Individual (cast) post-core: clinical and laboratory steps. Direct and indirect method of production.
1)Before starting tooth preparation make x-ray.
2)Preparation of canal - done by peeso-reamel or glidden gates. 1st we should remove gutta percha, when at least 3-5mm of canal apex should be left with gutta percha. The post length should be equal to the height of anatomical crown or 2/3 of root length.
The canal should be prepared to the length and width and it should not be bigger in diameter than 1/3 of root crossection in this area, with the root walls at least 1mm thick. Any undercuts in canal should be removed.
In single canal teeth make anti-rotational elements - not more than 2mm in apical direction.
In multiple canals teeth choose one main canal and the others will be additional (maxilla - palatal, mandibular - distal).
3)Preparation of crown of tooth - is made according type of restoration we are planning to make (metal / ceramic / metal-ceramic) and the step crown is made accordingly -
•Metal - 0.5-0.7mm
•Metaloceramic - 1mm.
At least 1.5mm of thickness of walls should be left - if after preparation the walls are thinner we must reduce from the height until we reach this thickness. If margins of the preparation don't coincide with the step - the step should be lowered so that the post won't break the root. Outer marginal bevel should be made so that the post will wrap around natural tissue.
4)Post production -
Direct method - check that the plastic pin is loose in the canal.
a.Lightly lubricate the canal with isolative material.
b.In a dappen dish mix acrylic resin monomer and polymer to a runny consistency.
c.Fill the orifice of the canal with the mixed material.
d.Put monomer on a plastic pin and insert it into the canal.
e.Do not allow the resin to harden fully within the canal. Loosen and reseat it several times while it is still rubbery.
f.Once the resin has polymerized, remove the pattern.
g.Form the apical part of the post by adding additional resin and reseating and removing the post, taking care not to lock it in the canal.
h.Additional resin should be added for the core part, which can be shaped by burs.
a.Lightly lubricate canal with isolative material.
b.Using lentula (to avoid bubbles) fill canal with low consistency silicone (wash)
c.With impression tray insert impression material (putty)
d.Remove the impression after setting.
•Direct method - the technician sprue the pattern and place it into investing material. The pattern is burned out in a furnace and then the post and core is casted in a centrifugal machine
•Indirect method - technician pours cast from the impression. Then he makes the pattern of the post and core, sprue it, place it into investing material. The pattern is burned out in a furnace, and the post and core is casted in centrifugal machine.
When the cast is prepared the doctor tries to fit it into the canal.
We can make groove for cement escape.
If it fits we cement it and then prepare the crown.