Current DBAs require an enamel margin for composite to adequately seal the tooth. Therefore sandwich techniques recommended to

Open sandwich- GIC into the base of a proximal cavity up the level of the DEJ. - Finally restore with composite, provides wear resistance and aesthetics

on the occlusal surface - Main advantage – l

o large SA of GIC for buffering any changes in pH acidico long term fluoride release creating fluoroapatiteo Similar thermal expansion properties as dentineo Less polymerisation shrinkage o Less technique sensitive

- Disadvantage – over time GIC braeks down resulting n food packing - Main use in a deep class II or a class V on a root surface where the margin

extends apically to the CEJ

Closed sandwich- Placing the GIC at the base but doesn’t extend to the cavosurface margins- It is encasd in composite - No protection from proximal caries unless failiure of the dentine bonding

agent or if RMGIC is used - Technique sensitive

Recognised that the marginal degradation of GIC over time. Recommendation for RMGIC because they have superior mechanical properties and bonding strength to dentine

Studies- Evaluation of RMGIC open sandwich after 6 years - Evaluated at 5 years

o 42 failures of 220 restorations over 6 years (19%)o Frequent reasons for failure

Material fracture, tooth fracture, secondary caries, dissolution of GIC

- Evaluated at 7 yearso 13 teeth of 160 restorations that were followed up failedo Reasons for failure

Dissolution of RMGIC, secondary caries, fractures

Leakage studies with dyes- Visible margins have lower leakage scores than those of proximal gingival

margins - Dentine bonding agents can maintain the peripheral seal for composites

only if seal is bound by enamel therefore recommended