Textbook Dental Materials

Question 1

Amalgam forms?

Answer 1

Lathe cut
Spherical
Admired

Question 2

What is the silver/tin phase?

Answer 2

Powdered alloy mixing with mercury

Question 3

What is the gamma 2 phase?

Answer 3

Causes increased corrosion and creep

Question 4

What is the reason that more copper is added to amalgam?

Answer 4

To turn gamma 2 phase to gamma 1 phase causing less corrosion and creep

Question 5

How is amalgam retained in a cavity?

Answer 5

Retention by grooves pits undercuts dovetail lock

Cavities must be over 1.5mm deep

Question 6

Why are amalgam cavities overfilled and condensed?

Answer 6

Condensed to bring mercury to surface, overfilling allows mercury rich surface to be carved away

Question 7

Disadvantages of amalgam?

Answer 7

Excess tissue removed for retention
Microleakage common
Potential mercury toxicity

Question 8

How is composite set?

Answer 8

Monomers undergo a polymerisation reaction.

Monomers join together to form large chain molecules which is initiated by free radicals

Question 9

How are light cure composites set?

Answer 9

Composed of resin, filler and camphorquinone

Camphorquinone bonds broken down by light at 470nm and free radicals are produced which initiate polymerisation

Question 10

How does shrinkage occur and how much?

Answer 10

Polymerisation encourages monomers to join together and resin shrinks
21%

Question 11

What monomers are used in the resin matrix and what are their jobs?

Answer 11

BISGMA - reduces shrinkage

TEGMA - controls viscosity

Question 12

What does addition of a filler do to composites?

Answer 12

Makes resin stronger
Reduces shrinkage
Reduced how flowable the material is

Question 13

What are the types of composites and their properties?

Answer 13

Macrofilled - quartz filler. Strong but poor aesthetics
Microfilled - silica filler. Problems with shrinkage (less filler)
Hybrid - quartz and silica
Nano composites - improved aesthetics

Question 14

What is the silane coupling agent?

Answer 14

ensures that the resin and filler work together

Question 15

What is the composition of flowable composite?

Answer 15

50-70% filler
Less viscous more flowable
Problems with shrinkage

Question 16

What are the basic components of glass ionomer materials?

Answer 16

Polyalkenoic acid (e.g polyacrylic acids) and ion leachable glass (e.g aluminasilicate with calcium)

Question 17

What is a cermet?

Answer 17

Metals added to powder
Gives unaesthetic grey material
Used as core build up in badly broken down teeth

Question 18

What is a compomer?

Answer 18

Polyacid modified resin composite

Question 19

Describe the action and composition of the etching stage of etch prime bond?

Answer 19

37% phosphoric acid
Etch removes the smear layer and opens dentinal tubules by dissolving the mineral portion up to 5um leaving collagen fragments exposed

Question 20

Describe the composition and action of the priming stage of etch prime bond?

Answer 20

HEMA dissolved in a solvent
HEMA has a hydrophilic terminal which adheres to dentine and a hydrophobic terminal that can polymerise with resin composite

Question 21

Describe the composition and action of the bond stage of etch prime bond?

Answer 21

Resin adhesive

Attaches to hydrophobic terminal of HEMA primer and locks onto exposed collagen when light cured

Question 22

Why is RMGIC left uncured in a bonded amalgam?

Answer 22

To allow chemical cure whilst adherent to tooth tissue and amalgam