Fundamentals of Enamel and Dentin Adhesion

Fundamentals of Enamel and Dentin Adhesion

• The presentation covers fundamental concepts of enamel and dentin adhesion.
• A key reference is the "Art and Science of Operative Dentistry" 6th edition, chapter 4, page 114.
• Learning objectives (ILOs) include understanding adhesion mechanisms of dental resins, determining enamel bonding procedures, identifying dentin adhesion challenges, and discussing current resin-dentin adhesion strategies.
• Introduction: Adhesion is crucial for restorative materials. Bonded tooth-colored restorations offer advantages over traditional methods, eliminating the need for extensive preventive procedures like those developed by G.V. Black.
• Bonded restorations encourage initial seal (preventing secondary caries), strengthening remaining tooth structure, and conservation (reducing mechanical preparation needed).

Basic Terminology

• Adhesion/Bonding: The state where two surfaces are held together by interfacial forces (valence, interlocking, or both).
• Adhesive: The bonding agent that joins surfaces, resists separation, and transmits loads across the bond.
• Adherend: The surface or substrate to which the adhesive is applied.

Bonding Mechanisms

• Micro-Mechanical: Resin penetration and creation of resin tags within tooth surfaces.
• Adsorption: Chemical bonding with tooth's inorganic (e.g., hydroxyapatite) or organic components (primarily type I collagen).
• These mechanisms often work in combination.

Requirements for Good Adhesion

• Surface Energy: Tooth surfaces need to be clean and wettable with high surface energy for proper adhesion.
• Low Surface Tension: Adhesion products should have low surface tension to effectively spread on the surface, having a low contact angle.
• Intimate Adaptation: A close fit between the adhesive and the tooth surface is necessary.
• Polymerization: The adhesive material needs proper curing/polymerization to strengthen the bond.
• Strong Bond Strength: Sufficient bond strength between the adhesive and the tooth surface is needed to resist de-bonding.

Bonding to Enamel

• Acid Etching: A critical step in enamel bonding; it creates micropores on the enamel surface, increasing surface energy, allowing for strong resin tags formation. Buonocore introduced it in 1955.
• Acid Concentration: Currently, 37% phosphoric acid is the preferred concentration.
• Etching Time: 15 seconds is the recommended etching time.
• Rinsing Time: The rinsing time should be double the etching time, using a continuous stream of air-water spray.
• Application Technique: Acid etchants may be available in liquid or gel forms; gel forms are more commonly preferred for improved control during application.
• Bonding Agents: These agents flow into the microporosities and, upon light activation, form resin tags that lock them into the tooth surface. Bond strength usually ranges from 20 to 50 MPa.

Bonding to Dentin

• Challenges Compared to Enamel: Dentin has significantly less mineral content and higher water content than enamel; water content significantly impacts bonding.
• Microstructure: Dentin tubules increase in size going from the outer to the inner aspects, potentially reducing bond strength in deeper sections. Dentin is considered a dynamic tissue, able to change due to aging, cavities or even restorative interventions (such as sclerotic dentin that resist etching).
• Smear Layer: A layer of debris and denatured collagen forms on cut dentin surfaces. This smear layer inhibits bonding by decreasing dentin permeability by 85%, blocking access for adhesives.

This quiz explores the foundational concepts of enamel and dentin adhesion, as outlined in chapter 4 of 'Art and Science of Operative Dentistry'. Participants will learn about adhesion mechanisms, enamel bonding procedures, and current strategies for resin-dentin adhesion. Understanding these principles is essential for advancing restorative dentistry practices.