Physical and mechanical properties of twisted or ground nickel-titanium instruments.

AIM: To compare the flexibility, torsional resistance and structural and dimensional characteristics of instruments produced by twisting with those of a geometrically similar nickel-titanium (NiTi) system produced by a grinding process. METHODOLOGY: The mean diameters along the flute and the pitch length of size 25, .04 taper, size 25, .06 taper, and size 25, .08 taper Twisted File (TF) (SybronEndo, Orange, CA, USA), and size 25, .04 taper, and size 25, .06 taper RaCe instruments (FKG, La Chaux-de-Fonds, Switzerland) (n = 10 each) were measured according to ANSI/ADA specification No. 101. Two pairs of instruments were found to have similar diameters at 3 mm from the tip: TF size 25, .06 taper and RaCe size 25, .04 taper, and TF size 25, .08 taper and RaCe size 25, .06 taper. The cross-sectional areas at 3 mm from the tip were determined. These instruments were then submitted to energy-dispersive X-ray spectroscopy, X-ray diffraction, differential scanning calorimetry (DSC), and Vickers microhardness measurements. Bending moment at 45° and maximum torque at fracture were measured (n = 10) according to specification ISO 3630-1. Data were analysed using analysis of variance (α = 0.05). RESULTS: The two types of instruments had approximately the same chemical composition, phase constitution, and austenite finishing temperatures. TF instruments had significantly (P ≤ 0.001) lower Vickers microhardness values and were more flexible than RaCe instruments (P = 0.016), but had similar (TF size 25, .08 taper and RaCe size 25, .06 taper, P = 0.916) or significantly higher (TF size 25, .06 taper and RaCe size 25, .04 taper, P ≤ 0.001) torsional resistance. CONCLUSIONS: Comparison of TF and RaCe instruments of similar measured dimensions revealed that the different manufacturing methods employed for producing these instruments gave rise to different mechanical behaviours.

Flexibility and torsional resistance of three nickel-titanium retreatment instrument systems.

AIM: To assess the dimensional characteristics, flexibility and torsional behaviour of nickel-titanium retreatment instruments. METHODOLOGY: Using image analysis software and high-resolution digital images, the instrument length, tip angle, diameter at 3 mm from the tip and the distance between the blades (pitch length) of the following eight instruments were measured (n = 12 for each measurement parameter): the ProTaper Universal retreatment (PTU-R) D1, D2 and D3 instruments; the R-Endo R1, R2 and R3 retreatment instruments; and the Mtwo retreatment (Mtwo-R) sizes 25 and 15 retreatment instruments. Maximum torque and the angular deflection at fracture as well as the bending moment at 45° were measured (n = 12) according to the International Standards Organisation (ISO) specification number 3630-1. Data were analysed using the analysis of variance (α = 0.05). RESULTS: The length of the active part of the instruments was found to vary according to the depth of the canal into which they were designed to reach. The pitch length also increased along the active length. The PTU-R D1 and the Mtwo-R instruments had active tips. Measurements of the bending moment at 45° revealed that the Mtwo-R 15 instrument was the most flexible, whereas the PTU-R D1 was the least flexible. The maximum torque tended to increase as the instrument diameter at 3 mm from the tip increased, whereas the angular deflection at fracture varied in the opposite direction. CONCLUSIONS: The geometrical characteristics of the retreatment instruments and their flexibility and torsion behaviour were consistent with their intended clinical application.

Synergic interaction between pomegranate extract and antibiotics against Staphylococcus aureus.

We evaluated the interaction between Punica granatum (pomegranate) methanolic extract (PGME) and antibiotics against 30 clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus (MSSA). Susceptibility testing of the isolates to PGME and antibiotics was performed by the broth dilution method. Synergic activity was detected between PGME and the 5 antibiotics tested, chloramphenicol, gentamicin, ampicillin, tetracycline, and oxacillin, ranging from 38% to 73%. For some isolates, PGME did not interfere with the action of any of the antibiotics tested. The bactericidal activity of PGME (0.1 x MIC) in combination with ampicillin (0.5 x MIC) was assessed using chosen isolates by time-kill assays, and they confirmed the synergic activity. Using this combination, cell viability was reduced by 99.9% and 72.5% in MSSA and MRSA populations, respectively. PGME increased the post-antibiotic effect (PAE) of ampicillin from 3 to 7 h. In addition, PGME demonstrated the potential to either inhibit the efflux pump NorA or to enhance the influx of the drug. The detection of in vitro variant colonies of S. aureus resistant to PGME was low and they did not survive. In conclusion, PGME dramatically enhanced the activity of all antibiotics tested, and thus, offers an alternative for the extension of the useful lifetime of these antibiotics.

Pomegranate extract inhibits Staphylococcus aureus growth and subsequent enterotoxin production.

In Brazil, pomegranate (Punica granatum L. (Punicaceae)) is widely used as a phytotherapeutic agent. This study evaluates the effect of pomegranate extract on Staphylococcus aureus FRI 722 growth and subsequent enterotoxin production. Bacterial susceptibility was determined by tube dilution method and production of enterotoxin was assessed using membrane-over-agar (MOA) plates. At a low extract concentration (0.01% v/v) bacterial growth was delayed, while a higher concentration (1% v/v) eliminated bacterial growth. Most interestingly, a 0.05% (v/v) concentration of extract was found to inhibit Staphylococcal enterotoxin (SE) A production. These data further implicate pomegranate extracts as potential antibacterial therapeutics with the added ability to inhibit enterotoxin production.