Adhesion 1 Flashcards
Issues with fillings without adhesion
- restorations need to be mechanically retained (need undercut design, leads to cutting of larger cavities - removing healthy tooth tissue)
- restricted ability to restore some teeth (incisors may lack sufficient bulk to have an undercut)
- marginal gaps may form (can cause staining and secondary caries, or thermal and electrical stimuli reaching the pulp)
Enamel and dentine do not adhere to what materials?
- amalgam
- composite
Enamel and dentine not bonding to composite/amalgam led to what?
- conservative dentistry
- resin-bonded bridges
- orthodontic bonding
- fissure sealants
Why is time an issue with adhesion?
- need effective bond within minutes
- most ‘glues’ take longer
Problem with cavity size effect in adhesion
- bigger cavities have more surface area
- more potential for the bond to fail
Problem with lack of natural affinity in adhesion
- tooth surface moist/hydrophilic
- resins hydrophobic
Problem with mouth being warm/moist in adhesion
- bonding may be destroyed
- adhesive needs to be stable in an aq environment
Problem with thermal fluctuations in adhesion
- thermal expansion/contraction
- put adhesive bond under repeated stress
3 requirements for adhesion
- need intimate contact
- need an adhesive
- the ability of a liquid to flow over a surface
Explain the need for intimate contact in adhesion
- the more contact between surfaces, the stronger the bond
- hard to achieve with two solids
- roughness can get in the way
An adhesive is …
The surfaces are called … so adhesives bonds …
- material that joins two surfaces together
- adherends
- adherends together
Most adhesives are what state?
Why?
- liquids
- can flow over surfaces
- need to make sure no droplets form and ensure the liquid won’t flow over surfaces
What is the term for the ability of a liquid to flow over a surface?
wetting
Wetting depends on what 2 factors?
- surface tension of the liquid
- surface energy of substrate
Liquids tend to form …
spherical droplets
Solid surfaces have … bonds
free
Wetting needs…
- surface energy to be higher than surface tension
- droplets start to flatten
- contact angle between droplet and surface
- primers
What is a primer?
Why do you need them?
- chemicals that modify the nature of the surface
- improves the wetting of the liquid
Mechanical bonding mechanisms
- macro-mechanical is the idea of the enamel undercut
- rough surface may have micro-undercuts
- liquid can flow into these and form tags when low viscosity
- liquid needs to flow well/wet
Chemical bonding mechanism
- ionic or covalent bonds possible
- bonds can be reversible or irreversible
- can be subject to hydrolysis
Complex bonding mechanism
- various contributory factors
- combination of mechanical and chemical
… is the pre-requisite for strong adhesion
intimate contact
What’s was the first approach to adhesive dentistry?
- enamel bonding
What’s the effect of pellicle in enamel bonding?
- pellicle is weakly adhered to enamel
- must be removed prior to adhesion
Effect of amorphous enamel outer layer on enamel bonding
- formed during normal remineralisation
- non-normal hydroxyapatite (HaP) structure
- not ideal for adhesion
Acid-etch technique was successful?
- yes - first successful procedure
- still commonly used for enamel bonding
Technique of acid-etch technique
- clean enamel
- apply acid
- apply resin-based material to enamel
How to clean enamel?
- pumice and water
- ensure water supply is oil-free
What does applying acid in acid etch do?
- acid dissolves enamel surface
- partially demineralises enamel
- makes it rough
What happens when resin-based material is added to enamel?
Important factors
- material flows under undercuts
- viscosity of material, surface wetting, setting time for materials is all important
Enamel is made of …
The main component is … which is susceptible to …
- biological apatite
- calcium hydroxyapatite
- acid dissolution
What is used for etching?
How is it given to dentist?
- phosphoric acid (around 37%)
- as a liquid or a gel
Different viscosities of etch effects what?
spread to the acid
Acid etch is usually used for … to … seconds
10-60
If etch is used for too short a time, what happens?
- insufficient etching
- leads to poor bonding
If etch is used for too long a time, what happens?
- apatite precipitation onto surface
- poor bonding
After you’ve finished etching, what do you do?
- rinse enamel with oil free water supply
- blow air over surface
- give a chalky white appearance, microscopically visible enamel prisms, etched prisms used as microscale undercuts
Things to beware of in acid etching
- avoid salivary contamination (reduces bond strength and re-etch if it has)
- differences in enamel (variation in teeth, in patients which leads to unpredictable results)
2 reasons you can’t apply composite straight onto enamel
- monomer viscosity (too viscous to flow into undercuts)
- filler particles (big particles occlude undercuts)
What is added for composite to bond to enamel?
bonding resins
Why do bonding resins help composite bond to enamel?
- monomer composition - similar to composite
- filler concentration - originally unfilled, modern materials can be filled with smaller particles
Setting mechanism of bonding resin
- originally chemically activated
- viscosity increases quickly with setting
- may not penetrate undercuts
- modern light activated
- command set - in theory better penetration
Applications of acid etch
- class IV restorations
- class V restorations
- resin bonding bridges
- bonding of orthodontic brackets
- fissure sealants
Is acid etch used for dentine bonding?
possibly
