Introduction to NiTi

The navy worked with NiTi alloy in the 1950’s and 1960’s

They were looking for a non-magnetic, waterproof, and salt resistant material

Initial tests found NiTi to be superelastic

NiTi particularly exhibits superelastic behavior between 10oC – 125oC

Other alloys with superelastic properties are the alloys of copper-zinc, copper-aluminum, or titanium-niobium

Ideal temperature range in endodontics is 23oC to 36oC, the temperatures found in the composition of 50% Ni and 50% Ti

Orthodontics began using NiTi in the late 1970’s

NiTi was also useful in wiring fractures in orthopedics and oral surgery

Initial work proved NiTi resisted corrosion in the body and was extremely biocompatible

The First Use of NiTi in Endodontic Hand Files

Walia, Brantley, and Gerstein conducted the first reported investigation of the NiTi alloy in endodontics in 1988

Testing concluded that the NiTi had two to three times the elastic flexibility and greater resistance to torsion fractures

By 1991 Quality Dental (Johnson City, TN), developed a process for grinding NiTi alloy files for NiTi Co. (Chattanooga, TN)

It was reported to be 500% more flexible than conventional stainless steel and said to be capable of withstanding 1000% more stress than conventional stainless steel

University of South Carolina conducted a study in 1992 with their pre-doctoral students

Fewer cases of broken instruments, perforations, and ledges occurred in the group using NiTi hand files

University of Tennessee conducted a similar study in 1993 with their pre-doctoral students

Students using NiTi hand files had significantly higher grades, instrumented the canals significantly faster, and had overall superior results

NiTi files seemed to work more efficiently in a reaming motion rather than a filing motion

Table 1: This table illustrates the procedural errors made by the students during their proficiency exam with the two sets of files. (* Statistically significant)

The First Use of NiTi in Endodontic Rotary Files

1991 NiTi Co. had two rotary file designs to make up their file line

These two file designs were developed uniquely for continuous 360o rotation

The first file design, U-File design, which continues to be offered today as the Profile, GT and LightSpeed, for sizes #15 through #35

The second file design, the Sensor File, was used in sizes #40-#60 and incorporated two sets of flutes having different helical angles

Oregon Health Sciences University compared four instrumentation techniques

1) Step-back preparation with K-files 2) Crown-down preparation with K-files3) Sonic instrumentation with Shaper-

Sonic files4) NiTiMatic preparation system with NiTi

rotary files

Incidence of zipping, ledging, and elbow formation was found to be the lowest with the use of the NiTiMatic preparation system with NiTi rotary files

In 1993 the University of Tennessee conducted a study comparing hand stainless steel, hand NiTi files, and the NiTiMatic preparation system with NiTi rotary files

They found the rotary files to have achieved the same shaping goals in about half the time of the other two groups:

Rotary 173 s Hand stainless 328 sHand NiTi 351 s

The NiTi rotary was found to have maintained the apical shape better, indicating fewer zip type procedural errors

Amount of material removed at the working length:

Rotary 0.017 mmHand NiTi 0.023 mmHand stainless steel 0.139 mm

They also found the canal width of the inner wall to be closer to the original width and more centered with the rotary group

This illustrates the increase in canal width on the inside of the curve at the point of curvature.