ENDODONTIC MOTORS

BELLS & WHISTLES OR USEFUL FUNCTIONS?

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There are many factors that contribute to predictable endodontics. Typically, a lot of focus is directed to the efficacy, safety and ease of use of the latest rotary NiTi file systems on the market and often there is less consideration afforded to the motors that drive these rotary systems. The objective of this article is to describe some of the latest features available in endodontic motors and consider if this technology has real value in practice.

Many of the currently available motors have preset speed and torque settings for popular file systems and sequences, however being able to customise the speed and torque settings to your own specific needs and then save them to the motor’s memory is a useful function. A conscious choice of settings rather than adopting a plug and play type approach is often a good idea, so you are always mindful of the appropriate speed, torque settings and safety features relevant to the size of the file and the stage of preparation.

With the exception of reverse cutting file systems that require a motor with a reciprocating action, forward cutting rotary endodontic files can be used in all manufacturer’s endodontic motors.

A light weight compact, cordless endodontic specific motor with a small handpiece head size, independent of the chair may provide easier access and greater tactile feedback.

In terms of each stage of canal preparation, the useful features of an endodontic motor include:

1. Coronal Flaring & Straight line access

Typically with crown-down preparation a larger taper file is used to create the coronal flare. As a general rule, for larger taper files the torque setting trigger can be set higher, but it is best to note the maximum speed and torque setting recommendations specific to the file system of choice. Setting the torque trigger at a specific value in Ncm allows torque reverse safety features to be employed. True torque reverse is one of the most important safety features in an endodontic motor. It ensures that when the torsional load on the file reaches the preset torque trigger, the motor will reverse the file, therefore releasing the torsional load on the file and reducing the risk of file fracture.

Some of the newer motors allow selection of multiple torque settings, even up to a high 5 Ncm. The speed settings available on most motors will range between 150 and 1000rpm. Traditionally most rotary file systems have optimal cutting speed recommendations around the 300rpm mark, but it’s a benefit to have adjustable speed settings as some of the newer file systems have a higher optimal cutting speed of up around the 500rpm mark.

2. Apex Location

Some endodontic motors also have an integrated apex locator built into the motor, which for workflow purposes is a convenient addition. The function and accuracy of the apex locator built into the Morita Tri Auto ZX2 cordless motor is comparable to that of the Morita standalone apex locators such as the Root ZX. Although apex location features can be employed in these units in an “automatic” function whilst instrumenting the canal, using the apex location function independently and then using your working length to instrument independently may offer more control and accuracy.

3. Preparation of the Glide Path

Traditionally glide path preparation has been achieved using stainless steel hand files. The advent of a patented glide path motion has enabled fatigue reducing, predictable and safer mechanical preparation of a glide path using .02 taper stainless steel or Ni-Ti rotary files. The OGP (Optimum Glide Path) mode in Morita’s Tri Auto ZX2 is a combination of a watch winding and balanced force motion. It is a constant action that replicates hand filing with a choice of 3 angles.

4. Canal shaping

Using a Crown Down file sequence can reduce the risk of file fracture during canal shaping and apical sizing. The latest intelligent torque reverse motions can reduce file fatigue and assist with increasing efficiency and safety. (Pedulla,E et al.)

OTR (Optimum Torque Reverse) is an Intelligent Torque trigger. This is a useful feature as it gives you feedback and awareness of the stresses on the files, as well as slowing the rotational speed down to reduce the risk of instrument fracture.

Reverse that is employed when the torsional load on the file reaches the preset torque trigger. Instead of the file reversing out of the canals, with the OTR function the file only reverses 90 degrees then returns to forward cutting for 180 degrees and continues to progress down the canal. The file will repeat this action until the torsional load on the file is relieved. This allows the file to continue and safely progress down the canals, whilst decreasing the risk of instrument fracture.

There are definite advantages to the latest advances in endodontic motors that potentially increase endodontic preparation predictability, safety and efficiency. Purchasing endodontic motors manufactured by reputable dental equipment manufacturers who will offer support and education is recommended.

Pedulla E, Corsentino G, Ambu E, Rovai F, Campedelli F,Rapisarda S,La Rosa GR, Rapisarda E,Grandini S. Influence of continuous rotation or reciprocation of Optimum Torque Reverse motion on cyclic fatigue resistance of nickel-titanium rotary instruments. Int Endo J.May;51(5) 522-528.Doi:10.1111/iej.127689. Epub 2017 Apr 25.