Principles of Adhesion, Acid Etch and Dentine Bonding Agents including self etch Flashcards
what does adhesive materials offer potential to?
- Seal vulnerable pits and fissures
- Conserve tooth tissue
- Reduce/eliminate microleakage
what are the 3 approaches to achieving adhesion?
-Micromechanical attachments
E.g. acid etch and application of resins
-Chemical adhesion to enamel/dentine
E.g. coupling agents/cements containing polyacids (not considered further in this lecture)
-Complex – involving wetting, penetration and formation of bound material of restorative substrate interface
E.g. modern dentine bonding agents
what helps achieving adhesion?
if the agents concerned demonstrate wetting (contact angle)
- lower the angle, the better wetting
why does good wetting help adhesion?
Attraction between adhesive and adherend lowers surface tension of adhesive so will flow into irregularities
what is the purpose of acid etch? (enamel)
Increases surface roughness microscopically
Increases enamel surface energy:
- removes surface contaminants
- increases wetting
- facilitates micromechanical retention
what factors affect adhesion?
- Etching time
- Washing
- Drying
Describe how etching time affects.
- Enough for effect
- Not to long as allows re precipitation of Calcium and Phosphate
- Typically 10-60 seconds
Describe how washing affects.
Approx 60s to remove debris
Describe how drying affects.
To enable hydrophobic resin to penetrate and attach
With adhesion to dentine , why is it important to stick to same manufacturer?
- to avoid potential chemical compatibility problems (composite and DBA)
- to avoid light curing problems especially if using LED (composite, DBA and curing unit)
What are the properties of an ideal dental adhesive?
- a high bond strength to enamel & dentine
- an immediate and durable bond
- a reliable bond
- prevent bacterial ingress
- be safe to use
- be simple to use
What are properties of dentine?
- hydrophilic (adhesives are hydrophobic)
- a vital tissue
- consists of inorganic & organic material
- is covered by a smear layer
What are problems with dentine bonding?
- Cavity preparation results in a smear layer that occludes tubules
- Dentinal tubules following removal of smear layer but no air drying
what is the manufacturer term for primer?
dentine conditioner
what is the manufacturer term for coupling agents?
Primers
what is the manufacturer name for sealer?
sealers
Describe primers.
- acids
- alter surface appearance and characteristics of dentine
Describe coupling agents.
components that do the sticking
Describe sealer.
- flows into dentinal tubules
- seals dentine with surface layer rich in methacrylates
- ensures bonding to the resin in the composite
Give example of dentine conditioners and describe how they work.
- Eg. Maleic, oxalic, phosphoric, nitric acids
- Acid base reaction with hydroxyapatite
- open dentinal tubules
- demineralize surface dentine to a depth of 4 microns
Describe how coupling agents (primers) work.
- Act as adhesives
- Bond hydrophobic composites to hydrophilic dentine
- General formula M-R-X dissolved in volatile solvent
what is the most popular coupling agent (primer)?
HEMA
Describe the effects of HEMA.
- Dermatological effects and rubber gloves
- Bonds to hydroxyl of the apatite and amino groups of the collagen
- Solvent (e.g. ethanol/acetone) enhances penetration by seeking and displacing water carrying the coupling agent with it
Describe sealers.
- Resins
- mix of BIS-GMA & HEMA
