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Impression Materials Dr. Md. Arifur Rahman Assistant Professor & Head Dental 1

Impression Materials (Dental)

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Impression Materials.

Impression MaterialsDr. Md. Arifur Rahman Assistant Professor & Head Dental UnitNortheast Medical College, SylhetE-mail: [email protected]

Impression MaterialsImpression : 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 TrayThe 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.

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Ideal Properties of Impression Materials1. 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 materialsThese 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 materials11Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC

PropertiesThey 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 compoundStearic 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 compoundThey 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 dont have sufficient flow and may cause internal compression.16Dr. 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

Clinicians 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 MaterialsHydro 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 AlginatePotassium 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- contd25Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC

Physical Phases of AlginateThe 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 AlginateContainers 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 29Dr. 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 AlginateIf 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 SettingsNormal set alginateWorking time of 2 minutes and a setting time of up to 41/2 minutes after mixing. Fast set alginateWorking time of 11/4 minutes and a setting time of 1 to 2 minutes. Working timeThe 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. 32Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC

Altering the Setting Times of AlginateCooler 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 ImpressionExplain 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 pasteComponents 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 ingradient1. 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 effectsAgar 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 AgarAccuracy: 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.

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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

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 PolysulphidesDimensionally stable. Excellent surface detail Viscosity depends on the brand usedVery small setting contraction (0.3-0.4% over the first 24 hrs)Very good tear resistanceGood shelf life50Dr. Md.Arifur Rahman, Asst. Professor & Head of Dental Unit, NEMC

PolysulphideADVANTAGESDimensional stable. AccuracyComes in a number of different viscosity'sLong working time (although this may be a disadvantage in some clinical situations)Long shelf lifeDISADVANTAGESLead oxide in base paste may have toxic effectsStaining of clothes due to the Lead oxideMessy to work with - unpleasant rubbery smellCan 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 PolyetherHydrophilic (i.e. absorbs water)Good shelf life of up to 2 yearsGood elastic recoveryNon toxicLow setting contractionPoor tear strengthExcellent surface detailGood dimensional stability53Dr. 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 SiliconesPROPERTIESHydrophobicHydrogen gas evolution on settingModerate shelf lifeModerate tear strengthGood surface detailShrinking of impression over timeNon toxic and non irritantVery 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 SiliconesCHEMISTRYSupplied 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 SiliconesPROPERTIESGood shelf lifeDimensionally stableModerate tear strengthExcellent surface detailNo gas evolutionNon 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