Effect of mechanical cycling on the flexural strength of densely sintered ceramics

Objectives. The aim of this study was to evaluate the effect of mechanical cycling on the biaxial flexural strength of two densely sintered ceramic materials.Methods. Disc shaped zirconia (In-Ceram Zirconia) and high alumina (Procera AllCeram) ceramic specimens (diameter: 15 min and thickness: 1.2 mm) were fabricated according to the manufacturers' instructions. The specimens from each ceramic material (N = 40, n = 10/per group) were tested for flexural strength either with or without being subjected to mechanical cycling (20,000 cycles under 50 N load, immersion in distilled water at 37 degrees C) in a universal testing machine (1 mm/min). Data were statistically analyzed using two-way ANOVA and Tukey's test (alpha = 0.05).Results. High alumina ceramic specimens revealed significantly higher flexural strength values without and with mechanical cycling (647 +/- 48 and 630 +/- 143 MPa, respectively) than those of zirconia ceramic (497 +/- 35 and 458 +/- 53 MPa, respectively) (p < 0.05). Mechanical cycling for 20,000 times under 50 N decreased the flexural strength values for both high alumina andSignificance. High alumina ceramic revealed significantly higher mean flexural strength values than that of zirconia ceramic tested in this study either with or without mechanical cycling conditions. (C) 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Nutrients cycling aspects in stands of Pinus-elliottii engelm var elliottii under differents resining intensities .1. litter fall

Litter production was measured for two years (november 1986 to october 1988) in a 29 year -old Pinus elliottii var. elliottii stand in differents resin treatments. Needle production comprised 9 to 93% of total litter fall, while the other categories (branches, barks, seeds and cones) were not significant. Maximum litterfall occurred in march to may 1987 (autumn) and the minimum was in august 1988 (winter) for all treatments and the control. No relationship appeared between annual litterfall and environmental factors, although there was a tendence to exhibit two periods of production: one in summer and other in winter. The results showed that in two years of resin extraction was not sufficient in interfering the litter fall and consequently the productivity.

Nutrient cycling aspects in stands of Pinus-elliottii engelm var elliottii under differents resining intensities .2. nutrients contents in litter

Annual and monthly quantities of nutrients wich returned to the soil through litter fall in Pinus elliottii Engelm. var. elliottii stand were estimated durint a two years period, in Experimental Station of Mogi-Guacu, SP. From the trees of the stand was extracted oleoresin according two differents techniques and control. The annual average of nutrients that returned to the soil was 72.2 Kg/ha, in following order: N > Ca > K > Mg > P. No relationship appeared between nutrient concentrations plus quantities when they were compared with oleoresin yields treatments and control. The differences in annual quantities were possibly due to climatic factors. The soil profile showed short concentrations in nutrient contents. Thus, the forest may be suffering by nutrient deficiences.

Fiber Post Cementation Strategies: Effect of Mechanical Cycling on Push-out Bond Strength and Cement Polymerization Stress

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Aerobic fitness level typical of elite athletes is not associated with even faster VO2 kinetics during cycling exercise

The aim of this study was to address the question if the VO2 kinetics is further improved as the aerobic training status increases from trained to elite level athletes. Maximal oxygen uptake (VO(2)max), work-rate associated to VO(2)max (IVO(2)max) and VO2 kinetics of moderate (Mod) and maximal exercise (Max) were determined in fifty-five subjects. Then, they were assigned into three groups: low (LF), intermediate (IF) and high (HF) aerobic fitness level. In average, the VO(2)max of LF, IF and HF groups were, respectively, 36.0 +/- 3.1, 51.1 +/- 4.5 and 68.1 +/- 3.9 ml . kg . min(-1) (p <= 0.05 among each other). VO2 kinetics mean response time of both exercise intensities were significantly faster (p <= 0.05) in HF (Mod, 27.5 +/- 5.5 s; Max, 32.6 +/- 8.3 s) and IF (Mod, 25.0 +/- 3.1 s; Max, 42.6 +/- 10.4 s) when compared to LF (Mod, 35.7 +/- 7.9 s; Max: 57.8 +/- 17.8 s). We can conclude that VO2 kinetics is improved as the fitness level is increased from low to intermediate but not further improved as the aerobic fitness level increases from intermediate to high.

Is maximal lactate steady state during intermittent cycling different for active compared with passive recovery?

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

Superovulation in Cycling Mares Using Equine Follicle Stimulating Hormone (eFSH)

Superovulation would potentially increase the efficiency and decrease the cost of embryo transfer by increasing embryo collection rates. Other potential clinical applications include improving pregnancy rates from frozen semen, treatment of subfertility in stallions and mares, and induction of ovulation in transitional mares. The objective of this study was to evaluate the efficacy of purified equine follicle stimulating hormone (eFSH; Bioniche Animal Health USA, Inc., Athens, GA) in inducing superovulation in cycling mares. In the first experiment, 49 normal, cycling mares were used in a study at Colorado State University. Mares were assigned to 1 of 3 groups: group 1, controls (n = 29) and groups 2 and 3, eFSH-treated (n = 10/group). Treated mares were administered 25 mg of eFSH twice daily beginning 5 or 6 days after ovulation (group 2). Mares received 250 (of cloprostenol on the second day of eFSH treatment. Administration of eFSH continued until the majority of follicles reached a diameter of 35 mm, at which time a deslorelin implant was administered. Group 3 mares (n = 10) received 12 mg of eFSH twice daily starting on day 5 or 6. The treatment regimen was identical to that of group 2. Mares in all 3 groups were bred with semen from 1 of 4 stallions. Pregnancy status was determined at 14 to 16 days after ovulation. In experiment 2, 16 light-horse mares were used during the physiologic breeding season in Brazil. On the first cycle, mares served as controls, and on the second cycle, mares were administered 12 mg of eFSH twice daily until a majority of follicles were 35 mm in diameter, at which time human chorionic gonadotropin (hCG) was administered. Mares were inseminated on both cycles, and embryo collection attempts were performed 7 or 8 days after ovulation. Mares treated with 25 mg of eFSH developed a greater number of follicles (35 mm) and ovulated a greater number of follicles than control mares. However, the number of pregnancies obtained per mare was not different between control mares and those receiving 25 mg of eFSH twice daily. Mares treated with 12 mg of eFSH and administered either hCG or deslorelin also developed more follicles than untreated controls. Mares receiving eFSH followed by hCG ovulated a greater number of follicles than control mares, whereas the number of ovulations from mares receiving eFSH followed by deslorelin was similar to that of control mares. Pregnancy rate for mares induced to ovulate with hCG was higher than that of control mares, whereas the pregnancy rate for eFSH-treated mares induced to ovulate with deslorelin did not differ from that of the controls. Overall, 80% of mares administered eFSH had multiple ovulations compared with 10.3% of the control mares. In experiment 2, the number of large follicles was greater in the eFSH-treated cycle than the previous untreated cycle. In addition, the number of ovulations during the cycle in which mares were treated with eFSH was greater (3.6) than for the control cycle (1.0). The average number of embryos recovered per mare for the eFSH cycle (1.9 ± 0.3) was greater than the embryo recovery rate for the control cycle (0.5 ± 0.3). In summary, the highest ovulation and the highest pregnancy and embryo recovery rates were obtained after administration of 12 mg of eFSH twice daily followed by 2500 IU of hCG. Superovulation with eFSH increased pregnancy rate and embryo recovery rate and, thus, the efficiency of the embryo transfer program.

Oxygen uptake kinetics and time to exhaustion in cycling and running: A comparison between trained and untrained subjects

The objective of the present study was to compare pulmonary gas exchange kinetics (VO 2 kinetics) and time to exhaustion (Tlim) between trained and untrained individuals during severe exercise performed on a cycle ergometer and treadmill. Eleven untrained males in running (UR) and cycling (UC), nine endurance cyclists (EC), and seven endurance runners (ER) were submitted to the following tests on separate days: (i) incremental test for determination of maximal oxygen uptake (VO 2max) and the intensity associated with the achievement of VO 2max (IVO 2max) on a mechanical braked cycle ergometer (EC and UC) and on a treadmill (ER and UR); (ii) all-out exercise bout performed at IVO 2max to determine the time to exhaustion at IVO 2max (Tlim) and the time constant of oxygen uptake kinetics (τ). The τ was significantly faster in trained group, both in cycling (EC = 28.2 ± 4.7 s; UC = 63.8 ± 25.0 s) and in running (ER = 28.5 ± 8.5 s; UR = 59.3 ± 12.0 s). Tlim of untrained was significantly lower in cycling (EC = 384.4 ± 66.6 s vs. UC; 311.1 ± 105.7 s) and higher in running (ER = 309.2 ± 176.6 s vs. UR = 439.8 ± 104.2 s). We conclude that the VO 2 kinetic response at the onset of severe exercise, carried out at the same relative intensity is sensitive to endurance training, irrespective of the exercise type. The endurance training seems to differently influence Tlim during exercise at IVO 2max in running and cycling. © 2003 Taylor & Francis Ltd.

Effect of fluoridated varnish and silver diamine fluoride solution on enamel demineralization: pH-cycling study

Objective: In the present investigation, the anticariogenic effect of fluoride released by two products commonly applied in infants was evaluated. Methods: Bovine sound enamel blocks were randomly allocated to each one of the treatment groups: control (C), varnish (V) and diamine silver fluoride solution (D). The blocks were submitted to pH cycles in an oven at 37°C. Next, surface and cross-sectional microhardness were assessed to calculate the percentage loss of surface microhardness (%SML) and the mineral loss (ΔZ). The fluoride present in enamel was also determined. Results: F/Px10 -3 (ANOVA, p<0.05) in the 1 st layer of enamel before pH-cycling were (C, V and D): 1.61 a; 21.59 b and 3.98 c. The %SMH (Kruskal-Wallis, p<0.05) were: -64.0 a, -45.2 b and -53.1 c. %ΔZ values (ANOVA, p<0.05) were: -18.7 a, -7.7 b and -17.3 a. Conclusion: The data suggested that the fluoride released by varnish showed greater interaction with sound enamel and provided less mineral loss when compared with silver diamine solution.

Bond strength of hard chairside reline resins to a rapid polymerizing denture base resin before and after thermal cycling

Purpose: This study assessed the shear bond strength of 4 hard chairside reline resins (Kooliner, Tokuso Rebase Fast, Duraliner II, Ufi Gel Hard) to a rapid polymerizing denture base resin (QC-20) processed using 2 polymerization cycles (A or B), before and after thermal cycling. Materials and Methods: Cylinders (3.5 mm x 5.0 mm) of the reline resins were bonded to cylinders of QC-20 polymerized using cycle A (boiling water-20 minutes) or B (boiling water; remove heat-20 minutes; boiling water-20 minutes). For each reline resin/polymerization cycle combination, 10 specimens (groups CAt e CBt) were thermally cycled (5 and 55°C; dwell time 30 seconds; 2,000 cycles); the other 10 were tested without thermal cycling (groups CAwt ad CBwt). Shear bond tests (0.5 mm/min) were performed on the specimens and the failure mode was assessed. Data were analyzed by 3-way ANOVA and Newman-Keuls post-hoc test (α=.05). Results: QC-20 resin demonstrated the lowest bond strengths among the reline materials (P<.05) and mainly failed cohesively. Overall, the bond strength of the hard chairside reline resins were similar (10.09±1.40 to 15.17±1.73 MPa) and most of the failures were adhesive/cohesive (mixed mode). However, Ufi Gel Hard bonded to QC-20 polymerized using cycle A and not thermally cycled showed the highest bond strength (P<.001). When Tokuso Rebase Fast and Duraliner II were bonded to QC-20 resin polymerized using cycle A, the bond strength was increased (P=.043) after thermal cycling. Conclusions: QC-20 displayed the lowest bond strength values in all groups. In general, the bond strengths of the hard chairside reline resins were comparable and not affected by polymerization cycle of QC-20 resin and thermal cycling.

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.

Adhesive cementation of zirconia posts to root dentin: Evaluation of the mechanical cycling effect

This study evaluated the effect of mechanical cycling on the bond strength of zirconia posts to root dentin. Thirty single-rooted human teeth were transversally sectioned to a length of 16 mm. The canal preparation was performed with zirconia post system drills (CosmoPost, Ivoclar) to a depth of 12 mm. For post cementation, the canals were treated with total-etch, 3-steps All-Bond 2 (Bisco), and the posts were cemented with Duolink dual resin cement (Bisco). Three groups were formed (n = 10): G1 - control, no mechanical cycling; G2 - 20,000 mechanical cycles; G3 - 2,000,000 mechanical cycles. A 1.6-mm-thick punch induced loads of 50 N, at a 45° angle to the long axis of the specimens and at a frequency of 8 Hz directly on the posts. To evaluate the bond strengths, the specimens were sectioned perpendicular to the long axis of the teeth, generating 2-mm-thick slices, approximately (5 sections per teeth), which were subjected to the push-out test in a universal testing machine at a 1 mm/min crosshead speed. The push-out bond strength was affected by the mechanical cycling (1-way ANOVA, p = .0001). The results of the control group (7.7 ± 1.3 MPa) were statistically higher than those of G2 (3.9 ± 2.2 MPa) and G3 (3.3 ± 2.3 MPa). It was concluded that the mechanical cycling damaged the bond strength of zirconia posts to root dentin.