FAQs about the FlexMaster System

1. Why should I change to the FlexMaster NiTi-system?
  • It takes half the time needed for preparation by hand.
  • The quality of your root canal preparation will be excellent and reproducible with significantly less effort.
  • You will achieve a uniform conical canal shape without any clinically significant transportation of the canal axis.
  • You do not need to use pressure as you will be working with a motor.
  • You will use simple and tested file sequences with only a few instrument changes.
  • You will significantly reduce the number of instruments you use.
2. Why nickel-titanium?

Because of its properties: Steel cannot be used with a rotary system in curved canals. Try bending the working part of a steel instrument to a 40° to 60° angle. You will now have a bent file. If you rotate this file around its axis and watch the radius of the file tip, you will see that this cannot work in the root canal. Transportation of the canal axis, zip and elbow effects as well as excessive dentin removal would be the result. Most importantly, the steel instrument would not be able to withstand the pressure in the canal and would fracture very quickly. For this reason, the giromatic principle of a 90° back and forth rotation was the limit for steel files.

Endodontists did discover that good results can be achieved with pre-bent steel files when preparing root canals by hand using the balanced force technique according to Roane. Nevertheless, this is a very time consuming and stressful procedure.

Nickel-titanium (NiTi) alloy behaves very differently. The material is extremely flexible and has a memory effect. If you bend a NiTi file to 40-60° you will immediately see the difference in flexibility. This exceptional flexibility is as important as the memory effect: If you release the bent NiTi file it will immediately resume its original position.

The combination of these two important factors makes nickel-titanium alloy the best material presently available in endodontics for rotary instrumentation.

3. How often can I use a NiTi-file?

Dentin removal with a rotary system – the stress on the material increases with the degree of canal curvature.

Steel instruments will deform when they undergo too much stress, so they can be identified before they fracture. NiTi files, however, do not bend or unwind, they fracture without warning. In order to reduce the risk of fracture, NiTi files must be used with a low torque and torque control drive system.

FlexMaster® NiTi files can be used repeatedly. The special autoclavable labels for the lid of the FlexMaster® SystemBox allow you to record frequency of use with a permanent marker. We recommend file replacement after 8 markings at the latest as risk of fracture increases significantly with instrument wear. When a file has been used in a strongly curved canal, mark two or even three boxes on the control label, depending on the stress it was subjected to. This method has been successfully tried and tested.

FlexMaster® is economical because few instruments are needed per treatment. In most cases, 4 instrument sizes will suffice to reach the apex, and apical enlargement can be made with 2 to 4 instrument sizes.

4. What exactly is nickel-titanium (Nitinol)?

‘Nitinol’, as a combination of the elements Nickel and Titanium, was developed by the Naval Surface Warfare Center in USA (formerly Naval Ordnance Laboratory). The result is an intelligent material with “memory effect”.

For the FlexMaster® instruments we use a special alloy consisting of 54% nickel and 46% titanium.

5. How important is the instrument design?

Experience gained with first generation rotary NiTi instruments showed how important it is for the design of the file to be suitable for anatomical conditions in different root canal sections (from coronal to apical), taking the specifics of the material into account.

One characteristic of the first generation NiTi instrument design was large contact surfacesto the canal wall causing high friction and highstress on the instruments due to the high torsional forces. This also resulted in higher temperatures generated by friction and in increased smear layer formation.

The second NiTi generation adopted the cuttingblade geometry of traditional steel files. But this not only weakened the instrument coreand reduced the memory effect of the material, it also favoured file deformation and made theinstruments with this cross-section vulnerableto fracture. Furthermore, the angle of the cuttingblades often caused instruments to screw into the canal, i.e. without any use of pressure the instrument screwed into the canal and was difficult for the practitioner to control.

VDW took all this experience into account and developed an intelligent instrument design, FlexMaster®. FlexMaster® uses the efficiency of traditional Ktypecutting blades, i.e. a convex cross-section to stabilize the instrument core and a cuttingblade angle suitable for rotary use.

6. Taper - what does that mean?

Taper means gradual increase in diameter over the length (conical shape). Traditional steel files have a 2 % taper in compliance with ISO no. 3630, i.e. taper .02.

The increase in cross-section diameter from the tip towards the end of the working part is 2 %, or 2/100 mm per 1 mm. A file of ISO size 20 with a 16 mm working part measures 20/100 mm at the tip and 52/100 mm at the end of the working part: (20 / 100) + (16 x 2%) = 0.52.

Taper .04 has a cross-section diameter increase of 4 %, i.e. a strongly tapered instrument. Taper .06 means an increase of 6 % etc.

7. Why doe I need instrument in different tapers?

The goal of root canal preparation is to create optimal conditions for a tightly sealed and long-lasting root filling, which includes a uniformly tapered canal shape. A fast and safe way to achieve this goal is with intelligently coordinated instrument sequences of different tapers:

  • large taper in the straight canal section
  • medium taper in the curved canal section
  • small taper for apical enlargement

Large and medium tapers allow speedy dentin removal. The number of instrument changes is reduced to a minimum. Small tapered files are used for better apical shaping and preservation of the original canal axis (centre line).

FlexMaster®: taper .02, .04, .06 and .11

  1. .11 for the IntroFile, for conical enlargement of root canal orifice, replaces 2 or 3 Gates enlargers
  2. .04 and .06 used for crown-down phase
  3. .02 for safe apical enlargement
8. Why do I need a special motor for NiTi instruments?

Steel files unwind before they break. They can be checked prior to sterilization and damaged files discarded. Due to nickel-titanium’s memory effect, NiTi files do not deform, they break without warning when submitted to excess stress or material fatigue. In order to take full advantage of the nickel-titanium material and effectiveness of the instrument design and in order to avoid the unpleasant consequences of instrument fracture, the file must be used in the canal with:

  • a constant rotation of approximately300 rpm and
  • a constant force (torque) accordingto the size of the file

For these reasons, you need an intelligently programmed motor with torque and speed control, which monitors the speed and torque of each instrument precisely and safely according to its specific mechanical data. Additional functions such as Auto StopReverse (ASR), which automatically frees instruments blocked in the canal, increase safety and reduce stress for the practitioner. On pages 15-16 you will find an overview of motors recommended by VDW.

9. What is Crown-Down pressureless?

It means preparing a root canalwith instruments in decreasing sizes step-by-step toward the apex without using pressure. To begin with, it is necessary to determine the approximate canal length withan initial x-ray. The exact working length will be determined when reaching approx. 2/3 of the estimated canal length. Using one of the new electronic length determination devices, e.g. Raypex 6, ismore accurate and faster than x-rayimaging.

After this, the apex is enlarged with instruments in increasing sizes (each instrument tothe full working length).The crown-down method for rotary root canal preparation has been widely tried and tested.