Dental Materials Flashcards
What 2 forms can GICs come in?
Encapsulated or hand mix (liquid/powder)
Why is encapsulated preferable?
Pre-measured
Mixed for you
Can out straight into mouth
How can self mix go wrong?
Too much powder or liquid will set slower/faster and alter consistency and binding properties
What are GICs used for?
Cement and fillings
What forms can zinc oxide eugenol and calcium hydroxide come in?
2 paste (temp-bond, Dycal) or liquid/powder
How are 2 paste ZOE and calcium hydroxide cements mixed?
Equal amount of both
15s mix time till creamy, no streaks
5-6 min set time
How is liquid/powder ZOE and calcium hydroxide cement mixed?
2 spoons power : 3 drops liquid
Add in powder small amount at time till right consistency
Clean spatula, put powder on spatula and roll towards you until sausage shaped
1-1:30min mix time
4-5 min set time
How is alginate mixed?
Powder fluffed - mix ingredients, remove clumps
Scoop in bowl, add room temp water
Mix for 30s, spread against side to remove air bubbles and thoroughly mix
1-2 min set time depending on temp - warm water sets faster
What 3 forms are most dental materials in unset?
- Power and liquid
- 2 paste
- 1 paste
What 2 forms do most dental materials cure to?
- Rigid/stiff
2. Rubbery, elastic material
Describe dis/advantages of powder/liquid materials
Depends on what using material for
Alginate is v easy, cements more difficult to incorporate all powder into liquid in short time
Need to avoid incorporating air into material
What are the dis/advantages of 2 paste materials?
Difficult to mix to give homogenous resulting mass
Need to avoid incorporating air while hand mixing
What are the dis/advantages of 1 paste materials?
Can be difficult to pack into cavity if v viscous
What are the dis/advantages of delivery gun/pentamix materials?
Easy to mix
Tips cannot be reused
Could two air while filling impression tray
What are the 3 methods of setting dental materials?
- Heat
- Root temp.
- Light cure unit
Compare the physico-mechanical properties of the 3 cure types of materials
- Heat: optimum physico-mechanical properties (dentures) but not feasible for chairside
- RT: compromised compared to heat set - denture repair material
- Light: physico-mechanical properties between RT and heat set - composite
What are the 5 ideal properties of dental materials?
- Biocompatible
- Mechanically stable
- Chemically resistant
- Dimensionally stable
- Minimal thermal and electrical conductivity
What are the 11 generic groups of dental materials?
- Impression
- Acrylics
- Soft liners and tissue conditioners
- Cements
- Resin composites
- Bonding agent
- Casting materials
- Investment and die materials
- Waxes
- Ceramics
- Dental alloys/amalgam
What 5 factors influence selection of material?
- Patient history
- Age of patient/dentition
- Patient compliance
- Location of tooth
- Depth of cavity
Compare the important factors for ant. and post. restorations
Ant: colour match, natural looking in all lighting conditions, compressive strength not necessity
Post: high compressive strength, aesthetics not necessity
If a carious cavity extends to the pulp what is required when restoring?
Cavity liner to act as thermal insulator so tooth not sensitive to heat changes
What is Grassman’s law?
Three parameters of colour:
- Dominant wavelength (hue)
- Excitation purity: saturation of colour; intensity 0-1
- Luminous reflectance: brightness (100) or darkness (0)
Why is colour important in DMs?
Wavelength material reflects may change w/ age thus colour may change
What is the importance of surface finish of a restoration?
When light reflects off a solid some reflects from surface and some reflects from body of solid
Surface reflection dilutes colour: rough surface is much lighter than smooth surface of same material thus colour of restoration could become much lighter w/ wear
What are metameric colours?
Colours that appear the same under 1 light source but different under another
What is the significance of metanerism in dentistry?
Need to match restoration colour to natural colour in light corresponding to that of use
What is fluorescence?
Phenomenon observed when material absorbs colour of one wavelength and emits colour of another wavelength
Why is fluorescence important in DMs?
Teeth emit fluorescent light (look whiter under fluorescent light) so materials need to look natural
Some porcelains contain fluorescing agents to mimic natural appearance
Define opacity, translucency, transparency
Opacity: selective absorbance of light
Transparency: no interaction w/ light, complete transmission
Translucency: mixture of absorption, refraction, transmission
What is the refractive index?
Ratio of velocity of light in a vacuum to velocity in selected medium
A large difference = opaque; identical = transparent
What are 3 areas in why temp. is important in dentistry?
- Use of drill
- Exothermic setting reactions: can’t do in mouth
- Effect of hot/cold on restoration
Why is knowing temp. important?
Temp change may alter properties of material
What is heat of fusion?
Energy required to convert 1g of material from solid to liquid at melting temp.
What is thermal conductivity?
Quantity heat/second passing through a 1cm thick substance w/ cross section of 1cm2 w/ temp. inc. of 1 degrees
I.e. ease with which heat is transferred through a material
What is the clinical significance of thermal conductivity?
Large amalgam filling close to pulp may be sensitive to hot/cold thus use a non-mental cement between tooth and filling to insulate
Metal denture base material will more closely follow temp. of oral mucosa
What is specific heat?
Quantity of heat required to heat 1g material by 1 degrees
What is thermal diffusivity?
Measure of transient heat flow: how long does cold end of material take to heat up?
Rate of transfer of heat from hot side to cold side of material
What is the clinical relevance of thermal diffusivity?
Good inlay, crown, amalgam have low specific heat but high thermal conductivity thus if close to pulp may get thermal shock
What is thermal expansion coefficient?
Change in length of material for a 1 degree change in temp.
What is the clinical significance of thermal expansion?
Tooth and material will expand and contract due to hot/cold
Could result in breaking of marginal seal of inlay/filling
What electrical conductivity and resistivity?
Ability of material to conduct electrical current
Why is electrical conductivity and resistivity important?
Correlation between electrical conductivity and change in physical and mechanical properties of material
E.g. gold alloys: change in resistivity changes internal crystal structure
What is electromotive force?
Difference in electrical potential that gives rise to current
What is the electromotive series?
List of metals ordered in dec. tendency to oxidise in solution
What is galvanism?
Induction of current due to chemical reaction
Why is galvanism important in dentistry?
If 2 fillings of different electronegativities touch will cause short circuit which if near the pulp will cause pain
Why does amalgam have a high copper content?
Copper-tin complex much harder and less corrodible than tin-mercury
How do GICs bond to enamel?
Bind to Ca2+ in enamel
Carboxyl group plays role in setting reaction and bonding mechanisms
What is solubility?
Of inorganic salt: number moles of pure solid that will dissolve in 1L solvent at given temp
Compare solubility of hydroxyapatite and fluoroapatite
FA less soluble than HA: remains supersaturated for longer than HA even at lower pH
What are the 6 optical factors important in DMs?
- Colour
- Opacity
- Fluorescence
- Surface finish
- Refractive index
- Metanerism
What are the 6 thermal factors important in DMs?
- Heat of fusion
- Thermal conductivity
- Thermal diffusivity
- Specific heat
- Temp
- Thermal expansion
What are the 3 electrical factors important in DMs?
- Conductivity and resistivity
- Electromotive force
- Galvanism
What are the 3 chemical factors important in DMs?
- Reactions
- pH and solubility
- Bonding
Define biomaterial
Natural or synthetic material that interfaces w/ living or biological tissue
Define biocompatible
Ability of material to elicit an appropriate biological response, in given application, in body/mouth
What is biocompatibility dependent on?
Physical function Biological response required Location Composition Interaction w/ OC
What are the 4 main reasons for restorations?
- Trauma
- Decay/caries
- Tooth loss
- Revisions: repair failed restoration
Define safe in terms of DMs
Must not cause any local or systemic adverse reactions
What are the 2 categories of research?
- Basic: lab research; pre-market
2. Clinical: post-market surveillance
What are the 2 types of lab research?
- In vitro
2. In vivo
What 5 basic factors are tested in in-vitro testing?
- Physico-mechanical properties
- Biological properties: cytotoxicity; organ, tissue, cell cultures
- Genotoxicity: damage to genetic info causing mutations
- Oestrogenic activity
- Basic sciences: efficacy and safety of therapeutic, rehabilitative, preventative regimes
What kind of tests are done in-vivo?
Implants: material implanted into animal
Allergy tests
Limited usage studies: animal/clinical testing; long, tedious but most clinically relevant
What types of animal tests are there?
Past: material ground and fed to animal; implanted into animal
Now: material used in required area
Why is clinical testing preferred?
Most accurate and efficacious depending on:
Number of patients
Group of patients
Length of trial
What is the downfall of clinical testing?
Clinical symptoms don’t evaluate real world damage
Will have material in OC for years not weeks
What are some of the ways in which post-market surveillance is important?
Provide early warning signs of unsuspected adverse effects
Elicit predisposing factors to adverse reactions
Compare adverse reactions between similar products
Permit continued safety monitoring
Who are at risk of adverse reactions from DMs?
Dentist
Dental nurse
Dentinal technician
Patient
Who is most at risk of adverse reactions to DMs? Why?
Dentist/technician
Inc. risk as inc. exposure to material
How can risks be reduced?
Proper packaging
Following manufactures instructions
Non-contact operative techniques
What are the 3 main types of force?
- Uniaxial
- Biaxial
- Triaxial
What are the 3 types of uniaxial force?
- Tensile: away from each other
- Compressive: towards each other
- Shear: towards, one from top side other from bottom side
What are forces defined by?
Where they are applied, in what direction and how big they are
What is stress?
Force applied per unit area
Define strain
Deformation of object due to stress
What is Hooke’s law?
Stress is proportional to strain
What is Young’s modulus?
Ratio of stress to strain i.e. stress/strain is a pressure (Pa)
What can be determined from a stress-strain curve?
Ductility, strength, elastic modulus, resilience, toughness, flexibility
What is a fracture?
Separation of a material into 2+ pieces under action of stress
What are the 2 types of fracture?
Brittle: little/no plastic deformation, low toughness
Ductile: significant plastic deformation, high toughness
What are the steps in a fractureb
- Crack formation
2. Crack propagation
Describe the stress-strain plot for a brittle material
Almost linear due to low plastic deformation
Describe a direct tensile measurement
Dumbbell shaped test specimens, ensures central fracture
Used for metals, rigid polymers, rubbery polymers
What are compressive tests used for?
Ceramics
Hard polymers
What is a diametral/indirect tensile test?
Compression across diameter
What are the 6 static strengths?
- Compressive
- Tensile
- Shear
- Torsion
- Flexure
- Diametral tensile
What is hardness?
Resistance to indentation/permanent deformation when compressive force applied
What is fracture toughness?
Resistance of a material to failure from fracture starting at pre-existing crack
Define tear strength and energy
Strength: force needed to initiate/continue tearing
Energy: measure of energy per unit area of newly torn surface
Define impact
Resistance to fracture from rapid loading measured as energy absorbed at fracture
What is fatigue?
Failure of material at force well below static strength due to repeated force/strain cycles
Define fatigue life, strength and limit
Life: number of cycles to cause failure at specified stress
Strength: level of stress at which failure will occur after specified number of cycles
Limit: level of stress below which fatigue failure will not occur
What is static fatigue?
Failure of material at small load after period of constant loading
Load required to cause failure will dec. w/ inc. time loading
What 4 things is wear a combination of?
- Abrasive
- Adhesive
- Fatigue
- Corrosive/erosive
Define abrasive wear
Materials against each other:
2 body: tooth-tooth
3 body: tooth-tooth w/ food stuff between
What is adhesive wear?
Material sticks to tooth and when pulled away removes part of tooth
What is fatigue wear?
Propagation and combining of micro-cracks w/ successive loading cycles
Define corrosive/erosive wear
Corrosive: acid attack remove weakened enamel
Erosive: grinding, bruxism
What is fluid flow governed by?
Strength of intermolecular forces and molecular entanglement
Define viscosity
Resistance to flow of a fluid
Measure of internal resistance of material
What is a Newtonian fluid?
Fluid in which applied shear stress produces flow w/ constant shear strain rate response
Water, solvents, mineral oils
What are non-Newtonian fluids?
Fluids in which there is no define viscosity
Viscosity changes with shear rate or shear rate history
What are the 5 types of non-Newtonian fluids?
- Pseudoplastic
- Dilatant
- Viscoplastic
- Thixotropy
- Rheopexy
Define pseudoplastic fluids
Dec. viscosity as shear rate inc.
plaster, stone
Define dilatant fluids
Inc. viscosity as shear rate inc.
composites, porcelains in water
Define viscoplastic fluids
Will not flow until initial shear stress has been reached then can have Newtonian, pseudoplastic or dilatant properties
Define thrixotropic fluids
Viscosity dec. w/ time at constant shear rate
Ketchup, toothpaste, clays, quicksand
Define theopoxic fluids
Viscosity inc. w/ time at constant shear rate
Some lubricants, v rare
Define stress relaxation and creep
Relaxation: time dependent dec. in stress at constant strain
Creep: time dependent dec. in strain under constant load (stress)
What are the 7 types of adverse reactions?
- Toxic
- Irritant contact dermatitis
- Allergic contact dermatitis
- Oral lichenoid
- Anaphylactoid
- Contact urticaria
- Intolerance
What are the 2 types of adverse effects?
- Dermatoses
2. Non-dermatological
Describe irritant dermatose reaction
May be of acute toxic nature causing direct and immediate cytotoxic effects to skin cells
Cumulative dermatitis is from repeated contact w/ chemical agent at sub-toxic conc
Localised and restricted to the area of exposure
Describe allergic dermatose reactions
Acquired by contact w/ haptens in materials
Tissue develops antigens by contact w/ dermal protein
Next contact produces allergic response
Define haptens
In/organic molecule that alone is not antigenic but is when linked to carrier protein
What are some of the materials that can cause dermatose reactions?
Metals Polymers/monomers Hydroxyethyl methacrylate Latex gloves Formaldehyde Eugenol Disinfectants Rubber dam: latex or nitrile
What is sodium hypochlorite and its risk?
Disinfectant used for irrigation in RCT
Can cause pain if introduced into periapical tissue, periapical bleeding and extensive swelling
What effects can acute systemic toxicity have?
Primarily eyes and airway
Long term exposure lead to renal, neural, liver disorders
Associated with repeated dosage