Precision Tech Apica Air Mode D'emploi page 36

Unsuitable situation of root canals for Electric Measurement
Cannot obtain precise measurements if the root canal conditions as below:
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Root canal with a large apical foramen
The root canal cannot be accurately measured because of the lesion or
incomplete development of the apical foramen. The results may show that
the length measured is shorter than the actual one.
Root canal blood overflow from the opening
If blood spills from the root opening and contacts the gums, it will cause
leakage of electricity, which cannot be accurately measured. Wait for
the bleeding to stop completely. Clean the root canal and the opening,
completely empty the root canal blood, and then measure it.
Chemical solution flowing out from the opening
If a chemical solution flows out of the root canal, it is impossible to get an
accurate measurement.
It is important to remove the overflow from the opening.
Broken crown
If the crown is broken, a segment of the gingival tissue enters the lumen,
and the contact between the gingival tissue and the root file causes
electrical leakage, which cannot be accurately measured. In this case, the
appropriate material should be used to isolate the gingival tissue.
The crack tooth Leakage through branch of the root canal
Broken teeth can cause electrical leakage and cannot be accurately
measured.
Branch tubes can also cause leakage.
Retreatment canal which was filled with gutta-percha
The gutta-percha must be completely removed to eliminate its insulation,
then pass a small file all the way through the apical foramen and then put
a little saline in the canal, but do not let it overflow the canal opening.