Composite Resin and Class I cavity

Question 1

List the different components in Composite Resin

6

Answer 1

• Inorganic fillers
• Organic resin matrix
• Coupling Agent
• Stabilisers and inhibitors
• Initiators and activators
• Pigments

Question 2

Discuss the purpose of “inorganic fillers” as a component of Composite Resin

Answer 2

Fillers are added for; radiopacity, strength and reduce polymerisation shrinkage

Question 3

List the types of “inorganic fillers” in Composite Resin

Answer 3

• Barium
• Strontium
• Zinc
• Silica
• Quartz
• Zirconia
• Lithium- aluminium containing silicate glass

Question 4

Describe “inorganic fillers”

Answer 4

• Filler size: determines smoothness. Larger= rough, smaller= smoother
• Volume: As filler content increases, resin content decreases
• Distribution: smaller filler particles fill spaces between larger particles

Question 5

Discuss “organic resin matrix” as a component of Composite Resin

Answer 5

• Resin is Bis-GMA or UDMA
• They are highly viscous and they polymerise and thus shrink
* Dilutant monomers like TEGDMA or HEMA is added to reduce this viscosity

Question 6

Discuss “coupling agents” as a component of Composite Resin

Answer 6

• Coupling agents help chemically bond filler particles with resin
• Silane is an organic silicane compound used
• CA’s inhibits leaching by preventing water penetration along the resin-filler interface
Silane also acts as a stress absorber; stresses are transferred from resin to filler particles

Question 7

Discuss “stabilisers and inhibitors” as a component of Composite Resin

Answer 7

• Prevent premature polymer formation due to heat and light
• Extends shelf life and working time
* Hydroquinone is the most common inhibitor

Question 8

Discuss “initiators and accelerators” as a component of Composite Resin

Answer 8

• Composites can be self-cured, light cured or dual cured

• Camphorquinone is added as an initiator (absorbs radiant energy)
• Organic amine is added as an accelerator (causes resin to polymerize)

Question 9

Discuss “pigments” as a component of Composite Resin

Answer 9

• Titanium dioxide and Aluminium oxide help with shading and opacity
* UV absorbers added to minimise colour changes caused by oxidation

Question 10

Explain the bonding mechanism of Composite Resin

Answer 10

• The bonding to enamel is entirely micromechanical achieved through acid etching of enamel
• Bonding may be conducted by using GI as a lining or base
• Dentine condition, apply GI
• Etch enamel and GI
• Apply bonding agent on GI and enamel
• Apply composite

Question 11

What are the benefits of acid etching?

Answer 11

• Cleans smear layer
• Increases surface area for bonding
• Lessens need for mechanical retention/ under cuts and thus preserves sound tooth structure

Question 12

Why is GI used as a lining or base in composite bonding?

Answer 12

The reason why GI is used as a base/ lining under composite is because it is much less prone to polymerisation shrinkage than composite and it bonds quite well to the floor

Question 13

Why does polymerisation shrinkage occur?

Answer 13

When the resin matrix is cured, it shrinks away from the cavity wall which placed stress in the walls and enamel

Question 14

What are the negative effects of polymerisation shrinkage?

Answer 14

• Marginal stains 
• Microleakage
• Debonding
• Secondary caries
* Sensitivity

Question 15

How is polymerisation shrinkage reduced?

Answer 15

• Using a GI base reduces the volume of composite required
• Adding the composite in 2 mm increments and polymerising each increment reduces the net effect of polymerisation
• A less amount of CR shrinks before the next one is applied = less stress
* The oblique layering technique also ensures less stresses are placed on surrounding enamel

Question 16

What is the pre-procedure in preparing a Class 1 cavity?

Answer 16

• A radiograph is taken to ensure a thorough diagnosis is made
• Assess occlusal relationships
• Restorative materials are chosen based on suitability
• Consent is taken
• Local anaesthetic applied and shade selection is made
• Rubber dam isolation
* Instruments are selected; high speed flat fissure, slow speed and spoon excavators for caries removal, flat plastic, dycal applicator

Question 17

What is the clincal procedure in preparing a Class 1 cavity?

Answer 17

• Dentine is treated with Dentine conditioner
• Mix the GI lining; power and liquid (vitrebond or fuji bond LC)
• Glass Ionomer lining is applied with ball applicator on pulpal floor ONLY. Light cure for 20 seconds
• Etch with 37% Orthophosphoric acid for 15 seconds on enamel and base. Wait for the frosty appearance on enamel
• Apply thin layer of bonding resin to all of the etched area. Wait for 15 seconds and dry it. Light cure for 20 seconds
• Apply composite resin
* CR is light cured for 40 seconds

Question 18

Examine each step of performing a Class I using cavity preparation principles

Answer 18

Outline form:
• Access direct to location of caries then extend to include pits and fissure system
• Extend outline to remove all diseased tissue
• Ensure bur is vertical to avoid undercutting
• The outline is conservative; try to preserve oblique ridge in upper molars for example
• The DEJ is reached
• Do not over extended or else occlusal bearing will become an issue

Removal of carious dentine:
• Slow speed or spoon excavator used to remove carious dentine
• Only remove infected dentine, not affected dentine
• Be aware of iatrogenic damage to pulp

Assess cavity:
• Resistance form; how well it withstands forces. Have smooth floors, defined line angles, with good depth 2.5- 3.0 mm
• Retention form; achieved with micromechanical bonding. No bevel and undercuts are required

Question 19

Discuss procedures in layering of composite restoration in Class I (process)

Answer 19

• An oblique layering technique should be used
  • Only one wall should be touched with the composite
  • It is built from the pulpal floor towards the cavo surface angle
  • Each increment should be cured for 40 seconds
  • There are 2 increments used in oblique layering
  • Ensure the instrument used is clean or else it will affect the integrity of resin
  • The third increment is for creating anatomy of the occlusal surface

Question 20

Discuss procedures in layering of composite restoration in Class I (the look of it)

Answer 20

When placing composite, do a shallow occlusal anatomy with minimal excess beyond cavosurface margin.
This will reduce the chances of needing to polish and thus reduces the chances of losing enamel to polishing