Study Of Three Kinds Of Nickel Titanium Instruments In Root Canal Preparation Of Root Canal After Crack And Cleaning Effect

Objective: To comparatively research on the generation of radicular dentin crack and the effect of root canal cleaning after root canal preparation by three different nickel-titanium rotary instrumentsMethod: 1.40 mandibular teeth with single-root canals which could not be retained for periodontosis or orthodontics in clinical treatment were selected,and they were randomly classified into 3 Experimental Groups(n=10)and 1 Control Group(n=10).The former three groups were performed with Protaper(Group P),Mtwo(Group M),and Protaper Next(Group PN)nickel-titanium instruments respectively,while the Control Group adopted K root canal preparation.The truncation surfaces at the distances of 2,4,6 and 8mm from root tip after root canal preparation were observed under the confocal laser scanning microscope(CLSM)and the cracks on tooth root were later recorded after root canal preparation.2.30 teeth with single-root canals which could not be retained and were extracted for periodontosis or orthodontics in clinical treatment were selected,and they were randomly classified into 3 groups(n=10),i.e.Group P,Group M and Group PN.After root canal preparation with nickel-titanium instruments,depth orientation grooves were achieved along the long axis in all the samples,which was tried to be done through apical foramen and by avoid piercing through the root canal.Afterwards,bone mallet and bone chisel were used by keeping off the longitudinal axis of teeth,during which re-pollution was avoided.Then,the specimens were immersed into 2.5% glutaraldehyde solution for 48 hours.After dehydration of gradient ethanol and drying effect,spray coating of rhotanium was done.At last,these teeth were once again put under the scanning electron microscope(SEM)to observe the debris inside the wall of the root canal as well as the distribution of smear layers.Result: No cracks were found in Control Group,and there was a significant difference in the cracks between Group P and Group M as well as Group PN,but no remarkable difference was found between Group PN and Group M;Under the same condition,there were no significant differences in debris cleaning at 1/3 of upper root in these three groups during root canal shaping(P>0.05);while differences were evident between 1/3 of middle root and of root tip(P<0.05).The result of Group PN was superior to that of Group P and Group N,but there was no significant variation between Group P and Group N.Conclusion: Dentin cracks after root canal preparation with Protaper Next and Mtwo nickel-titanium instruments are obviously less than those with Protaper universal nickeltitanium instruments,which can reduce the risk of vertical root fractures;under the same condition and during the root canal shaping,the cleaning effect by Protaper Next nickeltitanium instruments in the middle and lower part of the root canal is superior to that by Protaper universal and Mtwo nickel-titanium instruments.