Adhesion in operative dentistry- Basic concepts Flashcards
Define Adhesion:
Adhesion or bonding is the attachment of one substance to another. Force of interatomic attraction, strong (ionic, covalent, metallic) or the attraction between unlike molecules, weak (Van der Waals forces, hydrogen bonds)
What is chemical adhesion?
Interatomic attractions: swap or share electrons (ionic, covalent or metallic bonding)
What is physical adhesion?
Intermolecular attraction (Van der Waals forces, hydrogen bonds)
What is mechanical adhesion?
Macroscopic or microscopic interlocking and cementation.
Chemical adhesion (primary or real adhesion)
- It does not have much clinical significance.
- The adhesive resins (VERY WEAK), GICs and polycarboxylate resins
have real adhesion to the tooth (E and D). - Their carboxylic radicals bind to the Ca of the hydroxyapatite and
collagen organic portion.
What means adhesion in dentistry?
The forces or energies between atoms or molecules at an interface that hold two surfaces together.
Physical, chemical and mostly micromechanical interaction between an adhesive (C) and the substrates (A & B)
What components does Adhesion include?
- composite resins
- adhesion interface
- Dental tissue: enamel and dentin
What do we need to create in order the adhesive can penetrate?
micro retentions
How is the process called when we form micro retention?
This process is called CONDITIONING.
Whats chemical etching?
Etching: process of increasing the surface reactivity by
demineralizing the superficial calcium layer and thus creating enamel tags (5-50 m).
Whats physical mechanical procedure?
Procedures to get rough surfaces using direct erosion or an abrasive agent:
- with rotary instruments
- with inorganic abrasive particles at high speed (sand blasting)
We divide micro retention in two:
- chemical etching
2. Physical mechanical procedure
Adhesion with rotary instruments:
To create micro-retention areas we will use tools of cutting and abrasion as: burs, laser, polishing discs, grit blasting with small aluminumoxide particles.
Adhesion with abrasive particles at high speed:
Sand blasting
What is MACROretention?
Just for retained restorative materials, not adhered.
What macroretentions do we have?
- Adhesive forces
- cohesive forces
What are adhesive forces?
intermolecular forces which cause a tendency to resist separation in liquids. Between molecules of the same substance.
What are adhesive forces?
attraction forces between unlike molecules.
What`s an adhesive failure?
The bonding fails at the interface between the two substrates.
What’s a cohesive failure?
The bonding fails within one of the substrates.
What consequence does an adhesive failure have?
Lack of proper isolation will produce contamination with saliva and blood,(Tooth surface-Adh, RC-Adh)
What consequences do cohesive failures have?
- tooth surface
- contamination by saliva and blood etc.
- adhesive
Cohesive failures by tooth surface causes:
contamination, excessive etching (time, very strong acids or high concentration) or self cariogenic process, trauma or due to the technique (excessive traction when composite polymerizes if enamel is weakened- demineralised it is likely to break)
What’s a cohesive failure by RC?
Contamination by saliva and blood, trauma, improper technique especially polymerizing layers too thick.
What’s a cohesive failure due to the adhesive?
The causes are not well known, seems that the areas where most often the fault is the surface and deepest layer of the hybrid layer.
What’s Hydrophilic?
having strong affinity for water tending to dissolve in it, mix with it, or be wet by water.
What’s Hydrophobic?
is the physical property of a molecule that is repelled from a mass of water.
Whats surface energy (solid- adherend)?
ll the atoms that constitute a body are attracted to each other and at the same time they attract the surrounding atoms by electrostatic forces. The compensation of the forces helps the mass to be in balance.
Why the surface molecules are not in balance?
The surface molecules are not in balance as they are only surrounded by atoms on one side.
Whats the result of the molecule imbalance and how is it called?
The result of this imbalance of forces is known as surface energy , which is an energy that tends to attract other substances into the surface of the material.
What’s surface energy (adherend)?
Intermolecular forces that are on the surface of a material. Degree of attraction or repulsion force that a material surface exerts on another material.
What happens if we have a high surface energy? Explain the consequence:
If high surface energy: better reactivity, better adhesion. The increase in material surface = > surface energy.
Whats surface tension (liquid- adhesive)?
A manifestation of the intermolecular forces in liquids. Molecules with free ends can interact with other elements.
What do the molecules of the external surface have what the internal surfaces dont have in a liquid?
In a liquid, molecules of the external surface are provided with an additional energy compared to the internal surface.
How are drops in the liquid formed?
In liquids there is tendency that the force of the internal molecules pulls from the external ones- Drops are formed
Whats surface tension (adhesion)?
Resistance of a fluid to deform or break. Such resistance is defined directly by the intermolecular forces that are on the liquid surface.
Whats the surface tension (adhesive) formula?
ST < SE -> Adh++
When the surface energy tend to attract?
High surface energy material: it tends to attract
What happens if we have an adhesion with a low surface tension?
Adhesive with low surface tension: little resistance to deformation or rupture, so a good wetting/wettability of the adhesive on the substrate is produced.
What do you understand about wettability/ wetting?
Attractive forces between molecules of adhesive and surface. Process of obtaining molecular attraction.
The liquid must flow easily over the entire surface and adhere to solid
On what does the wetting ability depend on?
- Clean surface = > adhesion
- Surface energy: > surface energy = > adhesion
- Surface tension: liquid with high surface tension , less wetting
By what is the wettability be measured?
Wettability is measured by the Contact Angle:
Angle formed between the tangent to the surface of a liquid drop and its adherend surface at their interface.
When is the contact angle gonna be smaller?
The stronger the attraction of the adhesive for the adherend, the smaller the contact angle.
< contact angle,
> wettabiliy
What happens if the adhesion strength between solid- liquid is higher/bigger than the strength of cohesion liquid?
we get increased wettability
Regarding the wettability: increased angle
nonwetting
Regarding the wettability: low angle
good wettability
foto lesson 6 page 28
Regarding the wettability: “medium angle”
partial wetting
What’s capillary action?
The ascent of liquids through a slim tube, cylinder or permeable substance due to adhesive and cohesive forces interacting between the liquid and the surface.
Capillary action in relation with wetting, surface tension and equid viscosity:
when do we just observe capillary action?
Capillary action only occurs when the adhesive forces are > than the cohesive forces
Regarding the capillary action: what happens if the surface decrease?
increases capillary action
Decreased surface tension increases capillary action.
Regrading the enamel/ dentin adhesion:
is it easier to achieve the adhesion to enamel or dentin?
Adhesion to enamel is much easier to achieve than adhesion to dentin
(according to this theory of wetting and surface free energy)
What do we have a higher adhesion to enamel than to dentin?
We contain a high surface energy
•Enamel: contains hydroxyapatite ++: high inorganic content (95%), low organic (1%) and water content (4%
What are the components of dentin and to we contain a higher or lower surface energy?
Dentin: More collagen (22%) water (10%) Hydroxyapatite (68%): low surface energy.
The tooth covered with saliva and smear, do we obtain a higher or lower surface energy?
Tooth surface covered with saliva and smear layer: low surface energy.
Conventional adhesives: adhesion in dentistry (history, no one is interested in it)
1955: Buonocore applied acid to “render the tooth more receptive to adhesion”.
1956: 1st commercially available bonding agent (NPG- GMA).
1970,s: 2nd generation adhesives introduced.
1980 ́s: Total etch concept gains acceptance. 1982: Hybrid layer concept (Nakabayashi)
1990 ́s: Multistep and one step adhesive systems.
Adhesion in dentistry: what’s the adhesion between 2 solids?
Tooth structure + Obturation material
By what is the adhesion in dentistry achieved?
Achieved by:
• An adhesive substance (usually liquid)
• Ability to humidify the two solid surfaces (high wettability and low surface
tension).
• Chemical bond: Joining them.
• Micro-mechanic union: When setting, produces their union.
State the substrate properties:
- high surface energy
- microretention
- Accesible to the adhesive
State the adhesive properties:
1- low surface tension
- Hydrophilic
- Hydrophobic
- high wettability
State the substrate/ adhesive properties:
- wettability
- contact angle
- capillary
What’s dental adhesive?
It is a liquid resin-base material which is inserted into the microretentions created over the tooth surface forming an interface between the tooth
tissues and the restorative material)
Whats the aim of our adhesive restoration?
to get a good seal of the enamel
(With our adhesive restoration we try not only to keep the tooth and restorative material bonded together, but to get a good seal of the enamel or dentin injury).
What should we avoid by dental adhesives?
Avoid filtration and bacterial contamination as well as postoperative pain.
What should we do with the tooth before its suffering the injury?
Return the structural cohesion that the tooth had between its tissues before suffering the injury.
How do we achieve adhesion?
- Refers to: Micromechanical coupling of the restoration to the tooth structure.
- Dental adhesive system consists on: conditioner, primer and bonding agent.
After conditioning the tissues, what do we have to use that enters into the micro retentions that we have created?
A substance or adhesive:
Primer
(After conditioning the tissues, we will have to use a substance or adhesive that enters into the microretentions that we have created)
Explain the priming technique:
Deposit of a first layer of a substance (primer) that serves as a base and facilitates the subsequent permanent adhesion of other material (bonding)
Briefly state the dental adhesive components:
1. resin monomers: (primer, bonding/adhesive) 2. solvent 3. Photoinitiators 4. Catalyst 5. Inorganic fillers
What is a primer?
A resin monomer contains hydrophilic resin
Whats a bonding or adhesive?
Its a resin monomer, contains hydrophobic resins
Whats does a solvent contain?
Acetone, ethanol, water
What do inorganic fillers do?
compensate shrinkage
Where do we apply the primer?
Applied to the etched or conditioned substrate
Whats the function of the primer?
- They tolerate well the presence of H2O.
- They infiltrate well into the dentin under the presence of water.
- They form a thin film, low density.
- They polymerize easily creating polymers that join intimately to the tooth
(hybrid layer). - Chemically joined to the hydrophobic bonding resins
Whats the function of a bonding- HYDROPHOBIC RESIN?
- Usually a resin with hydrophobic methacrylate monomers. They have higher molecular weight than the hydrophilic ones.
✦ Bis-GMA: bisphenol A-glycidyl methacrylate ✦ UDMA: urethane dimethacrylate
What does the bonding absorb and avoid?
Thicker layer. Intermediate and flexible layer that absorbs the forces of polymerization shrinkage, avoiding the detachment and gaps at the resin-dentin interface.
Where does the bonding adhere to and by what?
Adheres chemically to the hydrophilic and composite resin by strong covalent bonds.
How does the bonding cure?
light cure
When does bonding NOT polymerise?
Does not polymerize in the presence of H2O.
What does bonding form?
It forms resin tags.
Does bonding have a high or a low contraction?
high contraction
How does the Hydrophilic resin work? (bonding)
fluid.
Penetrates into the demineralized tissue. adhesion to the tooth forming the hybrid layer
How does the Hydrophobic resin work?
viscous resin.
Penetrates into the tubules and prisms and forms resin tags. Union of the hybrid layer with composite resin
Regarding the solvent: is it a hydrophilic or hydrophobic resin and how does it work?
Hydrophilic Resin is transported by a solvent of low tension surface, akin to the water, and that evaporates easily.
What are the most used solvents?
The most used are alcohol and acetone.
What does the solvent displace?
They displace the water present in dentin and allow the impregnation by resin.
What do solvents contain which makes it hydrophilic?
Acetone is a very good solvent due to its hydrophilicity and so is ethanol, but is
very susceptible to the technique. Needs more wet dentin.
What are Photoinitiators?
Camphorquinone molecules that start the polymerization by light (light curing). If self-cured they are not necessary.
Whats a catalyst?
Necessary for some of the chemical reactions.
What are inorganic fillers and for what are they used for?
To strengthen the interface and compensate the shrinkage in polymerization, some adhesives incorporate small amounts of microfiller or nano particles.
