The document discusses root canal preparation techniques using rotary nickel titanium (NiTi) instruments. It introduces the concepts of "cleaning and shaping" root canals put forth by Schilder in 1974. It then discusses the design objectives and characteristics of different generations of NiTi rotary instruments, including taper, rake angle, radial land, helical angle, and pitch number. The document also covers the functions of NiTi instruments regarding torsional stress, bending fatigue, speed and torque. Finally, it compares root canal preparation techniques like crown-down versus step-back approaches and addresses advances in NiTi metallurgy.

1. Dr. Lena Ali Hassan
M.Sc. Conservative Dentistry
Endodontic Department

3. In 1974, Schilder introduced the concept of
“cleaning and shaping” root canals. “Cleaning” refers
to removing all contents of the root canal system before
and during shaping; “shaping” refers to a specific root
canal cavity form with four design objectives.

4. Design (Mechanical )Objectives:
 The opening should be a continuously tapering
funnel from the access cavity to the apical foramen.
 The root canal preparation should maintain the path
of the original canal.
 The apical foramen should remain in its original
position.
 The apical opening should be kept as small as
practical.

5. Rotary Instruments use
Stainless steel & NiTi
Use rotary or not depend on :
 Skill of the dentist
 Complexity of the case
The choice of a particular design depends on:
 Clinical experience
 Handling properties
 Usage safety
 Case outcomes

6. Types of rotary instruments according
to their action

7. Types of rotary instruments according
to their design
 Group I: (LightSpeed)
 Group II: rotary instruments with 2% (.04) & 6% (.06)
tapers (ProFile +other models)
 Group III: rotary instruments with specific design
changes(the ProTaper and RaCe)
 Group IV: thermomechanically treated NiTi
instruments.

8. Generations of NiTi Rotary Instruments

9. Nickel Titanium alloy
Nitinol 55
Characteristics:
• Softer
• Not heat treatable
• Tougher
• Low elastic modulous(Shape memory+super elasticity+high
resistance to cyclic fatigue)
• More resilient
Shape memory alloys(austenite +martensite phase or
crystalline structure)
More sensitive to Torque than SS files

11. Design features of rotary instruments:
Tip design and transition angle(cutting or not)
Taper (affects canal prep shape + decrease area
engagement if graduate or variable)
Rake angle
Radial Land
Helical or flute angle
Pitch Number

14.  Tip design and transition angle

15.  Taper (affects canal prep shape + decrease area
engagement if graduate or variable )

16.  Rake angle
.
 Rake angle is the angle formed by the cutting edge and
a cross section taken perpendicular to the long axis of
the instrument.
 The more positive the rake angle (closed), the greater the
cutting efficiency. Alternately, a neutral or negative rake
angle (open) reduces the file’s cutting efficiency.
 Most conventional endodontic files use a negative or
substantially neutral rake angle.
 Positive rake angles cut more efficiently than neutral rake
angles, which scrape the inside of the canal.
 Overly positive rake angle digs and gouges the dentin. This
can lead to separation.

17.  Rake angle

18.  Radial Land
 A surface that projects axially from the central axis, between
flutes, as far as the cutting edge (blade support).
 Blade support can be defined as the amount of material
supporting the cutting blades of the instrument.
 A radial land surface produces a planing or scraping effect
on the dentin walls, and a blade surface engraves them.
 The less blade support (the amount of metal behind the
cutting edge), the less resistant the instrument is to torsional
or rotary stresses.

19.  Radial Land
 With radial land surfaces, friction is enhanced, reducing the
mechanical resistance of the files.
 An attempt has been made to lower the friction, thus creating
a kind of recessed radial land (Quantec and K3 instruments).
This helps to prevent the propagation of cracks and reduces
the chances of separation and deformation from torsional
stresses.
 Rotary files with radial land areas are further subdivided
depending on the shape of the grooves, U-shaped or L-
shaped, resulting in a U-type or H-type file. The U-type file
is constructed by grinding three equally spaced U-shaped
grooves around the shaft of a tapered wire, whereas the H-
type file consists of a single L-shaped groove (Hedström
type) produced in the same way.

20.  Radial Land
 It is this combination of a noncutting tip and radial land that
keeps a rotary file centered in the canal and reduces the
chances of transporting the root canal. An important concept
of rotary instrumentation should be remembered. The
concept is not of drilling a hole in a root. Rather, it is one of
taking a small hole, planning the inside, and making it larger.

21.  Radial Land

22.  Radial land effect

23.  Helical Angle:
 The angle that the cutting edge makes with the long axis of
the file.
 Files with a constant helical flute angle :
1. Allow debris to accumulate, particularly in the coronal part
of the file.
2. More susceptible to the effect of screwing-in forces.
 By varying the flute angles,
1. Debris will be removed in a more efficient manner
2. File will be less likely to screw into the canal

24.  Helical Angle:

25.  Pitch number:
 The number of spirals or threads per unit length.
 The result of a constant pitch and constant helical
angles is a pulling down or sucking down into the canal.
This is of significance in rotary instrumentation when
using files with a constant taper. For example, the K3 file
has been designed with constant tapers but with variable
pitch and helical angles. This reduces the sense of being
sucked down into the canal

27. Functioning of NiTi rotary instruments
Torsional stress
 Very harmful and if they are of elevated intensity, they
rapidly cause the fracture of the instrument. This
generally happens in three situations:
1) when a large surface of the instrument rubs
excessively against the canal walls (taper lock)
2) when the instrument tip is larger than the canal
section to be shaped
3) when the operator exerts excessive pressure on the
handpiece

28. Functioning of NiTi rotary instruments
Torsional stress

29. Functioning of NiTi rotary instruments
Torsional stress
Initially a brief manual instrumentation, allows
us to:
– drastically reduce the torsional stresses, by
creating a canal at least as large as the diameter
of the NiTi rotary instrument tip with greater
taper, that will be used successively
– interpret the original anatomy.

30. Functioning of NiTi rotary instruments
Bending fatigue
 The main cause of strain
 Factors responsible for it are
1. Canal anatomy(curve radius)
2. Bending angle
3. Largeness of the instrument

32. Functioning of NiTi rotary instruments
Bending fatigue
Astationary rotary instrument inside a curved canal
,will be subjected to two different types of stresses :
– compression stress on the internal surface of the curve
– tensile stress on the external surfaces of the curve.

34. Spead and Torque
Speed
 Revolutions per minute but also to the surface feet per unit
that the tool has with the work to be cut.
 Endodontic motors range of speed: 150 rpm to 40,000
rpm.
 The greater the speed, the greater the cutting efficiency.
 Higher speed disadvantages:
1. of loss of tactile sensation.
2. Breakage of instruments preceded by flute distortion.
3. Change in anatomical curvature of canal.
4. Loss of control [22].

35. Spead and Torque
Torque(moment)

36. Spead and Torque
Torque(moment)
 Forces that act in a rotational manner.
 e.g. turning a dial, flipping a light switch, or tightening
a screw.
 Torque is the ability of the handpiece to withstand
lateral pressure on the revolving tool without
decreasing its speed or reducing its cutting efficiency
 Dependent upon the type of bearing used and the
amount of energy supplied to the handpiece .

37. Spead and Torque
Torque(moment)
 High torque advantage = very active instrument.
 High torque disadvantage = incidence of instrument locking
and consequently deformation and separation increase.
 low torque would= reduce the cutting efficiency of the
instrument, and difficult instrument progression in the
canal.
 The ideal configuration is slow-speed and low-
torque or preferably right-torque motors, because
each instrument has a specific ideal (right) torque.

38. Spead and Torque
Torque(moment)
The torque generated during the canal preparation
depends on a variety of factors, especially the contact
area .The size of the surface area contacted by
an instrument is influenced by the instrumentation
sequence or the taper of the instrument in use . In
straight canals where the resistance to dentin removal is
low, the high torque provided by the motor can lead to
fracture of the blocked instrument, especially because
the clinician usually has no time to stop or retract the
instrument. Hence, use of slow-speed, high-torque
NiTi rotary instruments leads to many iatrogenic errors.

40. Endodontic Motors
 Rotation
 Reciprocation

41. Rotation Vs Reciprocation
Reciprocation
• 1st used with stainless steel due to its safety(SS not sensitive
to Torque as NiTi)
• Now used with NiTi (Wave one, Reciproc ,Protaper F2)
• Can be 90degree CW vs CCW and non equal reciprocation
cycles
• Advantages :safe ,less torque, less torsional stress and less
cyclic fatigue
• Disadvantages
1. Debris accumulation =debris extruded apically =post -op
pain
2. With single file technique it exerts lot of force on canal
walls causing microcracks(high torque)

42. Rotation Vs Reciprocation
Reciprocation

43. Rotation Vs Reciprocation
Reciprocation

44. Rotation Vs Reciprocation
Rotation
• Only with NiTi
• Debris accumulates in file spaces
• Needs removal of the file and cleaning to remove debris
• Less post-op pain (less apically extruded debris)
• Less safe
• Less damage to canal walls
• File Fatigue and separation more frequent
• Needs torque monitoring
• Torsional stress and cyclic fatigue more frequent

45. Rotation Vs Reciprocation

46. Endodontic motors

47. Rotation Vs Reciprocation
Reciprocation

48. Preparation Techniques
Crown-down
versus step-
back
approach

49. Hybrid technique

50. Advances In NiTi matallurgy
Because the martensitic form of NiTi has remarkable
fatigue resistance, instruments in the martensite phase
can easily be deformed and yet recover their shape on
heating above the transformation temperatures. The
explanation for this may be that heating transforms the
metal temporarily into the austenitic phase and makes
it superelastic, which makes it possible for the file to
regain its original shape before cooling down again.

51.  M-wire NiTi(Dentsply Tulsa)
 Applying a series of heat treatments to NiTi wire blanks
 Greater flexibility and an increased resistance to cyclic
fatigue when compared to traditional NiTi alloys.
 Resistance to cyclic fatigue by almost 400% compared to
commercially available NiTi files
 ProFile Vortex, Vortex Blue, GT Series X, and ProTaper
Next files.

52.  R-phase NiTi (Sybron Endo)
 R-phase is an intermediate phase with a rhombohedral
structure that can be formed either during the martensite-
to-austenite or the austenite-to-martensite transition.
 Developed by transforming a raw NiTi wire in the
austenite phase into the R-phase through a thermal
process.
 advantages:
 It overcomes many of the limitations of ground file
technology
 and opens up new opportunities for improved file design,
such as twisting.
 It optimizes the molecular phase structure, thus resulting
in improved properties of nickel–titanium.

53.  R-phase NiTi (Sybron Endo)
Advantages:
 It employs a crystalline structural modification that
maximizes flexibility and resistance to breakage.
 The Twisted File (TF) and K3XF file (reduced stiffness
and more fracture ) and Adaptive files.
 Good superelasticity and shape-memory effects

54.  R-phase NiTi (Sybron Endo)

55.  Controlled-Memory (CM) (D&S Dental)
 Manufactured using a special thermomechanical process
that controls the memory of the material, making the files
extremely flexible but without the shape memory of other,
conventional NiTi files.
 Allows the instrument to be precurved before it is placed
into the root canal.
 Sterilization of these files returns them to their original
 shape.
 e.g. HyFlex (Coltène Whaledent) and Typhoon (TYP)
(Clinician’s Choice Dental products, USA).

56. Clinical Strategies to safely & successfully use
NiTi rotaries:
1. Assess case difficulty
2. provide adequate access preparation
3. Use hand files up to size #20 prior to rotary use
4. Proceed with crown-down sequence
5. Use light touch and low rpm
6. Don’t force files
7. Don’t overuse files

57. Clinical Strategies to safely & successfully use
NiTi rotaries:
8. Replace rotary instruments frequently
9. Don’t start and stop
10. Avoiding breakage takes practice
11. Don’t try to bypass ledges
12. Avoid cutting with the entire length of file
13. Length control is critical