Corrosion in Haas expanders with and without use of an antimicrobial agent: an in situ study

OBJECTIVES: The purpose of this study was to evaluate in situ the occurrence of corrosion in the soldering point areas between the wire, silver brazing and band in Haas expanders. MATERIAL AND METHODS: Thirty-four 7-12-year-old patients who needed maxillary expansion with a Haas expander were randomly assigned to two groups of 17 individuals each, according to the oral hygiene protocol adopted during the orthodontic treatment: Group I (control), toothbrushing with a fluoride dentifrice and Group II (experimental), toothbrushing with the same dentifrice plus 0.12% chlorhexidine gluconate (Periogard(®)) mouthrinses twice a week. The appliances were removed after approximately 4 months. Fragments of the appliances containing a metallic band with a soldered wire were sectioned at random for examination by stereomicroscopy, scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). Data were analyzed statistically by Fisher's test at 5% significance level. RESULTS: The analysis by optical microscopy revealed areas with color change suggestive of corrosion in the soldering point areas joining the band and the wire in all specimens of both groups, with no statistically significant difference between the groups (p=1). The peaks of chemical elements (Ni, Fe, Cr, O, C and P) revealed by EDS were also similar in both groups. CONCLUSION: Color changes and peaks of chemical elements suggestive of corrosion were observed in the soldering point areas between the wire, silver brazing and band in both control and experimental groups, which indicate that the 0.12% chlorhexidine gluconate mouthrinses did not influence the occurrence of corrosion in situ

Spatial and temporal distribution of spawning aggregations of blue ling (molva dypterygia) west and northwest of the british isles

Fisheries on blue ling in ICES Areas Vb, VI, VII, and XIIb have mostly targeted spawning aggregations. ICES has repeatedly advised that blue ling are susceptible to sequential depletion of spawning aggregations and that closed areas to protect spawning aggregations should be maintained and expanded where appropriate. Information from a range of sources, including fishers, is analysed, and five main spawning areas are identified: (i) along the continental slope northwest of Scotland (ICES Division VIa); (ii) on, around, and northwest of Rosemary Bank (VIa); (iii) on the southern and southwestern margins of Lousy Bank (Vb); (iv) on the northeastern margins of Hatton Bank (VIb); and (v) along the eastern and southern margins of Hatton Bank (VIb). From the information available, it is suggested that, for management purposes, peak spawning be considered to take place at depths of 730-1100 m between March and May inclusive in VIa and Vb, and during March and April in VIb. Based largely on this information, the European Commission (EC) introduced in 2009 protection areas for spawning aggregations of southern blue ling in European Union (EU) waters within ICES Division VIa

Effects of an External Magnetic Field on the Interband and Intraband Optical Properties of an Asymmetric Biconvex Lens-Shaped Quantum Dot

The theoretical investigation of interband and intraband transitions in an asymmetric biconvex lens-shaped quantum dot are considered in the presence of an external magnetic field. The selection rules for intraband transitions are obtained. The behaviors of linear and nonlinear absorption and photoluminescence spectra are observed for different temperatures and magnetic field strengths. The second and third harmonic generation coefficients as a function of the photon energy are examined both in the absence and presence of an external magnetic field