impression materials (dental)

Impression Materials

Dr. Md. Arifur Rahman Assistant Professor & Head

Dental UnitNortheast Medical College, Sylhet

E-mail: [email protected]

Impression Materials Impression : It is the negative

imprints of the natural teeth & their supporting tissue.

2Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC

Types of ImpressionA . Full mouth or full arch impression.1. For edentulous arch : a. Upper & Lower.b. Primary or initial. c. Secondary or final. 2. For dentulous arch : a. Upper. b. Lower.B. copper band or matrix band impression: It is used to take impression of a single tooth.C. Impression of a quadrant of the mouth (Sectional impression)D. Wash impression: It is done in the case of edentulous patient after taking primary impression. It can records more appropriate

3Dr. Md.Arifur Rahman, Asst. Professor

& Head of Dental Unit, NEMC

Impression Tray

The metallic or plastic carrier, which are use to take impression of natural teeth & their supporting oral tissues by the impression materials, are known as Impression Tray.



Types of Impression Tray : 1. Stock Tray:

a. Full tray : 1. Upper or lower. 2. metallic or nonmetallic. 3. Plane or perforated. 4. Rim lock. 5. Small, medium & large. 6. Special double chamber perforated with cooling arrangement. 7. Disposable. b. Half tray: 1. Upper or lower. 2 Metallic or non metallic. 3. Plane or perforated. 4. Disposable.c. Sectional tray: 1. Upper or lower. 2. Metallic or nonmetallic. 3. Plane or perforated. 4. Rim lock. 5. Disposable.

2. Individual or close fitting or Special tray or custom built tray or hand made tray : a. Upper or lower . b. Dental plastic. C Base plate. D. Impression compound. E. Plane or perforated. F. Disposable.

3. Copper band or matrix band tray: This tray is for taking the impression of a single tooth.

5

Impression materialsThe materials which are used to take impression of natural teeth and their supporting tissue they are called as Impression materials.

Classification of impression materials:According to the elasticity of the materials.

1 Non elastic : a. Rigid impression materials. Example- Plaster of Paris.b. Plastic impression materials: i. Thermoplastic impression materials. Example-Compo, Wax, Gutta-percha.

ii. Paste impression materials. Example-ZOEpaste im.



Classification of impressionmaterials:(Cont..)

2. Elastic : A. Hydrocolloid : 1. Reversible hydrocolloid (agar). 2. Irreversible hydrocolloid (alginate).B. Elastomer: a. Polysulphide. b. Silicones (1.Condensation Silicone. 2. Addition silicone.). c. Polyether.

According to the mode of setting (hardening) Set by chemical setting. Example:- Alginate, Elastomers. Set by physical setting. Example:- Agar, Wax, Compo.

7

Ideal Properties of Impression Materials

1. It should be nontoxic & non irritant.2. It should be elastic in nature.3. It should have good flow.4. Manipulation should be easy.5. It should be dimensionally stable after setting.6. It should be cheap and available.7. Setting should be less than 5 minutes.8. Its shelf life should be good.


8 Ideal requirements of Impression materials

(1) They should be fluid enough to adapt to oral tissues;

(2) They should be viscous enough to be contained in the tray that is seated in the mouth;

(3) While in the mouth, they should transform (set) into a rubbery or rigid solid in reasonable amount of time. Ideally the total setting time should be less than 7 minutes;

(4) The set impression should not distort or tear when removed from the mouth.



8 Ideal requirements of Impression materials

(5) The impressions made from these materials should remain dimensionally stable at least until the cast can be poured.

(6) The impression should maintain its dimensional stability after removal of a cast so that a second or third cast can be made from the same impression;

(7) The materials should be bio-compatible; and

(8) The materials, associated processing equipment and processing time should be cost-effective.



Thermoplastic impression materials

These are those materials which are when heated become soft and plastic again on cooling they become hard. Compo, Wax, Gutta-percha and zinc oxide eugenol paste these are the most commonly used thermoplastic impression materials



Properties They are thermoplastic in nature. It can use again and again. It is not hygienic. It is cheap and available . It does not have sufficient flow and may cause

internal compression.



Internal compression If we use thermoplastic / non elastic impression materials for taking impression , it has a limited flow. To make the materials flow we have to give an extra amount of pressure, which will compress the oral mucous membrane and it will set in this compress position. After preparation of model followed by any appliance, during supply the appliance will give same amount of constant pressure to the patient. This unwanted extra amount of pressure is known as Internal Compression.


Impression compound It is a non elastic type of

thermoplastic impression materials. Which has a limited uses in dentistry

now a days. It is only used to take primary impression of edentulous

patient.



Composition of impression compound Stearic acid -20 P/W ( It gives the plasticity and flow

to the compo) , Oleic acid-4 P/W ( It gives also plasticity and flow to

the compo) , Gum copal-19 P/W ( It gives the bulk to the compo it

also increase the hardness), Kauri resin-17 P/W ( It gives hardness to the compo) Powder soapstone or French Chalk -40 P/W ( It

gives hardness plasticity and hardness).



Properties of Impression compound

They are thermoplastic in nature.Advantages: 1. Can be reused, easy to use 2. Non-irritant and non-toxic 3.It is cheap and available .Disadvantages 1. Poor dimensional stability 2. Easy to distort when withdrawn from the

mouth 3. It don’t have sufficient flow and may

cause internal compression.16

Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC

Impression compound (Cont..) Types of compo : According to the fusing

temperature compo are of three types: (1) Low fusing (Type-I) : The compo which

become soft at 55-60C they are called low fusing compo. Uses: (a) To take primary impression of edentulous patient. (b) For making occlusal rim. (c) Making tampoon.

(2) High fusing (Type-II) : The compo which become soft at above 70C they are called high fusing compo. Uses: (a) Taking im for partial dentures with moderate undercuts. (b) For making special tray.

(3) Medium fusing (Type-III) : The compo which become soft at 60-70C they are called medium fusing compo. Uses: (a) To take primary impression of edentulous patient. (b) For making special tray. (c) Taking im for partial dentures with moderate undercuts

17

Impression compound (Cont..) According to the supplied form compo

are of three types: Sheet Form : Uses: (1) To take primary

impression of edentulous patient. (2) Tampon can be made for arrest of bleeding. (3) For making occlusal rim.(4) For making special tray.

Stick form : Uses: (1) It is used as a copper band impression materials.(2) Used for marginal addition of special tray, primary im.(3) To build up the post dam area. (4) Checked the undercut areas in the cavity.

Cone form: Uses: (1) Checked the undercut areas in the cavity (2) It is used as a copper band impression materials.(3) To build up the post dam area.



disadvantages of compound impression material while it is in

the mouth1. Its specific heat is low. So, it takes

more time to harden. 2. The impression because of gravity

may fall down. 3. It is viscid and it may not evenly

flow all over the tissues and tooth surface. So, fine details may not be recorded.



Clinician’s responsibility: 1. The clinicians should hold

impression tightly with tissues and tooth surface. The impression should be chilled with cool water inside mouth until it hardens.

2. The impression should be kept outside the mouth in the room temperature. As the dimensional stability of compo is less die/ model should be made as soon as possible after removal from mouth.



3. The compound has dimensional change. It has linear contraction of 1.5% when it is cooled from its mouth temperature to room temperature. So, the compound should be uniform and low thickness to reduce the contraction.



Hydrocolloid Impression Materials

Hydro means water. Colloid means gelatin

substance. Material used to obtain

preliminary and final impressions.



Irreversible Hydrocolloid

Material that cannot return to a solution state after it becomes a gel.

Alginate is the irreversible hydrocolloid most widely used for preliminary impressions.



Makeup of Alginate Potassium alginate (15% by wt)

Comes from seaweed; is also used in foods such as ice cream as a thickening agent. It soluble alginate

Calcium sulfate (16% by wt) Reacts with the potassium alginate to

form the gel. Sodium phosphate (2% by wt)

Added to slow down the reaction time for mixing.



Diatomaceous earth (60% by wt) A filler that adds bulk to the material.

Zinc oxide (4% by wt) Filler particles. Adds bulk to the

material. Potassium titanium fluoride 3%

Accelerator. Added so as not to interfere with the setting and surface strength.

Makeup of Alginate- cont’d



Physical Phases of Alginate

The first phase is a sol (as in solution). In the sol phase, the material is in a liquid or semiliquid form.

The second phase is a gel. In the gel phase, the material is semisolid, similar to a gelatin dessert.



Packaging and Storing of Alginate

Containers about the size of a coffee can are the most commonly used form of packaging.

Premeasured packages are more expensive, but save time by eliminating the need for measurement of the powder.

Shelf life of alginate is approximately 1 year.



Fig. 46-7 Examples of packaging for alginate.



Advantages of Alginate 1. It is cheap and easily available 2. It is easy to mix and manipulate 3. Elaborate arrangement does not

require 4. It is sufficiently elastic and

impression of moderate undercut area can be take.

5. Comfortable to the patient 6. It is hygienic 7. It gives good surface details 29


Disadvantages of Alginate

1. It can not be corrected if there is inaccuracy of the impression

2. It is elastic but not so adhesive. So, it should be held tightly against the tissue surface until it sets

3. On storage after impression it loses its dimension (it suffers from syneresis and imbibition).

4. Poor tear strength .



Causes for Distortion and Dimensional Change of

Alginate If an alginate impression is stored in

water or in a very wet paper towel, the alginate will absorb additional water and expand. This condition is called imbibitions.

If an alginate impression remains in the open air, moisture will evaporate from the material, causing it to shrink and distort. This condition is called syneresis.



Alginate Settings Normal set alginate

Working time of 2 minutes and a setting time of up to 41/2 minutes after mixing.

Fast set alginate Working time of 11/4 minutes and a

setting time of 1 to 2 minutes. Working time

The time allowed for mixing the alginate, loading the tray, and positioning the tray in the patient's mouth.

Setting time The time required for the chemical

action to be completed. 32


Altering the Setting Times of Alginate

Cooler water can increase the setting time if additional time is needed for the procedure.

Warmer water can reduce or shorten the setting time of the procedure.



Water-to-Powder Ratio An adult mandibular impression

generally requires two scoops of powder and two measures of water.

An adult maxillary impression generally requires three scoops of powder and three measures of water.



Fig. 46-8 Scoop and water measure for alginate.



Taking an Alginate Impression

Explain the procedure to the patient: The material will feel cold, there is no

unpleasant taste, and the material will set quickly.

Breathe deeply through your nose to help you relax and be more comfortable.

Use hand signals to communicate any discomfort.



An Acceptable Alginate Impression The impression tray is centered over the

central and lateral incisors. There is a complete "peripheral roll," which

includes all of the vestibular areas. The tray is not "overseated," which would

result in exposure of areas of the impression tray.

The impression is free from tears or voids. There is sharp anatomic detail of all teeth

and soft tissues. The retromolar area, lingual frenum,

tongue space, and mylohyoid ridge are reproduced in the mandibular impression.

The hard palate and tuberosities are recorded in the maxillary impression.

37

Fig. 46-12 An alginate impression.



composition of zinc oxide eugenol paste

Components Percentage Tube No. 1 (Base) Zinc oxide 87 Fixed vegetable or mineral oil 13 Tube No. 2 (Accelerator) Oil of cloves or eugenol 12 Gum or polymerized rosin 50 Filler(silica type) 20 Lanolin 03 Resinous balsam 10 Accelerator solution (CaCl2) and colour 05


Role of different ingradient

1. The vegetables or mineral oil acts as a plasticizer that aids in reducing irritating effect eugenol. 2. Oil of cloves: Use in preference to eugenol because it produces less burning sensation for patients when it comes in contact with soft tissues. 3. Rosin: It facilitates the speed of reaction and yields a smoother, more homogenous product. 5. Filler (wax) or an inert powder (such as kaolin, talc or diatomaceous earth). They are added to provide strength and smoothness.



Give the composition agar and its effects

Agar Brush-sheap structure 13-17Borate Strength 0.2-0.Sulfate Gypsum hardener 1.0-2.Wax, hard Filler 0.5-1.0 Thixotropic materials Thickener 0.3-0.5 Water Reaction medium Balance



Role of different ingredients

Agar : is an organic hydrophilic colloid extracted from certain types of seaweed. Water : It is the principle ingredient. Borax : Borax in small percentage. It strengthens the gel. Potassium sulfate : Acts as an accelerator. It is added to counter act the retarding effect of borax. Diatomaceous earth, clay, silica, wax, rubber and similar inert powder acts as filler to control strength, viscosity and rigidity. Thymol and glycerine : These are added to act as a bacteriocidal agent and plasticizer. Pigment and flavor are also included.


Properties of Agar• Accuracy: Fine detail of the tissues and prepared

tooth can be recorded. • Impression of the undercut areas can be taken. • It also suffers from shrinkage and imbibitions • Compatible with stone because of the presence of

counter part of Borax (K2SO4) • Non-toxic, non-irritant • Can be re-used • Can be sterilized • Manipulation is not so easy • Best material for duplication of the model • Cheap


Differentiate reversible and irreversible hydrocolloids.

44

Differentiate reversible and irreversible

hydrocolloids. (con.)



ElastomersThese are used where a high degree of accuracy is needed, especially in crown and bridge work. They have two main advantages over the Hydrocolloids - good tear resistance and dimensional stability. They are mainly hydrophobic rubber based materials. All of these materials come in different viscosity's ranging from low to high viscosity. The light bodied material maybe used as a wash impression over a medium or heavy-bodied material.


Elastomers

Silicone

Condensation

Addition

Polysulphide

Polyether


PolysulphidesUsed for crown and bridge work mainly, but

also used for partial dentures, and implants. Two equal lengths are mixed together with a spatula for about a minute. The tray needs to be treated with an adhesive (rubber solution in acetone) to provide retention for the polysulphide. Taking the impression is delayed by 5 minutes before the impression is placed in the patients mouth - the final setting time is usually about 10 minutes from the start of mixing - this delay therefore decreases the amount of time the impression tray is in the patients mouth. A one or two stage impression technique may be used. Although dimensionally stable, the impression should be cast within 24 hours.


CompositionSupplied as two pastes mixed in a 1:1 ratio.BASE PASTEPolysulphide (forms rubber on

polymerization)Filler (to give body)Plasticizer (control viscosity)ACTIVATOR PASTEInert oil (forms a paste)Sulphur (facilitates the reaction)Lead oxide (causes polymerization and cross-

linking)49Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC

PROPERTIES of Polysulphides

Dimensionally stable. Excellent surface detail Viscosity depends on the brand used Very small setting contraction (0.3-

0.4% over the first 24 hrs) Very good tear resistance Good shelf life



PolysulphideADVANTAGES Dimensional stable. Accuracy Comes in a number of different viscosity's Long working time (although this may be a

disadvantage in some clinical situations) Long shelf lifeDISADVANTAGES Lead oxide in base paste may have toxic effects Staining of clothes due to the Lead oxide Messy to work with - unpleasant rubbery smell Can only be used in a special tray.


PolyetherSupplied in two pastesBASE PASTEPolyetherFillerCATALYST PASTESulphonic acid ester (enhances further

polymerization and crosslinking) ,Inert oils (forms a paste)When mixed the polymer and sulphonic acid

ester react to form a stiff polether rubber. Setting time occurs in about 6 minutes.


PROPERTIES of Polyether

Hydrophilic (i.e. absorbs water) Good shelf life of up to 2 years Good elastic recovery Non toxic Low setting contraction Poor tear strength Excellent surface detail Good dimensional stability



PolyetherADVANTAGESAccuracyGood on undercutsEase of useDISADVANTAGESMay cause allergic reaction due to the

sulphonic acid esterPoor tear strengthRapid setting time (ie short working time)Stiff set material (sometimes hard to

remove from mouth) 54Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC

Condensation SiliconesCLINICALLY Used for crown and

bridge work mainly, but also for partial dentures, implants and over dentures. Used in stock trays or special trays. One or two stage impression stage. Although dimensionally stable the impression should be cast within 24 hours.



Condensation SiliconesSupplied as a paste and liquid or two

pastes, in light, medium, heavy or very heavy bodied (putty).

BASE PASTESilicone polymer with terminal hydroxy

groupsFillerCATALYST PASTECrosslinking agent (organohydrogen

siloxane)Activator (dibutyl-tin dilaurate)On mixing the two pastes react, cross

linking occurs and setting takes about 7 minutes.


Condensation SiliconesPROPERTIES Hydrophobic Hydrogen gas

evolution on setting Moderate shelf life Moderate tear strength Good surface detail Shrinking of

impression over time Non toxic and non

irritant Very elastic (near

ideal)

ADVANTAGESAccurateEase of useCan be used on severe

undercutsDISADVANTAGESHydrogen evolutionLiquid component of

paste/liquid system may cause irritation


Addition SiliconesCHEMISTRY

Supplied in 2 pastes or in a gun and cartridge form as light, medium, heavy and very heavy bodied.One paste contains a poly dimethyl siloxane polymer in which some methyl groups are replaced by hydrogen. The other paste contains a pre-polymer in which some methyl groups are replaced by vinyl groups, this paste also contains a Chloroplatinic acid catalyst.On mixing, in equal proportions, cross linking occurs to form a silicone rubber. Setting occurs in about 6-8 minutes.


Addition SiliconesPROPERTIES Good shelf life Dimensionally stable Moderate tear strength Excellent surface detail No gas evolution Non toxic and non irritant



Addition SiliconesADVANTAGESAccurateEase of useFast settingWide range of

viscosity's

DISADVANTAGESHard to mixSometimes difficult to

remove the impression from the mouth



Thank you


impression materials (dental)

Health & Medicine