endodontic treatment aims to disinfect and to shape the root canals in order to make 
 easy the irrigation procedures and the placement of root canal dressing of filling 
 material .
the preservation of 
 the radicular anatomy is one of the most important concerns during root canal 
 preparation .
some enlargement techniques have been developed to minimize errors , such as 
 ledging , zipping , loss of working length , and apical transportation .
apical transportation is defined as the 
 removal of canal wall structure on the outside curve in the apical half of the canal due 
 to the tendency of files to restore themselves to their original linear shape during 
 canal preparation .
the use of rotary nickel - titanium ( niti ) instruments allows easier and safer root canal 
 shaping with predictable results .
moreover , there is less iatrogenic damage even in 
 severely curved root canals . 
 however , complete instrumentation of the root canals is critical especially at the 
 apical third .
rdig and 
 kahlmeier ( 2007 ) stated that 
 in curved canals the instruments tend to straighten the root canal owing to the major 
 cutting effect toward the inner aspect of the curvature at the cervical root third and 
 toward the outer aspect of the curvature at the root canal end point .
previous reports 
 had pointed that niti instruments tend to be more centered , rapid , and attain a more 
 conservative shaping of canals than stainless steel instruments .
especially the centering ability of 
 niti instruments is owed to their super elastic behavior and shape - memory , even though 
 apical transportation occurs even when super elastic instruments are used .
several reports about apical transportation have been published regarding protaper 
 universal instruments ( dentsply maillefer , ballaigues , switzerland ) ; however , there are few reports 
 regarding wizard cd plus ( medin , prague , czech republic ) . according to the 
 manufacturers , wizard cd plus instruments
present a triangular cross section , with no 
 surface treatment , a working part taper ratio of 10% , 8% , 6% , 4% and 2% , and cutting 
 edges discontinued by grooves in the helix , which were intended for machine preparation 
 of root canals by means of the crown - down method .
protaper universal system has 
 triangular convex cross section and three cutting edges with a negative cutting 
 angle .
the shaping instruments 
 have a progressive taper sequence ( increasing from tip to coronal ) , whereas the 
 finishing instruments have a decreasing taper profile .
it is claimed that the 
 progressive taper sequence will enhance the flexibility of the files in the middle and 
 at the tip region , and that the decreasing taper sequence will enhance the strength of 
 the files while making them rather stiff . in endodontics ,
apical transportation is evaluated after superposition and subtraction 
 of two images ( i.e. , pre - operative and post - operative images ) .
autocad and adobe photoshop ( adobe systems inc , san jose , usa ) 
 are currently used for this purpose ; however , the main disadvantage of the autocad and 
 adobe photoshop is that both need manual superimposition of the images which depends on 
 the operator . in the beginning of the 2000s ,
the brazilian national institute for space research in 
 partnership with the electrical and computer engineering department from university of 
 california developed a computer program for mapping the earth through satellite images . 

this 
 software is called regeemy - image registration and mosaicking , version 0.2.43 can be 
 downloaded from the internet for free ( http://regima.dpi.inpe.br/download.html ) .
this program automatically 
 selects pixels of the same tone in two images and superposes them .
up to date , only one 
 study used the regeemy program to superpose images in dentistry .
the authors evaluated the ability of 
 the program in detecting simulated external root resorption . in the endodontic context
, the ability of regeemy in superposing and subtracting 
 tomographic or radiographic images is unknown .
thus , the aims of this study were : ( 1 ) to 
 evaluate the apical transportation of the wizard cd plus and protaper universal after 
 preparation of simulated root canals ; ( 2 ) to compare , with adobe photoshop , the ability 
 of a new software ( regeemy ) in superposing and subtracting images .
the hypotheses were : 
 ( 1 ) that wizard cd plus and protaper universal would promote similar apical 
 transportation ; and ( 2 ) regeemy would permit the superposition and subtraction of 
 images .
twenty - five simulated root canals made of clear resin ( endo training block ; dentsply 
 maillefer , ballaigues , switzerland ) with an initial .02 taper , 0.15 mm diameter at the 
 apex and 20 curvature were divided into two groups according to the rotary system ( 10 
 specimens per group ) and one control group ( n=5 ) .
every working length 
 was established to 15 mm ( 1 mm shorter than the apex ) by inserting a size 15 k - file 
 ( dentsply maillefer , ballaigues , switzerland ) into the simulated root canal .
thereafter , 
 the samples had previously been numbered and properly positioned in devices made of 
 acrylic resin and , with the file in position , a cone beam computed tomography ( cbct ) 
 ( icat cone beam , hatfield , usa ) was carried out .
all cbct was acquired with the same 
 setting at 70 kvp , 4 ma , 10 s and with the 88 cm field of view ( fov ) selection .
the 
 data set consisted of axial , sagittal and coronal reconstructions ; the size of the 
 reconstructed voxels was 0.16 mm .
images were saved on a computer for further evaluation 
 and comparison . in control group ,
the specimens were subjected to a new cbct under identical conditions 
 to assess the feasibility of the software ( regeemy and adobe photoshop ) in superposing 
 and subtracting both tomographic images .
simulated root canals in experimental groups were instrumented by the same operator , who 
 was previously calibrated to each one of techniques described below .
the resin blocks 
 were mounted on a vise ( neboluz , so paulo , brazil ) that kept them fixed , without 
 allowing the operator to see the instruments inside the simulated canals .
protaper group was prepared with the protaper universal system using the sx and s1 
 instruments for preparing the cervical third , followed by the s2 instrument in the 
 middle third .
the f1 and 
 f2 instruments were later used at the working length , and each instrument was used in a 
 uniform and continuous motion without applying pressure .
wizard cd plus group was 
 prepared using this system through the crown - down technique , with input motion , light 
 apical pressure and anti - curvature pressure .
next , a 25.4 file was used in middle third and the beginning of the apical 
 third and finally 20.04 and 25.04 files were used in full working length .
after each 
 instrument change , a size 10 k - file was inserted up to the entire working length and the 
 canal was irrigated with 1 ml of 2% sodium hypochlorite .
, jaguar , brazil ) electric 
 motor was used for simulated root canals preparation , at a speed of 250 rpm with a 
 torque of 2 n.cm .
after canal preparation , the acrylic blocks underwent a second cbct 
 scan under the preoperative conditions as described previously .
the tomographic images from the simulated canals were edited in the icat 
 vision and coreldraw software for precise standardization of the position 
 of the acrylic resin block with regard to the x and y axes .
the subtraction of post - instrumentation and pre - instrumentation cbct images of the 
 acrylic - resin blocks was performed using the regeemy and adobe photoshop software 
 according to their tutorials . once the final images were obtained 
 ( pre - instrumentation plus post - instrumentation image ) ,
the tips of the files in subtracted images were analysed using imagej software 
 ( national institutes of health , bethesda , usa ) under 25% magnification .
the scale was 
 calibrated using the bottom of the acrylic resin block ( 10 mm ) as reference to 
 convert pixels to millimetres .
a straight line was drawn joining the tip of the files in the subtracted images for 
 measuring ( figure 1 ) .
this process was 
 performed in all images and repeated three times at intervals of 48 hours , by one 
 blinded examiner who had previously been calibrated to the measurement procedure .
a ) 
 pre - instrumentation image ; b ) postinstrumentation image ; c ) regeemy : the tip of 
 the files was delimitated and a straight line was drawn joining both tips 
 ( black : file in the pre - instrumentation image ; white : file in the 
 post - instrumentation image ) ; and d ) adobe photoshop : white points indicated the 
 files tips in both images and then a straight line was drawn to join these 
 points the kappa test was used to analyze the agreement between the readings of the examiner 
 at different times .
shapiro - wilk normality test was used to assess if the data adhere 
 to a gaussian distribution .
student 's t - test for independent samples was used to 
 compare the means of the apical deviations between the two groups . and
finally , 
 student 's t - test for paired samples was used to compare the ability of each software 
 in superposing and subtracting images from one rotary system per 
 time .
the tomographic images from the simulated canals were edited in the icat 
 vision and coreldraw software for precise standardization of the position 
 of the acrylic resin block with regard to the x and y axes .
the subtraction of post - instrumentation and pre - instrumentation cbct images of the 
 acrylic - resin blocks was performed using the regeemy and adobe photoshop software 
 according to their tutorials . once the final images were obtained 
 ( pre - instrumentation plus post - instrumentation image ) ,
the tips of the files in subtracted images were analysed using imagej software 
 ( national institutes of health , bethesda , usa ) under 25% magnification .
the scale was 
 calibrated using the bottom of the acrylic resin block ( 10 mm ) as reference to 
 convert pixels to millimetres .
a straight line was drawn joining the tip of the files in the subtracted images for 
 measuring ( figure 1 ) .
this process was 
 performed in all images and repeated three times at intervals of 48 hours , by one 
 blinded examiner who had previously been calibrated to the measurement procedure .
a ) 
 pre - instrumentation image ; b ) postinstrumentation image ; c ) regeemy : the tip of 
 the files was delimitated and a straight line was drawn joining both tips 
 ( black : file in the pre - instrumentation image ; white : file in the 
 post - instrumentation image ) ; and d ) adobe photoshop : white points indicated the 
 files tips in both images and then a straight line was drawn to join these 
 points
the kappa test was used to analyze the agreement between the readings of the examiner 
 at different times .
shapiro - wilk normality test was used to assess if the data adhere 
 to a gaussian distribution .
student 's t - test for independent samples was used to 
 compare the means of the apical deviations between the two groups . and finally , 
 student 's t - test for paired samples was used to compare the ability of each software 
 in superposing and subtracting images from one rotary system per 
 time .
the regeemy software 
 provided the subtraction of the pre- and post - instrumentation tomographic images of the 
 acrylic blocks , allowing the analysis of apical transportation using protaper universal 
 and wizard cd plus systems . in control group ,
apical transportation did not occur ( figures 2a and 2b ) . the entire final image presented intermediate gray levels ( 128 grayscale 
 value ) when regeemy was used ( figure 2c ) .
figure 2d shows the coincidence of the tips of the 
 files in pre- and post - operative images when adobe photoshop was used .
the student 's 
 t - test did not reveal any difference between the experimental groups ( p>0.05 ) .
wizard 
 cd plus and protaper universal presented few apical transportation regardless of the 
 software used for image superimposition and subtraction ( p>0.05 ) ( table 1 ) .
the values of apical transportations 
 achieved using the regeemy were similar to those obtained using adobe photoshop 
 ( p>0.05 ) .
a and b ) in control group , five specimens were subjected to two cbct under 
 identical conditions ; c ) result of a superposition and subtraction using regeemy 
 ( note the intermediate gray levels ) ; and d ) result of a superposition and 
 subtraction using adobe photoshop ( note the coincidence of the tips of the files 
 in the final image ) means , standard deviations and confidence intervals of apical transportation after 
 using the two rotary systems and both software the student 's t - test did not reveal any significant difference between the 
 experimental groups ( p>0.05 )
both acrylic resin blocks and extracted human teeth are used for apical transportation 
 analysis . extracted human teeth provide similar conditions to the clinical situation 
 when compared with acrylic resin blocks .
moreover , they present actual surface texture , 
 hardness and cross - sectioning dentin areas . however , natural teeth present variation in morphology which impairs 
 the comparison of the experimental groups . on the other hand ,
acrylic resin blocks allow the observation of the 
 preparation in three dimensions along the whole canal length and a direct comparison of 
 the shaping ability of different instruments .
in addition , they provide standardized length , diameter and 
 angle of curvature of the simulated root canals . from a statistical 
 point of view
, the standard deviation might increase whenever a range of curvatures is 
 used , as opposed to the use of standardized acrylic resin blocks where this problem is 
 minimized .
the uses of acrylic 
 resin blocks facilitate the evaluation of the feasibility of the regeemy in comparison 
 with adobe photoshop in superposing and subtracting images .
however , owned to the 
 difference between materials nature ( i.e. acrylic resin and dentin ) , care should be 
 taken in the extrapolation of these findings to clinical use where dentine is 
 involved .
both rotary systems promoted similar apical deviation after preparation of the simulated 
 root canals ( p>0.05 ) .
similar to other 
 studies that have compared different rotary ni - ti systems regarding the apical 
 transportation , the present study did not detect significant differences between the 
 protaper and wizard cd systems .
good flexibility and the centralizing ability of root 
 preparation by the f2 ( protaper ) and 25.04 files ( wizard cd plus ) likely contributed to 
 the small and similar apical transportation values .
different cross - sectional geometries of rotary instruments are believed to increase 
 cutting efficiency , consequently reducing contact areas and torsional loads .
it is also known that the mass of the 
 instrument plays an important role on the centering ability of these instruments . 

it 
 also presents a triangular convex cross section with shallow u - shaped grooves .
all these 
 features try to improve the flexibility of the larger instruments . despite presenting the same taper along 
 the entire cutting blades ,
thus , continuous and multiple tapers did not 
 influence the apical transportation in simulated root canals .
the findings of 
 the present study agree with those published in a master 's dissertation in the year of 
 2012 .
moreover , the authors did not find differences regarding the 
 apical transportation between wizard cd plus and other two rotary systems ( protaper and 
 wizard navigator ) .
the author stated that irregularities in wizard cd plus surface may 
 have contributed with a poor standardization of centering ability , which was 
 corroborated by the high standard deviations observed .
the same did not occur in this 
 study , in which wizard cd plus ' standard deviation was similar to that observed in the 
 protaper group . according to 
 grazziotin - soares , et al.(2011 ) , 
 protaper instruments present lower flexibility after the third use .
thus , in order to 
 avoid apical transportation originating from repeated preparation , each instrument was 
 used in only three acrylic resin blocks and then discarded .
regardless of the final instrumentation size , the risk of transportation always 
 increases in curved canals with an increase of file size .
schafer and vlassis ( 2004 ) stated that protaper may induce apical transportation 
 towards the outer aspect of the root canal especially because of the progressive tapers 
 along the cutting surface of these instruments .
the decreasing taper sequence of the 
 finishing files enhances the strength of the files , but it increases the stiffness of 
 their tip . on that basis , in this 
 study the canal preparation was performed up to f2 instrument in protaper group .
other 
 reason for using f2 instruments was to permit direct comparison with wizard cd plus size 
 25.04 , which has similar mass and identical diameter of the tip .
wizard cd plus is a new 
 rotary system and due to that there are no studies related to its behavior regarding 
 cyclic fatigue and number of uses .
closing partially this gap , wizard cd plus seems to 
 promote similar apical deviation when compared with protaper files in acrylic resin 
 blocks . however , further investigations are needed to secure a better indication of its 
 use in clinical practice .
clinically , it seems questionable whether these comparably small values in apical 
 transportation have any clinical significance .
anyway , the apical transportation values 
 for the two systems are believed to be reliable because of the comparison of a new 
 software with a current one ( adobe photoshop ) to superpose and subtract images .
the 
 student 's t - test for paired samples revealed that the readings performed by each 
 software were similar ( p>0.05 ) .
the subtraction of one image from another requires superposing these images in order to 
 analyze the differences that have occurred over time .
regeemy software subtracts the structures that have not 
 changed between two radiographic / tomographic images pixel by pixel , resulting in a third 
 image that is surrounded by a neutral gray background with grayscale values of 
 approximately 128 for the unchanged areas .
patchy areas in the pre- and post - operative 
 images are conventionally shown by a dark - gray shade or black ( with grayscale values 
 approaching zero ) and by a light - gray tone or white ( with grayscale values close to 
 255 ) .
however , the process of superposition must be 
 performed manually with the post - instrumentation image separately positioned over the 
 pre - instrumentation image .
images must 
 be aligned manually and this process may be influenced by the operator . to avoid this 
 drawback , the present study performed three superposition processes and three readings 
 per resin block in both software .
therefore , the readings achieved 
 using regeemy and adobe photoshop were similar for the rotary systems .
the effectiveness of the software in superposing and subtracting pre- and 
 post - instrumentation images was confirmed by the control group .
all the specimens from 
 the control group were exactly superposed . after the subtraction process using regeemy 

when adobe photoshop was used , the accuracy of the 
 superposition process was assessed after marking the tip of the file in each image .
if 
 the points were coincident at the final image , then the superpose process was correct . 
 the inclusion of a control group aimed to validate the methods for superimposition and 
 subtraction of the cbct images from the experimental groups .
besides being originally developed to map the deforestation in native areas , regeemy was 
 used for the first time in dentistry in 2005 .
this software has proven to be an alternative technique to 
 current ones for subtracting radiographic / tomographic images .
it reduces the variation 
 of gray levels in the subtracted image , indicating that the software superposes the pre- 
 and post - operative images more accurately than a priori tools ( i.e. , 
 film , phosphor plates , radiographic film holders ) .
in addition , six years later , ono , et al . ( 2011 ) used this software to correct 
 geometric discrepancies and equalize the contrast of two sequential radiographs before 
 the use of the digital subtraction technique in cases of simulated root resorption .
the main difficulty that occurs when working with adobe photoshop is that this software 
 is not widely available because they are limited to institutions or are too expensive to 
 be easily purchased .
regeemy closes this gap because it is a program that can be 
 downloaded for free upon registration with the dpi - inpe .
this program provides the 
 necessary support for research because it performs superimposition , subtraction and 
 geometric correction of images by automatically marking multiple control points with the 
 same software .
moreover , it allows a 
 practical and simple process , with few variations , and costless .
two conclusions can be drawn : ( 1 ) wizard cd plus and protaper universal systems promoted 
 slight and similar apical transportation after the preparation of simulated canals ; ( 2 ) 
 regeemy consists in a feasible software to superpose and subtract images and appears to 
 be an alternative to adobe photoshop .
 objectivethis study has two aims : 1 ) to evaluate the apical transportation of the wizard cd 
 plus and protaper universal after preparation of simulated root canals ; 2 ) to 
 compare , with adobe photoshop , the ability of a new software ( regeemy ) in 
 superposing and subtracting images . 
 material and methodstwenty five simulated root canals in acrylic - resin blocks ( with 20 curvature ) 
 underwent cone beam computed tomography before and after preparation with the 
 rotary systems ( 70 kvp , 4 ma , 10 s and with the 88 cm fov selection ) . 
 canals were 
 prepared up to f2 ( protaper ) and 24.04 ( wizard cd plus ) instruments and the 
 working length was established to 15 mm . 
 the tomographic images were imported into 
 icat vision software and coreldraw for standardization . 
 the superposition of pre- 
 and post - instrumentation images from both systems was performed using regeemy and 
 adobe photoshop . 
 the apical transportation was measured in millimetres using image 
 j. five acrylic resin blocks were used to validate the superposition achieved by 
 the software . 
 student 's t - test for independent samples was used to evaluate the 
 apical transportation achieved by the rotary systems using each software 
 individually . 
 student 's t - test for paired samples was used to compare the ability 
 of each software in superposing and subtracting images from one rotary system 
 per time . 
 resultsthe values obtained with regeemy and adobe photoshop were similar to rotary 
 systems ( p>0.05 ) . 
 protaper universal and wizard cd plus promoted similar apical 
 transportation regardless of the software used for image 's superposition and 
 subtraction ( p>0.05 ) . 
 conclusionwizard cd plus and protaper universal promoted little apical transportation . 
 
 regeemy consists in a feasible software to superpose and subtract images and 
 appears to be an alternative to adobe photoshop . 
INTRODUCTION
MATERIAL AND METHODS
Image standardization
Image subtraction
Apical transportation analysis
Statistical analysis
RESULTS
DISCUSSION
CONCLUSIONS