Dental Biomaterials I - Adhesion Concepts

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Questions and Answers

What is the effect of a thicker adhesive film on adhesion strength?

It minimizes setting contraction stresses.

It reduces thermal stresses.

It enhances bonding strength.

It increases air voids. (correct)

Which factor has the least impact on the adhesive strength between enamel and dentin?

Surface cleanliness

Presence of water

Color of adhesive (correct)

Thickness of adhesive

How does thermal stress affect the adhesion strength?

It creates stresses in the bond. (correct)

It increases the bond strength.

It makes the adhesive more flexible.

It eliminates the need for a debubblizer.

What is a primary bond in adhesive applications?

Covalent bonds Signup and view all the answers

Which condition is most likely to prevent ideal adhesion in the oral cavity?

Presence of water in the cavity. Signup and view all the answers

What is the relationship between surface irregularities and adhesive application?

Irregularities hinder intimate contact. Signup and view all the answers

What happens if debris contaminates an adherent before adhesion?

Intimate contact is prevented. Signup and view all the answers

Why is close matching of thermal expansion coefficients important in adhesion?

It minimizes stresses in the bond. Signup and view all the answers

What effect does wetting have on the strength of the adhesive junction?

Increases the ability to spread over the adherend Signup and view all the answers

Which factor primarily influences the ability of an adhesive to spread over an adherend?

The surface energy of the adherend Signup and view all the answers

Thermal stresses can affect adhesive bond strength by:

Creating expansion or contraction of materials Signup and view all the answers

How does the cleanliness of the adherent influence adhesive strength?

Clean surfaces ensure better chemical bonding Signup and view all the answers

What is the likely effect of increasing the thickness of the adhesive layer?

Reduces bond strength due to increased distance Signup and view all the answers

Which type of bond is least effective in adhesion compared to others?

Physical bond Signup and view all the answers

What role does the setting contraction of adhesive play in bond strength?

It causes tensile stresses that may weaken the bond Signup and view all the answers

When considering factors for effective adhesion, which of the following is critical?

Intimate contact between materials Signup and view all the answers

What effect does increasing surface energy of a solid have on wettability?

Increases wettability Signup and view all the answers

How does surface tension in a liquid contribute to good wetting?

It attracts adhesive molecules more than themselves Signup and view all the answers

Which of the following statements about viscosity is correct in relation to adhesion?

Lower viscosity allows easier flow and spreading Signup and view all the answers

What impact do deep irregularities on an adherend's surface have on adhesive bonding?

Create air pockets that hinder bonding Signup and view all the answers

What is a consequence of regular and shallow surface roughness on an adherend?

Increases surface area and promotes good bonding Signup and view all the answers

Why is good wettability important in dentistry?

It prevents marginal leakage Signup and view all the answers

Which material is known for having low surface energy, making it difficult to wet?

Teflon Signup and view all the answers

What role do surface acting agents play in adhesion processes?

They promote better wetting of surfaces Signup and view all the answers

Study Notes

Dental Biomaterials I - Dental Adhesion

Course Title: Dental Biomaterials I
Course Code: BDS011
Topics to be covered include: basic concepts and definitions, importance of adhesion in dentistry and dental considerations, surface tension and surface energy, classification of adhesion, factors affecting the strength of an adhesive junction and method of testing, bonding to enamel and dentin.

Adhesion and Cohesion

Adhesion: Bonding between dissimilar atoms and molecules.
Cohesion: Bonding between similar atoms and molecules (e.g., gold foil dental restoration)

Adhesive and Adherend

Adhesive: Liquid material used to produce adhesion.
Adherend: Solid substance to which the adhesive is applied.
Key to adhesion: materials must be in close contact, adhesive must be in liquid state with low viscosity, and produce a thin layer.

Types of Adhesion

Chemical (true adhesion): Chemical bonding between dissimilar materials (e.g., glass ionomer and zinc polycarboxylate with the tooth). Glass ionomer and polycarboxylate cements contain COOH groups that react chemically with calcium in the tooth.
Mechanical (macro-mechanical & micro-mechanical): Bonding between dissimilar materials through mechanical interlocking. No actual bond is formed. Examples include implants, amalgam, composite, and zinc phosphate cement.
Physical: Weaker than chemical, using physical force.
- Example: complete denture.

Factors Affecting Adhesive Junction Strength

Wetting: Ability of adhesive to spread over the surface of the adherend.
- Measured by contact angle:
 - Θ > 90°: Poor wetting
 - Θ < 90°: Good wetting
 - Θ = 0°: Excellent wetting
- Factors affecting wetting include surface energy, surface tension, viscosity, and surface irregularities (roughness) of the adherend.
- Surface energy: Force of attraction between surface atoms of the solid. Surface atoms have higher energy than atoms inside.
- Surface tension: Force of attraction between surface atoms of a liquid. Atoms on the surface are strongly attracted to the interior. Increasing surface tension of adhesive decreases wettability.
Stresses due to setting contraction of adhesive
Thermal stresses: Large difference in coefficient of thermal expansion and contraction between adhesive and adherend can produce stresses in the bond. Needs close matching to minimize these stresses and increase the strength of adhesion.
Cleanliness of the adherend: Debris or surface contaminations prevent intimate contact, essential for adhesion. Adhesion to clean and dry surfaces (enamel and dentin) is better than to wet, contaminated surfaces.
Thickness of adhesive: Thinner adhesive films lead to stronger adhesive junctions with fewer air voids and less thermal stress due to setting contraction.
Type of bond formed: Primary bonds between adhesive and adherend produce stronger adhesion compared to secondary bonds (e.g., soldered joint stronger than glued joint).

Failure of Adhesive Junction

Adhesive failure: Adhesive-adherent separation
Cohesive failure of the adhesive
Cohesive failure of the adherend

Obstacles to Adhesion in the Oral Cavity

Inhomogeneous composition of enamel and dentin: Enamel and dentin are comprised of organic and inorganic parts; adhesion is not uniform over the entire surface.
Surface irregularities in the prepared cavity: Prepared cavity surfaces are full of pits and fissures, resulting in increased roughness, making it difficult for adhesives to flow and wet the entire surface.
Debris in prepared cavity: Debris prevents intimate contact, essential for adhesion.
Presence of water in the prepared cavity: Water from dentinal tubules forms a film preventing intimate contact between the adhesive and tooth.

Bonding to Tooth Structures

Enamel bonding involves acid etching, bonding adhesive application, and composite filling.
Acid etching (30-50% phosphoric acid for 30 seconds) removes 5 um of enamel and produces micropores, increasing surface energy and area for adhesion.
Application of adhesive and composite filling completes the process.
Dentin bonding presents greater obstacles due to higher water content, presence of a smear layer, and lower surface energy of dentin; it requires etching, primer application, bonding agent, and final composite application to complete the process.

Formation of Hybrid Layer

Resin infiltrated dentin, a resin-reinforced layer part tooth and part resin.

Additional Notes

Image descriptions and detailed materials are omitted per prompt instructions.

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Description

Explore the fundamental principles of dental adhesion in this quiz. Covering topics ranging from the importance of adhesion in dentistry to the types of adhesion and factors affecting adhesive strength, this quiz is essential for dental students. Test your knowledge on critical concepts that aid in understanding adhesive materials and their application in dental treatments.