Alginate

Question 1

What is alginate?

Answer 1

irreversible hydrocolloid

Question 2

colloid?

Answer 2

substance which is distributed evenly through another material

Question 3

Two phases of alginate?

Answer 3

dispersed

continuous

Question 4

What can alginate exist as?

Answer 4

either viscous liquid (sol) or as a solid (gel)

changes from solid to gel in the case of alginate

Question 5

2 components of alginate?

Answer 5

powder and liquid

mixed into paste

Question 6

What phase is alginate when it is a paste?

Answer 6

sol phase

Question 7

What phase is alginate when it sets?

Answer 7

gel phase

Question 8

composition of alginate?

Answer 8

sodium and potassium salts + alginic acid

Question 9

What constituent of alginate dissolves in water to form a hydrogel with calcium?

Answer 9

potassium alginate or sodium alginate

Question 10

Role of potassium alginate or sodium alginate?

Answer 10

What constituent of alginate dissolves in water to form a hydrogel with calcium

Question 11

What slows down the setting reaction of alginate?

Answer 11

sodium phosphate

acts as a retarder by preferentially reacting with calcium ions

Question 12

Role of calcium sulphate dihydrate?

Answer 12

reacts with soluble alginate to form insoluble calcium alginate

Question 13

setting reaction of alginate?

Answer 13

Question 14

What is the general term for the alginate setting reaction?

Answer 14

double decomposition reaction

Question 15

What acts as a retarder by preferentially reacting with calcium ions?

Answer 15

sodium phosphate

Question 16

When is the material set?

Answer 16

once the phosphate ions have been used up

Question 17

pH change of the material upon setting?

Answer 17

11 -> 7

Question 18

mixig time of alginate?

Answer 18

45-60 secs

Question 19

working time of alginate?

Answer 19

45s (fast set)

75s (regular set)

Question 20

setting time of alginate?

Answer 20

1-4.5 mins

can be variable to altering water temp

Question 21

What occurs hewn you remove alginate form the mouth?

Answer 21

impression material compressed when removed

distortion results which could be significant

remove quickly from mouth - snap out

Question 22

How to minimise distortion of impression?

Answer 22

reducing the amount of compression

reducing the rime the impression is under compression

allowing time for recovery before poring - decompress

Question 23

Alginate and syneresis?

Answer 23

gel contracts on standing and exudes liquid

lose moisture form impression - distortion

• need to control relative humidity and proper storage important

Question 24

How to minimise syneresis?

Answer 24

lose moisture form impression - distortion

• need to control relative humidity and proper storage important

Question 25

imbition of alginate?

Answer 25

takes up water and swells uncontrolled in extent and direction

Question 26

How to overcome imbition and syneresis?

Answer 26

wrap in damp tissue and store in sealed polythene bag until the impression can be cast

Question 27

what effects the strength f alginate

Answer 27

variation in water volume - reduction in powder/liquid ratio will weaken gel insufficient spatulation - ingredients not dissolved sufficiently , inconsistent chemical reaction over-spatulation - disruption of forming calcium alginate gel and reduce strength

Question 28

tear strength of alginate?

Answer 28

tear strength poor especially when removing from mouth

Question 29

advantages of alginate?

Answer 29

easy flow reproducible of detail adequate fast set minimal tissue displacement cheap pt tolerance good

Question 30

disadvantages of alginate?

Answer 30

poor dimensional stability poor tear strength distorts if unsupported 3mm minimum thickness requires - otherwise distortion occurs were thin sections are found, such as interproximal easy to include air

Question 31

minimum thickness of tray?

Answer 31

3mm thickness needed for alginate impression

Question 32

indications for alginate?

Answer 32

used in situations where less accuracy/ detail is required: study casts to pan case/design prosthesis denture construction (primary and working impressions) teeth opposing an indirect cast restoration removable orthodontics appliances other dental devised such as occlusal splints

Question 33

displace quickly or slowly form mouth?

Answer 33

quickly

Question 34

clinical tips for usage?

Answer 34

smooth impression surface smear some material into fissures pace some material into high palatal vault evert lip/retract cheeks careful not to pull tray towards dominant side hold still in the mouth ensure material fully set displace quickly from mouth

Question 35

reasons for a grainy material?

Answer 35

inadequate or prolnged mixing liquid/powder tatio too low

Question 36

reasons for tearing?

Answer 36

inadequate bulk premature removal from mouth

Question 37

Reason for external bubbles?

Answer 37

air incorporated during mix

Question 38

reason for rough or chalky model?

Answer 38

inadequate cleaning of impression excess water left in impression premature removal of model

Question 39

reason for distortion?

Answer 39

delayed pouring of impression movement of tray during impression taking premature removal from mouth of model

Question 40

product name at IOD?

Answer 40

tropicalgin

Question 41

Steps for impression decontaminatio?

Answer 41

Question 42

Can you leave gypsum in contact with alginate for hours?

Answer 42

affect surface quality of cast - remove when fully set