Dental Ceramics Bonding Principles

Introduction

• Clinical success of resin-bonded ceramic restorations depends on ceramic material properties, tooth prep design, impression technique, fabrication process, definitive insertion protocol, and bonding protocol.

Definitions

• Adhesion is the attraction between unlike molecules
• Cohesion is the attraction between like molecules
• An adhesive is a material that causes adhesion or bonding
• An adherend is the material to which the adhesive is applied

Importance of Bonding

• Bonding systems provide resistance to separation of adherend substrate
• Bonding systems distribute stress
• Bonding systems seal dentin and enamel

Bonding Principles in Dental Ceramics

• Strong and durable bond between ceramic materials and the tooth or prosthetic substrate is crucial
• Bonding is crucial for longevity, aesthetic quality, and function

Bonding to Silica-Based Ceramics

• HF Acid Etching: hydrofluoric acid (HF) selectively dissolves the glass phase to expose silicon dioxide (SiO2) and create microretentive surfaces
• Surface Topography: acid etching increases roughness, facilitating micromechanical interlocking with resin cements

Silane Coupling Agent

• A silane coupling agent is applied after etching to form chemical bonds between ceramic surface and resin cements.
• Silane enhances adhesion as it can create a covalent bond with both the ceramic and the resin

Silane Coupling Agent - Chemical Reaction

• Surface Activation (Etching) of the Glass Ceramic: Etching with HF creates microporosities and exposes silica (SiO2)
• Application of Silane Coupling Agent: Silane is a bifunctional molecule with Silicon (Si) and Methacrylate groups, allowing it to bond to the ceramic and resin
• Hydrolysis of Silane Molecule: Silane requires moisture to hydrolyze and activate
• Condensation Reaction with Ceramic Surface: Silane reacts with the ceramic to form a durable chemical bond
• Polymerization with Resin Cement: Silane forms a bond with the resin

Resin Cement Selection and Properties

• Light-Cure Resin Cements: provide extended working time and ease of removal
• Dual-Cure Resin Cements: combine light-activated and chemical-activated systems, achieving high degrees of polymerization while providing a longer working time

Bonding Protocols

• Total-etch systems provide stronger bonds and reduce microleakage

Microstructure and Mechanical Properties

• The microstructure of feldspathic ceramics influences their mechanical performance, particularly the balance between the glass and crystalline phases.
• Higher glass content generally enhances translucency but can compromise strength.

Acid Etching Chemistry

• HF etching involves the reaction of HF with silica to form soluble silicates
• Topographic Changes: Dissolution of the glass phase results in increased surface roughness

Bonding to Leucite-Reinforced Glass Ceramics

• Composition and Properties: Leucite-reinforced feldspathic ceramics contain up to 45% leucite, which enhances the material's mechanical properties.
• Flexural Strength: Leucite-reinforced exhibits medium flexural strength values of up to 140 MPa, exceeding traditional feldspathic ceramics.
• Crack Propagation Resistance: Leucite acts as a crack reflector, redirecting and mitigating crack propagation, enhancing the durability of the ceramic.

Bonding to Lithium Silicate Ceramics

• Resin Cement Performance: Various resin cements produce long-term durable bonds
• Mechanical Properties: Leucite and lithium disilicate enhance the ceramic's ability to withstand stress and resist fracture.
• HF Acid Etching Chemistry: HF selectively dissolves glass phase and increases surface area and roughness
• Silane Chemistry: Silane coupling agents form siloxane bonds with etched ceramic surface

Bonding to Polymer-Infiltrated Ceramic Network (PICN) Materials

• PICN is a dual-network structure with a ceramic skeleton and infiltrated resin phase
• PICN materials combine ceramics and polymers, featuring an interpenetrating network made of aluminum oxide-enriched leucite and urethane dimethacrylate and triethylene glycol dimethacrylate

Bonding to Metal-Oxide Ceramics

• Mechanical Properties: 3Y-TZP exhibits the highest fracture toughness and flexural strength among zirconia generations
• Transformation Toughening: The tetragonal-to-monoclinic phase transformation enhances fracture toughness

Bonding Procedures

• Surface Pretreatment Methods: effective techniques include APA, tribochemical silica coating, low-fusion porcelain application, and laser irradiation
• MDP Primers: application of 10-methacryloyloxydecyl dihydrogen phosphate (MDP) or phosphate ester monomer-based primers is essential for durable resin bonds
• Preferred Protocol:
  • APC Bonding Concept: APA with alumina or silica-coated particles, followed by priming with an MDP-based primer, followed by application of dual or self-cure composite resin cement

Considerations for Recent Zirconia Generations

• High-Translucent Zirconia: 4Y-TZP and 5Y-TZP zirconia generations enhance esthetics by increasing yttria content
• Bonding Protocols: bonding methods for 3Y-TZP also apply, but surface pretreatment is critical to avoid compromising mechanical properties
• Studies indicate that surface treatments do not adversely affect the flexural strength of newer zirconia generations

Cleaning and Contamination Prevention

• Importance of Isolation: proper isolation during resin bonding is crucial to prevent contamination, which can compromise bond strength
• Cleaning Methods:
  • Recommended Solutions: Alcohol solutions and phosphoric acid
  • Effective Decontamination: APA with alumina particles
  • Commercial Cleaning agents: Ivoclean, Katana Cleaner, and ZirClean effectively remove contaminants and proteins

Explore the essential aspects of bonding in dental ceramics, including definitions, importance, and techniques such as HF acid etching. This quiz will enhance your understanding of adhesive systems and their role in dental restorations.