsed with water and dried. The specimens were divided into two groups (N=20): 1-without neutralization; 2-with neutralization. All the restorations were silanized and adhesively cemented (self-curing and self-etching luting composite system, Multilink). Ten premolars from each group were submitted to mechanical cycling (1,400,000 cycles, 50N, 37 degrees C). After cycling, the samples were sectioned to produce non-trimmed beam specimens (vestibular dentin-restoration-lingual dentin set), which were submitted to microtensile testing. Results: Bond strength was significantly affected by the surface treatment (p<0.0001) (no neutralization > neutralization) and mechanical cycling (p<0.0001) (control > cycling) (2-way ANOVA and Tukey test, alpha=.05). Conclusion: Hydrofluoric acid precipitate neutralization appears to significantly damage the resin bond to glass-ceramic and should not be recommended. The clinical simulation of the specimens, by using mechanical cycling, is important when evaluating the ceramic-dentin bond.

Physical and mechanical properties of ceramics from clays of the west of S. Paulo State, Brazil

Argilas de interesse da indústria de cerâmica estrutural foram caracterizadas. Algumas propriedades físicas de diversas massas cerâmicas, preparadas a partir de material coletado em depósitos artificiais, também foram analisadas. Todas as massas investigadas exibem alta concentração de componentes finos (< 2 mim) e considerável grau de plasticidade, o que é compatível com a presença de elevado teor de argilominerais. Corpos de prova cerâmicos foram preparados por prensagem a seco e queimados em temperaturas ao redor de 855 °C. Os parâmetros resistência mecânica à flexão, retração linear, absorção de água, cor aparente e perda de peso foram medidos. Como resultado, as aplicações industriais destas matérias primas foram analisadas e revistas, bem como novas aplicações foram propostas.

Thermal and mechanical properties of PVDF/PANI blends

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

Modelling and optimization of the cephalosporin C production bioprocess in a fed-batch bioreactor with invert sugar as substrate

Cephalosporin C production process optimization was studied based on four experiments carried out in an agitated and aerated tank fermenter operated as a fed-batch reactor. The microorganism Cephalosporium acremonium ATCC 48272 (C-10) was cultivated in a synthetic medium containing glucose as major carbon and energy source. The additional medium contained a hydrolyzed sucrose solution as the main carbon and energy source and it was added after the glucose depletion. By manipulating the supplementary feed rate, it was possible to increase antibiotic production. A mathematical model to represent the fed-batch production process was developed. It was observed that the model was applicable under different operation conditions, showing that optimization studies can be made based on this model. (C) 1999 Elsevier B.V. Ltd. All rights reserved.

MIXMASTER NUMERICAL BEHAVIOR AND GENERALIZATIONS

The numerical simulation of the mixmaster universe serves the purpose of suggesting two kinds of results. The intrinsic time evolution, during contraction, will be seen to be nonchaotic. This is a necessary feature of relativistic cosmological models undergoing this kind of motion. The mixmaster model also provides a clue on how to define chaoticity for systems described by nonautonomous sets of differential equations.

Free activity in the cage associated with body weight and restoration of bone structural and mechanical properties in growing rats after hindlimb unloading

We investigated the importance of daily free activity in the cage and body weight gain during the recovering of bone structural and mechanical properties in growing rats after hindlimb unloading. Eight-week-old male Wistar rats were randomly divided into control (CG, n=24) and suspended (SG, n=24) groups. Animals from SG underwent a four-week hindlimb unloading period by tail-suspension. Animals from CG and those from SG after release were kept in collective cages and sacrificed at the age of 12, 16 and 20 weeks. Both femurs were removed and its area, bone mineral density (BMD), resistance to failure and stiffness were determined. Four-week hindlimb unloading decreased (p < 0.05) body weight (CG, 373.00 +/- 9.47 vs. SG, 295.86 +/- 9.19 g), BMD (CG, 0.19 +/- 0.01 vs. SG, 0.15 +/- 0.01 g/cm(2)), bone resistance to failure (CG, 147.75 +/- 5.05 vs. SG, 96.40 +/- 5.95 N) and stiffness (CG, 0.38 +/- 0.01 vs. SG, 0.23 +/- 0.02 N/m). Eight weeks of free activity in cage recovered (p > 0.05) the body weight (CG, 472.75 +/- 14.11 vs. SG, 444.75 +/- 18.91 g), BMD (CG, 0.24 +/- 0.01 vs. SG, 0.22 +/- 0.01 g/cm(2)), bone resistance to failure (CG, 195.73 +/- 10.06 vs. SG, 178.45 +/- 8.48 N) and stiffness (CG, 0.56 +/- 0.02 vs. SG, 0.47 +/- 0.03 N/m) of SG animals. Body weight correlated strongly with bone structural and mechanical properties (p < 0.0001). In conclusion, free activity in the cage associated with body weight gain restored bone structural and mechanical properties in growing rats after hindlimb unloading.

Processing and mechanical characterization of titanium-graphite hybrid laminates

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