One percent methylene blue applied with a microbrush is used on the dried resected root for 10-15 seconds before washing and drying60. Saline is used to wash away excess. The microscope is used at maximum magnification (16-25x). Methylene blue tints collagen fibers, so it is used for:
- root resection inspection, total (unbroken outline) or partial (broken outline)
- canal identification: calcified, accessories, canal fins, C-shaped
- isthmus identification
The outline of the resected root varies significantly with the tooth type, bevel angle and length of resection.
TIP Methylene blue helps the surgeon to see complete or incomplete root resectioning and all apical microanatomy.
TIP Apical microfractures stain and are caught by a microexplorer, while crazy lines are not.
One small detail left uncorrected can ruin the whole procedure. Therefore this "micro tissue" is as important as the "macro tissue" of the main canals.
Although isthmus is an important structure in endodontic microsurgery, it was ignored in dental textbooks and scientific literature until 1983. It represents the communications that normally exist, at different levels, between two canals inside a root, but surgically exposed at the resected apex root area. It contains pulp tissue and should be treated in the same way as the pulp tissue of the canals.
After root resectioning at 3 mm from the apex, a complete (type 2) or incomplete (type 1) isthmus is present in 90% of cases in the mesiobuccal root of a maxillary molar; in 80% of cases in a mesial root of mandibular molars; in 15% of cases in a distal root of mandibular molars and anterior teeth; and in 30% of cases in mandibular premolars.