NiTi

Rotary Ni Ti endodontic system

COMPARATIVE STUDY OF METALS
Nickel titanium Stainless steel

Excellent flexibility Less flexible

Conforms to canal Straightens and
curvature transports canal

Plastic deformation Permanent deformation .

• First NiTi instrument introduced by Walia et al in (1988) as hand instruments, the first generation has many faulty designs.



• 1- Extremely flexible 5 times than stainless steel, so less canal straightening i.e. less over instrumentation less post operative pain.
• 2- Ten times more resistant to stress and fatigue.
• 3- Decrease chance of breakage.
• 4-A gradual evenly tapered radicular access is produced, that facilitate canal irrigation and obturation.
• 5 - Does not weaken following sterilization.
Advantages Of NiTi Rotary instruments



• 6 - Electro chemical polishing make the instrument highly smooth, more sharp, decrease the torque required, and icrease resistence to fracture.
• 8 - Biocompatible and more resistance to corrosion.
• 9 - Rounded smooth apex give less canal transportation, ledge formation, and greater preservation of tooth structure.
• 10 -It takes shorter time to prepare the canal .
• 12 -Less fatigue and stress to the dentist and patient.

5






A clean and smooth surface after the electro-chemical treatment






Electrochemical polishing smoothen sharp blades with out loosing it’s sharpness Improve resistance to fracture 20%.

Surface treatment of the files can decrease the torque required in order to rotate nickel-titanium files by 25% without diminishing cutting ability.

After E.T.

Before E.T.

Disadvantages of NiTi

• 1- Sudden fracture unexpectedly without any sign of deformation and usually the fracture occurs at the apical part.
• 2- Small sizes are too flexible. So we start with hand stainless steel instrument.
• 3- Expensive and it is not easy to manufacture, (machined by computer controlled grinders).
• 3-Become dull quicker than stainless steel.
ERG-6 RoboGrind








9
Kuhn et al., (2001) observed a high incidence of machining marks and other defects on the surface of new Niti rotary instruments.

Under repeated cycling, these defects would grow into cracks that propagate and cause fatigue failure.
There are two main types of instrument fracture cyclic fatigue or torsional fatigue.

Along the RCT procedure the EDTA paste should be used

Followed by copious final irrigation of sodium hypochlorite to neutralize the EDTA effects
1-To prevent the dentine softening effect
2- To reduce the effect of EDTA in reduction of microhardness of dentin.

Intra appointment medications

11
Dentin deposits were thus created during preparation of the root canals, and they adhered tenaciously in surface cracks, despite of ultrasonic cleaning.
These lodged dentin chips clearly seem to cause a wedging action on the machining cracks, which may lead to their propagation from localized tensile stress during clinical use and eventually result in instrument fracture.





Tear off 1 « petal » after using it in Simple canal, 2 in a Medium canal, 3 or 4 in a Difficult canal.
12

Safety Memo Disc

Main Causes of Rotary NiTi files fracture

• 1- Miss preparation of glide path (manual or rotary).
• 2- Failure to follow manufacturer’s instructions.
• 3- Wrong speed (higher speed).
• 4- Too much pressure – forcing files in to canal.
• 5- Threading / screwing in.
• 6- Multiple uses more than manufacturing instruction.
• 7- Remaining file in the same vertical level without up down movement which lead to cyclic fatigue.
• 8- Miss recaptulation.
• 9- Neglecting Irrigation between each file.
• 10- Clean the file after each insertion.

New methods of improving physical properties of NiTi instruments

1- Ion implantation(nitrogen implantation) to increase surface hardness and wear resistance.

2- Thermal treatment my relief the residual stress of manufacturing process.

3- physical vapor deposition (PVD) surface coating titanium nitrate which improve cutting efficiency & will not affected by repeated autoclaving & NaOCl.


THANK YOU