Introduction to DMS

Question 1

What are the stages of a clinical episode affected by dental material behaviour? 5

Answer 1

Selection, preparation of cavity design and tooth surface, placement of material, performance of material and patients expectations

Question 2

How is safety of materials insured?

Answer 2

CE mark

Question 3

Does a CE mark guarantee the material is the best available?

Answer 3

No

Question 4

What do impressions record? 2

Answer 4

Negative replica of the teeth and a valuable record of space and shape of patient’s teeth

Question 5

What is gypsum used for?

Answer 5

Creates positive replica of the impression and can be used to create prostheses to fit patient and identify shape of teeth.

Question 6

What can stainless steel be used for?

Answer 6

Orthodontic appliances or denture base

Question 7

What is CoCr used for?

Answer 7

Partial denture

Question 8

What are mechanical properties?

Answer 8

Force applied to material

Question 9

What can forces applied to materials do?

Answer 9

Stretch/compress, deform or fracture

Question 10

How is force calculated? What is the units?

Answer 10

mass in kg x gravitational acceleration, units is N

Question 11

What are the different types of forces?

Answer 11

Compressive, tensile (stretch) and shear (pushing along contact area)

Question 12

How is stress calculated? What is the units?

Answer 12

Force / area, units is Pascals

Question 13

How is strain calculated?

Answer 13

change of length of material / original length of material for ratio, x100 for percentage

Question 14

On a stress strain curve, when is the material at maximum stress?

Answer 14

At maximum stress when stress and strain are proportional.

Question 15

On a stress strain curve, when will the material fracture?

Answer 15

After the proportional limit when the curve falls off.

Question 16

What is young’s modulus?

Answer 16

Stress/ strain, Measure of rigidity ( higher YM, more rigidity)

Question 17

When biting, which teeth is withstanding forces and which type?

Answer 17

Upper teeth- compressive force

Question 18

What is the typical biting force?

Answer 18

50-70 N

Question 19

When grinding/chewing, what type of force is applied and how?

Answer 19

Tooth slides along the surface of the other, frictional forces experienced

Question 20

Which has a greater YM, enamel or dentine?

Answer 20

Enamel

Question 21

What is the difference in cavity design between amalgam and composite?

Answer 21

Amalgam flares out from the tooth, requiring an undercut design whereas composite resin has a much smaller, minimal design

Question 22

Which material is held by mechanical retention and which material is bonded with adhesion?

Answer 22

Amalgam- mechanical retention
Composite- adhesion

Question 23

How should a material be transformed to fill a cavity?

Answer 23

Material must be pliable to fit shape of interest, and must set to form hard strong material

Question 24

What are some failure mechanisms that the likeliness needs to be assessed when working with dental materials?

Answer 24

Fracture, hardness, abrasion, abrasion resistance, fatigue, creep, deformation, de-bond and impact

Question 25

What is abrasion?

Answer 25

Tooth grinds/slides along the opposing tooth/material surface and the tooth/material surface is abraded, resulting in loss of surface layer and roughened surface

Question 26

What is fatigue?

Answer 26

Repeated loads applied causes small cracks in a material grow, allowing fracture when only a relatively small force is applied.

Question 27

What is creep?

Answer 27

Repetitive forces causes dimensional change

Question 28

If stress is over the elastic limit, what happens?

Answer 28

Permanent deformation

Question 29

What is debonding?

Answer 29

To apply shear stress, causing material to pull away from the tooth

Question 30

What is ductility?

Answer 30

Quality of being pliable and flexible.

Question 31

What is tear strength?

Answer 31

Material's ability to resist failure perpendicular to the stress being applied.

Question 32

What are the chemical properties you have to consider when choosing a dental material? 3

Answer 32

Setting mechanism, setting time and corrosive potential

Question 33

What are the physical properties you have to consider when choosing a dental material? 5

Answer 33

Viscosity, thermal conduction and expansion, density and radiodensity

Question 34

What do we have to consider in the oral environment when choosing a dental material? 4

Answer 34

Saliva, temperature variations, pH variations and oral bacteria