Original Article

Influence of cervical preflaring using different rotary

instruments on the accuracy of apical file size
determination: A comparative in-vitro study
Shiv Aditya Sharma, Shashi Prabha Tyagi, Dakshita Joy Sinha, Udai Pratap Singh, Priyanka Chandra,
Gagandeep Kaur
Department of Conservative Dentistry and Endodontics, Kothiwal Dental College and Research centre, Moradabad, Uttar Pradesh, India

Abstract
Aim: To investigate the influence of cervical preflaring using different rotary instruments on apical file size determination.
Aim
Materials and Methods
Methods: Extracted human molar teeth were randomly divided in to eight groups (N = 10): Control group (CG);
LA Axxess group (LA); HyFLex group (HF); GatesGlidden group (GG); ProTaper group (PT); Race group(RC); FlexMaster group
(FM); and K3 group (K3). Patency was maintained and working length was established under magnification. All instruments
were used according to manufacturers instructions. Steriomicroscopic images were taken to determine the discrepancies in
diameters. ProPlus software (USA) was used to determine the diameter of the root canal. ANOVA test and Post Hoc Tests
Bonferroni Multiple Comparisons were used for statistical analysis.
Results Canals preflared with LA Axxess burs showed the best results. Control group that is, the canals with no cervical
Results:
preflaring showed the maximum discrepancy between the initial apical file diameter and apical canal diameter.
Conclusion Cervical preflaring plays an important role in reducing the discrepancy between initial apical file diameter and
Conclusion:
apical canal diameter.
Keywords: Apical canal diameter; cervical preflaring; endodontic working width; file size; initial apical; molar teeth.

INTRODUCTION
Cleaning and shaping of the root canal are the current
standards in endodontic treatment.[1,2] Success of endodontic
treatment relies on the accurate determination of the
working length and adequate enlargement of the root
canal.[3] Gutierrez and Garcia.[4] showed that often canals
are improperly cleaned and attributed this to inadequate
instrumentation due to the fact that the root canal diameter
is larger than the instrument caliber used in each particular
case. In addition with shaping, determination of the anatomic
diameter is also related to cleaning of the root canal system.[5]
Determination of the anatomical diameter is based solely on
clinicians ability to detect the apical narrowing by tactile
sense which is an empirical and inaccurate method.[5] Tan and
Messer.[6] stated that traditional methods for determination
of the anatomic diameter at the apical third have under
estimated the real diameter of this region. Without adequate
scientific evidence decision cant be made that how large is
Address for correspondence:

MATERIALS AND METHODS

Tooth selection and preparation 80 extracted human
permanent maxillary first molars displaying normal pulp
Access this article online

Dr. Shiv Aditya Sharma, Department of Conservative Dentistry

and Endodontics, Kothiwal Dental College and Research Centre,
Moradabad - 244 001, Uttar Pradesh, India.
E-mail: shiv_28029@yahoo.co.in
Date of submission : 08.01.2014
Review completed : 25.06.2014
Date of acceptance : 04.10.2014

large enough. Thus the concept of cleaning the apical canal to

three sizes larger than the first file to bind is not based on the
scientific evidence.[7] There are many factors that affect the
determination of minimal initial working width at working
length, these are; canal shape, canal taper, canal curvature,
canal content, canal wall irregularities and instruments for
determining initial working width.[8] Preflaring of the cervical
and middle thirds of the root canal improves anatomical
diameter determination; the instrument used for preflaring
plays a major role in determining the anatomical diameter at
the WL.[9] Thus, the objective of this study was to investigate
the influence of cervical preflaring using different and
currently used instruments on the accuracy of apical file
size determination.

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Website:
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DOI:
10.4103/0972-0707.144608

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Sharma, et al.: Influence of preflaring on apical file size determination

chambers, patent root canals, fully formed apices without

any sign of resorption were collected. Maxillary molars with
degree of curvature of the mesiobuccal root between 10
and 15 were utilized.[5] Ethical clearance was taken from
the ethical committee of the institute. All teeth were placed
in 0.1% thymol solution and taken out 24 hours before use.
They were placed under running water for 15 minutes to
eliminate traces of thymol. Ultrasonic scaler was used to
remove calculus and other surface debris. The cusps of the
teeth were cut horizontally to get a plane occlusal zone
to determine the working length precisely. Standard access
cavities were performed and the pulp tissue was removed
with a barbed broach, avoiding contact with the root canal
walls. Canals were then irrigated with copious 2.5% sodium
hypochlorite solution (Qualigens Fine Chemicals, Navi
Mumbai, India).
Sizing of canals: After final irrigation with normal saline, the
canal was dried. To maintain the patency of canal, an ISO
06/.02 K-file (Dentsply) was inserted until it came out of the
apex. After maintaining patency an ISO 08/0.02 K-file was
inserted with gentle pressure in watch winding motion until
the tip of file was visible at the apex. This procedure was
carried under the endo-microscope with 5X magnification.
The overall canal length was thus determined by placing tip
of the file at the apex and working length was established
1 mm short of this length.
Cervical and middle third flaring- After working length
determination, the teeth were divided in to eight groups
(N = 10). One group was taken as control group that is
without pre-flaring, other seven groups received preflaring of root canals. All rotary instruments were used
in continuous rotary motion with the help of X-Smart
endomotor (Dentsply/Maillefer, Ballaigues, Switzerland).
All instruments were used according to manufacturers
instructions with proper lubrication and irrigation. LA
Axxess bur (SybronEndo) ISO 20/0.06 was introduced in
continuous rotary motion. The cervical and middle third of
canals were pre-flared 3-4 mm short of the working length.
Gates-Glidden drills (Dentsply Maillefer, size ISO 90-110)
were used until the binding sensation was felt in the middle
third. ProTaper files (Dentsply Maillefer) SX (ISO 20, taper
3.5-19%), S1 (ISO 17, taper 2-11%), S2 (ISO 20, taper 4-11.5%)
were used in respective order. Pre-flaring was done 3-4 mm
short of the working length. RaCe files (FKG Dentaire) with
ISO 40/0.10 and 35/0.08 were used respectively. Coronal
10 mm of canal was flared. K3 Files (SybronEndo) with ISO
size 25/0.08 and 25/0.10 were used respectively. Canals
were pre-flared 3-4 mm short of the working length. The
FlexMaster intro file (VDW) ( ISO 22/0.11) was initially
used for flaring followed by ISO 25/0.06 and 25/0.04 files
respectively. The canal was flared 3-4 mm short of the
working length. An ISO size 25/0.08 HyFlex CM file (Coltene)
was used to flare the canal followed by an ISO 20/0.04 file.
Flaring was done 3-4 mm short of the working length.

576

Determination of initial apical file- After pre-flaring of all teeth

was done, hand files were inserted in to the mesio-buccal
root canal starting with k-file ISO 08/0.02 at the working
length. An ISO 10/0.02 file was then inserted till the working
length. At ISO 10, the file size was increased in increment of
5 ISO units until slight friction was felt at the working length.
The first file that had binding sensation at the working length
was noted and fixed with methacrylate in the root canal.
One millimeter of the root apex was cut horizontally with a
microcutter so that the remaining tooth was at the working
length. The apical sections were visualized using stereo
microscope and images were recorded digitally for each
specimen.
The analysis of the images obtained was performed on
a computer using the Image Pro Plus software (Media
Cybernetics, USA). It was used to determine the diameter
of the root canal and diameter of the initial apical file. The
largest and smallest diameter of the root canal and the largest
diameter of the instrument were recorded. The differences
between these measures were submitted to statistical
analysis. The data were submitted to ANOVA test and Post
Hoc Tests Bonferroni Multiple Comparisons, to assess
the effect of pre-flaring techniques on the discrepancies
found between the diameter of the binding instrument and
the anatomic diameter of the root canal. Statistical analysis
was performed at the 0.05 level of significance.

RESULTS
Cervical preflaring and the type of instrument had a
significant effect on initial apical file size determination.
Preflaring with LA group burs leads to the most accurate
determination of the initial apical file size. In this group,
the maximal apical root canal diameter and the diameter
of the initial apical file had the lowest discrepancy (mean
0.015 mm 0.015) followed by HyFlex group (mean
0.017 mm 0.017) and there was no statistical difference
between these groups. Following HyFlex group were RaCe
instruments (mean 0.020 mm 0.020). ProTaper group
showed greater discrepancy than the former groups (mean
0.028 mm 0.028). After ProTaper came FlexMaster group
(mean 0.035 mm 0.035) followed by K3 (mean 0.048 mm
0.048) and GatesGlidden (mean 0.051 0.051) which
showed comparable results [Figure 1].
In order of minimal discrepancies between the initial apical
file diameter and apical root canal diameter. The results are
shown in [Table 1].

DISCUSSION
The biomechanical preparation of the apical zone has
been recognized critical and essential.[2] The instrument

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Sharma, et al.: Influence of preflaring on apical file size determination

least three sizes greater than its original diameter. However

this concept needs to be reviewed, as it is ineffective and
may leave canal walls untouched when no preflaring is
performed.[17]

Early flaring can be accomplished either by manual and

mechanical means. Mechanical (that is rotary flaring)
reduces treatment time, but is accompanied by a risk of
complications. Over enthusiastic use, inappropriate size
and excessive depth can result in lateral perforations,
ledges and instrument breakage.[18]

Figure 1: Stereomicroscopic pictures of transverse sections of

root canals at the WL with the IAF fixed in the root canal to
show the discrepancies of root canal diameter and diameter
of the IAF of (a) Control group (b) LA group (c) HF group
(d) RC group (e) PT group (f) FM group (g) K3 group (h) GG
group
Table 1: Discrepancies (in mm) between the diameter of
initial apical file and canals at the working length, for
different groups
Control group
LA Axxess group
Hyflex CM group
RaCe group
ProTaper group
FlexMaster group
K3 group
GG drill group

Number

Mean

Std. Deviation

10
10
10
10
10
10
10
10

0.066
0.015
0.017
0.020
0.028
0.035
0.048
0.051

0.004
0.003
0.002
0.003
0.002
0.002
0.003
0.003

P<0.05

binding technique for determining anatomical diameter at

working length is not precise; preflaring of the cervical and
middle thirds improve the determination of the anatomical
diameters at the working length and the type of instrument
play an important role.[10] The increase in file size after
preflaring can be explained by realizing that, within a
canal, irregularities and curvature produced contacts with
the file and interfere with its progression toward the apex.
Early flaring, regardless of the method used, removes these
contacts, opens the space and reduces file contact; thus, a
file progresses more easily towards the apex after flaring.
This was previously suggested by Leeb.[11] After flaring a file
comes to a stop only when the diameter of the canal begins
to apply pressure against the instrument.[12] The point in
the apical region of the canal at which preparation and
obturation should be terminated is determined by several
variables.[13-15] and apical constriction is considered as the
landmark for instrumentation.[16,17]
To what extent the canal is supposed to be prepared
has been a controversial issue in the endodontic field.
Grossman also stated that the canal should be enlarged at

The roots of the teeth in the present study were embedded

in methacrylate to preserve the apical region and to
avoid any destruction during root canal preparation and
cutting the root. The apical foramen was not covered by
methacrylate to be able to precisely measure tooth length
and exactly cut 1 mm of the apex with the IAF fixed in the
root canal.[2]
In the present study, cervical preflaring of the root canal
significantly increased the accuracy of determining the
initial apical diameter by the initial apical file compared
with non-flared root canals. The size of initial apical file in
the control group was three times smaller than that in LA
and HF groups.
Rotary instruments used in this study vary in ISO size
and taper. Each system has its own unique design feature
and hence has a characteristic preparation technique.
All instruments were used according to manufacturers
recommendations for each system.
Taper of instruments, used for preflaring, is a determining
factor in the accuracy for determination of initial apical file.
From all specimens evaluated, the root canal preflared with
LA Axxess instruments presented the least discrepancies.
This could be attributed to the configuration, metal
alloy properties and mode of operation. Moreover the
0.06 taper, safe end and flute design of LA Axxess burs
have been associated with complete removal of cervical
dentin projections without causing canal perforations and
transportations.[9] These results are in agreement with the
previous studies.[19,20]
The 0.08 taper of the HyFlex CM files could be associated
with the good results. They are manufactured by a unique
process that controls the material memory, making the
files extremely flexible but without the shape memory of
other NiTi files. This gives the file the ability to follow the
anatomy of the canal very closely. These advanced features
of HyFlex CM files increase its efficiency to remove the
dentin projections from cervical and middle thirds of root
canals more effectively and quickly. HyFlex CM files are never
been compared previously. This is the first study to compare
the effect of preflaring with this new and unique file system.

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Sharma, et al.: Influence of preflaring on apical file size determination

Similarly the greater taper of RaCe instruments that is, 0.10

and 0.08, effectively created the path for the initial apical
file to progress without touching canal walls (curvature)
and dentin projections, this could be attributed to its good
performance in reducing the discrepancy between the
apical canal diameter and initial apical file diameter. These
results are in agreement with previous study,[2] showing
better results of RaCe files over ProTaper and FlexMaster.
FlexMaster intro file has a 11% taper but its simple K-file
type design and less flute space for effective debris removal
can be associated with its lack of performance as compared
to previous instruments. These results are in agreement
with previous study.[2] showing better results of protaper
over FlexMaster.
K3 files having 0.10 and 0.08 taper has a positive cutting and
rake angle but its low flexibility as compared to other files
could reflect its results in reducing the discrepancies between
the initial apical file and apical canal diameter. Although the
results of K3 file are comparable with Gates Glidden drills.
Apical shaping is easier when early flaring is used, from the
data presented, one can speculate that early flaring reduces
the discrepancy between the initial apical file diameter and
apical canal diameter. An appropriate apical sizing method
can help operator to avoid unnecessary enlargement of the
apex. There is further need of research to develop methods
for optimal determination of root canal size in all dimensions
while respecting the complexity of apical anatomy. Although
early preflaring of the root canal could not guarantee that the
instruments bound only at the working length. Clinically, it is
not always possible to straighten the coronal two-thirds of
root canal because sometimes the radius of root curvatures
is long. However, it must not be forgotten that the capability
of the endodontist in applying all available information is
also a determinant for success.

CONCLUSION
Cervical preflaring plays a vital role in reducing the discrepancy
between initial apical file diameter and apical canal diameter.
Taper, cross sectional design and flexibility of the instrument
used for preflaring plays a vital role in determining its effect.
LA Axxess burs and HyFlex CM files showed best results in
comparison to all groups compared in this study.

578

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How to cite this article: Sharma SA, Tyagi SP, Sinha DJ,
Singh UP, Chandra P, Kaur G. Influence of cervical preflaring
using different rotary instruments on the accuracy of apical file
size determination: A comparative in-vitro study. J Conserv Dent
2014;17:575-8.
Source of Support: Nil, Conflict of Interest: None declared.

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