Impression materials

Question 1

what are the characteristics of alginate

Answer 1

irreversible hydrocolloid, mucodisplasive

Question 2

what are the advantages of aliginate

Answer 2

easy to use, low cost, comfort for patient, hydrophilic - less sensitive to moisture, the powder to water ratio can be altered to suit clinicians preference for viscosity

Question 3

what are the disadvantages of alginate

Answer 3

poor dimensional stability due to syneresis and imbibition of water, low tear resistance

Question 4

what are the characteristics of polyvinyl siloxane (PVS)

Answer 4

addition-reaction silicone elastomer, mucodisplasive and mucostatic impressions possible

Question 5

what are the advantages of PVS

Answer 5

range of viscosities available, long shelf life, good surface detail reproduction, good tear strength, low setting shrinkage, good dimensional stability, good elasticity - minimal permanent deformation upon removal from undercut region, automated mixing machines available - minimises air bubbles

Question 6

what are the disadvantages of PVS

Answer 6

hydrophobic - poor moisture control will reduce the accuracy of the impression, may cause breakage of the cast when pouring up, costly

Question 7

what are the characteristics of polyether

Answer 7

non-aqueous elastomer, mucostatic impressions

Question 8

what are the advantages of polyether

Answer 8

hydrophilic - less sensitive to moisture, 5 minute setting time, long shelf life, accurate, low setting shrinkage, good surface detail reproduction, good dimensional stability, good elasticity - minimal permanent deformation upon removal from undercut regions, automated mixing machines available - avoids air bubbles

Question 9

what are the disadvantages of polyether

Answer 9

single viscosity available, may cause breakage of the cast when pouring up, occasional allergies, difficult to remove from facial hair and adheres to clothing, bad taste, costly

Question 10

what are the characteristics of impression compound

Answer 10

non-elastic, low viscosity means only mucodisplasive impressions takem

Question 11

what are the advantages of impression compound

Answer 11

easy to use, the same material can be reused and manipulated

Question 12

what are the disadvantages of impression compound

Answer 12

poor surface detail, poor dimensional stability, may distort upon removal

Question 13

what are the characteristics of zinc oxide eugenol

Answer 13

non-elastic, mucostatic

Question 14

what are the advantages of zinc oxide eugenol

Answer 14

additions can be made, good dimensional stability

Question 15

what are the disadvantages of zinc oxide eugenol

Answer 15

cannot be used in deep undercuts and may distort upon removal, long setting time in thick sections, possible eugenol allergies

Question 16

what are the characteristics of intra-oral scanner

Answer 16

digital impression taking technique, no materials required

Question 17

what are the advantages of intra-oral scanner

Answer 17

accurate static image, no material costs, digital workflow is more efficient and products are returned sooner, same day indirect restorations possible

Question 18

what are the disadvantages of intra-oral scanner

Answer 18

moisture dependant, border moulding not possible - currently unsuitable for dentures, requires a large initial investment, large head - difficult to scan posteriorly, may trigger a gag reflex, working time ranges from 2-20 minutes depending on the clinicians expertise, large machine is space occupying, greater maintenance cost