Retrocavity obturation with MTA
Outside the retrocavity, the area should be covered by cotton pellets in order to prevent MTA excess from falling out.
A 1:2 powder/liquid ratio is mixed to putty consistency. Pieces of MTA can be delivered by using Lee's rule, syringes, or plastic sleeve.
Because it is a granular aggregate and sticks to itself, MTA does not stick to instruments. It is the author's preference to deliver the MTA almost as a liquid with the tip of a fine instrument, like a drop, right into the dry retrocavity. The liquid cement easily runs along the dentin walls, and it can be softly condensed by moving the carrying instrument up and down. When the retrocavity is totally obturated, a wet paper point can serve to remove MTA remnants outside the cavity; and a dry one to dry and condense the inside retrocavity cement (or, even faster, just get close with the aspirator to the retrocavity for a second). Final irrigation is forbidden because it can wash the MTA out from the retrocavity.
The area is finally checked under medium-to-high magnification (16-25x). Despite its moisture sensitivity while condensing and drying, its easier preparation, condensation and no polishing make MTA the best, easiest and biologically most reliable cement for retrocavity sealing. However, MTA cannot be used in difficult large cavities, like strip perforations with surgical access, where IRM should be used because of its better managability and longer setting time than superEBA.
Composite represents the opposite retrocavity situation to ultrasonic filing in long canal preparation. It should be used in cases when apicoectomy or retrocavity or both cannot be made due to:
- cast posts that fill the canal all the way down
- previous apicoectomy that has resected the root up to the level of the post • weak dentin walls remaining after apicoectomy that cannot support ultrasonic vibration, or short roots where apicoectomy will make the roots even shorter.
Two root preparations can be done: dome preparation, or cap preparation.
Composite leaks less than superEBA, IRM and GIC. However, it is a material that is more sensitive to technique because moisture and blood contamination during the bonding/setting process reduces bond strength and increases leakage. Also, certain components of composite resins and dentin bonding agents can have cytotoxic effects on cells; but when the composite sets, cells can grow on its surface.
Retroplast (Retroplast Trading, Rorvig, Denmark) is a two-paste system that forms a dual-cure composite resin when mixed. Paste A is bis-GMA/TEGGDMA 1:1, benzoyl peroxide and butylated hydroxytoluene (BHT). Paste В is ytterbium trifluorideaerosil ferric oxide. The bonding is a gluma-based agent. The working time is 1.5-2 minutes and it has radiopac-ity equivalent to 6 mm of aluminum.
Retroplast is well tolerated by the tissues and promotes cemen-tum layer deposition, insertion of new Shapey’s fibers, and periodontium regeneration. Long-term success has been reported.