Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Biomaterials > denture acrylics > Flashcards

denture acrylics Flashcards

1
Q

Methyl Methacrylate

A

Most important monomer that is derived from methacrylic acid- polymerizes to PMMA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

PMMA

A

material of choice for full denture bases and “gumwork” for removable devices-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Benzoyl Peroxide

A

Initiator- Breaks down into free radicals- the function is to START the setting reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

N,N-dimethyl-p-toluidine (DMPT)

A

Accelerator/activator- makes the initiator unstable and forms a free radical at ambient temperature

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

camphorquinone

A

photosensitizer- activator that transfers energy from light to the initiator to for a free radical

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

hydroquinone

A

inhibitor- free radical scavenger- function is to extend storage lifetime and working time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

glycol dimethacrylate

A

reacts with acrylic monomers to interconnect polymer chains in the resin (crosslinks). They are used to produce resins with greater rigidity, and be less susceptible to crazes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

four stages of heat curing

A
  1. activation- benzoyl peroxide breaks down into free radicals when heated
  2. Initiation- free radicals attack the double bonds of the acrylic monomers and initiate a chain growth reaction
  3. Propagation-monomers continue to add o the growing chain until most of the monomer is consumed - heat is given off in this reaction
  4. termination- monomer is depleted, two free radicals can react to form a stable molecule, and the reaction stops
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

stages that differ for cold curing

A
  1. activation- DMPT is used to make the Benzyole peroxide unstable- they must be mixed before polymerization will begin
  2. initiation- same as heat and light cure
  3. Propagation is the same as heat and light cure
  4. termination is the same
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

stages that differ for light curing

A
  1. an amine is a light sensitive initiator that decomposes to a free radial when exposed to visible light- camphorquinone is a activator that transfers energy from light to form the free radical
  2. initiation same as heat and cold cure
  3. propagation- same as heat and cold cure
  4. termination- same as heat and cold cure
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is the function of a plasticizer?

A

decreases dough-forming time and increases working time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

advantages of all 3 systems

A

heat cure is stronger

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

disadvantages of all 3 systems

A

cold-cure - low Mw, high porosity, lower strength, and requires the addition of an accelerator to cure at room temp

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

powder to liquid ratios

A

are 3/1 for both heat and cold cure- for heat cure the monomer from the initiator and to separate the initiator from the activator in cold cure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what are the components of the powder and what are their functions?

A

acrylic polymer beads- to reduce shrinkage and heat generated during polymerization
Initiator- break down into free radicals(start the setting reaction)
pigments- pmma is clear so pigments are locked or mechanically mixed with beads to give a tissue-like appearance
plasticizer- softens the polymer- interferes with the interaction of the polymers- this makes it easier for the monomer to diffuse into the beads and the doughy stage to occur sooner

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what are the components of the liquid and what are their functions?

A

monomer
inhibitor- interacts with free radicals to delay the setting reaction- this extends working time and shelf-life
accelerator/activator- makes the initiator unstable
cross-linking agent- interconnects polymer chains in the resin- produces resin with greater rigidity and reduces susceptibility to crazes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What happens when

p/m is too high?

A

porous resin- there will not be enough monomer to wet the powder and fill the voids between beads
polymerization will be incomplete-this makes the resin granular
the dough will not be plastic enough

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what happens when p/m is too low?

A

excess shrinkage and poor dimensional accuracy due to the excess monomer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what are the five stages in the physical reaction during acrylic processing for self-curing materials

A
  1. sandy stage
  2. sticky/stringy stage
  3. doughy stage
  4. rubbery stage
  5. solid stage
20
Q

sandy stage

A

polymer powder absorbs the monomer and forms a granular paste

21
Q

sticky/stringy stage

A

too soon to use- the initiator and polymer dissolve in the monomer- the paste becomes viscous and the adhesive forms strings

22
Q

doughy stage

A

most of the monomer has been absorbed into the polymer beads- the beads swell and coalesce- the mix loses all adhesiveness-this is the stage when denture flasks are packed

23
Q

rubbery stage

A

monomer will all be absorbed into the polymers particles and some will evaporate- too much evaporation will prevent rubbery stage

24
Q

particle size

A

decreases dough-forming time- smaller particles take up the monomer more rapidly

25
Q

powder Mw

A

increases- dough forming time and working time- absorption of monomer in the polymer decreases as the polymer Mw in the powder increases

26
Q

plasticizer

A

decreases dough forming time and increases working time

27
Q

temperature

A

cooling increases working time

28
Q

polymer/monomer ratio

A

too little monomer will result in going directly from sticky stage to doughy stage- the less monomer to be absorbed, the faster the dough stage is reached

29
Q

self-curing

A

shorter working time than heat cure

30
Q

what is the function of mold lining

A

minimize- monomer penetration into gypsum and resulting roughness and adhesion to the mold- minimize diffusion of water from gypsum into the dough and possible blanching, and crazing

31
Q

packing in the sticky stage

A

causes excess air to be trapped in the mix, bubbles remain in the packed flask, and insufficient pressure to develop in the closed flask- the material will not be viscous enough and will flow out of the flask

32
Q

packing in the rubbery stage

A

the material will have insufficient flow to completely fill the mold cavity, preventing metal-metal contact of the flask halves

33
Q

packing in the doughy stage

A

this is when it should be packed! it will have enough firmness to overfill the mold

34
Q

compression molding

A

heat and chemically activated resins- flask is assembled and placed into a press, and pressure is applied incrementally- this squeezes out air and causes elastic deformation of the mold- polymerization proceeds and the dough shrinks relieving the elastic deformation, and this prevents the shrinkage from affecting the denture dimensions- flask carrier maintains pressure throughout processing

35
Q

injection molding

A

heat and chemically activated resins- sprues that lead to a pressure port are placed in the wax denture base- - flask segments are separated during the wax elimination process and then reassembled- after this the resin is injected and placed in a water bath if heat cure is used- tend to have improved accuracy because resin viscosity must be lower so a lower p/m ratio is used resulting in increased shrinkage compromising palatal fit

36
Q

fluid resin technique

A

completed tooth arrangement is placed in a specially designed flask - filled with reversible hydrocolloid investment medium- after gelation, the cast with the tooth arrangement is removed from the flask sprues and vents are cut into the flask and wax is eliminated from the cast with hot water- - low viscosity, chemically activated resin is poured into the mold cavity- pressure is increased and polymerization occurs at ambient temperatures- advantages-

37
Q

advantages of fluid resin

A

mproved adaptation to underlying soft tissue- decreased probability of damage to prosthetic teeth and denture base during deflasking- reduced material costs-and simplification of flasking, deflasking, and finishing procedures

38
Q

disadvantages of fluid resin

A

shifting of prosthetic teeth during processing, air entrapment within denture base, poor bonding between the denture base and acrylic teeth- technique sensitivity, inferior physical properties to heat processed

39
Q

effects of rapid cooling and finishing and polishing after heat curing

A

rapid cooling will not allow sufficient time for the acrylic to flow to relieve the stresses- these stresses will be frozen into the denture bases and lead to stress relaxation and warping
F&P- some stresses are unavoidable- this must be done slowly and wet to prevent overheating and warping

40
Q

problems of having too much residual monomer after curing

A

residual monomer plasticizes the denture causing weakness and deformation- they can also release and irritate the oral tissues

41
Q

problems of repeated wet-drying of a denture and how that can be alleviated

A

may cause warping and crazing- crosslinking reduces water sorption

42
Q

porosity

A

under-packing leads to polymerization shrinkage- there are also usually voids throughout the resin- can also be formed if p/m is too low and excessive shrinkage occurs- if the temperature is too high

43
Q

crazing

A

tensile stresses in the surface result in a network of microcracks that eventually lead to fractures- can be formed by stress-relaxation, contact with the solvent adn repeated wetting and drying- resistance is improved by crosslinking

44
Q

crazing

A

tensile stresses in the surface result in a network of microcracks that eventually lead to fractures- can be formed by stress-relaxation, contact with the solvent and repeated wetting and drying- resistance is improved by crosslinking

45
Q

dimensional inaccuracy

A

caused by polymerization shrinkage- each volume has an effective volume and shrinks when added to a polymer because it is less free to move- reduced by p/m ratio- mold cavity expansion resulting from over packing and thermal expansion- thermal contraction- cooling from curing temperature-

46
Q

dimensional instablity

A

overheating will result in stress relief and warping- - cold cure are a little more stable than heat cured- carful processing

47
Q

fracture

A

impact resistant resins–

Biomaterials (5 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions