Composite Resin Part 3 Flashcards
What are clinical requirements of composite?
- Large posterior cavity
- high strength, high YM, high abrasion resistance - Deciduous (large pulp)
- strong in thin section
- wear = wear of tooth (not amalgam)
- other properties more important - bonding, micro leakage
Compare pros/cons of conventional vs microfine vs hybrid composite resins
- Conventional:
- strong but problems with finishing and staining due to soft resins and hard particles - Microfine:
- smaller particles - smoother surface better aesthetics for longer period
- inferior mechanical properties (elastic limit and Young’s modulus) - Hybrid:
- improved filler loading and coupling agents have led to improvement in mechanical properties
(Originally compromise between conventional and microfine)
What is the definition of ‘hardness’
The measure of how resistant a material surface is to indentation
What is the definition of abrasion (wear)?
Removal of surface layers when two surfaces make frictional contact
How is hardness tested?
Known weight is placed on top of indentor which is used to make a notch on the material being measured.
Smaller notch = greater hardness
What is the main consequence of abrasion?
Increase in roughness
What 3 factors can be influenced by surface roughness?
- Appearance
- Plaque retention
- Sensation when in contact with tongue
What diameter of filler particles will have greatly increased roughness due to wear of the material?
> 80 micrometers
What material factors affect wear in direct filling materials?
- Filler material
- Particle size distribution
- Filler loading
- Resin formulation
- Coupling agent
What clinical factors affect wear in direct filling materials?
- Cavity size and design
- Tooth position
- Occlusion
- Placement technique
- Cure efficiency
- Finishing methods
What % of phosphoric acid is used for etching?
30%
What is the typical bond strength of composite to enamel or dentine?
40MPa
What are the advantages of a good bond to tooth surfaces?
- Reduce microleakage
- Counteract polymerisation shrinkage
(Reduces likely hood of gap between restoration and tooth) - Stress transfer
- stress transferred to tooth and bone
How does poor tooth bonding affect stress?
Concentrated stress at the interface so failure more likely
What is the compressive strength, rigidity, tensile strength and hardness of hybrid composite?
Compressive strength =300MPa
Rigidity = 14GPa
Tensile strength = 50MPa
Hardness = 90 Vickers Hardness Units
