Dental Bonding Techniques Overview

Introduction

• Adhesion is an essential requirement for restorative dental materials.
• The development of bonded tooth-colored restorations has revolutionized restorative dentistry, eliminating the need for the "extension for prevention" concept.

Benefits of Bonded Restorations

• Initial seal: Prevents microleakage, postoperative sensitivity, and secondary caries.
• Strengthening: Contributes to the "one block concept" by reinforcing the remaining tooth structure.
• Conservation: Minimizes the need for additional mechanical retention, preserving sound tooth structure and maximizing restoration durability.

Terminology

• Adhesion/Bonding: The process of holding two surfaces together using interfacial forces, including valence forces and interlocking.
• Adhesive: A bonding agent that joins surfaces, resists separation, and transmits loads across the bond.
• Adherent: The surface or substrate being adhered to.
• Adhesive joint/bonded interface: The area where the adhesive and adherent meet.

Bonding Mechanisms

• Micro-Mechanical: Resin penetrates the tooth surface, forming resin tags.
• Adsorption: Chemical bonding to inorganic (hydroxyapatite) or organic (mainly type I collagen) components of tooth structure.
• Combination: Incorporates both micro-mechanical and adsorption mechanisms.

Requirements for Good Adhesion

• Clean and Wettable Surface: Requires high surface energy for proper adherence.
• Low Surface Tension: Adhesive should have a low contact angle, wet the substrate effectively, and spread evenly.
• Intimate Adaptation: The adhesive should fit closely with the adherent.
• Curing/Polymerization: The adhesive must be properly cured or polymerized for optimal bond strength.
• Strong Bond Strength: Sufficient bond strength resists debonding.

Enamel Bonding

• Acid Etching: Introduced by Buonocore in 1955, this technique transforms smooth enamel into an irregular surface with micro-pores, increasing surface free energy.
• Bonding Agents: These agents flow into the microporosities of etched enamel and form resin tags when polymerized by light activation, locking them to the enamel surface.
• Bond Strength: The bond strength between composite resins and etched enamel ranges from 20 to 50 Mpa, providing adequate retention for various procedures and preventing leakage around restoration margins.

Acid Etching Process

• Acid Concentration: 37% phosphoric acid is the preferred concentration.
• Etching Time: 15 seconds is standard.
• Rinsing: The etched surface should be rinsed with a continuous stream of air-water spray for double the etching time.
• Drying: Proper drying produces a frosty white appearance.
• Optimum Etching: Creates a mono-calcium phosphate monohydrate precipitate that can be easily rinsed off.

Acid Etchant Forms

• Liquid and Gel Forms: Gel etchants are preferred because they provide better control over placement on the enamel surface.
• Syringe Application: Allows for easy and precise placement of the acid gel.

Dentin Adhesion

• Hybrid Layer: The adhesive monomers penetrate collagen fibers exposed by acid etching, forming a hybrid layer.
• Resin Tags: Adhesive monomers also penetrate dentinal tubules, forming resin tags.

Challenges in Dentin Bonding Compared to Enamel

• Chemical Composition: Dentin has a lower mineral content (more water and organic material) and a higher organic content (primarily type I collagen) than enamel.

Explore the essential concepts of dental adhesion and bonding techniques used in restorative dentistry. This quiz highlights the benefits of bonded restorations and key terminology related to the adhesion process. Understand how these techniques enhance dental restorations and preserve tooth structure.