Class III restoration

Question 1

What is a class III?

Answer 1

Interproximal lesion on anterior teeth

Question 2

What does placing a floss ligature enable?

Answer 2

Retracts the gingivae and inverts the margins of the dam = improved isolation

Question 3

Where may caries initiate if oral hygiene practices are not practiced?

Answer 3

The natural stagnation area (just below the contact point)

Question 4

Where is a class III cavity placed?

Answer 4

Just below contact point, in the middle third of this tooth surface inciso-gingivally and and labio-palatally

Question 5

When should the composite shade be selected?

Answer 5

Immediately before the tooth has had a chance to dry out under the rubber dam (tooth begins to lighten as it dries)

Question 6

What is the air turbine hand piece used for?

Answer 6

To gain access to caries and bevel margins

Question 7

What is the slow speed contra angled hand piece used for?

Answer 7

To remove caries and prepare mechanical retention if required

Question 8

How should you approach a tooth for cutting this cavity if the cavity is on the mesial surface?

Answer 8

From the distal

Question 9

What is the problem with approaching fat right angles to the palatal surface?

Answer 9

Unnecessary removal of enamel fro marginal ridge

Question 10

What may happen if composite is placed in areas where the incisal edges of the opposing dentition contact the opposing marginal ridge?

Answer 10

Wear

Question 11

How much of the marginal ridge should be removed?

Answer 11

Half of the width

Question 12

What should you use to remove caries from areas where the cavity depth is deep and approaching the pulp?

Answer 12

Excavators

Question 13

How do we gain retention in a class III cavity?

Answer 13

• Acid etching the names
• Use total etch technique = allows bonding to dentine and enamel
• Bevelling of enamel margins (produce a larger surface area)
• Preparing retention grooves (rosehead) -> only consider for larger cavity sizes as most small and medium sized cavities will be naturally undercut due to caries removal

Question 14

What are the advantage of bevelled enamel margins?

Answer 14

• Provides a larger surface area for bonding
• Reduces the amount of micro-leakage
• Cross cuts the prisms and gives a better etch pattern
• Blends the composite into the surrounding tooth surface

Question 15

What are the disadvantages of bevelled enamel margins?

Answer 15

• Damage to adjacent teeth
• Lacerate gingivae (bleeding contaminate restorative material) and rubber dam
• Increase in subsequent cavity size

Question 16

When is bevelling recommended clinically?

Answer 16

Only consider bevelling where the labial margin of the cavity is visible and damage to adjacent tooth and supporting structures is minimal

Question 17

Which materials can we line the cavity with?

Answer 17

• Light cured GIC
• Setting calcium hydroxide cement
• Total etch and adhesive hydrophilic bonding resin alone (does’t have visible barrier to see where restoration ends -> used in shallow/moderate depth cavities in the hope it won’t hydrolyse with time)

Question 18

Which etch is used?

Answer 18

36% buffered phosphoric acid gel

Question 19

What is the solvent of the bonding resin?

Answer 19

Acetone

Question 20

How long should bonding resin be left to allow penetration into the etched pores of enamel and the porosity of the lining material?

Answer 20

30 seconds