Intro to dental material science

Question 1

what 5 things do you need to consider before choosing a dental material?

Answer 1

selection: adequate/best type
preparation: cavity design, tooth surface
placement: technique
perfomance: quailty of fit, longevity
patient expectations: aesthetics, durability

Question 2

give examples of some retorative materials

5

Answer 2

alamgam
composite
glass ionomer cements
compomers
porcelain

Question 3

give examples of impression materials

4

Answer 3

impression compound
impression paste
hydrocolloids - alginate
elastomers - polyethers, silicones, polysulphides

Question 4

give examples of matals/alloys

5

Answer 4

amalgam
cobalt chromium
titanium
gold
stainless steel

Question 5

what is the definition of stress, strain and young modulus?

2

Answer 5

stress = force/unit area
strain = change in length/original length
YM = stress/strain

Question 6

what is fractre stress on the SS curve and what is the value for enamel and dentine?

Answer 6

where the graph stops as the material has fractured
enamel: 262MPa
dentine: 234MPa

Question 7

what is proportional limit on the SS curve and what is the value for enamel and dentine?

Answer 7

the highest stress that the stress-strain curve is a straight line
enamel: 235MPa
dentine: 176MPa

Question 8

what is elastic modulus on the SS curve and what is the value for enamel and dentine?

Answer 8

EM/YM is the initial straight gradient of the curve
enamel: 33.6GPa
dentine: 11.7GPa

Question 9

describe the difference between enamel and dentine as shown on the graph

Answer 9

enamel
* steep initial slope = high stiffness / YM
* low elasticity as fractures suddenly after PL
* brittle as sharp drop off at breaking point
dentine
* gentler slope = lower stiffness / YM
* higher elastricity as greater elongation after PL
* tougher as longer region before failure

Question 10

what is the difference between amalgam and composite cavity preparation and how is it retained?

Answer 10

amalgam: undercut design, mechanical retention
composite: minimal design, adhesive retention

Question 11

define fracture

Answer 11

large force causes catastrophic destruction of material’s structure

Question 12

define hardness

Answer 12

ability of a surface to resist indentation

Question 13

define abraision

Answer 13

material surface removal due to grinding

Question 14

define abrasion removal

Answer 14

ability to withstand surface layers being removed, compromising surface integrity

Question 15

define fatigue

Answer 15

repetitive “small” stresses cause material failure

Question 16

define creep

Answer 16

gradual dimensional change due to small repetitive forces e.g. amalgam

Question 17

define deformation

Answer 17

applied stress causes permanent change in material’s dimensions but does not fracture it

Question 18

define de-bond

Answer 18

applied forces suffient to break the material-tooth bond

Question 19

define impact

Answer 19

large, sudden force causes fracture e.g. denture hitting floor

Question 20

what are chemical properties to consider with materials

3

Answer 20

setting mechanism
setting time
corrosive potential

Question 21

what are physical properties to consider with materials

5

Answer 21

viscosity
thermal conductivity
thermal expansion
density
radiodensity