The concept behind master cone filling is basically that it is possible to get a gutta percha cone to fit a canal well enough that any discrepancies can be taken up by the sealer.
It is essential that the preparation be almost the same shape as an endo file, that is, evenly tapered and conical.
Then gutta percha cones are tried in until one is found that approximates the size of the canal.
A radiograph is made to determine if the point is near the apex.
Any excess is trimmed.
The point is warmed and re-inserted repeatedly until it conforms to the canal as closely as possible. Sometimes a solvent is used to soften the exterior of the point to accomplish the same purpose. The solvent is then encouraged to evaporate with an air spray.
When the cone fits, sealer is applied to the canal and/or the point and the point is seated with apical pressure.
Additional pressure may be applied with a condenser from the coronal end.
Any gp in the pulp chamber is removed with a heated instrument.