priciples of adhesion, acid etch and bonding agents Flashcards
how has adhesive material aided preventative and restorative dentistry?
seals vulnerable pits and fissures
allows conservation of tooth tissue
reduced microleakage
three approached to achieving attachment to tooth
micromechanical attachements
chemical adhesion to enamel/ dentine
complex
what is an example of micromechanical?
acid etching
what is etching?
introducing pits and imperfections to allow resin to flow into these
what is chemical adhesion?
coupling agents bond to material and tooth (poly acids)
what is an example of chemical adhesion?
glass polyalkenoates
what is complex?
wetting, penetration and formation of bound material and restorative substrate interface
how can good wetting be determined?
small angle… low wetting
large angle- high wetting
who introduce acid etch for enamel margins?
Buonocore 1955
what is the bond strength re acid etching?
20-25mpa
how does acid etch work?
increased surface roughness
increases enamel surface energy
how does etch increase enamel surface energy?
removes surface contaminants
increases wetting
facilitates micro mechanical retention
what factors effect etching?
time 10-60 seconds
washing- 60 seconds
drying
what is the purpose of drying?
enables hydrophobic rein to penetrate and attach
what happens if etched for too long?
precipitation of calcium and phosphate
what properties does the ideal dental adhesive have?
high bond strength
immediate and durable bond
reliable bond
prevent bacterial ingress
what problems re. dentine bonding?
dentine is hydrophilic
vital
consist of inorganic and organic material
covered by smear layer
what is a primer?
acid
dentine conditioner
alters surface appearance and removes smear layer
what is the function of coupling agent?
component that does the sticking
what does the sealer do?
flows into dentinal tubules
seals dentine with surface layer rich in methacrylate
ensures bonding to resin
what are dentine conditioners?
materic
oxalic
phosphoric
nitric acids
what is the reaction re etch and priming?
acid based reaction with hydroxyapatite- opens dentinal tubules
what depth of deminerlisation?
up to 4 micron
what do primers do?
bond hydrophobic composites to hydrophilic dentine
act as adhesive
what is the general formula for primers?
M-R-X
M=?
methacrylate group in resin matrix
R=?
pacer that allows resin to move
X=?
component that interacts with dentine
what is a popular primer?
HEMA- hydroxyethylmethacrylate
what are the negative effects of HEMA?
dermatological effects
What are sealers?
resins
BISGMA & HEMA
What effect longevity of bond?
acid opening of tubules risks nano leakage
dentine tubules etched greater than resin penetrates= leaves denatured dentine… bond eventually fails
