Dentine bonding Flashcards
structure of dentine
70% hydroxyapitie
20% organic material
10% water
dentine has more of a .. composition
heterogeneous
more difficult substrate to bond to an adhesive
whats found in dentine
dentinal tubules
extend from the external surface to the pulp
transmit pain to the pulp when dentine is exposed
what is a condiitoner
substance that modifies the characteristics of a substance so a bond can be created e.g. acid etch
what is coupling agent/primer
intermeidiary substance able to bond to a substrate and adhseive
what is a sealer
substance that flows into dentinal tubules creating a methacrylate based layer
- ensures adhesion
what does the dentine conditioner do
modify the smear layer
dissolves the hydroxyapatite and opening tubules
what is the smear layer
mixture of proteins, hydroxyapatite
what acids are usually used
EDTA maleic acid oxalic acid phosphoric acid nitric acid
is dentine hydrophobic or philic
hydrophilic
resin is hydrophobic
what can dentine bond to
as it is hydrophilic
- hydroxyl groups
- carboxyl groups
- phosphate groups
what can you now also bond hydrophobic resins to
methacrylate groups
- use a spacer to stick them together
what is a spacer used for when bonding resin to methacrylate groups
long enough to prevent rigidity and allow both ends to bond freely/move around
what is a coupling agent and what does it do
bifunctional monomer
combines 3 parts
what parts does a coupling agent bind
polar group
spacer
methacrylate group
what does the polar group do in the bond of the spacer
affinity for the dentine
what does the spacer do in the bond
allows the two parts to attach
what does the metharcylate group do in the mond
produces the polymerisation
examples of a bifunctional monomer
HEMA
MEP-P
NPG-GMA
what are bifunctional monomers and what are they composed of
dentine primers/coupling agents made of - polar group -space -metharylate/acrylate/functional group
what is needed to carry monomer into the collagen
solvent or water
what does the dentine look like after priming
surface of hydrophobic methacrylate groups
what does the surface of hydrophobic methacrylate groups allow
direct bond to the surface with methacrylate based resin
what are methacrylate based resin examples
Bis-GMA
UDMA
light or chemical cure
stages for dentine bonding
apply conditioner
apply primer
apply sealer
what does conditioner do
removes smear layer and opens tubules
what does primer do
bonds to the hydrophilic collagen and hydroxyapitie
leaves the methacrylate free on the other side
what does sealer do
seals tubules and bonds to the primer
concerns with dentine bonding
not as durable as enamel bonding
- complex/heterogenous substrate
- dentine is permeable and dynanic
- lower surface energy than enamel
- formulation of smear layer
- hydrophilic dentine/hydrophobic resins
- problems associated to wetting
- problems with polymer shrinkage
what is the issue of surface energy with enamel and dentine
less spreading of adhesives in dentine due to the lower SE
what is smear layer
coagulated protein/HA layer which includes accumulation of debris formed on the dentine during instrumentation
enamel crystals are
solid crystals and non dynamic
dentine is permeable and dynamic
How does polymer shrinkage occur
monomer molecules are converted into polymer network
exchanging van der walls forces in covalent bond spaces
- creates contraction stresses
issues with polymerisation shrinkage
creates contraction stresses
- shrinkage can result in bond failure and poor marginal adaptation
- gap formation between the cavity and restorative material may lead to bacterial penetration and plural damage
- sensitivity/pain , recurrent caries, bacteria
how to reduce polymerisation shrinkage effects
- filler particles
- new monomer systems
- curing in small intervals
what happens if you dry dentine too mcuh
collagen collapses
- formation of a dense layer that the primer cannot penetrate
what does the solvent do and what does it carry
carries the primer
- displaces the water out of collagen and brings in the bifunctional monomer allowing good penetration
wet dentine
porous collagen
- primer can penetrate and produce molecular entanglement
- good bond strenght
dry dentine
- dense collagen
- primer cannot penetrate and cannot produce molecular entanglement
- weak bond strenght
Type 1 bonding agents
3 stage systems
- etch
- prime
- seal
give some examples to type 1 bonding agents/brands
allbond
optibond
scotch bond MP
type 2 bonding agetns
combined 2 final steps
1- etch then rinse
2- prime and seal
commercial examples of type 2
one step
optibond solo
scotch bond 1
type 3 bonding agents
self etching primers
combines 1st 2 stages of the 3 stage (acidic monomers that etch and prime)
commertial example of type 3
clearfil SE bond
type 4 bonding agent
condition prime and seal
simplest
- weakest bond
which type of bonding agent is the hardest to use
type 1
- requries excellent technique
type 2 vs 1
almost equallly difficult
bond strength is generally worse
