Pulp is the life of the tooth . So during any kind of conservative procedure .. protection or conservation of pulp is one of the most essential steps. Pulpal injury is one of the main reason for the failure of conservative treatment.
How can a pulpal injury happen ?
Galvanic currents ( due to the contact between dissimilar metal restorations that in the oral cavity fluid acts like a circuit)
Chemical from the restorative materials ( Constant seeping chemicals from the overlying restorative material can cause necrosis of pulp)
Restorative material with good thermal conductivity. ( certain restorative materials are not good thermal insulators)
Heat generated by injudicious cutting( necrosis due to heat generated by excessive cutting and improper drilling instruments)
The two most common agents used in pulp protection are Liners and Bases.
Liners are volatile or aqueous suspensions or dispersion of zinc oxide or calcium hydroxide that can be applied to the cavity surface in a relatively thin film.
Bases are those cements, which are applied, in thicker dimensions beneath permanent restorations to provide for mechanical, chemical and thermal protection of the pulp.
Mostdentists use some type of cavity liner or base in almostall cavity preparations. They are used primarily toprotect the pulp and to aid the pulp in recoveringfrom irritation resulting from cavity preparation.Liners and bases are placed when the cavitypreparation is completed, just before insertion of restorative material .
Glass ionomer cements and dentin bonding agentsare used primarily to seal the dentin and protect thepulp from bacterial invasion. Calcium hydroxide canbe used in extremely deep areas as an antibacterialagent and/or as a pulp capping material.
Most bases are applied best when the assistant wipes the instrument clean between each small application.The dentist will hold a gauze sponge in thetransfer zone and quickly wipe the end of theinstrument as the dentist moves toward the base mix. Ifthe dentist inadvertently gets the base on the enamelwalls of the cavity preparation, you will pass aninstrument for removal of the material.
Cavity varnish/ Bases
is a liner used to seal the dentinaltubules to help prevent microleakage and is placed in acavity to receive amalgam alloy after any bases havebeen placed.
Cavity varnish is being used less and less with amalgam restorations, and dentin bonding agentsare replacing cavity varnish as the liner of choice.
Cavity varnish has an organic solvent of ether orchloroform that quickly evaporates, leaving the resinas a thin film over the preparation.
This varnish shouldbe slightly thicker than water. If it becomes very thick,discard it.
Cavity varnish is not used with compositessince the varnish retards the set of composites andinterferes with the bonding of composites
A small cotton pellet held by cotton forceps isdipped into the varnish just enough to wet the pellet
The cavity varnish is applied to the pulpal area, wallsof the cavity preparation, and onto the edge of themargins of the preparation.
Any excess varnish can beremoved from the enamel with a fresh cotton pellet.
A second application of cavity varnish is placed over the first to thoroughly coat the surfaces of the dentin and fill any voids from bubbles created when the firstapplication dries. After liners and bases are placed intothe cavity preparation, the tooth may be restored withmaterials, such as amalgam, composite resin, or GIC.