Dental Materials Flashcards
(183 cards)
1
Q
Define an alloy
A
A mixture of two or more metals
2
Q
The process that occurs in the formation of a crystal from a solution, liquid or vapour
A
Nucleation
3
Q
What two types of nucleation are there?
A
Heterogenous & Homogeneous
4
Q
Describe heterogenous nucleation
A
Many sites of nucleation
5
Q
Describe homogeneous nucleation
A
Single site and requires specialised equipment
6
Q
What type of nucleation is more common in dental applications
A
Heterogenous nucleation
7
Q
What does grain size refer to?
A
Crystal size
8
Q
What promotes a small grain size?
A
-rapid solidification
-provision of ‘extra’ nucleation sites
9
Q
What ways can metals and alloys be shaped?
A
-hammering
-rolling
-pressing
-drawing into a wire
10
Q
What happens to grains when a metal/alloy is drawn into a wire?
A
They are elongated
11
Q
The maximum degree of extension in response to an applied tensile force
A
Ductility
12
Q
The maximum degree of compression in response to an applied compressive force
A
Malleability
13
Q
What is a solid solution? Give an example.
A
Where two metals dissolve in each other and then harden to give a solid solution.
E.g. copper and zinc dissolve in each other and harden to give a solid solution called brass.
14
Q
Ordered, random and interstitial are three types of what?
A
Solid solution
15
Q
What are solid solutions in comparison to metals?
A
-harder
-stronger
-higher elastic limits
-hardening effect
16
Q
What does Tm indicate on a phase diagram?
A
Melting point
17
Q
What does the plateau on a phase diagram indicate?
A
Temperature constant during crystallisation
18
Q
Why are phase diagrams useful?
A
Can construct series of cooling curves for alloys of different composition
19
Q
When one component in an alloy solidifies before the other, this has less than optimal properties. What is this process called?
A
Coring
20
Q
Which line on a binary alloy graph represents the liquidus
A
The top line
21
Q
Which line on a binary alloy graph represents the solidus?
A
Bottom line
22
Q
What would a large separation between liquidus and solidus lines on a binary alloy graph indicate?
A
That the alloy is more susceptible to corrosion and there is greater coring
23
Q
What application do eutectic alloys have?
A
Solders
24
Q
Where alloy components are insoluble in each other, there is a specific point where crystallisation occurs at specific temperature. What is this point called?
A
Eutectic point
25
In dentistry, what are solders used for?
-attach a metal component to an appliance
-fit golden laced teeth to restore them
26
When an alloy reacts with mercury what does this form?
Amalgam
27
What are the two compositions of amalgam?
Conventional and high copper
28
What effect does copper have on amalgam?
It strengthens it
29
What is the role of zinc in alloy production?
It acts as a scavenger
30
How does zinc act as a scavenger?
It oxidises in preference to the other metals, attracts oxygen so that the other metal won’t.
31
What is another word for mixing?
Trituration
32
When mercury diffuses into alloy during setting reaction what occurs?
Small shrinkage
33
What is there risk of if we have a material that expands or contracts too much?
-a gap around the restoration
-forces that could shred off cusps of teeth filled with an alloy
34
What do the international standards organisation (ISO) limit expansion/contraction to?
+/- 0.1%
35
What happens to zinc containing alloys if placed in a moist or contaminated environment?
They expand, this is because the zinc ion reacts with water, liberating hydrogen.
36
How long does it take for final strength of amalgam to be reached?
24 hours
37
What is the minimum depth of amalgam required to counteract weakness in thin sections?
2mm
38
What is strength of amalgam dependant upon?
The mercury content
39
What is the optimum Hg concentration?
44-48%
40
What does packing of amalgam into a cavity do to the mercury?
Forces it to the surface
41
Define creep
Plastic deformation under load
42
How does creep clinically manifest?
As protrusions at restoration margins.
(This can fracture off producing a ditch and predisposing area to caries.)
43
What is the gamma 2 phase largely responsible for?
Creep
44
What is the theory of mercuroscopic expansion?
Localised expansion of amalgam due to release of Hg into marginal crevice
45
What can corrosion products provide?
Marginal seal
46
What is the most accurate way to dispense mercury?
Capsules containing mercury and alloy
47
What particle size of an alloy achieves higher strength?
Smaller particle size
48
What happens if particle size is too small?
It will be too rapid a set and cannot remove Hg by manipulation
49
What material was used as a restorative material in 1950’s-60’s?
Silicates
50
What material was used as a restorative material in 1960’s-80’s?
Acrylics
51
What form could acrylic take?
Powder or liquid
52
What is the type of reaction in the setting reaction for both powder and liquid acrylics?
Free radical addition polymerisation
53
What is a consequence of fast setting of acrylics?
Limited working time
54
What is the bond that splits in a free radical addition polymerisation reaction?
C=C
55
What is a key organic compound used to demonstrate a free radical addition polymerisation reaction?
Methyl methacrylate (MMA)
56
What are the four stages of free radical addition polymerisation reaction?
1.activation
2.initiation
3.propagation
4.termination
57
What happens in the initiation stage?
C=C cleaved
58
What happens in the propagation stage?
Multiple units join
59
What happens in the termination stage?
Two free radicals merge/meet which terminates the joining of units
60
What happens to materials when they undergo polymerisation?
They contract
61
What type of reaction is the contraction of materials upon polymerisation?
Exothermic
62
What is very key, important feature of acrylics?
They exhibit low thermal diffusivity (heat transfers slower)
63
What are some disadvantageous qualities of acrylics?
-can be irritant to pulp
-May interact with Eugenol
-poor abrasion resistance
64
What is a eutectic alloy?
An alloy that has a very defined, very narrow ranged melting point and properties
65
What has been used in acrylic to try and reduce shrinkage, however may also weaken the material?
Inert filler
66
What is the setting reaction for resin composites?
Free radical addition polymerisation
67
What are the two main components of resin composite?
-resin matrix
-inhibitors
68
What does the comonomer,TEGMA, control?
Viscosity
69
What is the role of inhibitors in resin composite?
They prevent polymerisation kicking off too readily
70
What benefit does the use of siloranes have?
May minimise polymerisation shrinkage
71
What is the setting reaction for siloranes?
Cationic ring-opening polymerisation
72
What two important substances do resin composites contain?
Fillers and coupling agents
73
What are the three types of fillers?
1. Quartz
2. Silica
3. Glasses
74
Which type of filler contains a heavy metal within them that allows for opaque radiopacity?
Glasses
75
What is an example of an excellent coupling agent?
Vinyl silane
76
What must fillers be coupled with?
Coupling agent
77
As % volume of filler content increases, what happens to the surface hardness?
It increases
78
The addition of filler will have what effect on the % volume of setting contraction?
Will decrease it
79
What effect does the addition of filler have on the coefficient of thermal expansion?
It decreases it
80
How can resin composite set?
1. Chemical
2. Light
81
In a light set, what photosensitiser is often used?
Camphorquionone
82
What does camphorquinone do?
Yields necessary free radicals to start polymerisation when it becomes excused by blue light
83
What material is a shock absorber?
Filler
84
What is resin susceptible to upon polymerisation?
Shrinkage
85
What controls properties of resin composite?
The type, concentration and particle size distribution of fillers
86
What are the four classification of resin composites?
1. Conventional
2. Microfilled
3. Hybrid
4. Nano-composite
87
What classification of composite has large size of filler particles which in turn can result in poor aesthetics
Conventional resin composite
88
What classification of resin composite has smaller filler particles, therefore a larger surface area and difficulty gaining high filler loading?
Microfilled resin composite
89
What classification of resin composite is a blend of conventional and Microfilled composite?
Hybrid resin composite
90
What classification of resin composite is most commonly used today and could be described as a variation of microfilled composite?
Nano-composite
91
What standard must resin composites conform with to be on the market?
ISO 4049
92
Composite sets toward light source. True or false?
False.
This is a common misconception that composite sets towards light source
93
What is the effect on the working time of resin composite if it is chemically activated?
Limited working time
94
What is the effect on working time if resin composite is light activated?
Extended working time
95
What is required for good light curing?
Light must be in very close proximity to composite restoration
96
What do thermal (mechanical) properties depends upon?
- filler content type
- efficiency of coupling
- degree of porosity
97
What influences overall success of restoration?
Cavity shape
98
What is the equation for C-factor?
C-factor = number of bonded surfaces/number of un-bonded surfaces
99
Why does C-factor matter?
The higher the c-factor, the greater the stress from polymerisation shrinkage. Risks of debonding and micro leakage of restorations.
100
What photosensitiser do modern resin composites contain that means they can be light activated?
Camphorquinone
101
Camphorquinone becomes excited on exposure to what type of light and at how many nanometres?
Blue light ( 460-480nm)
102
What is good practice in order to maximise curing of resin composite?
To have the light as close to the composite as possible
103
What are the two different types of light sources for curing units?
Quarts Tungesten Halogen
LED’s
104
What is a downside to quartz tungsten halogen curing units and why?
They generate a fair amount of heat which may distress and cause damage to the pulp
105
What light source is known for having a narrow spectrum?
LED’s
106
What should be avoided when using LED light curing units?
Sequential activation as this may damage the pulp. Wait at least 30n seconds between activations.
107
Due to the narrow spectrum of LED’s, what are the risks?
That the light unit may nit coincide with the photosensitiser in some resin composites. If this is the case, another light unit must be used.
108
What happens to a resin composite material when it cures?
It contracts
109
When should you change your light curing unit?
Once it reads a measurement that is 25% lower than it’s original maximum radiation measurement.
110
What are the three main wear mechanisms of resin composites?
- abrasive
- erosive
- fatigue
111
How does abrasion effect a resin composite restoration?
Hard angular particles (asperities) penetrate polymer matrix removing material by sheering and cutting
112
How does erosion effect a resin composite restoration?
Hard angular particles (asperities) damage polymer matrix
113
How does fatigue effect resin composite restorations?
Localised deformations of the polymer are subject to repeated stresses and this can result in failure.
114
How can various stages of resin composite wear be visualised?
By staining with silver (Ag)
115
What are the two main factors that cause softening of the resin matrix?
- inhibition of polymerisation due to entrapped air pockets
- chemical softening ( foods and plaque acids)
116
What coupling agent unites resin and filler?
Vinyl silane
117
Why might the resin/filler interface become stressed?
- thermomechanical fatigue
- water sorption
- polymerisation shrinkage
- mechanical stresses upon restoration
118
How do cracks propagate at the resin/filler interface?
Leakage of filler constituents
119
What is hydrologic filler degradation a result of?
Stress corrosion
120
What are the tow main consequences of polymerisation shrinkage of resin composite?
- leakage
- cuspal flexural and post operative sensitivity
121
What restorative material contains nano fillers?
Resin composites
122
What are the potential downfalls of nano materials?
They are thought to have potential toxilogical and environmental concerns
123
Describe the “ ideal restorative material”
- strong
- good marginal seal
- bonds to tooth substance
- wear resistant
- cariostatic
- goof aesthetics
- easy to manipulate
- non-toxic
- non irritant to dental tissues
124
What does cariostatic mean?
Inhibits the formation of dental caries
125
What happens to the flexural strength of a tooth the closer you get to the root apex?
Flexural strength decreases
126
What is the filler in resin composites made up of?
Ground down glass
127
How are resin composite post-op fracture risks counteracted?
By placing the resin composite in increments before curing
128
What is the preferred name for glass ionomers?
Glass polyalkeonate cements
129
What are the two earlier cements that glass polyalkenoate cements derive from?
- silicate cements
-polycarboxylate cements
130
What early version of polycarboxylate cement had unfavourable characteristics such as poor appearance and mechanical properties?
Zinc containing polycarboxylate cements
131
What material was used to replace zinc in polycarboxylate cements so that appearance, solubility and mechanical properties would improve?
Ion leachable glass
132
What are the three presentations of glass polyalkenoate cements?
1. Powder + liquid
2. Powder mixed with water
3. Encapsulated form
133
What material is the powder component of glass polyalkenoate cements made up of?
Sodium aluminosilicate glass
134
What is the most beneficial quality of sodium aluminosiliacte glass as a restorative material?
It has contains high concentration of fluoride
135
What component of the liquid aspect of glass polyalkenoate cements is important in controlling setting characteristics of the material?
Tartaric acid
136
What two ways can encapsulated glass polyalkenoate cements be mixed?
By hand spatulation
OR
By oscillator
137
Are cements normally viscous or fluid?
Viscous
138
Will viscous cements have low or high porosity and why?
Low porosity as difficult to incorporate air
139
What makes mechanical mixing of fluid cements incorporate more porosity?
The frothing of mixed material due to oscillation
140
What group of chains of poly-acid cross link in acid base setting reaction?
COO-
141
What two components react together in the setting reaction of glass polyalkenoate cements?
Aluminosilicate glass reacts with poly acid
142
What do the side chains present in the setting reaction of glass polyalkenoate cements require in order to improve handling properties of the material?
Modifying and cross-linking agents
143
what does an acid base reaction produce?
Salt + water
144
What do set glass polyalkenoate cements consist of?
- glass particles
- silaceous hydrogel
145
What are the two phases of the setting reaction of glass polyalkenoate cements?
- initial set
- final set
146
When does initial set of glass polyalkenoate cement occur and what ions ( liberated from glass particles) cross-link the poly acid chains?
Occurs in the first few minutes of mixing. Ca2+ ions predominate
147
When does final set of glass polyalkenoate cements occur? And what ions ( liberated from glass particles) involve cross linking of poly acid chains?
Finals et occurs 24 hours after set. Al3+ ions predominate
148
Why does initial reaction use Ca2+ ions over Al3+ ions?
- Ca2+ ions are:
More accessible ( on outer surface of glass particle)
More mobile, due to relative ionic radii ( come along first before Al3+ which are less mobile)
Ca2+ only has to cross link with two chains whereas Al3+ has to cross link with 3 chains
149
Until final set of glass polyalkeonate cements is complete, what is the material rendered?
Moisture sensitive
150
How would you protect glass polyalkeonate cements from moisture?
Using a varnish to infilled resin
151
What substance could you use to prevent drying out of glass polyalkenoate cement on polishing?
Vaseline ( as a lubricant)
152
What would enhance adhesion of glass polyalkenoate cements to tooth substance?
Application of a tooth cleanser
153
What are the two common examples of tooth cleansers?
- critic acid
- poly acrylic acid ( increases bond strength)
154
How do tooth cleansers enhance adhesion of glass polyalkenoate cement to tooth substance?
They remove smear layer
155
What are the beneficial properties of glass polyalkeonate cements?
- tooth coloured and translucent
- adhesion to tooth substance
- fluoride release from glass
- biocompatible
156
What property is the ‘selling point’ of glass polyalkeonate cements?
Fluoride release from glass component
157
What is the disadvantages of glass polyalkenoate cements?
Brittle and relatively poor abrasion resistance
158
What are the three applications of glass polyalkenoate cements?
- restorative material
- luting cements
- lining/base material
159
What is the disadvantages of glass polyalkenoate cements on a radiograph?
They lack radiopacity
160
What are the three variants ( related materials) of glass polyalkeonoate cements?
1. Modified composite
2. Giomers
3. Resin modifies glass ionomer cements (RMGIC)
161
Why is HEMA an important component of RMGI cements?
It allows resin + acid to coexist in aqueous solution
162
What does removal of the smear layer on dentine, through acid etch, achieve?
Exposes tubules (collagen networks), resin and solvents able to penetrate tubules, soaking into collagen networks and locking in.
163
What can be a result of over-drying etched dentine?
Collapse of the collagen lattice, resulting in reduced bond strength.
164
What does acid etch facilitate?
Micro-mechanical retention
165
What is the cause of the smear layer on dentine that includes tubules?
Cavity preparation
166
What are the three main components of dentine bonding agents?
- dentine conditioners
- primers
- sealers
167
What are dentine conditioners and what do they do?
They are acids that alter the surface appearance and characteristics of dentine
168
What are two examples of dentine conditioners?
- phosphoric acid
- nitric acid
169
What does a primer do in dentine bonding?
Acts as the adhesive, bonding hydrophobic composites to hydrophilic dentine
170
What do sealers do in dentine bonding?
Flow into dentinal tubules, sealing dentine and ensuring bonding to resin composite
171
What is the most common example of a primer used fro feint bonding?
HEMA
172
What procedure risks nano-leakage?
Acid etch
173
What are the three presentations of dentine and enamel bonding?
- three stage bonding
- two stage bonding
- one stage bonding
174
What are three different types of cements that can be used as lining/base materials?
- phosphoric acid based cements
- zinc oxide euganol cements
- calcium hydroxide cements
175
Which cement based lining is the most irritant to the dental pulp and why?
Phosphoric acid based cements, because of their low pH and molecular weight of parent acid
176
Which cements lining contains euganol and why is this important to consider if you aim to place a resin composite restoration?
Zinc oxide euganol cement
Euganol is not compatible with resin composites as it impairs their polymerisation. Therefore another lining material or restorative material should be used.
177
What effect does euganol have on the pulp?
A calming/cooling effect
178
Which lining cement has insufficient strength to withstand amalgam condensation and packing?
Calcium hydroxide cement
179
What is a commonly used resin-modified glass ionomer for lining on clinic?
Vitrebond
180
What are the advantages of a composite bulk fill?
Reduces polymerisation shrinkage and clinical working time
181
What lining technique is claimed to foster formation of reparative dentine and posses excellent adhesive properties prior to placement of restorative material?
Bulk dentine replacement
182
What is beneficial irritancy?
Stimulation of the pulp by the lining material being slightly acidic or alkali to produce tertiary dentine which protects the pulp
183
what restorative material can you not place in a pregnant or breastfeeding woman?
Amalgam
