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BDS3 Dental Materials > Introduction to impression materials > Flashcards

Introduction to impression materials Flashcards

1
Q

what is a dental impression?

A

means of recording intra-oral structures

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2
Q

uses of casts produced by taking impression?

A

study casts

construction of dental appliances

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3
Q

use of stidy casts?

A

diagnosis

tx planning

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4
Q

Why use a cast to construct dental appliances?

A

orthodontic appliances and retainers

removable dentures
- complete
- partial

other appliances such as implants, mouthguards, bleaching trays etc

fixed prosthesis
- inlays
- onlays
- inlay/onlays

crowns
- partial
- full

bridges

implant retained prostheses

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5
Q

requirements of an impression tray?

A

rigid and non-flexible under load when taking impression

extend sufficiently to support the impression material in the region being reproduced
- if want a crown the full sulcus depth not paramount

fit loosely around the dental arch and not touch the soft tissues

have adequate means of retaining the impression material in the tray

have a robust (integral) handle - facilitate clinical manipulation of tray

be able to be adequately decontaminated (if not meant for single use)

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6
Q

types of stock trays?

A

taken for first impression

plastic or metal

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7
Q

what are plastic stock trays made from?

A

high impact styrene

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8
Q

2 types of stock trays?

A

metal - very rigid, no distortion of material

plastic

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9
Q

retention for material in metal impression tray?

A

metal rim lock tray

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10
Q

adequate extension?

A

no - not good sulcus extension

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11
Q

what is wrong about the tray here?

A

tray close to teeth - not allow sufficient bulk material in that area

overextended on the buccal sulcus and underextended n the lingual

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12
Q

Why do we need rigidity in impression tray?

A

stresses form within material

tray reverts to original shape when removed

distorted imp material

cast inaccurate

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13
Q

methods for material retention in tray?

A

1) tray design
- perforations
- rim lock (periphery where material can get locked in there)

2) tray adhesive
- types
- usage

ideally both

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14
Q

perforation as a retentive denture?

A

material extrudes through perforations so retaining the material in the tray mechanically

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15
Q

How to extend peripheries of imp tray?

A

1) periphery wax

  • contains beeswax, paraffin and other soft waxes

2) greenstick

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16
Q

Why use peripheral extension of stock tray?

A

helps to contain the fluid imp material in the stock impression tray

17
Q

what is greenstick used for?

A

extend peripherals of stick tray

18
Q

is greenstick better than wax for tray extension?

A

better alternative to wax to contain the fluid impression material in the impression tray

rigid (non-elastic) impression material

19
Q

chemical constituents of greenstick?

A

resins (such as shellac)
waxes (such as bees wax)

  • used to control consistency

calcium carbonate
limestone
talc

  • used as fillers, control consistency and rigidity and colouring agent
20
Q

Is greensick a thermoplastic material?

A

yes, transition temp 55-60 dc

softened by exposure to hot water or naked flame

21
Q

Where in the tray is greenstick most used?

A

post-dam region

22
Q

what tray adhesive is used for alginate?

A

toluene alcohol

isopropyl alcohol is volatile, leaving the toluene behind

23
Q

2 presentataions of tray-adhesives?

A

spray
- can get pooling but is good for contamination

pain-on
- cross contamination and crusty bits around neck of bottle, get poor seal and volatile substance can evaporate

24
Q

why make special trays?

A

accuracy in impression

permits equal thickness of impression material

equal in all dimensions - minimal distortions of material

get proper extensions into sulcus

25
Q

what are special trays made from?

A

polymethylmethacrylate - acrylic

shellac

26
Q

appropriate space for alginate impression material for second imp?

A

3mm

27
Q

appropriate space for C-silicone impression material for second imp

A

2mm

28
Q

appropriate space for impression paste and impression plaster impression material for second imp

A

1mm

29
Q

primary cast material?

A

plaster of paris

30
Q

secondary cast material?

A

dental stone aka gypsum

31
Q

refractory model?

A

material which can be heated up - it is chemically and physically stable at different temps

32
Q

desirable properties of impression materials?

A

easy to handle

compatible with oral fluids

reproducible detail accuracy

have good tear resistance

have no adverse effects on pt

have pleasant taste

easily removable from the mouth especially from undercut area

be able to be adequately decontaminated

remain dimensionally stable after removal

compatible with all model construction

33
Q

impression decontamination?

A

BDS3 Dental Materials (13 decks)

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