CA2 TYS Learning Pts Flashcards
(246 cards)
1
Q
(T/F) Type IV gold alloy has the highest tarnish resistance
A
False
- type I highest tarnish resistance, type IV lowest
- type IV: extra hard gold alloy, lowest gold %
2
Q
(T/F) acrylic soft liners are brittle but become soft when soaked in water
A
True
- soft liners absorbs shock between hard base of denture and gums
- more comfortable
3
Q
(T/F) passivation is the process of enhancing the titanium oxide layer to increase resistance to ion release and degradation
A
True
Passivation=> enhance oxide layer to minimise release of metal ions => minimise corrosion/improve corrosion resistance
- via immersion in 40% nitric acid/anodisation for titanium based alloys (implant materials)
4
Q
(T/F) the benefits of APS are fast setting time, no by-product and high molecular weight
A
True
- addition polymerise silicones
- notes say it has moderately low mw silicone tho
- from internet: high mw, higher degree of entanglement, more bonding, can absorb more energy b4 failing
5
Q
(T/F) CPS setting time is 6-10mins and the setting shrinkage is 0.6% after 24 hours
A
True
6
Q
(T/F) using amalgam w smaller particles will result in a net contraction
A
True
- smaller particle size => increased SA, G1 grows faster => increased consumption of mercury => more initial contraction (net contraction)
-smaller particles of silver tin
7
Q
(T/F) resilient liners can be cleaned w a soft brush and hypochlorites
A
False
- using soft brush is correct
- but shd not use hypochlorite (bleach)
- to be cleaned w WATER
Topic: resin based materials
8
Q
(T/F) flux is added to alloy to increase the melting temperature and dissolve oxides that form during casting
A
False, dosent increase the melting temp (it makes it more fluid so means decrease melting temp?)
Functions of flux:
- prevent O2 in air from contacting hot metal => prevent oxidation
- dissolves oxides that may form when metal heated
- increases fluidity of metal
- minimise porosity
9
Q
(T/F) cristoballite expands to a greater extent than quartz
A
True
- cristoballite is a mineral polymorph of silica
- topic: investment materials, silica-bonded investment
10
Q
(T/F) the thickness of bonding resin/adhesive does not affect bonding strength
A
False
11
Q
(T/F) tissue conditioners bond well to metal framework but need to be changed regularly due to intraoral degradation
A
False
- tissue conditioners = ‘acrylic temporary soft liner’ in dentures
- temporary soft-denture liners that help your gums and soft tissue recover from damage caused by old or poorly-fitting dentures
- formed in situ
- i think why this statement is wrong is cuz it doesnt bond well to metal framework??
12
Q
(T/F) work hardening for ductile materials such as metals decreases corrosion resistance and increases brittleness
A
True
- increases: hardness, tensile strength, brittleness
- decreases: ductility, corrosion resistance
13
Q
(T/F) the amt of silica is proportional to the amt of thermal expansion of the investment
A
True
- silica is added as a binder
14
Q
The decrease in creep from low to high-copper content amalgams is due to..
A
Lower mercury content
15
Q
(T/F) shape memory is the ability of the alloy to deform to its preheated shape
A
True
- topic: wrought metal alloys
- shape memory
-> the ability to return to previously manufactured shape, induced thermally (oral temp)
-> deformed when cold, returns to pre-deformed shape when heated
16
Q
(T/F) elongation is defined as the length over initial length after breakage
A
True
17
Q
(T/F) modulus of elasticity is a measure of fracture strength, and is found by taking the stress over the resulting elastic deformation
A
False
- fracture strength is measured by UTS, MoE measures only elastic region
- MoE = stress/strain
18
Q
(T/F) ductility is defined as the ability of the metal to be stretched into a wire
A
True
19
Q
(T/F) corrosion resistance is influenced by the composition of the alloy and roughness
A
True
20
Q
(T/F) work hardening decreases corrosion resistance
A
True
21
Q
(T/F) corrosion of amalgam alloys is always good because the products aid in marginal retention
A
False
- tho corrosion at interface btw tooth & restoration actually forms corrosion products that seal space
- but not ALWAYS good cuz corrosion also causes harm => 1. Wet corrosion: galvanism, short circuit pulp, pain or 2. Mercuorscopic expansion, pushes restoration away from tooth
22
Q
(T/F) passivation decreases corrosion resistance
A
False
- increases corrosion resistance
23
Q
(T/F) using too much wetting agent can cause a poor fitting casting
A
False
24
Q
(T/F) inadequate setting expansion can cause a poor fitting casting
A
True
25
(T/F) using a sprue with a diameter too wide can cause a poor-fitting casting
False
26
(T/F) hardness is not affected by the water/powder ratio for investment material
True
- hardness is the resistance to surface deformation/scratches
27
(T/F) thermal expansion is not affected by water/powder ratio for investment
False
- increase water/powder ratio = decrease thermal expansion
28
(T/F) setting expansion is not affected by water/powder ratio for investment
False
29
(T/F) fracture strength is affected by water/powder ratio for investment
True
- increased w/p ratio = decreased strength
- fracture strength: the amt of force it can take b4 permanent deformation
30
(T/F) lower colour stability is directly related to insufficient polymerisation time
True
- topic: resin based materials
- mostly referring to denture acrylics
- heat cured resins => higher colour stability than autopolymerised resins
31
(T/F) lower water sorption is directly related to insufficient polymerisation time
false
- topic: resin based materials (denture resins)
- auto-polymerised resins => higher water sorption than heat cured resins => presence of water affects physical & dimensional properties more
- water absorbed preferentially into polymer component of CR (increased resin content = increased sorption)
- if bis-GMA polymerise poorly => more space for water to enter => high water sorption
32
(T/F) lower volumetric shrinkage is directly related to insufficient polymerisation time
False
- seems to be related to the size of the CR molecule, the larger the molecule, the less shrinkage
- topic: CR
33
(T/F) higher polymerisation shrinkage stress is directly related to insufficient polymerisation time
False
- Shrinkage stress is the pressure put on the adhesive and surrounding tooth structure during the polymerization process.
- related to the number of bonded surfaces
- topic: CR
34
(T/F) CoCr has high ductility and is used as a denture base
False
- its used as denture base
- but not ductile
35
(T/F) silver-palladium is white and has acceptable corrosion resistance
True
- silver-palladium precious alloy issa alternative to dental casting gold alloys
- prolly for cast crowns
36
(T/F) higher gold content indicates higher ductility
True
37
(T/F) Zinc polycarboxylate has chemical bonding to tooth structure
True
- topic: zinc cements
- radioopaque cement that can be used to cement crowns, bridges, onlays, inlays
- **provides chemical adhesion to tooth structure**
38
(T/F) zinc phosphate has anti-cariogenic properties
False
- lacks anti-cariogenic properties
- is brittle w poor tensile strenght
- no chemical adhesion
- but one of the earliest and universal luting cement w high strength & low film thickness
39
(T/F) GIC can prevent secondary caries effectively
False
40
(T/F) ZOE has low solubility
False
- high solubility, eugenol disintegrates cement => thus, used for temporary resto
- but eugenol has sedative effect on pulp! Good
41
(T/F) ZnOE (provisional cement has high wash out resistance
True
42
(T/F) ZnOE is easily cleaned out from internal surface of provi shell and tooth surface
True
43
(T/F) ZnOE provides a good marginal seal to prevent microbial ingress
True
44
(T/F) ZnOE provides high retention resistance and cohesion
False
- used as temporary cement
- no chemical adhesion + high solubility
45
(T/F) type I cements effectively prevents secondary caries
False
- type I cements =luting cements
-> small particle size
-> fast set w early resistance to water uptake
-> radioopaque
- topic: GIC
- other types of cements
- type 2.1 restorative aesthetic
- type 2.2 restorative reinforced
- type 3 lining or base cement/pit & fissure sealant
46
(T/F) zinc polycarboxylate adheres chemically to tooth structure
True
47
(T/F) zinc phosphate is an adequate anticariogenic
False
48
(T/F) ZOE has limited solubility in oral fluid
False
49
(T/F) ZOE has high tensile strength and can be used for both temporary and permanent restorations
False, only used for temporary restorations
50
(T/F) improved ZOE materials serve as a good temporary restoration pending placement of a permanent restoration because they maintain the opposing and adjacent teeth in their respective positions
True
51
(T/F) improved ZOE materials serve as a good temporary restoration pending placement of a permanent restoration because they have thermal insulation qualities comparable to those of dentine
True
- yep thermal insulation is about same as dentine
- biological properties, aka pH is also least irritating to pulp at 6.6-8
52
(T/F) improved ZOE materials serve as a good temporary restoration pending placement of a permanent restoration because they have a therapeutic palliative effect on the dental pulp
True
53
(T/F) improved ZOE materials serve as a good temporary restoration pending placement of a permanent restoration because they have excellent marginal seal
True
54
(T/F) the addition of ortho-ethoxy benzoic acid to ZOE cement decreases the solubility but increases the strength of the cement
False
- it increases both the strength and solubility of the cement
55
(T/F) ZOE can be used on a rigid/flexible tray
False
- must use a rigid tray
56
(T/F) ZOE cannot be used for undercuts
True
57
(T/F) ZOE has low dimensional stabilty
False
- high dimensional stability as compared to alginate
58
(T/F) ZOE is thermoreversible
False
59
(T/F) ZOE has poor detail reproduction
False
60
(T/F) ZOE is most commonly used as temporary cement because of its better tooth sealing properties
True
61
(T/F) ZOE impression paste has low viscosity
True
62
(T/F) ZOE impression paste needs a rigid tray
True
63
(T/F) CoCr is very hard and this facilitates manual polishing
False
64
(T/F) CoCr has a high modulus of elasticity and this allows it to have thin clasps
True
65
(T/F) CoCr is very ductile and this allows for easy manipulation of clasps
False
66
(T/F) work hardening decreases corrosion resistance and brittleness
False
- increases corrosion resistance and brittleness
67
Carbon content of CoCr alloys should not exceed..
0.4%
- excess carbide will result in severe brittleness
68
(T/F) CoCr denture is easy to manipulate and repair
False
69
(T/F) CoCr dentures cannot be used with denture cleansers
True
- corrosion will occur if used w hypochlorites or other chlorine containing compounds
- oxygenating denture cleaners will stain alloy
-
70
(T/F) CoCr has high MOE and high scratch resistance, facilitating manual polishing
False
- high MOE
- high hardness, so difficult to polish
71
(T/F) CoCr has high MOE and demands a high force to elastically deform a wire
True
- more rigid and less likely to deform
- stiffer material will have a higher elastic modulus
72
(T/F) main reason for fracture of partial denture casts made from CoCr alloy during service is the low yield strength of the alloy
False
- CoCr has high yield strength
Strength of material can be described by the following properties:
1. Proportional limit
- stress above which stress is no longer proportional to strain
2. Elastic limit
- maximum stress a material can withstand before it becomes plastically deformed
3. **Yield strength/proof stress
- stress required to produce a given amount of plastic strain**
4. Ultimate tensile strength, shear strength, compressive strength, flexural strength: each of which is a measure of stress required to fracture a material
73
Proportional limit is..
The stress above which stress is no longer proportional to strain
74
Elastic limit is..
The maximum stress a material can withstand before it becomes plastically deformed
75
Yield strength/proof stress is..
The stress required to produce a given amount of plastic strain
76
What does ultimate tensile strength measure?
Stress required to fracture a material
- so does shear strength, compressive strength, flexural strength
77
(T/F) Carbon is the most critical component of CoCr alloys in which a small change causes a great variation in physical properties?
True
- carbon variations produces pronounced effects on strength, hardness and ductility
- it forms carbides w the metallic constituents
78
(T/F) in CoCr alloys, cobalt contributes to the passivating effects of the alloy
False
- chromium contributes to the passivating effects of the alloy by forming a ‘passive’ chromium oxide layer over the surface
79
(T/F) low density of CoCr allows it to be light and good for denture base
True
80
(T/F) CoCr is easy to maintain and repair
False
- difficult to repair
81
(T/F) type IV partial denture gold alloy exceeds a base-metal partial denture alloy in hardness
False
- CoCr is very very hard!!
82
(T/F) type IV partial denture gold alloy exceeds a base-metal partial denture alloy in specific gravity
True
- specific gravity = relative density!
- CoCr is not that dense! Thats why it can be light and used for dentures
83
(T/F) type IV partial denture gold alloy exceeds a base-metal partial denture alloy in casting shrinkage
False
Casting shrinkage is (for Co-Cr: 2.3%, Ni-Cr: 2.0%, gold: 1.25 +/- 0.1%)
- so casting shrinkage is larger in CoCr than in gold
84
(T/F) type IV partial denture gold alloy exceeds a base-metal partial denture alloy in fusion temperature
False
(Co-Cr: 1250-1500 deg celcius, gold: 870-950 deg)
- fusion temp for CoCr is higher than for gold
85
(T/F) type IV partial denture gold alloy exceeds a base-metal partial denture alloy in modulus of elasticity
False
(Co-Cr: 200 X 10^3 N/sq mm, which is twice that of gold)
86
(T/F) passivating effect CoCr -nickel alloy is due to the formation of chromium carbide
False
- due to formation of chromium oxide
87
(T/F) gold content decreases from gold I to IV
True
88
(T/F) ductility decreases from gold I to IV
True
89
(T/F) MOE decreases from gold I to IV
False
- MOE decreases, the alloy gets stronger
90
(T/F) type IV gold alloy has the highest tarnish resistance
False
- cuz less gold, so less tarnish resistance
91
(T/F) localised shrinkage porosity generally occurs at the region of the sprue and the restoration
True
- localised shrinkage porosity is caused by a lack of molten metal during solidification, which occurs when 1. Sprue diameter is too small 2. Investment is not sufficiently heated
- the porosity occurs at the region of the ingot
92
(T/F) solid solutions: solute in random positions in solvent lattice structure, single phase
True
93
What are the alternatives to dental casting gold alloys?
1. Low gold alloys
- noble metal content is below 60%=> lower tarnish resistance
2. Silver-palladium precious alloys
- 60-70% silver & 25% palladium
3. Non-precious alloys (Ni-Cr-Be)
- consists mainly of nickel and chromium
94
(T/F) Type IV gold alloys in hardened condition have a lower MOE than chromium-nickel alloys (in partial denture framework)
True
95
(T/F) Type IV gold alloys in hardened condition are heavier than chromium-nickel alloys (in partial denture framework)
True
96
(T/F) Type IV gold alloys in hardened condition are lower density than chromium-nickel alloys (in partial denture framework)
False
- cobalt nickel is lower density than type IV
97
(T/F) Type IV gold alloys in hardened condition have a higher hardness than chromium-nickel alloys (in partial denture framework)
False
- cobalt nickel is harder than type IV gold framework
98
(T/F) zinc is added to dental casting alloys to improve corrosion resistance of alloy
False
- zinc is added to increase hardness (w palladium) & improve castability and reduce melting temp
99
(T/F) zinc is added to dental casting alloys to improve castability of alloy
True
100
(T/F) zinc is added to dental casting alloys to serve as an oxide scavenger
True
101
(T/F) zinc is added to dental casting alloys to reduce coring
False
- copper is added to reduce coring, it reduces difference between solidus and liquidus temp
- coring is basically segregation of different metals in an alloy?
102
(T/F) chromium is present in a type IV gold alloy
False
103
(T/F) palladium is present in a type IV gold alloy
true
104
(T/F) indium is present in a type IV gold alloy
True
105
(T/F) copper is present in a type IV gold alloy
True
106
(T/F) gold alloy does not shrink due to presence of palladium
False
- palladium is there to increase 1. Tarnish resistance 2. Corrosion resistance 3. Hardness
- higher melting temp/range correlates to higher shrinkage
107
(T/F) type I gold alloy is considered a noble alloy because of high gold %>90%
True
- noble alloys are those w >25% wt noble
108
(T/F) increase in gold content => decrease in ductility and corrosion resistance
False
- more gold = more ductile n more corrosion resistance
109
(T/F) type IV is the hardest because it has the highest gold content
False
- least gold content thats why hardest
110
type IV gold alloys are usually utilized for
Partial denture frameworks or complete denture bases
111
Type I & II gold alloys are usually utilized for..
Restorations which are not subjected to great amounts of stress
- prolly direct gold fillings
- class III & class Vs & inlays (type I) & onlays (type II)
112
Type III gold alloys are usually used for..
- have generally replaced type I n II for general use
- indicated for crowns or bridge/abutments
113
(T/F) type IV gold alloys are heavier than chromium-nickel alloys
True
114
(T/F) gold alloys have less resistance to fracture than chromium-nickel alloys
False
115
(T/F) back pressure porosity can result from low investment permeability
True
- back pressure porosity occurs because air in the mold space cannot escape
- if density of investment is too high ( too low W/P ratio) => can lead to insufficient porosity
116
(T/F) back pressure porosity can result from insufficient wind-up of the casting machine
True
- i think the it means not enough casting pressure cuz the machine nvr spin fast enough
117
(T/F) back pressure porosity can occur due to sprue being too narrow
True
- metal cant flow in easily enough so the space is occupied by air
118
(T/F) back pressure porosity can occur because pattern is too far from ring opening aka sprue too short
True
119
(T/F) type IV gypsum has the lowest water/powder ratio
True
120
(T/F) dental plaster causes a higher temperature rise during setting per unit volume than improved stone (densite)
True
- conversion of hemihydrates to dihydrate is exothermic
- greater conversion in plaster than in stone, so plaster setting releases more heat
121
(T/F) dental plaster has higher setting expansion than improved stone (densite)
False
- the lower the W/P ratio, the higher the setting expansion
- stone expands more than plaster
122
(T/F) in mixing of dental plaster, W/P ratio can influence setting time
True
123
(T/F) in mixing of dental plaster, W/P ratio can influence setting expansion
True
124
(T/F) in mixing of dental plaster, W/P ratio can influence hygroscopic expansion
True
125
(T/F) in mixing of dental plaster, W/P ratio can influence strength
True
126
(T/F) plaster powder differs from the powder of dental stone in that plaster is the hemihydrate of calcium sulphate and stone is the dihydrate of calcium sulphate
False
- unreacted powder always contains only hemihydrates
- dihydrates form when powder is mixed w water
- in plaster, theres a greater conversion of hemihydrate to dihydrate due to higher w/p ratio
127
(T/F) stone particles are smaller & more regular than plaster particles which are big and irregular
True
128
(T/F) plaster is less porous than stone
False
- plaster is more porous than stone
129
(T/F) stone has greater dimensional accuracy than plaster
True
130
(T/F) the higher dry strength and hardness of die stone (type IV) as compared to plaster (type II) is due to the addition of modifiers to die stone
false
131
(T/F) the higher dry strength and hardness of die stone (type IV) as compared to plaster (type II) is due to the difference in chemical composition of these materialsf
False
132
(T/F) the higher dry strength and hardness of die stone (type IV) as compared to plaster (type II) is due to lesser amt of water required by densite for its chemical reaction
False
133
(T/F) the higher dry strength and hardness of die stone (type IV) as compared to plaster (type II) is due to lesser amt of water required for solution and wetting during mixing
True
134
(T/F) upon setting, class I dental laboratory stone will exhibit contraction
False
- expansion, due to outward thrust of the growing crystals against one another
135
(T/F) upon setting, class I dental laboratory stone will exhibit loss in compressive strength
False
- it will gain strength
136
(T/F) setting expansion of gypsum investment material compensates for casting shrinkage
true
137
(T/F) gypsum-bonded investments are not recommended for metal-ceramic alloys cuz they decompose when heated to the temperature needed for casting these alloys
True
- idky tho
138
(T/F) accelerators decrease the setting time of plaster and retarders decrease the setting expansion
True
- but **both accelerators and retarders** generally reduce setting expansion
139
(T/F) within practical limits, when the w/p ratio is increased beyond the recommended amt in mixing plaster, the setting time is increased
True
140
(T/F) within practical limits, when the w/p ratio is increased beyond the recommended amt in mixing plaster, the setting expansion is increased
False
- setting expansion will decrease, cuz got more water
141
(T/F) within practical limits, when the w/p ratio is increased beyond the recommended amt in mixing plaster, the compressive strength increases
False
- compressive strength will decrease, cuz w/p ratio increases
- so more empty space left behind when the water evaporates
142
(T/F) within practical limits, when the w/p ratio is increased beyond the recommended amt in mixing plaster, surface hardness is decreased
True
- surface becomes easier to scratch
- hm? Another anki said surface hardness not affected by w/p ratio tho that doesnt make sense but which is true?
143
compared to calcium sulphate dihydrate, the solubility of hemihydrate calcium sulphate at 20 degrees is…
Higher
- hemihydrate is 4x more soluble in water than dihydrate near room temp
144
(T/F) vigorous mixing of gypsum will decrease setting time
True
145
What is hygroscopic expansion?
- expansion that occurs when the setting process is allowed to occur under water
- on air, the superficial tension of water limits crystal expansion
146
(T/F) hygroscopic expansion increases w a higher w/p ratio
False
- hygroscopic expansion decreases w a higher w/p ratio
147
(T/F) increase w/p ratio leads to increase in porosity, expansion and decrease in setting time
False
- increased porosity
- decreased expansion
- increased setting time
148
(T/F) more vigorous mixing of gypsum multiplies nuclei, leading to faster setting
True
149
(T/F) dental stone is harder than dental plaster because the particles of stone are harder
False
- particles are the same
- stronger, cuz less water added during mixing, since its easier to wet stone particles which are smaller and more regular
150
How does accelerator affect gypsum setting time?
- increase rate of dissolution of hemihydrate => saturates solution form faster => crystallise faster
Some accelerators:
NaCl, Na2SO4, K2SO4
151
The setting of gypsum is least affected by
1. Spatulation time
2. Room temp
3. W/P ratio
4. Chemical accelerators
5. Chemical retarders
Room temp
152
Gypsum primarily occurs in nature as
Di-hydrate
- then gotta dry it out into a hemihydrate
153
Gypsum products shd be kept in airtight containers to prevent..
Airborne dust from reducing the setting time of w/p mix by providing too many nuclei of crystallization
154
(T/F) wax reservoir should be larger than the sprue to alloy easy flow of molten alloy
True
155
(T/F) 6mm of investment above position of wax pattern is to prevent investment breakage
True
156
(T/F) wax pattern that is sprued w a diameter too large may result in casting w rounder margins
True?????
157
(T/F) surface irregularities on casting can be caused by too high casting pressure
True
158
(T/F) surface irregularities on casting can be caused by too rapid elimination of wax/too rapid heating
True
159
(T/F) surface irregularities on casting can be caused by inadequate wetting agent
True
160
(T/F) surface irregularities on casting can be caused by too short sprue
False
161
(T/F) boron can be used as an antiflux
False
- boron is used as a flux in casting
162
(T/F) graphite can be used as an antiflux
True
163
(T/F) flux is added to alloy to increase the melting temperature and dissolve oxides that form during casting
False
- increases fluidity of metal (decreases melting temp)
- but yes, dissolve oxides that form during heating
164
(T/F) the **oxidising** part of the flame has no colour and a **low** temperature, thus, it should be kept **away** from the alloy during casting
True
165
The metal constituent that helps reduce oxide formation during the casting of (crown) alloy is..
Zinc
166
The major reason for pickling a casting is to..
Remove oxides or carbonaceous residues
167
(T/F) Greatest amount of alloy shrinkage occurs when the molten alloy cools from solidus to room temp
False
- when molten alloy cools to solidus
168
(T/F) in type II gypsum-bonded investment, hygroscopic expansion is used for compensation of alloy casting shrinkage
True
169
(T/F) silicone, which is used as a refractory in inlay investment material, helps to prevent the contraction of the gypsum binder when the investment is heated
False
- silica, not silicone, provides a refractory during the heating of the investment
-> provides for high temp strength and also expands when heated due to a change in crystalline form (a-form to b-form)
- modifiers like boric acid and NaCl are responsible for preventing shrinkage of the gypsum when it is heated above 300 deg celsius
170
(T/F) It is an ideal property of investment material for the microstructure to not have porosities
False
171
(T/F) it is an ideal property for investment material to have high mechanical strength in room temp and high temp>400
true
172
(T/F) in type II investment materials, the finer the particle size of the silica, the more the hygroscopic expansion
True
173
(T/F) modifiers such as boric acid and sodium chloride are added to gypsum bonded investment material to prevent most of the shrinkage of gypsum when it is heated above 300 deg
True
- consider borax as a constituent of AE sol
- shrinkage happens due to loss of water
- boric acid and sodium chloride prevent most of the shrinkage of gypsum when it is heated above 300 deg
174
(T/F) the refractory in dental investments serve to increase the setting expansion of the material
False
- refractory material here refers to the silica (quartz & cristoballite)
- a refractory investment material is **one that is high temp resistant**
175
(T/F) refractory in dental investments serve to increase the thermal expansion of the material
True
- silica provides refractory in investment material
-> regulates thermal expansion
-> we use quartz and cristobalite
- heating of silica causes change in crystalline from at transition temp
-> from α to β-form => decreases density => increases volume (thermal expansion)
176
(T/F) gypsum-bonded investments are generally not used for casting metal-ceramic alloys because of their lower strength as compared to phosphate-bonded investments
True
177
(T/F) in type II investment materials, the finer the particle size of the silica, the more the hygroscopic expansion
True
178
During inversion, the expansion of cristoballite is..
Greater than quartz and tridymite
- inversion refers to the conversion from α to β forms of quartz/cristoballite
- inversion comes w expansion
179
What is the inversion temp of quartz?
575 degrees celsius
180
What is the inversion temp of cristobalite?
200-270 degrees celsius
181
Strength of dental investment for gold alloys is dependent on the amount of..
Hemihydrate gypsum
- investment for gold alloy is commonly gypsum-bonded
- gypsum-bonded means gypsum is the binder used, thus hemihydrates gypsum determines the strength!
182
(T/F) Largest hysteresis looks like the one with the most deviation from the linear graph
True
- think the blue line qns
183
(T/F) an investment material used for casting of gold alloys cannot be used as a soldering investment because it does not possess adequate strength
false
- a material strong enough and able to withstand high enough temperature to cast a gold alloy is good enough for soldering
184
The refractory in dental investments serve to..
Increase the setting expansion of the material
185
(T/F) w/p ratio of investment material will not affect the hardness
true
186
(T/F) the larger monocyclic phase of Y-TZP will arrest crack propagation but increases low temp degradation
True
187
(T/F) passivation increases fracture strength
False
- only increases corrosion resistance
188
(T/F) YTZP has high fracture strength
True
189
(T/F) YTZP ceramic arrests crack propagation because of high brittleness of YTZP
False
190
How does YTZP resist crack propagation?
1. Crack propagation => tetragonal to monoclinic transformation at surface => substantial increase in volume
2. Induce surface compressive stresses => crack tip closes => enhance resistance to further propagation
191
What is low temperature degradation?
- slow surface transformation of metastable tetragonal to stable monoclinic structure, in presence of water/water vapour
1. Stress corrosion mechanism => transformation at surface
2. Transformation of one grain => increase in volume => stress neighbouring grains
3. Generate microcracking => enable further water penetration, crack propagation & phase destabilisation
4. Cycle repeats as stressed neighbouring grains also transform => further increase in volume & stress
192
What are 2 other properties of YTZP other than high flexural/fracture strength?
- excellent corrosion & wear resistance
193
What is shape memory?
E.g. martensite to amtensite, return to original shape when exposed to heat
194
(T/F) ortho wires hysteresis is different between final & initial length
False
195
(T/F) twinning allows permanent deformation w/o breaking of atomic bonds
True
196
(T/F) NiTi has high fatigue life & corrosion resistance
True
- nickel titanium => wrought metal alloys
- used for orthodontic wires, crowns, clasps, root canal reamers and surgical instruments
197
(T/F) NiTi work hardening decreases corrosion resistance and increases brittleness
True
198
(T/F) austenite is converted to martensite by heating
False
- austenite to martensite transition is induced by stress (superelasticity)
199
(T/F) austenite is converted to martensite by force application
true
200
(T/F) parent form is martensite
false
- shd be austenite
201
(T/F) austenite allows permanent deformation
False
202
(T/F) austenite form has superelasticity
false
203
(T/F) Ti6Al4V has shape memory
false
- issa implant material
204
(T/F) Ti6Al4V is less brittle than ceramics
True
205
(T/F) Ti6Al4V has high corrosion resistance
True
206
(T/F) presence of dissolved oxygen, proteins, pH changes may cause corrosion in implants
True
207
(T/F) YTZP has high fracture strength but limited designs
True
208
(T/F) titanium implants fracture uncommonly but fracture due to high impact
False
- fracture from inappropriate implant design
- manufacturing defects
- non-passive fit of framework/physiological & biochemical overload
- main mechanism: metal fatigue from high cyclic occlusal loading
209
Work hardening of NiTi..
Increases hardness + decreases ductility + corrosion resistance
210
(T/F) NiTi has high fatigue strength & excellent corrosion resistance
True
211
(T/F) self etching primer is 37% phosphoric acid and primer in definite amounts
False
- iirc self etching primer it itself is a weak acid
- no additional phosphoric acid added to it
212
(T/F) hybrid layer is the layer where exposed collagen from demineralised dentin is embedded in adhesive resin
True
213
(T/F) water primer must be used when using the dry technique to expand the collagen network
True
214
(T/F) mechanical agitation of collagen by the primer allows impregnation of the collagen with the amphiphilic molecules
True
215
(T/F) alcohol primer is a versatile material that cannot be used for the dry technique
True
216
(T/F) acid etching of dentine will remove both the smear layer and collagen from the dentine
False
- wont remove the collagen
217
(T/F) water and acetone-based primers are applied to dry dentine to ensure adequate permeation of the collagen matrix w monomers
False
- acetone based primers shd be applied on wet dentine
218
(T/F) impregnation of primer into porous dentine forms hybrid layer
True
219
(T/F) etching is done to produce microporosities in enamel and to increase surface area for bonding
True
220
(T/F) water-based primer on wet dentine promotes impregnation of collagen
False
- has to be dry dentine
221
(T/F) primer has no effect on enamel
True
222
(T/F) 37% phosphoric acid removes smear layer & doesnt demineralise dentine
false
223
(T/F) bonding to enamel depends on micromechanical interlocking w unfilled resin & acid-etched enamel
True
224
(T/F) dry technique w dentine can usewater/alcohol based primer
False
- dry dentine technique=> only for water based
225
(T/F) bonding to dentine depends on chemical bonding (major) & micromechanical bonding (minor)
False
- its mostly micromechanical bonding
226
(T/F) over drying of dentine causes the collapse of collagen fibres
True
227
(T/F) tin in dental amalgam reduces strength
true
228
(T/F) tin in dental amalgam reduces hardness
True
229
(T/F) tin in dental amalgam increases expansion
False
- tin reduces expansion in amalgam
230
(T/F) tin increases flow when added to amalgamt
True
231
(T/F) dental amalgam best withstand forces of tension
False
- best withstand forces of compression!
232
(T/F) Hg increases fracture resistance
False
233
(T/F) amalgam reinforces tooth structure
True
234
(T/F) Cu and Ag decrease corrosion resistance in amalgam
False
235
(T/F) when polishing a dental amalgam restoration, heat generation shd be avoided as this will bring free mercury to the surface
True
236
The phase in dental amalgam that is considered most noble is..
Gamma I and gamma
237
(T/F) water contamination of dental amalgam will result in excessive expansion
True
238
(T/F) the creep value in a high copper content amalgam is lower than that in the conventional amalgam
True
239
delayed expansion of dental amalgam is caused by the formation of..
H2
- due to moisture contamination, zinc gets corroded & H2 is produced => expansion from within
240
The amount of mercury present in amalgam after condensation directly affects
1. Creep
2. Flow
3. Compressive strength
241
(T/F) amt of mercury in amalgam aft condensation affects the creep
True
242
(T/F) amt of mercury in amalgam aft condensation affects the porosity
False
243
(T/F) amt of mercury in amalgam aft condensation affects the flow
True
244
(T/F) amt of mercury in amalgam aft condensation affects the surface finish
false
245
(T/F) amt of mercury in amalgam aft condensation affects the compressive strength
True
246
(T/F) in dental amalgam, zinc serves as an oxide scavenger as well as increases the plasticity of the amalgam
True
Zinc:
- decreases brittleness of alloy
- increases plasticity
- acts as oxide scavenger
- responsible for delayed expansion on moisture contamination
