Impression Materials (Dental)

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Impression Materials.

Impression MaterialsDr. Md. Arifur Rahman Assistant Professor & Head Dental UnitNortheast Medical College, SylhetE-mail: arahman@neub.edu.bd1

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 hydrocol