Dental Materials

Question 1

From what age should fissure sealants on the permanent molars be done on a patient at high risk of caries/predisposing factors/ortho appliances etc?

Answer 1

children from age 7

Question 2

What are 4 contraindications for placement of fissure sealants?

Answer 2

• adequate isolation cannot be achieved
• hypoplastic teeth
• proximal/occlusal decay is present
• uncooperative patients

Question 3

When should susceptible teeth be fissure sealed?

Answer 3

as soon as the occlusal surface is fully erupted into the mouth

Question 4

What are 5 ideal properties of fissure sealants?

Answer 4

• cariostatic action (fluoride release)
• resistant to oral fluid and diet
• low viscosity
• should be detectable
• non toxic

Question 5

What is the most common reason for sealant failure?

Answer 5

saliva contamination during placement

Question 6

What are 2 indications for sealant restorations (PRR)?

Answer 6

• caries confined to one part of fissure system
• cavitation has occurred (either micro cavity in enamel or cavity with dentine at base)

Question 7

What is the most commonly used dental composite?

Answer 7

BisGMA (bisphenol glycidyl methacrylate)

Question 8

Which composition of composite give it radio opacity?

Answer 8

glass particles

Question 9

What are 6 roles of fillers in composite materials?

Answer 9

• strength
• reduction in polymerisation shrinkage
• reduction in thermal expansion
• improved optical properties
• radio opacity
• reduced water absorption

Question 10

How much polymerisation shrinkage do you get for most composites?

Answer 10

2-3%

Question 11

What depth of composite is the maximum to be packed at a time?

Answer 11

2mm

Question 12

What is meant by C factor?

Answer 12

number of bonded surfaces / unbounded surfaces

Question 13

What are 4 clinical impacts of polymerisation shrinkage for direct restorations?

Answer 13

• loss of adaptation to cavity walls - micro leakage
• sensitivity
• restoration fracture
• caries

Question 14

What are 4 advantages of indirect composites?

Answer 14

• potential improvement of degree of cure
• potential improvement in mechanical/physical properties
• reduced impact of polymerisation shrinkage
• improved shape/finish

Question 15

Which phase of amalgam can be described as?
- most electropositive phase in amalgam
- most susceptible to corrosion
- weak and soft phase - reduces strength of amalgam
- causes static creep (gradual plastic deformation at loads well below the yield point)

Answer 15

gamma 2

Question 16

What is the function of copper in amalgam?

Answer 16

less than 6% = increased strength
more than 6% = excessive expansion

Question 17

What is the function of zinc in amalgam?

Answer 17

• prevents alloy becoming brittle
• at 1-2% scavenges contaminants
• increases toughness and ease of polishing

Question 18

Which 4 metals are constituents of dental amalgam?

Answer 18

• silver
• tin
• copper
• zinc

Question 19

What are 5 advantages of amalgam?

Answer 19

• good wear resistance
• antibacterial
• good compressive strength
• radio opaque
• chemical set

Question 20

What are 4 disadvantages of amalgam?

Answer 20

• non-adhesive
• weak in thin sections
• thermal conductor
• not tooth coloured

Question 21

What is the cavosurface angle for amalgam cavity preps?

Answer 21

90 degrees for retention and resistance

Question 22

Amalgam cavity preps need which minimum depth?

Answer 22

2mm

Question 23

What are 6 indications for the use of amalgam?

Answer 23

• class I and class II occlusal and proximal
• where heavy occlusal forces are encountered
• where aesthetics are not important
• building up broken down teeth prior to crowning
• where moisture control is limited
• high caries rate

Question 24

Which phase of amalgam can be described as the strongest phase due to presence of silver?

Answer 24

gamma 1

Question 25

What are 5 advantages of composite?

Answer 25

• tooth coloured
• no mercury
• adhesive
• command set
• conservative prep

Question 26

What are 4 disadvantages of composite?

Answer 26

• polymerisation shrinkage
• prone to chipping and fracture in bruxists
• margin leakage
• marginal discolouration

Question 27

What are 4 contraindications for the use of composite?

Answer 27

• poor moisture control
• habitual bruxism/chewing
• large cavities and reduced enamel
• deep sub gingival preparations and lack of enamel seal

Question 28

What are 3 factors affecting dentine bonding?

Answer 28

• dentine bonding is less effective in deeper dentine than superficial
• dentine permeability is more in coronal dentine than root dentine
• difference in the number/diameter/size of dentinal tubules in deep/superficial dentine

Question 29

What are 5 advantages of rubber dam?

Answer 29

• patient comfort
• prevents moisture contaminaion
• excludes salivary borne bacteria
• protection of patients airway
• retracts and controls soft tissues

Question 30

What are 4 disadvantages of using rubber dam?

Answer 30

• patient communication
• gingival discomfort
• colour matching and occlusal checking
• latex allergies

Question 31

What are 6 advantages of GI?

Answer 31

• direct bond to tooth - no bonding agent required
• bonds to moist tooth
• fluoride release = caries prevention
• excellent marginal seal - controlled shrinkage
• thermal expansion
• biocompatible

Question 32

What are uses for GI?

Answer 32

• cement
• restoration: atraumatic restoration technique, primary teeth
• lining: good sealing, good pulp response

Question 33

What are 4 disadvantages of GI?

Answer 33

• prolonged water sensitivity
• low strength
• low bond strength
• limited aesthetics

Question 34

What are 4 advantages of resin modified GI?

Answer 34

• less moisture sensitive
• improved aesthetics
• self adhesive
• fluoride release (temporary)

Question 35

What are disadvantages of resin modified GI?

Answer 35

• limited working time
• reduced biocompatibility
• increased setting shrinkage
• reducing sealing
• expansion up to 8%