d. Mixing. As with unfilled resins, the manufacturer's directions should be
followed when mixing composites. There are several types available and each requires
a specific mixing procedure. To mix the two-paste system, equal parts of the pastes are
mixed with a folding motion to a uniform color within 20 to 30 seconds. The average
working time from start of mixing to insertion of product is 1 1/2 to 2 minutes. It is
important to avoid cross-contamination between jars of universal and catalyst pastes.
The double-ended spatula provided with the kit has differently shaped ends, one clearly
labeled "uni" and the other labeled "cat." Improper mixing could cause failure of the
restoration. Also, improper ratio of pastes will decrease the strength as will insufficient
spatulation. Use of a metal spatula will result in discoloration of the material, giving
poor esthetics. However, the single paste, lightproof syringe is the most common form
used. Light-cured resins do not require mixing, but are used directly from the syringe.
This single-paste contains both the photoinitiator and the amine activator and requires
the use of a curing light to polymerize. The exact curing time depends on the
manufacturer's instructions (most often 20 to 60 seconds) and the thickness and size of
ACID ETCH TECHNIQUE
Cavities requiring added retention (to hold firmly) are treated with an acid etching
technique. This technique improves the seal of the composite resin to the cavity wall.
The enamel adjacent to the margins of the preparation is slightly decalcified with a 40 to
50 percent phosphoric acid solution. This etched enamel enhances the mechanical
retention of the composite resin. In addition, the acid etch technique is used to splint
unstable teeth to adjacent teeth. The acid is left on the cut tooth structure only 15
seconds, in accordance with the directions for one common commercial brand. The
area is then flushed with water for a minimum of 30 seconds to remove the decalcified
material. Etched tooth structure will have a chalky appearance.
PIT AND FISSURE SEALANTS
Pit and fissure sealants are similar to the unfilled resin portion of acid etch
composite filling materials. This plastic resin is used as a prophylactic seal of occlusal
pits and fissures. The purpose is to prevent carious destruction of tooth structure. The
sealant is used when there is a deep occlusal pit or fossa or a lingual pit, when there is
an intact occlusal surface with a carious or restored contra lateral tooth surface, and
where there is high carious activity, poor oral hygiene, or newly erupted posterior teeth.
INTERMEDIATE RESTORATIVE MATERIAL
Intermediate restorative material (IRM) is a zinc oxide and eugenol cement that
has been reinforced for increased strength. It is used as an intermediate base beneath
a metallic restoration and also as a temporary restoration.