The Effect of Silver Nanoparticles Size, Produced Using Plant Extract from Arbutus unedo, on Their Antibacterial Efficacy.

Silver nanoparticles (AgNPs) have been demonstrated to restrain bacterial growth, while maintaining minimal risk in development of bacterial resistance and human cell toxicity that conventional silver compounds exhibit. Several physical and chemical methods have been reported to synthesize AgNPs. However, these methods are expensive and involve heavy chemical reduction agents. An alternative approach to produce AgNPs in a cost-effective and environmentally friendly way employs a biological pathway using various plant extracts to reduce metal ions. The size control issue, and the stability of nanoparticles, remain some of the latest challenges in such methods. In this study, we used two different concentrations of fresh leaf extract of the plant Arbutus unedo (LEA) as a reducing and stabilizing agent to produce two size variations of AgNPs. UV-Vis spectroscopy, Dynamic Light Scattering, Transmission Electron Microscopy, and zeta potential were applied for the characterization of AgNPs. Both AgNP variations were evaluated for their antibacterial efficacy against the gram-negative species Escherichia coli and Pseudomonas aeruginosa, as well as the gram-positive species Bacillus subtilis and Staphylococcus epidermidis. Although significant differences have been achieved in the nanoparticles' size by varying the plant extract concentration during synthesis, the antibacterial effect was almost the same.

Observations on an in-vivo failure of a titanium dental implant/abutment screw system: a case report.

Titanium and its alloys are widely used in prosthetic dentistry, due to their biocompatibility, excellent mechanical and anti-corrosion behavior. However, delayed fracture of dental prosthetics is frequently encountered. Mechanisms leading to fracture are not generic but are strongly related to the particular environmental (quality of biological fluids) and mechanical loading conditions (mastication habits, presence of prosthetic metallic/ceramic components) in the patients' oral cavity. In this study, a commercially pure titanium implant-screw system has failed after 15 years of operation in the oral cavity of an old female. The system was retrieved in three pieces: the upper part of the implant, part of the abutment screw, and the apical part of the implant to which a part of the screw was embedded. This is considered as a rare case, where the whole dental assembly was retrieved after fracture allowing the extensive fractographic analysis of the conjugate pieces and the establishment of a thorough in-vivo failure scenario. Scanning electron microscopy observations performed on all three retrieved parts indicated a synergistic effect of distinct mechanisms, which led to total failure under extrinsic common fatigue loading. The principal mechanism was the propagation of a main crack, which was previously initiated in the body of the implant and affected by a wedging mechanism due to Ca/P aggregates developed within the crack. Because of the strong fixation between the implant and the abutment screw, this main crack was transferred to the latter causing eventually total failure of the assembly.