Class II Amalgam Preparation Technique

Posted on Feb 10, 2025 in Biology

Clinical Technique for Class II Amalgam Preparations

Class II Cavity – develops slightly gingival to the proximal contact

  • 1 occlusal box and 1 proximal box

Principles of Tooth Preparation

  • Establishing outline form
  • Establishing convenience form
  • Establishing resistance form
  • Establishing retention form
  • Removal of remaining caries
  • Finishing of the enamel wall
  • Cavity debridement

Cavity Preparation

Initial Prep (Occlusal Outline Form) / Occlusal Box or Occlusal Step

  • Similar to a Class I Cavity Prep
  • Use 1/4 or 1/2 on the pits, connect using a straight fissure bur and follow the grooves
  • Place Margins on sound tooth structure
  • Maintain isthmus width
  • Establish initial depth
  • Change to an inverted cone bur for buccal and lingual wall convergence
  • Make sure the pulpal wall is flat
  • Before extending into the involved proximal marginal ridge, visualize the location of your buccal and lingual proximal walls
  • Presence of reverse curve on the buccal, no reverse curve on lingual
  • Proximal Outline Form / Proximal Box (Create a ditch, Depth of proximal box, Gingival floor)

Ditch = canal with 0.5mm depth

  • Leave at least 0.5 to 1 mm of tooth structure to avoid damaging the adjacent tooth (break with a chisel)
  • In amalgam preparation, there is an extension for prevention
  • CSM must be a butt joint
  • S-curve / Reverse curve in buccal [not in lingual] – out of contact with the adjacent tooth, an explorer can pass through to place margins in a self-cleansing area
  • No contact in lingual

FIRST create a Class I cavity

Outline Form Occlusal Box

  • Extend until sound tooth structure is obtained and no unsupported and/or weakened enamel remains
  • Avoid terminating the margins on extreme eminences such as cusp heights and ridge crests
  • Extend to include all fissures that cannot be eliminated by enameloplasty
  • Restrict initial pulpal depth to 1.5 mm from the cavosurface margins / 2 to 5 mm beyond the DEJ (natural tooth)

Proximal Box

  • Extend until sound tooth structure is obtained and no unsupported and/or weakened enamel remains
  • Avoid terminating the margins on extreme eminences such as cusp heights and ridge crests
  • Extend the margins to allow access for proper manipulative procedures
  • Restrict the initial axial depth of the proximal preparation to a maximum of 0.2 – 0.8 mm into dentin
  • Extend the walls of the proximal box (cervical, facial, and lingual) 0.5 mm out of contact

The axial wall should be slightly convex

Bevel the axiopulpal line angle for resistance → if not, it will be fractured due to forces

Factors Affecting Resistance

  1. Following the directions of the walls of the cavity (follow the direction of rods to avoid unsupported enamel)
  2. Cavity width 1/4 intercuspal distance
  3. Cavity depth .5 mm beyond DEJ
  4. Removal of unsupported and undermined enamel
  5. Flattened pulpal
  6. Rounded line angle
  7. Adequate bulk of restoration
  8. Beveled A-P line angle
  9. Correct carving and proper occlusion
  10. Butt-joint margins for amalgam
  11. Reverse curve or S curve
  12. Depth of proximal box
  13. Flat gingival floor
  14. Axial wall slightly convex
  15. 0.5 mm out of contact