Dental Materials Flashcards
What are the 3 phases within Composite, which are `hydrophilic/phobic?
1) Organic Matrix (Hydrophobic)
2) Inorganic Filler (Hydrophilic)
3) Coupling Agent (Silane)
Why isn’t MMA used as monomer in Composite organic matrix?
Its molecular weight and volume are too low –> resulting in polymer shrinkage
What monomer(s) are usually found in organic matrix of Composite? What polymerisation reaction do they undergo?
ALL MONOMERS HAVE DIMETHACRYLATE GROUPS + UNDERGO FREE RADICAL ADDITION POLYMERISATION (no by-products, reduced shrinkage)
BisGMA
or UDMA/ Ethoxylated BisPhenol A derivative (less viscous)
Diluent monomer(s) added to reduce viscosity = Glycol dimethacrylates (e.g. TEGDMA, EDGMA and THFMA)
In composites, what are “diluent monomers” added to organic matrix?
Added as viscosity controllers to reduce viscosity (which increases with filler)
They’re Glycol Dimethacrylates (e.g. TEGDMA, EDGMA and THFMA)
What is Camphorquinone?
Activator/Initiator system for light cure composites, Camphorquinone absorbs light within range 460-480nm to produce free radicals and initiate polymerisation setting reaction
What are the main components (monomers) within (new) Bulk Fill Composite?
Aromatic Dimethacrylate monomers: DDDMA + UDMA
Silorane Resin: Made from Siloxane and Oxirane monomer ring, which opens upon polymerisation to reduce polymerisation shrinkage
What are 5 advantages of inorganic filler in composites?
1) Reduced polymerisation shrinkage
2) Reduced thermal expansion coefficient
3) Enhanced mechanical properties
4) Radiopacity
5) Improved aesthetic control
What are the 3 main types of Inorganic Filler and how do they differ (Composites)?
1) Macro-filler (QUARTZ)
Large particle size, good strength but dull appearance - POSTERIOR
2) Micro-filler (COLLOIDAL SILICA)
Small particle size, less strength - ANTERIOR
3) Hybrid filler
Either Hybrid/Blended or Small Particle Hybrid
Other than primary monomer (e.g. BisGMA), what are 5 other components within the organic matrix?
1) Hydroquinone (retarding agent?)
2) Activator/Initiator system (Room Temp Cure = DHPT or Benzoyl Peroxide & Light Cure = Benzoyl Peroxide or Camporquinone)
3) Pigments (e.g. Iron Oxide)
4) UV Stabilisers
5) Optical Brighteners (fluorescence)
What is the filler loading + maximal theoretical packing density?
Filler loading = 30-70 vol% (50-85 wt%)
Theoretical packing density = 74%
This is least in MICROfillers… (20% wt)
What are 2 advantages of Coupling Agents in Composites?
1) Bridge between hydrophilic filler and hydrophobic matrix
2) Improved mechanical properties
What does the Coupling Agent bond to (Composites) and what reactions take place?
1) Hydrophilic filler via Condensation reaction (filler -OH and coupling agent -OCH3/-OH)
2) Hydrophobic matrix via chemical bond (matrix methacrylate group and coupling agent methacrylate group)
What is meant by Composite “Degree/Depth of Conversion” and which type of cure has the best?
How do we overcome restrictive curing issues?
The proportion of reacting C=C double bonds, want it as high as possible.
Light Cure = 65-80%
Room Temp Cure = 60-75%
Heat Cure = 90% (but cannot be used at chair side)
Limited depth of cure overcome by Incremental curing (2mm)
What are the 4 main methods of light cure for Composites? What is the wavelength of the first 2 and how does this relate to Camphorquinone?
1) Quartz- Tungsten Halogen (broad spec: 400-500nm)
2) LED (narrow spec: 460-480nm)
3) PAC (Plasma Arc)
4) Argon Laser
Camphorquinone = activator which absorbs light in 460-480nm range, so 2 can only use Camphorquinone, whereas 1 can use multitude of photoinitiators
What is the Oxygen Inhibition Layer of Composites?
How can it become an issue and what are 3 main ways a clinician could overcome these?
Air and resin sticky interface layer that helps the next layer of composite to stick in incremental placement. Issue when its top layer 1) Clear matrix strip use 2) Overfill, cure and polish down 3) Apply bonding agent (clinician fav)
What is the difference between “Flowable” and “Packable” Composites?
Flowable = Less resin, reduced mechanical properties
Difficult to control and used on Anterior teeth
Packable = More resin, enhanced mechanical properties but compromised aesthetics (Posterior teeth)
Which Impression materials are used on:
1) Dentate Px?
2) Edentulous Px?
1) Elastic
Hydrocolloids (Agar or Alginate)
Elastomers (Addition/Condensation Silicone, Polysulphides or Polyethers)
2) Non-Elastic (Impression Plaster, Compound or ZOE)
What is the difference between Agar and Alginate?
Agar = Reversible Hydrocolloid (undergoes PHYSICAL reaction) Alginate = Irreversible Hydrocolloid (undergoes CHEMICAL Cross-linking reaction)
Alginates can be fast, regular or slow set, what does this depend on?
Depends on composition, how much CaSO4 (cross-linking agent, speeds up setting) vs. Na3PO4/Na2CO3 (retarder agent, slows down set)
What is the bulk component of Alginate (70%)?
Diatomaceous earth (filler - for strength)
What are the 6 main components of Alginate and their functions?
1) Sodium/Potassium Alginate (thickener)
2) Diatomaceous earth (filler - for strength)
3) CaSO4 (cross-linking agent)
4) Na3PO4/ Na2CO3 (retarding agent - slows reaction)
5) Sodium Silicofluoride/Fluorotitinate (pH controller)
6) Magnesium Oxide (pH controller)
What are the 3 main pH controllers present in Alginate? Why are they necessary?
1) Sodium Silicofluoride
2) Sodium Fluorotitinate
3) Magnesium Oxide
pH changes occur throughout the setting reaction - initially decreases to below 3.5 then increases to 9 upon set due to build up of sodium and potassium ions
Outline the main steps in the Alginate setting reaction…
Water added to powder and forms “Colloidal suspension” (large powder particles suspended in water)
1) CaSO4 (cross-linking agent) ionises to Ca and SO4 ions
2) Na3PO4 (retarder) ionise to Na and PO4 ions
3) Ca and PO4 ions react to form insoluble calcium phosphate
Cross-linking reaction suppressed whilst Phosphate ions used up (N.B CO3 may be present instead of phosphate)
What is an example of a “Dust-free” Alginate?
Triethanolamine alginate
How is Alginate disinfected?
In what material, how long for and why?
Disinfected in: Sodium Hypochlorite
For: 10 mins
Why: Too little = Swelling (imbibes water), Too much = Shrinkage (water soluble ions leach out)
After: Rinse under tap water, wrap in damp gauze and place in polyethene bag (cast within 24 hours)
How does Agar set?
PHYSICAL (instead of chemical) reaction so “Reversible” Hydrocolloid
Solid (gel) at room temp
Heat to 60 C = Viscous liquid
(Cool to 40 C before placing in mouth)
What are the 5 main components of Agar and their functions?
1) Agar (colloid)
2) Borates (strengthen gel - also found in Gypsum as retarder)
3) Potassium sulphates (accelerates stone set)
4) Thixotropic material/ Wax (filler - strength)
5) Water (dispersion medium)
What is meant by the following (N.B. Both occur in Agar and Alginate)
1) Synerisis?
2) Imbibition?
1) Synerisis = Expulsion of liquid from solid due to shrinkage from water loss
2) Imbibition = Swelling due to absorption of water (e.g. from disinfectant)
What is the viscosity of elastomers affected by?
What are the 5 viscosity levels and which is used on clinics?
Affected by filler content More filler = More viscous 1) Putty (most filler) 2) Heavy-bodied 3) Medium-bodied - Used on clinic! 4) Light-bodied 5) Wash (least filler) N.B. Mixture can be used (e.g. putty for strength with light-bodied/wash for fine details)
Out of the Elastic Impression Materials, which are Hydrophobic and which are Hydrophilic?
Hydrophobic = Addition & Condensation Silicones Hydrophilic = Hydrocolloids (Agar and Alginate), Polysulphides and Polyethers
In Addition and Condensation Silicones:
1) What type of reaction takes place (duh)?
2) What monomer is present (therefore what polymer is made)?
1) Addition = Addition
Condensation = Condensation (Ethanol by-product so shrinkage)
2) Addition = PVDMS Poly(Vinyldimethylsiloxane)
Condensation = PDMS Poly(Dimethylsiloxane)
What are 8 desirable properties of an Impression material?
1) Easy to use
2) Good odour, taste, texture and colour
3) Cheap
4) Good dimensional stability (and readily disinfected without losing accuracy)
5) Good (long) storage life
6) Good tear strength
7) Good elastic recovery and flexibility
8) Non toxic/Irritant
What are the 3 main Non-elastic Impression Materials?
Which ones are Mucostatic and which are Mucocompressive - what does this mean?!
Mucostatic = Doesn’t displace soft tissues
Mucocompressive = DOES displace soft tissues
1) Impression Plaster (Mucostatic)
2) Impression Compound (Mucocompressive)
3) ZOE (Mucostatic)
Which 2 Elastomeric Impression materials set via Addition reaction?
Addition Silicone
Polyethers
Which 2 Elastomeric Impression materials set via Condensation reaction?
Condensation Silicone
Polysulphides
What are the 2 main problems with bonding/adhesion to enamel and how do we overcome these problems?
1) Enamel surface area/tension lower than that of adhesive resin (34-38 mJ/m2) and made even smaller by enamel pellicle (28mj/m2) which reduces adhesive wettability
2) Adhesive resin non-polar, requires dry environment!
Enamel surface acid-etched with 37% (30-50%) Phosphoric Acid to remove enamel pellicle and disrupt enamel prism structure. Allows increased wettability (enamel surface tension increased to 48mj/m2) and formation of Micromechanical bonds as unfilled resin readily flows down etched prism areas to form “Resin tags”
