Pulp Protection in Dentistry

Objectives of Pulp Protection

• Dentinal Tubules contain cellular extensions surrounded by dentinal fluid
• Odontoblasts are columnar cells embedded in predentin
• Insult (trauma, bacteria) can cause fluid flow in/out of dentinal tubules, triggering sensitivity (mechanoreceptors) and inflammation.
• Smear Layer (compacted cutting debris) provides partial dentinal tubule sealing (25-30% porous)
• Pulp Defense Mechanisms:
  • Sclerotic Dentin: Forms in response to stimuli like aging or mild irritation, sealing dentinal tubules, appearing dark and harder than normal dentin
  • Tertiary Dentin (Reparative): Forms in response to acute stimuli (caries, procedures), less mineralized, containing irregular dentinal tubules

Terminology and Classification

• Liners: Thin layers placed in deep cavities beneath restorations

  • Actions:
    • Prevent chemical passage
    • Eugenol (sedative) relieves pulpal inflammation
    • Calcium Hydroxide stimulates reparative dentin and dentin bridging

• Bases (Cement Bases): Thick layers used beneath restorations

  • Actions:
    • Mechanical support for restorations, preventing disruption of the pulp
    • Thermal protection for the pulp
  • Materials:
    • Zinc Phosphate
    • Zinc Oxide-Eugenol
    • Zinc Poly-carboxylate
    • Glass Ionomer

Requirements of Ideal Dental Cements

• Nontoxic, Nonirritant
• Insoluble in Fluids
• Antibacterial Effect
• Obtunding Effect (Pain Relief)
• Chemical Adhesion to Tooth
• Low Film Thickness
• Thermal Expansion Matches Tooth Structure
• Dimensional Stability

Zinc Phosphate Cement

• Powder: 90% ZnO
• Liquid: 50% H3PO4
  • Aluminum Phosphate and Zinc Phosphate decrease reaction rate and stabilize pH

Zinc Polycarboxylate Cement

• Powder: Zinc Oxide
• Liquid: Poly-acrylic Acid or acrylic acid copolymer
  • Types: Conventional (separate powder and liquid), Water-Settable (powder and freeze dried poly-acid mixed with water)

Biocompatibility of Polycarboxylate Cement

• More compatible than Zinc Phosphate Cement:
  • Lower intrinsic toxicity
  • Faster rise in pH towards neutrality
  • Larger molecular size blocks dentinal tubules
  • Minimal fluid movement in dentinal tubules

Bonding to Tooth Structure

• 10% Polyacrylic acid conditioning for 10 seconds increases bond strength
• Chemical bonding (primary) via COOH groups with Calcium in hydroxyapatite
• Hydrogen bonding (secondary) between hydrogen and organic components of enamel and dentin

TheraCal LC

• Light-cured, resin-modified calcium silicate
• Actions:
  • Stimulates hydroxyapatite and secondary dentin bridge formation
  • Alkaline pH promotes healing and apatite formation
  • Protects and insulates the pulp
  • Moisture tolerant and radiopaque

Clinical Considerations

• Factors Influencing Liner/Base Choice:
  • Remaining Dentin Thickness (RDT)
  • Adhesive Materials
  • Type of Restorative Material
• Shallow Excavation (≥1.5-2 mm RDT):
  • Amalgam: Varnish, Dentin Sealer, or Bonding system
  • Composite: Bonding System
• Moderately Deep Excavation:
  • Amalgam: Liner (ZOE or Calcium Hydroxide)
  • Composite: ZOE contraindicated
• Deep Cavities: Calcium Hydroxide or RMGI (Glass Ionomer)
• Remaining Thickness: Ensure adequate final restoration thickness after liner/base placement

Summary

• Pulp protection is achieved through liners and bases to protect the pulp from irritation and inflammation.
• The choice of liner and base depends on the depth of the excavation, the material used for the final restoration, and the remaining dentin thickness.
• TheraCal LC is a light-cured, resin-modified calcium silicate ideal for pulpal protection due to its apatite-stimulation ability.

This quiz explores the objectives and mechanisms of pulp protection in dentistry. Learn about dentinal tubules, odontoblasts, and the body's defense mechanisms like sclerotic and tertiary dentin. Test your knowledge on linings and their purpose in dental procedures.