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BDS Exam style questions > DMS > Flashcards

DMS Flashcards

1
Q

What concerns may patients have about safety of amalgam?

A

Aesthetics

Mercury poisoning

Environmental impact

Discolouration of teeth

Metal Allergy

Concerns in pregnancy

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2
Q

What can we tell patients to reassure them about amalgam safety?

A

Amalgam is a compound- mercury is more stable

Historic material

Amalgam waste is dealt with in special way to protect environment

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3
Q

Describe the mechanism by which composite resin is bonded to teeth?

A

Smear layer is removed by acid etch- 35% phosphoric acid
-> opens dentine tubules and decalcifies dentine to expose collagen network

DBA- combined primer and sealer
-> hyrdophillic end bonds to dentine
-> hydrophobic end bonds to resin in composite

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4
Q

What are the ideal properties of a denture base ?

A

Dimensionally accurate
High softening temperature
Non-toxic or irritant
Low density
Easy to repair
High thermal conductivity
Unaffected by oral fluids
Thermal expansion = tooth

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5
Q

What are the constituents of PMMA?

A

Powder- Benzoyl peroxide, PMMA, plasticiser, pigments, co-polymers

Liquid- Methacrylate monomer, hydroquinone, co-polymer

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6
Q

What are the causes of the different types of porosity/faults in PMMA dentures and why they occur ?

A

Gaseous porosity- fast curing (monomer boiling) in bulky parts of acrylic

Contraction porosity
-> Too much monomer
-> insufficient clamp pressure, excess material, dough packing

Granular porosity- too little monomer

Internal stresses- thermal expansion, incorrect cooling/curing cycle

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7
Q

What are the advantages of CoCr as denture base?

A

Radiopaque

Strong

High YM- rigid

Low density

Can be made thin

High thermal conductivity

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8
Q

What are disadvantages of CoCr as denture base?

A

Difficult to add to/repair

Expensive

Low ductility

Poor aesthetics- not gum coloured like acrylic

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9
Q

What are the ideal properties of an impression material?

A

Low viscosity

100% elastic recovery (or low viscoelasticity)

High Wettability

Low polymerisation shrinkage

High tear resistance

Acceptable taste and smell

No dimensional change

Compatible with cast material

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10
Q

What are the non-elastic impression materials?

A

Compound

ZOE

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11
Q

What are examples of elastic impression materials?

A

Polyether

Silicones
-> addition- PVS
-> condensation silicone- putty

Polysulphide

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12
Q

What are the hydrocolloid impression materials?

A

Alginate (irreversible)

Agar (reversible)

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13
Q

What are the constituents of alginate?

A

Sodium Alginate

Calcium sulphate

Trisodium phospate

Fillers

Flavourings

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14
Q

What is the setting reaction for alginate?

A

Sodium alginate + Calcium sulphate = Calcium alginate and sodium suphate

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15
Q

What are the advantages of alginate?

A

Flows- replicates surface detail

Acceptable
-> taste/smell
-> setting time

Non-toxic or irritant

Cheap

Easy to use

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16
Q

What are the disadvantages of alginate?

A

Lacks perfect elastic recovery

Poor tear strength- not suitable for deep undercuts

Storage issues
-> syneresis and imbibition can affect dimensions and accuracy

17
Q

What are the uses of alginate?

A

Impressions for study models

Primary/master impressions for dentures

18
Q

What are the advantages of elastomeric impression materials over alginate?

A

Better accuracy/surface detail reproduction

Better tear strength

Easier storage- doesn’t dry out

19
Q

What are the components of GIC?

A

Powder:
Silica
Alumina
CaF
NaF
Aluminium fluoride
Aluminium phosphate

Liquid:
Polyacrylic acid
Tartaric acid

20
Q

Describe the setting reaction of GIC?

A

Dissolution
-> H ions attacks glass surface releasing Ca, Al, Na and F ions
-> Silica gel forms around glassy matrix

Gelation- initial set occurs
-> Ca ions (bivalent) crosslink with poly-acid by chelation with carboxyl groups

Hardening
-> Trivalent Al ions ensure good cross-linking and increased strength (starts after 30 mins and can continue for up to a week)

21
Q

What are the uses of GIC?

A

Temporary

Lining material

Luting cement

Fissure sealant

Restorative material

22
Q

What are 4 advantageous properties of GIC?

A

Tooth coloured

Fluoride release

Thermal expansion similar to dentine

No contraction on setting

23
Q

What are 4 negative properties of GIC?

A

Poor aesthetics

Susceptible to desiccation

Poor mechanical properties

Brittle

24
Q

What are the advantages of RMGIC over GIC?

A

On demand set

Better physical properties

Better aesthetics

Easier handling

Lower solubility

25
Q

Why is GIC a poor luting cement?

A

Short working time

No on demand set

26
Q

What luting cement is used for a metal post core?

A

GIC

27
Q

What luting cement is used for porcelain veneer?

A

Light cure resin and DBA

28
Q

What luting cement is used for Carbon fibre post?

A

Dual cure composite with DBA

29
Q

What are the ideal properties of a luting cement?

A

Low viscosity
Low film thickness- less than 25 microns
Aesthetic
Radiopaque
Low solubility
Cariostatic- F release
Biocompatible

30
Q

Why is RMGI not used as a luting cement?

A

Contains HEMA which absorbs water
-> also cytotoxic to pulp

31
Q

How do you bond a porcelain veneer?

A

Etch with HF acid

Use DBA to bond composite luting agent to tooth

Use silane to bond porcelain with luting agent

32
Q

How do you bond a NP metal restoration?

A

Sandblast

Use DBA to bond composite luting agent to tooth

Use Metal bonding agent containing 4-meta/MDP
-> acid groups bond with oxides in NP metal

33
Q

What are the components of Temporary Luting agent?

A

Accelerator- resin, orthodontic EBA, wax, eugenol

Base- ZnO, Starch, mineral oil

34
Q

Why can’t zirconia be bonded?

A

It cannot be etched so chemical bond is not possible
-> retention is micromechanical

35
Q

What makes Lithium Disilicate crowns strong?

A

BDS Exam style questions (15 decks)

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