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(1) Adhesion - 09052018 (Uses (1) Reduce prep needed
For retention (CR)
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(1) Adhesion - 09052018
Uses
1) Reduce prep needed
- For retention (CR)
- Resin vs Amalgam
2) Reduce marginal leakage
- By setting contraction (CR)
- Polymerization contraction
- Adhesion compensates
4) Reduce caries
- Sealing pits and fissures
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3) Reduces post-op pain and pulp sensitivity
Definitions
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Adhesive/Adhesion: By chemical reaction or mechanical
Adherent: Solid substance which Adhesive is applied
Smear Layer
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Components
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Organic
- Gelatin (Heat friction deteriorated collagen)
- Pulp tissue
- Saliva, cells, microorganisms
Advantages:
- Physical Barrier for bacteria
- Resist fluid movements
- Restricting surface area available
Disadvantages:
- Causes weak bonding
- Nonhomogenous
- Might encourage
Principles of Adhesion
1st Law: Sufficiently close / related
- eg. Chemical Adhesion requires close contact
- Hydrogen bonding
- Covalent
- Ionic
- Visual inspection insufficient, microscopically?
2nd Law: Debris reduces contact
3rd Law: (Viscosity) Good adhesion requires <90deg contact angle :explode:
- High wetting
- High surface energy (Difference of intermolecular force between liquid bulk & liquid surface)
- High surface energy (Molecules on surface less bonded to other atoms, hence more energy)
- Low surface tension (Intermolecular force between atoms)
- (?) Does hydrophobicity and hydrophilicity affect? :question:
Clinical Applications
Scenarios
Adherent failure
- Separation between adhesive/adherent
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Challenges
A) Enamel vs Dentin
- composition
- unhomogenous
- Dynamic vs Static
- Constant outflow
- Closer to pulp
B) After caries free
- Debris
- Surface irregularities
C) Presence of water
- Prevents intimate contact
- Lower surface energy of surface :explode:
- Plasticizer
Solutions
1) Enamel - Acid Etching (B)
- Debris / Smear Layer
- Pores; Resin tags
- Increase surface area
- Increase surface energy of enamel :question:
- Might damage pulp! - if used on dentin
2) Dentin - Etch / Condition (B)
- Debris / Smear Layer
- Demineralize surface, increase pores :explode:
- Expose dentinal tubules :explode:
- Collagen Remains
3) Dentin - Primer (A + C) :explode:
- Composition
- Hydrophilic resin monomer (e.g HEMA)
- Organic solvents/vehicles (eg. Alcohol/Water/Acetone)
- Hydrophobic group
- Purpose
- HEMA: Improve Wettability + Expand collagen network
- Solvent: Displace water + Carry resin primer into dentin
- Hydrophobic group: Affinity for resin
4) Dentin - Adhesive (A)
- Composition
- Hydrophilic low viscosity resin
- Bond with hybrid layer & primer
Clinical Steps
- Isolation: Rubber dam, Saliva
- Pulp Protection: Calcium hydroxide liner
- Etching 37% Conditioning 10%
- Dentin Surface: Moist (Not over dried)
Types of Adhesion
Chemical
2) Thickness
- Less air voids
- Within interphase
- Between adherent/adhesive
3) Irregularities
- Increase bonding surface (and mechanical interlocking)
- Increasesd difficulty for viscous adhesives
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5) Bond Type
- Covalent & Ionic (stronger)
- Hydrogen (weaker)
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Generations of Adhesive
1st & 2nd: 1960-1970
- No dentin etching
- Adhesion to smear layer
- Weak (2 - 6 MPa)
3rd: 1980
- Acid dentin etching
- Remove smear layer
- Untouched smear plugs
- Separate primer
- Increased bond strength (12-15 MPa)
- Margin staining; clinical failure
4th: early 1990
- Acid dentin etching
- Separate primer
- Increased bond strength (~20 MPa)
- Adhesive penetrate etched (no smear) + decalcified dentin tubules (resin tags)
- Hybrid layer: Collagen & resin (Micro-mechanical)
- Bonding to wet substrate
- Margin staining; clinical failure
5th: mid 1990
- Primer + Adhesive combined
- ~20 MPa
- Unit dose packaging
6th: late1990, early 2000s
- Self-etching primer
- Reduce post-treatment sensitivity
- Lower bond strength
- Lower shelf life
7th: early 2000s
-Etchant, primer, adhesive all in 1 (3 in 1)
Acid Etching
- Remove 10um of enamel
- 5 - 50um porous layer
- Resin attracted to microporosities by capillary attraction
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Hybrid layer:
- Intermingled collagen & resin
- Resin interlock with tooth
- Micromechanical bonding
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Process:
1) Conditioner (10% polyacrylic acid) / Etchant
- Demin + Porosity + Smear
- Filled with water, collagen soft (Dry collapse)
2) Low viscosity monomer
- Fill porosity resin tags (capillary attraction) + etched surface
:question: Line?
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Top: Collagen fibrils spaces filled w resin
Middle: Collagen fibrils HA crystals replaced by resin
Bottom: Unaffected dentin' partial demineralized
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Enamel
- HA regular
- Less wetting
- Static structure/compo
Dentin
- HA irregular
- More wetting (difficult)
- Dynamic structure/compo
- Constant outflow of fluid
- Tubules pulp
- Closer to pulp
Too Dry: Collagen fibres collapse, ineffective penetration of adhesive into dentin
Just Right: Expansion of dentin
Too Wet: Dilute primer, competes for space in collagen network
Hydrophobic: Adhesive / Composite Resin
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