Removing Carious Dentin and Old Restorative Material

Removal of Remaining Carious Dentin or Old Restorative Material

• Teeth with frank deep carious lesions require removal of infected dentin and old faulty restorative material after initial tooth preparation.
• The floor of the cavity may be composed of:
  • Hard, sound, healthy dentin (free from lateral spread of decay or discoloration, with a CP depth of 0.2 mm beyond the DEJ)
  • Hard but discolored dentin (stained from pigments produced by chromogenic bacteria, not considered carious)
  • Carious dentin (area of decalcification precedes penetration of microorganisms, often appears discolored, but has no soft texture of caries)

Carious Dentin

• Carious dentin is formed of two distinct layers:
  • Infected dentin (outer layer, softened, contaminated with bacteria, includes superficial, granular, necrotic tissue, and softened, dry, leathery dentin)
  • Affected dentin (inner layer, slightly softened, demineralized dentin, not invaded by bacteria)
• Clinically, carious dentin is characterized by:
  • Infected dentin: soft texture, discolored, bacterial invasion, non-vital, no pain
  • Affected dentin: slight softening, demineralization, not invaded by bacteria, vital, painful

Techniques for Removal of Carious Dentin

• Rotary instruments: carbide bur, ceramic bur, CMCR
• Directions for removal:
  • Moderate, deep, extensive caries: use soft or hard caries removal techniques
  • Tools: hand (soft) or rotary (hard)

Pulp Protection

• Deep dentin is very porous and susceptible to desiccation
• The thin remaining dentin provides little protection from:
  • Heat generated by rotary instruments
  • Noxious ingredients of various restorative materials
  • Thermal changes conducted through restorative materials
  • Forces transmitted through materials to the dentin
  • Ingress of bacteria and toxins

Secondary Retention and Resistance Features

• Proximal axial grooves (locks): prepared at the axio-buccal and axio-lingual line angles in extensive cavity preparations
• Axial coves: prepared with a No. ¼ round bur
• Horizontally oriented axial retention grooves: prepared in most Class V preparations for amalgam and in some root surface tooth preparations for composite
• Skirt: preparation features used in extensive Class IV, cast gold restorations that extend the preparation around some or all of the line angles of the tooth
• Horizontal Slots: retentive groove in dentin, prepared approximately 0.6 mm deep and 0.5 to 1 mm inside DEJ
• Pins: pin retention used in preparation with few or no vertical walls

Finishing External Walls and Margins of CP

• Objectives:
  • Create the best marginal seal possible between the restorative material and the tooth structure
  • Afford a smooth marginal junction
  • Provide maximum strength of both the tooth and the restorative material at and near the margin
• Ideal finished enamel wall is gained by:
  • Removal of undermined enamel
  • Adjustment of CSA according to the physical properties of the restoration
  • Smoothening of walls for better adaptation
  • Making the outline in sweeping curves
  • Rounding of line and point angles

Cleaning and Preparation of the Cavity

• Objectives:
  • Removal of bacteria, loose caries debris after using sharp excavator, temporary restoration, and saliva
  • Improvement of adaptation and avoidance of caries recurrence around the restoration
  • Preparation of the tooth surface to receive the selected restorative material
• Technique of cleaning:
  • Scrap the cavity walls and floors with a hand instrument
  • Flush the cavity with air–water spray
  • Dry the cavity with cotton pellets, then gentle dryness with oil-free air blowing