Week 6- biomaterials Flashcards
silicate glass particles
provide mechanical reinforcement of the mixture (reinforces fillers)
produce light transmission and scattering
how does composite get its enamel like translucency?
silicate glass particles
composite is a mixture of:
silicate glass particles and acrylic monomer that is polymerized during application
how are composite parts chosen?
with purpose of averaging properties of the different parts
results in intermediate properties
composites are typically a dispersed phase of ______ distributed within _________
filler particles distributed within continuous matrix phase
matrix phase of composite
(acrylic monomer?)
least desirable
transiently fluid during application/manipulation
minimizing matrix = more desirable composite
categories of material properties
physical
mechanical
chemical
biologic
examples of physical properties
mass thermal electrical optical surface
examples of mechanical properties
stress/strain relationship
examples of chemical properties
chemical and electrochemical interactions
4 categories of materials
metals
ceramics
polymers
composites
why do we need bonding agent?
flow of uncured composite is limited
bonding systems are made up of:
unfilled acrylic monomer mixture (similar to composite) placed on etch surface of tooth to make thin film
purpose of bonding system
micromechanical interlocking with etched surface
seals prep walls
co-polymerizes with composite
true/false? many dental tissues are composites
true
Methyl methacrylate monomer problems
contracts excessively
marginal leakage
PMMA problems
not strong enough for occlusal loads
difunctional monomers:
BIS-GMA and UDMA
BIS-GMA and UDMA
extremely viscous
difunctional monomers
need to be diluted
dilution of difunctional monomers BIS-GMA and UDMA
TEGDMA, low viscosity
modification of filler components
ions to make glass easier to crush = small particles
ions to produce filler radiopacity
Pure silica can be ______ or ______. _______ is stronger but harder to finish and polish
crystalline or noncrystalline
crystalline is stronger but harder to finish
what controls fluidity?
friction between filler particle surfaces and monomer
as filler surface area increases, fluidity:
decreases
larger filler = ______ surface area = _____ fluidity
less surface area
= increased fluidity
filler particles with 1/10th diameter (smaller) ______ surface area by
increase factor of 10
microfiller particles with silicon dioxide (SiO2)
tend to agglomerate into chains
a given material that is used must allow for what steps
gross cutting (grinding) fine cutting (finishing) smoothing (polishing)
cannot be too hard (crystalline)
filler particle size has a direct effect on:
surface roughness of ground, finished, or polished composite
effectiveness of restoration finishing and polishing depends on:
use of successively finer abrasive materials
composite classification
- filler content, particle size, method of filler addition**
- matrix composition
- polymerization method
important qualities of composites are improved by:
using higher filler levels
disadvantage - decreased fluidity
composite filler particles
macrofillers midifillers minifillers microfillers nanofillers
drawback of using small filler particles
compromises amount of filler you can use due to increased SA
flowable composites (first generation)
low-viscosity
reduced filler content
allows increased resin to DECREASE viscosity of mixture
second generation flowable composite
properties resemble traditional composite
lower filler content (first generation) flowable used for
pit and fissure sealants
small anterior restorations
higher filler content (second generation) flowable used for
class I-V restorations
first increment during composite restoration
repair resin for margins and non-occluding surfaces
best suited for conservative restorations
true/false? packable composite is comparable to amalgam in that it undergoes condensation
false; does not undergo condensation
packable composite
"condensable composites" handling characteristics similar to amalgam intended for class I and II restorations less sticky, high viscosity do not undergo condensation
microfill and hybrid composites usually use _______ as microfillers
Silicon Dioxide (SiO2)
Colloidal silica
chemically precipitated from liquid soln as amorphous silica
Pyrogenic silica
precipitated from gaseous phase as amorphous silica
matrix monomers in USA usually based on _______ as primary monomer
BIS-GMA
light intensity can be inadequate if composite exceeds
1.5-2mm
light curing methods
Quartz Tungsten Halogen (QTH) curing units
Plasma arc curing (PAC) lights
Lasers
LED curing units
photoinitiator of composites
camphoroquinone
camphoroquinone MOA
absorbs photons of light energy at ~470nm
light curing variables
curing equipment
clinical manipulation of light
restoration effects on light absorption
fiberoptic light tip should be placed where?
adjacent to surface being cured
filler particles do what to curing light?
scatter
smaller filler particles maximize scattering
darker colorants do what to curing light?
absorb
depth of cure
boundary between somewhat cured and uncured material
5mm for shades A2 and A3 material
what to do in cases of poor access or dark shades
place and cure in 1.5-2mm increments
true/false? increasing curing time helps with light penetration significantly
false
curing time
at least 20 seconds
true/false? You can postcure to ensure adequate curing
true; improves surface layer properties such as wear resistance
acrylic resin monomer polymerization stages
- activation
- initiation
- propagation
- termination
acrylic resin monomer activation stage
production of free radicals
affected by light curing
acrylic resin monomer initiation stage
free radicals react with monomer to start polymer chain
acrylic resin monomer propagation stage
addition of monomer to growing chain
acrylic resin monomer termination stage
end
result of steric hindrance, lack of monomer, etc
makes up most of unreacted monomer in system
TEGDMA
why are BIS-GMA restorative matrices poorly converted ?
problems with steric hindrance (leads to termination stage)
why does shrinkage occur?
during polymerization monomer -> polymer = monomer-monomer bonds lead to shrinkage
LCTE for composite
28-45ppm/*C
2x amalgam
3-4x tooth structure
consequences of interfacial bond failure
microleakage - staining
pulpal sensitivity from dentinal fluid flow
pulpal irritation from bacteria
recurrent caries
true/false? well cured composites are resistant to chemical change
true
most composites can be cured to ________ degree of conversion
55-65%
composite with high elastic modulus
cannot accomodate changes in tooth shape associated with flexural forces (esp cervical restorations on facial surfaces)
high elastic modulus limitation
result in debonding of composite restoration from enamel or dentin
composite wear events
- contract free area (food) (CFA)
- occlusal contact area wear
- functional contact area wear
- proximal contact area wear
- toothbrush abrasion
CFA wear resistance related to
filler spacing (smaller, better) filler particles harder than polymer matrix and resist wear
microprotection
filler particles closely spaced and shelter intervening matrix polymer
_______ composite shows exceptionally good CFA wear resistance due to ___________
microfill composite
particles are very small with small spacing
macroprotection
restorations with narrow preps minimize food contact and shelter restoration
composite monitoring categories
color matching interfacial staining secondary caries anatomic form marginal integrity
true/false? color matching goes beyond initial color matching
true; also in relative changes that occur with time
when should color matching be done?
when tooth is properly hydrated
composite type most likely to undergo yellowing
anterior restorative materials with high matrix content and self cured
composite yellowing
matrix polymer chemical changing
accelerated by UV light, oxidation, moisture
qualities that resist color change
visible light cured
higher filler contents
modified with UV absorbers and antioxidants
true/false? it is difficult to avoid a color mismatch after several years
true due to color changing of dentin in middle age
true/false? bleaching affects when a restoration should be done?
true, wait until teeth have assumed a stable lighter shade
transition in color between restoration and tooth structure
beveling enamel blends color difference associated with margin over 0.5-1mm
instead of abrupt transition
incidence of secondary caries after 10 years
3%
primary reasons for composite failure
poor aesthetics
excessive wear
causes of postoperative sensitivity
marginal diffusion of species that induce fluid flow in dentin
dimension changes of actual restoration
composite biocompatibility
unpolymerized matrix cytotoxic and carcinogenic
poorly soluble and polymerized into bound state before dissolution/diffusion can occur
glass ionomers
ion-cross-linked polymer matrices surrounding glass reinforcing filler particles
early glass ionomer based on
polyacrylic acid liquid + aluminosilicate powder with Ca and Fluoride
advantages of glass ionomer
chemical adhesion and fluoride release
aqueous systems that wet tooth structure well
disadvantages of glass ionomer
high viscosity
do not readily adapt to micromechanical spaces
glass ionomer adhesion achieved not by acid etch but instead by
mechanical retention and partly by chemical chelation
silicate cement
fluoride containing
no associated secondary caries
significant marginal disintegration and restoration solubility
cause of replacing glass ionomer restoration
aesthetic problems
who are good candidates for glass ionomer restorations?
high caries risk
more caries susceptible
reduced or no saliva flow
oral diseases that accelerate pathogenicity
method to reduce caries risk during microleakage in gingival areas with little or no enamel
glass ionomer liner extended just short of margin
when glass ionomers exposed to unusually high levels of external fluoride ions (topical fluoride, rinses, etc)
concentration gradient reverses and fluoride diffuses into glass ionomer
recharging
when glass ionomer exposed to high external fluoride levels and concentration gradient reverses, allowing fluoride to diffuse into GI
discharging occurs just as quickly
doesn’t significantly improve secondary caries prevention
true/false? recharging provides a steady, continuous release of fluoride
false; discharging occurs as quickly as recharging began
biocompatibility issues with glass ionomers
sensitivity and pulpal irritation at time of initial mixing
pH starts very low (1)
why are GI pulpal effects limited to area immediately adjacent to material?
acid groups are attached to polymer molecules that have limited diffusibility
when is it necessary to use a liner with glass ionomer?
if remaining dentin thickness less than 0.5mm
protect from unset glass ionomer
type of liner used for glass ionomer
calcium hydroxide
fluid filled dentin tubules in direct contact with setting cement what happens?
- high ion concentrations in unset GI cause dentinal fluid to diffuse out into cement. fluid movement sensed by pressure receptors = pulpal sensitivity
- unset components such as hydrogen ions move into tubules and towards pulp. Tubule fluid contents buffer ions when RDT is adequate
methods to increase mechanical strength of GI materials used for restorations
mix at higher powder:liquid ratio
(higher filler:matrix)
reduced matrix content decreases postop sensitivity or pulpal problems.
Line preps with CaOH to provide barrier from unset GI while material is curing
true/false? It is safe to dry demineralized dentin during etch and rinse adhesives
no! can result in collagen collapse
goal of etch and rinse adhesives
find moist bonding techniques by combining hydrophilic and hydrophobic monomers into organic solvent
advantage of etch and rinse adhesives
can re-wet dentin after drying to raise bonding strengths
demineralized dentin collagen matrix reexpands and recovers original dimensions
2 step self etch
nonrinsing conditioners of self priming etchants
prime/etch enamel and dentin simultaneously
not as good as phosphoric acid
no deep depth of demineralization or resin infiltration
doesn’t completely remove smear layer = less postop sensitivity
1 step self etch
etch, prime, bond in one solution
uncured, ionic monomers that contact restorative resin directly
some hydrophilic = water degradation
multiple coats increase bond strength, decrease leakage
hydrophobic bonding layer is helpful
do NOT provide hermetic seal for deep dentin
etch and rinse adhesive solvent
displaces water from dentin surface and promotes infiltration of resin monomers throughout nanospaces of collagen web
if you get too much water onto primer can you continue?
no, excess moisture makes it ineffective
what should happen BEFORE application of etch and rinse adhesive system?
uniform layer of water over dentin
role of water in self-etch systems
added to ionize acidic methacrylate monomers
solubilize calcium and phosphate ions that form from interactions of monomer with dentin/enamel
true/false? water can compromise properties of one step self etch adhesives
true (hydrophilic monomers = water degradation)
role of protein in dentin bonding
partial removal of phosphor-proteins from root lesions enhances remineralization otential
demineralized dentin treated with adhesive layer leads to
remineralization
nanoleakage
small porosities in hybrid layer or transition between hybrid and mineralized dentin allow penetration of AgNO3 dye
nanoleakage results in
reticular pattern on adhesive layer and spotted pattern on hybrid layer
