Stepwise stress testing of different CAD-CAM lithium disilicate veneer application methods applied to lithium disilicate substructures.

STATEMENT OF PROBLEM: Whether a computer-aided design and computer-aided manufacture (CAD-CAM) fabricated high-translucency lithium disilicate veneer on a lithium disilicate substructure would increase the strength of the restoration compared with a traditional feldspathic porcelain veneer is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the effect of different lithium disilicate veneer application methods on a lithium disilicate substructure on their biaxial flexural stress (BFS). MATERIAL AND METHODS: Lithium disilicate disks were fabricated so that when combined with the veneering disks, they had a dimension of 12×1.2 mm. Experimental groups were as follows (n=15): resin-bonded lithium disilicate veneer, lithium disilicate veneer adhesively cemented to lithium disilicate; sintered lithium disilicate veneer, lithium disilicate veneer sintered to lithium disilicate; sintered feldspathic veneer, feldspathic porcelain applied to lithium disilicate; and monolithic lithium disilicate, the control group. Weibull distribution survival analysis was used to compare the differences in the resistance to fracture after fatigue. The total number of cycles was analyzed by using 1-way ANOVA (α=.05). A finite element analysis (FEA) was also performed. The maximum principal stress (MPS) was used as the failure criterion. RESULTS: The sintered feldspathic veneer group had significantly lower fatigue resistance than sintered lithium disilicate veneer or resin-bonded lithium disilicate veneer (P<.05). The resin-bonded lithium disilicate veneer group showed significantly more fractured fragments than the other groups. No statistical difference was observed in the number of cycles. The lithium disilicate veneered groups presented similar resistance to fatigue as the monolithic specimens of the same overall dimensions. Higher peaks of MPS were observed for groups monolithic lithium disilicate, sintered lithium disilicate veneer, and sintered feldspathic veneer than for resin-bonded lithium disilicate veneer. CONCLUSIONS: Veneering a lithium disilicate substructure with a lithium disilicate veneer, bonded or sintered, increased resistance to fatigue compared with a feldspathic porcelain veneer. The lithium disilicate veneer groups had similar fatigue resistance to that of the monolithic group.

The Effect of Plasma Nitriding on the Fatigue Behavior of the Ti-6Al-4V Alloy.

The Ti-6Al-4V alloy is widely used in the manufacture of components that must have low density and high corrosion resistance and fatigue strength. The fatigue strength can be improved by surface modification. The aim of this study was to determine the influence of plasma nitriding on the fatigue behavior of a Ti-6Al-4V alloy with a lamellar microstructure (Widmanstätten type). Nitriding was executed at 720 °C for 4 h in an atmosphere with N2, Ar, and H2. Microstructure characterization of the samples was carried out by X-ray diffraction analysis, optical microscopy, and scanning electron microscopy. The average roughness of the specimens was determined, and fatigue tests were executed in a bending⁻rotating machine with reverse tension cycles (R = -1). X-ray diffraction analysis of the nitrided alloy revealed the following matrix phases: α, ß, ε-Ti2N, and δ-TiN. A nitrogen diffusion layer was formed between the substrate and the titanium nitrides. Plasma nitriding resulted in an increase in low-cycle fatigue strength, whereas at high cycles of 200 MPa, both conditions exhibited similar behaviors. The fracture surface of the fatigue-tested specimens clearly revealed the lamellar microstructure. The fracture mechanism in the non-nitrided specimens appears to be due to cracking at the interface of the α and ß phases of the lamellar microstructure.

Complete Genome Sequence of Xanthomonas campestris pv. viticola Strain CCRMXCV 80 from Brazil.

Here, we report the complete 5.3-Mb genome sequence of Xanthomonas campestris pv. viticola (CCRMXCV 80), which causes grapevine (Vitis vinifera L.) bacterial canker. Genome data will improve our understanding of the strain's comparative genomics and epidemiology, and help to further define plant protection and quarantine procedures.

In situ evaluation of fluoride-, stannous- and polyphosphate-containing solutions against enamel erosion.

OBJECTIVE: To evaluate the anti-erosive effect of solutions containing sodium fluoride (F: 225ppm of fluoride), sodium fluoride+stannous chloride (F+Sn: 225ppm of fluoride+800ppm of stannous), sodium fluoride+stannous chloride+sodium linear polyphosphate (F+Sn+LPP: 225ppm of fluoride+800ppm of stannous+2% of sodium linear polyphosphate), and deionized water (C: control), using a four-phase, single-blind, crossover in situ clinical trial. METHODS: In each phase, 12 volunteers wore appliances containing 4 enamel specimens, which were submitted to a 5-day erosion-remineralization phase that consisted of 2h of salivary pellicle formation with the appliance in situ, followed by 2min extra-oral immersion in 1% citric acid (pH 2.4), 6x/day, with 90min of exposure to saliva in situ between the challenges. Treatment with the test solutions was performed extra-orally for 2 min, 2x/day. At the end of the experiment, surface loss (SL, in µm) was evaluated by optical profilometry. Data were analyzed using ANOVA and Tukey tests (α=0.05). The surface of additional specimens was evaluated by x-ray diffraction after treatments (n=3). RESULTS: C (mean SL±standard-deviation: 5.97±1.70) and F (5.36±1.59) showed the highest SL, with no significant difference between them (p>0.05). F+Sn (2.68±1.62) and F+Sn+LPP (2.10±0.95) did not differ from each other (p>0.05), but presented lower SL than the other groups (P<0.05). Apatite and stannous deposits on specimen surfaces were identified in the x-ray analysis for F+Sn and F+Sn+LPP. CONCLUSIONS: Sodium fluoride solution exhibited no significant anti-erosive effect. The combination between sodium fluoride and stannous chloride reduced enamel erosion, irrespective of the presence of linear sodium polyphosphate. CLINICAL SIGNIFICANCE: Under highly erosive conditions, sodium fluoride rinse may not be a suitable alternative to prevent enamel erosion. A rinse containing sodium fluoride and stannous chloride was shown to be a better treatment option, which was not further improved by addition of the sodium linear polyphosphate.