Dental material science

Question 1

Why is dental materials science important?

Answer 1

dentists constantly use materials, need to communicate with other professionals e.g. technicians, need to evaluate new materials

Question 2

What are the types of dental materials?

Answer 2

restorative, impression, dentures, metals and alloys, …others

Question 3

What are restorative materials used for?

Answer 3

to fill a cavity after caries removal

Question 4

What are the restorative materials?

Answer 4

amalgam, composite resin, (resin-modified) glass ionomer cement

Question 5

How does the cavity design differ for amalgam and composite resin?

Answer 5

amalgam has a more flared out cavity (need to remove more hard tissue) whereas composite resin only requires caries to be removed (more rounded shape)

Question 6

Example of a failure of an amalgam restoration?

Answer 6

ditched margins

Question 7

Possible cause of ditched margins in amalgam restoration

Answer 7

amalgam creep

Question 8

Outline the process of amalgam creep

Answer 8

1. low level forces applied continuously
2. amalgam protrudes around margins - vulnerable to fracture
3. exposed amalgam fractures - forms ditched margins

Question 9

Danger of ditched margins

Answer 9

possible site for secondary caries

Question 10

What technique is used to bond composite resin to the tooth?

Answer 10

acid etch technique

Question 11

What chemical is applied to the tooth surface and for how long for acid etching?

Answer 11

30% phosphoric acid for 20 sec

Question 12

Function of acid etching

Answer 12

improves the shear strength of composite resin (doesn’t slide of enamel when force applied due to rough surface created)

Question 13

Which restorative material has a thermal expansion rate almost identical to enamel?

Answer 13

(renin-modified) glass ionomer cement

Question 14

What is the cavity shape for (resin-modified) glass ionomer cement?

Answer 14

shape of caries (rounded) as glass ionomer cement binds to enamel so no excess hard tissue needs to be removed

Question 15

What is an advantage specific to the use of (renin-modified) glass ionomer cement?

Answer 15

releases 1ppm fluoride per day which increases enamel’s resistance to caries

Question 16

What is the pattern of fluoride release by glass ionomer cement?

Answer 16

high F release initially (8ppm/day) which rapidly decreases to 1ppm/day from day 10 onwards (is this sufficient?)

Question 17

What quality of the restorative material determines how well it resists fracture?

Answer 17

compressive strength

Question 18

Important features fore restorative materials?

Answer 18

high shear strength, high compressive strength, thermal expansion similar to tooth

Question 19

What happens if the restorative material does not expand/contract as the tooth does?

Answer 19

Microleakage

Question 20

How does microleakage occur?

Answer 20

cold stimulus causes thermal contraction of the restoration only. Gaps form between the enamel and restoration which allows saliva and bacteria to ingress

Question 21

Function of impression materials

Answer 21

to record a patient’s dentition (size, shape, position, orientation of each tooth)

Question 22

Definition of viscosity

Answer 22

a measure of a fluid’s resistance to flow

Question 23

Which has the lowest viscosity: water, ketchup, syrup?

Answer 23

water

Question 24

Which has the highest viscosity: water, ketchup, syrup?

Answer 24

syrup

Question 25

What is the advantage of using a low viscosity impression material?

Answer 25

Captures the most accurate record of tooth surface details

Question 26

What is the advantage of using a high viscosity impression material?

Answer 26

most dimensionally stable after setting and removing

Question 27

Describe the two step technique that can be used for impression taking

Answer 27

high viscosity material is placed in the tray and impression taken. Then, low viscosity material is placed around individual teeth and the impression tray is reinserted

Question 28

Important property for impression material

Answer 28

elasticity

Question 29

Why is it important for an impression material to have elasticity?

Answer 29

once impression material is set around tooth, it can endure elastic strain during removal and then elastic recovery to its original shape

Question 30

What is an elastic material?

Answer 30

material that undergoes full recovery of shape after force removal

Question 31

What is a non-elastic material?

Answer 31

material that has a permanent deformation after force removed

Question 32

What type of replica of the dentition is created by the impression material?

Answer 32

negative replica

Question 33

How is a positive replica of the dentition obtained?

Answer 33

dental stone (gypsum) is poured into the negative replica (impression material)

Question 34

Example of denture material

Answer 34

acrylic resin denture

Question 35

Why does an upper acrylic denture require transverse strength?

Answer 35

under pressure of 3 point loading (masticatory force acting down from palate, supportive force acting up from teeth)

Question 36

What are metals and alloys used for?

Answer 36

partial denture frameworks, orthodontic wires, denture bases

Question 37

Feature of partial dentures used to retain denture

Answer 37

clasps

Question 38

Definition of a rigid material

Answer 38

undergoes a little change in shape when large stress is applied

Question 39

opposite of rigid

Answer 39

flexible

Question 40

Describe the rigidity of alloys

Answer 40

very rigid (particles different sizes so cannot slide)

Question 41

What material may be used for orthodontic wires?

Answer 41

stainless steel

Question 42

What are the categories that properties are divided into?

Answer 42

mechanical, thermal, flow, miscellaneous (e.g. creep)

Question 43

List mechanical properties

Answer 43

strength (shear, tensile, compressive, flexural, tear), rigidity, hardness (abrasion resistance)

Question 44

List thermal properties

Answer 44

expansion coefficient, conduction

Question 45

List flow properties

Answer 45

viscosity, visco-elasticity

Question 46

Example of several terms illustrating same idea (importance of property definitions)

Answer 46

rigidity = stiffness = elastic modulus = Young's modulus

Question 47

Definition of viscosity *

Answer 47

ability to flow (resistance of flow)

Question 48

Definition of elasticity

Answer 48

ability of material to return to its original shape on removal from mouth using an applied force

Question 49

Definition of rigidity

Answer 49

measure of how much force is needed to cause a temporary change in shape of material

Question 50

Definition of compression strength

Answer 50

ability to withstand applied compressive forces without fracturing

Question 51

Definition of hardness *

Answer 51

ability of surface to withstand indentation and resistance to abrasion (e.g. removal of surface layer)

Question 52

Definition of creep

Answer 52

change in shape due to repetitive application of small forces