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BDS 2 OSCE > DMS > Flashcards

DMS Flashcards

1
Q

What is the smear layer?

A

An adherent layer of organic and inorganic debris - remnant of the dentine surface after preparation of the dentine

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2
Q

Describe self etch

A

Incorporates the smear layer
1 stage
Uses Scotch bond I

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3
Q

Describe total etch

A

Removes the smear layer in 2 stages:
Etch
Prime and bond

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4
Q

How is the hybrid layer formed?

A

37% phosphoric acid etch removes the smear layer exposing the collagen network
Primer penetrates collagen network making the surface hydrophobic
Adhesive resin forms micro mechanical adhesion with tubules and exposed collagen network

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5
Q

What products are found in composites?

A 
Resins
Camphorquinone
Low weight methacrylates 
Silane coupling agents
Filler particles
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6
Q

What resin is commonly found in composite?

A

Bis-GMA

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7
Q

What is camphorquinone?

A

A blue light photoinitiator

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8
Q

What role do low weight methacrylates play in composite?

A

Improves viscosity and reactivity

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9
Q

What role do silane coupling agents play in composite?

A

Provides good bond between filler particles and resin

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10
Q

What filler particles are commonly used in composite?

A

Glass

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11
Q

What reaction takes place in the setting of composite?

A

Free radical addition polymerisation

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12
Q

What are the advantages of light cured composite?

A 
Extended working time
Less finishing
Can be finished immediately
Less waste 
Less porosity
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13
Q

What are the disadvantages of light cured composite?

A 
Absorption/light spectrum mismatch
Cure prematurely under dental light
Depth of cure is optimistic
Polymerisation shrinkage can occur
Recommended setting times may be too short
Ocular damage
Soft tissue damage
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14
Q

What is the depth of cure of composite?

A

2mm

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15
Q

What is the bond strength of composite?

A

40MPa

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16
Q

Give some advantages of using composite

A 
Strong - 350MPa
Rigid - 15GPa
Abrasion resistant
Low thermal conductivity
Can be light cured on demand
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17
Q

What liquid is used in amalgam?

A

Mercury

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18
Q

What are the powder constituents of amalgam and why is each element used?

A 
Tin - intermetallic compound
Silver - intermetallic compound
Zinc - scavenger (removes impurities)
Copper - increased strength and hardness
Mercury - increases rate of reaction
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19
Q

What are the different types of amalgam particles?

A

Lathe-cut

Spherical

20
Q

Describe the amalgam setting reaction

A

Powder and liquid react to form the amalgam matrix (Gamma-1 and Gamma-2) alongside unreacted particles (Gamma)

21
Q

Describe Gamma, Gamma-1 and Gamma-2

A

Gamma - strong, corrosion resistant
Gamma-1 - not strong, corrosion resistant
Gamma-2 - not strong, not corrosion resistant

22
Q

Describe copper enriched amalgam

A

Contains more than 6% copper

No Gamma-2 phase

23
Q

What are the advantages of copper enriched amalgam?

A

Increased strength
Increased corrosion resistance
Higher marginal integrity
Less creep

24
Q

What are the advantages of amalgam?

A 
Strength - 500MPa
Abrasion resistant
Viscosity ideal for packing
Radiopaque
Okay working time
25
Q

What are the disadvantages of amalgam?

A 
Poor aesthetics
Not anti cariogenic
Experiences creep
Corrosion
Microleakage can occur
26
Q

Describe creep

A

Repeatedly stressed for a long time
This results in flow and permanent deformation
Amalgam sits proud of the surface and vulnerable to fracture

27
Q

Who should amalgam not be used on?

A

Children under 15
Pregnant women
Breastfeeding women

28
Q

What do cavity lining materials allow protection from?

A

Unreacted chemicals
Thermal stimuli
Bacteria and endotoxins

29
Q

What are the ideal properties of a cavity lining material

A 
Low thermal conductivity
Thermal expansion coefficient similar to dentine
High compressive strength
Radiopaque
Low solubility
Cariostatic
Biocompatible
30
Q

What are the most common lining materials?

A

Calcium hydroxide

GI and RMGIC

31
Q

What is GI made up of?

A

Acid - polyacrylic acid and tartaric acid

Powder - Mainly silica

32
Q

What are the setting phases of GI?

A

Dissolution
Gelation
Hardening

33
Q

Describe Dissolution of GI

A

Acid is added to solution
H ions attack the glass surface
Ca, Al, Na and F ions are released
Left with silica gel around unreacted core particle

34
Q

Describe Gelation of GI

A

Calcium ions released are bivalent so cross linking occurs

Polyacrylic acid reacts with carboxyl groups to form calcium polyacrylate

35
Q

Describe Hardening of GI

A

Trivalent aluminium ions cross link to increase strength
This forms aluminium polyacrylate
Starts after 30 minutes and can last up to a week

36
Q

What is RMGIC made up of?

A

Powder - Glass

Acid - Polyacrylic acid, tartaric acid, HEMA (monomer), water

37
Q

Describe the setting reaction of RMGIC

A

Acid base reaction takes several days
Redox reaction takes 5 minutes
Free radical polymerisation reaction (light activated) takes 20 seconds

38
Q

What are the advantages of GI?

A 
Release flouride
Forms chemical bond to enamel and dentine
Little microleakage occurs
Good thermal properties
No contraction on setting
39
Q

What are the disadvantages of GI?

A 
Brittle
Poor wear aesthetics
Poor handling characteristics
Poor aesthetics - opaque
Moisture dependant
40
Q

What are the advantages of RMGIC?

A 
Releases flouride
Forms a chemical bond to enamel and dentine
Little microleakage occurs
Better physical properties than GI
Better handling properties than GI
Lower solubility than GI
Better translucency and aesthetics
Stronger
41
Q

What are the disadvantages of RMGIC?

A

Polymerisation contraction takes place
Monomer leaching - uncured HEMA can be toxic to the pulp
Reduced strength from uncured material
Exothermic acid base reaction
Swelling due to uptake of water due to HEMA

42
Q

What is used clinically as a setting calcium hydroxide liner?

A

Two pastes - a base and a catalyst

eg - Life or Dycal

43
Q

When is Zinc Oxide Eugenia Cement used?

A

Linings in deep cavities
Temporary restorations
Root canal sealer
Periodontal dressing

44
Q

What are the properties of ZOE?

A 
Adequate working time
Relatively rapid setting time
Low thermal conductivity
Low strength
Radiopaque
High solubility
45
Q

What are the properties of calcium hydroxide?

A 
Quick setting time
Radiopaque
Easy to use
Low compressive strength 
Unstable and soluble
46
Q

What should be done after placing a calcium hydroxide lining?

A

Should be covered with RMGIC prior to a final restoration being placed to protect the calcium hydroxide and prevents its dissolution

47
Q

What glass ionomer is used clinically?

A

Vitrebond

BDS 2 OSCE (24 decks)

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