Dentine chips produced by nickel-titanium rotary instruments

This study aimed to compare the cross-sectional shape of two nickel-titaniu m rotary instruments, namely Profile and Quantec files, both ISO 25, 0.06 t aper, and sought to relate this to the chips produced by cutting dentine. A limited comparison was made with stainless steel engine reamers. First, fi ve files of each type were sectioned transversely at 12 mm, 8 mm and 4 mm f rom the tip and examined by scanning electron microscopy. The cutting angle s were assessed by a direct measurement technique which allowed for the inc lination of a cutting edge to the root canal. Second, eight samples of cutt ing debris were collected from instrumentation by each type of nickel-titan ium file and four samples from the engine reamers. The major and minor axis , area and roundness of the dentine chips in each sample were measured usin g computerized par-tide analysis. The results demonstrated that all files h ad a negative cutting angle which varied at the different levels (ProFiles range 69.4 degrees to 58.4 degrees and Quantec range 74.8 degrees to 56.8 d egrees). The consistency within files of the same type was good as demonstr ated by low standard deviations, except for Quantec files at the 4 mm level where higher standard deviations of 4.1 degrees and 5.5 degrees for the tw o blades were found. The chip analysis showed significant differences betwe en chips produced by Profile and Quantec files (P<0.05). The latter were la rger and rounder. The chips from the Profile and the engine reamer chips we re similar in dimension (P>0.05). No simple relationship existed between fi le geometry and the dentine chips produced during instrumentation.