Lecture 3 Flashcards
What are composite resins cured by?
Visible light
Esthetic direct restorative
Composite resin
What is the primary benefit of composite resins?
Esthetics and ease of placement
- Easy to Place
- Excellent Clinical Outcomes
- Poor Esthetics
Amalgams
- Good Esthetics
- Excellent Clinical Outcomes
- More Difficult to Process
Ceramics
- Easy to place
- Moderate clinical outcomes
- Good esthetics
Composite
Hybrid Material of an organic phase (resin) and an Inorganic (filler) phase
Composite
Are teeth composites?
Yes
Are composites direct restoration?
Yes
Advantages of Both Organic and Inorganic
Components
Composites
Tend to be Tougher but not as Strong or Wear Resistant
Organic polymers
Tend to be Strong and Wear Resistant but Brittle
Inorganic Materials
Second Component of
the ‘Ease of Use’ in resin
Visible light curing
Allows for long working time in resins
Command set
What does curing develop?
Mechanical properties
One of the Most Important Processes in Dental
Polymers
Polymerization
Another name for polymerization
crosslinking
How do you change crosslink density?
Number of crosslinking groups and the degree of crosslinking
Another name for degree of crosslinking
Degree of curing
Types of curing
Mixing (chemical)
Heat
Light
- Operator Dependent – Working Time
- No Special Tools
- Chairside
Mixing (chemical) curing
- Consistent, High Degree of Cure
- Not good In Vivo
Heat curing
- Command Cure
- Good In Vivo
- Lower Degree of Cure – Limited Thickness
Light curing
- Resin System
- Filler
- Bonding Agent
- Visible Light Initiator
Components of composite resin
Most common resin system
BisGMA-TEGDMA
Stuctural component and diluent
Resin system
BisGMA-TEGDMA
- Activation of initiator molecule to generate free radical
- Initiation of monomer to generate a free-radical
- Propagation of Free-Radical with Four Monomers
- Termination of Free- Radical
Polymerization Process
Why type of bonds are polymer bonds?
Covalent
Do polymer bonds have a high of low molecular weight
High
Long molecules composed principally of nonmetallic
elements (organic chemistry C,O,N,H)
Polymer bonds
Entangled long chains
Polymers
Derive strength and properties from the entanglement
Polymer bonds
Allows for the relative ease of processing
Resin system
Unpolymerized resin …
Flows like honey
Provides the physical properties to resin systems
BisGMA
How is the viscosity in resin systems?
Very high and cannot be used alone
What is used with resin systems?
A reactive diluent (TEGDMA)
-30%-50%wt
More stain stiffness =
More viscosity
- Silica or Zirconia Based Inorganics
- 50-80 wt% of the Composite
- Has Surface Hydroxyl Groups
Filler
Types of fillers
- Micron (fine)
- Nano (microfine)
- Nano (microfine) in polymer matrix
Higher filler loading results in a
Higher modulus
- Teeth are Nanocomposites
- Smaller Fillers Should have Better Wear Properties
- Allows for betting Polishing and Finish
- Expectation of Better Mechanical Properties
Why smaller filler size
- Early Composites Had 20-30 µm Filler Particles
- Fine Fillers 3-0.5 µm
- Can be loaded at 77-88 wt percent in a Composite
Micron (fine) particles
- Typically 0.2-0.04 µm in Size
- Very High Surface Area
- Tendency to Aggregate
- Maximum Loading 38 wt%
Nano (microfine) filler
Filler with very high surface area
Nano (microfine) filler
Filler with tendency to aggregate
Nano (microfine) filler
-Microfine Fillers Polymerized in Matrix and Ground to 20-30 µm Particles
-Allows for Inorganic Loading up to
50-60 wt %
-Reduces Aggregation
-Poorer Filler to Matrix Bonding - No
Coupling Agent
Nano (microfine) in polymer matrix
Filler that reduces aggregation
NANO (MICROFINE) IN POLYMER MATRIX
Poorer filler to matrix bonding- no coupling agent
NANO (MICROFINE) IN POLYMER MATRIX
- Mixtures of Filler Sizes
- Can Take Advantage of Having Some Microfill
- Still have Loading of 70%
Hybrid composites
Perma flow is a
Flowble composite
Low viscosity composites have
better handling
- Low Viscosity – Better Handling
- Lower Filler Content
- Low Modulus
- Higher Shrinkage
- Cervical Abfraction Areas
Flowable composites
- Contains both 0.4 µm and 0.02-0.05 µm Fillers
- 78% Filled
- Nanofiller is Prepolymerized
Herculite Ultra- microhybrid (nanohybride)
Nanofiller is prepolymerized in
- Herculite ultra- microhybrid (nanohybrid)
- Filtrek Supreme (nanofill)
Prepolymerized Nanofiller
78% Filled
Filtrek supreme (nanofill)
Results from a Density Change of Monomer to Polymer
Polymerization shrinkage
Inherent Property of Double Bond Polymerization
Polymerization shrinkage
Has Less Molecular
Volume than the Sum
The Two Monomers
Methacrylate dimer
How is polymerization shrinkage measured?
Density change
Density change
Dilatometer
-Important for Direct Composite Restoratives
-Important for any Material that Required Dimensional
Stability
Polymerization shrinkage
What are the effects of polymerization shrinkage
- Stress on tooth structure
- Microleaks and lead to secondary carries
Has Both Hydrophobic and Hydrophilic Character
Adhesive layer
Water sorption mechanisms of degradation
- Hydrolysis of coupling agent
- Hydrolysis of TEGDMA
Most of the lab data is focused on
Mechanical properties
Components of biomechanical unit
- Restorative material
- Tooth structure
- Interface
- -stress transferred
Two component cement
Glass ionomer cement
Two components of glass ionomer
- Acidic polymer in aqueous solution
- Basic glass
What is glass-ionomer cement cured by
Acid-base reaction
What does glass ionomer cement release?
Fluoride
What does glass ionomer have good adhesion to?
Tooth structure
- Polyacid
- Basic Glass
- Water
- Modifiers (+) tartaric acid
Components of glass ionomer
-Aluminafluorosilicate Glass
-Components Sintered at 1100-1500 oC
-Molten Glass Poured on Metal Surface and
Cooled in Water ‘Shock Cooling’
-Ground into 45 µm particles
Basic glass
Reacts with basic glass
Poly Acid
Is all glass consumed in the setting reaction?
No
Form from the polyacid and glass
Salt bridges
Not a well characterized process
Setting reaction
- Cleans smear layer
- Leaves smear plugs
Condition dentin
Dissolves periphery of glass in glass ionomer reaction
Acid matrix
What ions does glass release
Ca2+, Al3+, F-
Quickly chelate with
acid polymer chain
Divalent Ca ions
- Al+3 replace Ca+2
- Increase strength
- F- released
24-72 hours into glass ionomer reaction
What do acid side groups chelate with?
Glass and HA
Attacks the surface of the glass. No coupling agent needed
Polyacid after glass ionomer setting
Released upon setting
Sodium and Flouride ions
Continue to be released over time
Na and F
Hybrid Between Glass Ionomer and Compostie
Resin
Resin modified glass ionomer
Has Both VLC and Acid-Base Curing
Mechanisms
Resin modified glass ionomers
What does resin modified glass ionomers increase
Physical properties
What does resin modified glass ionomers decreased
Initial solubility of GI in solution
Improved over glass ionomer but inferior to composit resin
Resin modified glass ionomer
Shows Initial Polymerization Shrinkage but
Expansion Upon Water Sorption
Resin modified glass ionomer
-Will Release Fluoride at Levels Similar to
Conventional Glass Ionomers
-Will Have Some Polymerization Shrinkage but
Offset by Swell
Physical properties of RMGI
