Class II Inlay Cavity Preparation - Steps

Initial Procedures (Pre-Preparation)

1. Occlusion assessment - Mark and study occlusal contacts; identify centric stops and lateral excursion contacts before any tooth reduction.
2. Radiographic examination - Assess caries extent, proximity to pulp, root morphology.
3. Rubber dam isolation - Mandatory for moisture control and soft-tissue retraction.
4. Local anesthesia administration
5. Pre-operative impression (if needed for diagnostic reference)

Step 1 - Occlusal Step (Initial Preparation)

• Enter the occlusal surface at the central fossa or primary groove at an initial depth of 1.5-2 mm (into dentin)
• The bur is held parallel to the long axis of the tooth
• Extend the preparation along the occlusal fissures following the primary groove pattern (including any fissures that run toward the proximal surface)
• The walls are cut with a slight 2-5° occlusal divergence (draft/taper) toward the occlusal opening to allow path of withdrawal for the wax pattern
• Establish the isthmus (the narrowest portion connecting occlusal and proximal components) - should be no wider than necessary (ideally just wider than the bur width) to conserve the transverse ridge
• Extend the occlusal step distally (or mesially) into the marginal ridge area to expose the enamel-dentin junction at the proximal surface, progressively widening the faciolingual dimension

• Pulpal floor depth: 1.5-2 mm
• Faciolingual width: 1/4 to 1/3 of intercuspal distance

Step 2 - Proximal Box Preparation

a) Breaking into the proximal surface

• Continue from the occlusal step, direct the bur at the proximal surface to break through the marginal ridge
• The facial and lingual walls of the proximal box must clear the adjacent tooth by 0.2-0.5 mm (to allow for flares and margins)

b) Establishing the proximal box walls

• Facial wall (buccal proximal wall) and lingual wall: extend far enough to place the margins in a self-cleansing area, free of contact with the adjacent tooth
• Gingival wall (floor): extend gingivally until the caries is cleared or until the contact with the adjacent tooth is broken; ideally 0.5-1.0 mm below the gingival contact area
  • Gingival floor is at right angles to the long axis (flat or slightly beveled)
• Axial wall: follows the external contour of the tooth; depth ~0.5 mm into dentin; should be slightly convex faciolingually
• Axiofacial and axiolingual line angles: should be slightly rounded, not sharp
• Axiopulpal line angle (junction of axial wall and pulpal floor): lightly beveled to provide thicker metal at this region

Step 3 - Resistance and Retention Form

• The pulpal floor is flat and perpendicular to the long axis - provides resistance to masticatory forces
• Axial wall depth and flat gingival floor provide resistance to lateral loading
• Occlusal dovetail (if needed): increases retention by locking the restoration against displacement from the proximal surface
• Walls with slight occlusal divergence (2-5°) ensure the wax pattern can be removed; no undercuts
• Wall convergence would lock the pattern; wall divergence beyond 5-10° would reduce retention

Step 4 - Final Preparation - Bevels and Flares

• A 30-40° metal angle at margins (ideal for cast metal burnishability and marginal seal)
• Extension of margins to self-cleansing areas

Types applied in Class II inlay:

Step 5 - Removal of Infected Carious Dentin

• If caries remains after the initial preparation, it is removed now using round burs (No. 2 or No. 4) or spoon excavators
• The prepared floor need not be at a uniform depth - caries removal takes priority
• Apply base/liner as needed (e.g., calcium hydroxide over near-pulp exposures, glass ionomer base if pulpal floor is deep)

Step 6 - Pulp Protection

• Liner (e.g., calcium hydroxide): when pulp is very close (< 0.5 mm remaining dentin)
• Base (e.g., glass ionomer): when significant dentin is missing and a flat surface is needed for seating

Step 7 - Final Finishing of Walls

• Enamel walls and margins are refined with chisels, hatchets, and angle formers
• Smooth all walls; ensure there are no unsupported enamel rods
• Re-check that all walls have the correct occlusal divergence (no undercuts)
• Inspect under magnification for irregularities

Modifications

Summary Sequence

1. Initial procedures (occlusion, anesthesia, rubber dam)
2. Occlusal step - depth 1.5-2 mm, following grooves
3. Proximal box - break through marginal ridge; establish facial, lingual, axial, and gingival walls
4. Resistance and retention form
5. Removal of remaining caries + pulp protection
6. Bevels and flares (gingival bevel, occlusal bevel, primary and secondary flares)
7. Final wall finishing and inspection