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Impression Materials
- 1. Impression Materials KEY TERMS IMPRESSIONTRAYS HYDROCOLLOIDS CRITERIA FOR CLINICALLY ACCEPTABLE IMPRESSIONS ALGINATE IMPRESSIONS DISINFECTION
- 2. Overview Used primarilyto 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 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.
- 4. Types of modelsmade from impressions Diagnostic casts Study models Die: when an impression is made of a tooth that has already been prepared for a restoration Used for the fabrication of the restoration in the dental laboratory Allows the dentist or lab tech to perform procedure by the indirect technique.
- 5. Types of Impressions Dentalimpressions can be categorized into three basic types based on how they will be used: 1. Preliminary impressions 2. Final impressions 3. Bite registration (occlusal) impressions 5
- 6. Preliminary Impressions Preliminaryimpressions are made as precursor to other treatment. Also called “pre-impression” Often used for: Planning purposes Diagnostic casts Temporary crowns Custom trays Working models
- 7. Final Impressions Finalimpressions 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. We will talk more about final impression materials in a later lecture.
- 8. Bite Registration Biteregistration 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. An impression is made that captures the relationship, so it can be used in the office or sent to the lab where the restoration is being fabricated. Used to help mount diagnostic casts in their proper relationship on an articulator Used with a facebow
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- 10. Types of ImpressionMaterials Two major groups Elastic materials Hydrocolloids, polysulfides, silicone rubber materials (condensation and addition; polyvinyl siloxane), polyethers, and hybrid of polyether and PVS PVS, Alginate, Polyethers are most commonly used Inelastic materials Older impression material Will talk about more later
- 11. Key Properties Accuracy Whenthe impression is made the impression material must closely adapt to and flow over the surface of the tooth prep and tissues to record the minute detlails in order to be accurate. The material will tend to flow if it has low viscosity and there is pressure on the material as the tray is seated
- 12. Key Properties TearResistance After the impression material sets, it must have good tear resistance to prevent tearing during removal from the mouth With a crown impression the material in the gingival sulcus is very thin, and would tear if the tear resistance was poor
- 13. Key Properties Dimensional Stability Afterthe impression is removed, the set material must remain dimensionally stable, otherwise casts and dies poured from it would be inaccurate
- 14. Impression Trays Trayscarry the impression material to the mouth and to support it until it sets, is removed from the mouth, and is poured into dental plaster or stone They should be rigid to prevent distortion of the impression They can be made for arches with teeth or for edentulous ridges Edentulous: having no teeth
- 15. Stock trays Premanufacturedtrays Purchased in a variety of sizes Small, medium, large, extra large For adults and children Can be metal or plastic Plastic trays are inexpensive and disposable Metal trays are more expensive and must be cleaned and sterilized between uses Solid or perforated Perforated have holes in their sides and bottom to help retain impression material as it extrudes through the holes and locks it into place Solid trays often have raised borders on the internal surface that help lock in the impression material Rim lock Require the use of adhesive to retain the impression and prevent distortion
- 16. Stock trays Becauseof the wide variation in size and shape of patient’s arches, stock trays may not fit some patients well Ideally, the tray should conform to: length size and height of the arch Depth of the palatal vault Position of teeth
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- 18. Custom Trays Custommade Usually constructed in the lab with chemical-cured, light-cured or thermoplastic resins on casts of teeth Custom fit to the mouth of an individual They can also be made by lining a stock tray with a putty material that is adapted to the dental arch of the individual Can be made for full arch or sectional impressions for part of an arch
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- 20. Triple Trays Aka:Double-bite, dual-arch, check-bite trays Used to make impression of teeth being treated and the opposing teeth at the same time Can capture the correct centric occlusion (bite) of the patient Used to take the (1) impression of the preparation, (2) opposing arch, (3) relationship of the arches (hence TRIPLE TRAY)
- 21. Bite Registration Trays TRIPLE TRAY Typically U-shaped Plastic Frames with thin fiber mesh stretched between the sides and is thin enough not to interfere with the patient’s bite Mesh retains bite registration material Material is placed on both sides of the mesh Frame is positioned over the teeth to be recoded Patient closes into normal bite relationship until the material sets
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- 23. Hydrocolloids Colloid: glue-likematerial composed of two or more substances in which one substance does not go into solution but is suspended within another substance Hydrocolloid: water-based colloids that function as elastic impression materials Two hydrocolloids used in dentistry Alginate Irreversible hydrocolloid Agar Reversible hydrocolloid
- 24. Agar Hydrocolloid Likegelatin When agar powder is mixed with water, it forms a glue-like suspension that entraps the water, making a colloidal suspension called sol Heating will disperse the agar in the water faster When the agar sol is chilled, it will gel Becoming semisolid or jelly-like (Jell-O) When agar is heated it will reverse its state back into a liquid suspension (sol) AKA reversible
- 25. Alginate Irreversible hydrocolloid Alginate powder also forms a gel that sols, but chemical reaction occurs that prevents it from reversing back to gel when heated By far the most widely used impression material Inexpensive Easy to manipulate Requires no special equipment Reasonably accurate for many dental procedures
- 26. Alginate- Irreversible Hydrocolloid Used for: Making impressions for diagnostic casts Partial denture frameworks Repairs of broken partial or complete denture Fabrication of provisional restorations Fluoride and bleaching trays Sports protectors Preliminary impressions for edentulous arches Removable ortho appliances And MANY MORE
- 27. Alginate- Irreversible Hydrocolloid Not accurate enough for final impressions for: Inlay Onlay Crown Bridge Does not capture the fine detail of the preparation needed for a precise fit of such restorations It is thick and does not flow well into the embrasures or occlusal surfaces Final impressions are made with one of the elastomers PVS or Polyether
- 28. More uses forAlginate Impressions Diagnostic casts (study models) Preliminary impressions for complete dentures Partial denture frameworks Opposing casts for crown and bridge tx Repairs of partial and complete dentures Provisional restorations Custom trays for home-use fluoride or bleaching Sports protectors and night guards Removable orthodontic appliances
- 29. Composition and SettingReaction Main active ingredient in alginate is potassium or sodium alginate Makes up 15%- 20% of the powder Produced by derivatives of seaweed Alginate dust contains silica particles Potentially a health hazard if inhaled What do we do to avoid this??
- 30. Composition and SettingReaction When alginate powder is mixed with water, calcium sulfate dehydrate reacts with sodium alginate to form calcium alginate Calcium alginate is insoluble and causes the sol of the mixed powder and water to gel Caused by chemical reaction, so it cannot be reversed Rapid chemical rxn so trisodium phosphate is added as a retarder to delay the reaction The amount of retarder that is added will control the time of the set and will differentiate between regular-set, fast-set, extra fast set
- 31. Working Times Regular-setalginates have a working time of 2 to 3 minutes. Fast-set alginates have a working time of 1.25 to 2 minutes. Working time starts when the materials—powder and liquid—are joined. The longer one takes to mix the material, the less time one has to load and seat the tray.
- 32. Setting Times Regular-setalginates take from 2 to 5 minutes to set completely. Fast-set alginates take from 1 to 2 minutes to set completely. Setting time may be adjusted by altering water temperature. The impression is left in the mouth beyond the appearance of set to reduce tearing and distortion.
- 33. Permanent Deformation Alginatewill be compressed when it is removed from undercuts in the mouth. The greater the compression, the more likely it is that the alginate will be permanently deformed to some degree. The ideal thickness of the impression is 2 to 4 mm. Thin alginate deforms and tears easily. When removing the impression from the mouth, one should use a rapid snap movement to decrease deformation. The impression must be kept wet until the assistant is ready to pour up the impression in dental plaster (gypsum). Impressions also must be disinfected.
- 34. Dimensional Stability Theimpression must be kept wet. Once removed from the mouth, the impression should be rinsed and disinfected. Wrap in damp (not dripping wet) paper towel and sealed in Ziploc bag If the impression loses too much moisture, it will shrink and become distorted Some moisture will still be lost, even in 100% humidity from syneresis Contract and some part of the liquid is squeezed out
- 35. Tear Strength Alginate mixedwith too much water will be weaker and more likely to tear. Thin sections are also prone to tear. Slow removal from the mouth may cause the material to tear. Removed from mouth in rapid “snap” to prevent tear
- 36. Making Alginate Impressions The objective of impression making is to reproduce the oral structures with acceptable accuracy while practicing good infection control and maintaining patient comfort. The dental assistant and the dental hygienist can make alginate impressions. They will need to prepare the patient for the impressions and to dispense, mix, and load the alginate into trays. After removal of the impression, the assistant or the hygienist disinfects and properly handles the impression until it is poured with the appropriate gypsum material. The assistant or hygienist also may be responsible for clearing residual alginate from the mouth and face of the patient.
- 37. Selecting the tray The borders of the tray should be approximately ¼ to ½ inch away from the soft tissues and the teeth. The posterior of the lower tray should extend to include the retromolar pad The posterior of the upper tray should extend to include the tuberosity and the hamular notch Beading wax or utility wax may be placed on the borders of the impression tray for further extension and adaptation to the patients mouth
- 38. Background information Retromolarpad-triangular area located behind the last molar Hamular notch- slender projection of bone that lies behind/posterior and medial to the maxillary tuberosity Tuberosity- the bulging lower extremity of the posterior surface of the body of the maxilla, behind the root of the last molar tooth.
- 39. Selecting the Tray The trays must be clean and sterile before placing them in the patient’s mouth Tray adhesives are applied to Teflon and solid trays after they have been initially fitted in the patient’s mouth When the proper trays have been selected, assemble the materials and equipment to mix the impression material (alginate) Measure and mix the impression material according to manufacturers instructions.
- 43. Criteria for ClinicallyAcceptable Alginate Impressions All teeth and alveolar processes are recorded Peripheral roll and frenums included No large voids and few small bubbles present Good preproduction of detail Free of debris No distortion Alginate firmly attached to tray
- 44. Criteria for ClinicallyAcceptable Alginate Impressions Maxillary Impressions: Palatal vault recorded Hamular notch area included Mandibular Impressions Retromolar areas included Lingual extensions recorded
- 45. Loading the tray(MANDIBULAR) Gather the impression material together Pick up one half of the material with spatula and place it into the left side of the tray from the lingual Pick up the other half of the material with spatula and place it into the right side of the tray being careful not to trap air Overfill the tray slightly and smooth material with spatula Remove excess material from the outside of the tray The tray is now ready to be inserted into the patient’s mouth
- 46. Loading the Tray(MAXILLARY) Gather the impression materials together Pick up material and place on the posterior palatal area of the tray Press the material and place on the posterior palatal area of the tray Overfill the tray slightly and smooth material with spatula Remove excess material from the outside of the tray The tray is now ready to be inserted into the patient’s mouth
- 47. Troubleshooting Alginate Impressions REVIEW TABLE 15-3 ON PAGE 251
- 48. A few videos… https://www.youtube.com/watch?feature=player_detailpage&v=QiJ5WeE96bg https://www.youtube.com/watch?feature=player_detailpage&v=e6sxxNuuBKk https://www.youtube.com/watch?feature=player_detailpage&v=ZGFCi2tcfEA