Alginates

Question 1

What is the meaning of an Irreversible Hydrocolloid?

Answer 1

A one way chemical reaction that cannot revert to its original state

Question 2

What is Dental Alginate made of?

Answer 2

Algin: sourced from brown seaweed/algae

Question 3

What are the clinical applications of Dental Alginate?

Answer 3

1) Occlusal Analysis
2) Treatment Planning - for creating good baseline records or diagnostic tool
3) Fabrication of Dental Appliances - Night Guards, Mouth Guards, Occlusal Splints. They are used for primary impressions to create initial casts

Question 4

What are advantages of using dental alginate?

Answer 4

1) Easy to Manipulate
2) No Elaborate Equipment
3) Comfortable for Patient
4) Records most details in mouth
5) Sufficiently elastic so easy to remove
6) Non-Irritant
7) Non-Toxic
8) Taste/Odour acceptable
9) Low Viscosity (thickness) on mixing
10) Controllable setting time (adjusting water temp)
11) Compatible with Gypsum and Dental Stones for reduction
12) Hydrophilic - so saliva present is fine
13) Good value for money

Question 5

What are disadvantages of dental alginate?

Answer 5

1) Low Surface Reproducibility
2) Dimensionally Unstable
3) Low Working Time
4) Single Cast Only
5) Requires tray stability whilst in mouth
6) Poor Mechanical Properties
7) Inconsistency in setting time (sets to teeth first)
8) Silica Dust Hazard
9) Incompatibility with Epoxy Resin Dyes

Question 6

What is the working time of dental alginate at 23 degrees from mixing to final set?

Answer 6

Total Time: 3 minutes

1) Mixing Time: 45 Seconds (Purple)
2) Working Time: 1:45 mins (Pink)
3) Time in Mouth: 30 seconds
4) Final Set: 45 seconds

Question 7

How can setting time of alginates be altered?

Answer 7

1) Alter Water : Powder Ratio
2) Introduction of gelation retarder
3) Alter temperature of water

Question 8

T/F: Increasing the temperature shortens the setting time of alginates

Answer 8

True: increases the rate of sodium phosphate consumed in the reaction

Question 9

How might you obtain consent for taking an dental impression?

Answer 9

1) Inform why the impression is important: to have a baseline model of your teeth before we start treatment
2) Warn about gagging: “might be uncomfortable”
3) Inform about taste: “a bit bland and gritty, feel like custard but will harden”
4) Warn about size of trays into mouth: “Might feel a bit bulky”
5) Inform about trying out different trays to fit - “find the right tray for you”

Question 10

What should be observed before taking a dental impression?

Answer 10

1) Deep Undercuts
2) Arch Size/Shape
3) Bony Protrusions
4) Deep Palatal Vaults
5) Mobile Teeth
6) Tilting/Overerupted Teeth
7) Teeth out of alignment
8) Debris
9) Presence of implants, fixed prosthetics, orthodontics
10) Lip Tone / Health

Question 11

What bony protrusions might be an obstacle for taking a good dental impression?

Answer 11

Buccal Exostosis

Bilateral Mandibular Tori

Question 12

Why might you use blue periphery wax on an impression tray?

Answer 12

To accommodate height, 3rd molars, prevent material leaking on deep palatal vaults

Question 13

Which tray should you try to take an impression of first?

Answer 13

Mandibular - more comfortable for the patient to do initially

Question 14

What are the 5 criteria for clinical acceptability for a dental impression?

Answer 14

Acronym: MSTAR

1) Mix is homogenous and smooth
2) Appropriate Tray Size
3) Adequate time to insert, seat, set
4) Adequate amount of alginate used in tray
5) Tray has been removed correctly

Question 15

T/F: 23 Sized Tray is a medium size

Answer 15

False
23 - Small
24 - Medium
25 - Large (use if 3rd molars are present)

Question 16

How many scoops are used for a Mandibular Impression?

Answer 16

2P : 2L

Question 17

How many scoops are used for a Maxillary Impression?

Answer 17

3P: 3L

Question 18

What are the 3 reasons alginates are dimensionally unstable?

Answer 18

1) Evaporation - loss of water from surface (causes shrinkage)
2) Imbibition: swelling if immersed in water (causes swelling and distortion)
3) Syneresis: loss of fluid when gel structures reconfigure to achieve equilibrium through stress relaxation (causes shrinkage)

Question 19

What are strategies to ensure patient comfort when taking alginate impressions?

Answer 19

Distraction technique Upright position
Minimise excess
Appropriate tray size Controlled breathing Awareness of anatomy (lip tightness, bony protrusions)

Question 20

What is the chemical reaction for alginates?

Answer 20

Potassium Alginate + Calcium Sulphate -> Potassium Sulphate + Calcium Alginate

Question 21

What is the shelf life of alginates?

Answer 21

1 Year

Question 22

What are the different ingredients of alginate?

Answer 22

Potassium Alginate (Soluble Alginate), 
Calcium Sulfate (Reactor) 
Diatomaceous Earth/Silicate Powder (Filler)
Trisodium Phosphate (Retarder, preferentially used Calcium Sulphate), Potassium Titanium Fluoride (Accelerator)