PubMed · 8422313
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G K Balfry. 1993-01-23. Re-using disposables.. https://doi.org/10.1038/sj.bdj.4808074
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Much has been reported on the qualitative, and to some degree, the quantitative effects of wear and sharpening of the periodontal curet's cutting edge. Presented here is an engineering model of the periodontal curet's cutting edge during wear and sharpening, and an estimated life of a typical periodontal curet. Although not confirmed by scientific experiments, this engineering model provides a framework for further scientific analysis. It also gives a clinical appreciation for the longevity of such periodontal instruments.
A total of 460 roots of extracted human teeth were divided into three groups i.e. straight, apically curved and entirely curved groups. Each of the three groups were divided into seven subgroups according to instrumentation by conventional hand, K-Flex file, 3-LD, 3-LDSY, Excalibur. MM 1400 and Endo Sonic. Radiographs were taken both clinical and proximal views before and after the enlargement of canals. An assessment of shaping characteristic of instrumentation was made on the basis of overimposed radiographs including perforation, ledge formation smoothness of wall contour incidence of elbow and zip measurements at the elbow level and asymmetry measurements. The majority of enlarged root canals were asymmetrical in shape. High differences were found between the incidence of elbow and zip formation. Under laboratory conditions the K-Flex file produced minor canal aberrations and significantly less asymmetry than the conventional instruments. But both the above mentioned instruments caused perforations on curved canals, such as the instrumentation by Excalibur. The loss of working distance was significant in all canal forms prepared with 3-LD and 3-LDSY instruments, which could have occurred through the packing of debris towards the apical constriction. The Excalibur appeared to be superior to the conventional hand instrument in straight canals, but its shaping characteristic was similar to conventional hand instrument in curved canals. The MM 1400 handpiece and ultrasonic instruments resulted in less aberration and significantly less asymmetry than the other tested instruments.
Certain asymmetry of root canal preparation can be observed in the straight root canal group, as well. The modification of original root canal shape in this group usually is not substantial. Using hand instruments for shaping curved canals special tecniques are required to minimize the asymmetry. Though tendencies of different shaping characteristics can be observed on the mesiodistal and oro-vestibular views there are no statistically significant differences between the asymmetries measured on the oro-vestibular and mesio-distal views. The three dimensional form of canals usually exclude the possibility of forming the same asymmetry on both projections, but the difference between the two views is not striking, therefore the conventional clinical radiographs usually do not give complete information about the asymmetry of preparation.