Dental Materials Pt. 2(12-26) Flashcards
hydrophobic surface properties
composite put into tooth
hydrophilic surface properties
tooth surface
composite and tooth being opposite of each other (hydrophobic vs philic) adds…
strength to the bond
the angle a force by the jaw is applied to a tooth or composite effected the amount of force
the contact angle
different angles of the jaw can have
different forces
molecules can have both hydrophobic
and hydrophilic components (adhesives- bind to composite and tooth so compatible with both surfaces)
types of corrosion in metals
Galvanic corrosion
structure selective corrosion
crevice corrosion
stress corrosion
degredation in ceramics caused by
hydrolysis
hydolysis in ceramics
dissolution of oxides created by H-bonds (fluoride treatments dissolve ceramics)
polymers degraded by
hydrolysis
hydrolytic degredation in polymers caused by
water (absorb water and causes dimensional changes)
enzymes
bacteria
degradation products are related to
toxicity (mercury and plastics absorbed by body over time and cause harm)
Stress strain curve y axis
stress
stress strain curve x axis
strain
steep angle on stress strain curve
stiff and brittle, shatters with sharp forces
food resembling steep angle
pretzel
middle angle on stress strain curve
stiff and ductile, deforms then fails
food resembling middle angle
tootsie roll
low angle on stress strain curve
flexible and ductile, lots of manipulation before it breaks
food resembling low angle
liquorish
tendency to deform along an axis with opposing forces (stress and strain)
modulus
before failure or fraction occurs
toughness
before deformation occurs
resilience
how does heat affect mechanical properties
decrease strength because material becomes pliable and easily manipulated
creep
solid material moves slowly/deforms permanently under mechanical stress (long term)
impressions want to be taken out____ to retain___
quickly to retain best impression without deformation
the ability of a material containing a crack to resist further fracture
fracture toughness
single cycle (force) overload such as biting on popcorn cornel leads to
cracks
cyclic stresses are
slow cracks propogating over time (fatigue of teeth) caused by soft foods
teeth are not completely rigid and can lead to
abfractions
how the teeth articulate with each other creating an ideal environment for mastication
buccal lingual stability
how do cavities lead to B-L instability?
taking out cavity removes tooth material and weakens structure, putting more stress on remaining tooth and causing cusp fractures
in composite resins, resin helps
processing and handling
in composite resins, filler helps
modulus and wear resistance
in composite resins, the role of coupling agent
bonding between filler and matrix
resin ______ viscosity and filler _____ viscosity, but decreases flowability
increases viscosity, increases viscosity (which ultimately improves mechanical properties)
types of curing
chemical
heat
light
what is corsslinking
the linking of polymers within resin which can alter density with number and degree of crosslinking
crosslinking increases or decreases strength
increases
cross linked groups need to be ______ for this process to be effective in increasing strength
bonded together
smaller fillers are
better
smaller fillers match
tooth structure and have better wear properties
smaller fillers allow for better/worse polishing and finishing
better
micron (fine) fillers
.5-3 um
loaded at 77-88wt%
nano (microfine) fillers
.04-.2um
tendency to aggregate
38% maximum loading percentage
nano in polymer matrix
20-30um particles
loading up to 50-60%
reduces aggregation and no coupling agent
these form very strong bonds between fillers and resin
coupling agents
coupling agents add what groups and what do they bond to
add methacryalte groups that can bond with polymer chains to surface of filler
Shrinkage
density change of monomers into polymers
shrinkage is important for
direct compostite restorations and materials that require dimensional stability
shrinkage can cause cracks that lead to
secondary caries
Components of glass ionomer cements
acidic polymer (polyacid)
basic class
water
modifiers (tartaric acid)
glass ionomers are cured by
acid- base reaction
reaction of poly acid and glass creates
salt bridges that form from poly acid to glass
difference between composite bonds and glass ionomer bonds
composite has cross bridges between polymers and glass ionomer has salt bridges between poly acid and basicglass
glass ionomers release
fluoride to help tooth strength once set
difference between adhesives and composites
adhesives are 0-10% filler and composites are 70-80% filler
adhesives are base on
composite resin chemistry
hydrophilic modifiers promote
bonding
enamel and dentin are hydrophilic/phobic
hydrophilic
compsites are hydrophilic/hydrophobic
hydrophobic
ahesive layers are hydrophibic/philic
both
how do sealants differ from composites?
preventative material low viscosity (easy to flow/coat surface) bonding is mostly mechanical (etching) not for longevity
oxygen inhibition layer in sealants interferes with
radical polymerization
why is oxygen inhibition a problem?
surface is uncured and this is problem because sealants are so thin
classes of impression materials
hydrocolloid and elastomers
properties of hydrocolloid
alginate, irreversible, lacks some accuracy, sets via chemical and temperature
properties of elastomers
higher tear strength, stable dimensions, rubber like polymer
con of elastomers
expensive
alginates are ___based
water based
alginate is ___ crosslinked
calcium cross linked
calcium cross linked is part of
initial reaction while material is still workable
calcium cross links react with
sodium alginate to form gel
advantages of alginate being water based
use water temp to manipulate setting time
the colder the water
the slower the setting time
advantages of alginate
cheap, easy, fast, tastes fine, hydrophilic, displaces blood and saliva
disadvantages of alginate being water based
undergoes shrinkage or expansion with loss/gain of water
syneresis
loss of water to surroundings
imbibition
gain water from surroundings
other disadvantages of alginate
limited detail, single pour only, work quickly, low dimensional stability
what determines time alginate material will set
sodium phosphate levels (water temps)
heating
expand
cooling
contract
fillers reduce
water soprtion
water sorption promotes
hydrolysis
water sorption degrades
matrix and matrix filler bonding
smear layer is removed by
etching
spherical
molten alloy blown through nozzle (wetted with less mercury than lathe cut
expansion vs contraction steps
- initial contraction when alloy is absorbing mercury
- expansion from formation and growth of y1 and y2
- final absorption of mercury again causes contraction
