Flashcards
Year 2 Biomaterials 3
Cards in this deck (200)
- 1What are the two types of RMGIC setting reaction?Conventional - acid-base reaction
Light-cured - photopolymerisation of HEMA monomer to provide a rapid set ("command-set) - 2What does the conventional setting reaction of RMGICs involve?Acid-base reaction between polyalkenoate acid and fluoro-alumino-silicate glass continues as normal until the material is set
- 3What does the light-cured setting reaction of RMGICs involve?Photopolymerisation of HEMA monomer to provide a rapid set ("command-set)
- 4What undergoes photopolymerisation when RMGICs are light-cured?HEMA monomer
- 5What is the approximate maximum depth of light-curing for RMGICs?~ 4 mm
- 6How are the chemical properties of RMGICs similar to conventional GICs?Inherently adhesive to enamel and dentine
Fluoride-releasing
Cariostatic - 7How do the physical properties of RMGICs compare to those of conventional GICs?RMGICs have better physical properties:
- Better fracture toughness
- Better tensile strength
- Improved aesthetics - 8What are the drawbacks of RMGICs?The HEMA monomer, if unreacted, can diffuse through the dentinal tubules and irritate the pulp
- 9How can the HEMA monomer of RMGICs be problematic?If unreacted, the monomer can diffuse through the dentinal tubules and irritate the pulp
- 10What is not a component of calcium silicate cements?Acid
- 11What do calcium silicate cements only use for the setting reaction? What are they therefore also known as?Only use water
Hydraulic calcium silicates - 12Why are calcium silicate cements also known as hydraulic calcium silicates?They only use water for the setting reaction
- 13Give 2 examples of calcium silicate cements.Biodentine
MTA (mineral trioxide aggregate) - 14What are the components of mineral trioxide aggregate (MTA)?Tricalcium silicate
Dicalcium silicate
Calcium aluminate
Calcium sulphate
Bismuth oxide (for radiopacity) - 15What is the purpose of the bismuth oxide component of mineral trioxide aggregate (MTA)?Radiopacity
- 16What is the approximate setting time for MTA?3-4 hourse
- 17Which company introduced Biodentine?Septodont
- 18What is Biodentine designed to do?Set quicker than MTA
Be used as a dentine replacement (i.e. a restorative material)
Excellent for pulp capping (direct and indirect) and repairing RCT perforations (same as MTA) - 19What is the main core material of Biodentine?Tricalcium silicate
- 20What are the constituents of the powder component of Biodentine?Tricalcium silicate (main core material)
Calcium oxide (reactive filler)
Calcium carbonate (reactive filler)
Zirconium oxide (radiopaque)
Iron oxide (gives white colour) - 21What are the constituents of the liquid component of Biodentine?Water (solvent and reacting agent)
Calcium chloride (accelerates reaction of water with fillers) - 22What type of setting reaction occurs with Biodentine?Water hydration reaction (like concrete setting)
- 23Describe the setting reaction of Biodentine.Water hydration reaction:
1. Hydration reaction of tricalcium silicate
2. Partial dissolution of tricalcium silicate, a hydrogel of hydrated silicates is formed, and sodium hydroxide is produced (lots of Ca2+ and OH- released)
3. Over time, the hydrated gel of calcium silicate polymerises forming a solid network - 24How long does the curing of Biodentine take from the moment the water is mixed with powder?12 minutes
- 25How long is Biodentine mixed for?30 seconds
- 26What are some of the clinical applications of Biodentine?As a base material under composite (sandwich technique)
Restoration of deep class V or root surface cavities
Restoration of large deep class I or II posterior cavities
Direct or indirect pulp capping - 27What are all composite resin materials made from?2 or more individual materials combined together that result in the physical and chemical properties of the composite being better than the original constituents
- 28Name the 5 fundamental components to all composite resins.Organic resin monomers
Inorganic filler
Coupling agent
Initiator
Dyes/pigments - 29What is the purpose of the following fundamental component of all composite resins: Organic resin monomer?Binds everything together in a resin matrix
- 30What is the purpose of the following fundamental component of all composite resins: Inorganic filler?Provides the physical properties
- 31What is the purpose of the following fundamental component of all composite resins: Coupling agent?Sticks the filler to the resin monomer and matrix
- 32What is the purpose of the following fundamental component of all composite resins: Initiator?Starts the setting reaction
- 33What is the purpose of the following fundamental component of all composite resins: Dyes/ pigmentsAesthetics
- 34As well as the 5 fundamental components of all composite resins (organic resin matrix, inorganic filler, coupling agent, initiator, dyes/pigments), what do modern composites contain? What is the purpose of this?Inhibitor
Keeps the composite shelf-stable - 35The organic resin matrix of modern composites is composed of two types of resin - high molecular weight and low molecular weight organic resins. Why is this?The high molecular weight organic resins form the majority component while the low molecular weight organic resins act as a viscosity controller
- 36What is the chemically active component of composite?Organic resin matrix
- 37How does the organic resin matrix start off as?A liquid of unreacted monomers
- 38What happens to the unreacted monomers of the organic resin matrix?They polymerise into polymers after activating the initiator component - this is why a composite turns from an initially liquid or soft material into something very hard
- 39What are the commonly used organic resin monomers in composites?Bis-GMA (original and most common)
UDMA (urethan dimethacrylate) - 40Bis-GMA and UDMA are both high molecular weight monomers. What does this mean?On their own, without anything added, they are highly viscous liquids
This means that when you add inorganic filler particles, you produce a composite which is extremely stiff that you would not be able to use clinically due to the poor handling properties - 41What may happen if Bis-GMA and UDMA are left on the shelf?May undergo premature polymerisation
- 42How are the problems associated with Bis-GMA and UDMA being high molecular weight monomers overcome?Viscosity controllers
Inhibitors - 43What are the viscosity controllers part of?Organic resin matrix - they are low molecular weight organic resins
- 44What are viscosity controllers?Low molecular weight organic resins that help dilute the HMW organic resins, which allows more filler particles to be added to the composite mixture and change the physical and handling properties of it
- 45What are some examples of viscosity controllers?TEGDMA (triethylene glycol dimethacrylate)
EDMA (ethylene glycol dimethacrylate)
MMA (methyl methacrylate) - 46What are inhibitors?Components of the organic resin matrix, added in very small amounts, to prevent unwanted premature polymerisation of the organic matrix during storage/handling/placement. They increase the shelf-life and handling ability of the composite.
- 47What are some examples of inhibitors?Hydroxyquinone
4-methoxy phenol (PMP)
Butylated hydroxy-toluene (BHT) - 48What are the benefits of having inorganic filler particles in composites?Help reduce the overall polymerisation shrinkage
Help reduce the coefficient of thermal expansion (similar to tooth - prevents cracking, pain)
Improve physical/mechanical properties
Improves radiopacity (if use barium or strontium)
Can control optical properties - 49What do the filler particles of composites consist of?Non-ion leachable glass of amorphous particles:
- Quartz - SiO4 (most common form of crystalline silica)
- Silica (SiO2)
- Zirconia (ZrO2)
- Barium glass (radiopacity) - 50What are the inorganic filler particles (quartz, silica, zirconia, barium glass) not involved in? What are they there for?The curing/setting reaction of composites
They are there to add structural support - 51What do the inorganic filler particle sizes impact?Dramatically impact on the physical and optical properties of composites
- 52What do larger filler particles provide? What do smaller filler particles provide?Larger - better structural support
Smaller - better polished finish
Note// All modern composites exist as a blend of different sizes - 53Composites can be classified according to their inorganic filler particle size. Name the groups they can be divided into.Hybrid (nano and macro particle size) - anterior and posterior use
Microfill (nano and micro) - anterior
Packable (nano, micro, macro) - posterior
Nano-hybrid (nano, micro) - anterior and posterior - 54What are the main two types of composite, based on how they are used?Flowable
Packable - 55What are flowable composites formulated to be?Runny/ flowable - flowability can vary from very flowable to slightly viscous (gel-like)
They can be highly filled (up to 70%) or as low as 30-50% - 56How are packable composites formulated to be used?Packed with instruments into the cavity
They are highly filled (70% and maybe more)
Excellent physical properties - 57You cannot simply mix filler particles into resin and expect to form a composite. What needs to happen to these components?The organic resin monomers and inorganic filler particles must be BONDED together because the monomers are hydrophobic and fillers are hydrophillic
- 58Why do the organic resin monomers and inorganic filler particles need to be bonded together?Because the monomers are hydrophobic and fillers are hydrophilic - they cannot simply be mixed together
- 59What is bonding of organic resin monomers and inorganic filler particles key to?The mechanical properties of a composite
- Polymerised resin matrix cannot take much loading/stress
- Fillers stop cracks propagating
- Bonding resin and fillers helps prevent cracks occurring - 60What is used to bond the organic resin monomers and inorganic filler particles in composites?Silane coupling agent (γ-MPS)
- 61What does the silane couple agent (γ-MPS) do?Covalently bonds to both the filler particle and resin monomer
- 62Why is bonding of the organic resin monomers and inorganic filler particles key to the mechanical properties of a composite?The polymerised resin matrix cannot take much loading/stress on its own
Fillers stop cracks propagating
Bonding the two together helps prevent cracks occurring - 63What are initiators?Chemicals added to the composite which start the resin monomer polymerisation process
- 64What are the 3 ways composites can set?Chemical cure (self-curing)
Light-cure (command-set)
Combination of chemical and light cure - 65When might dual-cured composites be used?When light curing is difficult
- 66What type of setting reaction occurs for any composite?Free-radical polymerisation of the resin monomers (Bis-GMA, UDMA, TEGMA, etc.)
- 67How are the free radicals in the composite setting reaction generated in the first place?Chemically - using two pastes (initiator and catalyst)
Photoinitiated - photoinitiator and amine activator - 68What will the free radicals in the composite setting reaction react with? What will this cause?The resin monomers
Causing a chain reaction of polymerisation:
- Organic resin monomers polymerise together and form many crosslinks
- Filler particles become entrapped and bonded to the polymerised resin via the silane coupling agent - 69How many stages does free-radical polymerisation occur in?3
- 70Name the 3 stages of free-radical polymerisation.Initiation
Propagation
Termination - 71Describe the initiation stage of the composite setting reaction.Free radicals created either by:
- Light activation of a light-sensitive initiator
- Chemical decomposition benzoyl peroxide and amine activator
Free radicals attack the double bond of the methacrylate groups of organic monomers
This creates monomer free radicals leading onto a chain polymerisation reaction - 72Describe the propagation stage of the composite setting reaction.Monomer free radicals continue attacking the double bonds of other organic monomers and form polymers crosslinked together
The extent of polymerisation that occurs is dependent on the ratio of the amount of uncured monomer to begin with: total amount of monomer present (degree of cure or conversion) - 73Describe the termination stage of the composite setting reaction.The free radicals have all reacted, resulting in chain polymer formation and cross links
All composites will never have 100% cured monomers - will always have some uncured monomer left
Degree of conversion is between 40-78% - 74What are some composite and handling factors that can affect the effectiveness of light curing?Product - chemistry
Shade - darker need more irradiation
Filler particles - do they help or not help light transmission
Composite cap (if left uncovered will affect shelf-stability)
Composite age (inhibitor concentration decreases with age)
Composite thickness (light transmission decreases with thickness) - 75What are some light curing factors that can affect the effectiveness of light curing?Type of curing light - wavelength output (nm) and power (W)
Age of curing light - deterioration of light source
Distance of curing light - intensity reduced if curing light moved away
Angulation of curing light - reflection loss increases the more you angle the light - 76Why does polymerisation shrinkage occur?Because the monomers with their double bonds occupy a larger volume before polymerisation - after polymerisation, the new polymers formed are smaller in volume
- 77What component of composites does polymerisation shrinkage affect? What component does it not affect?Affects organic resin monomer
Does not affect filler - 78What are some ways of overcoming the problems associated with polymerisation shrinkage?Incremental build-up technique
Using a bulk fill composite
Using a dual-cure composite
Using a liner under composite - 79What is the oxygen inhibition layer?A sticky, uncured layer that forms on the surface of a composite material when it is exposed to air during light-curing (the oxygen reacts with the free radicals during light curing)
- 80What does the oxygen inhibition layer inhibit?Monomer polymerisation at the surface
- 81What will all composites, when cured in air, have?Oxygen inhibition layer
- 82What can the oxygen inhibition layer easily attract?Stains
- 83How should the final layer of anterior composites be cured? Why?Under a barrier (e.g. glycerine, Vaseline)
Because the oxygen inhibition layer can attract stains easily - 84What can be done after curing to remove/minimise the presence of the oxygen inhibition layer?Polishing
- 85What are dual-cured composites best used in?Fibre-post cementation
Crown core build ups
Very large/ deep cavity restorations
Building up very broken down teeth - 86What are the advantages of composite resins?Excellent aesthetics
No mercury
Can be bonded to tooth - achieve a sealed restoration
Tooth preparation can be minimal
Low thermal conductivity - 87What are the disadvantages of composite resins?Moisture control is crucial
Polymerisation shrinkage
Technique-sensitive
Bonding agent can degrade with time
Secondary caries rate higher than GIC or amalgam (nothing to protect itself from bacteria) - 88What are the contraindications of using composite resins?Do not use if moisture control is not possible
Allergy to any monomers or other components
Subgingival restorations
Margins finishing on dentine or subgingival - 89What are compomers and giomers also known as?Polyacid-modified resin-based composites
- 90How are compomers different to composite resins?They are composite resin materials which also contain:
- Some polyacrylic acid
- Ion-leachable fluor-alumino-silicate glass filler - 91What type of setting reaction do compomers have?Free-radical addition polymerisation
- 92What are giomers?A compomer produced by one company (Shofu)
- 93What material are the clinical usage and contraindications of compomers exactly the same as?Composite resins
- 94Is there water involved in the setting reaction of a compomer?No
Water is absorbed later (days/weeks) after the compomer has been placed and cured - the water then allows for the acid-base reaction between the acidic monomer with the FAS glass to allow fluoride release - 95Water is not involved in the setting reaction of a compomer but is absorbed later (days/weeks) after the compomer has been placed and cured. What does this allow?Allows for the acid-base reaction between the acidic monomers (TCB and carboxylic acids) with the fluoro-alumino-silicate glass to allow fluoride release
- 96While there are two hypothetical methods of how compomers stick to teeth, they are not self-adhesive materials in practice. What does this mean the clinician must do?Etch and bond them in place just like a composite resin
- 97What properties of compomers are inferior to that of composite resins?Aesthetics
Compressive strength
Bond strength
Marginal leakage - 98What property do compomers have that composites do not?Fluoride release
- 99What are some of the perceived negative attributes of amalgam?Metallic appearance
Concerns regarding safety and risk of leakage
Risk of recurrent caries given that it is not normally bonded to remaining tooth tissues - 100With amalgam, what is there a high risk of that is associated with the poor tooth reinforcement and need for unnecessary removal of sound tooth structure to provide mechanical retention?High risk of tooth fracture
- 101What is the high risk of tooth fracture with amalgam linked to?Poor tooth reinforcement
Need for unnecessary removal of sound tooth structure to provide mechanical retention - 102Why is there a risk of leakage and recurrent caries with amalgam restorations?Because it is not normally bonded to the tooth tissue
- 103Why has the use of amalgam been massively reduced?The Minamata Convention on Mercury - a global treaty that aims to reduce the negative impact of mercury on the environment and human health
The EU regulation includes reducing the use of dental amalgam, which therefore reduces the environmental burden of mercury products arising from dentistry. - 104What do the EU regulations state about dental amalgam?Restrictions on how dental amalgam can be disposed of
Specifies that (from 1 July 2018), dental amalgam should not be used for the treatment of deciduous teeth, or in children < 15 years, or pregnant and breastfeeding women, except when deemed strictly necessary - 105Is mercury in dental amalgam a risk to health?There is no evidence that dental amalgam presents a direct risk to patients who have amalgam restorations. The elemental mercury found in dental amalgam is more stable than organic methylmercury, which is found in fish and other marine species. This is the most toxic form of mercury and the main source of exposure for the general population. However, dental amalgam can indirectly contribute to mercury’s risk to human health as, when released into the environment, it can undergo conversion to methylmercury by aquatic microorganisms.
- 106What are the benefits of using composite over amalgam?Facilitates a more conservative tooth preparation
Avoids unnecessary removal of healthy tooth tissue
Increases the strength of the restored tooth unit
More aesthetic
Better marginal integrity
Effectively increases the longevity of the restored tooth - 107What are some problems associated with using composite resins instead of amalgam?Much more technique sensitive than amalgam
More expensive
More time-consuming to place
Can present with post-operative problems that can be difficult to manage (e.g. unpolymerised monomer)
Not suitable for every scenario (e.g. subgingival margins, poor moisture control, high caries risk) - 108When should composite be used in posterior teeth?New carious lesions
When replacing old dental amalgam restorations
Tooth fracture
Repair/refurbishment of existing restorations - 109What shape should the internal line angles of cavity preparations for composites be? Why?Rounded internal line angles
Sharp internal line angles can produce stress points and result in fracture - 110When do composite cavity preparations need bevelling? When do they not need bevelling?Bevelling - labial surface
No bevelling - occlusal - 111Why do we not bevel occlusal surfaces?It results in thin occlusal extensions which fracture under loading
- 112What does the European Society of Endodontology (ESE) recommend the use of in deep carious cavities?Rubber dam isolation
- 113Which base material is recommended to be used under composite in a deep carious cavity?Hydraulic calcium silicate cement (e.g. Biodentine)
- 114What are the two rules regarding filler inorganic filler particle size in composite resins?The more filler, the better - increases strength, reduces amount of polymerisation shrinkage
The smaller the average filler particle size, the better - more polishable, retain polish for longer, improved wear resistance - 115In what direction does polymerisation contraction as a result of shrinkage occur?Away from the tooth surface
- 116When placing composite, what should not be linked to avoid the problems associated with polymerisation shrinkage?Do not link opposing walls
- 117What is the C-factor?Configuration factor
The ration of bonded to unbonded surfaces in a composite restoration
E.g. 2 sided restoration surface - 2 bonded: 4 unbonded = C-factor of 0.5
4 sided restoration surface - 4 bonded: 2 unbonded = C-factor of 2 (greater polymerisation shrinkage) - 118What does a higher C-factor indicate?A greater amount of polymerisation shrinkage
- 119How many restoration surfaces are there in a class I cavity? What does this mean the C-factor is?5
C-factor = 5 bonded:1 unbonded surface = 5
Polymerisation shrinkage is greatest with a class I composite restoration - 120C-factor diagram
- 121C-factor in different tooth preparations
- 122What light curing units are available?Quartz-Halogen
LED - 123Describe Quartz-Halogen light curing units.Still 'gold-standard'
Emit light and lots of energy
Need 30-40s curing time
Can lose power - power output should be monitored - 124What are the advantages and disadvantages of LED light curing units?Advantages:
- Narrow band width
- Ultra-energy efficient
- Very mobile
- Lightweight
Disadvantage:
- Heat production reduces performance - 125What does dentine provide for the pulp that no material placed in the tooth can?Better protection
- 126What is remaining dentine thickness (RDT)?The thickness of healthy dentine between the pulp chamber roof and the pulpal floor
- 127What is the single most important factor in protecting the pulp when preparing a cavity?The remaining dentine thickness (RDT) from the depth of the cavity preparation to the pulp
0.5 mm RDT reduces effect of toxins by 75%
1.0 mm RDT reduces by 90%
> 2.0 mm RDT leads to little pulpal reaction - 128What are some of the uses of cements/ linings/ bases?Luting agents for indirect restorations
Cavity bases - structural
Cavity linings - thermal protection, chemical protection, electrical insulation
Temporary dressings - 129What is the function of lining materials?Protect the vital pulp from bacterial, chemical, thermal, and electrical insult
- 130What are the ideal physical properties of cements and lining materials at the time of placement?- Moisture tolerant
- Flow and hydrophilicity
- Suitable working and setting times
- Bonding (ideally chemical and micromechanical)
- Curing and setting characteristics
- Easy to clean up
- Radiopaque - 131What are the ideal physical properties of lining materials after placement?- Durable bond strength
- Suitable compressive strength
- Suitable tensile strength
- Dimensional stability (low coefficient of thermal expansion, insoluble, acid resistant, resistant to water sorption)
- Surface smoothness
- Resistance to biofilm accumulation
- Antibacterial
- Obtundent - 132What are some of the common issues with cements/ linings/ bases?They often don't have the ideal physical properties
- Low strength
- Solubility
- Shrinkage on setting
- Not permanent - 133What are resin cements?Luting cements used to cement crowns, onlays, inlays on teeth
They are essentially low viscosity composite resins - 134What type of cement is formed when zinc oxide powder is combined with phosphoric acid liquid?Zinc phosphate cement
- 135What type of cement is formed when zinc oxide powder is combined with eugenol liquid? Give an example of a dental cement of this type.Zinc oxide eugenol cement
e.g. Kalzinol - 136What type of cement is formed when zinc oxide powder is combined with polyacrylic acid? Give an example of a dental cement of this type.Zinc polycarboxylate cement
E.g. Poly-F - 137What type of cement is formed when fluoro-alumino-silicate glass is combined with polyacrylic acid?Glass ionomer cement (GIC)
Note// This can then be modified by adding resin cements to create resin-modified glass ionomer cements - 138What are the main uses of zinc phosphate cements?Cementing indirect restorations (luting agent)
Structural lining (good thermal insulator) - 139What are some of the reasons for zinc phosphate cements becoming less favourable?Exothermic - if there was very little RDT, there was risk of thermal insult affecting the pulp
Mixed with acid (phosphoric) - if not mixed properly, there is risk of the acid causing dissolution of the enamel and dentine
Liquid - if the cap was not replaced properly, the solvent evaporates, leaving a thickened liquid that was not easy to mix
Not adhesive - 140What are some of the uses of zinc oxide eugenol cement?Many uses, from temporary restorative material to pulp capping agent
But, it cannot be used as a base under composite - 141What can zinc oxide eugenol not be used as?A base under composite
- 142Name an example of a zinc oxide eugenol cement.Kalzinol
Sedanol - 143What are the useful properties of zinc oxide eugenol cements (e.g. Kalzinol)?Good thermal insulator
Good marginal seal
Bacteriocidal - 144What are some of the uses of zinc polycarboxylate cements?Temporary restorative material
Cement
Liner
Base - 145What does the powder component of zinc polycarboxylate (Poly-F) contain?Zinc oxide
Magnesium oxide
Aluminium oxide
Fluoride - 146Why is Poly-F mixed with water instead of the polyacrylic acid? What is the benefit of this?The powder contains the dehydrogenated/freeze dried components (the usual powder and liquid (polyacrylic acid) are pre-mixed by the manufacturer)
We do not risk having improper mixing leading to acid dissolution of the enamel or dentine - 147What are the useful properties of zinc polycarboxylate cements (e.g. Poly-F)?Good thermal insulator
Adhesive (issue with steel instruments)
Radiopaque
Releases fluoride - 148What are the uses of calcium hydroxide cements (e.g. Dycal)?Lining in deep cavities
Pulp capping - 149What are the properties of calcium hydroxide cements (e.g. Dycal)?Bacteriostatic
pH 9-11 (strongly alkaline)
Induces mineralisation (reparative dentine formation)
Radiopaque
Poor compressive strength
Soluble in water/ acid/ saliva
Non-adhesive to wet surfaces - 150What are the properties of note of resin luting cements?Very good bond strength
High compressive strength
Moisture sensitive
Might irritate pulpal tissues - 151Name an example of a resin cement.Panavia
Rely X - 152What are the desirable attributes for a dental cement?- Machine mixed
- Easy to use and apply
- Suitable viscosity and flow
- Moisture tolerant
- Adjustable working and setting times
- Easy to remove when set
- Non-exothermic set
- Obtundent (pain-relieving)
- Resists biofilm
- Universal in use
- Biocompatible
- Radiopaque - 153What is metallurgy?A field of materials science and engineering that studies the physical and chemical behaviours of metallic elements
- 154What is a metal usually defined according to?Various chemical and physical properties
- 155What are the usual properties of metals?[Exceptions in bracket]
- Heavy (aluminium)
- Hard (lead)
- Can be deformed plastically (titanium)
- Conduct heat
- Conduct electricity
- Have a metallic lustre
- Opaque - 156What is density of a metal related to?The atomic weight of the metal and the arrangement/packing of atoms
- 157What are solids with a regular arrangement of atoms known as?Crystalline (e.g. metals and ionic solids)
- 158What are solids with an irregular arrangement of atoms known as?Amorphous
- 159What are the 3 most common atomic structures of metals?Body-centred cubic
Face-centred cubic
Hexagonal close-packed - 160What is the atomic structure of metals determined by?The way the metal atoms pack together to minimised empty space
- 161What is a body-centred cubic atomic structure?Where the nearest neighbours of the metal atom are the corners of a cube surrounding it - one atom at the entre of the cube and one at each of the eight corners (the corner atoms are shared by eight unit cells)
- 162What is a face-centred cubic atomic structure?Where there is one atom at the centre of each of the six faces and one at each of the eight corners (the corner cells are shared by eight unit cells and each face-centred atom is shared with an adjacent atom)
- 163What is a hexagonal close-packed atomic structure?A type of atomic packing where spheres are layered in a repeating pattern, with each layer overlaying the previous layer in an alternating pattern
- 164What do the properties of gold alloys depend on?The thermal and mechanical treatments
Composition - 165How many types are gold alloys classified into?4 (I-IV)
- 166How are gold alloys classified into type I-IV?Dependent on the amount of gold we put into the alloy
Type I has the highest % gold content
Type IV has the lowest % gold content - 167When would Type I gold alloys be used? Why?Inlays - sit between the cusps of the tooth so do not face the highest forces
Gold is a relatively soft metal and type I gold alloys have the highest gold content so will be softer than something like a type IV gold alloy - 168When would Type IV gold alloys be used? Why?Crowns, bridges
Type IV gold alloys have the lowest % content of gold of all of the gold alloy types - this means the relatively soft property of gold is less of a problem as it is strengthened by other metals - 169What are the effects of each of the following components on an alloy: 1) Gold 2) Copper 3) Silver 4) Palladium 5) Platinum 6) Zinc1 - corrosion resistance
2 - increased hardness
3 - counteracts orange colour of copper
4 - increased melting point and hardness
5 - increased melting point
6 - oxygen scavenger (important for amalgam - prevents oxidation during manufacturing) - 170What is amalgam an alloy of?Silver
Tin
Copper
Mercury - 171What alloys are inlays and onlays usually?Gold and palladium alloys
- 172What alloys are crowns usually?Stainless steel (iron, carbon, nickel, chromium)
Gold alloys
Palladium alloys
Nickel chromium alloys - 173What alloys are bridges usually?Gold alloys
Palladium alloys
Nickel chromium alloys - 174What alloy is usually used in dentures?Cobalt chromium
- 175What alloys are usually used into orthodontics?Stainless steel
Nickel titanium - 176What alloy is usually used in dental implants?Titanium alloy
- 177What alloys are usually used in endodontics?Nickel titanium
Stainless steel - 178Why is gold used in alloys?To improve corrosion resistance
- 179What is dental amalgam an alloy of?Mercury
Silver
Tin
Copper - 180Dental amalgam comes as two capsules - one containing mercury and the other containing a metal alloy powder. What shape and size particles can the alloy powder be?Either lathe-cut particles of spherical particles
- 181What does the shape and size of the alloy particles affect?The handling characteristics and final properties of the restoration
- 182What are amalgams which contain a mixture of lathe-cut and spherical particles called?Admixed or dispersed phase amalgams
(Majority of modern amalgams fall into this category) - 183What percentage of the total mass of amalgam does the mercury form?40-50%
- 184Why is the mercury that goes into amalgam triple distilled?It needs to be very pure, as any contaminants interfere with the setting reaction
- 185What are each of the common components of amalgam responsible for: 1) Silver 2) Tin 3) Copper 4) Mercury 5) Zinc?1 - hardening
2 - controlling expansion
3 - increases hardness, reduces corrosion, reduces creep
4 - initiates setting reaction
5 - oxygen scavenger (prevents oxidation) - 186Which component of dental amalgam is responsible for reducing corrosion?Copper
- 187What are the 3 types of amalgam metal alloys?Lathe-cut
Spherical
Dispersed phase (combination) - 188Silver and tin are mostly present as what compound in the alloy?Intermetallic compound - Ag3Sn
- 189Which phase of the system is Ag3Sn?Third pure phase - γ phase (gamma)
- 190What is the setting reaction between the Ag3Sn (γ phase) and the mercury initiated by?Vigorous mixing of the two ingredients
- 191What does the vigorous mixing of the Ag3Sn (γ phase) and mercury cause?Causes the outer layer of the alloy particles to dissolve in the mercury, forming two new phases, which are solid at room temperature
- 192What does the mixing of the powder alloy (Ag3Sn) and liquid (Hg) produce?Amalgam matrix
Ag3Sn + Ag2Hg3 + Sn7Hg - 193What effect does adding copper to the amalgam have on the chemical setting reaction?It eliminates the γ2 phase (Sn7Hg) which is weak and subject to corrosion
This γ2 phase (Sn7Hg) reacts with the copper to form the copper-tin phase
The γ2 phase exists as an intermediate reaction for a short time during setting - 194What are some of the issues with amalgam as a restorative material related to biocompatability?Lichenoid reactions
Allergies
Contact hypersensitivity
Amalgam tattooing - 195What are some issues with the interface properties of amalgam as a restorative material?Does not adhere to tooth tissues
Relies on mechanical retention - 196What are some of the dimensional changes that occur with amalgam as a restorative material?Initially - contraction, as the mercury diffuses into the alloy particles
Overall, the setting reaction results in slight expansion
Creep is the time-dependent dimensional change that occurs when a material is subjected to stress or load - 197What is creep? What are the clinical consequences of creep?Dimensional change when a material is subjected to stress of load
It leads to the restoration becoming deformed and protruding from the cavity margins. The unsupported material is weak and subject to corrosion which results in ditching and failure of the restoration. - 198What is amalgam ditching?A defect that occurs at the junction of a tooth and an amalgam restoration
- 199Describe the thermal properties of dental amalgam and why this needs to be considered clinically.High value for thermal diffusivity - an appropriate lining needs to be placed
Coefficient of thermal expansion is three times greater than that for dentine - mismatch of thermal expansion may cause microleakage - 200Why should dental amalgam be placed with a minimum thickness of 2 mm?Amalgam is weak in thin sections
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- Undergraduate Restorative Dentistry (Dental Materials) Flashcards on Year 2 Biomaterials 3, created by Riya X on 15/12/2024.
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- Riya X
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