Operative Dentistry - Adhesive Dentistry I

Operative Dentistry - Adhesive Dentistry I

• The introduction of enamel and dentin adhesion marked a new era in Operative Dentistry.
• Adhesive techniques allow for more conservative tooth preparation.
• Less enamel removal is possible during procedures.
• Restorations can be repaired more effectively.
• Conservative aesthetic procedures are also facilitated.
• Resin-based dentistry relies on dental adhesives.

Adhesion

• Adhesion is the state where two surfaces are held together by interfacial forces, potentially including valence forces and interlocking forces.

Mechanisms of Adhesion in Dentistry

• Mechanical penetration: Resin penetrates the tooth surface forming resin tags.
• Adsorption: Chemical bonding to inorganic components (hydroxyapatite) or organic (type I collagen).
• Diffusion: Precipitation of substances on tooth surfaces for mechanical or chemical bonding with resin monomers.
• A combination of the above three mechanisms is often observed.

Failure of Adhesion

• Cohesive failure can occur in the substrate, adhesive, or restorative material.
• Adhesive failure occurs at the interface between the substrate, restorative material, and adhesive.

Bonding System Considerations

• Adhesive strategies (e.g., dry vs. wet bonding, direct vs. indirect).
• Materials compatibility (e.g., silica-based porcelain, zirconia).
• Factors like solvent use, dual curing, and sensitivity.

Enamel Adhesion

• Acid etching (using phosphoric acid, 35% for at least 30 seconds) prepares the enamel surface.
• The etched surface creates resin tags in the enamel.
• This process leads to high bond strength and a reliable bond.

Dentin Adhesion

• Materials can bond with dentin either mechanically or chemically, or both.
• Micromechanical interlocking of resin into the collagen fibrils, left exposed by acid etching, is a primary mechanism.
• Glass ionomer cements and some phosphate-based self-etch adhesives facilitate chemical bonding.

Dentin as a Dynamic Substrate

• Dentin is a dynamic tissue, making adhesion difficult and unpredictable.
• Dentin contains water and organic substances (mainly type I collagen).

Challenges in Dentin Adhesion

• Dentin's dense network of tubules connecting the pulp with the DEJ.
• Increasing number and size of tubules closer to the pulp.
• Lower adhesion quality closer to the pulp (tubules occupy only 1% of the surface near the DEJ vs 22% near the pulp).
• Dentin is an intrinsically hydrated tissue with collagen-lined intertubular dentin.
• Resins are hydrophobic.
• Collagen degradation by dentin proteinases can negatively affect the bonded interface.
• Smear layer: formation of organic/inorganic debris on the tooth surface after preparation with a bur or instrument.
• Smear layer fills dentin tubules forming "smear plugs", decreasing dentin permeability by nearly 90%.

Dentin Adhesion - Steps

• Step 1: Acid etching (remove smear layer, demineralize inter-tubular and peri-tubular dentin, expose collagen fibrils).
• Step 3: Application of liquid acrylic monomers (hydrophobic) as a final layer.

Hybrid Layer Formation

• Resin infiltration of acid-etched dentin transforms the surface from crystalline to an organic, acid-resistant, and hydrophobic structure.

Wet Dentin Adhesion

• A method of bonding tooth structure using phosphoric acid as a conditioner. Improves bond strength through acid-etching of dentin and bonding to wet dentin surfaces.
• Drying etched dentin greatly reduces its volume and leads to a poor hybrid layer.
• The collagen fiber network of etched dentin literally floats in water.