Materials Study Sheet Flashcards
Proportional limit
Greatest stress a material can withstand before deviating from the proportionality of stress to strain
Elastic limit
Greatest stress a material can withstand without permanent deformation
Elastic region
- What happens to atom bonds?
Linear portion of the stress/strain diagram, stress is proportional to strain
Bonds between atoms stretch, recoverable
Plastic region
- What happens to atom bonds?
Non-linear portion of the stress/strain diagram
Bonds between atoms break, non-recoverable
Yield strength
Stress at which a material exhibits a specified deviation from proportionality of stress to stain
Modulus of elasticity
- Discovered by?
- Do metals or ceramics have a larger E? Which can handle tensile forces better?
Slope of the stress/strain curve at the elastic portion
Hooke
Ceramics have larger E as they are bonded covalently/ionically, which is stronger than metallic bond. Metals can tolerate large tensile strain, but not as much compression
Resilience
Amount of energy required to deform a material to its proportional limit (elastic to plastic)
Toughness
Amount of energy required to fracture a material
- Area under elastic and plastic region
- Combination of strength and ductility
Tensile test
- What properties can be obtained?
Measure change in gage length as you apply tensile force.
This is how you generate a stress/strain curve
- Elastic region, plastic region, elastic modulus, yield strength, proportional limit, ductility, ultimate yield strength
Offset yield strength
Amount of stress that results in a plastic strain of 0.2%
Ductility
Amount of deformation before rupture
- Not found on stress/strain curve
Resilience
Area until elastic region (only really good for orthodontic wire)
Impact testing and hardness testing
Impact - pendulum into the specimen
Hardness testing - resistance to penetration. Measurement of indentation width or depth
Creep
Slow elongation and eventual failure at elevated temperatures
- Materials with lower melting temp creep at lower temperatures (dental amalgam and many polymers)
Vita shades of A, B, C, and D?
A: Red-brown
B: Red-yellow
C: Gray
D: Red-gray
What is the ratio of rods to cones?
What does squinting do?
Visible light is from what wavelengths?
19:1
Squinting emphasizes rods to pick up value
380-760 nm
How do you lower value?
How do you raise chroma?
How do you lower chroma?
Lower value with complimentary color
Raise chroma with dominant hue
Lower chroma with complimentary color
Baseplate wax follows what ADA specification
Type I, II, III?
ADA spec no. 24
Type 1: Soft setup
Type 2: Medium, normal climate
Type 3: Hard, tropical climate
Baseplate wax ingredients (5) and short descriptions
Paraffin (40-60%) - Petroleum product, controls melting temp, dull, flakes easily
Dammar gum - (pine trees) - ↑toughness, ↑flake resistance, ↑luster, ↑smoothness
Carnauba - Hard, high melting temp, contributes gloss, decrease flow, from palm leaves
Candelilla - substitute for carnauba, not as hard
Ceresin - Can replace paraffin to modify toughness
Modeling plastic
- High or low thermal conductivity
- ADA spec #?
- Flows at what temp?
- Green softens at?
- Gray softens at?
- Red softens at?
- Low thermal conductivity
- ADA spec #3
- Flows at 98.6
- Green: 123
- Gray: 130
- Red: 132
Modeling plastic ingredients (6)
- Rosin (pine resin) - flow/cohesion
- Copal resin (tropical tree resin) - flow/cohesion
- Carnauba (hard, high melting temp, contributes gloss)
- Talc (filler)
- Color (rogue)
- Stearic acid (lubricant, plasticizer)
Ultimate tensile strength
Maximum stress that a material can withstand while being stretched (apex of the curve)
- Important for brittle items, not ductile - like ceramics.
Plaster/dental stone
- ADA spec no?
- Formula for making gypsum?
- How is plaster of Paris made?
- How is Type III dental stone made?
- How is Type IV dental stone made?
- No. 25
- Calcium sulfate dihydrate + heat -> calcium sulfate hemihydrate
- Plaster - β - open kettle
- Type 3 - α - autoclave under steam
- Type 4 - modified α - autoclave with CaCl2
Ingredients (besides hemihydrate) to stone
- K2SO4 (accelerator, hardener)
- Terra alba (accelerator)
- NaCL (↓ setting time, ↑ setting expansion)
- Borax (retarder)
W:P ratio of gypsum ideally
- Why is more water added?
- How much water for plaster?
- How much water for Class 1?
- How much water for Class 2?
- 18 ml of water
- More water added to obtain a workable mixture
- 0.45
- 0.30
- 0.19
How does temperature and dihydrate/hemihydrate ratio affect setting time?
↑temp and ↓dihydrate / hemihydrate ratio = ↑ setting time
Compressive strength
- Plaster
- Stone
- Improved stone
- Plaster 12.5 MPa
- Stone 34 MPa
- Improved stone 45 MaP
Rank alginate, addition reaction silicone, polyether, and polysulfide in terms of least Dimensional changes to most
ARS (0.05%) < PE (0.1%) < PS < Alginate
Elastomeric impression materials are ADA specification no?
- Impression and die stone materials are compatible if it can reproduce what?
No 19
If it can reproduce a 20μ line
Reaction of addition reaction silicones
Catalyst?
Byproduct?
Vinyl terminal siloxane crosslinks with silane terminal siloxane
Catalyst is platinic salt
Reaction products H2 gas as a secondary byproduct, PT absorbs
Reaction of condensation reaction silicones
Catalyst?
Byproduct?
Base: Dimethylsiloxane with reactive -oH groups, silica added for consistency and stiffness
Catalyst: Tin oxtoate suspension and alkyl silicate
Reaction: Dimethylsiloxane + o-ethylsilicate + tin octoate → silicone rubber + ETOH
Byproduct: Ethanol
Polyether
Reaction?
Base: ethylene imine rings
Catalyst: Sulfuric esters
Polymerizes by cross-linking reaction
Polysulfide
- Base
- Catalyst
- Reaction
- Byproduct
Base: Mercaptan rubber with sulfhydryl groups (-SH)
Catalyst: Lead peroxide, tert-butyl-hydroperoxide, or copper salt; dibutyl phthalate, and sulfur
Reaction: Condensation/exothermic -Terminal sulhydryl groups are oxidized by PbO2 accelerator which causes chain extension/cross linking
Byproduct: Exothermic and water
Alginate
- Ingredients and %
- Reaction
Na Alginate (18%), Ca sulfate dehydrate (14%), K sulfate (10%), Na phosphate (retarder) (2%), diatomaceous earth (56%), glycols (taste), and pigments
Reaction: Na Alginate + Ca2SO4 → Ca alginate + NaSO4
Retarder in alginate
- How does this affect Type 1 fast set and Type 2 regular set?
Sodium phosphate
At first calcium sulfate reacts with sodium phosphate to produce calcium phosphate, rather than sodium alginate.
Once sodium phosphate depleted, then it reacts with sodium alginate.
Fast set: Less sodium phosphate
How does blood and saliva affect gypsum?
They adsorb onto CaSO4
Reversible hydrocolloid
- Ingredients
- At what temp does material form agar?
- What does hysteresis mean?
Agar (15%) Water (80%) Borax (.2% - strength) Sodium benzoate (.1% - preservative) Potassium sulfate (for hard stone surface)
- <110 degree
- Lag between liquification temperature and gelation temp
What is syneresis and imbibition?
Syneresis: Liquid collects on surface and shrinkage occurs
Imbibition: Taking up water with net increase in volume
Denture base polymers ADA spec no?
Type I and the three classes?
Type 2 and the one class? (via what method)
ADA Spec No 12
Type 1: heat-polymerization
C1: Powder and liquid
C2: Plastic cake
C3: Moldable blank/powder
Type 2: Auto (chemical)-polymerized (via tertiary amine)
C1: Powder/liquid
Lucitone denture base resin - what class?
- Composition of monomer and polymer
Class: Type 1, Class 1
Monomer: Methylmethacrylate Territory amines (N,N dimethyl-para-toluidine) for accelerator in autocure Glycol dimethacrylate for cross-linking Hydroquinone (inhibits polymerization) Dibutyl phthalate (plasticizer)
Polymer: PMMA Benzoyl PEROXIDE (initiator), pigments, dyes, opacifiers, organic fibers
Processing PMMA Type 1
- Volume ratio
- Temperature and time for packing of heat cured PMMA?
3:1 powder/liquid ratio
165° F for 1.5 hours, then 212° for .5 hours
OR
165° for 9 hours, then 212° for .5 hours if lucitone 199
Processing PMMA
- Activator for Type 1 or Type 2
- Activator leads to what which triggers the reaction?
- What % monomers remaining?
Activator T1: Heat
Activator T2: tertiary amine or dimethyl-p-ptoluidine
This produces free radicals which then activate monomer molecules to form chains
5% free monomer remaining in auto compared to .2 to .5 in heat polymerized polymers
Polymerization shrinkage
- Type 1 (Heat)
- Type 2 (Chemical)
- 0.2%
2. 3-7%
Advantages and disadvantages of alginate
Adv: Accuracy is good, cheap, reliable
Disadvantages: Low tear strength, dimensional stability
Advantages and disadvantages of polysulfides
Adv: Tear strength, working time, accuracy
Disadv: Slow setting, affected by temperature/humidity, odor, mixing technique, dimensional stability?
Addition Silicones - Adv/Disadv
Adv: Accurate, tear strength, dimensional stability
Disadv: Cost
Condensation Silicones - Adv/Disadv
Adv: Accurate
Disadv: Dimensional stability (alcohol evaporation)
Polyether - Adv/Disadv
Adv: Accurate, dimensional stability, hydrophilic
Disadv: tear strength
High impact PMMA is reinforced with what?
Butadiene-styrene rubber
Light activate UDMA uses what photoinitatior system at what wavelength?
Camphoroquinone at 400-500 nm (pale yellow color)
Plasticizing agents do what in addition to making a material softer and flow easily?
Increase strength but decrease hardness, proportional limit, elastic modulus, and compressive strength
Chemical cure PMMA has what reaction to trigger free radicals?
Do they reach the same level of polymerization?
Amine accelerator reacts with peroxide initiator to produce free radicals
(N,N-dimethyl-para-toludiene with benzoyl peroxide)
No, as the higher residual monomer acts as a plasticizer
Denture liners
- How long do they last?
- Powder composition (2)?
- Liquid (4)?
Last a few weeks
P: Ethyl methacrylate and peroxide initiator
L: Aromatic esters, ethanol, and tertiary amines, (dibutyl phthalate?)
Tissue conditioners
- How long do they last?
- Powder?
- Liquid?
Good for three days
P: Poly ethyl methacrylate
L: Aromatic ester, ethyl alcohol, dibutyl phthalate
Xylocaine ingredients (6)
- Lidocaine
- Epi (vasoconstrictor)
- Sodium bisulfate (preservative for vasoconstrictor)
- Methyl paraban (preservative - allergic potential)
- Sodium chloride
- Distilled water
From Impression Materials (Bayne)
For polymerization shrinkage, distortion occurs in which direction?
Towards the impression material tray
Most important characteristic for an elastic impression material?
Withdrawal without permanent deformation (not surface detail)
Temperature at which denture base curing begins?
Temperature at which acrylic monomer boils? What about water?
What temp does Ivobase require?
~163
~213 vs 212 for water
Ivobase: 104
Describe the PMMA polymerization process according to Ivobase scientific documentation
Liquid (MMA) and resin powder (PMMA) are mixed together to form a dough-like kneadable substance.
The initiator is split into radicals either by heat or by chemical reaction with the catalyst. It interferes with the electron system of the double bond of the monomer molecule ands splits this bond. After the addition of the monomer molecule, a chain radical is formed which then attacks another monomer and links with it. Chain growth occurs then chain radicals connect to form a macromolecule.
This would usually result in volume loss due to the individual molecules being closer to each other. Injection based system overcomes this.
Typical pros/cons for chemical cure
What about Ivobase?
- total cure time
- How many lb’s of constant pressure?
Weaker, less total polymerization (3-5% vs .2 to .5 for heat), greater dimensional accuracy (due to incomplete curing), working time is shorter, color stability is inferior usually for chemical, weaker bond to tooth
Ivobase: Stronger, monomer conversion is less than 1%, minimal shrinkage, no direct skin contact with monomer. Total cure time is one hour. 15 pounds of constant pressure.
What is your framework made out of?
What does each component contribute?
Is it stronger or weaker than commercially pure titanium?
Corrosion resistance?
Ti-6Al-4V ELI - Grade 23 titanium
(extra low interstitial)
Al - Stabilizes alpha hase (reducing density)
V - Beta Stabilizer - Greater amount of ductility
Stronger - tensile strength is 1000
Improved corrosion resistance
Five stages of mixing denture acrylic
Typical ratio of monomer to polymer?
- Sandy stage - Fluid mass occurs as polymer is settling into monomer
- Stringy stage - Monomer starts to attack the polymer - very sticky, tacky and adheres to sides of the jar
- Smooth dough like stage - Monomer diffuses into polymer. Does not adhere to sides; No tackiness
- Rubber like stage - Further penetration of monomer into polymer; resin cannot be packed
- Stiff (set)
A: 1 monomer to 3 polymer
Types of errors during packing dentures? (3)
- Porosity due to not enough packed material or pressure is lost
- Gaseous porosity due to excessive heat (above 212°F) due to gaseous - If thick denture base can rise in heat too quickly
- Granular porosity due to usage of inadequately mixed resin - Not enough monomer - Dried out monomer
Why Ivobase injection?
- Monomer?
- Fracture strength?
- Fit of intaglio?
- Bacterial load?
- User friendliness?
- Time of cure?
- Denture teeth compatibility?
- Polymerization shrinkage?
Low monomer
High fracture strength (81 versus 60
Injection technique leads to better accuracy of fit due to continual supply of material.
Very smooth finish leading to decreased bacterial load
Don’t have to mix materials by hand or guess how long to mix
Very user friendly - pressure/heating phase all automated
Overall curing time is shorter (50 minutes) then 15 minute cold running water time
Very compatible with Ivoclar phonares teeth
Shrinkage: Less than 1% vs up to 7% for Lucitone
