Final Impression Materials

DLA 1201, exam 6

1. Final Impression Materials Chapter 15

2. Impression Material Used primarily to reproduce the form of the teeth in a negative reproduction This includes existing restorations, hard and soft tissues, and preparations Also used to fabricate prostheses and other oral devices 2

3. Impression Material Making impressions of oral structures is an almost everyday occurrence in a busy dental practice. Selection of the impression material will be influenced by what the impression will be used for. Typically , a material must be in a moldable or plastic state that can adapt to the teeth and tissues. 3

4. Types of Impressions Dental impressions can be categorized into three basic types based on how they will be used: Preliminary impressions Final impressions Bite registration (occlusal) impressions 4

5. Types of impressions Preliminary impressions are made as precursor to other treatment. Final impressions are more accurate in their replication of the oral structures. They are used to make final restorations, such as crowns, bridges, partials, and complete dentures. Bite registration is a replication of the patient’s bite and is used to establish the proper relation between a restoration or prosthesis and the opposing teeth. 5

6. Types of Impression Materials Two major groups: Elastic materials Inelastic materials 6

7. Types of Impression Materials Elastic impression materials include the hydrocolloids (agar and alginate), polysulfides , silicone rubber materials, polyethers, and a hybrid of polyether and polyvinyl siloxane. Inelastic materials are the older impression materials and include dental compound, impression plaster, zinc oxide eugenol , and impression wax. 7

8. Key Properties The key properties of impression materials are their accuracy, tear resistance, and dimensional stability. When the impression is made, the impression material must closely adapt and flow over the surface of the tooth preparation and tissues to record the minute details in order to be accurate . After the impression material sets, it must have good tear resistance to prevent tearing during removal from the mouth. After the impression is removed, the set material must remain dimensionally stable. 8

9. Elastomers Four types of elastomers: Polysulfides Polyethers Condensation silicones Addition silicones (polyvinyl siloxane) 9

10. Elastomers The two most widely used elastomers are polyvinyl siloxane (PVS) and polyether. More recently, a hybrid material, vinyl polyether, has been introduced that combines the best properties of polyethers and polyvinyl siloxane.

11. Elastomers They are not water based, so they are not as sensitive as the hydrocolloids to water loss or imbibition (water uptake) Shelf life is ~12-18 months Storage in refrigerator to lengthen shelf life

12. Adhesives Elastomers do not adhere well to metal or custom acrylic impression trays. An adhesive is placed in the tray to prevent the material from separating from the tray and causing distortion. Each type of elastomer has its won adhesive with which it is compatible. Therefore, adhesives should not be interchanged among different types of materials. Tray adhesive should be placed in a thin layer and allowed to dry If it is not applied in advance to allow drying, use an AW syringe to dry faster.

13. Elastomers Elastomers are highly accurate elastic impression materials that have qualities similar to rubber and are often called rubber materials . Because of their rubbery nature, elastomers have a certain amount of elastic recovery or rebound from deformation. Rebound reduces distortion in the cast that is poured from the impression PVS has the best elastic recovery of the elastomers 13

14. Wettability Elastomers generally are not wet well by water, and are therefore referred to as hydrophobic, because the water forms a high contact angle with them. In other words, water beads on their surface much like raindrops on a newly waxed car. Of the elastomers, the polyethers are the most hydrophilic, or wettable . Wettability can be seen clinically when impression materials are able to capture the detail of the tooth preparation when the surface is moist (but not submerged in water or saliva). It also means that gypsum materials will flow better into the fine details of the prep when the impression is poured.

15. Elastomers- Polysulfides Polysulfides are the oldest of the elastomers; they are more dimensionally stable and have greater tear strength than alginate or agar hydrocolloids . More dimensionally stable and have greater tear strength than alginate or agar hydrocolloids. More accurate than alginate, but not as accurate as other elastomers. Have been used successfully for crown and bridge impressions and for partial and complete denture impressions. Cannot be used in an automix , must be hand mixed Messy, and have an unpleasant sulfur odor. Still used by some practitioners for complete dentures, but not really used much since PVS and polyethers. 15

16. Silicone Rubber Impression Materials Two types of silicone impression materials have been developed and are named according to the type of the polymerization reaction they undergo during setting. Condensation silicones were introduced in the 1960’s and were useful for crown and bridge procedures. Addition silicone in the form of polyvinyl siloxane was introduced in the late 1970’s and because of its superior properties, it soon replaced condensation silicone.

17. Addition Silicone Properties provide greater dimensional stability and accuracy. They are clean and easy to use, with no foul odor or taste. As a result of these improvements, they have become the most popular materials for crown and bridge procedures. Most expensive of the impression materials.

18. Polyvinyl siloxane (PVS) AKA vinyl Polysiloxane Addition silicone Smallest dimensional change on setting High elasti c recovery after removal Resist tearing (high tear strength Cannot be poured until at least 2 hours after set due to hydrogen being released Will cause porous surface

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20. PVS Can be poured in stone several times Dimensionally stable for at least a week without distortion. Exhibits little flow (deformation when subjected to load after setting) This accounts for their accuracy even after repouring .

21. Polyvinyl siloxane Polyvinyl siloxane (PVS) materials are hydrophobic by nature and must be used in a dry field . Little moisture on prepped tooth will result in the loss of surface detail PVS is manufactured in light, extra light, regular (monophase), and heavy viscosities . Materials come in an assortment of fast to regular set materials. https :// www.youtube.com/watch?feature=player_detailpage&v=MgdHWSUb2UA 21

22. “hydrophilic” nature of some Some materials are called “hydrophilic” but in actuality they are hydrophobic materials that a wetting agent, a soap like surfactant has been added, so that it can tolerate the presence of a small amount of moisture. In a newly placed impression, it takes several seconds for the surfactant to move to the surface. Initially, the material Is not hydrophilic when it first contacts the teeth and tissues, but becomes more moisture tolerant as the surfactant rises to the surface. This delay in the emergence of the surfactant means that the preparation needs to be dry when the wash material is placed. However, the set impression will be more receptive to pouring with die stone.

23. PVS The accuracy of an impression material is measured by how well it captures the surface detail of a structure. To capture the detail, it must wet (have low contact angle) and flow over the surface well. Low-viscosity materials (wash/syringe) wet and flow better than high-viscosity (tray/heavy body), therefore capture more detail. Two-chamber cartridge is the most popular dispensing system A mixing tip fits over the end, and a hand-operated gun-type dispenser pushes out the base and catalyst through the mixing tip at the same time.

24. Clinical Tip Before placing the mixing tip onto the syringe, extrude a little to ensure no blockages from set material. Also extrude the first inch of the mixed material, to ensure homogeneous mixing throughout.

25. Polyvinyl siloxane (PVS) Examix - yellow- heavy body Automix - pink- light body Final impression material for crown and bridges Has smallest dimensional change High elastic recovery with removal form from undercuts Mixing time is 30-45 seconds for syringe Mixing time is 45-60 seconds for tray 4-6 minutes vinyl polysiloxane 25

26. PVS Putty/Wash Techniques Some like to use putty for the tray material, and a light body wash material to syringe around the prepared tooth. They feel that with subgingival margins on the preparations, the stiff putty causes a hydraulic pressure that forces the wash material into the gingival sulcus to better capture the margins in the impression. There are two techniques. One-step technique Two-step technique

27. One-step Putty is mixed and loaded into the tray by the assistant, while the operator injects the syringe material around the prepared tooth. An indentation should be made in the putty in the area of the prep to allow wash material to cover the prep without being displaced by the putty The tray is seated while the putty and syringe material are still unset, allowing them to bond together.

28. Two-step Putty is used to create a custom tray within a stock tray. In the first step, the putty is mixed and placed in the stock tray. It is seated over the teeth with a plastic sheet placed between the putty and the teeth to create room for light body material. Some prefer to cut away some of the putty after it has set to create space for the light body material, rather than using the plastic sheet. In the second step, light body is syringed around the prepped teeth, and some is injected into the space in the putty created by the teeth. The tray with the putty is seated over the teeth. The putty should NOT show through the wash material. Show-through areas are pressure spots where the preparation hit the putty. The putty will compress while the tray is in the mouth, and then rebound after the tray is removed. This will cause distortion in the impression.

29. Polyvinyl siloxane Paint tray with adhesive Lubricate the plunger of syringe Dispense equal lengths of catalyst and base Place syringe material on one pad, and the tray material on the other Use stiff bladed spatula to pick up catalyst and incorporate into base Load syringe by wiping barrel across the material on the mixing pad, wipe excess Pass loaded syringe to operator While operator injects, mix the tray material and load tray Receive the syringe from operator and pass loaded tray Set timer https:// www.youtube.com/watch?feature=player_detailpage&v=0RjUBTF8RJ0 29

30. Clinical Tip PVS putty should NOT be mixed while latex gloves are worn. Sulfur products from the gloves can interfere with the material. Washed hands, covered with vinyl gloves should be worn.

31. Polyether Polyethers Hydrophilic nature: Good wetting properties for making detailed impressions in presence of small amount of moisture 31 Pentamix; 3M ESPE.

32. Polyether Polyethers are very accurate materials with good flow and tear strength and are excellent for use in crown and bridge procedures. They are more hydrophilic than PVS. They do not release hydrogen gas, so they can be poured immediately. They have excellent mechanical properties with good elastic recovery, and they do not shrink. Originally a very stiff material but newer formulas have made the material more flexible. 32

33. Polyether With all elastomers, undercuts around bridge pontics, open embrasures around periodontally involved teeth, and fixed implant fixtures should be blocked out with utility wax,. This will prevent the impression material from flowing under them and locking the impression tray in the mouth. It is a very unpleasant experience for both the patient and the assistant to have locked-in impression trays cut with burs to remove them from the mouth.

34. Before taking a polyether impression… 34

35. Polyether Polyethers are supplied as light, medium and heavy body viscosities. Regular set materials have a working time of 2 to 3 minutes and setting time of 5 to 6 minutes. Fast set materials have a working time of 1 minute and a setting time of 4 minutes. https:// www.youtube.com/watch?feature=player_detailpage&v=RpKXYWTEXKg 35

36. Polyether Mixing time- 30-45 seconds Setting time- 5-7 minutes Paint tray with adhesive Lubricate plunger of syringe Equal lengths of catalyst and base Mix syringe material on one pad, and tray material on another (need two pads and two spatulas) Load syringe and pass to operator Mix tray material and load tray Receive syringe and transfer tray Set timer 36

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38. Polyether Impressions from this material can be poured up repeatedly for up to a week and can be shipped to a dental laboratory and remain dimensionally stable for up to 14 days if properly stored. 38

39. Pentamix https:// www.youtube.com/watch?feature=player_detailpage&v=z20Yk1O68bk https:// www.youtube.com/watch?feature=player_detailpage&v=bxowdm6Nn4Q 39

40. Impression Material Cost Surface Detail Dimensional Stability Tear Strength Ease of Use Pour Within Ability to Re-pour Alginate Low Lowest Low Low High 1 hour No Addition Silicone (PVS) High High Highest Medium High 1 week Yes Polyether High High High Low to medium High 1 week yes

41. Suggested Homework Review information on chapter 15 at https:// evolve.elsevier.com/cs/product/9781455773886?role=student