During instrumentation of the root canal, it is important to develop a continuously tapered form and to maintain the original shape and position of the apical foramen. However, the presence of curvatures may cause difficulty in root canal instrumentation. The ability to keep the instruments centered is essential to provide a correct enlargement, without excessive weakening of the root structure. Several studies have shown that Ni-Ti instruments remain significantly more centered and demonstrated less canal transportation than stainless steel files. Considerable research has been undertaken to understand the several factors related to an instrument's canal-centering ability. In this article, we have discussed the influence of various parameters such as alloys used in the manufacture of instruments, instrument cross-section, taper, and have given tips on canal-centering ability.

Aim:To evaluate the bonding ability of composite to unset glass-ionomer cement (GIC) using different self-etching bonding systems.Materials and Methods:One hundred samples of composite bonded to unset GIC were prepared and were divided into four groups. In Group A, composite was bonded to unset GIC employing a strong (pH 1) self-etch primer was used. In Group B, intermediary strong (pH 1.4) self-etch primer was employed. In Group C and D, mild (pH 2) and (pH 2.2) self-etch primer was employed. Shear bond strength analysis was performed at a cross-head speed of 0.5 mm/min.Results:Statistical analysis performed with one way analysis of variance and Tukey's test showed that the bond strength of composite to unset GIC was significantly higher for the mild self-etch primer group. In addition, energy dispersive x-ray (EDX) analysis was used to determine the composition of various structural phases identified by FE-SEM along the GIC-bonding agent interfaces.Conclusion:Hence this present study concludes that clinically the use of mild self-etching bonding agent over unset GIC has improved bond strength compared to the use of strong and intermediate self-etching bonding agent.

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