What parts of composite bonding involve chemical bonding with enamel and micromechanical retention with dentine, compared to Glass Ionomer Cement (GIC)?

Composite Bonding vs GIC: Mechanisms in Enamel and Dentine

Direct Answer

Composite bonding to enamel relies on micromechanical retention through acid-etched enamel tags, while bonding to dentine involves both micromechanical retention (via resin tag formation in dentinal tubules) and minimal chemical bonding; in contrast, GIC achieves true chemical bonding to both enamel and dentine through ionic exchange with hydroxyapatite, making it fundamentally different from composite systems. 1, 2

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Composite Resin Bonding Mechanisms

Bonding to Enamel

• Micromechanical retention is the primary mechanism when bonding composite to enamel, achieved through phosphoric acid etching that creates microscopic irregularities and tags in the enamel surface 1, 3
• The acid-etch technique creates a retentive surface by forming crystalline interfaces that allow resin penetration, providing purely mechanical interlocking without chemical bonding 3
• No chemical bonding occurs between composite and enamel—the bond is entirely dependent on mechanical interlocking of resin into etched enamel porosities 1

Bonding to Dentine

• Dentine bonding involves predominantly micromechanical retention through resin tag formation within dentinal tubules and infiltration of the demineralized collagen network (hybrid layer) 1, 4
• Some minimal chemical interaction may occur between dentine bonding agents and collagen/hydroxyapatite, but this is secondary to the micromechanical component 1
• The bond to dentine is significantly weaker than to enamel (approximately 12 MPa vs 20 MPa), reflecting the more challenging nature of dentine bonding 5
• Multi-step dentine bonding systems can achieve continuous margins in dentine ranging from 37% to 91.2% depending on the system and technique used 4

Critical Moisture Sensitivity

• Composite bonding is highly moisture-sensitive and requires absolute dryness—moisture contamination prevents proper adhesion and leads to restoration failure 6, 7
• Contamination with saliva, plasma, or other substances can lower bond strength by 20% to 100%, though re-etching can restore bond strength to control levels 5
• Resin-modified glass ionomer cement (RMGIC) shares this moisture sensitivity with composite systems and requires completely dry surfaces for proper adhesion 8, 6

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Glass Ionomer Cement (GIC) Bonding Mechanisms

Chemical Bonding to Both Substrates

• GIC achieves true chemical adhesion to both enamel and dentine through ionic exchange between the polyalkenoic acid in the cement and calcium ions in tooth hydroxyapatite 2
• This chemical union between GIC and dentine is accepted as a long-term, stable bond that does not rely on mechanical retention 2
• The chemical bonding mechanism makes GIC fundamentally superior to composite in terms of adhesion reliability, particularly in compromised clinical situations 2

Unique Moisture Tolerance

• Traditional GIC tolerates moisture during setting, making it the material of choice when optimal moisture control cannot be achieved 8, 6
• This moisture tolerance is recommended for managing cavitated lesions in young, uncooperative children and field settings where dental therapists work without optimal moisture control 8
• GIC should be used only when traditional moisture control is impossible—it represents a compromise in material selection based on isolation limitations rather than optimal treatment 6

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The "Sandwich Technique" Concept

Combining Both Mechanisms

• The sandwich technique uses GIC as a base (providing chemical bonding to dentine) with composite overlay (providing superior aesthetics), creating a mechanical union between GIC and composite 2
• This approach leverages the chemical adhesion of GIC to dentine at margins located in dentine, while using composite for the bulk restoration 4, 2
• The strength of the GIC-to-composite union varies widely depending on materials and handling methods, requiring careful technique 2

Clinical Application Considerations

• Studies show that using resin-modified GIC liners had no beneficial effect on marginal parameters in either dentine or enamel when compared to total bonding techniques with state-of-the-art multi-step bonding systems 4
• The sandwich technique is most relevant when gingival margins are located in dentine, where composite bonding alone may be compromised 4, 2

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Key Clinical Distinctions

Material Selection Algorithm

1. When optimal moisture control is achievable: Use composite with multi-step dentine bonding systems for superior aesthetics and mechanical properties 6, 4
2. When moisture control is compromised: Use traditional GIC, which tolerates moisture during setting 8, 6
3. Never use RMGIC or composite without adequate moisture control—these materials are moisture-sensitive and will fail 6

Common Pitfalls to Avoid

• Do not proceed with composite bonding if complete dryness cannot be achieved—moisture contamination is a primary cause of restoration failure 6, 7
• Recognize that dentine margins are inherently more challenging than enamel margins, with lower bond strengths and higher risk of marginal gap formation 4, 5
• Re-etching after contamination can restore bond strength to control levels, but prevention of contamination is preferable 5
• Ensure meticulous incremental filling technique when using composite in Class II restorations to minimize marginal defects 4