What the ReFlex movement has over reciprocating and fully rotating drives

The next generation of reciprocating drive: the ReFlex movement

Fully rotating and reciprocating drive systems work with a continuous forward or forward/backward movement and only measure the torque on the instrument shaft. They react in a standardised way to torque limits, regardless of the file range in which the torque limit is exceeded.
The patented ReFlex movement of the EndoPilot² starts in fully rotating mode and, in addition to the torque, continuously determines the torsional stress occurring on the file by means of small, barely perceptible measuring pauses. Torsional stress acts on the file when it encounters resistance during rotation, which generates a force directed against the rotational movement. This can be caused, for example, by the walls of the root canal or by hardening in the canal. This method can be used to determine in which area (coronal, central or apical) the torque limit has been exceeded. Depending on the intensity and location of the load, the endomotor adapts the movements individually. If, for example, the apical torsional load suddenly increases significantly, the file switches to reciprocating mode in order to immediately reduce the excessive torsion and prevent a file fracture. The ReFlex movement is therefore an individually reactive pattern. This intelligent differentiation minimises file fractures and optimises the performance of the file by always cutting forwards under normal operating conditions and only switching to reciprocating mode in the event of apical clamping. When the file is under low load, the motor does not perform an active relief movement. This also does not occur under heavy coronal load, as the larger file cross-section is hardly subject to torsion. Instead, a higher torque is made available in the coronal, stronger area of the file. Avoiding unnecessary backward rotation reduces wear on the file and increases the efficiency of the preparation.

Experiment ReFlex vs. Reciprocal

The advantages of the ReFlex movement over the reciprocating movement can be illustrated by a simple experiment.
To simulate jamming of the instrument, the file is clamped firmly at the tip. The instrument is then operated once with the reciprocating movement and once with the ReFlex movement. The result of this experiment was recorded with an ultra slow motion camera.
As can be seen in the video, a file breakage occurs after a short time in reciprocating mode, as the reciprocating movement does not register the load on the file and rotates in the cutting direction despite the blockage. This leads to a steadily increasing load on the instrument tip and ultimately to breakage.
The ReFlex movement, on the other hand, detects the location and intensity of the load via the torsional stress of the file. It recognises that the file is jammed and reacts with gentle relief movements until no more blockage is registered.

Unlike Reciprocal, the ReFlex movement does not push debris apically

The overpressing of infected material via the apex is often accompanied by postoperative pain. Reciprocating drives have the disadvantage that they transport debris apically by moving backwards in a fixed pattern. While cutting movements transport debris coronally, reverse movements transport the infected material further apically. At the apex, this can have serious consequences for preparation, as infected material that is pushed beyond the apex cannot be removed without the risk of over-instrumentation. Bürklein and Schäfer carried out an in-vitro study to investigate the extrusion of debris with reciprocating instruments. In their publication, they wrote that almost twice as much debris is extruded with reciprocating instruments than with rotating systems. The ReFlex movement prevents contamination of the periapex by not performing a reverse rotation in every cutting cycle, unlike the reciprocating movement. Instead, it only rotates backwards if the load on the file becomes too high and there is a risk of fracture. With the help of this intelligent control, the ReFlex movement combines the best of both worlds of fully rotating and reciprocating endo motors.

Technical functionality of the ReFlex movement

The ReFlex movement rotates in the cutting direction for a defined time. This is followed by a barely perceptible measuring pause, during which the active drive is switched off. Due to the tension, the file itself now acts as a drive and passively rotates the motor backwards, which generates a measurable motor voltage. Based on this, the software can evaluate the strength and position of the tension on the file.
Depending on the assessed tension, the file continues to rotate forwards or performs gentle relief movements to prevent a fracture. Although fatigue fractures can still occur, the risk of overload fractures is minimised. A comparison of the three different types of movement - full rotation, reciprocal and ReFlex - is shown in the following table.

ReFlex - Implementation in EndoPilot²

Differences:

- ReFlex smart is noticeably sensitive to tension. Safety is particularly high here.
- ReFlex dynamic works particularly quickly and therefore offers increased efficiency during reprocessing.

For difficult canal configurations, you should switch to the more tactile smart mode.  

ReFlex smart
In ReFlex smart mode, the control reacts noticeably sensitively depending on the location of the load on the file. If the file is clamped in the apical area, the motor reacts with a gentle relief movement. If, on the other hand, the tension is in the coronal, strong area of the file, a higher torque is provided. The intelligent ReFlex smart movement works carefully and gently as well as effectively and quickly when necessary.
- Increased safety and tactile working during use
- Ideal for more complex canal anatomies thanks to a sensitive approach with strong torsional tension on the instrument
- Load-dependent, intelligent root canal preparation  
- Tactile when required, effective and rapid when possible

ReFlex dynamic
In ReFlex dynamic mode, the focus is on efficiency during preparation. The motor only switches to a short backward movement to relax the file once the file has reached a defined tension. It then moves forwards again as quickly as possible. The ReFlex dynamic movement enables very fast and efficient preparation of the root canals. The torque and tension limits are significantly higher in this mode.
- Very fast and maximally efficient work
- Ideal for simple canal anatomies
- Comparably efficient to the fully rotating movement

Dr Rüdiger Lemke, Senior Physician at Hamburg University Hospital about ReFlex

Dr Rüdiger Lemke, lecturer at the University of Hamburg and senior physician at the Polyclinic for Periodontology, Preventive Dentistry and Tooth Preservation, assesses the ReFlex movement in an interview after initial test experiences.

Dr Lemke, let's talk about ReFlex Smart first. What is behind the new movement pattern?

Dr Lemke: The interesting and innovative aspect is actually already in the product name, the reflex, i.e. the immediate reaction to a situation. ReFlex Smart works in full rotation, during which measurements are taken continuously within very short time intervals. They record the torque load depending on the tension of the file. This enables the device to recognise in which area the reprocessing instrument is currently under load, i.e. whether the tension is more apical or more coronal. The values determined allow ReFlex Smart to react individually: Depending on the intensity and location of the tension or clamping - i.e. apical, in the centre area of the instrument or coronal - the system deals with it in different ways. If the file is clamped coronally, for example, the risk of fracture is lower than if this were to happen apically. This is exactly what the reactive pattern of ReFlex Smart is designed for. Instead of initiating a generalised backward movement, it reacts individually, possibly even with an increased forward movement if the clamping was measured more in the coronal area. This differentiation makes it possible for the files to function in a controlled manner during root canal preparation according to their stress load. There is no differentiation here.
ReFlex Smart, on the other hand, differentiates in which section of the file the torque load of the instrument is present and reacts individually to this. This is definitely a novelty. The system checks the stress load on the reprocessing instrument at very short intervals and then reacts individually. This is a completely new approach to dealing with torsional tension in files. In this respect, the control mechanisms of the drive systems are becoming increasingly intelligent.

Let's now move on to the second mode of the new ReFlex movement in the EndoPilot. What is behind ReFlex Dynamic?

This is also a full rotation that is interrupted by ‘measurement checks’. In this respect, ReFlex Dynamic is similar to the Smart version. ReFlex Dynamic works even more efficiently due to the higher rotation speed of the instrument, among other things. In contrast, the torsional stress measurements in ReFlex Smart mode are more sensitive and, as a result, the reactions in the drive system are also more customised. The safety aspect is therefore even more in focus in this mode. In principle, however, both systems rotate fully when the file is running without torque load and this basic principle of full rotation also tends to reduce debris transport apically.


What does this situational adaptation mean for the dentist during treatment?

The individualised control pattern is intended to further reduce the residual risk of file fracture, which is low but always present, particularly in the apical region, while ensuring efficient preparation. In this respect, ReFlex Smart provides the dentist with increased safety during root canal preparation. This applies in particular to complex canal anatomies, as it counteracts pinch fractures in the apical area.

ReFlex Smart is a patented movement. As a clinician with an eagle eye, would you go so far as to describe this as a genuine innovation for endodontics?

Fully rotating and reciprocating drive systems work with a continuous forward or forward/backward movement and with torque limits to which they react in a standardised way, i.e. stop in a specific case. They do this regardless of the
in which section of the instrument this torque limit has occurred.

Does the regular control function of the ReFlex movements come at the expense of treatment time?

The ‘measuring pauses’ of both systems are so short that they are barely perceptible to the practitioner. Visually, it therefore looks almost like a continuous full rotation. As a result, the preparation times do not differ significantly from other drive types. In combination with the new file system, the ReFlex Dynamic version in particular enables fast and efficient preparation of root canals. A direct comparison between ReFlex Smart and ReFlex Dynamic shows a difference in preparation time in favour of the ReFlex Dynamic version. However, this also shows that the control mechanism and the associated reactions of ReFlex Smart are more sensitive to torsional stresses.

In your opinion, which of the two movements does the dentist decide in favour of on the EndoPilot?

Primarily, it will be experience in handling mechanical endodontics. The ReFlex Smart mode offers advantages for less experienced practitioners. ReFlex Smart is better able to compensate for uncertainties in handling, such as excessively long standing times in the canal or too much preparation pressure. ReFlex Smart therefore offers a potential ‘safety margin’. Those who are more focussed on treatment efficiency will choose the ReFlex Dynamic variant. However, this should not prevent them from possibly switching to the more tactile Smart mode for difficult channel configurations. Combinations of the two movements are therefore conceivable depending on the situation. But you should know this: Both movements are customised to the Procodile system.

Thank you for the interview.

Source:
"Komet Dental." Interview with Rüdiger Lemke. ZMK, 2019, https://contenthub.kometdental.com/infocenter/files/201904_ZMK.pdf.