Composite Resin and Class I cavity Flashcards
List the different components in Composite Resin
6
- Inorganic fillers
- Organic resin matrix
- Coupling Agent
- Stabilisers and inhibitors
- Initiators and activators
- Pigments
Discuss the purpose of “inorganic fillers” as a component of Composite Resin
Fillers are added for; radiopacity, strength and reduce polymerisation shrinkage
List the types of “inorganic fillers” in Composite Resin
- Barium
- Strontium
- Zinc
- Silica
- Quartz
- Zirconia
- Lithium- aluminium containing silicate glass
Describe “inorganic fillers”
- 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
Discuss “organic resin matrix” as a component of Composite Resin
• 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
Discuss “coupling agents” as a component of Composite Resin
• 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
Discuss “stabilisers and inhibitors” as a component of Composite Resin
• Prevent premature polymer formation due to heat and light
• Extends shelf life and working time
* Hydroquinone is the most common inhibitor
Discuss “initiators and accelerators” as a component of Composite Resin
• 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)
Discuss “pigments” as a component of Composite Resin
• Titanium dioxide and Aluminium oxide help with shading and opacity
* UV absorbers added to minimise colour changes caused by oxidation
Explain the bonding mechanism of Composite Resin
- 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
What are the benefits of acid etching?
- Cleans smear layer
- Increases surface area for bonding
- Lessens need for mechanical retention/ under cuts and thus preserves sound tooth structure
Why is GI used as a lining or base in composite bonding?
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
Why does polymerisation shrinkage occur?
When the resin matrix is cured, it shrinks away from the cavity wall which placed stress in the walls and enamel
What are the negative effects of polymerisation shrinkage?
• Marginal stains • Microleakage • Debonding • Secondary caries * Sensitivity
How is polymerisation shrinkage reduced?
• 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
What is the pre-procedure in preparing a Class 1 cavity?
• 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
What is the clincal procedure in preparing a Class 1 cavity?
• 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
Examine each step of performing a Class I using cavity preparation principles
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
Discuss procedures in layering of composite restoration in Class I (process)
- 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
Discuss procedures in layering of composite restoration in Class I (the look of it)
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
