all topics Flashcards
(200 cards)
1
Q
What is the medical devices directive? What year was it brought about?
A
Statement of manufacture offered to all patients receiving dental appliances. March 2010.
2
Q
What is the oral enviroment subject to?
A
- loading (6kg)
- on/off cyclical forces
- chemicals
- temp. changes in microseconds
3
Q
What does the pdl act as for teeth?
A
shock absorber
4
Q
what is tensile strength?
A
tensile=pulling strength
5
Q
what is the unit of strain?
A
It has no unit because it is a ratio
6
Q
what is compressive strength?
A
measuring how brittle something is
7
Q
what is diametral tensile strength?
A
useful for brittle materials where conventional strength is not aceptable
8
Q
what is flexural strength?
A
how much bend it has
9
Q
what is shear bond strength?
A
test used to measure the overall strength of a material
10
Q
what is cyclical stress?
A
application of cyclical loading for a defined number of cycles. Material will either fail/survive
11
Q
how is surface roughness measured?
A
profilometer
12
Q
what is meant by rheological properties?
A
study of materials flow properties eg. composite in syringe, impression materials. how viscous things are
13
Q
biological properties are measured at three levels. What are these three levels?
A
- lab testing
- limited lab(in.vivo) usage testing
- human randomised controlled clinical trial
14
Q
what properties would the ideal material have?
A
non-toxic
non irritant
harmless to dental pulp
no carcinogenic potential or irritancy
15
Q
metals at an ambient temperature are what?
A
hard and lustrous
closely packed
opaque
conductors of heat and electricity
16
Q
what is an alloy?
A
a mixture of metals
17
Q
what is an alloy system?
A
the consideration of all possible combinations of that alloy
18
Q
what are crystals termed in a metal?
A
grains
19
Q
what is a grain boundary?
A
where the crystals in a metal meet, its a source of tension
20
Q
nucleation of a metal may be heterogenous or homogenous. what is meant by:
- heterogenous
- homogenous
A
- many sites of nucleation
2. single site of nucleation
21
Q
in a metal, what does grain size influence?
A
physical properties
22
Q
how do you visualise grain boundaries?
A
- light reflecting microscope
- application of acid etch as the etch will attack the grain boundaries
23
Q
what is malleability?
A
the max. degree of compression in response to an applied compressive force
24
Q
what is ductility?
A
the max. degree of extension in response to an applied tensile force
25
there are three types of solid solution. what are these three types?
1. ordered solid solution
2. random solid solution
3. interstitual solid solution
26
what is ordered solid solution?
atoms have specific sites in common lattice
27
what is random solid solution?
atoms have random sites in common srystal lattice
28
what is interstitual solid solution?
atoms lie within the primary lattice sites of the other
29
what do phase diagrams do?
phase diagrams construct a series of cooling curves for alloys of different compositon
30
what is a eutectic alloy?
very specific composition of 2 binary alloys
31
what are the two different compositions of amalgam?
conventional and high copper
32
what is the composition of conventional amalgam?
65% Ag, 29% Sn, 6% Cu, 2% Zn, 3% Hg
33
what is the composition of high copper amalgam?
40% Ag, 32% Sn, 30% Cu, 2% Zn, 3%Hg
34
what are the two variations in amalgam morphology?
lathe cut or spherical
35
is the gamma 2 phase present in both conventional and high copper amalgam?
yes, but is much less in the high copper amalgam
36
what effect does Cu have on amalgam?
strengthening effect
37
what does Zn act as in alloy production?
Zn acts as a scavenger for oxygen
38
what is the mixing of amalgam termed?
mixing of amalgam = trituration
39
Does the net expansion/contraction of amalgam balance itself out
yes
40
What is the percentage of expansion/contraction set by the ISO?
+/- 0.1%
41
the release of hydrogen gas results in what?
uncontrolled expansion
42
amalgam is fully set after how many hours?
24 hours
43
is amalgam strong or weak in thin sections?
weak
44
spherical amalgam has a larger what that results in it setting faster?
spherical amalgam has a larger surface area
45
what is creep?
protrusions at restoration margins
46
creep causes what?
ditching. Bits of amalgam to fracture of
47
what is largely, but not exclusively responsible for creep?
gamma 2 phase
48
How is the gamma 2 phase reduced?
adding more copper
49
corrosion of alloy exacerbates the release of what at the marginal crevise?
mercury
50
what is the theory of mercuroscopic expansion?
localised expansion of amalgam. Where the amalgam wants to create small balls of mercury and trap them between the restoration and the tooth
51
why is an advantage of corrosion?
corrosion provides marginal seal
52
does amalgam have a high thermal diffusivity?
yes
53
what are four properties of amalgam?
1. creep
2. corrosion
3. thermal
4. biological
54
mercury compounds are known to be toxic to what part of the body?
CNS
55
some reports have linked amalgam to what?
- ms
- behavioural problems
- psychiatric disturbances
56
drier mixes are achieved by what?
mechanical mixing
57
nowadays, how is amagalm normally dispensed?
its normally encapsulated
58
what was the earliest tooth coloured restorative material?
silicates
59
what are some of the properties of silicates?
- release flouride
- moisture sensitive
- erosion prone
- brittle
60
what was used as a restorative material between the 1960s and 1980s?
acrylics
61
what were the components of the powder in acrylic restorative materials?
Pmma(polymethylmethacrolate)
- chemical initiator(usually peroxide)
- pigment(makes it tooth coloured)
62
what was in the liquid component of acrylics?
- mma monomer( methyl methacrolate monomer)
| - chemical activator(amine)
63
what was the initial thing that set of the acrylic setting reaction?
amine (chemical activator)
64
what are the four stages of free radical polymerisation of methyl methacrolate?
1. activation
2. initiation
3. propogation
4. termination
65
what do the stages of free radical polymerisation mean for the clinician?
- material contracts on setting
| - reaction is exothermic
66
how were acrylics better than silicates?
acrylics are:
- less prone to erosion
- less soluble
- less acidic
- less brittle
- low thermal diffusivity
67
In 1951, what did Knock & Glen do to acrylics?
they introduced inert filler particles that reduced shrinkage
68
In 1963, what did Bowen do?
covered the filler particles in a coupling agent, this overcame weaknesess. It was now known as composite.
69
laser light curing technology was developed to give what?
command curing
70
what are resin matrix generally based upon?
methacrolate or dimethacrolate monomers.
| eg. BISGMA, Urethane, dimethacrolate
71
carbon to carbon double bond in the matrix takes part in what?
free radical polymerisation
72
what is a silorane?
where there is a ring and it opens up
73
what is the photosensitiser in composites?
camphorquinone
74
what in a silorane, is involved with the ring opening polymerisation?
oxirane
75
what in the filler causes radiopacity?
quartz
76
what are some examples of the glasses used as fillers?
- aluminosilicates
- boro silicate
- barium oxide
77
what is the most common coupling agent used?
gamma silane(gamma-methacryloxypropyltrimethoxysilane) only need to know gamma silane!!
78
more filler results in what?
less contraction
79
how does the polymerisation of camphorquinone begin?
camphorwuinone yeilds the necessary free radicals to begin polymerisation
80
what is the most readily generated light that is used?
quartz halogen lights
81
what does the coupling agent do?
coupling agent transfers the stress generated under loading from the rigid brittle filler to the more flexible and ductile polymer matrix.
82
what types of resin composites are there?
conventional, microfilled, hybrid, nano composites
83
what is hybrid?
mix of conventional and microfilled
84
what is the difference between type 1 and type 2 classifications according to ISO 4049?
type 1. restoration of cavities including occlusal surfaces
| type 2. all other polymer based filling and restorative materials
85
does the viscosity of resin composite increase when leaving the tube?
yes it does.
86
what are three mechanisms that result in wear?
1. abrasive
2. erosive
3. fatigue
87
polycarboxylated cements replace what?
- ion leachable glass
- polycarboxylic acid
- set cement
88
the setting reaction in glass polyalkenoate, powder & liquid is essentially what?
acid based
89
the powder in glass polyalkenoate is what?
sodium aluminosilicate glass
90
porosity causes stress. stress causes what?
stress causes cracks
91
what is the setting reaction in glass polyalkenoate?
glass + acid =cored structure
92
what is the outer layer in the cored structure of glass polyalkenoate?
outer layer = rich in calcium
93
what is the inner layer in the cored structure of glass polyalkenoate?
inner layer = aluminium
94
what is the charge in the calcium and aluminium ions in glass polyalkenoates?
Ca2+
| Al 3+
95
how do the calcium and aluminium ions play a part in the setting reaction of glass polyalkenoate?
the cross link acid chains
96
in the initial set, is it the calcium or aluminium ions that are predoinant?
calcium ion is predominant over aluminium
97
why is the calcium ion predominant over aluminium ion in the initial set?
- calcium is on the outer surface of glass so its the first thing that the acid meets
- calcium is more mobile in solution than aluminium
- -more statistically likely that two chains will come along rather than three chains( transport analogy)
98
why is vaseline used after placing glass polyalkenoate?
as the final set (aluminium) has to be protected from water
99
how does the glass polyalkenoate bond to tooth substance?
via calcium inos
100
what does citric acid do?
citric acid removes the smear layer
101
what does polyalcrylic acid do?
increases bond strength
102
what are some of the properties of glass polyalkenoate?
- thermal diffusivity is close to dentine
- chemical set is exothermic
- flouride release
- brittle
- poor abrasion resistance
- susceptible to acid erosion
- good appearance
103
in modified composites, the filler is replaced with what?
aluminosilicate glass. This encourages flouride release
104
what is a giomer?
modified composite, however aluminosilicate glass is pre-reacted with polyacid to form a pre reacted glass polyalkenoate complex
105
what are the two types of reaction involved with giomers?
1. surface reaction
| 2. full recation
106
what is dark cure?
-doesnt really work, where both setting reactions have occured and the last setting reaction (dark cure) is where it sets in the presence of no light. But this doesnt actually happen!!
107
is there a greater release of flouride when the pH is lower?
yes
108
what are some advantages of composite?
strong, tough, insoluble, radiopaque, quick setting
109
what are some disadvantages of composite?
no inherent adhesion, shrinkage, no flouride release
110
what are some advantages of glass polyalkenoate?
inherent adhesion, little shrinkage, flouride release, bicompatible
111
what are some disadvantages of glass polyalkenoate?
brittle, soluble, not radiopaque, slow set
112
where does the setting reaction happen in phosphoric acid based cements?
at the surface of the powder
113
Phosphoric acid based cements have a low pH and low molecular weight, what does this mean?
it can penetrate more dentinal tubules
114
Phosphoric acids are radiopaque, what is the constituent of phosphoric acid that causes it to be radiopaque?
zinc oxide
115
does phosphoric acid based cements have an obtundent effect?
no
116
how does zinc oxide eugenol cements set? by what reaction?
chelation
117
are reinforced zinc oxide eugenol cements obtundant?
yes
118
are reinforced zinc oxide eugenol cements strong that just zinc oxide eugenol cements?
yes
119
is VLC exothermic or endothermic?
exothermic
120
what are some of the properties of calcium hydroxide cements?
- high pH gives beneficial irritancy and renders it bacteriocidal
- thermal and electrical insulator
- radiopaque
- not adhesive so there is no coronal seal
121
polycarboxylates are acidic but have a gih molecular weight, what does this reduce?
reduces penetration and therefor it is mildly irritant to the pulp
122
glass ionomers are bacteriostatic due to what?
flouride release
123
what cements have zinc oxide in them?
poly F, calcium hydroxide, zinc oxide eugenol, phosphoric acid based cements
124
poly F cross links with what ions?
calcium ions
125
what is the test that can be done to measure strength?
shear bond strength test
126
glass polyalkenoates have a cord structure, what is this due to?
this is due to the concentration gradients
127
where does the setting reaction happen in glass polyalkenoates?
setting reaction happens at the surface
128
what is the C factor?
ratio of unbound to bound surfaces, most unfavourable = occlusal
129
hydrocolloid impressionmaterials are hydrophobic. what does this mean?
moist surfaces will repel against it. Tissues that are moist will come close to the tissue but not actually touch it
130
what would the ideal impression material be?
- no changes when exposed to disinfectants
- no interaction with model/die materials
- non toxic
- easily manipulated
- palatable taste
- realistic working/setting time
131
what are the classifications of hydrocolloid impression materials?
non elastic or elastic
132
is non elastic hydrocolloid materials highly mucostatic?
yes
133
is non elastic or elastic hydrocolloid impression materials more commonly used?
elastic is more commonly used
134
hydrocolloid are either reversible or irreversible. What is an example of them both.
1. reversible=agar
| 2. irreversible=alginate
135
what features do reversible and irreversible hydrocolloids both have in common?
both colloidal suspensions of polysaccharides in water
136
alginate can only go from sol to gel, is agar the same?
no. Alginate can go from sol to gel, and from gel to sol.
137
what is agar?
complex polysaccharide from seaweed
138
what does borax do in agar?
borax gives it more body
139
what are the temperatures that agar requires water bath conditioning?
100. 65 and then to 45 which is the clinical usage temperature
140
what are some of the disadvantages of agar?
- cost
- cross infection concerns of reuse
- low tear strength
- dimensionally unstable due to water content
141
what is the composition of alginate, an irreversible hydrocolloid?
1. sodium or pottasium salt
2. calcium sulphate dihydrate
3. sodium phosphate
4. inert filler
5. reaction indicator in some to signify set
142
give two examples of mucostatic materials.
plaster and alginate
143
in alginate, sodium phosphate limits the availability of what?
calcium ions
144
what units is strain?
doesnt have a unit because it is a ratio
145
why are impressions disinfected?
to prevent the transmission of blood borne viruses to patients, potential workers and members of the dental team
146
what impression disinfection is used in DDH?
artichlor tablets, rinse and immerse in solution for 2 minutes
147
give two examples of alternatives to impressions?
- CAD CAM
| - Intra oral scanner
148
what are the 3 gypsum products?
1. dental plaster
2. dental stone
3. densite
149
at what temperature does gypsum turn into dental plaster?
120 degrees
150
at what temperature is gypsum steam into dental stone?
steamed at 125 degrees
151
what is gypsum boiled in to make densite?
calcium chloride
152
does plaster or densite have larger particle size?
densite has larger particle size and has more porosities than plaster
153
does plaster require more water than stone when mixing?
yes
154
on mixing gypsum, air incorporation leads to what?
- loss of detail
| - weakness
155
what happens in the 1st stage of setting in gypsum?
water becomes saturated with hemihydrate
156
what happens in the 2nd stage of setting in gypsum?
conversion of hemihydrate to dihydrate
157
what happens in the 3rd stage of setting in gypsum?
dihydrate crystalises out initiated by exposure to nuclei of crystallisation
158
what is meant by the gilmore needles in gypsum setting?
where the initial set goes to intermediate set but not final
159
what increases solubility of hemihydrate in gypsum?
hydrogen sulphate
160
what is the retarder in gypsum?
borax
161
Dyes are often added to gypsum, what colour is related to the following
1. plaster?
2. stone?
3. die stone?
1. white
2. yellow
3. blue/pink
162
what are some of the properties of gypsum?
- brittle
- low flexural strength
- good detail reproduction
- soluble in water
163
what are some of the advantages of gypsum?
- inexpensive
| - easy to use
164
what are some of the disadvantages of gypsum?
- may interact with the borax in alginate(Rare)
| - hypochlorite may interact if not rinsed off implression before casting
165
what are the three approaches to adhesion?
1. micromechanical attachment
2. chemical adhesion to enamel/dentine
3. complex adhesion
166
low contact angle means what?
high wetting ability
167
what are the 3 factors effecting acid etch?
1. etching time
2. washing
3. drying
168
what does washing acid etch do?how long do you wash?
washing acid etch removes any debris. Wash for 60 seconds
169
what does drying acid etch do?
drying enable hydrophobic resin to penetrate and attach
170
what are some features of an ideal resin?
- high bond strength to enamel and dentine
- immediate,durable and reliable bond
- prevent bacterial ingress
- simple and safe to use
- fit for purpose
171
what are some of the problems that may occur in dentine bonding?
- dentine is hydrophilic but adhesives are hydrophobic
- dentine is a vital tissue
- consists of inorganic and organic compounds
- covered by a smear layer
- smear layer occludes the dentinal tubules
172
what do sealers do?
sealers flow into the dentinal tubules.
Seal the dentine with surface layer rich in methacrolates
ensures bonding to the resin composite
173
what do dentine conditioners do?
dentine conditioners open dentinal tubules and demineralize surface dentine to a depth of 4 microns
174
what do primers act as?
adhesives.
175
what is the general formula of primers?
M-R-X
M=methacrolate group
R=spacer to allow system to move
X=interacts in some way to help dentine move
176
What is a popular primer?
HEMA
177
what are sealers a mix of?
BIS-GMA and HEMA
178
There are three approaches to etching. What is involved in each of these approaches?
1. 3 stage- etch prime and seal on different stages
2. 2 stage- etch and then prime and seal together
3. 1 stage- etch prime and seal all in the same stage
179
what is an ormocer?
monomer free nanohybrid composite material
180
what are the three components of an ormocer?
silicones, organic polymers and ceramic glasses
181
what is meant when it is said that hydrocolloid impression materials are hydrophobic?
moist surfaces will repel against the material
182
what are some ideal features of hydrocolloid impression material?
- non toxic
- easily manipulated
- palatable taste
- realistic working/setting time
- no interaction with model/die materials
183
there are two classifications of impression materials. What are they?
non-elastic or elastic
184
is non elastic used regularly?
no, not commonly used anymore
185
give an example of elastic impression materials.
hydrocolloids
186
there are two types of hydrocolloid impression material. What are these two types?
reversible and irreversible
187
what is an example of 1. reversible hydrocooloid and 2. irreversible hydrocolloid
reversible=agar
| irreversible=alginate
188
what features do reversible and irreversible hydrocolloids both have?
they are both colloidal suspensions of polysaccharides in water
189
ISO4823 classifies according to what?
- chemical nature
| - consistency
190
in the base paste of polysulphides, what makes it smell very bad?
thiol
191
as cross linking occurs in polysulphides, what increases?
increased viscosity and elasticity
192
what are some properties of polyshulphides?
- high tear resistance
- reaction continues with water loss
- bad odour and taste
- impression is easily read
193
what is the setting reaction of silicon rubbers (condensation)?
cross linking of hydroxyl terminated polydimethylsiloxane chains
194
what is the by product of silicon rubbers(condensation)?
alcohol. specifically ethyl
195
what are some of the properties of silicon rubbers(condensation)?
- set time is less than polysulphides
- hydrophobic
- tear resistance is adequate
- good elastic recovery
- considered non toxic in intra oral application
196
what is the setting reaction of silicon rubbers addition curing?
platinum catalysed addition reaction
197
is there a by product from silicon rubbers addition curing?
no. there is only a by product from condensation curing.
198
what is the setting reaction of polyethers?
sets by cationic ring opening addition polymerisation
199
how many types of ISO standards for dental gypsum products are there?
5
200
what are the 3 types of gypsum products?
plaster, stone, densite
