Evaluation of surface characteristics of rotary nickel-titanium instruments produced by different manufacturing methods

BACKGROUND

Instrument fracture is a serious concern in endodontic practice.

OBJECTIVE

The aim of this study was to investigate the surface quality of new and used rotary nickel-titanium (NiTi) instruments manufactured by the traditional grinding process and twisting methods.

MATERIALS AND METHODS

Total 16 instruments of two rotary NiTi systems were used in this study. Eight Twisted Files (TF) (SybronEndo, Orange, CA, USA) and 8 Mtwo (VDW, Munich, Germany) instruments were evaluated. New and used of 4 experimental groups were evaluated using an atomic force microscopy (AFM). New and used instruments were analyzed on 3 points along a 3 mm. section at the tip of the instrument. Quantitative measurements according to the topographical deviations were recorded. The data were statistically analyzed with paired samples t-test and independent samples t-test.

RESULTS

Mean root mean square (RMS) values for new and used TF 25.06 files were 10.70 ± 2.80 nm and 21.58 ± 6.42 nm, respectively, and the difference between them was statistically significant (P < 0.05). Mean RMS values for new and used Mtwo 25.06 files were 24.16 ± 9.30 nm and 39.15 ± 16.20 nm respectively, the difference between them also was statistically significant (P < 0.05).

CONCLUSION

According to the AFM analysis, instruments produced by twisting method (TF 25.06) had better surface quality than the instruments produced by traditional grinding process (Mtwo 25.06 files).

Observations of Earth space by self-powered stations in Antarctica

Coupling of the solar wind to the Earth magnetosphere/ionosphere is primarily through the high latitude regions, and there are distinct advantages in making remote sensing observations of these regions with a network of ground-based observatories over other techniques. The Antarctic continent is ideally situated for such a network, especially for optical studies, because the larger offset between geographic and geomagnetic poles in the south enables optical observations at a larger range of magnetic latitudes during the winter darkness. The greatest challenge for such ground-based observations is the generation of power and heat for a sizable ground station that can accommodate an optical imaging instrument. Under the sponsorship of the National Science Foundation, we have developed suitable automatic observing platforms, the Automatic Geophysical Observatories (AGOs) for a network of six autonomous stations on the Antarctic plateau. Each station housed a suite of science instruments including a dual wavelength intensified all-sky camera that records the auroral activity, an imaging riometer, fluxgate and search-coil magnetometers, and ELF/VLF and LM/MF/HF receivers. Originally these stations were powered by propane fuelled thermoelectric generators with the fuel delivered to the site each Antarctic summer. A by-product of this power generation was a large amount of useful heat, which was applied to maintain the operating temperature of the electronics in the stations. Although a reasonable degree of reliability was achieved with these stations, the high cost of the fuel air lift and some remaining technical issues necessitated the development of a different type of power unit. In the second phase of the project we have developed a power generation system using renewable energy that can operate automatically in the Antarctic winter. The most reliable power system consists of a type of wind turbine using a simple permanent magnet rotor and a new type of power control system with variable resistor shunts to regulate the power and dissipate the excess energy and at the same time provide heat for a temperature controlled environment for the instrument electronics and data system. We deployed such systems and demonstrated a high degree of reliability in several years of operation in spite of the relative unpredictability of the Antarctic environment. Sample data are shown to demonstrate that the AGOs provide key measurements, which would be impossible without the special technology developed for this type of observing platform.

Canal preparation with Hero 642 rotary Ni-Ti instruments compared with stainless steel hand K-file assessed using computed tomography

AIM

To compare ex vivo root canal preparation with conventional stainless steel K-files and Hero 642 rotary Ni-Ti instruments.

METHODOLOGY

Mesiobuccal canals of 20 maxillary first molars (with angles of curvature between 25 degrees and 35 degrees ) were used. After preparation with Hero 642 rotary instruments and stainless steel K-files, the amount of transportation that occurred was assessed using computed tomography. The teeth were scanned by computed tomography before instrumentation. One millimetre thick slices were prepared from the apical end point to the pulp chamber. The first two sections were 3 mm from the apical end of the root (apical level) and 3 mm below the orifice (coronal level). A further section (mid-root level) was recorded, dividing the distance between the sections of apical and coronal levels into two equal lengths. Ten teeth were instrumented using Hero 642 rotary instruments and another 10 teeth were instrumented using stainless steel K-files. Following the completion of the instrumentation, the teeth were again scanned and compared with the cross-sectional images taken prior to canal preparation. Amount of transportation and centreing ability was assessed. Student's t-test was used for statistical analysis.

RESULTS

Less transportation occurred with Hero 642 rotary instruments than stainless steel K-files at the mid-root and coronal levels (mid-root: P < 0.05 and coronal: P < 0.001). Hero 642 rotary instruments had better centreing ability than K-files at all three levels (apical: P < 0.05, mid-root: P < 0.05 and coronal: P < 0.001).

CONCLUSIONS

Hero 642 rotary instruments transported canals less, especially at the middle and coronal thirds of the root canals than stainless steel K-files. Hero 642 instruments had better centreing ability.

The effect of propolis extract in experimental chemical corneal injury

PURPOSE

To investigate the effect of propolis, a natural resin produced by honeybees, in the treatment of alkali-injured rabbit eyes.

METHOD

A corneal alkali burn was induced by applying filter paper immersed in 1 N NaOH on the central axis of the right corneas of 24 rabbits for 30 s. The animals were divided into three treatment groups: group 1 (control) was given 0.3% tobramycin and phosphate-buffered solution; group 2 was treated with antibiotic coverage and topical 1% ethanolic extract of propolis; group 3 received antibiotic coverage and topical 1% dexamethasone. The dexamethasone-treated group was maintained as the positive control. Drugs were instilled 4 times a day for 7 days. The corneal inflammation was evaluated by calculating the average inflammatory index obtained from clinical observation of the ciliary hyperemia, central and peripheral corneal edema at 24 h, 48 h, on day 5 and day 7, before sacrificing the animals. Then, the corneas underwent routine histological examination.

RESULTS

The effects of dexamethasone and propolis on healing of injured corneas were similar (p>0.05) and significantly better than controls at 24 h (p<0.01, p< 0.05, respectively), and on day 7 (p<0.05) with respect to the inflammatory index. On histological observation, inflammatory cell infiltration was lower as compared to control in both the dexamethasone and propolis groups (p<0.001) and similar with each other (p>0.05).

CONCLUSIONS

Our study shows that propolis has an anti-inflammatory effect comparable to dexamethasone in chemical corneal injury.