Influence of Sodium Hypochlorite on Mechanical Properties of K3 Nickel-Titanium Rotary Instruments

Electrochemical Properties of Nickel-Titanium Rotary Endodontic Instruments

INTRODUCTION

Nickel-titanium rotary endodontic files have been commercially available for decades, but more recent innovations have introduced heat-treated and surface-treated files. This study investigated the corrosion properties of various nickel-titanium files in normal saline and sodium hypochlorite (NaOCl).

METHODS

Ten different file brands of size 40 with a 0.04 taper were subjected to electrochemical testing in 0.9% NaCl (saline) and 5.25% NaOCl at room temperature. The Open Circuit Potential (OCP) was observed for 1 hour followed by a cyclic polarization test from -300 to 700 mV and back to -300 mV (vs OCP). Nonparametric ANOVA and a pairwise comparison (P < .05) were used for statistical analysis of the OCP at 1 hour and the corrosion current (Icorr) obtained via the cyclic polarization test.

RESULTS

Significant differences (P < .05) were found between files with respect to OCP and Icorr in both solutions. Nine files exhibited significantly greater (P < .05) Icorrs in NaOCl than in saline. Conversely, pitting corrosion was observed in the saline solution but not NaOCl. Weak and/or moderate correlations existed between OCP and Icorr measures in the 2 solutions.

CONCLUSION

Significant differences in electrochemical properties were observed among the 10 brands of files. Overall, there was not a clear trend between conventional, heat-treated, or surface-treated files among OCP or Icorr in either solution.

Electrochemical-induced dissolution of stainless steel files

AIM

To investigate the effectiveness of the dissolution process when hand stainless steel files are polarized in solutions containing chloride and fluoride to promote their dissolution.

METHODOLOGY

Redox curves and anodic polarization curves were obtained to determine the conditions necessary for the dissolution of stainless steel endodontic files. Anodic polarization of sizes 20 and 30 files was performed, and a t-test (P < 0.05) was used to compare the weight loss, the time of dissolution and the electrical charge generated by both groups of files. Fragments were polarized in simulated root canals to evaluate the dissolution process. After the tests, a size 10 K-file was used to verify the possibility of bypassing the fragment. Radiographic analysis of the simulated canals was used before and after the tests to verify fragment dissolution.

RESULTS

A progressive consumption of the sizes 20 and 30 files was observed with total polarization times of 7.0 and 9.0 min, respectively. Files with the larger diameters exhibited greater weight loss, longer times of dissolution and generated a greater electrical charge during the active dissolution process (t-test, P < 0.05). After 60 min, the anodic polarization of file fragments in simulated root canals resulted in their partial dissolution.

CONCLUSION

A 60-min anodic polarization of stainless steel K-file fragments in simulated root canals resulted in their partial dissolution. The fragments could be bypassed after the test.

Alteration in the inherent metallic and surface properties of nickel-titanium root canal instruments to enhance performance, durability and safety: a focused review

The expanded use of nickel-titanium (NiTi) rotary instruments in root canal procedures has led to the development of a wide variety of shapes, designs and applications. Root canal anatomy has not changed, however, and the same challenges exist in both initial treatment and the revision of unacceptable treatment. These challenges include application with high levels of achievement and low to no levels of adverse effects, such as instrument fracture, root canal wall ledging, dentine wall perforation and so forth. To that end, many manufacturers have been seeking ways to alter the presently available and wide range of root canal instrument designs, with a focus on altering the surface of the alloy or altering the alloy microstructure with post-machining or post-twisting heat treatment. This focused review will address the impact that these modifications have had on instrument flexibility, resistance to cyclic fatigue and cutting efficiency.

Root canal irrigants

Successful root canal therapy relies on the combination of proper instrumentation, irrigation, and obturation of the root canal. Of these three essential steps of root canal therapy, irrigation of the root canal is the most important determinant in the healing of the periapical tissues. The primary endodontic treatment goal must thus be to optimize root canal disinfection and to prevent reinfection. In this review of the literature, various irrigants and the interactions between irrigants are discussed. We performed a Medline search for English-language papers published untill July 2010. The keywords used were ‘root canal irrigants’ and ‘endodontic irrigants.’ The reference lists of each article were manually checked for additional articles of relevance.

Influence of previous angular deformation on flexural fatigue resistance of K3 nickel-titanium rotary instruments

Several studies have evaluated the influence of torsion and bending loads on the mechanical resistance of nickel-titanium instruments. The aim of the present study was to analyze the influence of previous angular deformation on K3 files resistance to flexural fatigue. New files and files previously submitted to different angular deformation were tested for flexural fatigue, and the number of cycles to fracture was compared. The results indicated that as the angular deformation increases, the number of cycles attained under flexural fatigue condition decreases. A reduction of fatigue resistance was registered even when a significant plastic deformation was not imposed. From the obtained results, it may be suggested that the sequential loading, including torsion and flexural fatigue, can be responsible for instrument separation during clinical practice. Successive torsion overloads, occurring together with flexural fatigue, reduce the mechanical resistance of nickel-titanium files.