Dental Materials - Bonding systems Flashcards
What is dental bonding?
process of attaching a resin composite based material to the underlying tooth tissue using some form of intermediate material
What is sealing?
achievement of an impermeable barrier between the cavity wall and the restorative material to prevent the passage of bacteria
What is the difference between bonding and healing?
although a material may appear to be stuck to another material every part of the 2 surfaces may not be in intimate contact with each other
What is wetting?
the ability of a material to achieve an intimate microscopic contact with another
How is adhesive usually applied as?
a liquid
allows surfaces to be bonded
What needs to occur for good binding to occur?
wetting (adhesive)
what is high viscosity?
thick liquid
What is surface tension?
the ability of the surface of a liquid to resist an external force
What are the 3 types of adhesion?
mechanical
physical
chemical
What types of surface does mechanical adhesion rely on?
rough microscopically
How does mechanical adhesion work?
if both surfaces are uncontaminated, the irregularities may connect with one another
depending on their respective roughness, the two surface may become intimately related
any attempt to slide one against the other is resisted by friction.
How does physical adhesion work?
between 2 surfaces
the molecular charges (opposite charges of substrates attract)
substrates orientate so the oppositely charged molecules are adjacent to each other
Is the physical adhesion bon weak or strong?
relatively weak, readily breaks down
What factor gives the physical adhesion more chance for the forces to attract?
greater surface area
cohesive vs adhesive failure
cohesive = chemical adhesion… one of the substrates dissociates
adhesive = at the interface
What is the aim of dental bonding?
- surface of the tooth is rough
- intervening layer of resin fills these micro- and macroscopic irregularities
- the restorative material is rough (bonding agent)
what is the bonding agent?
liquid resin
How would you describe the bond between the restorative material and tooth?
micro-mechanical bond
What are the essential prerequisites for a substrate surface?
rough
high surface area
good wetting properties
high surface energy
free from debris an organic material
dry
What is prophylaxis?
treatment given or action taken to prevent disease
What is the first step (removing the pellicle)?
use a pumice slurry
(volcanic stone and water)
Is enamel mainly organic or inorganic?
inorganic
Why is bonding to enamel complicated?
the outer 5um of the enamel surface is amorphous
provides very limited means of retention for restoration
no form and limited means for restoration
The outer layer of enamel is amorphous, how do you overcome this? (prepare the substrate)
acid etch technique
What is the acid etch technique?
acid partly demineralises the crystalline structure of enamel
What does the acid etch technique remove?
removal of the crystallites (interprismatic enamel)
Is this image before or after the acid etch technique?
after
clefts has formed
Why use the acid etch technique?
create a tight micro-mechanical lock
wetting can flow between prisms
What bond is formed with acid etch technique?
micromechanical bond
What is achieved with etching with an acid? (learn)
Wat appearance does etched enamel formed?
frosted appearance
What is bevelling enamel?
quality of etching pattern is improved by bevelling the enamel (margins prepared at an angle of c120 degrees using a diamond bur)
What does bevelling enamel cause?
removes the outer amorphous enamel exposing fresh enamel of boding and roughening its surface
Alters the angulation of the enamel prisms ad ensures that no unsupported prisms remain
What need longer etch time?
older enamel
Why does older enamel need a longer etch time?
exposed to fluoride
What considerations should you take with primary enamel?
more prismless enamel at the surface
acid takes longer to penetrate the enamel layer and create the etch pattern
increase etch time
Are bond strengths higher or lower in children and why?
lower
teeth are less calcified than permanent enamel
What is the problem of over-etching?
the porosities produced are not so numerous
decalcifies the substrate to too great a depth so losing the etch pattern
decrease ability of the resin to form tags to penetrate into the etched pattern
lower bond strength results
Can you determine clinically if the enamel is over-etched?
no
What side is the ideal-eched and the over-etched side?
left is ideal
right is over-etched
Describe the over-etched enamel on the right
lost the inter-prismatic layer
clefts are a lot deeper
not a great surface area, not good for resin infiltration
Can you repeat the etching step on the same surface?
no
When will etching need to be repeated?
if the area becomes contaminated by blood or saliva during the bonding process
Are bonding agents hydrophilic or hydrophobic?
hydrophobic
What acid is used with etching?
ortho-phosphoric acid
What is the optimum concentration of ortho-phosphoric acid?
30-50%
What is the problem of the ortho-phosphoric acid being too concentrated?
small amount of water present does not get saturated with reaction by-products quickly as this would slow the dissolution rate
What is the most common concentration of ortho-phosphoric acid and applied for how long?
35-37% for 15-30 seconds
