Composite Resin types and properties Flashcards
Identify classification of Composite Resin
- Macrofilled (not used much anymore): large particles hard to polish, resin matrix wears faster than the filler particles producing a rough surface, susceptible to discoloration and extrinsic staining.
- CR is classified as; microfilled or hybrid
Describe microfilled CR
- Has prepolymerised silicon dioxide filler particles
- Poorer physical properties due to lower filler volume, less wear resistant because more resin than filler particles, thus not suitable for restorations on occlusal loading
- High volume of resin, higher polymerization shrinkage
- Has a smooth polished surface
- Used for the restoration of anterior teeth, high polish and excellent enamel-like transluency, not suitable for occlusal loading
- Inferior to hybrid composites due to lower percentage of filler content, higher coefficient of thermal expansion, lower fracture toughness, lower modulus of elasticity
Describe hybrid CR
- Contain a heterogeneous aggregate of filler particles
- High polishability when compared with macrofilled composites
- But problem of inability to maintain their gloss
List the 4 different types of Composite Resin
Microhybrid Composite Resins
Nanofilled Composite Resins
Nanohybrid Composite Resins
Bulk fill composites
Describe microhybrid Composite Resins
- Stronger than microfilled
- Can be used in both anterior and posterior teeth
- Most have medium viscosity
Other types can be classified as:
High-viscosity packable Composites
• Filler particles - 80% in volume
• Indicated for the re-establishment of the contour and proximal contacts in Class II
• Due to its high viscosity, subject to layering problem, one increment may not completely join into another leaving gaps and porosities
Low-viscosity: Flowable Composites
• Filler particles - 50% in volume
• Inferior mechanical properties
• Greater degree of polymerisation shrinkage
Describe nanofilled Composite Resins
- Consist of nanomers and ‘nanoclusters’ as the fillers
- Nanoclusters are clusters of primary zirconia/silica nanoparticles fused together at points of contact, and the resulting porous structure is infiltrated with silane
Describe nanohybrid Composite Resins
- Nano-sized particles in CR formulation
- Composites present similar mechanical and physical properties to those of microhybrid
- Better polish and gloss retention than microhybrid
Describe bulk fill composites
- Developed to speed up placement process
- Can place one large increment and cure
- Depth of cure is 4mm or more (light can reach that deep)
- To achieve this, manufacturers have increased the translucency or reduced the amount of filler or change the chemical make up
- Has limitations on proximal box of Class II cavities: more than one increment should be used in proximal box
- Polymerisation shrinkage has been reduced by adding special modifiers
- Shrinkage about 1.3% to 2.4%
- May need to be covered by a nanocomposite to achieve aesthetics and wear resistance
- Shades are limited
List the physical and mechanical properties of composite Resin
Biocompatibility
Strength
Wear
Polymerisation shrinkage
Degree of conversion
Thermal conductivity
Coefficient of thermal expansion
Water sorption
Elastic modulus
Radiopacity
Describe the biocompatibility of CR
- Newly placed composite can release chemicals. This can diffuse through dentinal tubules into pulp causing an inflammatory reaction
- Unbound monomers can be dissolved out by water or solvents in the diet, degrading overtime
- Bisphenol A, a polymer in some composites and fissure sealants, may induce cellular changes
- By product of polymerisation may cause soft tissue reaction resemble lichen planus – lichenoid reactions
Describe the strength of CR
- Most composites commonly used today are similar in compressive strength
- Not as strong as amalgam, but stronger than GIC
- Microfilled composites are weaker than hybrid and nanocomposites
Describe the wear of CR
- Wears faster than amalgam, new generation composites more wear resistance than early composites
- Microfilled and flowable wear faster than more heavily filled composites
- Bruxers wear down composites at a much faster rate
Describe the polymerisation shrinkage of CR
- Occurs when composite is cured
- Shrinkage stresses the bonds, pulling away from the opposing walls
- Causes microleakage, staining, recurrent caries, tooth sensitivity
To reduce shrinkage:
• Use composite with higher filler content by volume
• Use pre-polymerised filler, such as microfilled and nanofilled – shrink less as a portion of the volume has been pre-polymerised
• Using small incremental layers and oblique layering
• Using less shrinkage monomers, eg Silorane, N’Durance
• Use GIC to replace loss dentine – reduce volume of composite used
Describe the thermal conductivity of CR
• Composites transmit hot and cold temperatures much like tooth structure, but much lower than metal, such as amalgam and gold
Describe the coefficient of thermal expansion of CR
- The CTE of composite is greater than the tooth structure
- Result in debonding and leakage
- The greater the filler content, the lower the CTE
- Microfilled and flowables have higher CTE because of higher resin
