Class II Silver Amalgam Restoration

Definition & Classification

• Two-surface: MO (mesio-occlusal) or DO (disto-occlusal)
• Three-surface: MOD (mesio-occluso-distal)
• Four or more surfaces: complex/compound restorations

Steps in Cavity Preparation

Stage 1 - Initial Tooth Preparation

Step 1: Outline Form and Initial Depth

• Enter the pit nearest the involved proximal surface using a No. 245 bur (punch cut at high speed)
• The long axis of the bur must remain parallel to the long axis of the tooth crown throughout
• Initial depth: 1.5-2 mm (just inside the dentinoenamel junction, DEJ)
• Extend outline to include the central groove and opposite pit (provides dovetail retention)
• Isthmus width should be as narrow as possible - no wider than 1/4 of intercuspal distance (ICD)
• Preserve marginal ridge strength: maintain at least 2 mm thickness of marginal ridge

Step 2: Resistance Form

• Facio-lingual width should not exceed 1/4 ICD (wider surface = more force = fracture risk)
• Cavosurface line angle should be 90°-110° (>110° leads to restoration fracture)
• Occlusal amalgam thickness: 1.5-2.0 mm minimum to resist fracture during function
• Rounded internal line angles to reduce stress concentration
• Pulpal floor and gingival seat must be flat and smooth
• Axio-pulpal line angle must be rounded
• Facio-lingual walls converge occlusally

Step 3: Retention Form

• Facial and lingual walls should be parallel to each other or slightly convergent occlusally (creates undercuts)
• Provide dovetail retention in the occlusal step
• Retention grooves or locks at axio-facial and axio-lingual line angles in the proximal box

Step 4: Convenience Form

Proximal Box Preparation

• Begin with a proximal ditch cut: place bur over DEJ in the pulpal floor near marginal ridge, cut gingivally, then extend facially and lingually along DEJ - creates the axial wall
• Extend gingivally just beyond the carious area or proximal contact
• Final proximal margins (facial, lingual, gingival) should be established with hand instruments (chisels, hatchets)
• Establish no more than 0.5 mm clearance from adjacent proximal surface (facially, lingually, and gingivally)

Stage 2 - Final Tooth Preparation

Step 5: Removal of Remaining Carious Dentin

• Use a spoon excavator or large round bur at slow speed
• Remove all infected/softened dentin

Step 6: Pulp Protection (if needed)

• Indirect pulp cap: calcium hydroxide liner + resin-modified glass ionomer (RMGI) base if cavity is deep
• Dentin desensitizer applied after liner placement

Step 7: Finishing Enamel Walls

• Remove all unsupported enamel (enamel rods must be supported by dentin)
• Smooth all cavity walls

Step 8: Toilet of the Cavity

• Rinse and dry the cavity; inspect for remaining debris or caries

Matrix Band Placement

• Restore the contact area
• Prevent excess amalgam from extruding gingivally
• Allow proper condensation against the gingival seat

Matrix System (Tofflemire Retainer)

1. Head - U-shaped with three guides/slots
2. Locking vise - sliding body that holds the band
3. Long knob - adjusts diameter of the loop
4. Short knob - locks the band within the sliding body

Procedure for Matrix Placement

1. Try the wedge - select appropriate size wooden wedge
2. Burnish the matrix band - introduce curvature to match proximal contour of the tooth
3. Place band into retainer
4. Fit matrix onto tooth:
   • Occlusal edge extends 1.5-2.0 mm above marginal ridge and cavosurface margin
   • Gingival edge extends 0.5 mm below gingival cavosurface margin
5. Place wedge - seat firmly in gingival embrasure
6. Tighten matrix band - turn long knob; then loosen 1/4 turn after wedge placement (prevents open contact and allows proper condensation at gingival margins)
7. Burnish band to adjacent proximal contact with a spoon excavator or burnisher

Amalgam Insertion and Condensation

1. Trituration - mix amalgam to a homogeneous, slightly reflective mass (flattens slightly if dropped on a surface)
2. Incremental insertion - insert small increments at a time using an amalgam carrier
3. Condensation - use overlapping strokes with a condenser; work from the proximal box first, then occlusal
   • Use small condensers in the proximal box; larger condensers for the occlusal surface
   • Condense firmly to minimize voids and eliminate mercury-rich surface layer
   • Over-pack the preparation to ensure well-condensed margins
4. Pre-carve burnishing - immediately after packing, use a large burnisher with heavy strokes mesiodistally and facio-lingually; burnisher contacts cusp slopes but NOT the margins - produces denser marginal amalgam

Carving

1. Remove matrix band and wedge carefully to avoid fracturing the new marginal ridge
2. Use carvers (discoid-cleoid, Hollenback, IPC carver) to restore tooth anatomy
3. Carver should rest partially on the adjacent external tooth surface to prevent over-carving
4. Restore:
   • Marginal ridges
   • Occlusal grooves and fossae
   • Proper contact area
   • Proximal contour

Finishing and Polishing

• Not performed within 24 hours of insertion - amalgam crystallization must be complete
• Use finishing burs (No. 4 or No. 6 round) with long axis perpendicular to the margin - unprepared tooth structure guides the bur and prevents over-removal
• Define groove and fossa anatomy with small round finishing burs without reducing centric holding areas
• Smooth surfaces are less prone to tarnish and corrosion
• Note: high-copper amalgams require less polishing than older low-copper alloys

Key Dimensions Summary

Key Points to Remember

• The dovetail in the occlusal step provides primary retention and prevents proximal displacement
• No bevel is placed on enamel margins for amalgam (unlike composite) - butt-joint margins only
• The axio-pulpal line angle must be rounded to prevent stress concentration
• The proximal box walls should diverge facially and lingually to facilitate carving and removal of the matrix band
• Contact area must be restored to prevent food impaction and periodontal problems