Composite may not bond adequately to dentin, therefore during polymerisation, it may lead to formation of a gap at the cavity margin situated in dentin.This bond can be improved by placing GLASS IONOMER CEMENT lining between the composite and the dentin.This is called the sandwich technique.
GIC bonds chemically to the tooth dentin and micromechanically to the composite.
The GIC is etched for retention of the composite.Also the anti-cariogenic effect is beneficial.
-Lesions where one or more margins are in dentin like cervical lesions.
-Class II composite restorations.
The dentinis conditioned and a thin layer of GIC liner cement is applied.The cement must be exposed at the margins to ensure fluoride release.
Phosphoric acid is used to etch the enamel portion and also the lining GIC, to increase surface roughness.
Light cured gic need not be etched.
After adequate drying, bonding agent is applied to the cement surface and etched enamel.
This is followed by the usual method of composite insertion.
Closed Sandwich technique: This technique is used when a glass
ionomer is placed in an area where there is no contact with the cavosurface
of the preparation. The material is completely covered with
the restorative material. (Base and liners) A liner should be used as a
very thin covering over deep and questionable dentin surfaces. A
base should be selected anytime the material is placed thicker than
.25 mm and should be a high strength restorative material. Tooth
conditioning is not required with this technique.
Open Sandwich technique: This technique is used when a Glass
ionomer is placed in an area where there is contact with the cavosurface
on the preparation. The margin of the preparation is sealed
with the Glass Ionomer material. A restorative material should
always be used here and the tooth conditioner is indicated.
Class II Open Sandwich: Used when any part of the gingival
margin of a Class II preparation has been extended past the CEJ and
no longer has an enamel cavo-surface.
1. After placement of the matrix, condition the gingival floor with GI
conditioner for 10 seconds and wash off.
2. Place either a pure glass ionomer or a resin modified glass
ionomer interprox. to the start of enamel margins. Do not build
interproximal or occlusal contact in this material. Make sure that
there is a minimum of 2mm of the final restorative material above the
Glass Ionomer to support the marginal ridge.
3. Continue with step 4 with the above composite technique if final
material is a composite restoration.
Although the sandwith technique has proved its utility and predictability in durable composite restoration , the time has changed so the techniques and material science ,which led to the fact that there is hardly any need to use glass ionomers as base before placing composite restorations.
There is predictable bond between the dentin and the composites leading to successful restoration even in reversible pulpits situations ... If bonded well and protocol followed ..
What about the polyacrylic acid from gic which is more irritating to pulp than the shrinkage in composites..
Why to use so many dissimilar material rather than using single material creating good integrated bond.. when the science and innovations permits and allow us to use materials /composites in predictable way.