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The sandwich technique in restorative dentistry involves using resin-modified glass ionomer cement (RMGIC) as a liner beneath a composite restoration. The RMGIC layer mimics the properties of dentin, while the composite serves as the enamel layer. This technique is useful for achieving a strong bond, reducing microleakage, and providing good esthetic results.
Steps of sandwich technique:
STEP 1. Tooth Preparation
🦷Prepare the tooth by removing caries and shaping the cavity as required for a composite restoration.
🦷Ensure that the cavity is clean and free of any debris or moisture, but keep it slightly moist to enhance bonding with the RMGIC.
STEP 2. Application of RMGIC (Dentin Layer)
🦷Place the RMGIC as a liner or base in the deepest portion of the cavity, especially near the dentin.
🦷The RMGIC serves as the "dentin layer" because it bonds well to both dentin and enamel, and it releases fluoride, which helps in preventing secondary caries.
🦷Smooth and shape the RMGIC, leaving enough space for the composite layer above. Allow the RMGIC to self-cure or light-cure as recommended.
STEP 3. Etching and Bonding
🦷If performing an open sandwich technique (where RMGIC is exposed at the gingival margin), skip this step for the RMGIC margin.
🦷If it’s a closed sandwich technique (where RMGIC is not exposed to the oral environment), etch the enamel margins and remaining dentin lightly with phosphoric acid for about 15 seconds.
🦷Rinse thoroughly and dry, keeping the RMGIC layer slightly moist to prevent desiccation.
🦷Apply a bonding agent to the etched surfaces and light-cure, following the manufacturer’s instructions. Be careful to avoid applying bonding directly over the RMGIC layer unless specified.
STEP 4. Application of Composite (Enamel Layer)
🦷Place the composite incrementally over the RMGIC layer.
🦷Each composite increment should be no thicker than 2mm to ensure proper curing, and should be shaped to match the natural contours of the tooth.
🦷Light-cure each increment according to the composite manufacturer's guidelines.
STEP 5. Finishing and Polishing
🦷Once the composite has fully cured, finish and polish the restoration to achieve a smooth surface and proper anatomical contours.
🦷Carefully adjust the occlusion to ensure that the restoration does not interfere with natural biting forces.
Benefits of the Sandwich Technique
🦷RMGIC as Dentin Substitute: RMGIC provides a good seal to dentin, reduces sensitivity, and acts as a stress-absorbing layer.
🦷Composite as Enamel Substitute: Composite provides excellent esthetics, wear resistance, and a smooth finish that mimics enamel.
🦷Fluoride Release: RMGIC releases fluoride, which can help reduce secondary caries risk.
🦷Enhanced Bonding and Marginal Adaptation: By using both RMGIC and composite, this technique maximizes bonding and reduces marginal gaps.
In summary, the sandwich technique combines the advantages of both RMGIC and composite to create a restoration that is strong, esthetic, and long-lasting.