2/8: Composite Resins Flashcards
When was Silicate cement used?
1870s
What is silicate cement?
- high solubility
- severe surface wear
- low mechanical properties
When was polymethylmethacrylate (PMMA) used?
1940s
What is polymethylmethacrylate?
- initially unfilled: high curing shrinkage
-high thermal expansion and contraction - stress at the cavity margins (marginal leakage)
-Later, filler added (without coupling agent-no
bonded) = poor wear resistance and staining.
When was composite resin used?
1960s
What is composite resin?
- BisGMA
- fillers bonded (silane coupling agent)
*Improved properties: - low thermal coefficient of
expansion and dimensional change
on setting - higher wear resistance
- improved clinical performance
What is the definition of composite?
material containing at least two components (phases) with distinct chemical and physical properties that after blended, they show unique and superior properties as compared to the individual
components.
What are examples of composite?
Concrete: cement + gravel
Dentin: collagen matrix + hydroxyapatite crystals
Dental composites: Resin + Filler particles
What are tooth colored restorative materials?
composite resin, resin composite, composite
What is the resin matrix reinforced by?
dispersed filler particle phase bound to the resin by a silane coupling agent and an initiator-accelerator system
What are uses of composites?
- Tooth-colored restorative material (direct or indirect rest. technique)
- Bonding agents (filler may be present)
- Sealants (filled)
- Composite resin luting agents (cement)
- Resin-modified glass ionomer material
- Light-activated liner materials
- CAD/CAM blocks
- Resin endodontic sealers, etc.
How is dental composite packaged?
To protect against visible light (opaque) and moisture
* Plastic syringes
* Unit-dose capsules
* Dual paste syringes (dual curing – core build-ups)
What are components of composite?
- Resin matrix
- Filler particles
- Coupling agent
- Activator-initiator system
- Pigments and other components
What 3 things make up the resin matrix?
Bis-GMA
UDMA
TEGDMA
What are the filler particles of composite?
Crystalline silica (quartz), Ba, Li, Al silicate glass, amorphous silica
Where are filler particles disbursed and what does the distribution vary depending on?
- dispersed in resin matrix
- varies dependent on material (filler loading %, expressed by weight or volume & filler size/combination)
What are the benefits of filler particles?
Reinforcement of resin matrix
* Increase the mechanical and physical prop. (hardness,
strength, elastic modulus, and wear resistance)
DECREASED polymerization shrinkage
-The reduced shrinkage is proportional to the filler vollume
DECREASED thermal expansion and
contraction
* Higher filler amount reduces the thermal expansion
and contraction coefficients
Viscosity control
* Improved workability, handling
DECREASED water sorption
* Decreases the water sorption
INCREASED radiopacity
* Barium, Strontium, Zirconium
What does silane act as?
Interfacial bridge (strongly binds the filler to the resin matrix)
What are the benefits of silane as a coupling agent?
- Better stress distribution
between resin matrix and
filler particles - Improves the mechanical
properties - Decreased water sorption
along filler-resin interface
Describe composites as chemicals
Monomers to be converted into polymers
What is the process of activating and initiating triggered by?
Free radicals (Chemical activation, heat or light)
What is the activator and initiator of chemical or self-curing composite?
What is the activator and initiator of light-cured composite?
What do polymerization inhibitors prevent?
Spontaneous polymerization
What do polymerization inhibitors stop?
Polymerization from brief room light exposure (reacts with free radicals)
What happens once the blue light is used on composite?
All inhibitor quickly consumed = polymerization chain reaction starts
What chemicals increase the shelf-life of composite resins?
Butylated hydroxytoluene (BHT)
- food preservative, reduce oxidation
Hydroquinone
What are pigments of optical modifiers?
Metal oxides
What are opacifiers?
➢ Titanium and aluminum oxide
➢ Control opacity or translucency (enamel vs. dentin)
➢ Brand differences
What are the different classifications of composites?
✓ Filler particle size and size distribution
✓ Handling characteristics
✓ Type of polymerization
How can you classify composite by filler size and distribution?
- Macrofill
- Midifill
- Microfill
- Hybrids
a. Midi-Micro Hybrid (Midi- or Microhybrid)
b. Mini-Micro Hybrid (Microhybrid)
c. Mini-Nano Hybrid (Nanohybrid)
What kind of classification is not used much today?
Macrofill and midfill composites