Impression Materials in Dentistry - Definition, Classification, and Uses

1. Good Morning

2. Prof. Dr. Manal A. El Ebiary Dental Bio- Materials Department Faculty of Dentistry Tanta & MUST Universities

3. Impression Materials

4. Definition • substances used for recording the form and dimensions of the oral tissues • They are used to record a negative replica to teeth and/or supporting tissues

5. Material is introduced in the mouth in a plastic condition to set against the oral tissues. It is then removed from the mouth when hardened. 2 3 1 4 6 5

6. The set impression is a negative reproduction of the oral tissues. A positive reproduction is obtained by pouring a suitable model or die material into it.

8. 1. Accuracy: a restoration or an appliance fabricated in the laboratory cannot be more accurate than the impression from which the used model is prepared.

9. 2. Biologically acceptable: • non-toxic • non-irritant • acceptable odor and taste.

10. 3.It should not be affected by the oral fluids. • 4. Easily manipulated, with minimal equipment. • 5. It should have a suitable working time to allow for placement of the impression material in the tray and then insertion of the tray into the mouth before beginning of hardening

11. Accuracy of the impression materials

12. 1- High flow at the beginning, i.e. the material must be in a fluid or plastic state on insertion into the mouth, to record fine details. 2.Dimensionally accurate:should not expand, contract or warpduring setting. 3.Dimensionally stable: on storage of the impression in the dental laboratory before pouring the cast

13. 4. Should be elastic on removal from the mouth so that undercuts can be recorded without distortion of the impression. 5. During removal from the mouth, it should be adherent to the tray. 6.Compatible with the gypsum products: not need a separating medium.

14. Classification of Impression Materials

15. I-According to manner of setting 1) Chemical (irreversible): • plaster impression, • zinc oxide eugenol, • alginate • rubber base 2) Physical (reversible): • agar agar, • impression compound • impression waxes.

16. II- Behavior after setting

17. Depending on their ability to regain their original shape after removal from the undercuts. • 1. Inelastic • wax • Plaster of Paris, • ZnO/eugenol and • impression compound. • 2. Elastic • hydrocolloids and • rubber impression materials.

18. Impression Materials Inelastic Elastic Plaster of Impression Zinc oxide Paris compound eugenol Hydrocolloids Elastomers Agar Agar Alginate Polysulphide Silicones Polyether Condensation Addition

19. III- According to uses Edetulous Patient Partialy edentulous patient Plaster, impression compound and Zinc oxide and eugenol, hydocolloids, rubbers Hydocolloids, rubbers

21. According to the Accuracy 1ry Impression (stock tray) 2ry Impression (special tray) Compound impression material Plaster impression material Zinc oxide/eugenol impression material Alginate impression material Agar Agar impression material Rubbers impression materials

22. Plaster of Paris powder Water

23. 1-  - CaSO4.1/2H2O; notα and/or improved stone • Weaker: So it will break during removal from the undercut and thus avoids injury to the patient and the fractured part can be reassembled accurately. • Higher W/P ratio, which increases the flow at the beginning and thus records fine details. • Less exothermic heat evolved during taking of the impression.

24. 2. Modifiers: ** 4% K2SO4decreases the setting expansion and the setting time → ** 1% boraxas a retarder

25. 3. Natural gums: Improve its handling characteristics. They increase its cohesion and facilitate border molding of the impression. 4. Flavoring agent: More acceptable to the patient, through agreeable taste.

26. 5. Coloring materials: Distinguish the impression from the cast, which will also be made of gypsum products. 6. Potato starch: To obtain the soluble plaster. After the impression is cast and hardened, it is soaked in hot water and the starch swells and the impression disintegrates and will be easy to remove.

27. Accuracy of plaster impression : a. Material is semi-fluid when inserted into the mouth it has excellent recording of the fine details. b. The dimensional changes on setting in the mouth are negligible due to anti-expansion additives.

28. c. A plaster impression fractures on removal from undercuts and can be reassembled. e.Elasticity:Being inelastic, it will not record the form of the under cut. • separating medium should be used The use of a separating medium is considered a disadvantage since fine details might be obliterated.

29. Impression Compound Non elastic impression materials Assoc. Prof. Dr. Manal

30. Type (I) Low fusing Impression Compound Prof. Dr. Manal A. El-Ebiary

31. Type ( II) high fusing Impression Compound Prof. Dr. Manal A. El-Ebiary

32. Application: 1. Full jaws impression in edentulous mouth. 2. Impression trays 3. Peripheral seal materials. 4. Single impression with copper band for inlays and crowns.

34. Composition Filler Thermo- plastic plasticizer Impression Compound Prof. Dr. Manal A. El-Ebiary

35. Thermoplastic material:e.g. Natural resins and waxes. They soften by heating and give the qualities of flow and cohesion. 2. Fillers:e.g. Talc, soapstone or diatomaceous earth. They add body and give a suitable working consistency. 3. Plasticizers:e.g. Stearic acid or stearin. These act as lubricants and together with fillers control the flow and consistency of the material. 4. Coloring agents:e.g. Rouge. It produces characteristic reddish brown color most commonly used. Black and green colors are also available.

36. Types Low fusing High fusing

37. Type (I ) low fusing compound

38. A- For recording prosthetic impressions: Such as preliminary impressions of edentulous patients, supplied in sheets about 4-5 mm thick. B- Peripheral seal materials. C- copper band impression for inlay and crown

40. Type (II) high fusing compound • Used as tray materials, which are sufficiently rigid to support other impression materials (wash impression).

41. Properties

42. Accuracy Flow Dimensional stability

43. not sufficiently fluid to record all the fine details. • Type (I) materials is 85% at 45ºC but less than 65 at 37ºC, • Type (II) materials is 70% at 45ºC but less than 2% at 37ºC.

44. Causes of dimensional changes:- 1- High coefficient of thermal expansion. 2- shrinkage occurs on cooling from high temp. to mouth temp.. 3- Shrinkage occurs on cooling from mouth to room temperature (0.3-0.4%). Heating the surface of the set material in a flame and remaking the impression minimizes the actual magnitude of the contraction.

45. 4-Distortion:- Stresses can be set up within the material, subsequently distortion can occur during storage of an impression due to relief' of these stresses. Then the impression should cast within an hour. 5- The material is non-elastic the most serious drawback of this material is that it drags and distorts when being removed from an undercut area.

46. compatible with model and die materials and do not need a separating medium. • Conductivity: Compound has poor thermal conductivity Time must be allowed during either heating or cooling to allow the dental compound to come to a uniform temperature.

47. These impression can be removed from the mouth, re-softened and reinserted for any corrections required.. • Accept additions to the impression • Can be electroplated with copper.

48. Zinc oxide eugenol Zinc oxide eugenol impression Prof. Dr. Manal A. El-Ebiary

49. Zinc oxide eugenol impression Prof. Dr. Manal A. El-Ebiary

50. One paste called the base paste • Zinc oxide 80%. • Inert oil 15% to form a paste. • Hydrogenated resin.