Abstract: PURPOSE: To investigate the effect of titanium nitride (TiN) coatings with different thicknesses on microhardness and cutting efficiency of nickel-titanium (NiTi) instruments, and to provide a basis for improving the efficiency of clinical root canal preparation. METHODS: Fifteen KV4 NiTi alloy sheets and sixty KV4 rotary NiTi files were selected and randomly divided into 5 groups: uncoated group, coating 1 h group, coating 2 h group, coating 3 h group and coating 4 h group. A layer of TiN 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 NiTi alloy sheets was measured by a Vickers hardness tester. Sixty transparent resin modules were selected and each resin module was prepared with one NiTi file. The cutting efficiency of each group was measured by the weight loss method. SEM was used to examine the surface of NiTi instruments in 5 groups before and after preparation. One-way variance analysis was used to determine the statistical differences with SPSS 22.0 software package. RESULTS: With the increase of the thickness of titanium nitride coating, the microhardness of NiTi alloy gradually increased(P<0.05). With the increase of the thickness of titanium nitride coating, the cutting efficiency of NiTi instrument was improved, and the cutting efficiency was the largest when the coating thickness was 860 nm(P<0.05). The surface morphology of the coated group was better than that of the uncoated group. CONCLUSIONS: The thickness of TiN coating affects microhardness and cutting efficiency of the nickel-titanium instruments, the microhardness and cutting ability enhanced as the thickness increased. If the thickness is too large, the cutting efficiency will be reduced.

Key words: TiN coatings, NiTi instruments, Microhardness, Cutting efficiency