Composite Flashcards
Accelerator
Substance that facilitates decomposition of an initiator.
Initiator
Substance capable of decomposing into free radicals that initiate polymerization.
Rheology
Science of the deformation and flow of matter.
Addition Polymerization
polymerization process involving free radicals in which no by-product is formed as the chain grows.
Condensation Polymerization:
polymerization process in which a by-product, such as water or alcohol, is formed as the chain grows.
Copolymer
polymer consisting of two or more different types of monomers (mers) or units joined together.
Crazing
Minute surface cracks on polymers; precursors to crack growth and subsequent failure of the material.
Cross-linking agent
monomer having two or more groups per molecule capable of polymerization (for example, a dimethacrylate). When polymerized, each active group is capable of incorporation in a growing polymer chain, causing either a loop in the chain or a cross-link between two chains.
Degree of Conversion or Polymerization
percentage change in the number of methacrylate (C=C) groups which have polymerized and converted into units (-C-C-) of the polymer system. The total number of mers in one polymer molecule.
Glass-Transition Temperature (Tg)
(softening temperature) The temperature at which the polymer ceases to be a glass (ie, fractures in a brittle manner) and becomes a rubber or leather (ie, tends to permanently deform under a load too small to cause fracture).
Glassy polymer:
amorphous polymer (those with irregular molecular arrangements, i.e. non-crystalline molecular arrangements) that behaves as a brittle solid.
Molecular weight:
sum of the molecular weights of the mers (monomers) of which the polymer is made.
Oligomer
polymer made up of two, three, or four monomer units.
Polymer
molecule made up of thousands or millions of repeating units. Polymers may be linear, branched, or cross-linked.
Polymerization
process by which monomers unite to form a polymer.
Thermoplastic
polymer that softens upon heating and rehardens upon cooling
Thermoset
polymer that is not able to undergo softening upon heating.
Free Radical
Free radicals are compounds with a free electron.
Monomer
molecule that can be bonded to other identical molecules to form a polymer.
Characteristics of THERMOPLASTIC Polymers:
o 1) Linear or branched polymers o 2) Weak bonds break with heat o 3) Bonds reform on cooling o 4) Can be molded with heat 6,6 Nylon
Characteristics of THERMOSET Polymers:
o 1) Crosslinking between chains o 2) Strong covalent bonds o 3) One big macromolecule o 4) Cannot be softened by heat PMMA, BisGMA/TEGDMA
The chemical stages of polymerization are:
o 1) Initiation by activation of monomer
o 2) Propagation by chain growth
o 3)Termination by reaction completion
The polymerization of polymethylmethacrylate (PMMA) is
ADDITION polymerization (Free radical initiation); No by-product formed. o Free radical à acting on C double bonds o We see shrinkage
Free radical polymerization can be initiated by:
o 1) Heat (thermal decomposition of an initiator like BPO)
o 2) Light energy (Visible light energy absorbed by CQ and accelerated by an amine)
o 3) Chemical [chemical reaction between an initiator (BPO) and chemical accelerator (an amine)
BPO (for the purposes of polymerization of dental polymers) is initiated (decomposed) by two methods:
o 1) Heat (i.e., polymerization of PMMA dentures)
o 2) Chemical (co-initiated/ accelerated by a tertiary amine)
The Polymethylmethacrylate (PMMA) polymer system has several intended uses in dentistry:
o 1) Denture base polymer
o 2) A resin material for temporary crowns and bridges
o 3) Orthodontic resin or resin for night guards
o 4) A repair material for items 1-3
The Polymethylmethacrylate (PMMA) polymer system involves two components:
o 1) PMMA Powder (in the form of microscopic polymer beads) + Initiator- small amount of benzoyl peroxide - responsible for starting the polymerization process initiator
o 2) Methyl methacrylate monomer liquid + Inhibitor- small amounts of hydroquinone (inhibitor) - prevents undesirable polymerization during storage.
In pmma what can be added to the monomer liquid
▪ A cross-linking monomer (glycol dimethacrylate) at low levels (1-2%) can also be added to the monomer liquid
What is the purpose of the inhibitor (hydroquinone) in mma monomer liquid
prevents undesirable polymerization during storage.
Components of a PMMA Polymer Product:
POLYMER: powder/ MONOMER:liquid
EXAMPLE: Heat activated denture base resins
Composition of pmma
Powder
- Prepolymerized spheres of PMMA
- Initiator- small amount of benzoyl peroxide
- responsible for starting the polymerization process initiator
Liquid
- Methyl Methacrylate
- Inhibitor- small amounts of hydroquinone(-inhibitor)
inhibitor - prevents undesirable polymerization during storage
- Cross linking agent - glycol dimethacrylate.... 1-2%
Surface chemistry of PMMA/MMA polymerization:
o Monomer is rapidly ab- and adsorbed by the PMMA polymer beads, causing swelling of the PMMA polymer bead with monomer
o Monomer polymerizes linking PMMA beads together in rigid polymer
Increased crosslink of polymer systems can cause an increase in the following parameters:
o STRENGTH, HARDNESS, BRITTLENESS, STIFFNESS, CREEP RESISTANCE
Polymer resin systems for composite resins include
Bis-GMA: bisphenol A-glycidyl methacrylate; UDMA: urethane dimethacrylate; TEGMA: triethylene glycol methacrylate (diluent to decrease viscosity).
What can be used for reduced polymerization shrinkage compared to PMMA polymer.
Higher molecular weight oligiomers
How do Oligomers like Bis-GMA compare to mma
still flexible but stiffer than MMA.
Viscosity higher to permits better handling than PMMA/MMA.
Chemical Initiated Polymerization (i.e., BPO/Amine) also is referred to by other names:
o Autopolymerizing
o Cold-curing
o Self-curing
How do physical properties change with molecular weight
the physical properties increase as the molecular weight increases up to a level when there are approximately 150 to 200 recurring monomer units in the polymer chain; more strength between polymer units
What molecular weight distribution yields best polymers
In general, a narrow molecular weight distribution yields the most useful polymers
Physical Stages of PMMA Polymer Change (After Mixing Powder & MMA Liquid):
o 1: SANDY
o 2: RUNNY OR LIQUID
o 3: PUTTY OR DOUGH
o 4: RUBBERY; HARD
Usual stage at which the mixed PMMA material is placed in a matrix of some type to then conform to the shape of a temporary prosthesis or a denture
3: PUTTY OR DOUGH
PROBLEMS WITH ACRYLIC-BASED MATERIALS:
Polymerization shrinkage: (from 10 to 21%, pure monomer highest)
Water sorption (highest with chemical-cold cure)
Porosity (inclusion of air bubbles)
Conversion (lowest with chemical-cold cure)
Single Component, Light-Cured Alternatives To PMMA/MMA Polymers:
o 1) TRIAD Light-Activated Resin (Custom trays, temporary dentures and retainers, temporaries for crowns and bridges, surgical stents, etc)
o 2) Radica Light Activated Resin System (Denture Bases - Temporaries)
Composition of lights cured composite resin
o Base Oligomer - Urethane dimethacrylate
o Other Resin Oligomers - HMW acrylic monomers
o Fillers -Microfine silica, Acrylic resin beads
o Camphorquinone initiator:Amine Accelerator - LIGHT ACTIVATION
Why lights cured composite resin over pmma
- No residual monomers
* Command Curing (Light Activation by Handheld and High intensity Light Box)
Disadvantages of light cures composite resin
o 1) Need light-access to all areas of the material-prosthesis
o 2) For dentures or large prosthesis - lower properties than heat-processed PMMA/MMA material
COMPOSITE MATERIALS HAVE, AT LEAST, TWO DISTINCT PHASES:
two or more distinct substances (metals, ceramics or polymers)
o 1- ORGANIC POLYMER MATRIX (continuous phase)
o 2- INORGANIC PARTICULATE FILLER (dispersed phase)
Composites are
solid formed from two or more distinct phases that have been combined to produce properties superior to or intermediate to those of the individual constituents
DENTAL RESIN COMPOSITE
• 3 components:
1- Resin matrix continuous phase
2- Inorganic filler dispersed phase
3- Coupling agent (silane)
Resin Matrix:
Oligomers/monomers, initiator/accelerator, inhibitors, pigments
Inorganic Filler:
glass, quartz, colloidal silica (hard, inorganic-filler
particles - ceramic based)
Coupling Agent
Silane à link the particulate phase to the resin phase
o Without this linking phase à no stress distribution
FILLERS in composite (Rationale & Effect):
o The inorganic and/or organic resin particles that are designed to strengthen a composite, decrease thermal expansion, minimize polymerization shrinkage and reduce the amount of swelling caused by water sorption.
COMPOSITION OF FILLERS:
o Quartz o Amorphous Silica o Glass fillers with metals (Barium-Boro-Alumino-Silicate Glass) o Colloidal Silica o Ceramics o Organically modified Ceramics/ORMOCERS
TYPES OF FILLERS:
o 1) Conventional
o 2) Microfine
o 3) Hybrid
CONVENTIONAL FILLER:
o Irregular glass or ceramic o 4µm - 40µm o Used in 1960’s- 1970’s o First generation Composites: ▪ 1-50µm ▪ 60-80 wt% o Later - Small Particle Composite: ▪ 1-5µm ▪ Ba, Sr, Zn, Yb glasses- fine fillers -Radiopacity
MICROFINE FILLER:
o Pyrogenic silica: 0.01µm- 0.1µm
o Colloidal silica: 30-60 wt%
o To increase filler loading - organic filler - colloidal silica filler added to resin-heat cured-ground to large particles (organic filler)-remixed with more resin and colloidal/pyrogenic filler to make microfill composite resin
o Rare earth metal compounds (YbF3) are added for radiopacity (microfil not radiopaque)
o Homogeneous Microfill (no organic filler - only fumed silica) & Heterogeneous Microfill (organic filler - plus fumed silica)
HYBRID FILLER:
o Conventional glass/ ceramic filler particles - Produced by grinding/air-impact classification/sol-gel synthesis- Zirconia/ Silica: 0.5µm - 10µm plus Pyrogenic silica: 0.01µm - 0.1µm
o Bariumaluminoborate & Sr glasses- Radiopacity 78-85 wt%
Ways that the Amount of Filler Is Measured:
o 1) By weight percent of filler content (Filler Wgt/Total Composite Wgt x 100)
o 2) By volume percent of filler content (Filler Volume/Total Composite Volume x 100)
STURDEVANT’S CLASSIFICATION
- HOMOGENEOUS: One primary particle size
- HETEROGENEOUS: Mixture of cured + uncured, but one primary particle size
- HYBRID: Mixtures of various particle sizes
Classification based on largest, primary particle size:
- Megafill: 0.5 - 2 millimeters
- Macrofill: 10 - 100 microns
- Midifill: 1 - 10 microns
- Minifill: 0.1 - 1 microns
- Microfill: 0.01 - 0.1 microns
- Nanofill: 0.005-0.01 microns
Hybrid means
Combining two different types (by composition & size) of fillers.
the combination of microfiller (fumed & agglomerated silica 0.04 - 0.1 micron) plus minifiller (heavy metal ceramic glass-silica filler - 0.1 to less than 1 micron) is called
microhybrid
nanofiller (nanoparticles 0.01 - 0.001 micron) plus minifiller (heavy metal ceramic glass-silica filler - 0.1 to less than 1 micron) is called
nanohybrid
WAYS OF CLASSIFYING COMPOSITE RESINS:
• By filler composition (inorganic/organic)
• By filler mean particle size. (macro/small particle/mini/micro/nano)
• By composite resin viscosity (flowable/universal/packable)
• By whether filler composition is homogeneous or
heterogeneous (multiple sized filler-various compositions)
• By polymerization reactions (Light Cure/Chemical Cure/Dual Cure)
Eugenol inhibits the setting of all dental polymeric materials that cure by
free-radical (addition) polymerization
composite resins have a significantly higher coefficient of thermal expansion (CTE) compared to
tooth structure or ceramic materials, but lower than metals.
Polymer matrix absorbs water which causes
expansion,
▪ This expansion is LESS than the polymerization shrinkage.
Composite resins are also soluble in water (1-2% weight), but can be more soluble in
organic solvents (alcohol, acetone).
Curing light intensity is measures by the units
milliwatts/square centimeter (MW/cm2).
Curing light intensities range from
300 - 800 MW/ cm2 for QTH and 800 - 1400 MW/ cm2 for LED lights.
Two types of curing lights are
- Quartz-Tungsten-Halogen (QTH) and 2. Light-Emitting-Dioide (LED) Lights.
COMPOSITE TYPES/EXAMPLEs
Lowest viscosity o 1. Sealants (filled)
o 2. Flowable Composite
o 3. Anterior/Posterior (midrange viscosity /non-sticky)
Highest viscosity o 4. Packable (condensable)
increasing filler loading of composite resin materials improves
physical properties, including improving wear resistance, and reducing polymerization shrinkage
DEGREE OF CONVERSION:
The percentage of initial monomer that is converted to polymer after the completion of the polymerization reaction:
Mi – Mf / Mi
Inadequate polymerization results in
inferior physio-mechanical properties, such as poor resistance to wear, poor color stability, secondary caries and adverse soft tissue/pulp reactions, increased water sorption, solubility, and early restoration failure.
The “depth of cure” (DOC) – usually referring to the thickness of a RBC that is “adequately” cured – is limited by
light absorption and scatter within the material, irradiation source, material shade, and irradiation duration
Color Stability:
Yellowing due to tertiary amine accelerator breakdown in chemically-cured systems.
Light-cured systems do not contain tertiary amine and so have improved
color stability
CLINICAL PERFORAMANCE & LONGEVITY OF COMPOSITE RESINS:
- Annual clinical failure rates are lower for anterior composite resin restorations as compared to posterior composite resin (PCR) restorations.
- Overall annual failure rates for posterior PCRs are 50 - 100% or more higher than amalgam.
- Annual failure rates for multi-surface (MO, DO, MOD) posterior PCRs are even higher compared to similar amalgam restorations. Class 1 (occlusal only) failure rates for PCRs are similar to amalgam failure rates.
- MAIN REASONS FOR FAILURES: Secondary Caries & Restoration Fracture
