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Operative Dentistry Y2 > Prosthetics > Flashcards

Prosthetics Flashcards

1
Q

What percentage of the UK population are edentulous ?

A

13

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2
Q

What are the stages of denture construction ?

A

Primary impression, primary cast, special tray, secondary impression, master cast, record block, occlusal registration, shade colour and size, set up teeth, try in, process trim and polish, fit, review

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3
Q

What preparations may be necessary for edentulous patients for dentures ?

A

Treat infection

Improve contour

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4
Q

What features of the denture should the dentist check at the try in stage?

A

Vertical height, midline, labial contour, aesthetics, occlusion

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5
Q

What factors does facial surface anatomy depend on ?

A

Skeletal form, muscles of mastication and facial expression, age, gender, race, disease, dentition

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6
Q

What is occlusal vertical dimension ?

A

The superior inferior relationship between the maxilla and mandible when in maximum intercuspation

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7
Q

What is resting vertical dimension ?

A

The superior inferior relationship between the maxilla and mandible when the mandible is at rest. This depends on posture and muscle tone

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8
Q

What is free way space ?

A

RVD-OVD, 2-3 mm in dentate adults

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9
Q

What is aesthetics ?

A

Recreating what is considered the norm

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10
Q

What is cosmetics ?

A

Creating aesthetics above the norm

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11
Q

What is the golden ratio ?

A

1:1.618 (phi)

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12
Q

Which factors affect the appearance of dentures ?

A

Tooth selection , modification, position, vertical height, flange colour and design, position and material of clasps

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13
Q

Which factors should be considered when positioning the teeth ?

A

Occlusal plane, interpupillary and alar tragus lines
Lip support
Arrangement

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14
Q

What alternative materials are there to stainless steel and cobalt chrome for clasps?

A

Gold
Nylon
Acetal
Sandblasting to give Matt finish

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15
Q

Why replace missing teeth ?

A

Improve aesthetics, function, speech, confidence, prevent drifting, over eruption, open contacts

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16
Q

What is the Frankfort plane ?

A

External auditory meatus to the lower border of the orbit

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17
Q

What are the advantages of gypsum ?

A

Good colour contrast
Dimensional stability
Cheap

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18
Q

What are the disadvantages of gypsum ?

A

Poor surface detail
Poor tensile strength
Poor abrasion resistance
Poor wetting of rubber based impressions

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19
Q

How is beta type I I gypsum made ?

A

Heat in open vessel 150-160 degrees

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20
Q

What is type II beta gypsum used for ?

A

Mount models on articulators, flask dentures, basing models

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21
Q

What is the structure of type II gypsum ?

A

Large irregular orthorhombic crystals

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22
Q

How is type III gypsum produced ?

A

Heat in autoclave under steam pressure 120-150 degrees

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23
Q

What are the uses of type III gypsum ?

A

Can be used 50/50 with white plaster for edentulous models

Used on its own for dentate models and denture flasking to minimise acrylic shrinkage

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24
Q

What structure is type III gypsum ?

A

Small irregularly shaped prismatic particles

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25
Q

What are the properties of alginate ?

A

Mucostatic
Viscoelastic
Inexpensive
Susceptible to syneresis and imbition
Dimensional stability depends on humidity
Satisfactory reproduction of hard and soft details

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26
Q

What are the uses of alginate ?

A

Full and partial dentures - use 3 mm spaced special tray

Duplicate denture moulds

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27
Q

What are the constituents of alginate ?

A 
Sodium alginate 
Calcium sulphate dihydrate 
Sodium phosphate 
Potassium sulphate 
Filler 
Sodium silicoflouride
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28
Q

What are the relative amounts of the constituents of alginate (%) ?

A 
Sodium alginate 18
Calcium sulphate dihydrate 14
Sodium phosphate 2
Potassium sulphate 10
Filler 52
Sodium silicoflouride 4
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29
Q

What is The purpose of each of the constituents of alginate ?

A 
Sodium alginate - hydrogel former 
Calcium sulphate dihydrate - calcium ions 
Sodium phosphate - control working time 
Potassium sulphate - setting 
Filler - consistency 
Sodium silicoflouride - control pH
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30
Q

What is the setting equation for alginate ?

A

Sodium alginate + calcium sulphate ——> sodium sulphate and calcium alginate (insoluble )

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31
Q

What is dental wax ?

A

Thermoplastic material that melts without decomposition and is usually composed of two or more natural or synthetic compounds

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32
Q

What is modelling wax ?

A

Tough, used for occlusal rim and try ins

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33
Q

What is beading wax ?

A

Soft, easily distorted at room temperature, used for adjusting impression trays

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34
Q

What is casting wax ?

A

Used for patterns on metal castings

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35
Q

What is sticky wax ?

A

Rigid, brittle, used to fix things together

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36
Q

What are the thermal properties of dental wax ?

A

Coefficient of thermal expansion that minimises dimensional change
Well defined melting point
Softening point above the mouth
Poor thermal conductivity meaning that the outer surface hardens before the inner mass

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37
Q

What are the mechanical properties of dental wax ?

A

Flows well at moulding point
Little or no flow at mouth or room temperature
Brittleness which allows it to be removed from undercuts

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38
Q

What are the constituents of dental wax ?

A

Paraffin wax
Bees wax
Synthetic materials eg carnauba to improve toughness and melting range

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39
Q

What is the melting range of dental wax ?

A

49-58 degrees

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40
Q

What are the special tray design principles ?

A

2 mm from sulcus

Relief for frenae

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41
Q

What angle should the handle be at for an upper special tray ?

A

45 degrees

42
Q

What angle should the handle be at for the lower special tray ?

A

10 degrees

43
Q

When might a finger rest be included in a special tray ?

A

For close fitting lower trays a finger rest may be placed on the crest of the ridge in the premolars region

44
Q

What are the properties of light cured special tray wafer ?

A

Transverse strength 80 mpa

Shelf life 3 years

45
Q

What are the uses of the special tray wafer ?

A

Special trays
Occlusal rim and try in baseplate
Neutral zone base plates

46
Q

What are the constituents of the special tray resin wafer ?

A 
Glass filler 
Additives 
Catalyst 
Pigment 
Pyrogenic resin 
Vinylic ester resin 
UDMA
TEDMA
47
Q

Which factors influence dimensional stability?

A

Continuation of setting reaction after setting time
Slow elastic memory
Internal stress from mouth to room temperature
Loss of volatile products leading to shrinkage

48
Q

When is plaster used as an impression material ?

A

Edentulous, mobile soft tissue

49
Q

Describe plaster as an impression material

A

Similar to Dental plaster with higher water to powder ratio to record fine detail
Additives increase working time and reduce setting expansion
May give patient dry mouth

50
Q

How is plaster disinfected ?

A

Places in sodium hypochlorite for 10 mins

51
Q

What is impression compound used for ?

A

Primary impressions for full dentures

Base for wash impression

52
Q

What types of impression compound are there ?

A

Type 1 low fusing impression material

Type 2 high fusing tray material

53
Q

For how long is impression compound heated and under what temperature ?

A

Several minutes 55-60 degrees

Flow rate for type 1 is substantial over 45 degrees but poor below 37

54
Q

What are the properties of impression compound ?

A

Muco displasive
Non elastic
High viscosity
Can be re adapted

55
Q

What causes internal stress in impression compound ?

A

High coefficient of thermal expansion
Change in temperature from softening to room
Poor thermal conductivity

56
Q

What are the constituents of impression compound ?

A

47 % thermoplastic material eg wax or raisin characterises softening temperature
50% filler eg limestone increases viscosity and reduces Thermal contraction
3% lubricant eg stearin acid or gutter percher improves flow properties

57
Q

Which other material are impression waxes most commonly used with?

A

Zinc oxide eugenol

58
Q

What so zinc oxide eugenol impression material used for ?

A

Edentulous master casts

59
Q

What are the properties of zinc oxide eugenol impression material ?

A 
Non toxic 
Irritant 
Persistent taste 
Good dimensional stability 
Good detail reproduction 
Moco displasive
60
Q

What are the constituents of paste 1 of zinc oxide eugenol impression material ?

A

Zinc oxide
Water
Olive oil
Zinc acetate

61
Q

What are the constituents of paste 2 of zinc oxide eugenol impression material?

A

Eugenol

Kaolin

62
Q

What is agar ?

A

15% colloidal suspension of agar in water

Includes borax to give body and potassium sulphate to increase setting of gypsum as this is retarded by borax

63
Q

What is agar susceptible that could compromise its dimensional stability?

A

Imbition

Syneresis

64
Q

What should the casting of addition cured silicone impression materials be delayed ?

A

They release hydrogen which could cavitate the gypsum

65
Q

What chemical on some synthetic gloves can retard the setting of some silicone impression materials?

A

Dithiocarbonate

66
Q

Do addition cured silicones have a high or low setting shrinkage ?

A

Low so no space for cement

67
Q

What is the by product of condensation cured silicone ?

A

Alcohol

68
Q

Do condensation cured silicones have a high or low setting shrinkage ?

A

High so allows space for cement

69
Q

What sis a disadvantage of condensation cured silicone impression materials ?

A

TES is hydrolysed easily and can become inactive if contacts water

70
Q

To which component of a poly ether can patients be allergic ?

A

Sulphonic acid catalyst system

71
Q

What is any advantage of poly ether imoression materials ?

A

Less hydrophobic than silicones

72
Q

How long does poly sulphide impression material take to set ?

A

10 mins

73
Q

What are the advantages of polysulphides?

A

Can be electroplated

Highest tear strength

74
Q

What are the disadvantages of polysulphides?

A

Bad smell and taste
Humid and temperature dependent
Erratic setting

75
Q

What are the main types of articulators ?

A

Simple hinge
Average value articulators
Semi adjustable
Fully adjustable

76
Q

What are the 2 types of average value articulators called ?

A

Ash freeplane 75 and dentatus ARS

77
Q

What are the average vales for average value articulators and what plane are they in ?

A

Incisal plane 10 degrees, horizontal
Condylar plane 30 degrees horizontal
Bennett angle 15 degrees Saggital

78
Q

What are the 2 types of semi adjustable articulators called ?

A

Dentatus ARH non arcon

Denar mark 2 arcon

79
Q

What are the angles and planes for a semi adjustable articulator ?

A

Incisal, angle custom table, horizontal
Condylar, set to patients protrusive wafer, Frankfort
Bennett, set to patients lateral wafer, Saggital

80
Q

What is the type of fully adjustable articulator called ?

A

Denar D5A

81
Q

What are the angles and planes for the fully adjustable articulator ?

A 
Incisal, custom table, horizontal
Condylar, set to pantograph , Frankfort 
Bennett , set to pantograph , Saggital 
Inter condylar distance, adjustable width 
Pantograph, recordings are transferable
82
Q

What are the uses of heat cured acrylic resin ?

A

Denture bases
Splints
Artificial teeth
Rebases

83
Q

What are the physical properties of acrylic resin ?

A

Thermal conductivity
Radiopaque
Low specific gravity and density
High glass transition temperature to prevent distortion

84
Q

What are the mechanical properties of acrylic resin ?

A

Flexural and impact strength
High modulus of elasticity
High elastic limit

85
Q

What are the chemical properties of acrylic resin?

A

Does not absorb water
Inert
Insoluble

86
Q

What are the biological properties of acrylic resin?

A

Non toxic
Non irritant
Resists bacteria and fungi

87
Q

What Is the boiling point if the acrylic resin monomer ?

A

100.3 degrees

88
Q

What is the monomer in acrylic resin ?

A

Methylmethacrylate

89
Q

What is the ideal ratio of powder to liquid for acrylic resin ?

A

2.5 to 1

90
Q

What is the ideal polymerisation shrinkage for acrylic resin?

A

5-6 %

91
Q

What are the transitional stages of the polymerisation of acrylic resin ?

A 
Sand 
Sticky 
Dough 
Rubber 
Hard
92
Q

What should be taken into consideration regarding the polymerisation of acrylic resin?

A

Above 65 degrees benzoyl peroxide evaporates forming free radicals
Above 100.3 degrees the monomer boils in the hottest parts of the denture leading to gaseous porosity
The polymerisation is very exothermic
High conversion rate of monomer to polymer

93
Q

Describe a typical polymerisation cycle for acrylic resin ?

A

Heated to 70 degrees over several hours then 100 degrees for 3 hours
Majority of polymerisation occurs at 70 degrees, 100 degrees at end ensures thinnest parts of denture polymer missed as less exothermic heat is generated in these areas

94
Q

How many times greater is the coefficient of thermal expats nil of acrylic than gypsum ?

A

Ten

95
Q

What is the powder on acrylic resin composed of ?

A 
Polymer - polymethylmethacrylate 
Initiator benzoyl peroxide 
Pigment, slats of iron or organic dyes 
Synthetics eg acrylic or nylon 
Plasticiser dibutyl phthalate
96
Q

What is in the monomer of acrylic resin ?

A

Methyl methacrylate
Inhibitor hydroquinone
Cross linking agent ethylenglycoldimethacrylate

97
Q

What lowers the flexural modulus in high impact acrylic resin ?

A

Butadiene styrene

98
Q

What are the ideal properties of denture base materials ?

A

High thermal conductivity,
Low density,
Resistant to bacterial growth and absorption of oral fluids,
Radio opaque

99
Q

What amount of undercut is required for a cobalt chrome clasp ?

A

0.25mm

100
Q

What amount of undercut is required for stainless steel or cast gold clasps ?

A

0.5 MM.

101
Q

What amount of undercut is required for wrought gold claps ?

A

0.75mm

Operative Dentistry Y2 (7 decks)

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