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Week 1 Flashcards

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1
Q

what- type of replica is an impression.

A

Negative replica of object

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2
Q

3 classification of denture types

A

1.Chemistry
* Silicon
* Hydrocolloids
* Polyether
* Polysulfide
* Zinc/oxide-eugenol
* Impression compounds
* Plasters properties
2. Before setting
3. properties After setting

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3
Q

What are the properties of impression materials before setting?

A

Based on viscosity: low, medium, and high.

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4
Q

Examples of high viscousity impression materials

A
  1. Putty and heavy body
  2. IM Compound
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5
Q

Example of high visosity impression material

A

Putty and heavy bodied, IM compund

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6
Q

Medium viscosity impression material examples

A

Regular bodied if elastomers

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7
Q

Name the types of viscosity in impression materials.

A
  • High viscosity
  • Medium viscosity
  • Low viscosity
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8
Q

Medium Viscosity impression material

A

Regular body elastomers

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9
Q

Low viscosity impression materials

A

IM plaster, hydrocolloids, Light bodied of elastomer

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10
Q

What are the properties of impression materials after setting?

A
  • Elastic
  • Non-elastic
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11
Q

Low viscosity impression materials

A

1.IM plasters
2. Hydrocolloid
3. Light bodied of elastomers

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12
Q

Examples of elastic and non-elastic impression materials

A

Elastic: Synthetic elastomers(polysulphides, silicones, polyether
Non-elastic: IM plasters, IM waxes, IM compound, ZOE

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13
Q

What does ‘hydro’ mean in hydrocolloids?

A

Water

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14
Q

What does ‘kola’ mean in hydrocolloids?

A

Glue

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15
Q

What is a solution?

A

A homogeneous mixture consisting of a single phase.

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16
Q

which retraction method to use for excessiv tissue/ inflammation

A

Electrosurgery, lasers, pharmacological treatment

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17
Q

What is a suspension?

A

A mixture of two phases.

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18
Q

Define a colloid.

A

A heterogeneous mixture of two phases, where the two phases are not readily differentiated.

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19
Q

Give examples of hydrocolloid impression materials.

A
  • Agar
  • Alginate
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20
Q

What are reversible hydrocolloids?

A

E.g. agar, formed through cooling and heating.
When cooled it becomes gel
When heated it becomes Solution
Secondary Bonding

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21
Q

What are irreversible hydrocolloids?

A

E.g. alginate, formed through a chemical reaction.
Primary bonding

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22
Q

What is the composition of alginate impression materials?

A
  • Sodium alginate(hydrogel former)
  • Calcium sulfate dihydrate(Provide calcium ions)
  • Sodium phosphate(controls working time)
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23
Q

What is the role of calcium ions in alginate impression materials?

A

They displace sodium ions in the sodium alginate polymer during crosslinking.

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24
Q

List some properties of alginate impression materials.

A
  • Cheap
  • Limited shelf life
  • Dust free powder
  • Well controlled working and setting times
  • Mucostatic
  • Hydrophilic
  • Poor surface detail reproduction
  • Poor storage stability
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25
What is permanent deformation in impression materials?
The inability to recover 100% of original dimensions after removal.
26
What handling characteristics are required for alginate impressions?
Requires a spaced tray (3-4mm). Heating warm water/oral environment Excess gypsum impurity reduces working and setting time
27
how does warm water reduce working time
Accelerates sodium phosphate consumption
28
Which side does setting start?
From tissue side towards tray side
29
what happends due to immature removal of impression
distortion
30
What effect does heating have on working and setting time of alginate?
It reduces working and setting time by accelerating sodium phosphate consumption.
31
How should models be poured after taking an impression?
In a short time and kept humid.
32
What are the setting times for fast set alginate?
* Mixing Time (MT): 45 sec * Working Time (WT): 1.5 min * Setting Time (ST): 2.5 min
33
What are the setting times for regular set alginate?
* MT: 1 min * WT: 2.5 min * ST: 3.5 min
34
What factors should be considered when selecting impression materials?
* Accuracy * Stability * Type of tray * Price * Handling characteristics
35
What is the requirement for impression materials regarding biocompatibility?
They should be biocompatible.
36
37
mWhat is the main disadvantage of polysulfide impression materials?
Bad odor and taste due to thiol groups.
38
What is a major drawback of polyether impression materials?
Rigidity, making it unsuitable for deep undercuts.
39
What is the main advantage of polysulfide impression materials?
Very good tear resistance.
40
What are the types of impression trays?
* Stock tray (prefabricated) * Rim lock tray * Custom trays
41
What is the function of the impression tray?
To give rigid support to the impression materials and carry it to the mouth.
42
What should be avoided when selecting trays for alginate impressions?
Flexible trays.
43
What is the recommended position for the patient during impression taking?
Upright or semi-upright position.
44
What should be done after taking the impression?
Disinfect the impressions and pour the alginate impression within 1 hour.
45
What is the significance of internal stress in wax handling?
It can create dimensional changes due to thermal conductivity.
46
Doing what can result in internal stress(residual stress)
Moulding before uniform softening of the wax
47
What are the properties of polysulfide impression materials?
* Very good tear resistance * Adequately elastic * Moderately hydrophilic * Radiopaque because of Pb However, it has viscoelastic behavior Poor odour and taste(thiol group) Poor dimensional stability
48
general structure of polysulphide impression materials
polymer with termianl and pendant mercaptan group(-SH). Condensation polymerisation
49
What is the presentation of polyether impression materials?
* Base paste: Polyether, filler, plasticizer * Activator paste: Aromatic sulphonate ester, filler, plasticizer
50
binding of polyether impression material
cross linking reaction with amine end groups. Cationic- addition polymerisation
51
What is the main characteristic of silicone impression materials?
Condensation cured.
52
What is a major drawback of polyether impression material?
Rigidity, making it unsuitable for deep undercuts ## Footnote This is particularly relevant in cases with big interproximal spaces.
53
What can cause allergic reactions in impression materials?
Sulphonic acid ## Footnote Allergic reactions can complicate the use of certain impression materials.
54
What are the components of condensation cured silicone impression material?
A. Base paste: Hydroxyl-terminated polydimethylsiloxane, Filler (colloidal silica) B. Activator paste: Alkylsilicate, Filler (colloidal silica), Tin compound ## Footnote Tin compound is specifically dibutyl tin dilaurate.
55
What are the viscosities available for condensation cured silicone impression material?
Light bodied, medium bodied, heavy bodied, putty ## Footnote These viscosities can be used with stock or special trays.
56
What is the pouring time for putty and wash in condensation cured silicone impression material?
6 hours ## Footnote This is the recommended time before pouring.
57
What are the components of addition cured silicone impression material?
A. Base paste: Polydimethylsiloxane with hydrogen groups, Filler (colloidal silica), Silanol B. Activator paste: Polydimethylsiloxane with vinyl groups, Filler (colloidal silica), Pt catalyst ## Footnote The Pt catalyst is crucial for the curing process.
58
What are the viscosities available for addition cured silicone impression material?
Light bodied, medium bodied, heavy bodied, putty ## Footnote Similar to condensation cured silicones, these can also be used with stock or special trays.
59
What is a key feature of vinyl terminated polydimethyl siloxane?
Cross-linking reaction with no byproduct and good dimensional stability ## Footnote This feature ensures accuracy in impressions.
60
Which elastomeric impression material is considered the easiest to handle?
Addition-cured silicones with a gun delivery system ## Footnote This system simplifies the mixing and application process.
61
What is the stiffness order of elastomeric impression materials?
PS < CCS < ACS < PE ## Footnote PS stands for polysulphides, CCS for condensation-cured silicones, ACS for addition-cured silicones, and PE for polyethers.
62
True or False: Polyethers have very consistent working and setting times.
True ## Footnote This makes them reliable for various dental applications.
63
What is the recommended action for condensation-cured silicone impressions after taking them?
Pour as soon as possible due to continued setting and alcohol evaporation ## Footnote Delayed pouring can lead to inaccuracies.
64
Which type of impression materials shows excellent reproduction of surface detail on dry surfaces?
All types show excellent reproduction; however, polyethers are generally best ## Footnote Their hydrophilic nature aids in detail capture.
65
What happens to polysulphides during storage?
They contract ## Footnote This can affect their performance if not managed properly.
66
properties based on viscosities
Accuracy: low viscosity better Polymerisation shrinkage: low Cooling contraction: low is better than high
67
What is the role of aluminum chloride in gingival retraction?
Provides hemostasis by constricting capillaries ## Footnote Commonly used in various hemostatic agents.
68
What is a disadvantage of using retraction cords?
Can be time-consuming and may traumatize tissues if improperly handled ## Footnote Proper technique is crucial for effective use.
69
advantages and disadvantages of copper band/matrix band
Advantages: i.Combined with impression materials or retraction cords Dis: limited in precision and control
70
What is the effect of epinephrine in gingival retraction?
Causes vasoconstriction and reduces bleeding ## Footnote Caution is advised in patients with cardiovascular issues.
71
What is the recommended action if an impression is grossly contaminated?
Clean in an ultrasonic bath containing detergent and rinse ## Footnote This ensures thorough cleaning before disinfection.
71
What are common failures with impressions?
Poor reproduction of surface detail, incomplete set, air bubbles, distorted impressions ## Footnote These issues can arise from various factors including improper mixing and contamination.
71
What can cause rapid setting in impression materials?
Humidity, temperature, wrong mix ## Footnote Environmental factors can significantly affect setting times.
71
disadvantage of using ferric sulphate
can cause temporary gingical discolouration
72
What are the sizes available for gingival retraction cords?
Small (000 to 0), Medium (1 to 2), Large (3) ## Footnote Size selection is based on the sulcus depth and tissue type.
73
What is the main purpose of gingival retraction?
Displace gingival tissues to provide access to preparation margins ## Footnote This is crucial for effective dental procedures.
74
What is the function of viscosity-enhancing agents in gingival retraction pastes?
To thicken the paste and enable sulcular displacement ## Footnote Polyvinylpyrrolidone is a common example.

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