Mechanical properties of nickel titanium and steel alloys under stress- strain test / 대한치과교정학회지

The great variety of commercial brands of orthodontic wires available on the market, stimulated by the so called superior wires (nickel titanium with shape memory effect and superelastic nickel titanium), makes the professional choice for a suitable and less expensive material difficult. The in vitro study of the mechanical properties of the orthodontic wires acts as an auxiliary tool for the professional. In this paper, a comparative study of mechanical properties was made, using stress strain tests for 4 types of orthodontic wires (conventional stainless steel, multistranded steel, superelastic nickel titanium and thermoactivated nickel titanium) separated into 5 groups. A series of 6 tests were tested for each group of wires. Initially, each group was tested 3 times until the wires broke. Furthermore, 3 more tests for each group were performed, stretching the wires under standardized activation loads, for a reliable comparison of their mechanical properties, during loading and unloading. t tests were applied to check differences among the groups. In vitro, the results suggest that regarding the mechanical properties supposedly desirable for physiological teeth movement, such as resilience, elasticity modulus, strength liberated during unloading, and the way that strength is liberated, thermoactivated nickel titanium wires, acting under mouth temperature, seems to be a good choice, followed by superelastic nickel titanium, multistranded stainless steel, and conventional stainless steel. Superelasticity was demonstrated for superelastic nickel titanium wires. When at 37degrees C, thermoactivated nickel titanium wires showed shape memory effect, showing that temperature is important for enhancing the mechanical properties.

[Correlation between methicillin-resistance and resistance to fluoroquinolones in Staphylococcus aureus and Staphylococcus epidermidis]. / Correlazione della resistenza alla meticillina e ai fluorochinoloni in Staphylococcus aureus e Staphylococcus epidermidis.

Fluoroquinolones resistance in Staphylococci is associated to point mutations in grlA (80,84 and 116) grlB, gyrA (84,88) and gyrB genes. Almost all MRSA strains are ciprofloxacin and levofloxacin resistant while, in a lesser degree, MRCoN staphylococci show to be resistant to levofloxacin. This observation made possible to predict a different correlation between methicillin-resistance and the resistance to FQs in this two different species. In this study, we compare genomic analysis of S. aureus and S. epidermidis with the resistance to FQs. Our results show that strains of MRSA are distributed in 4 different PFGE-types while 12 MRSE strains are distributed in 9. MRSA resistant to FQs showed a unique PFGE pattern; on the contrary of FQs susceptible MRSA and MSSA. Furthermore mecA and gyrA genes are located in the same SmaI fragment in MRSA and in different in MRSE. MSSE and MRSE show more ClaI/mecA polymorphisms than MRSA. All this data confirm the clonal origin of MRSA and show that FQs resistance is linked to the presence of mec locus and both clonally spread. On the contrary in MRSE FQs-resistance is independent from MR and arise with the normal frequence of antibiotic induction.