Primary impression

impression is negative likeness or copy in reverce of the surface of and object.
in dentistry impression making very important

1. Primary impression 1

2. Definations ; Impression: A negative likeness or copy in reverse of the surface of an object. Primary impression: A primary impression is an impression made for the purpose of diagnosis or for the construction of tray. 2

3. Objectives of impression making; Preservation of residual alveolar ridge. Retention aEsthetics press Stability Support 3

4. Preservation of residual alveolar ridge “its important to preserve what already exists than to replace what is missing”_ devan Hence while making impressions , one should keep in mind to reduce soft tissue abuse, minimize bone resorbtion and to cover maximum support areas. 4

5. Retention Retention to denture is the resistance to the forces acting in vertical directiom . Factors responssible for retention Adhession Cohesion Interfacial surface tension Peripheral seal Atomospheric pressure Oral and facial musculature 5

6. Aesthetics During impression making , eshthetics is achieved by Adequate support for the lips and cheeks during border moulding of labial and buccal borders 6

7. Stability Stability is ability of the denture to be firm , steady and constant and the resistance of the denture to forcces acting in a lateral or horizontal direction. 7 7

8. Support Support is the ability of the denture to resist vertical and other forces in a direction towards the basal seat. The support of denture is achieved by wider coverage of the maxillary and mandibular support areas,like Ant. And post. Ridges and slopes within limitations Horizontal surface of hard palate Buccal shelf 8 8

9. Selection of tray Requirements of tray Rigid Diamentionally stable Should provide space for impression material Smooth borders Borders should easy to trim 9 9

10. Types of tray based on purpose or use; Prefabricated tray / stock tray Custom tray/ individualized tray Sectional tray Triple tray 10 10

11. Sectional tray Triple tray Custom tray Stock tray 11 11

12. Stock tray Edentulous – 1. perforated tray 2. non perforated tray Dentulous tray 12 12

13. Types of tray Based on material; 1. Plastic tray 2. Resin heat cure resin cold cure resin 3. Shallac base plate 4. metalic 13 13

14. selection of material Alginate is prefered material used for primary impression But impression compound is also used. A heavy consistancy alginate should be used to record ridge anatomy. For alginate- 2-3mm gap bet’ tray and tissue For impression compound- 5-6 mm gap 14 14

15. alginate When a alginate is mixed with water, a sol is formed which later sets to gel by chemical reaction. However the reaction is too fast , there is not enough working time , so a reaction is delayed by addition of a retarder i.e. sodium phosphate 15 15

16. Advantages Moist field application Clean and pleasant Long shelf life Low cost Disadvantages Can not be corrected Poor tear strength Can retard setting of gypsum Not accurate 16 16

17. Laminate technique It is combined agar-alginate technique. Agar in syringe applied on the areas to be recorded, impression tray is containing alginate. Since its agar and not alginate which is in contact to teeth maximal accurations can be obtained. Diamentionally inaccuracy of alginate limits its single use 17 17

18. Impression compound Its is mucocompressive thermoplastic and rigid impression material. Two types of impression material Type 1= low fusing (impression compound) Type 2= high fusing ( tray compound) Type 1 used for recording impression edentulous . 18 18

19. Compound softened in water bath kneaded with finger to improve qualities. Temperature of water bath 55-60 degree celcius is ideal for 4-5 mins to ensure complete softening Gauze is placed to prevent adherence Soften by heat , inserted in an impression tray and placed against tissue before it cools to rigid mass. 19 19

20. Maxillary impression 20 20

21. Maxillary impression Patient is seated in upright position Gravity affects the position of oral tissuesw . If reclining position is used , then there is denger of impression material flowing down the palate , causing discomfort or gagging, which can hamper impression procedure. Gagging is mostly controlled by upright position. The operator stand behind and to the right of the patient. 21 21

22. Mandibular impression 22 22

23. Mandibular impression The mandibular impression also made with upright position. Unlike maxillary impression ,the operator stands infront and right side of the patient. 23 23

24. Types of impression Based on purpose of impression: Primary impression/ diagnostic impression; for purpose of diagonosis and treatment planing an impression of edentulous arch is used to make cast for the fabrication of the custom tray or individualized tray. alginate impression material or impression coumpound in a stock tray for making priliminary impression 24 24

25. Based on purpose Master/ final impression for purpose of fabrication of prosthesis an impression that represent the completion of the registration of the surface or objects Elestomeric impression material or zinc oxide eugenol impression material is used for making final impression using a custam tray or individualized tray. 25 25

26. Based on theories of impression making Impression technique are based on the amount of pressure applied during making of impression Mucocompressive theory Mucostatic theory Selective pressure theory 26

27. Mucocompressive theory The tissues of the oral cavity are recorded in the functional position. Impression is recordedwhen pressure is applied on the stress bearing and non-stress bearing areas causing maximum tissue displacement. Impression with high viscosity like impression compound is prefered 27

28. Mucostatic impression therory The tissues are recorded in rest position. Pressure applied is very minimal. There is no displaceability of tissue. Impression material with low viscosity is prefered like alginate 28

29. Selective pressure theory Employs both mucostatic and mucocompressive technique. Pressure is applied on stress bearing areas and less pressure is applied on non-stress bearing areas. This achieved by using custam tray with spacer wax. 29

30. Thank you! 30