essay 24 - adhesive sustems - definition, classification, types, properties and indications. Characteristics of the micromechanical bond to enamel and dentin

define adhesive systems

• Adhesion is the process where two surfaces are held together by interfacial forces (mechanical interlocking, valence forces or both)

• an adhesive is a material that joins two substrates and transfers load between them

• In dentistry, adhesion is often referred to as bonding forming adhesive joint between tooth surfaces (enamel/dentin) and restorative materials

classification of adhesion

• adhesion is classified based on the bonding mechanism

1. mechanical bonding - interlocking with surface irregularities; most common in dentistry. This bonding occurs when a bonding agent is mechanically interlocked into micro-undercuts on tooth surfaces

2. Chemical bonding - ionic and covalent bonds across the interface. This bonding occurs as reactive sites on polymers form primary bonds with surfaces of tooth structure

3. Physical bonding - weak van der waals or electrostatic interactions. This bonding occurs when negative and positive sites on polymer and on tooth structure are attracted electrostatically

what are classification of bonding (adhesion) systems by the number of application steps?

1. Three step (fourth generation) - etch + prime + bond (E+P+B)

2. Two step (fifth generation) - etch + combined prime/bond (E+PB)

3. self etching primers (SEPs) - combine etch and prime (nEP+B)

4. self etching adhesives (SEAs, all in one) - etch, prime and bond in one bottle

types of adhesives systems

• Enamel bonding systems - unfilled/lightly filled acrylic monomers applied to acid - etched enamel

• Dentin bonding systems (total etch) - hydrophilic primers and bonding agents applied after etching

• Self etch systems - combine etching with priming and bonding, do not require rinsing

• Universal adhesives - bond to various substrates (enamel, dentin, ceramic and composite, metals)

properties of adhesive systems

• Bond strength:

— enamel = -18-22 MPa (macrotags and microtags)

— dentin = 22-35 MPa (mainly micromechanical with hybrid layer)

• micromechanical retention is critical for both enamel and dentin

• Smear layer must be modified or removed for effective bonding

• wetting ability: good wetting (low contact angle) is essential for adhesion

• moist bonding: preferred for dentin to avoid collagen collapse

• hybrid layer: zone where resin intermingles with etched dentin for bonding

• postoperative sensitivity: less with self-etching systems

• durability: enamel bonding is more stable; bonding is more complex and moisture sensitive

indications for use of adhesive systems

1. class I-V composite restorations

2. aesthetics procedures (veneers, contour modifications)

3. bonding indirect restorations (ceramic, resin, metal)

4. orthodontic bracket bonding

5. pit and fissure sealing

6. dentin desensitization

7. periodontal splinting

8. repair of existing restorations

9. bonding posts and core build ups

10. sealing root surfaces and apical restorations

characteristics of the micromechanical bond to enamel and dentin

1. to enamel

• achieved by acid etching (30-40% phosphoric acid)

• Creates:

— macrotags: form between enamel rods

— microtags: form within enamel rods

• microtags provide most of the bond strength

• Three etching patterns:

— Type I: prism cores dissolved

— Type II: prism peripheries dissolved

— Type III: irregular pattern

2. To dentin

• More challenging due to:

— high water content

— organic collagen matrix

— tubule fluid flow (pulpal pressure)

• etching removes the smear layer, exposing the collagen network

• hydrophilic primers (e.g HEMA) used for wetting

• formation of hybrid layer and resin tags

• majority of bond strength (-90%) is micromechanical

• Moist bonding prevents collagen collapse and improves monomer particles

characteristics of the micromechanical bond to enamel

• achieved by acid etching (30-40% phosphoric acid)

• Creates:

— macrotags: form between enamel rods

— microtags: form within enamel rods

• microtags provide most of the bond strength

• Three etching patterns:

— Type I: prism cores dissolved

— Type II: prism peripheries dissolved

— Type III: irregular pattern

characteristics of the micromechanical bond to dentin

• More challenging due to:

— high water content

— organic collagen matrix

— tubule fluid flow (pulpal pressure)

• etching removes the smear layer, exposing the collagen network

• hydrophilic primers (e.g HEMA) used for wetting

• formation of hybrid layer and resin tags

• majority of bond strength (-90%) is micromechanical

• Moist bonding prevents collagen collapse and improves monomer particles