NiTi Rotary files - Endodontic review reports

Endodontic

1. NiTiRotary
報告者：PGY戴子竣

2. BACKGROUND
•Engine-driven instruments for root canal preparation
made of stainless steel have been in use for more than
half a century.
•The major two problems with this type of instrument
were canal transportation and file fracture.
Cohen's Pathways of the Pulp, 11th edition (2016)

3. BACKGROUND
•This changed with the advent of NiTirotaries from
about the early 1990s; the much more flexible alloy
allowed continuous rotation and reduced both canal
preparation errors and instrument fracture compared
to earlier engine driven techniques.
Cohen's Pathways of the Pulp, 11th edition (2016)

4. BACKGROUND
•Currently, more than 50 types of rotary instrument
systems have been described and more continue to be
developed.
•Theinstruments vary greatly in terms of design, alloy
used, and recommended cutting movement.
Cohen's Pathways of the Pulp, 11th edition (2016)

5. BACKGROUND
Cohen's Pathways of the Pulp, 11th edition (2016)

6. BACKGROUND
•Group I: Passive Preparation; Presence of
Radial Lands
•Considered very safe
•Fracture resistance to torsional loading and
cyclic varies depending on specific instrument
design.
•The limited cutting efficacy of these files was
perceived as a downside and is a reason that
the market share has diminished.
Cohen's Pathways of the Pulp, 11th edition (2016)

7. BACKGROUND
•Group II: Active Cutting; Triangular Cross
Section
•Higher efficacy
•The overall incidence of clinically relevant
preparation errors appears to be low, in spite
of more aggressive cutting by files without
radial lands.
•Higher potential for preparation errors, in
particular when the instrument is taken
through the apical foramen
Cohen's Pathways of the Pulp, 11th edition (2016)

8. BACKGROUND
•Group III, Special Cases
•Reciprocation: +144°→ -72°
•Self-Adjusting File: a cylindrical, hollow
device, designed as a thinwalledNiTi
lattice with a lightly abrasive surface
•Sonic and Ultrasonic Instruments: higher
incidence of preparation errors and to
reduced radicular wall thickness
Cohen's Pathways of the Pulp, 11th edition (2016)

9. BACKGROUND
•Clinicians must fully understand the factors that control
the forces exerted on continuously rotating NiTi
instruments.
Cohen's Pathways of the Pulp, 11th edition (2016)

10. BACKGROUND
•The incidence of instrument fracture can be reduced
to an absolute minimum if clinicians use data from well-
designed torque and stress studies.
•Adequate procedural strategies,
•Adequate glide path
•A detailed knowledge of anatomic structures
•With avoidance of extreme canal configurations
•Specific instrumentation sequences
Cohen's Pathways of the Pulp, 11th edition (2016)

11. Received 13 August 2015; accepted 23 January 2016

12. INTRODUCTION
•nickel –titanium (NiTi) instruments to clinical endodontic
practice has improved the mechanical preparation of
the root canal space (de MeloRibeiro et al. 2013)
•Avoiding problems associated with stainless steel
instruments, such as ledges, zips, perforations and root
canal transportation (Peters 2004).
•Maintain a satisfactory canal shape and shorten the
duration of preparations (Loizideset al. 2007).
•Compared to stainless steel hand files, preparations are
rounder and centredin the canal, helping to maintain
the original root canal anatomy (Bergmanset al.2001).

13. INTRODUCTION
•Rotary instruments are more susceptible to fracture due
to torsion and/or flexion(Pasqualiniet al. 2008).
•Torsional fatigueoccurs when the tip of the instrument
binds in the root canal whilst the file continues to turn
(Peters & Barbakow2002).
•Flexural fatiguedevelops when the instrument rotates
inside a curved root canal over an excessive number of
tension–compression strain cycles in the region of
maximum curvature (Pruett et al. 1997, Sattapanet al.
2000).

14. INTRODUCTION
•The efficiency of reciprocating motion has been
compared with continuous rotation in terms of the time
required to prepare a curved root canal, the cutting
efficiency and cyclic fatigue resistance (Plotinoet al.
2015).

15. INTRODUCTION
•The aim of this review is to provide a detailed analysis
on the correlation between movement kinematics and
the cyclic fatigue resistance of NiTiinstruments,
considering the levels of safety of the different
movement protocols used during root canals
procedures.

16. STUDY DESIGN
•From June 2014 to August
2015, 4 independent
reviewers comprehensively
and systematically searched
the Medline (PubMed),
EMBASE, Web of Science,
Scopus and Google Scholar
databases for works
published since January 2005,
using the following search
terms: endodontics; nickel–
titanium rotary files;
continuous rotation;
reciprocating motion; cyclic
fatigue.

17. STUDY DESIGN

18. REVIEW

19. CONCLUSION
•The use of reciprocatingmotion can improve the
mechanical properties of instrumentsand increase
fatigue resistance, compared to continuousrotation
(Kim et al. 2012).

20. CONCLUSION
•Because ofthe differences amongst the various
reciprocatingmotions (different speeds and angles),
further studies areneeded to determine the most
suitable motions for rootcanal treatment.
•The mean time to fracture is not directly proportional to
the increase in the number of reciprocations required
tocomplete a full 360 rotation, probably because the
resulting speeds are not directly proportional.
•Thisshould be considered in future studies concerning
thedefinition and measurement of reciprocating
motionspeed (Gambarini et al. 2012a,b).

21. JOE —Volume 43, Number 5, May 2017

22. INTRODUCTION
•Nickel-titanium (NiTi) endodontic rotary files possess
superelasticity, which is of great benefit during
instrumentation of curved endodontic canals.
•These instruments have an austenite phase at higher
temperatures and, upon cooling or applying stresses,
can transform into the martensitephase.
•The transition phase temperatures of files can differ
depending on the alloys and heat treatments used for
processing

23. INTRODUCTION
•The increased ductility of a file in its martensitephase
allows it to be highly elastic.
•This also improves damping properties, resistance to
crack growth due to fatigue, and provides a higher
resistance to cyclic fatigue.
•The use of heated or cooled irrigantsmay favor the NiTi
phase transition of the instrument toward a more
austenitic or martensitic phase, respectively, which can
affect its cycles to fracture.

24. INTRODUCTION
•The purpose of this study was
to examine the effect of
temperature changes on the
cyclic fatigue of 3rotary NiTi
instruments tested in a metal
block submerged in a water
bath.
•EdgeFile
•Vortex Blue
•ESX (BrasselerUSA)

25. METHODS
•120 NiTirotary endodontic files
were used for each of the 3
experimental file groups:
•EF (EdgeFilefiles)
•VB (Vortex Blue files)
•ESX (ESX files)
•All files were size #25 with a .04
taper and 25-mm length.
•The entire length of each file
was placed into a simulated
canal in a metal block, which
was submerged in a water bath.

26. METHODS
•Within each group of 120 files, files were
randomly subdivided for testing at 4
different temperature cycles, with 30
files per temperature cycle.
•The 4 different temperature cycles were
•ice water (3°±0.5°C)
•room temperature(22°±0.5°C)
•body temperature (37°±0.5°C)
•hot water(60°±0.5°C).
•Time to fracture was converted into
number of cycles to fracture (NCF).

27. RESULTS

28. DISCUSSION
•The findings of this study showed that temperature has
a significant effect on the NCF for all rotary NiTi
endodontic files tested.
•Files in the EF group are predominantly in a martensitic
phase at room temperature, which is responsible for
their lack of shape memory. (Heat-treated)

29. DISCUSSION
•An irrigantchilled below room temperature seems
favorable to increase NCF, except for files that are
already in a martensitic phase such as the files in the EF
group.
•In addition to increasing NCF, another benefit of a cold
irrigantmay be to provide an anti-inflammatory effect.
(Vera et al 2015)

30. DISCUSSION
•Because the cyclic fatigue of various file types was
found to be significantly affected by temperature,
future cyclic fatigue studies are recommended to be
conducted at body temperature.

31. JOE —Volume 43, Number 7, July 2017

32. INTRODUCTION
•The traditional NiTialloy shifts to the stress-induced
martensitic phase thanks to the mechanical stress that
files undergo during shaping procedures.
•This feature is the superelasticbehaviorof the
traditional NiTialloy.
•The improved flexibility and mechanical properties of
NiTifiles may be obtained differently with a thermal
treatment that permanently modifies the
thermomechanical history of the alloy at room T°.

33. INTRODUCTION
•Another feature of the NiTi
alloy that is not used in the
endodontic field is the
transitory martensitic
transformation that the
metal undergoes when
subjected to low T°.
•By cooling the metal to a T°
lower than the transitional
T°, the percentage of the
martensitic phase could
reach the maximum range
possible for the alloy itself.

34. INTRODUCTION
•The aim of the present study was to analyze how a low
environmental temperaturecan affect the fatigue life
of instruments made by different types of heat-treated
nickel-titanium alloys.

35. METHODS
•The flexural cyclic fatigue of 40 new specimens for
each of the following systems was tested for cyclic
fatigue resistance:
•ProTaperUniversal F2 (DentsplyMaillefer, Ballaigues,
Switzerland)
•ProTaperGold F2 (DentsplyTulsa Dental Specialties, Tulsa,
OK)
•TwistedFiles SM2 (SybronEndo, Orange, CA)
•Mtwo#25.06 (VDW, Munich, Germany)
•Vortex Blue #30.04 and #40.06 (DentsplyTulsa Dental
Specialties).

36. METHODS
•Instruments were tested at 2 different environmental
temperatures(n = 20):
•20°C (±2°C) for room temperature (RT) group
•-20°C (±2°C) for the cooled environment (CE) group
•The number of cycles to failure (NCF) and the length of
the fractured fragment (FL) were recorded.
•The means and standard deviations of NCF and FL
were calculated; NCF data were statistically analyzed
using a paired t test between groups RT and CE for
each instrument tested (P < .05), whereas FL data were
analyzed using analysis of variance (P < .05).

37. RESULTS

38. DISCUSSION
•Flexural and torsional cyclic fatigue failure are the main
mechanisms leading to intracanalfailure of NiTirotary
files.
•Many improvements have been introduced in
instrument design and manufacturing methods to
overcome this problem.

39. DISCUSSION
•Recently, the environmental T°has been investigated
as a possible variable influencing the fatigue resistance
of the files.
•However, there have been no studies investigating the
impact of T°lower than the average clinical T°and RT
on the cyclic fatigue resistance of NiTiinstruments.

40. DISCUSSION
•The results of the present study support the evidence
that a low environmental T°may have a dramatic
impact on the fatigue life of NiTiinstruments used in
rotation in a curved artificial root canal.
•However, there have been no studies investigating the
impact of T°lower than the average clinical T°and RT
on the cyclic fatigue resistance of NiTiinstruments.

41. DISCUSSION
•Fragment length did not show any statistically
significant different between the groups, demonstrating
that the point of maximum stress was similar for both
groups, as already reported in similar studies.(Gambarini
G et al. 2008; Grande NM et al. 2006)

42. CONCLUSIONS
•Based on the results discussed earlier, it is clear that the
environmental T°plays a key role in the fatigue behavior
of NiTiendodontic instruments.
•Both traditional and thermally treated files registered a
statistically significant higher cyclic fatigue resistance
when tested at a low T°.
•However, the impact of an environmental T°below the
standard clinical use T°range in root canals in vivo has
not been yet determined and should be the aim of
further investigations in the near future.

43. Thank you for
listening!