The functional properties of nickel-titanium endodontic instruments, especially their flexible bending load level, were closely related to the transformation behaviour of the alloys.

Change in the transformation behaviour by heat treatment may be effective in increasing the flexibility of nickel-titanium endodontic instruments.

The new method of manufacturing NiTi instruments by twisting coupled with heat treatment might contribute to the increased phase transformation temperatures and superior flexibility.

Based on these preliminary data, canal shaping appears to cause apical microcracks regardless of the type of rotary instrument motion. Contrast-enhanced micro-CT was able to identify microcracks in roots.

Additional heat treatment of hybrid nickel-titanium instruments may be effective in increasing the flexibility of nickel-titanium rotary instruments.

No abstract

Background and Objective New techniques for non‐invasive early detection and diagnosis of oral dysplasia and carcinoma are required. Our objective was to determine in the hamster cheek pouch model whether differentiation between the healthy tissue and the different stages of oral premalignancy and malignancy is possible using laser‐induced fluorescence after tissue exposure to 5‐Aminolevulinic acid (ALA). Study Design/Materials and Methods DMBA carcinogenesis was applied to one cheek pouch in 18 hamsters for 0–20 weeks. Prior to sacrifice, 20% ALA was applied to the cheek tissues. Excised cheek tissues were cryosectioned and imaged using fluorescence microscopy with excitation at 405 nm, detection at 635 nm. After fluorescence measurement, H&E staining and histopathological evaluation were performed. Results Fluorescence intensity was significantly lower in healthy tissue than in pathological tissues. Significantly higher intensities and more “fluorescence hot spots” occurred in severe dysplasia and carcinoma than in healthy tissue, hyperkeratosis, mild and moderate dysplasia. Conclusions Light‐induced fluorescence after ALA exposure can differentiate between the different stages of premalignancy and malignancy. Its ability to differentiate between healthy tissue and early pathology is particularly interesting Lasers Surg. Med. 32:17–24,2003. © 2003 Wiley‐Liss, Inc.

The purpose of this study was to test nickel titanium (NiTi) instrument performance under different surrounding temperatures. Twenty-four superelastic NiTi instruments with a conical shape comprising a 0.30-mm-diameter tip and 0.06 taper were equally divided into 3 groups according to the temperature employed. Using a specially designed cyclic fatigue testing apparatus, each instrument was deflected to give a curvature 10 mm in radius and a 30° angle. This position was kept as the instrument was immersed in a continuous flow of water under a temperature of 10, 37, or 50 °C for 20 s to calculate the deflecting load (DL). In the same position, the instrument was then allowed to rotate at 300 rpm to fracture, and the working time was converted to the number of cycles to fracture (NCF). The statistical significance was set at p = 0.05. The mean DL (in N) and NCF (in cycles) of the groups at 10, 37, and 50 °C were 10.16 ± 1.36 and 135.50 ± 31.48, 13.50 ± 0.92 and 89.20 ± 16.44, and 14.70 ± 1.21 and 65.50 ± 15.90, respectively. The group at 10 °C had significantly the lowest DL that favorably resulted in the highest NCF. Within the limitations of this study, the surrounding temperature influences the cyclic fatigue resistance and DL of the superelastic NiTi instruments. Lower temperatures are found to favorably decrease the DL and extend the lifetime of the superelastic NiTi instrument. Further NiTi instrument failure studies should be performed under simulated body temperature.