Comparison of Retention of Two Different Attachment Systems Used in Implant-Supported Overdentures.

Aim: This study aims to compare the retentive capacity of two attachment systems after manual thermocycling. Settings and Design: In vitro study and Comparative trail. Materials and Methods: An edentulous mandibular Polymethyl Methacrylate model was fabricated to receive the overdentures with the two attachment systems to be compared. Two dental implants were placed in the predetermined right and left mandibular canine regions of the model. A total number of eight overdentures, four per group, were fabricated over the two implants with two attachment systems to be compared; Bar and clip attachment system (Group-1) and Locator attachment system (Group-2). All the overdentures were subjected to 5000 alternating thermal cycles using manual thermocycling. Then the samples were subjected to 100 vertical pulls each in the anterior and posterior regions using a universal testing machine and the mean retentive forces were calculated for each sample in the anterior and posterior regions, respectively. Results: The mean retentive forces after 100 vertical pulls, were calculated and tabulated for each sample in the anterior and posterior regions separately. Then, the cumulative mean of the anterior and the posterior regions were calculated for each group. The cumulative mean retentive forces of both the attachment groups were-Group-1 (Bar and clip attachment system) = 27.87 N ± 4.01 and Group-2 (locator attachment system) = 18.85 N ± 2.50 with a P value of 0.021. This difference was found to be statistically significant. Conclusion: Within the limitations of the present in vitro study, the bar and clip attachment system offered better retention than the locator attachment system.

2,6-Dibromo-4-formyl-phenyl 3-phenyl-prop-2-enoate.

Mol-ecules of the title compound, C(16)H(10)Br(2)O(3), adopt an E conformation about the C=C double bond. The dihedral angle between the two aromatic rings is 78.0 (7)°. In the crystal, mol-ecules are linked through weak C-H⋯O hydrogen bonds.

The measurement of attogram mass accumulation on nanostructures during e-beam scanning, using carbon nanopillars in resonant mode.

We present a 'universal' phenomenon of mass accumulation and its sensing on nanostructures due to electron beam cracking of residual gas molecules during electron beam scanning. Though the extent of this phenomenon is limited to a very small increment in mass or thickness, it has significant implications for both the scientific and technological aspects of almost all processes in the nanodomain. Mass accumulation in every frame scan (or per second) is of the order of a few attograms and the thickness of deposition is of the order of picometre (fraction of a monolayer) only. Direct measurement of a mass or thickness of this order is difficult. Nanopillars having a high resonance 'Q-factor' have been successfully exploited for such high precision measurements. The mass accumulation rate has been characterized with respect to (i) electron energy and beam current, (ii) environment within the chamber (presence or absence of a precursor gas) and (iii) partial exposure of the nanopillars to the e-beam.

Controlled manipulation of carbon nanopillars and cantilevers by focused ion beam.

We explore a novel phenomenon of focused ion beam (FIB) induced bending of carbon nanopillars or cantilever structures. The bending occurs towards the ion beam during scanning. The explanation of this bending has been sought on the basis of a model which considers temperature rise and gradients caused by the impinging ion beam. The process is controllable and reversible, which makes it highly suitable for in situ manipulation to make desired 3D shapes by the piecewise bending of the nanopillars and cantilever structures during their fabrication using electron beam or FIB chemical vapor deposition (EB-CVD or FIB-CVD). Its usefulness in the fabrication of nanosize mechanical components has been demonstrated by making a branch structure from a single cantilever.

Raman and AFM studies of swift heavy ion irradiated InGaAs/GaAs heterostructures.

The effect of swift heavy ion (SHI) irradiation on InGaAs/GaAs heterostructures is studied using Raman spectroscopy and atomic force microscopy (AFM). The structures consist of molecular beam epitaxy (MBE) grown InGaAs layers on GaAs(001), having layer thicknesses of 12, 36, 60 and 96 nm. After irradiation, the GaAs type longitudinal optical (LO) mode blue shifted to higher frequency in thin samples and red shifted towards lower frequency in thick samples. These results are discussed invoking the penetration depth of the probe radiation (λ = 514.5 nm) in InGaAs. Deconvoluting the Raman spectra of thin samples indicates a compressive strain developed in the substrate, close to the interface upon irradiation. This modification and diffusion of indium across the interface results in an increase of strain and reduction of the defect densities in the InGaAs layer. The variations in FWHM of the Raman modes are discussed in detail. The surface morphology of these heterostructures has been studied by AFM before and after SHI irradiation. These studies, combined with Raman results, help to identify different relaxation regimes.

Toxigenicity & drug sensitivity of Vibrio mimicus isolated from patients with diarrhoea.

In a total of 720 faecal specimens from patients with secretory diarrhoea, vomiting, dehydration, gastroenteritis, cholera and cholera like illnesses, 18 strains of V. mimicus were isolated as pure culture. These were characterized for various toxin types and virulence factors using conventional in vitro and in vivo assays. Labile and stable toxins were elaborated by 15 and 2 strains respectively by ligated rabbit ileal loop (RIL) and suckling mouse assays. While 15 of the whole cell culture elaborated labile toxin, only 7 strains produced the same when culture filtrate was tested in RIL assay. Culture filtrates of 15 strains exhibited vascular permeability factor (PF) on adult rabbit skin, none of the strains were invasive as indicated by Sereny's test. Culture supernatants of all strains produced a cytotoxic factor to Vero and Chinese hamster ovary cells. Four of the 18 strains (22%) were resistant to multiple drugs (a combination of 3 or more drugs). The results emphasize the significance of continuous screening and identification of V. mimicus and to include in the differential diagnosis of patients with acute diarrhoea.

A retrospective analysis of the Madras epidemic of non-01 Vibrio cholerae new serogroup 0139 Bengal.

During the recent epidemic of cholera in Madras from October-December 1992, a total of 11,100 patients with acute secretory diarrhoea have been admitted to the Communicable Diseases Hospital, Madras, when compared to a total of 2,440 patients admitted during the pre-epidemic period studied between January - September 1992. A novel strain of non-01 V. cholerae was found to be the most predominant agent during the epidemic period. A representative sample of 84 non-01 strains isolated during the epidemic period were confirmed as V. cholerae non-01 and newly designated as serogroup 0139 at National Institute of Cholera and Enteric Diseases, Calcutta. All 84 strains of non-01 were found to elaborate cholera toxin (CT). Fourteen strains were also confirmed as serogroup 0139 from our non-01 stock recovered during the pre-epidemic period. Of the 17,540 patients admitted during the post epidemic period, studied from January 1993 - June 1994, 3.8 and 37.8 per cent patients were infected by 01 and non-01 serogroup 0139 respectively. The new serogroup 0139 continued to be the predominant isolate even during the post epidemic period.