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Materials Science Exam III


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a dimensionally stable material that is plastic during manufacture and contains large molecules is called
a chemical compound consisting of large organic molecules formed by the joining of many small repeating monomers is
the temp at which thermal coefficient of expansion increases abruptly and the material gets increased mobility
Tg - glass transition temp

characteristic of glassy structures
What kinds of materials are used at temps abover their Tg
Maxillofacial prosthetics and impression materials
What kinds of materials are used at temps below their Tg
restorative resins
a resin that softens on reheating above Tg and is fusible, soluble in organic solvents has better flexural and impact properties and generally not cross linked is called

generally have 2ndary bonds between chains(impression compounds, acrylic resins, denture teeth)
What are the 4 steps of free radical polymerization
activation and initiation, propagation, termination, chain transfer
What is step growth or condensation polymerization
simple chemical reactions that form byproducts, eliminate small molecules or repeated functional groups

slow(seen in polysulfides and condensation silicone -both impression materials)
the amount of monomer available for reactino whcih actually took part is called
Degree of monomer conversion
the avg number of monomer units which have been incorporated into a polymer chain
Degree of polymerization
total number of monomer units divided by total number of molecules is what
Number Average degree of Poly. IE Xn
weight of the sample divided by the number of moles it contains is called
Weight Average degree of Polymerization. IE Xw
t or f typicall Mw is >= to Mn

Mo = molecular weight of structural unit
Mn = number average mol wt = Mo * Xn

Mw = weight average mol wt = Mw * Xw

Polydisperity = Mw/Mn
what is the formula for polydispersity
Mw / Mn
What type of polymerization reaction forms no by products, needs double bonds and radicals to proceed, has no change in composition and is a fast reaction
Free Radical or Addition Polymerization
why is UV light not used to activate polymerization
it can hurt the retinal and unpigmented eye tissues. It also gives poor depth of cure
What is the wavelength that we must use to activate our polymerization reactions
470-500 nm
What is methyl ether of hydroquinone used for
inhibition of polymerization by preventing spontaneous poly, affecting working and storage times and degree of polymerization
What inhibitor causes a sticky layer of underpolymerized resin on the restoration surface
What do plasticizers do
Added to reduce the softening temp by neutralizing secondary bonds or intermolecular forces.

they also reduce strength, hardness
T or F plasticizers can be both internal(by copolymerization) or external(not commonly used)
What are the three types of copolymers
Graft or Branched
What are the rheometric properties of polymers caused by
plastic flow when polymer chains slide over one another and relocate

elastic recovery in amophorous regions when coiled chains straighten under force and recoil after force is gone
What kind of deformation and recovery due polymers undergo
Elastic def,plastic def and viscoelastic def(slow recover after stress is eliminated)
T or F plastics have high degree of permanent deformation and small amount of elastic recover(viscoelastic behavior)

note its elastomers that have a small amount of plastic deformation
What does the solvation properties of polymers depend on
polydispersity, cross linking, crystallinity and chain branching
T or F polymers tend to absorb water, swell and become soft in solvents
Do highly crosslinked polymers dissolute in water easily
If inter carbon distances increase during polymerization then why is shrinkage a problem
inter carbon distances definitely increase during polymerization but the overall effect is shrinkage due to going from a liquid(4.0 ang) to a solid(1.9 ang)
For small amounts of shrinkage, volumetric shrinkage is approx how many times linear shrinkage
What are the four types of dental resins
Methyl methacrylate
poly(methyl methacrylate)
Multifunctional resins- bis-GMA, TEGDMA, HEMA, UEDMA, PAA, PENTA-P
what type of resin is an ethylene derivative with a vinyl group and are hard, transparent and imbibe water
Acrylic REsins
What are the physical properties of methacrylate resins
strong, resilient, resist wear and occlusal forces, dimensionally stable and have low specific gravity if used for dentures(helps suction activity with saliva)
A liquid monomer that is clear, transparent has a high vapor pressure and is an excellent solvent that can be activated by light heat or chemicals is called
Methyl Methacrylate

also can polymerize at room temp in air and has 21% volumetric shrinkage upon polymerization
what monomer is hard, transparent, transmits uv light, is stable and doesn not color with age
poly(methyl methacrylate)
what monomer is an aromatic ester of dimethylacetylate that is synthesized from expoy resin(ethylene glycol of bis phenol A) and methyl methacrylate

also very viscous so TEGDMA is used to thin it out
a compound of two or more distinctly different materials such that the compounds properties are superior to that of the constituents is called a
what are the compositions of enamel, dentin and
enamel 1%wt enamelin and 90-92 hydroxapetite and water

dentin 18 wt% collagen and 75 wt% hydroxyapetite and water
in the 40s and 50s what esthetic, insoluble, insenstive to dehydration and inexpensive material that was easy to manipulate was used
unfilled acrylic resin
why were filler particles added to acrylic resin
reduce the high polymerization shrinkaage and high thermal expansion coefficient

note the lack of filler to resin chemical bonding resulted in high wear, filler loss and roughening/staining of surface
What are the components of a composite resin
REsin matrix(continous phase- he stressed this)
filler particles(dispersed phase- stressed this to)

coupling agent
modifiers, opacifiers and UV absorbers
Who developed bis GMA(bisphenol A-glycidyl methacrylate)
Dr. R. L. Bowen
describe bis GMA
high weight, highly viscous, very cross linked multifunctional resin that has better properties than acrylic resins like methyl methacrylate
BisGMA has ____ times molecular weight and ____ density of methyl methacrylate double bonds
5, 1/5

this leads to a proportionately less polym shrinkage than
name some dimethylacrylate monomers that are resin matrix materials
bis GMA(widely used)
UDMA - monomer with one or more urethane groups and two methacrylate end groups
TEGDMA - low mol weight, diluent monomer that permits addition of a high filler content and creates a composite resin with a usable consistency HOWEVER IT INCREASES POLY SHRINKAGE AND WEAR OF THE RESIN
what was the first filler particle used that was hard and abbrasive
Quartz, glass amorphic silica fillers
how are microfillers made
precipitation of pyrolytic processes, they add viscosity and improve consistency
What are some radiopaque fillers and why are they used
Ba, Sr, Zr glasses, used so you can see where fillings are on radiographs
what is the primary purpose of fillers
strengthen composite resin and reduece amount of matrix material
what properties are improved due to increased filler loading
Reinforcement of matrix resin which gives higher hardness, strength and decreased wear
reduction in poly shrinkage
reduction in thermal exp coeff
improved workability due to incr viscosity
reduction in water sorption, softening and staining
increased radiopacity and diagnostic sensitivity(Ba, Zr, Sr)
what does the matrix-filler thermal coeff mismatch help do
toughens material
name some things the filler-matrix comb does
lowers pol shrinkage,
lowers CTE-(produces less interface stress)
improves compressive and tensile strengths
reduces water sorption and softening
what are organosilanes(gamma-MPS and vinyl tricholrsilane) used as
Coupling agents -they bridge the Silanol groups on the filler surface to the siloxane bonds of the coupling agent as well as binding covalently to the methacrylate groups of the resin
what permits transfer of stresses from matrix to stiffer filler particles
coupling agents(organosilanes)

they improve mechanical and physical properties and provide hydrolytic stability
what are the 4(loosely used cause he said 3 in class but were four in handout) types of activator initiator systems
chemically acitvated - 2 pastes benzoyl peroxide initiator and tertiary amine activator

light activated - single paste containing camphoroquinone (photosensitizer molecule of wavelength about 470 nm <= .2 wt%)and aliphatic amine initiator(.15 wt% DMAEMA)

dual cured systems(usually in resin cements nor restorative materials) - two pastes, benzoyl peroxide and camphoroquinone in one and tertiary amine activator in the other paste - then light cured for -usually for places where light may not completely penetrate

heat activated - direct and indirect composites can be subjected to additional curing by heat in an oven
what is the inibitor added into the composite resins today
.01 wt% butylated hydroxytoluene)

minimize spontanteous polym.
ensure good work time
and extend shelf life
T or F ligher and less opaque shades are more difficult to polymerize
F, darer more opaque shades are tougher to polymerize

NOTE place in thinner layers to get complete polymerization
what are two problems caused by air bubbles that are formed when mixing chemically activated resins
trapped air bubble voids
Oxygen in voids inhibits polymerization
Whats some more disadvantages of chemically activated resins
no control on work time - once mixed you only have so long

disturbing polymerization during setting causes problems, so you cant disturb it for a few minutes after inserting it
What do voids in chemically activated resins cause
Voids relieve stress by relaxtion and slower curing results in internal flow to compensate for polym shrinkage
What is an advantage of light activated resin systems
you can work it and contour then light cure it(COMMAND POLYMERIZATION)

note- not as sensitive to oxygen inhibition
What wavelength range is used in most light cure systems
400-500 nm
Describe the QTH light system
Quartz tungsten halogen - they need a filter to produce inthe 400-500 range has 350 mW/cm^2 radiant poer density
what is another word for light intensity
radiant power density
describe the blue light emmiting diode light system
blue light emitting diode - emit light in very narrow range 440-480 nm, can be battery powered, have long moderate curing times, compact mobile, generate less heat so they dont have cooling fans, light filters not needed

describe plasma arc curing lights
have gas like xenon ionized to produce plasma(thus high intensity 1800-2000 mW/cm^2), must be filtered to get 400-500 nm range, have short curing times but create tremendous heat which might be hazardous to soft tissue and pulp, have smaller diameter tips and are 2-3 times more expensive
describe argon laser lights
very high radiant power density, very narrow spectrum(around 490 nm so may not cure all types of resins), 3-4 times more expensive, small diamter tips, short cure times, high maintenance costs and is very bulky, requires dedicated power source
what is DC
degree of conversion - percentage of C=C bonds consumed based on the formula below

DC= (1-R) * 100

R = ratio of unreacted methacrylate groups before and after polymerization
What oes a higher DC value mean
better strength and wear resistance
What does DC depend on
composition, transmission of light, and amounts of activator, initiator and inhibitor
What is the typical DC value
50-70 %
what is the thickness of a resin that can be converted from a monomer to a polymer under a specific light curing condtion
depth of cure
what things can changed light intensity of QTH unit
age and quality of light source, orientation and distance of light from tooth and contamination of tip

what are the classifications of composite resins(4)
Traditional - (macrofilled) 8-12 micrometers
Small particle Filled - (SPF) 1-5 micrometers
Hybrid - .5- 1.0 micrometers = filers from 2 different size ranges
Microfilled - .04 - .40 micrometers - can be home or heterogeneous
Whats in a traditional(conventional or macrofilled composite)
70-80 wt% or 60-70 vol% ground amorphous silica and quarts filler which are radiolucent

phys and mech properties much better than unfilled acrylic resins
How does a traditional composite compare to unfilled acrylic resin
higher compressive and tensile strength, hardness, elastic modulus and wear resistance

lower CTE and less polym shrinkage
what is a drawback of traditional composites
rough surface due to wear by selective abrasion of softer resin matrix which allows discolorization
Describe small particle filled composites(usually in posterior teeth)
more inorganic filler (80-90 wt% or 65-77 vol%) than traditional composites.
Why is amorphous silica filler added to small particle filled composites
Which composite of the 4 types has the best physical and mechanical properties
small particle filled- thats why they are used in posterior teeth most oftenly

also has best wear resistance and surface smoothness

heavy metal fillers hydrolize soften and wear
which composites of the 4 types is used most oftenly for ant teeth
microfilled - has very smooth surface finish but have weak bonds between composite particles and matrix which cause wear by chipping, staining and cracking --DONT USE IN WEIGHT BEARING RESTORATIONS
t or f microfilled particles have superior properties than traditional composites
F, traditional have better properties than microfilled but small particle have best of all 4
describe the hybrid composite
filler content 75-80 wt% of colloidal sillica filler and heavy metal containing glass fillers. esthetic with very smooth surface

Properties range between traditional and small particle filled but are superior to microfilled and can be somewhat stress bearing
what is a flowable composite
modified hybrid and SPF composite

flowable composites have properties similar to what
compomers - have high flexibility, low elastic modulus but are more susceptible to wear and have higher polymerization shrinkage
T or F direct posterior composites are better for conservative restorations
T, amalgams should be used for more invasive restorations
what are some drawbacks of direct posterior composites
poor interproximal contacts
gingival margins can have interfacial gap due to pol shrinkage when restorations are in dentin or cementum
not as polishable
high rates of occlusal wear in contact and non contact areas(10-20 micrometers/year)
what are packable composite resins commonly mistermed as
condensable resin

they are highly filled composite resins(>80 wt%)
T or F packable composite resins can be bonded to the mandible
F all composites must be bonded to the tooth with some form of bonding resins
what are the advantages of packable composite resins
low shrinkage 2-3% vol
low wear rates - comparable to indirect composite and amalgam
high depth of cure(>5 mm)
no sticking or slumping of resin
high elastic modulus(stiffness)
what are the disadvantages of packable composites
poor interproximal contacts
poor adaptation to tooth due to high viscosity
not many shades
mot very polishable
high spots not burnished away as in amalgams DONT OVERFILL MATERIAL IN PREP
some products crumble easily
what are the 2 types of posteriior composite resins
indirect - fabricated in lab then cemented to tooth, have less wear and shrinkage you can do direct inlay made in patients mouth and further polymerize in lab or do indirect inlay where you take impression and inlay fabricated in lab on a die

what were veneer resins originally made of
poly (methyl methacrylate)

now made of bisGMA
How are veneers installed
polymerized by light or heat+pressure
retained by bonding agents such as 4-META micromechanical retention or silicoating
what are some advantages of veneers
ease of fabrication, intraoral repairability and less oppossing wear
what are some disadvantages of veneers
low proportional limit, distorting on occlussal loading, leaking, staining, and less stress resistant
what can lead to marginal leakage in composites
poly shrinkage, CTE mismatch with tooth structure(percolation)
water sorption
low wear resistance
What are some limitations of composites
Mechanical properties not as good as amalgam
technique sensitive
mechanical and chemical degradation in oral fluids
does not directly bond to tooth
if unpolymerized resin is to close to pulp what can happen
it can leach components and cause chronic inflammation - very few people show true allergic response to resins
What causes marginal leakage on composites
polym shrinkage, can lead to secondary decay and pupal reactions

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