Mechanical Properties Of Nickel-titanium Dental Instruments With Different Shapes After Preparation And Filling

Objective:The purpose of this study was to investigate the types and tapers of nickel-titanium instruments selected to control root canal infection and preserve the remaining dentin to the maximum extent by analyzing the mechanical properties of nickel-titanium prepared and filled teeth of different shapes,so as to reduce the incidence of tooth fracture.Methods:Forty-five maxillary anterior teeth,premolars and molars were extracted out of mouth.WaveOne group(n=45),Protaper Next group(n=45),Protaper Next group(n=45),and TF group(n=45)were randomly divided into three groups to conduct root canal preparation with WaveOne nickel-titanium file,Protaper Next nickel-titanium file,and TF nickel-titanium file,respectively.The maximum stress value of teeth under vertical pressure was recorded.Results:There was no significant difference in the maximum resistance of root fracture between the three groups after the preparation of anterior teeth,premolars and molars by Crown-Down technique(P > 0.05).The resistance values of WaveOne nickel-titanium files S(21/06),P(25/08),L(40/08)had statistical significance(F = 45.861,P = 0.001).The resistance values of WaveOne nickel-titanium files S(21/06)and P(25/08)and L(40/08)had statistical significance(P < 0.05),P(25/08)and L(40/08)had no statistical difference(P >0.05).The resistance values of Protaper Nextnickel-titanium file X1(17/04),X2(25/06)and X2(25/06)were significantly different(F = 50.362,P = 0.001).There was no statistical difference between Protaper Next nickel-titanium file X1(17/04)and X2(25/06)(P > 0.05),but X3(30/07)and X1(17/04)and X2(25/06)had statistical significance(P < 0.05).The resistance values of TF nickel-titanium files T1(25/04),T2(25/06)and T3(25/08)were significantly different(F = 64.978,P = 0.001).There was statistical significance between TF nickel-titanium files T3(25/08)and T1(25/04)and T2(25/06)(P < 0.05),but there was no statistical difference between T1(25/04)and T2(25/06)(P > 0.05).There was no statistical difference between different nickel-titanium files in the same taper and cross-sectional area(i.e.25/06,25/08),but there was no statistical difference between Protaper Next and WaveOne,TF in 06 taper(P > 0.05).Conclusion:(1)TThe resistance value of WaveOne nickel-titanium file decreased with the taper of the niti file increasing after the canal preparation and filling,and L(40/08)file had the lowest resistance value after the canal preparation.(2)There was no significant correlation between the root resistance of the posterior teeth prepared and filled with the samenickel-titanium instruments and the tooth morphology.(3)There was no significant correlation between the root resistance of the same shape(tooth shape)and the preparation and filling of different nickel-titanium instruments.(4)Protaper Next nickel-titanium file and TF nickel-titanium file make the tooth root resistance value after root canal preparation and filling decreases gradually with the increase of nickel-titanium file taper after 06 taper.