Root-canal preparing instruments are commercially available in the form of root-canal files, root-canal drill bits or root-canal rasps and are used to widen a root canal and to clean it.
The tool proper of such root-canal preparing instruments may assume various thicknesses, there being presently twenty one different thicknesses beginning with a tip diameter of 0.06 mm up to one of 1.4 mm.
As a rule the tool proper consists of a vacuum-molten, high-alloy chromium-nickel steel evincing high strength regarding tensive, torsional and elongation stresses and required to be such that tools with initial dimensions of 0.06 mm can be manufactured.
In use, that is when such an instrument is operated by the dentist to widen or clean a root canal, said instrument is subjected to compressive, torsional and bending stresses at various rates, directions of rotations and with simultaneous up-and-down motion, i.e. an axial motion.
Furthermore root-canal preparing instruments are exposed to chemical stresses on account of disinfectants and thermal loads during heat sterilization.
Such stresses applied to root-canal preparing instruments leave traces on them such as warping, twisting by excess rotation etc. Consequently the preparing instruments and in particular those with thin tools already must be discarded possibly after being used only three times but assuredly after five-fold use as otherwise there would be danger of breakage with continued use.
While in principle used instruments may be visually checked using a magnifier, such checks on the other hand will only reveal external changes, not internal structural ones arising from material fatigue.
Accordingly it would be advantageous to the dentist if he were able to discard a root-canal preparing instrument after a specific number of uses. Such a feature however requires that he should always know how often a specific root-canal preparing instrument already has been used and sterilized. Root-canal preparing instruments known heretofore do not provide this type of information.
Consequently it is an object of the invention to create a dental root-canal preparing instrument of the initially cited kind revealing how many times it already has been used.