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DMS Flashcards

1
Q

A 23 year old woman who is a science teacher arrives at the surgery for a regular check-up. She is an NHS patient.
Although she has no existing restorations, you discover that she requires a minimal disto occlusal restoration in a
lower molar. When you tell her this, she expresses concern at the possibility that you will use amalgam for this
filling and asks about alternative treatments.

What concerns do patients commonly have about the use of amalgam? (6 marks)

A

Aesthetics,
Mercury poisoning,
Discolours teeth,
Environmental impact,
Radiotransmitter,
Metal allergies,
Affects foetal development in pregnancy

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2
Q

A 23 year old woman who is a science teacher arrives at the surgery for a regular check-up. She is an NHS patient.
Although she has no existing restorations, you discover that she requires a minimal disto occlusal restoration in a
lower molar. When you tell her this, she expresses concern at the possibility that you will use amalgam for this
filling and asks about alternative treatments.

State what reassurance you could give her about the safety of amalgam. (4 marks)

A

government agencies have investigated using epidemiological studies and no conclusions been made that use of amalgam affects health.
350- 400 amalgam restorations are needed to achieve toxicity.

Environmentally: Amalgam has less of an environmental impact than eating seafood (in terms of toxin methylmercury)

There is no reliable evidence for not using amalgam. It is being phased out in:
Kids - idea that cavities will be smaller so there are better material choices to be minimally invasive.
Pregnant mothers- dentistry is supposed to be limited while a patient is pregnant anyway.

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3
Q

You have successfully reassured her and she agrees to have an amalgam placed. You proceed to prepare the disto
occlusal cavity.

What aspects of cavity preparation ensure;
i) the caries is adequately removed (2 Marks)
ii) the finished restoration margins are cleansable (3 Marks)

A

i) We remove the enamel to find the extent of the lesion at the ADJ.
Then we remove caries from dentine starting from the outside and working our way in.
Lastly we remove any deep caries over the pulp
Cavity is probed to ensure hard dentine remains caries free
ensure no caries at ADJ margins.

For cleansability:
Smooth the cavosurface margins
Ensure there are no overhangs - floss margins
Smooth the occlusal surface - ensure margins flush with the tooth surface.

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4
Q

If the patient insisted on a restoration with a tooth coloured material and you elected to use a direct resin
composite.
Describe the mechanism by which resin composite is bonded to dentine (5 Marks)

A

We use acid etch & Dentine bonding agent.
= mechanical bonding

  1. Etch:
    ● remove the smear layer
    ● decalcify the dentine
    ● open up the dentinal tubules
    The remaining (dentine) collagen is hydrophillic and has low surface energy
  2. DBA
    Primer and adhesive resin
    The primer e.g. HEMA 4-META
    ● bifunctional molecule with a hydrophilic end to bond to the wet dentine surface and a hydrophobic, methacrylate end to bond to the resin = increases dentine surface energy
    ● The molecule must also have a spacer group to make it long enough to be flexible when bonding.

The Adhesive (mix of resins) e.g. HEMA or Bis-GMA
● Absorbed and penetrates into the primed surface and attached to the hydrophobic end of the molecule
● Forms a micro-mechanical bond with the tubules and exposed dentinal collagen fibres = molecular entanglement
● Forms the HYBRID LAYER of collagen (from dentine) plus resin (from adhesive)

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5
Q

What are the ideal properties of a denture base? (7)

A
  • Dimensionally accurate and stable in use- so it can fit and be retained in the patient’s mouth.
  • High softening temperature (don’t want to distort the denture when ingesting hot foods or when cleaning)
  • Unaffected by oral fluids.
  • High youngs modulus (rigidity)
  • High elastic limit (the stress beyond which the material is deformed)
  • Low Thermal expansion
  • High thermal conductivity- we want the thermal stimuli to be sent to the mucosa to avoid scalding of the back of the throat or the oesophagus.
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6
Q

What are the constituents of PMMA?

A

Powder
* Benzoyl Peroxide (initiator),
* PMMA particles (speed up curing)
* Plasticisers (allow quicker dissolving in the liquid)
* Pigments (give natural colour)
* Co-polymer (improved mechanical properties)
Liquid
Methacrylate monomer (dissolves the PMMA particles),
Hydroquinone (inhibitor),
Co-Polymer (improves mechanical properties)

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7
Q

Give 4 possible faults during denture base production and explain why they occur

A

Contraction porosity- Too much monomer/ insufficient pressure (material expands then relaxes producing porosities)

Granularity- not enough monomer: to powder causing the roughened surface.

Gaseous porosity- when you boil the monomer and gas bubbles are released- these are found at the bulkiest part of the denture.

Polymerisation shrinkage- too much monomer/ insufficient excess material/ insufficient clamp pressure.

Crazing-internal stresses produced due to a fast curing rate.

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8
Q

Give 4 advantages of co/cr as a denture base?

A

High youngs modulus (rigidity)
Greater hardness.
high thermal conductivity,
high softening temperature

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9
Q

Give 4 disadvantages of co/cr as a denture base?

A
  • Aesthetics
  • More expensive
  • Difficult to make (Cold working & stress relief annealing to achieve the ideal properties of the denture base.)
  • Difficult to add to
    *
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10
Q

What undercuts are required for clasps of stainless steel, gold and cobalt chrome?

A

Wrought stainless steel- 0.75mm (3 marks on gauge) remember as SS = longer word
Gold- 0.5mm (2 marks on gauge)
CoCr- 0.25mm (1 mark on gauge)

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11
Q

What are the ideal properties of an impression material?

A

Good interation between material and toothsurface:
* High flow (more viscous - like mucous- less flow)
* High surface wetting - we want hydrophobic/hydrophillic.
* Setting without dimensional contraction.

Accuracy-
* Surface reproduction (affected by viscosity- we want the material to flow into smaller gaps)
* High elasticity (elastic recovery when removed from the mouth)
* Low thermal contraction (moving impression between the mouth & the room)

To be able to deal with undercuts:
High tear strength- To withstand the stress of removal without fracture.
Rigidity- You want it to be less rigid (more flexible- will ease the removal of the material)

Comfort for the patient- Non toxic/ non irritant/ short setting time.

Convenient for the operator- convenient working and setting times.

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12
Q

Name 4 non-elastic impression materials

A

Impression compound
Impression paste
ZOE
Impression waxes

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13
Q

Name 4 elastomer materials used for impression taking.

A
  • Polyether (impregum)
  • Silicones: addition silicone - PVS (Extrude, President) & condensation silicone (lab putty),
  • polysulphide.
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14
Q

Name 2 hydrocolloids used for impression taking.

A

Hydrocolloids consist of fine particles dispersed in water-
Alginate- irreversible
Agar- reversible

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15
Q

What are the constituents of alginate? (4)

A
  • Sodium alginate (reacts with the calcium ions)
  • calcium sulphate (provides the calcium ions)
  • trisodium phosphate (Delays the gel formation)
  • Filler
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16
Q

What is the setting reaction of alginate?

A

Sodium alginate + calcium sulfate → calcium alginate + sodium sulfate

2Nan Alg + n CaSO4 —> nNa2SO4 + CanAlg

The tri-sodium sulphate reacts with the calcium ions causing alginate delay. One Trisoidum sulphate is used up sodium alginate reacts with calcium ions to produce alginate.

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17
Q

Give 2 advantages of alginate (6)

A
  • Nearly elastic
  • Non toxic
  • Non irritant
  • Ok setting time
  • Easy to use
  • Cheap
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18
Q

Give 2 disadvantages of alginate

A

Storage: Alginate can release (syneresis) or take up water over time (imbibition) causing distortion.
Poor tear strength.

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19
Q

Give 2 uses of alginate

A
  • primary impressions for dentures
  • Master impressions (study models)
  • Wash impressions e.g. replica
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20
Q

Give 3 advantages of elastomeric impression materials over alginate

A

elastomeric = polyether, silicones, polysulphides

  • better accuracy
  • better tear strength
  • better surface detail reproduction
  • better impression life - doesn’t dry out,
  • limited permanent deformation
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21
Q

What is the composition of glass ionomer?

A

Powder → silica, alumina, calcium fluoride, sodium fluoride, aluminium fluoride, aluminium phosphate,
Liquid → polyacrylic acid (forms matrix) and tartaric acid (to decrease setting time. )

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22
Q

Briefly describe the setting reaction of glass ionomer

A

This is an acid base reaction. (3 stages)

Dissolution-Acid attacks the glass surface releasing ions (Ca/ Al/ Na/ F)

Gelation- Calcium ions crosslink with polyacrylic acid by chelation with the carboxyl groups. This forms Calcium polyacrylate.

Hardening- Trivalent aluminium ions cross link to increase strength- forming aluminium polyacrylate.

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23
Q

Give 4 uses for GIC

A
  • luting
  • temporary restoration
  • definite restoration
  • fissure sealant
  • lining material.
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24
Q

Give 4 properties of GIC

A

Handling- tartaric acid is used to decrease setting time.
Bonding- by chelation (carboxyl groups & surface calcium) Hydrogen bonding & metallic ion bridging to collagen.
Aesthetics- lacks translucency so not suitable for anteriors.
Poor tensile strength
Low compressive strength
Poor wear resistance
Low hardness
More soluble (when first placed- so use vaseline)
Good thermal expansion- similar to dentine
Does not contract on setting
Less susceptible to staining.
Fluoride release
reduced microleakage

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25
Q

RMGI liner vs GI liner (3)

A

On demand set (RMGI is light cure)
Higher mechanical strength
Lower solubility

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26
Q

Why is it a bad idea to use GIC luting agent as a conventional restorative material ?(2)

A

It has less filler/glass < 20 microns to enable low film thickness and seating of the indirect

therefore;
* It has low mechanical performance, such as low fracture strength, toughness and wear.
*poor aesthetics (not translucent due to smaller particle size)

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27
Q

List the Luting cements for a metal post core.

A

GI luting cement

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28
Q

What Luting agent is used to bonds a porcelain veneer (3)

A

dual/light cure resin luting agent + DBA & silane CA - to make the luting agent hydrophillic & allow bonding

  • Nexus
  • RelyX
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29
Q

What Luting cement is used for a carbon fibre post?

A

​Dual cure composite resin cement & dentine bonding agent.

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30
Q

What are the ideal properties of a luting cement? (8)

A
  • Viscosity (low to allow seating of the restoration without interferene.
  • low film thickness (should be thin below 25 microns),
  • Ease of use (easily to mix/long working time/short settig time)
  • Radiopaque- allows you to se the margins more carefully for marginal breakdown or secondary caries)
  • Low solubility
  • Cariostatic (to be antibacteiral around the restorative margins)
  • Biocompatable- not damaging the pulp by the pH or heat.
  • Good marginal seal (by chemical bonding to the tooth and the indirect restoration.
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31
Q

Why is RMGI not good as a luting cement? (2)

A

Contains HEMA (monomer) which:

  • Absorbs water and swells- so cannot be used for porcelain crowns (will crack ) or post crowns (will split the root)
  • HEMA = Is cytotoxic to the pulp if unreacted
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32
Q

How do you bond a porcelain veneer? (3)

A
  1. place a DBA on the tooth
  2. Etch porcelain w/ hydrofluoric acid
  3. Use a dual/light cured resin cement with silane coupling agent to make the luting agent hydrophillic.
    This allows bond with c=c hydrophobic composite luting cement.
33
Q

How do you bond non-precious metal? (2)

A

-place a DBA on tooth

-Use GIC luting agent or dual cured composite rein

Metal
Use a metal boding agent e.g. MDP or 4META

or
panavia (self adhering luting agent that has a metal bonding agent within MDP)

Sandblast with aluminium oxide
(+/- electrolyte etching = not commonly used)

34
Q

What are the components of temp bond?

A

Base→ Zinc oxide, starch and mineral oil.
Accelerator → resins, carnuba wax, eugenol or EBA.

35
Q

Can you bond zirconia?

A

Metal infused ceramic

It cannot be etched so will not chemically bond.
Its retention is micromechanical as it can be sandblasted

(with use of a metal coupling agent eg MDP/ 1-META in composite luting agent)

36
Q

Why are lithium disilicate (EMAX) crowns strong?

A

Lithium disilicate crystals;
- stop crack propagation
- provide good flexural strength (the more crystals, the greater the flexural strength)

37
Q

Patient attends with intention of an amalgam restoration.
What are the benefits of copper enriched amalgam? (4)

A

This is amalgam with no Y2 phase (tin and mercury) and more copper.

  • Increases early strength (stronger before the 24 hour mark) & hardness.
  • Increased corrosion resistance
  • Increased margin durability
  • Less creep.
38
Q

Patient attends with intention of an amalgam restoration.
Originally, why was it necessary for manufacturers to add zinc to amalgam alloy? (1)

2020 Q2

A

Zinc acts as an oxygen scavenger & prevents the oxidation of the other metals in the alloy.

39
Q

Patient attends with intention of an amalgam restoration.
(b) How does the manufacturer reduce γ2 from the structure of amalgam??

2020 Q2B

A

This is made by adding spherical silver-copper eutectic particles to the silver tin lathe cut particles to produce the high copper Y-2 free amalgam.

40
Q

Patient attends with the intention of an amalgam restoration.
Explain the process of delayed expansion?

what are the consequences of delayed expansion? (4)

A

Alloys containing zinc, if contaminated with water produce H gas.
H gas builds up (internal pressure) in the amalgam causing a large expansion.

Expansion can lead to:
- Pressure on the pulp causing pain
- High points in the rx = occlusal interference.
- Greater susceptibility of corrosion
- Expansion over the cavity margins causing fractures.

Most amalgams are now made without zinc.

41
Q

The patient attends with the intention of an amalgam restoration.
What is creep?

A

When there are repeated low level stresses (below the elastic limit) on the material
= causes flow = causes permanent deformation
= change the shape & affect it’s marginal integrity.

This means the amalgam does not maintain good contact with the tissue around it and stands proud of the tooth
= amalgam is vulnerable to fracture at the margins/ditched margins
risks: secondary caries

42
Q

Patient attends with the intention of an amalgam restoration.
What are the main symptoms of creep (3)

A

Amalgam sitting proud of the cavity (It has changed shape) = abnormal occlusal contacts??

Ditched margins = vulnerable to fracture at the margins

Microleakage - The passage of fluid and bacteria in micro-gaps between the restoration and the tooth.
This can cause;
- secondary caries under the restoration
- pulpal irritation
- Infection
- Discolouration

43
Q

What makes RMGIC better than GIC? And why can it be used for ED fractures instead of GI?

A

RMGIC- is stronger/lower solubility/ higher bond strength to enamel and dentine.

It is used because it less soluble (ED fractures would be more difficult for moisture control) so prevents leakage & seals the cavity from the surrounding environment.

44
Q

How is porcelain treated to improve it’s retention

A

Porcelain is etched with hydrofluoric acid to produce a rough retentive surface.
It is then treated with Silane coupling agent (a surface wetting agent) to produce a strong durable covalent bond.

45
Q

Describe how a resin based luting agent bonds to porcelain.

A

Porcelain is treated with hydrofluoric acid to etch the surface (producing a rough retentive surface that is hydrophillic)
We need a surface wetting agent e.g. silane coupling agent to make the luting hydrophillic to allow bonding.

46
Q

Two Impression trays are given one with green stick on posterior saddles and one with Impression taken in alginate.
What are the constituents of alginate and green stick?

A

Alginate- Sodium alginate/ Calcium sulphate/ Trisodium phosphate/ Filler.
Greenstick- Carnauba wax, Talc, Stearic acid.

47
Q

You are about to restore the tooth wear with composite. Name 4 constituents of composite and give an example
for each of the constituent. (4)

A

Resin: bis-GMA,
glass particles: silica or quartz,
Low weight dimethacrylate: TEGDMA,
Light activator: camphorquinone
Silane coupling agent: bifunctional molecule binding resin and filler

48
Q

Cervical abrasion cavity. Why would you use RMGI instead of composite resin? (3)

A
  • Moisture control
  • Less polymerisation shrinkage
  • lower modulus which has better flex strength
49
Q

What metals can be used for an adhesive bridge?

A

Cobalt chrome or a nickel chromium alloy

The fitting surface is sandblasted with 50 micron aluminimum oxide particles.

50
Q

What cement is used for an adhesive bridgework

A

Self adhering composite luting cement
Panavia 21ex (dual affinity cement)

51
Q

Mrs Dodds is a 45 year old women who has a large MOD composite on 46 6 months ago. She presents complaining that a bit of filling has come away and she is not
happy. You suspect that this may have something to do with bonding and placement of composite. She is adamant she wants a crown and heard that porcelain is the best and demands this,
- Name 2 luting cements other than resin based that could be used to bond a crown.

A

Zinc phosphate cement
(Zinc polycarboxylate??)

GIC
(but bond is better with resin modified cements)

52
Q

Endo on 16 for 49 year old patient. Root canal system has been prepared over 2 visits (including Mesio-palatal canal). On 3rd visit you plan to obturate.
** The canal is to be obturated with GP cones via cold lateral compaction. Name 3 constituents of GP in addition to GP**

A

65% zinc oxide
10% radiopacifiers
5% plasticizers

53
Q

Patient arrives with MCC from tooth 11, the dentine core has fractured off inside the crown. The retained root is restorable and the patient has requested a new crown is made.
Name 4 post core materials.

A

Post material
Cast metal (Type IV gold/ Stainless steel)
Ceramics (Aluminia/ zirconia)
Fibre (carbon/ glass fibre)

Core materials
Composite
Glass ionomer
Amalgam

54
Q

Give 2 materials used for cementing a post and core.

A

Glass ionomer luting cement (Metal post)

Dual cure composite resin luting agent & dentine bonding agent (Fibre post)

55
Q

What are the components of composite? (5)

A

Filler particles (Silica or quartz)
Resn (Bis GMA)
Camphorquinone (Light cure)
Low weight dimethacrylates (Improve the material by adjusting the viscosity and reactivity)
Silane coupling agent (Used to bond to filler and resin allowing a good bond between)

56
Q

Name 4 different types of composite

A

Microfilled
conventional
Hybrid

Flowable
Nanofilled

57
Q

What are the clinical disadvantages of composite and how are they minimised? (4)

A
  • Composite is moisture sensitive- we use a dental dam to keep the area dry.
  • Polymerisation contraction shrinkage- the mateiral shrinking in the cavity. We avoid this we place the composite in increments touching as few walls as possible (consider configuration factor on placement)
  • 2mm depth of cure so we need to ensure that we do not add increments greater than this (not all of the composite will set causing a soggy bottom)
  • Post operative sensitivity (Ensure correct placement/Moisture control/ adequate bonding procedure)
  • premature cure - move dental light away when applying
58
Q

Give 3 advantages of composite over amalgam

A

Aesthetic- white filling

Minimal preparation needed for composite (less removal of healthy tooth tissue)

Composite bonds well to the tooth surfaces (amalgam does not bond) and reinforces remaining tooth structure

59
Q

What are the advantages of amalgam (7)

A
  • high mechanical strength (high hardness, high compressive strength, high abrasion resistance)
  • radiopaque
  • long lasting/better prognosis
  • cheap
  • easy to handle - less moisture sensitive
  • fast setting time.
  • similar thermal expansion to tooth
60
Q

What are the disadvantages of amalgam? (9)

A
  • Excessive tooth preparation as not bonded,
  • aesthetics,
  • mercury toxicity,
  • creep - marginal integrity/microleakage
  • weak in thin sections,
  • high thermal conductivity, high thermal expansion coefficient,
  • allergy
  • tattoo
  • galvanic reaction.
61
Q

In amalgam- How to remove y2 (2)

A

Copper enriched, polishing margins - avoiding galvanic cells

62
Q

Why was zinc added to amalgam (1)

A

Zinc acts as an oxygen scavenger & prevents the oxidation of the other metals in the alloy.

63
Q

What occurs as a result of zinc being added to amalgam restorations
& what is the mechanism for this
&what symptom does the patient experience?

A

Interaction of zinc with water (saliva/blood) forms bubbles of H2 within amalgam pressure build up causes expansion

Zn+H2O=ZnO+H2

Downward pressure causing pulpal pain.
Upward pressure- the restoration is sitting proud.

64
Q

What is the setting reaction for amalgam?

A

Ag3Sn = γ, Ag2Hg3 = γ1, Sn7Hg9 = γ2
γ + Hg = γ + γ1 + γ2
Copper enriched: γ2 + AgCu = Cu6Sn5 + γ1 OR Ag.Sn.Cu + Hg = Ag.Sn.Cu + γ1 + Cu6Sn5

65
Q

What changes have been made to modern amalgam to improve it? (2)

A

γ2 phase (tin and mercury) has poor strength and abrasion resistance.
Modern amalgam is copper enriched (>12%) content to reduce/remove this phase.
Copper reacts with tin to reduce the availability of tin for γ2 phase.

Zinc is also no longer used as it reacts with saliva and blood and causes delayed expansion = pulpal irritation or restoration sitting proud = a poor marginal seal.
Use of spherical cut.

66
Q

Advantage of using non y2 amalgam (2)

A

think copper enriched:

  • Higher early strength
  • Less creep
  • Higher corrosion resistance
  • increases marginal durability
67
Q

How do you cement a porcelain bridge?

A

Dual cure composite resin (nexus) + Dentine bonding agent.

self etching composite resin (Rely x unicem)

68
Q

How do you cement a metal bridge? (3)

A

Self adhering composite luting cement (Panavia) = for adhesive or conventional

dual cured composite luting cement (+Dentine bonding agent)

GI - only for conventional bridges

69
Q

How is the surface of porcelain veneers treated in the lab to improve adhesion?

A

It is etched with hydroflouric acid

70
Q

You have selected a composite resin cement for the veneer. What material esures a good bond with porcelain and chemically- how does it work?

A

Use silane coupling agent

This allows a covalent bond with the oxide groups on the porcelain surface

Porcelain surface - hydrophilic.
Composite luting agent has hydrophobic covalent bonds

Silane coupling agent is hydrophilic & reacts with the composite luting cement (makes it hydrophilic) to allow the chemical bond with the hydrophilic porcelain

71
Q

Where is Silane coupling agent used in dentistry? (2)

A

In composite = To allow bonding of filler and resin within composite resins.

Facilitates bond with composite resin luting agent and porcelain.

72
Q

When is a dual cure cement indicated for cementation?

A

When we are cementing a thick or opaque indirect restoration that light cure would be unable to penetrate fully.

73
Q

Give 4 disadvantages of Glass ionomer cement?

A

Brittle with poor wear resistance
Moisture susceptible when first placed (need to apply vaseline)
Poorer aesthetics
Poor handling characteristics

74
Q

How do you cement a resin retained bridge?

A

Self adhering composite luting cement (Panavia) = for adhesive or conventional

dual cured composite luting cement +Dentine bonding agent.

(X - GI - only for conventional bridges)

75
Q

What are the features of a cavity for composite? (3)

A

No unsupported enamel,
no sharp internal line angles
bevel cavosurface margin angle to increase area for bonding.

76
Q

What techniques are used for successfully placing composite? (3)

A
  • Condition with etch, primer and adhesive applied then;
  • Flowable at the base to reduce polymerisation contraction stress and aid adaption
  • incremental placement (2mm) to ensure;
  • a low configuration factor
  • avoid soggy bottom.
77
Q

What are the features of a cavity for amalgam? (5)

A
  • Undercuts for retention,
  • other retention factors e.g. lock and key, grooves, dovetail/isthmus
  • greater than 2mm depth for sufficient strength
  • flat occlusal floor
  • cavosurface margin angle 90°
  • no unsupported enamel
78
Q

What effect could occur in a freshly placed amalgam restoration as a result of the presence of zinc in the amalgam alloy?

Explain the mechanism of this effect.

2020 Q2

A

Build up of pressure causing delayed Expansion of the restoration over the cavity margins which can
- Pressure on the pulp (pain)
- High points- interfeering with occlusion
- Expansion over the cavity margin (causing fracture)
- Greater susceptibility of corrison.

Mechanism.
- Zinc can react with saliva/ blood causing the formation of hydrogen gas.
- This increases pressure below the restoration causing the restoration to:
- Expand upwards causing the high points on the restoration that interfere with occlusion, are at risk of fracture.
- Expand downwards putting pressure on the pulp.

Most amalgams are now made without zinc.

79
Q

The patient has a freshly placed amalgam restoration.
The amalgam chosen contains zinc which can affect the restoration.
What is the main symptom that the patient could experience should this occur?

2020 Paper A Q2

A

Pain

BDS4 Revision (14 decks)

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