Composites Flashcards
Composite definition
Material with 2+ distinct, structurally complementary substances (metals, ceramics, glasses, polymers) combine to produce structural/functional properties not present in any individual component
Composite structures
MACRO composites
Separate materials bonded together
Ex: metal-ceramic restorations, veneers
Composite materials
MICRO composites
constituent added to material to enchance its properties
composite material fibers can be arranged…
aligned
random
Particulate fillers
widely used in polymer-ceramic composites
Resin-based composites
What are the constituents of dental resin composites? which are the main ones?
DIMETHACRYLATE RESIN INORGANIC FILLERS coupling agents polymerization inhibitors initiator/activator systems UV stabilizers
**if you increase the % of one of these, the composite increases the properties of that constituent
Dimethacrylate resins
vinyl polymer - addition polymerization
Set resin - rigid and tough
What are the most common monomers in dimethacrylate resins? what are they combined with?
Bowen’s resin - Bis-GMA
Urethane dimethacrylate - UDMA
These are combined with TEGDMA
What is the function of TEGDMA in dimethacrylate resins?
reduces viscosity of liquid resin before setting
Name the types of fillers used in resin composites
silica
barium glass
zirconia/silica
Inorganic/mineral/ceramic
functions of fillers in resin composites
Improve strength and wear resistance
Less shrinkage on setting
radiopacity
How much of resin composites do fillers make up? %
50-80%
What is the function of coupling agents in resin composites
Covalently link the polymeric resin (organic) to the ceramic fillers (inorganic)
Important: provide mechanical continuity
Transfer loads between fillers/resin without disruption of the material - strengthens interface
What kind of coupling agents are used in resin composites?
Silane compounds
Function of polymerization inhibitors in resin composites
Stability on storage
Function of initiator/activator systems in resin composites
Start polymerization of resin
Usually for visible light curing
What is the function of UV stabilizers in resin composites
Prevent yellowing in sunlight
What are the conditions for polymer reinforcement in resin compsites
- Adhesion between polymer and filler
- Filler should be more rigid than polymer (higher modulus of elasticity)
- Filler can act as load bearing component of composite
What are the effects of inorganic fillers (particulate) in resin composites?
improve compressive strength increase hardness less setting shrinkage lwoer coefficient of thermal expansion radiopacity esthetics
What are the two sizes of particulate fillers in resin composites
microcomposite
nanocomposite
Nanocomposite particulate fillers
Developed to improve polishing and wear characteristics of composite in relation to esthetics
Why are MCR/PFMs used in dentistry?
Get benefit of good mechanical properties of metallic metal & esthetics and wear performance of ceramics
= esthetic, strong, tough restoration
What are the 2 main concerns when using MCRs?
- color of alloy - esthetics
2. ceramic-alloy interface adhesion
What is the nature of ceramic-metallic bonding
micromechanical
chemical
micromechanical bonding in MCRs
Microabrasions on surface of alloy coping improves friction/retention of ceramic
Chemical bonding in MCRs
OXIDE LINKS
Oxides already present in ceramic can chemically bond to oxide in alloy at the high temps of firing the porcelain
How the esthetic concern of MCRs dealt with
DIFFERENT LAYERING OF CERAMIC
Layer adj to alloy - opaque to hide color of alloy
Top layers - tooth looking appearance
Veneer
Thin, semi translucent shell
Usually made from porcelain
Made to fit over existing tooth
Applications of veneers
Cosmetic alternative for conditions affecting anteriors:
- Closing space
- Chipped teeth
- Whitening
- Ortho concerns
Treating a tooth with a veneer is considered a ____ approach
conservative
Little/no tooth reduction
How are veneers bonded
Adhesive resin
PERMANENT - extremely strong and durable
Alone, veneers are very ____, but when bonded to enamel, the resulting structure is _____
brittle
strong, tough, durable (biomimetics)
