Effect Of Titanium Nitride Coatings With Different Thickness On Microhardness And Cutting Efficiency Of Nickel-titanium Instruments

Objective: Nickel-titanium(Ni Ti)root canal instruments are preferred for root canal preparation.The cutting efficiency of nickel-titanium instruments is of great significance for removing root canal infected dentin and effectively controlling infection.It has been found that surface modification technology can improve the cutting efficiency of Ni Ti instruments.Among them,the surface coating technology is a common method for surface modification.At present,no research on improving its cutting efficiency has been reported.The purpose of this experiment was to investigate the effect of titanium nitride(Ti N)coatings with different thicknesses on microhardness and cutting efficiency of Ni Ti instruments,and to provide a basis for improving the efficiency of clinical root canal preparation.Methods: Fifteen KV4 Ni Ti alloy sheets and sixty KV4 rotary Ni Ti files were selected and randomly divided into 5 groups: uncoated group,coated 1 h group,coated 2 h group,coated 3 h group and coated 4 h group.A layer of Ti N coatings of different thicknesses was prepared on the surface of the coated groups by controlling the deposition time.The film thickness of each group was measured by scanning electron microscopy(SEM).The microhardness of each group of Ni Ti alloy sheets was measured by a Vickers hardness tester.Sixty transparent resin modules were selected and each resin module was prepared with one Ni Ti file.The cutting efficiency of each group was measured by the weight loss method.SEM was used to examine the surface of Ni Ti instruments in five groups before and after preparation.One-way variance analysis was used to determine the statistical differences with SPSS 22.0 software package.P<0.05 is considered statistically significant.Results:(1)With the increase of the thickness of titanium nitride coating,the microhardness of Ni Ti alloy gradually increased(P<0.05).(2)With the increase of the thickness of titanium nitride coating,the cutting efficiency of Ni Ti instrument was improved,and the cutting efficiency was the largest when the coating thickness was(854±8)nm(P<0.05).(3)The surface morphology of the coated group was better than that of the uncoated group.Conclusion: The thickness of the Ti N coating affects microhardness and cutting efficiency of the nickel-titanium instruments.The microhardness and cutting ability enhanced as the thickness increased within certain range.If the thickness is too large,the cutting efficiency will be reduced.