Surface Chemistry in Dentistry

Surface Chemistry (Bonding and Adhesion)

• The presentation focuses on surface chemistry, particularly bonding and adhesion, in dentistry.
• Learning objectives include defining bonding types, understanding bonding and adhesion mechanisms, recognizing factors affecting adhesion, understanding clinical significance, and familiarity with acid etching.
• Surface properties are crucial in dentistry because of the importance of interfaces, such as implant-cells, enamel-dentin-bonding resin, and orthodontic bracket-enamel.

Introduction

• Scientific understanding of materials-tissue and materials-materials interfaces is increasing in dentistry.
• Interfaces in dentistry include implant-cells, enamel-dentin bonding resin, and orthodontic bracket-enamel.

Implant-tissue Interface

• Depicts a diagram of an implant and natural tooth, highlighting the implant-tissue relationship.
• The implant is a porcelain crown with a metal implant embedded in the jawbone.

Bonding of Orthodontic Brackets

• Shows images of orthodontic brackets on teeth.

Cementation of Artificial Crowns

• Illustrates the process of cementing artificial crowns onto teeth.

Bonding Composite Resin Filling

• A visual example of composite resin fillings on teeth.

Bonding Mechanisms

• Bonding can be achieved chemically (cohesion and adhesion) or mechanically (interlocking).

Cohesion

• The attraction between atoms or molecules of the same kind within a material.
• Primarily involves chemical primary bonds.

Adhesion

• The attraction between atoms or molecules of different kinds in contact.
• Surfaces can be divided into substrate and adsorbed layers.
• Adsorption can involve chemical reactions (chemisorption) or weaker interactions (physisorption).

Definitions

• Adhesive: The material applied to create adhesion.
• Adherend (substrate): The material the adhesive is applied to.

Adhesion between Two Solid Surfaces

• Illustrates a diagram of two surfaces with an adhesive in between them.

Dental Bonding Challenges

• True chemical bonding between tooth structure and restorative/luting materials is difficult in dentistry due to the complex composition of substrates (such as dentin), the presence of contaminants, and water.

Exceptions to Chemical Bonding

• Zinc polycarboxylate, glass ionomer, and resin-modified glass ionomer are dental materials capable of chemical interaction with hydroxyapatite.

Primary Adhesion Mechanism

• Micro and macro mechanical interlocking are the primary mechanisms of adhesion used in dental practice.

Physical Bonding

• Physical bonding (van der Waals forces) exists between any two contacting materials, but it is especially weak in wet environments.

Factors Affecting Adhesion (Bonding)

• 1. Surface Energy of the Solid: Surface energy is higher than the interior of solids; higher surface energy of the solid increases adhesion.
• 2. Surface Tension of the Liquid: Surface tension of liquids, like an adhesive, influences adhesion and can be altered based on the nature of liquid molecules, temperature, or the presence of impurities. Lower surface tension increases adhesion.
• 3. Wettability: A liquid's tendency to spread over a solid surface. Increased wettability leads to higher adhesion. Wettability is demonstrated by contact angles.
  • Contact angle, the angle created between a liquid and a solid surface, determines wettability. Smaller angles lead to greater wettability.
    • Hydrophilic materials have contact angles < 90°
    • Hydrophobic materials have contact angles > 90°
• 4. Other Factors: Affecting adhesion include:
  • Viscosity: Low viscosity of adhesive increases bonding.
  • Impurities: The less impurities on surfaces, the greater the adhesion.
  • Surface roughness/area of contact: Wider contact areas between two materials and more roughness improves adhesion.
  • Dimensional stability, temperature, film thickness.

Mechanical Bonding (Interlocking)

• Macro-interlocking: Occurs due to the shaping of the tooth structure and the surface roughness of the tooth and crown.
• Micro-interlocking: Achieved by acid etching.

Acid Etching

• Acid etching involves applying an acid (e.g., 37% phosphoric acid) to tooth structures for a short period to remove inorganic content, creating micropores.
• These micropores are subsequently filled with bonding agents and restorative materials.

Acid Etching and Composite Filling Procedure

• Showed step-by-step instructions on acid etching and composite filling procedures.

Etched Enamel/Resin Tags

• Scanning electron micrographs showing etched enamel surfaces with resin tags.

Etching of Dentin

• Scanning electron micrographs showing dentinal surfaces before/after etching, highlighting changes to tubules.

Bonding Composite Resin with Dentin

• Illustration of the composite resin bonding process with dentin.
• Involved steps of acid-etching, rinsing, applying bonding agent, applying composite, and curing.

Capillary Rise

• Penetration of liquids into narrow spaces, relevant to caries progression and the way restorative materials fill cavities.
• Occurs only when the contact angle between the solid and liquid is less than 90 degrees
• Capillary rise is affected by the gap width.

Clinical Significance of Surface Energy and Wettability

• Waxes are hydrophobic and need wetting agents on their surface for adhesion.
• Fluoride reduces plaque accumulation on teeth by decreasing enamel surface energy.
• Surfactants are added to hydrophobic impression materials to enhance wettability.

Lost Wax Technique and Porcelain Making

• Describes the steps involved in creating dental prostheses using the lost wax technique.

Spraying Wax Pattern with Surfactant and Investing

• Explains the steps in preparing a wax pattern for casting.

Casting Ring Before and After Filling with Investment

• Illustrates the steps in preparing a casting ring for use.

This quiz explores the principles of surface chemistry as they relate to bonding and adhesion in dentistry. Key topics include bonding mechanisms, factors that influence adhesion, and the clinical significance of these concepts in dental practice. Enhance your understanding of how interfaces between materials affect dental procedures.