Dental Materials - Bonding systems Flashcards
How can you increase viscosity of etching agent?
addition of fine particles of colloidal silica
Would you rather use an etching gel or liquid?
gel
What is a pure chemical - liquid or gel etchant?
liquid
What penetrates the enamel to a greater depth, liquid or gel etchant?
liquid
What is an example of an etchant gel?
Scotchbond etchant (3M) (35% phosphoric acid gel)
Once the acid is placed where you want, what should you do?
gently agitate, removing the contaminated etch, adding new uncontaminated etch to the enamel
enhance efficacy
What is applied after the etch is applied?
bonding material (adhesive)
resin
What are the properties of bonding materials?
low viscosity dilute dimethacrylate resin system
What is the most Commonly used bonding material?
bis-GMA diluted with TEGDMA
What happens to the resin monomer when cured?
is then polymerised to form a solid polymer
Dentin is heterogeneous, what does this mean?
organic phase (10% water) and inorganic phase
What is the problem with dentin?
large water component…
- always wet
- surface is difficult to clean
- frequently contaminated with debris from the cutting process (smear layer)
What is the smear layer?
frequently contaminated with debris from the cutting process
What are the steps to bonding dentin? (long)
What are the 3 steps in bonding dentin? (short)
- priming
- coupling agent
- sealer
What is the coupling agent?
impregnation of the dentine by a water-miscible fluid or one which will substitute for water
Is the smear layer boded to the dentin?
no
What are acids used to remove the smear layer?
phosphoric acid
nitric acid
maleic acid
citric acid
EDTA
Is the surface of dentin hydrophobic or hydrophilic and is the resin hydrophobic or hydrophilic?
dentin - hydrophilic
resin - hydrophobic
= PROBLEM
What chemical connects the resin and dentin together?
amphiphilic
polar water end attached to a non-polar insoluble hydrocarbon chain
In bonding agents you have a ‘glue’ and what else?
a carrier
What is the role of a carrier in a bonding agent?
hydrophilic chemicals which rapidly pass through the conditioned dentine carrying the coupling agent with them
Where does the carrier in bonding agents infiltrate into?
dentinal tubules
What are the common carriers in bonding agents?
alcohol (ethanol or butanol)
acetone
What is the primary objective in the priming stage?
hybridisation
What is the hybridisation during the priming stage?
infiltration of the partly demineralised dentine with the conditioning agent is known as hybridisation
forms the hybrid layer
What happens if you fail to achieve the hybrid layer?
results in voids leading to microleakage in the long term
What is WET bonding?
care must be take not to over-dry the dentine or the collagen becomes desiccated and the scaffold of collagen collapses
What happens if the dentine is dried too much?
the scaffold of collagen collapses
How do you evaporate residual solvent?
light air from 3 in 1
Why is it important to keep the area dry (bonding agents)?
they are hydrophobic
maximise bond strengths
