Dental Material Test 2

Front 1

History of Dental Amalgam

Back 1

-First used in the US in 1833
-In 1896 Flagg and Black worked on a balanced formula of tin and silver
-1920s ADA said that amalgam must be 69 percent silver and 29% tin
-Later on the mid-1900s micro-lathe cut, spherical particles, and high copper amalgam dispersallow (admix high copper) introduced
-Tytin developed by Kamal Asgar, it is a single composition, spherical, and high copper (10-30%)

Front 2

Dangers of Mercury

Back 2

-Mercury vapor is the biggest risk, and the dentist and assistants are at risk, not the patients
-Replacing amalgam restorations just because they're amalgam is unethical
-Mercury in the environment and dental disposing of it is also a major concern

Front 3

Intro to Amalgam Types

Back 3

1. What is it? - Amalgam is a mixture of silver (Ag), copper (Cu), Tin (Sn) and mercury (Hg)

2. Shapes? - Lathe cut and spherical (single composition)

3. Types of Alloys? Lathe cut, spherical, and admixed (combination of the two)

Front 4

Amalgam Alloy Classification

Back 4

1) Lathe-Cut - Irregular particles (rod shaped). It is low copper

2) Spherical - From atomizing molten metal. High copper
-Ag and Sn dissolve in Hg. Gamma 1 crystals grow. Little Cu dissolves so Eta crystals are meshes of rod-like crystals. The result is a bigger particle tht icnrease resistance to deformation

3) Admix (Disperalloy) - Mixture of spherical and lathe cut. High copper (at least 12% to get rid of the gamma 2)
-Ag (from AgCu) mixed with Hg and Ag and Sn from AgSn dissolve into Hg. You want Sn and Cu to react forming Eta and getting rid of Gamma 2. The result is Gamma 1 and Eta (CuSn).
-Gamma 1 is the matrix binding unused particles


4. Roles
a) Cu and Ag cause expansion and increase strength and corrosion resistance
-Tin causes contraction and decreases strength and corrosion resistance
-Zinc is a deoxidizer and make amalgam less brittle
-Amalga with lower Hg usually has better properites

Front 5

Amalgam Phases

Back 5

-Before mixture there is mercury and gamma, or silver-tin
-When the powder is triturated the silver-tin alloy dissolves into mercury and vice versa. Once solubility is exceeded crystals precipitate into mercury. These include body-centered cubic silver-mercury and hexagonal tin-mercury. The silver-mercury is the gamma 1, named because the silver solubility in mercury is the lower so it precipitates first. Tin-mercury is gamma two.
-The gamma 1 and 2 crystals grow, with primarily more gamma 1

Front 6

Low vs. High Copper

Back 6

Low Copper - Only given by Lathe cut. Less than 6% copper.
-Has gamma 1 and gamma 2 precipitation on the original alloy and this continues until mercury is consumed

High Copper - Given by single composition or admixed.
-Better than low copper since weak gamma phase 2 (tin-mercury) is eliminated
-High composition has increased strength, decrease corrosion, and decrease marginal breakdown

Front 7

High Copper Amalgam

Back 7

1. Admix
a) Lathe-Cut : Low copper
b) Spherical: 72% Ag and 28% Copper. Finaly copper ranges from 9-20%
-Ag from AgCu dissolves into Hg and Ag and Sn from AgSn dissolve into the Hg. Sn diffuses to the surface of AgCu and reacts with Cu forming Eta. Gamma 1 and Eta (CuSn) form simultaneously. Gamma 1 is the matrix binding unused particles meaning that it binds the uncomsuned alloy particles together.
-Callede admixed because final powder is a mixture of 2 particles. The lathe-cut low copper and spherical silver-copper alloy.
-Contains a little gamma as well around the epsilon particle which are Sn-Cu
2) Spherical High-Copper Amalgam (Tytin) - High copper
-Ag and Sn dissolve in Hg. Gamma 1 crystals grow and form matrix. LIttle Cu dissolves. Eta crystals are meshes of rod-like crystals at surfaces of the alloy particles. The particles are bigger than in admixed and increase resistance to deformation. Contains a little gamma too
-End up with unconsumed alloy particles surrounded by gamma-1

Front 8

Amalgam Properties

Back 8

a) Creep - Time-dependent strain produced by stress. Can cause amalgam to extend out of the cavity prep, increassing susceptibility to marginal breakdown. Like a slow squeeze
- If amalgam initially contaminated with body fluid then it creeps over time, meaning it will expand along marginal edges causing sensitivity. Zinc and water results in H2 formation
-ADA requires less than 3% deformation

b) Compressive Strength - Strength of amalgam measured under compressive stress. Should be 310 MPa. After 1 hour the single composition is the highest, and after 7 days the high copper have a higher compressive strength than the low copper.
-Strength if effected by trituration, porosity, and condensation
-Amalgam has low tensile and shear strength so it needs tooth support
-If you don't condense the amalgam enough it becomes porous and weak. Additionally, mercury increases the strength until a certain point at which it will decrease the compressive strength (54% mercury)

c) Dimensional Change - Expansion or contraction of amalgam. Should be small cause large changes lead to microleakage, plaque accumulation, and recurrent caries
-When the alloy and mercury mix there is initialy contraction for 20 minutes as the particles dissolve and gamma 1 grows. As gamma 1 grow they impinge against one another producing outward pressure leading to expansion. After 24 hours the amalgam has set.
-Contamination of Zinc containing allows with water results in excessive delayed dimensional change

Front 9

Amalgam Properties 2

Back 9

Tensile Strength - Amalgam by itself doesnt have a high tensile strength so we design cavities to reduce these stresses.
-Over and under triturating decreases strength of spherical alloys.

Amalgam Fracture - Caused by the cavity prep and usually done by an isthmus that is too small and bitting down causes a fracture.

Front 10

Tarnish and Corrosion

Back 10

-done by formation of chlorides and oxides of tin. This is a good thing because oxides seal the margins and prevent recurrent cavities
-Tarnish is the formation of surface discoloration or loss of luster
-The amount depends on the individuals oral environment and alloy used
-Corrosion occurs on the surface between tooth and resotration. This microspace allows microleakage of electrolyes and this seals the space
-Corrosion can liberate mercruy which can contaminate and weaken a gold restoration if the two are in contact.

Front 11

Trituration

Back 11

-Initially the mercury and alloys are separated by a oxide film which is difficult for mercury to penetrate. During trituration the oxide is rubbed off and the alloy and mercury mix
-The goal is to form a round and soft (not dry) amalgam
-Increasing the triturating time or speed shortens the working and setting times
-High copper requires higher speed
-Over or under triturating reduces compressive and tensile strength and increases creep
-Usually amalgam comes in capsules with different amounts, most common are 400, 600, and 800 mg
-Usually the capsule acts as a mortar and inside is a metal or plastic pestles. During on the machine creates a mixture

Front 12

Condensation

Back 12

-Condensation produces the amount of Hg that remains in the restoration and this influences dimensional change, creep, and compressive strength. Condensation pressure influences amount of Hg
-Initially a 1P should be used along the margins, and after this a large end should do the remaining condensing
-If you try to condense a partially set amalgam the result is a broken up matrix

Front 13

Amalgam Bonding

Back 13

-Bonding refers to an adhesive that helps bond amalgam to the tooh
-The adhesive is usually 4-META (4-methacryloxyethyl trimellitic anhydride)
-Bonding increases fracture resistance and decreases marginal leakage.
-However, after bonding the strength between amalgam and dentin is half of dentin to a composite

Front 14

Finishing Amalgam and Uses

Back 14

-Amalgams used for non-esthetic restorations, core buildups, and retrograde endodontic treatment following an apicoectomy
-After anatomy sets a bit you should carive the primary anatomy. You can developmental grooves and major fossa. After this you burnish to bring mercury to the surface and make it shiny. Finally, you polish after 24 hours. Polishing before 24 hours the additional heat takes too much mercury to the surface and this weakens and discolors the amalgam

Front 15

Insurance

Back 15

-Insurance companies only pay for posterior amalgams and anterior composites. If you do a posterior composite the company will pay the price had you chosen amalgam and your patient will pay the rest.

Front 16

Introduction to Dental Polymers

Back 16

-a polymer is a molecule made up of many units (mer = unit)
-in dentistry polymers are used for many materials like impressions, denture based, and composite resin
-A composite is a material composed of two or more phases like a soft material with a hard ceramic particles included.
-Some examples of composite resins are Bis-phenol A glycidyl methacrylate (Bis-GMA) and urethane dimethacrylate. These utilize the esthetics and ease of use of polymerizable resin base and strong properties of a ceramic filler

Front 17

Impressions and Denture Base Resins

Back 17

Impressions - Start viscous and when it polymerizes it hardens. Takes a negative impression of the teeth into which a cast material (stone) is poured for the impression
Denture Based - Include PMMA or acrylic
Resins - Metallic material synthesized from organic compounds that is molded when soft and hardened for use

Front 18

Classification of Polymers

Back 18

1) Thermal Behavior
a) Thermoplastic - No chemical reaction involved. They are softened under heat and pressure, and hard when cooled. They are soluble in organic solvents
-These are linear or branched and bonded weakly so that heat makes them slide past one another. Includes PMMA
b) Thermoset - Hardened by a chemical reaction and insoluble in organic solvents
-These are cross-linked molecules that form a giant molecule via the covalent bonds. Do not soften when heated. Include cross linked PMMA, and bisphenol A-diacrylate
2) Origin
a) Natural - proteins, nucleic acids, polysaccharides (sugar, starch, agar, alginates), and polyisoprenes
-polyisoprenes include rubber and gutta percha. Used for orthodontics
b) Synthetic
-PMMA, nylon, and teflon

Front 19

Polymerization

Back 19

-series of chemical reactions by which a macromolecule polymer is formed from single molecules
1) Condensation (Step Growth) Polymerization -Repeating units joined by functional groups. The reaction is slow and giant molecules are hard to form.
-A low-molecule by product is also formed like water or alcohol so the product shrinks during formation. The reaction also continues for hours are initiation
-Example is lead oxide attacking 2 molecules with SH. The result is a disulfide bond attachment, lead oxide, and water
-Examples are impression materials like polysulfide impression and condensation silicone

2) Addition Polymerization - A free radical (benzoyl peroxide) is formed. It attacks a molecule with a double bond (unsaturated) forming a free radical. This will continue to attack similar polymers forming a giant molecule that can grow indefinitely
-No volatile by-product is formed, and it forms by a exothermic reaction
-Stages: First is initiation in which the free radical is produced. The free radicals attack double bonds of monomers resulting in the unpaired electron th the end of the monormer. Next is propagation where the monomer attack the DB of another monomer. Finally is termination where two radicals come together or a inhibitor like hydroquinone is added

Shrinkage - As the composite density increases through polymerization the molecule will shrink and this can introduce gaps between tooth and material. Each material has a different shrinkage percentage and filler content

Front 20

Activators of Addition Polymerization

Back 20

1) Heat - Thermal initiators have 1 weak bond that breaks at a significant rate at moderate temperature to yield a free radical. Examples are peroxides and azos (nitrogen bonded to nitrogen)
2) Tertiary Amines
3) Light - Range is 350 to 800 nm. Molecules react to light at various wavelengths so before buying a composite ask what wavelength of light it works at
4) Microwave Energy

Front 21

Inhibitors of Polymerization

Back 21

-used to store polymers
1) Impurities
2) Hydroquinone - most common
3) Oxygen - Oxygen binds the top layer so increments of composite can be added with oxygen working at the top. When you reach the correct amount of composite you need to grind and polish this top layer away

Front 22

Properties of Polymers (book notes)

Back 22

-properties of polymers affected by chemical composition, degree of polymerization, and number of branches of cross-links
-Longer chain and higher molecule weight makes the polymer stronger, harder, but also stiffer and less resistant to creep. For example, resin composites are highly crosslinked and it is rigid. In contrast, elastomeric impression material has coiled chains with a few cross-links and this makes them flexible
-Another property is the amount of crystallinity. Crystallinity is atoms with regular arrangement in space making them stronger, stiffer, and absorb less water.
-Most dental materials are amorphous and have irregular arrangements. These are often called glassy polymers
-Plasticizers, when added to a stiff un-cross-linked polymer, REDUCE its rigidity. The small plasticizers surround the larger molecules making the move more easily. Therefore, these plasticizers reduce the glass-transition temperature of the polymer so that a material becomes flexible at a temperature it used to be rigid at.
-The glass transition temp is the temp when a polymer ceases to be glassy and brittle and becomes rubberlike

Front 23

Properites of Polymers (class notes)

Back 23

-polymers can be linear or branches
-a polymer that is linear and coiled is usually elastic. These are held by 2nd bonds
-When you crosslink a polymer you form a bridge between polymer chains to create a 3d structure. The result is increased glass transition temperature, increased strength, decreased solubility, and decreased water absorption (important since mouth full of fluid, don't want material to absorb water and change properties)

Front 24

Plasticizers (class notes)

Back 24

-added to monomer to increase solubility and decrease brittleness
-Plasticizers facilitate slipping of polymer chains past one another to reduce strength, reduce hardness, and reduce glass transition temperature
-A plasticizeris used if dentures cause sores. The plasticizers allow the material to use rigidity providing pateint relief and allowing inflammation to heal

Front 25

Physical Properities of Polymers

Back 25

-Avg degree of polymerization - avg. number of repeating units in a polymer
-Degree of conversion - fraction of DB converted to SB after polymerization
-Higher degree of poly and conversion increase strength
Molecular Weight - Can be based on the average number of molecules in the polymer of the average weight of the polymer. Often there is a distributyion of molecular size in a material so the weight is an average
-Strength Properties - influened by temperature, composition, molecular weight, stucture, and residual monomers (never polymerized monomers decrease strength and introduce toxicity as it leaks into the mouth)
-Biological Properties - taste, small, soft tissue irritation, toxicity. These properties are influenced by residual monomers, solubility, water uptake, bonding to the tooth structure

Front 26

Composite Resins

Back 26

-when we combine materials and each retains its identity and the properties are additive
-Usually a composite include the matrix (main material that a polymer was made of) and the filler
-examples include impression materials and composite restorative materials
resin = matrix + filler

Front 27

Fillers

Back 27

-inorganic composition
-can be fine-sized particles like quartz or borosilicate glasses. Can be colloidal silica particles which makes microfilled composites. Can be radioopaque composites made by incorporating particles of a high molecular weight like barium alumin silcate or strontium glass
-Resin composites classified according to the size of the ceramic filler particle
1) Fine-particle resin composites - contain ground glass or quartz. Occupy 60-77% by volume and 70-90% by weight since filler has a greater density than the polymer
2) Microfilled resin composites - Contain spherical colloidal silica particles. This greatly increases the viscosity of the polymer matrix. Filler loading is limited to 30-55 by volume and 35-60 by weight. Can also make a microfilled composite, grind it down to 10-20 microns and use it as a filler, increasing the filler content
3) Hybrid - Combination of colloial and fine particles as filler. Colloidal particle fill the matrix between fine particles and the filler content is 60-65% by volume. Hybrids dominate the market now.

-filler properties - the higher a filler volume the stronger the material will be. Fillers also give different optical properties, polishability, and usage (anterior esthetics vs. posterior teeth).
Microfilled are optically similar to enamel, highly polishable, and usually for non-stress bearing esthetic restorations.

Front 28

Fillers 2

Back 28

-fillers must be coated with a coupling agent to allow for bonding with the matrix. The coupling agent is a organic silicon, and the silane has reactive groups at both ends and coats the filler.
-During polymerization the silane DB react with the polymer matrix. The bond allows for distribution of stresses, higher strength, and reduced absorption of water
-Smaller fillers have better polishability
-Right now we use nanofillers - due to the small size they canbe polished more and blend shades better with natural tooth structure and create a better esthetic restoration. Also good for posteriors. Recommended...

Front 29

Components of a Composite Resin

Back 29

1) Polymer Matrix
-An aromatic or urethane diacrylate oligomer like (Bis-GMA) or urethane dimethacrylate
-Oligomers have a reactive DB at each end and undergo addition polymerization in the presence of free radicals
-They are highly viscous and require addition of low molecular weight diluent monomers so they can be workable clinically. Example of a filler is triethylene glycol dimethacrylate (TEGDMA)
2) Activator/Initiator
3) Coupling Agent
4) Inorganic Pigments - Inorganic oxide pigments are added to composites in small amount to provide a range of standard shades
5) Inhibitors - Lengthen the shelf life. Include butylated hydroxy toulene

Front 30

Activation and Initiation

Back 30

-Polymerization of composites initiated by chemical means (self cure) or by visible-light. Dual cure is a combination of the two
-Curing needs an initiator (catalyst) that causes the double bond to form in a accelerator
Chemical Self Cure - Organic peroxide is the initiator and the accelerator is a tertiary amine that produces the free radicals. The systems usually come as 2 pastes or a powder-liquid system that react when mixed. Set time is 3-5 minutes. Not used frequently these days due to shrinkage causing tooth-resin gaps
-Light Activated - The initiator is a diketone (camphorquinone) that is provoked to produce a free radical on a aliphatic amine when irradiated with blue light at 468nm
-Blue light causes a DB break in the camphorquinone leading to the unstable triple state that leads to more DB breaks
-Supplied as a single paste in a opaque/black container/syringe


Pros and Cons
Light Cure - Great esthetics, less porous, more working time. Also less complete cure and you need a curing light
Chemical Cure - OK esthetics, no curing light and a more complete cure. Disadvantage is more poorosity, less color stability, and less working time, and more shrinkage, and a high wear rate due to porosity

Front 31

Light Cured System

Back 31

-the initiator is usually hydroquinone which is best activated at 468nm but can be activated over a range. A number of light sources can be used to achieve this wavelength
-Halogen lamps are the most common and emit a large range of blue wavelength light
-Other lights have higher intensities for faster polymerization. These include plasma arc lamps and laser lights. Although more intense, these don't have the same range of halogen lamps so you have to be careful in matching the spectrum of light absorption characteristics of the initiator
-The best measure of effectiveness of a light/resin composite combination is the depth of cure that can be obtained within the specific material. Depth of cure makes sure both the surface and interior are properly cured all the way

Front 32

Comparing Different Composites

Back 32

1) Microhybrid or all purpose - Combination of microfillers and ultrafine glass particles. Offer both esthetics and enhanced wear resistance for use in all teeth. Filler size is .04 - .2, volume is 60-70%, and it gives high strength
2) Microfilled - Filler size .04, filler volume 32-50, best polish, esthetics, and high shrinkage
3) Package - Filler size .04, .2-20, volume is 59.80, and these are package, less shrinkage, lower wear
4) Flowable - Filler size is .04, .2-3, volume is 42-62, and these are syringable, lower strength, and higher wear
5) Laboratory - Filler volume is 60-70%. They give best anatomy, best contacts, lowest wear. Requires special equipment and resin coment to use so the cost is a little higher

Front 33

Impression Materials

Back 33

-there are many ways to take an impression. The low viscosity material syringed directly onto the teeth is great for detail. The heavier viscosity material put in the tray is great to support the light material. Putty is great for materials that shrink.

Single Mix - 1 material syringed onto the teeth and into a tray, followed by a tray on the teeth, and you get the impression. Putting the syringe on the teeth helps capture detail for a crown or class I inlay. This one material is viscous enough and is syringable

Double Mix - 2 materials, the light body material is syringed directly onto the teeth and the heavy body more viscous material is added to the tray and seated on the light body. The heavy body force the syringe material to adapt to the prepared tissues. The two materials bond together upon setting

Double Arch - Similar to double mix but both arches are captured

Disinfectants
-1% sodim hypochlorite, 2% glutaraldehyde, and iodophors

Front 34

Putty Wash

Back 34

Putty - The base and catalyst are kept separate and then mixed together using nitrile gloves because latex has sulfur which affects the putty. Putty wash is used for condensation silicone to minimize the effect of polymerization shrinkage on the dimensional change
-Essentially the putty is molded to a tray and put on the teeth. Next, the light body material is syringed into the putty tray and on the teeth and the final impression is made

-All impressions must be disinfected, some have a spray and some are put in bags with disinfectant

Front 35

Trays

Back 35

Stock Trays
-Can be plastic or metal (reusable)
-Can be molded for people with or without teeth
-You need to hold the material in the tray. Perforations help adhere the material to the tray. For trays without perforations, adhesives help hold the material to the tray. Adhesives are good for alginate, silicones, and polysulphides
-Metal trays can also be rim locked which helps hold the material in the tray

Custom Tray - Stock trays are universal, custom is patient specific. These are made from your first impression stock tray. The material is molded to the stock tray to give detail
-These can be acrylic (light or cold cured) or shellac (thermoplastic)
-If the tray is closed there is no space between the stock and custom. This is good for ZOE and impression wax
-If the tray is spaced then this is good for alginate, impression plaster, and elastomeric impression material

Front 36

Properties of an ideal impression material

Back 36

Big 4 ideal properties are accuracy, manipulation, biologic, and economic considerations

Accuracy - Not only is the tooth anatomy detail reproduced, but there is dimensional stability without any shrinkage
Elastic - Helps the impression material from cracking
Adherence to the impression tray - If it comes off the tray you must redo. Adhesi8ve improves accuracy of impressions, without adhesive the shrinkage pulls the material from the walls and you get a tight impression. Inadequate adhesion leads to dislodgement and distortion
Compatibility with die materials - The common dye is dye stone
-Standard for ADA is that the impression measures 25 microns in depth

Front 37

Ideal Properties 2

Back 37

Working Time - The amount of time before the material is no good for impressions. Measured at room temperature. Basically, amount of time you have to get it into the mouth

Setting Time - Longer than working time, amount of time until the material has completely set and is ready to be removed. Meausred from beginning to end

Shelf Life - Amount of time before the material has expired and is no longer good to use

Front 38

Ideal Properties 3

Back 38

Biologic
-The toxicity and discomfort is important to note.
Economic Considerations
-You have to take into account the initial cost of equipment, basically the cost to set everything up. Then you have to consider the cost of materials, how much it cost for each additional usage

Front 39

Classifying Impression Materials

Back 39

-it is based on the physical state of the set materials
1) Elastic - these can be aqeuous hydrocolloids (agar and alginate) and non aqueous (polysulfide, polyethers, silicones - addition and condensation)

2) Non-elastic - Include impression plaster, impression compound, ZOE, and impression wax. These are hardly used anymore

Can be classified based on their use in dentistry
1) Used for edentulous - all materials
2) Used for dentate - elastic materials

Can be classified on the mechanism of setting
1) Reversible physical change heating or cooling can switch states- compounds, waxes, and agar hydrocolloids
2) Irreversible chemical reaction can't get back to original once you start the process - alginate, impression plaster, ZOE, non-aqueous elastomers

Front 40

Non-Elastic Impression Materials - Impression Compound

Back 40

1) Types - Type 1 is preliminary impressions, peripheral seal materials, and copper tube impressions. Can be used for full-crown impressions and impressions of partially or completely edentulous jaws. Type 2 is tray material (not used anymore) to make a impression tray

2) Composition - Natural resins give the compound its thermoplastic character, 40% of the material. Shellacs also used. Waxes (7%) have thermoplastic properties, and stearic acid (3%) acts as a lubricant and plasticizer. Fillers like diatomaceous earth, talc, and soap stone) and inorganic pigments account for the rest. Shellac and steric acid added to improve plasticity and workability. The filler increases viscosity at temperatures above that of the mouth.

3) Manipulation - These are thermoplastic meaning they soften when heated and cool when hard. The higher the bulk the longer you must wait to heat and cool. Can soften using a direct flame or water bath. After this you knead to the shape desired, place in tray, and record impression. You must cool thoroughly (can use water spray) and then you must make the cast immediately. Because it is thermoplastic, it is a reversible physical process rather than a chemical one.
-Becuase their thermal conductivity is low they will heat or cool on the outside but not inside so you must really wait the full time before taking it out of the mouth.
-Because they have resins and waxes they have high thermal expansion and contraction so they should be poured immediately
-If you overheat the material you can burn the soft tissue, if cooling water is too cold you can cause thermal shock

4) Accuracy - not great because it is very viscous. To get optimal accuracy ensure complete softening and once in mouth make sure it is completely hard. Lose accuracy due to thermal contraction from mouth to room temp .3%.

Front 41

Impression Compound 2

Back 41

Biological Properties
-Can disinfect without distortion. Be careful of heat burn and thermal shock

Economic Considerations
-Very cheap but a temperature controlled water bath is needed

Advantage
-Compatible with die and cast materials
Disadvantage
Accuracy - Low flow and high thermal expansion/contraction
Non-elastic so they may distort after removal from mouth, should pour cast immediately

Front 42

ZOE Impression Material

Back 42

-rarely used anymore, comes as 2 pastes (black and white) and use stainless steel spatula to mix
-Good for dentures on edentulous ridges, wash impression over the compound in a tray or custom acrylic tray, and as a bite registration material.

1) Composition - One paste is the base/catalyst, and it has zinc oxide, oil, and rosin. The second paste is an accelerator with 12-15% eugenol, oils, rosin, and a filler like talc or koalin

2) Usgae -Zinc oxide, in the presence of moisture, reacts with eugenol to form zinc eugenolate which acts as a matrix holding together unreacted zinc oxide. The setting time is shortened by increasing temperature and/or humidity, so on hot humid days this isn't great to use.

3) Manipulation -The two pastes are mixed on a mixing pad with spatula for 30-40 seconds. You can speed setting with a drop of water and slow set by adding petroleum jelly

4) Properties - ZOE gives good accuracy of soft tissue due to low viscosity. It has minimal shrinkage during setting (.1%) due to dimensional stability. You can immerse in 60 degree water after it sets to remove it easily from the cast. Setting time is 2.5 - 6 minutes

Biologic Properties
-Eugenol is irritating to soft tissue and can cause burning sensation. Also, some people have eugenol allergies. Instead of eugenol you can use chlorothymol, carboxylic acids (lauric acid) and o-ethoxybenzoic acid. These avoid the burning sensation.

Advantages - Give good accuracy, inexpensive, adheres well to dental impression compound

Disadvantage - Messy, variable setting time due to temp and humidity, irritating to soft tissue. Also, the material is nonelastic and can fracture if undercuts present

Disinfectants - iodophors and glutaraldehydes