success of endodontic treatment relies on the accurate determination of the working length and adequate enlargement of the root canal .
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 .
determination of the anatomical diameter is based solely on clinician 's ability to detect the apical narrowing by tactile sense which is an empirical and inaccurate method .
tan and messer . 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 ca
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 .
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 .
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 .
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 .
tooth selection and preparation 80 extracted human permanent maxillary first molars displaying normal pulp 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 .
all teeth were placed in 0.1% thymol solution and taken out 24 hours before use .
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 .
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 pre - flaring of root canals .
all rotary instruments were used in continuous rotary motion with the help of x - smart endomotor ( dentsply / maillefer , ballaigues , switzerland ) .
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 .
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 .
an iso size 25/0.08 hyflex cm file ( coltene ) was used to flare the canal followed by an iso 20/0.04 file .
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 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 .
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 ] .
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 in order of minimal discrepancies between the initial apical file diameter and apical root canal diameter .
discrepancies ( in mm ) between the diameter of initial apical file and canals at the working length , for different groups
the instrument 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 .
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 .
comes to a stop only when the diameter of the canal begins to apply pressure against the instrument .
the point in the apical region of the canal at which preparation and obturation should be terminated is determined by several variables . and
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 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 .
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 .
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 . 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 .
each system has its own unique design feature and hence has a characteristic preparation technique .
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 .
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 .
this is the first study to compare the effect of preflaring with this new and unique file system .
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 , 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 . 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 .
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 .
 aim : to investigate the influence of cervical preflaring using different rotary instruments on apical file size determination.materials and 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 manufacturer 's 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 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 apical canal diameter . 
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSION