Despite the improvement of diagnostic technologies, which allow a better understanding of endodontic anatomy, and despite the presence of increasingly improved endodontic instruments, the adequate shaping of root canal systems is one of the most urgent goals to be achieved in order to optimize root disinfection using irrigants and their subsequent activation, and to support obturation techniques in root canal systems. The instruments currently in use, in addition to making the shaping of canals much faster, have made the entire endodontic practice much safer, considerably limiting the risk of iatrogenic errors or intracanal separation.

Depending on the characteristics required by the specific clinical case, it is possible to use the nickel titanium (NiTi) rotary instrument which is best suited to the characteristics sought. The current challenge is to work with rotating instruments capable of overcoming the anatomical difficulties that arise in the most complex cases. The outcome of endodontic therapy is still very dependent on the mechanical shaping of the root canal system. It is now clear that resistance to cyclic fatigue and resistance to torsional stress are inversely proportional, but the new heat treatments to which NiTi alloys are subjected allow very interesting results to be achieved. Current tools are increasingly suitable for the different situations that may arise, therefore, further studies are needed that highlight the strengths and weaknesses of these NiTi rotary instruments.

The aim of this Special Issue is to understand the development of new NiTi rotary instruments, the changes that have been introduced by heat treatments, and the actual improvements in daily endodontic clinical practice. Although the mechanical characteristics of NiTi instruments have been deeply studied in recent years, it is not yet clear the role that different heat treatments have on the modification of the characteristics of rotary instruments and their mutual relationship. We expect to receive articles regarding improvements in the mechanical characteristics of NiTi rotary instruments and their development. We welcome both original research and review articles that aim to enrich scientific knowledge and help not only clinicians, but also researchers involved in the development of new dedicated software, diagnostic tools, and technological improvements.

Potential topics include but are not limited to the following:

• Cyclic fatigue resistance
• Torsional stress resistance
• Cutting efficiency
• Operative torque
• Bending properties
• Preparation technique and time
• Lubricants and irrigants
• Heat treatment
• NiTi alloys