| Root canal preparation is always a key step in root canal therapy(RCT),which determines the success of RCT.The nickel titanium instruments the first choice for root canal preparation,and the cyclic fracture resistance of nickel titanium instruments have been the focus of attention in clinics.To increase the shaping ability and cyclic fracture resistance of instruments,manufacturers have attemped to develop the material,cross section and cutting-edge design of them.Furthermore the motion of an instrument also develops from the initial Continuous rotation to three different motions: continuous rotation,reciprocating motion and adaptive motion.In this study,two different nickel titanium instruments were used to observe the influence of three different motions on the shaping abilities and the ability cyclic fracture resistance of them.Part 1 Influence of three different motions on the shaping abilities of TF Aaptive,and Hyflex CMObjective Two different nickel titanium instruments were applied,Hyflex CM and Twisted File Adaptive,to shape 3D-printed root canal using continuous rotation,reciprocating motion and adaptive motion.By combinative using Micro-CT and 3D reconstruction technology,analyse the root canal volumn,surfacearea and the amount of deviation degree change before and after root canal preparation.To evalute the canal root shaping capability of nickel titanium instruments of diffenent motions.Expermental data for clinical work is expected.Methods 54 3D printing resin maxillary second molar teeth with 50° bending mesial buccal root canals were prepared for the experiment.The apical diameter is 0.20 mm and the root canal total length is 15 mm.Divide those 3D printing resin teeth into 6 groups evenly and randomly,i.e.9 teeth for each group,and number each of them sequentially.Then,fix every one 3D simulated resin teeth at an individual location and apply Micro-CT on all of them.In the group1,2,and 3,the Hyflex CM were performed in canal shaping using continuous rotation,reciprocating motion and adaptive motion respectively.And in the group 4,5 and 6,,the Twisted File Adaptive were performed in canal shaping using continuous rotation,reciprocating motion and adaptive motion respectively.After that,place each of 3D simulated resin teeth at the exact position as before and apply Micro-CTagain.3D reconstruction technology was used to analyze and compare the before-and after-preparation root canal morphology parameters(volume,surface,area and straightening)obtained from Micro-CT scanning.With SPSS 17.0 statistical analysis,then,the shaping abilities of these two instruments in three different motions could be evaluated.Reasult In the three experimental groups,which prepared by Hyflex CM,The root canal volume change of the group of continuous rotation is less than other two groups,significant statistical difference between them.No statistically significant difference between group of reciprocating motion and group of adaptive motion.The root canal surface area change the group of continuous rotation is less than other two groups,significant statistical difference between them.No statistically significant difference between group of reciprocating motion and group of adaptive motion.For the root canal deviation,the group of reciprocating motion is less than other two groups.But no statistically significant difference between three groups.In the three experimental groups,which prepared by Twisted File Adaptive.The group of continuous rotation has the least change of root canal volume compared with other two experimental groups,but no statistically significant difference between the three groups.For The root canal surface area change,The group of adaptive motion has the most change compared with other two experimental groups,but also no statistically significant difference between the three groups.For the root canal deviation,there is no statistically significant difference between the group of continuous rotation,group of reciprocating motion and group of adaptive motion.Conclusion: Among three groups of different motions,the both brands of NITI instruments,Hyflex CM and Twisted File Adaptive,in reciprocating motion has highest cutting effectiveness.In three different motions,Hyflex CM and Twisted File Adaptive both shown preferably shaping ablility,the small deviation of root canal caused by reciprocating motion.Part 2 Influence of three different motions on cyclic fatigue of TF Aaptive,and Hyflex CMObjective Treat extracted teeth root canal with Reciproc and Pro Taper preparation system respectiv Two different nickel titanium instruments were applied,Hyflex CM and Twisted File Adaptive,to shape resin block containing an artificial canal using continuous rotation,reciprocating motion and adaptive motion.All instruments were analyzed using scanning electron microscopy(SEM)after 6 canals preparation.The suface microcracks of instruments were compared among the groups of three different motions.After that,the instruments was used to test the cyclic fatigue fracture,To evaluate the cyclic fatigue resistance of instruments.In order to provide experimental basis for clinical work.Methods The cyclic fatigue tests were performed by using resin blocks(DENTSPLY)containing simulated canals with 60° angle of curvature and a 5-mm radius of curvature.A total of 270 canals were used,all with a 16 mm work lenght.All of simulated canal was randomly allocated into the nine groups(n=30).A sample of 45 new files was used: 15 HF(#25,0.04 taper),15 TFA(#25,0.08taper),15 RE(#25,0.08taper).All files had been previously inspected by using an optical stereomicroscope with 30 magnification for morphologic analysis.If any defects were found,the instrument would be discarded.Every brand of instruments were divided into three groups.The first group(CR group)were used with a continuous rotation,the second group(RM group)were used with a reciprocating motion,while the third one(AM group)with adaptive movement.Based on these standards,there were 9 experimental groups(n=5).Group 1: HF CR group;Group 2: HF RM group;Group 3: HF AM group;Group 4: RE CR group;Group 5: RE RM group;Group 6: RE AM group;Group 7: TFA CR group;Group 8: TFA RM group;Group 9: TFA AM group.The instruments of CR groups and RM groups were activated by using a 6:1 reduction handpiecepowered by a torque-controlled motor(VDW Silver,VDW).The motor was set to perform continuous rotation(CR group)at a rate of 500 rpm and reciprocating motion(RM group),characterized by rotation in 150 degree of CCW and in 30 degree of CW.Whereas the instruments of AM groups were activated by using a 8:1 reduction handpiece powered by a torque-controlled motor(Elements Motor,Sybron Endo)by using apative movement,rotation of CW and CCW angles that vary from 600 degree to 0 degree up to 370 degree to 50 degree.Following the mode of motion setted by this experiment,the files were used to shape the simulated canals.Canal patency were determined with size 10 K-files.All the 45 instruments were used by the same operator.Duing the process of shaping for each instrument,Irrigation of each canal was carried out with tap water using a disposable syringe.All instruments were analyzed using scanning electron microscopy(SEM)after 6 canals preparation.The suface microcracks of instruments were examined with five visions of 200 magnification along the shaft.And the Spiral distortion of instruments were examined with 50 magnification.All the electron micrographs of each of the 45 instruments analyzed were coded and stored digitally for analysis.Three observers scored each instrument for surface deformation using the scoring standard described.Results After five resin canal shapings,the surface of instruments which are Hyflex CM and Twisted File Adaptive in the three motion showed different degree of wear.Both of Hyflex CM and Twisted File Adaptive in the continuous rotary groups exhibited significantly higher surface wear compared with the reciprocating and adaptive motion groups(P<0.05).No statistically significant difference between group of reciprocating motion and group of adaptive motion.(P>0.05).15 seconds of fatigue fracture cycle number of Hyflex CM,the continuous rotary group is 10.4+3.33 times,the number of cycles shorter than adaptive motion group which is 19.7+6.00 times and reciprocating motion group which is 15.7+5.54 times.There was no statistical difference between the reciprocating and adaptive motion groups,while the continuous rotation group was statistically different from the previous two groups.About Twisted File Adaptive,the continuous rotary group is 11.8+4.34 times,the number of cycles shorter than reciprocating motion group which is 18.5+5.08 times and adaptive motion group which is 16.7+6.36 times.There was no statistical difference between the reciprocating and adaptive motion groups,while the continuous rotation group was statistically different from the previous two groups.Conclusion: The Ni Ti instruments that were used with reciprocating motion and adaptive motion exhibited less surface wear compared with those that were used with continuous rotation.While the reciprocating motion and the adaptive mtion of the Ni Ti instruments' fracture time is also significantly longer than the continuous rotation of the instruments,and the instruments in reciprocating motion exhibited best capability in the cyclic fracture resistance. |
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