the purpose of ergonomics applied to dentistry is to obtain means and systems to 
 decrease physical and mental stress , as well as prevent diseases related to dental 
 practices . work - related 
 musculoskeletal disorders ( wmsd ) have increased in recent decades and are factors that 
 commonly lead to professionals being unable to work , with financial and medical 
 consequences . in the case of 
 dentists , incorrect posture is a cause of cervical column , neck , and shoulder disorders , 
 besides hand neuropathies , due to the continuous use of dental instruments and 
 tools . alexopoulos , stathi and charizani ( 2004 ) observed that 52% of the greek dentists who 
 participated in a related study , reported at least one osteomuscular disorder . adapting 
 working positions to ergonomic rules is one of the measures to prevent wmsd , which can 
 significantly contribute to a reduction in physical effort , thereby bringing benefits to 
 the daily routine of professional activities . another consideration is equipment design which is extremely important in terms of 
 decreasing muscular fatigue and , consequently , reducing physical and mental stress , as 
 highlighted by parsell , et al . posture - comfort stools with arm supports can offer musculoskeletal benefits when 
 cavity preparations are carried out by dentists . ( 2006 ) reported that it is possible to 
 reduce wmsd with ergonomic adaptations to the clinical mirrors . ( 2003 ) also reported an association 
 between an increase in the hours of use the ultrasonic scaler , the instrument of choice 
 for calculus debridement , and an increase in tendonitis in the upper extremities 
 resulting from dental hygiene procedures . rgis - filho ( 1997 ) demonstrated , by 
 the muscular biomechanics expressed by kinematic registrations ( working angles ) , kinetic 
 ( muscular torque ) and electromyographic ( neuromuscular activity graphically represented 
 by the electrical activity of the muscle ) , that endodontics , and more specifically root 
 canal preparation , is a dental practice that commonly causes wmsd , surpassing the 
 clinical procedures of extractions , scaling and curettage , as well as amalgam 
 condensation . ( 1998 ) reported that 
 of a group of 192 dentists 79.2% had fatigue and pain in the hands and forearms , which 
 occurred with greater intensity during or after root canal preparation . with the aim of 
 reducing these symptoms , endodontic instrument handles manufactured according to 
 ergonomic principles have been proposed , since larger diameters facilitate the gripping 
 of the instruments and reduce muscular electromyographic activity . as in the case of several other medical and dental specializations , endodontics has 
 evolved in recent years , setting forward greater precision , reduced possibility of 
 mistakes and injuries , less discomfort to the patients and faster procedures . some authors have suggested that , in 
 addition to these factors , root canal preparation with nickel - titanium ( niti ) 
 instruments is associated with the least stress and operating fatigue , especially due to 
 the decrease in working time when compared with manual instrumentation with stainless 
 steel . the development of endodontic instruments made from niti alloy has the potential 
 to enhance the shaping of narrow , curved canals , a procedure which has proved difficult 
 to achieve using stainless steels instruments because of their inherent 
 stiffness . the objective of this study was to verify , in vivo , the results 
 obtained from the kinematic kinetics , and electromyographic records in endodontists 
 during the preparation of simulated root canals using rotary and manual instrumentation 
 techniques . eight right - handed healthy subjects , four females and four males , between 23 and 39 
 years of age , participated in this study . all of them were endodontists with clinical 
 experience accumulated over at least 2 years . each endodontist , seated on a dental stool in the " 12 o'clock " position , prepared two 
 simulated canals with 20 mm in resin blocks with diameters corresponding to an 
 instrument size 20 and curvatures of 40 ( crinodonto produtos race 25.02 rotary ni - ti ( fkg , la chaux - of - fonds , orbe , switzerland ) and 
 flexo - file 25.02 ( dentsply - maillefer , ballaigues , orbe , switzerland ) instruments were 
 used . prior to the use of the above - described instruments , the resin blocks were 
 attached to a lathe machine and prepared . in the cervical third , the preparation was 
 carried out with rotary pre - race instruments 40.10 and 35.08 ( fkg , reads chaux - de - fonds , 
 orbe , switzerland ) , following the crown - down instrumentation procedure , where the 
 dentist essentially works from the crown of the tooth , shaping the canal towards the 
 apex . flexo - files 40.02 , 35.02 
 and 30.02 were used by the manual group , race 25.06 and 25.04 instruments by the rotary 
 group . the purpose was to reach the working 
 length ( wl=20 mm ) with the 25.02 instrument . once the wl was reached , 10 repetitions of 
 3 seesaw movements each were carried out while data was collected on muscular activity 
 over 4-s periods . the reading of the movements would be very extensive if it were done 
 throughout the whole preparation procedure , using all the instruments , thence , only the 
 last instrument employed for each preparation was used ( 25.02 , which correspond to 0.25 
 mm diameter in the initial tip with 0.02 mm taper at each millimeter in the active part 
 of the instrument ) . that was true for the manual method , where the instrument is handled 
 with fingers tips , as well as for the rotating instrument . in the rotary method , the 
 instruments , which are driven by electric or pneumatic motors , make a continuous 360 
 rotation . instrumentation steps for manual and rotary methods electromyographic ( emg ) data were collected using surface electrodes attached to the 
 skin over the muscle of interest . the skin was cleaned to adherence of the electrodes 
 and detection of the emg . , boston , 
 ma , usa ) were attached over the flexor carpi radialis , extensor carpi radialis , 
 brachioradialis , biceps brachii , triceps brachii , middle deltoid , and upper trapezius . the electrodes were positioned in parallel with the muscular fibers , at approximately 
 two centimeters from each muscle motor point ( between the motor point and the tendon ) . the 
 emg signals were amplified ( x2000 ) , band - pass filtered ( 20 - 450 hz ) and recorded . the 
 data were digitized at 12 bits and collected by an ibm computer at 1000 hz . for the analysis of the movements , x , y , and z coordinates were recorded utilizing led 
 ( light emission diode ) markers fastened to the temporomandibular joint , to the hip ( over 
 the iliac crest ) , shoulder ( lateral portion of acromion ) , elbow ( lateral epicondyle ) , 
 wrist ( lister 's tubercle ) , and hand ( metacarpal head ) . the infrared signal emission of 
 these markers was captured at a frequency of 100 hz , by a three - dimensional optotrak 
 3020 optical system ( digital northern inc . , the resulting electromyographic emg signals in millivolts ( mv ) , and the x , y , and z 
 positional data were synchronized by an odau ii - optotrak data acquisition unit ii , 
 and mathematically treated using matlab code ( math works inc . , version 6.0 ) . the emg signals were rectified , filtered ( low - pass at 20 hz using a second - order 
 butterworth filter ) , and normalized by the maximum voluntary isometric contraction 
 ( mvic ) of each subject . the averaged emg of the mvic was calculated within the 
 500 - 1000 milliseconds ( ms ) interval from the beginning an isometric contraction . for 
 all mvic tests , the linear displacement of the markers , the joint torque generated by the shoulder , 
 elbow , and wrist , as well as deviations , angular velocity , and accelerations , were 
 also calculated . the anthropometric data , center of mass , and moment of inertia of 
 the segments were calculated based on the weight and sex of the subject , according to 
 zatsiorsky 's model , modified by de leva ( 1996 ) . based on these data , the joint torque of the shoulder , 
 elbow , and wrist were calculated through inverse dynamics and later 
 normalized to each subject 's body weight . the joint torque averages ( nm / kg ) for the shoulder , elbow , and wrist , as well as the 
 emg signal normalized values were calculated at intervals of 100 ms each , starting 
 from the beginning of the movement of the wrist assessed by measuring the angular 
 displacement . the student t - test for paired samples was applied according to the experimental 
 design and type of variable , considering that this study involved a parametric 
 variable and two experimental groups . for this analysis , the average of the angular displacement , joint torques and emg 
 across all subjects during the movement was calculated across intervals of 100 ms , 
 for each instrumentation method . after , the methods were compared through the paired 
 test , because the same individuals carried out the instrumentation with both methods . the resulting electromyographic emg signals in millivolts ( mv ) , and the x , y , and z 
 positional data were synchronized by an odau ii - optotrak data acquisition unit ii , 
 and mathematically treated using matlab code ( math works inc . , version 6.0 ) . the emg signals were rectified , filtered ( low - pass at 20 hz using a second - order 
 butterworth filter ) , and normalized by the maximum voluntary isometric contraction 
 ( mvic ) of each subject . the averaged emg of the mvic was calculated within the 
 500 - 1000 milliseconds ( ms ) interval from the beginning an isometric contraction . for 
 all mvic tests , the linear displacement of the markers , the joint torque generated by the shoulder , 
 elbow , and wrist , as well as deviations , angular velocity , and accelerations , were 
 also calculated . the anthropometric data , center of mass , and moment of inertia of 
 the segments were calculated based on the weight and sex of the subject , according to 
 zatsiorsky 's model , modified by de leva ( 1996 ) . based on these data , the joint torque of the shoulder , 
 elbow , and wrist were calculated through inverse dynamics and later 
 normalized to each subject 's body weight . the joint torque averages ( nm / kg ) for the shoulder , elbow , and wrist , as well as the 
 emg signal normalized values were calculated at intervals of 100 ms each , starting 
 from the beginning of the movement of the wrist assessed by measuring the angular 
 displacement . the student t - test for paired samples was applied according to the experimental 
 design and type of variable , considering that this study involved a parametric 
 variable and two experimental groups . for this analysis , the average of the angular displacement , joint torques and emg 
 across all subjects during the movement was calculated across intervals of 100 ms , 
 for each instrumentation method . after , the methods were compared through the paired 
 test , because the same individuals carried out the instrumentation with both methods . 
 a significance level of 5% was established . it was ascertained that there were differences between 
 the results obtained with the use of manual and rotary techniques with regard to the 
 variables of the minimum ( min . ) , maximum ( max . ) , and angular extension ( ae ) 
 techniques for the shoulder , and low and maximum techniques for the wrist . distribution of the sample based on maximum ( max ) , minimum ( min ) angular 
 displacement and angular excursion ( ae ) between the articulations over all 
 repetitions across all subjects regarding the direction of joint movement . this angle are of 
 the flexion / extension for shoulder and elbow ( external angle ) , and radial / ulnar 
 deviation for wrist the average measured joint torque values for the shoulder , elbow , and wrist ( nm / kg ) 
 are given in table 2 . it can be observed that 
 the instrumentation method did not influence any of the analyzed variables in a 
 statistically significant way . the use of the rotary technique led to a higher 
 uniformity of the results obtained regarding the torque values during the time 
 intervals . the manual technique showed high oscillations during the time intervals 
 analyzed ( figure 2 ) . joint torque values normalized to each subjects body weight for the shoulder , 
 elbow , and wrist ( nm / kg ) during the moviments for the preparation of simulated 
 root canals with manual and rotary instruments . the positive and negative values represent the 
 clockwise and counterclockwise directions respectively average and standard error across all subjects of the normalized 
 electromyography ( emg ) activity of the extensor carpi radialis ( a ) , 
 brachioradialis ( b ) , flexor carpi radialis ( c ) , biceps brachii ( d ) , upper 
 trapezius ( e ) and middle deltoid ( f ) during all intervals calculated for each 
 instrumental method normalized emg values expressed as a percentage of mvic are given in table 3 . it was observed for the manual method that there was a higher emg activity in the 
 extensor carpi radialis , flexor carpi radialis and brachioradialis muscles , and lower 
 emg activity in the middle deltoid and upper trapezius compared with the rotary 
 method . the biceps brachii and triceps brachii did not show statistically significant 
 differences in relation to the preparation methods ( figure 3 ) . comparison between the manual and rotary methods according to the average and 
 standard error across all subjects of the joint torque ( nm / kg ) for the wrist 
 ( a ) , elbow ( b ) and shoulder ( c ) , during all intervals calculated ( each 100 ms ) 
 for each instrumental method it was ascertained that there were differences between 
 the results obtained with the use of manual and rotary techniques with regard to the 
 variables of the minimum ( min . ) , maximum ( max . ) , and angular extension ( ae ) 
 techniques for the shoulder , and low and maximum techniques for the wrist . distribution of the sample based on maximum ( max ) , minimum ( min ) angular 
 displacement and angular excursion ( ae ) between the articulations over all 
 repetitions across all subjects regarding the direction of joint movement . this angle are of 
 the flexion / extension for shoulder and elbow ( external angle ) , and radial / ulnar 
 deviation for wrist the average measured joint torque values for the shoulder , elbow , and wrist ( nm / kg ) 
 are given in table 2 . it can be observed that 
 the instrumentation method did not influence any of the analyzed variables in a 
 statistically significant way . the use of the rotary technique led to a higher 
 uniformity of the results obtained regarding the torque values during the time 
 intervals . the manual technique showed high oscillations during the time intervals 
 analyzed ( figure 2 ) . joint torque values normalized to each subjects body weight for the shoulder , 
 elbow , and wrist ( nm / kg ) during the moviments for the preparation of simulated 
 root canals with manual and rotary instruments . the positive and negative values represent the 
 clockwise and counterclockwise directions respectively average and standard error across all subjects of the normalized 
 electromyography ( emg ) activity of the extensor carpi radialis ( a ) , 
 brachioradialis ( b ) , flexor carpi radialis ( c ) , biceps brachii ( d ) , upper 
 trapezius ( e ) and middle deltoid ( f ) during all intervals calculated for each 
 instrumental method it was observed for the manual method that there was a higher emg activity in the 
 extensor carpi radialis , flexor carpi radialis and brachioradialis muscles , and lower 
 emg activity in the middle deltoid and upper trapezius compared with the rotary 
 method . the biceps brachii and triceps brachii did not show statistically significant 
 differences in relation to the preparation methods ( figure 3 ) . comparison between the manual and rotary methods according to the average and 
 standard error across all subjects of the joint torque ( nm / kg ) for the wrist 
 ( a ) , elbow ( b ) and shoulder ( c ) , during all intervals calculated ( each 100 ms ) 
 for each instrumental method with the advent of rotary instruments , general dentists and endodontists can carry out 
 treatments faster and with a better final quality of the preparations . rotary instruments , however , should 
 allow less physical effort and a lower probability of injury for dental professionals . 
 however , no study has ever compared rotary and manual techniques with regard to the 
 muscular and biomechanical aspects of these devices . bramson , smith and romagnoli ( 1998 ) 
 verified that the repetitive movement of an articulation has a limit before the 
 appearance of wmsd and that depending on the extent to which this limit is exceeded the 
 risk of wmsd is classified as low , medium or high ( figure 4 ) . through the comparative kinematic analysis performed in this 
 study , the angle displacements for the wrist and elbow verified during the preparations 
 using rotary or manual instruments angular movement of the articulation limit before the appearance of work - related 
 musculoskeletal disorders ( wmsd ) classified as low , medium or high risks by 
 bramson ( 1998 ) the joint torque represents the muscular action on the articulation added to the passive 
 elements of which it is composed , such as ligaments , tendons , and articulation 
 capsules . through the results 
 obtained , we can observe that , despite the lack of a statistically significant 
 difference between the root canal preparation techniques , the quality analysis of the 
 behavior of the shoulder , elbow , and wrist joint torques revealed a greater uniformity 
 of values during the intervals for the rotary instrumentation , allowing for a more 
 homogeneous effort without high peaks . on the other hand , the analysis revealed many 
 oscillations in joint torque behavior for the manual instruments in the three 
 articulations , thus suggesting the need for recruitment of a greater number of muscles 
 to generate such torques and execute the task . it can be observed , through the emg results , that there was a difference between the 
 instrumentation techniques for most of the muscular groups under analysis . except for 
 the middle deltoid and trapezius , where use of rotary instrumentation resulted in a 
 higher emg level , the explanation for the occurrence of a higher emg activity during use 
 of the manual instrumentation lies in the very fact that there is a need greater 
 apprehend of instruments to execute the task . the wrist and the elbow position are 
 fundamental for this execution . during use of rotary instruments , there is the need to 
 hold the equipment , but less effort is required to penetrate and work inside the root 
 canals . in this case the professionals employ a different motor strategy , using the 
 muscles closer to the shoulder . it is important to emphasize that the continuous activity of both the extensor carpi 
 radialis and flexor carpi radialis observed in this study with the manual technique , as 
 well as of the brachioradialis muscle , upper trapezius and middle deltoid with the 
 rotary instrumentation , characterize a static contraction . the tension generated by the 
 static contraction may contribute to the alteration of microcirculation in the 
 muscle , thus determining the 
 appearance of painful points called " trigger points " , characteristic of myofascial 
 pain . myofascial pain causes more muscular tension , which can lead to 
 poor blood circulation , which yields more pain , thence generating a vicious cycle . myofascial pain affects various regions of the body , but one of the most common points 
 is the trapezius muscle region , which is important for the head posture positioning , as 
 well as for the execution of the scapulae function . the muscular recruitment for performing articular movements for root canal preparation 
 with either the rotary or manual techniques is distinct . nevertheless , the rotary 
 instruments presented less difficulty in modulating the joint torque in each 
 articulation , thus , presenting a greater uniformity of movements . concerning the 
 ergonomic aspect , alternating rotary and manual instrumentation for root canal 
 preparation might contribute to a decrease in the occurrence of wmsd . in other words , 
 alternating the use of the manual and rotary techniques would produce a better balance 
 in the activation of the muscles , because the motor strategies are different . different 
 motor strategies can be found when there is variability of the tasks and when pain is present , and they can be a mechanism of 
 protection against wmsd . based on the methodology used and the results obtained , it can be concluded that :   the angular displacement of the wrist and elbow during root canal preparation using 
 rotary and manual instruments were classified as low risk in terms of the occurrence of 
 wmsd ; there were no significant differences between the kinetic records for the two 
 instrumentation techniques ; a higher level of muscular activity was verified in the majority of the muscles assessed 
 ( extensor carpi radialis , flexor carpi radialis , brachioradialis and triceps brachii ) , 
 although the motor strategy was shown to be distinct for each of the two techniques 
 tested .
objectivethis study assessed the muscular activity during root canal preparation through 
 kinematics , kinetics , and electromyography ( emg ) . 
 material and methodsthe operators prepared one canal with race rotary instruments and another with 
 flexo - files . 
 the kinematics of the major joints was reconstructed using an 
 optoelectronic system and electromyographic responses of the flexor carpi 
 radialis , extensor carpi radialis , brachioradialis , biceps brachii , triceps 
 brachii , middle deltoid , and upper trapezius were recorded . 
 the joint torques of 
 the shoulder , elbow and wrist were calculated using inverse dynamics . in the 
 kinematic analysis 
 , angular movements of the wrist and elbow were classified as 
 low risk factors for work - related musculoskeletal disorders . 
 with respect to the 
 shoulder , the classification was medium - risk . 
 resultsthere was no significant difference revealed by the kinetic reports . 
 the emg 
 results showed that for the middle deltoid and upper trapezius the rotary 
 instrumentation elicited higher values . 
 the flexor carpi radialis and extensor 
 carpi radialis , as well as the brachioradialis showed a higher value with the 
 manual method . 
 conclusionthe muscular recruitment for accomplishment of articular movements for root canal 
 preparation with either the rotary or manual techniques is distinct . nevertheless , 
 the rotary instrument presented less difficulty in the generation of the joint 
 torque in each articulation , thus , presenting a greater uniformity of joint 
 torques .