Impression Materials (Dental)
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Transcript of 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.
4Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
6Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
8Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC
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.
9Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
10Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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
11Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
12Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
13Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC
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.
14Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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).
15Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
18Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
19Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
20Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
21Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
Hydrocolloid Impression Materials
Hydro means water. Colloid means gelatin
substance. Material used to obtain
preliminary and final impressions.
22Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
23Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
24Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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
25Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
26Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
27Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
Fig. 46-7 Examples of packaging for alginate.
28Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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
Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC
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 .
30Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
31Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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
Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC
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.
33Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
34Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
Fig. 46-8 Scoop and water measure for alginate.
35Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
36Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
38Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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
39Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC
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.
40Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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
41Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
42Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC
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
43Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC
Differentiate reversible and irreversible hydrocolloids.
44
Differentiate reversible and irreversible
hydrocolloids. (con.)
45Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
46Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC
Elastomers
Silicone
Condensation
Addition
Polysulphide
Polyether
47Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC
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.
48Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC
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
50Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
51Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC
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.
52Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC
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
53Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
55Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
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.
56Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC
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
57Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC
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.
58Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC
Addition SiliconesPROPERTIES Good shelf life Dimensionally stable Moderate tear strength Excellent surface detail No gas evolution Non toxic and non irritant
59Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
Addition SiliconesADVANTAGESAccurateEase of useFast settingWide range of
viscosity's
DISADVANTAGESHard to mixSometimes difficult to
remove the impression from the mouth
60Dr. Md.Arifur Rahman, Asst. Professor
& Head of Dental Unit, NEMC
Thank you
61Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC