SUMMARY:The behaviour of catalytic systems based on zirconium compounds for the copolymenzation of ethylene with 1-hexene and 1-octene is reported. The metallocenes (CH3),SiCp2-ZrCI,, Cp2ZrC1, (Cp = q5-cyclopentadienyl), (C2H, [Ind],ZrCl2 and [Ind],ZrCl, (Ind = qxindenyl) were chosen for this study. The bridged catalysts, (CH3),SiCp2ZrC1, and C,H,[Ind],ZrCl,, and the metallocene Cp2ZrCI2 showed similar catalytic activities for homo-and copolymerization of ethylene with 1-hexene. 13C NMR analysis showed that the composition of copolymerization products depends on the catalytic system, in other words, on the ligand structure of the transition metal. Copolymers obtained using the bridged catalysts have greater incorporation of comonomer. Thermal analysis and viscosity measurements demonstrated that an increase of the comonomer concentration reduces the melting point, the crystallinity and the molecular weight of the copolymer. Results from infrared spectroscopy showed that p-elimination is one of the possible termination reactions. The monomer reactivity ratios r were determined for all catalytic systems using Fineman-Ross and "C NMR methods. The values of r, (M, = ethylene) and r2 (M, = aolefin) showed an effect of the type of metallocene and of a-olefin on the structure of the copolymer obtained.

4,5,6,7-Tetrahydro-5-methylimidazo[4,5,1-jk][1,4]benzodiazepin-2 (1H)-ones (TIBO), 1, have been shown to significantly inhibit HIV-1 replication in vitro by interfering with the virus's reverse transcriptase enzyme. They have also demonstrated potential clinical efficacy in combating HIV-1, on the basis of a preliminary study. Our prior publications have discussed the discovery of this series of compounds and reported some preliminary chemical and biological studies around N-6 substitutions and 5-membered ring variations of 1. This manuscript describes our synthetic endeavors around 4, 5, and 7 mono- and disubstitutions of 1 and discusses related HIV-1 inhibitory structure-activity relationships. On the basis of inhibition of HIV-1's cytopathic effects in MT-4 cells, we found that 5-mono-Me-substituted analogues, the original substitution in the early lead compounds, and 7-mono-Me-substituted analogues of 1 were comparable as being consistently the most active compounds. Although generally less active, the 4,5,7-unsubstituted, 4-mono-substituted, cis- and trans-5,7-di-Me-substituted, and cis-4,5-di-Me-substituted analogues of 1 also exhibited some significant desired activity. The remaining trans-4,5-di-Me-substituted, cis- and trans-4,7-di-Me-substituted, and all 4,5-, 5,6-, 6,7-, and 7,8-fused disubstituted analogues of 1 possessed no noticeable desired activity.

In previous papers, we have described the discovery of a new series of compounds, 4,5,6,7-tetrahydro-5-methylimidazo[4,5,1-jk][1,4]benzodiazepin-2(1 H)- ones, TlBO (1 and 1a), with potent anti-HIV-1 activity and the synthesis of analogues to better define the structure-activity relationships (SAR) in terms of changes in substituents at the N-6 position and variations of the five-membered urea ring as well as the seven-membered diazepine ring. This paper describes the synthesis of TlBO analogues with various substitutents on the aromatic ring and their SAR in terms of anti-HIV-1 properties. Substituents on the 8-position furnished the most rewarding results and gave a large improvement in potency versus the parent compound. These included halogen, thiomethyl, and methyl. Analogues like 8-cyano, -methoxy, and -acetylene were equipotent, while 8-amino, -acetylamino, -dimethylamino, and -nitro were inactive (Table 1). Substituents at the 9-position tended to have little effect on activity, and 10-substituents decreased activity. The 8-chloro compound 6a with IC50 = 0.0043 microM is currently under clinical development.

The aim of this study was to evaluate the accuracy of three implant transfer impression techniques. Four groups (n = 5) were defined, according to the technique: TC -tapered copings without splint; SCsquare copings without splint; SCS -square copings splinted with dental floss and acrylic resin, and CG (control group) -master model with four external hexagonal implants and a superstructure. Individual trays and polyether were used for the impression. All casts were checked for their fit into the master superstructure; for this, all four screws were placed in the implants. Digital photos were taken and images were analyzed using UTHSCSA ImageTool software. Statistical analyses were performed using one-way analysis of variance and Student's t test (p < 0.05). The means and standard deviation were (µm): CG = 2.03 ± 0.00, TC = 14.74 ± 3.41, SC = 12.08 ± 2.56, and SCS = 6.51 ± 0.09. The control group was found to be statistically different from the TC and SC groups. Within the limitations of this study, all groups presented clinically acceptable standard gap values, and the SCS group showed no statistical difference in relation to the CG (control group), demonstrating more accuracy and fidelity to transfer implants.

Clinical RelevanceAs a result of variations in accurate shade perception, considerations should be given to using multiple opinions to compensate for errors caused by gender or inexperience, especially when lighter shades are involved. SUMMARYStatement of the Problem: Precise shade matching can be one of the most difficult tasks for the dentist and some variables may influence the process of shade comparison.Purpose of the Study: This study tested the differences in shade perception between genders, the influence of the observer's clinical experience, and the value of ceramics in correct shade selection. Results: The results indicated that there were statistical differences among gender, clinical experience, and shades in discriminating ceramics.Conclusions: Men and observers with more clinical experience were more successful in discriminating shades, although darker shades were selected more correctly than the lighter ones.

The results of this study showed that understandability of speech was the only predictor of overall QoL scores.

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Objective To evaluate the shear bond strength between different artificial teeth and denture base polymerized by two polymerization methods submitted to thermocycling. Materials and Methods Two acrylic resins were selected according to the polymerization method (water-bath and microwave), and four different artificial teeth (Biotone, Dentsply; Trilux, Vipi Dent; Premium 8, Heraeus Kulzer; Soluut PX, Yamahachi) were also tested. The polymerization of the acrylic resin was performed by using conventional cycle (8 h at 74°C) in water-bath and using two cycles (20 min at 270 W + 5 min at 360 W) by the microwave method. The shear bond strength was evaluated after 24 h of water storage at 37°C (immediately) and after the thermocycling test (5,000 cycles, 5–55°C). The shear bond strength (n=10) was performed using a universal testing machine (Instron 4411) at a crosshead speed of 1.0 mm/min. Modes of failures were classified as cohesive and adhesive. The data (MPa) were statistically analyzed by three-way ANOVA, and the mean values were compared by the Tukey test (α = 0.05). Results In general, the polymerization by microwave showed the highest shear bond strength values, and Trilux artificial teeth had the lowest bond strength values (p < 0.05). Thermocycling did not affect the shear bond strength (p < 0.05). There was a predominance of cohesive failures for all groups. Conclusions The chemical composition of the artificial teeth affects the bond strength, and the microwave method is preferable to perform the acrylic resin polymerization.