dental materials

Question 1

All porcelain is ceramic but not all ceramic is porcelain.

1. What are the two main differences in composition between decorative and dental ceramic.
   (2 marks)

Answer 1

composition = decorative ceramics contain kaolin = clay
dental ceramics need to be translucent so kaolin is removed and feldspar and silica replace it
dental ceramic contains up to 15% glass

processing = dental ceramics undergoes sintering or CAD/CAM milling to achieve strength and fit

Question 2

Ceramics are the most aesthetic materials used in dentistry.
2. Explain what the following terms mean with regard to optical properties of the materials.

i) Translucency
(2 marks)
ii) Opalescence
(2 marks)

Answer 2

i) translucency = allows light to pass through it partially

ii) opalescence = material exhibits a play of colours, typical milky or iridscent appearance

Question 3

Silane coupling agents are used when bonding composite to most ceramic surfaces.

3. How can you modify the ceramic surface to make it more retentive prior to using silane?
   (1 mark)

Answer 3

By etching the ceramic surface with hydrofluoric acid (HF) to create a microscopically rough surface which enhances mechanical interlocking between the ceramic and bonding agent

Question 4

4. Chemically how does a silane coupling agent work when bonding composite to ceramic?
   (2 marks)

Answer 4

hydrolysis
condensation
adhesion

Question 5

Silane coupling agents are a component part of composite resin materials

5. What is the function of silane in a composite restorative material? (1 mark)

Answer 5

improve bond strength between the filler particles and the resin matrix

Question 6

8.) a.) How is porcelain surface prepped in lab for bonding (1)

Answer 6

by etching with hydrofluoric acid (HF)

Question 7

b.) What do you use to bond porcelain to composite luting resin (1)

Answer 7

silane coupling agent

Question 8

c.) How does silane coupling agent act chemically (2)

Answer 8

hydrolysis
condensation

Question 9

d.) When would you use a dual cured (1)
e.) Why would you still light cure a dual cured (1)

Answer 9

d) best to use in areas where light curing might be hard to achieve, such as deep and inaccessible areas within the mouth

e) it’s still necessary to light cure to ensure complete polymerisation
it can speed up setting process

Question 10

g.) What would you do to metal in a lab to prepare (1)
h.) What chemical agent to bond metal (1)
i.) What metal can be used for an acid-etch retained bridge (1)

Answer 10

g) is prepared by sandblasting or airborne particle abrasion to create roughened surface

h) s a metal primer, which typically contains a combination of agents such as MDP

i) cobalt-chromium alloy

Question 11

a) Components of Stainless Steel and Percentage?

Answer 11

Iron - 72%
Chromium - 18%
Nickel - 8%
Titanium - 1.3%
Carbon - 0.7%

Question 12

b) Describe work hardening?

Answer 12

Work done on a metal at low temperature which causes slip, which is where dislocations collect at grain boundaries, thus resulting in a stronger harder material.

Question 13

c) What is meant by springiness?

Answer 13

Ability of a material to undergo large deflections
Can undergo large deflections without permanent deformation

Question 14

d) name 2 disadvantages of self cure PMMA

Answer 14

Poor Mechanical Properties - poor compressive strength, poor tensile strength
Residual monomer (Allergy)

Question 15

a) How would you determine if this impression is usable? (3 marks)

Answer 15

No air blows present on the impression the preparation.
Ensure impression is not separated from the impression tray.
Ensure all soft tissue anatomy for example gingival margin should be recorded.

Question 16

b) List 4 potential faults with the impression (4 marks)

Answer 16

Voids
Airblows
Dragging due to removal prior to material set
Tear upon removal
Wrong or no adhesive applied to the impression trays prior to loading of
impression material.
? Hydrophobic impression used when haemostasis or moisture control is poor.
Retraction cord or paste not used to retract soft tissue.
Wrong ratio of base paste and catalyst paste.
Impression material used is expired.

Question 17

c) How would you decontaminate the impression (3 marks)

Answer 17

Rinse impression under cold running water prior to putting into the perform to
remove gross debris and saliva.
Inspect impression prior to disinfection.
Disinfect in perform for at least 10 minutes.
Perform consists of sodium benzoate or potassium peroxomonosulphate.
Take it out and rinse under cold water, wrap in damp gauze and put it in a
polyester bag with patient’s demographic and send it to relevant laboratory