Electrochemical Disinfection of Dental Implants Experimentally Contaminated with Microorganisms as a Model for Periimplantitis

Despite several methods having been described for disinfecting implants affected by periimplantitis, none of these are universally effective and may even alter surfaces and mechanical properties of implants. Boron-doped diamond (BDD) electrodes were fabricated from niobium wires and assembled as a single instrument for implant cleaning. Chemo-mechanical debridement and air abrasion were used as control methods. Different mono-species biofilms, formed by bacteria and yeasts, were allowed to develop in rich medium at 37 ◦C for three days. In addition, natural multi-species biofilms were treated. Implants were placed in silicone, polyurethane foam and bovine ribs for simulating different clinical conditions. Following treatment, the implants were rolled on blood agar plates, which were subsequently incubated at 37 ◦C and microbial growth was analyzed. Complete electrochemical disinfection of implant surfaces was achieved with a maximum treatment time of 20 min for Candida albicans, Candida dubliniensis, Enterococcus faecalis, Roseomonas mucosa, Staphylococcus epidermidis and Streptococcus sanguinis, while in case of spore-forming Bacillus pumilus and Bacillus subtilis, a number of colonies appeared after BDD electrode treatment indicating an incomplete disinfection. Independent of the species tested, complete disinfection was never achieved when conventional techniques were used. During treatment with BDD electrodes, only minor changes in temperature and pH value were observed. The instrument used here requires optimization so that higher charge quantities can be applied in shorter treatment timesITI Foundation, Switzerlan

New Topological Indices for Alternant Polycyclic Aromatic Hydrocarbons

Pairwise orthogonal topological indices A and Woo derived from the characteristic graphs of alternant polycyclic aromatic hydrocarbons (kata-annellated and peri-condensed systems) correlate with resonance energy per electron, energy of the HOMO and total ;i: electron energy respectively. For topological indices a high discrimination power is necessary but not sufficient to correlate with molecular properties. However, the indices and properties must be related similarly to topology and the size of the systems. Accordingly Type-A indices and properties which depend comparably strongly on both topology and size (e.g. A and resonance energy per electron) and Type - B indices and properties which depend predominantly on size (e. g. Woo and total ;i: electron energy) are distinguished