DENTAL MATERIAL

Question 1

a. Define the Proportional limit of a material (1)

Answer 1

Proportional limit
 Stress above which proportionality between the applied stress and the resulting strain in a body

would no longer be observed.
 The limit at which stress after this limit would result in distortion

Question 2

a. Complete the table below about alginate as an impression material (5)

Answer 2

Question 3

3. Evaporation, imbibition and syneresis of alginate. List the causes, consequences and prevention. (Formative, 2016)

Answer 3

Question 4

4. What does glass transition temperature means? How would that affect a heat cures acrylic denture being thrown into boiling water?

Answer 4

 The temperature where amorphous polymers transit from a hard and brittle state into a molten rubbery state

 Its change contribute dimensional stability of the acrylic?

Question 5

5. Brief description for impression compound. (2 marks)

Answer 5

 Made of resin (e.g. wax), filler, lubricants

 A thermoplastic materials which soften at 60 degree water bath for 5 mins (prolonged soaking cause constituents leaching out altering the properties)

 Functions are modifying impression tray, impression for edentulous dentition, record palatal prior to alginate impression)

 Reusable, but poor surface detail, poor dimension stability and can’t used in undercut

Question 6

Perio Given I/O photos of upper occlusal, lower occlusal and frontal view. 22 pontic, 23 abutment.
Upper missing 16 or 18?
And missing 26. Lower missing 35-38, 45-48.

Spacing for lower incisors and gingival recession

a. What is the setting contraction of polysulphide during the initial 24 hours (1)

Answer 6

(BDS III CPA Past Paper Collections (2005-2014))

 0.3 - 0.4% over first 24 hours

Question 7

Perio Given I/O photos of upper occlusal, lower occlusal and frontal view. 22 pontic, 23 abutment.
Upper missing 16 or 18?
And missing 26. Lower missing 35-38, 45-48.

Spacing for lower incisors and gingival recession

b. Arrange by dimensional stability: Polysulphide, polyether, Additional silicone, hydrocolloids (1)

Answer 7

 Additional silicone > polyether > polysulphide > condensation silicone > hydrocolloid

Question 8

7. What is modulus of elasticity and proportional limit? (2)

Answer 8

 A number that measure an object’s resistance to being deformed elastically when force applied to it

 Point up to which stress remain directly proportional to strain, object can regain its original shape if stress is removed before this, while permanent deformation occur beyond this point