Powering RNT files: What’s needed in a motor?

May 1, 2007
Having your equipment organized and knowing how to use it is essential to provide excellent and efficient service.

by Richard Mounce, DDS

Having your equipment organized and knowing how to use it is essential to provide excellent and efficient service. For example, having all the needed rotary nickel titanium files for a given indication, using them correctly, and having the means to power these files with the correct rotational speed, torque control, and auto reverse can go far toward tangibly producing the best possible results in a given root curvature.

The converse is true. Knowing when, how, and at what level to set torque control values for auto reverse can help minimize fracture risk, and if used judiciously, also maintain a high level of efficiency.

Most clinicians, endodontists, and general practitioners desire two primary attributes in an RNT file - safety and excellent cutting ability. Safety in this context means diminished fracture potential. The worst scenario would be the RNT file that fractures without warning. Fortunately, such fracture is almost always preventable and highly operator-dependent. It is important that the clinician not wait for an audible warning signal before withdrawing the file. Such a scenario can occur, though, when the clinician is using the file and expecting to be able to push it apically, then the warning sound of an audible alarm alerts them to withdraw. In essence, the auto reverse has been used as a speed limit. If the tip of the file were to track a canal fin that previously had not been negotiated with hand K files, or in which a glide path had not been created, it is easy for the tip of the file to lock. While the larger portion of the file away from the tip might have the torque to rotate, such a locked tip often fractures in an instant and without warning.

Using RNT files with gentle touch, passive insertion, minimal engagement, and hand file negotiation and glide path creation are essential strategies for the best results of any RNT file system. This is irrespective of system design or manufacturer. Having used hundreds of packs of nearly all U.S. files available, I use K3 (SybronEndo, Orange, Calif.). I do so because of this product’s cutting efficiency, durability, tactile control, fracture resistance, and flexibility as well as other features. Irrespective of the system, though, it is highly informative and valuable to practice extensively with any new RNT system in extracted teeth before bringing it to the operatory.

Which motor can most effectively utilize the best features of an RNT system? Through the years, I have used numerous motors. I have found that two stand out for their ease of use, cost effectiveness, and reliability. For a single, stand-alone motor, the TCM III (SybronEndo) is an excellent choice. The corded electric motor has a maximum 900 RPM at 18:1, and multiple levels of auto reverse. In addition, after having recently expanded my office and looking for a comprehensive solution for handpiece needs, the ELECTROtorque TLC (KaVo, Lake Zurich, Ill.) electric motor system is a solid option. This system comes in the form of a box that attaches to the dental unit. With the change of only an attachment, it has the ability to provide electric high speed, low speed, and endodontic motor function. When combined with the Quatrocare system (KaVo) for lubricating handpieces and attachments, it represents a comprehensive solution to the management of handpiece needs - both operative and endodontic. Each of these motor systems has performed solidly.

I run K3 at 900 RPM with the torque control off, although for the novice clinician or someone new to K3, this is not advised. Despite saying this, bumping up the RPM slowly to higher speeds can make a cutting file - like K3 - become even more efficient. Many endodontists run RNT files with the torque control off. It is my empirical opinion that doing so allows the greatest tactile control for any RNT, K3, or other file.

In summary, utilizing RNT files to their greatest efficiency is a combination of three things: choosing the right file design (i.e., selecting the right brand for the given clinician’s needs), using the files appropriately, and determining the right source to power these files.

I welcome your questions and feedback.

Dr. Mounce has no commercial interest in any of the products mentioned in this column.

Dr. Richard Mounce lectures globally and is widely published. He is in private practice in endodontics in Vancouver, Wash. Among other appointments, he is the endodontic consultant for the Belau National Hospital Dental Clinic in the Republic of Palau, Korror, Palau (Micronesia). He can be reached at [email protected].

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