Optimal cleaning and shaping of root canal systems requires, among many things, the coincident integration and tangible application of numerous anatomical, clinical, and technique driven considerations. For example, the case must be diagnosed correctly; the clinical risk assessed; the technique, clinical supplies, and instruments selected; and all of the above used correctly and simultaneously to achieve the treatment objectives.
The first generation of Ni-Ti was ground from Ni-Ti file blanks and not heat-treated. Such first-generation instruments are superelastic. Superelasticity denotes the ability of the file to deform (strain) from its original shape under a physical load (stress). Clinically, this is manifest as a Ni-Ti file rotating in a curved canal and returning to its original shape upon removal from the root canal treatment equipment.
In essence, the Ni-Ti undergoes a transformation (the instrument is “strained”) from its harder austenite crystalline phase configuration to its softer martensitic crystalline phase configuration while under such “stress.” When the stress is relieved, it returns to its original shape (austenite). Such behavior is termed “shape memory.” First-generation (nonheat-treated) Ni-Ti instruments can generally accommodate approximately an 8% strain before fracture. In contrast, CM instruments do not possess superelasticity and do not undergo the aforementioned transformation.
The second generation of Ni-Ti files is heat-treated, either in the bulk raw material stage before grinding or, alternatively, after grinding. CM instruments are a subset of this second generation of heat-treated instruments. CM technology was introduced in 2010. Heat treatment processes are proprietary.
Interestingly, there is a new file that is heat-treated only in the apical 10 mm of its cutting flutes, providing flexibility at its working end. To the author’s knowledge, for all other current systems, heat treatment encompasses the entire instrument.
CM files are unique among the commercial products available at this time. While made of heat-treated Ni-Ti, they remain curved as they rotate around a curved canal. CM files do not regain their original shape after use. Hence, they have “controlled memory.” The literature suggests this CM feature reduces transportation and conserves tooth structure. The literature also states that CM files are 300% to 900% more resistant to cyclic fatigue and have a statistically significant greater flexibility than their first generation superelastic counterparts. Aside from flexibility, CM files have essentially equivalent torsional strength to nonheat-treated files.
In the existing scientific literature published to date, there are no unfavorable reported findings on CM attributes. The current literature file on CM technology is available by email from the author on request.
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